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 9780841214057, 9780841211889, 0-8412-1405-0

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ACS SYMPOSIUM SERIES 345

Design Considerations for Toxic Chemical and Explosives Facilities Ralp Defense Explosives Safety Board

Laurence J. Doemeny,

EDITOR

National Institute for Occupational Safety and Health

Developed from a symposium sponsored by the Division of Chemical Health and Safety at the 194th Meeting of the American Chemical Society, New Orleans, Louisiana August 30-September 4, 1987

A m e r i c a n C h e m i c a l Society, W a s h i n g t o n , DC 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Library of Congress Cataloging-in-Publication Data Design considerations for toxic chemical and explosives facilities. (ACS symposium series; 345) Includes bibliographies and indexes. 1. Explosives—Safety measures—Congresses. 2. Chemicals—Safety measures—Congresses. I. Scott, Ralph A., 1930. II. Doemeny, Laurence J. III. American Chemical Society. Division of Chemical Health and Safety IV American Chemical Society. Meeting (194th: 1987: TP270.A1D47 1987 ISBN 0-8412-1405-0

660.2'80

Copyright © 1987 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each chapter in this volume indicates the copyright owner's consent that reprographic copies of the chapter may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc., 27 Congress Street, Salem, M A 01970, for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating a new collective work, for resale, or for information storage and retrieval systems. The copying fee for each chapter is indicated in the code at the bottom of the first page of the chapter. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN T H E UNITED STATES OF A M E R I C A

American Chemical Library

Society

1155 16th St., N.W.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; Washington, D.C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

ACS Symposium Series M. Joan Comstock, Series Editor 1987 Advisory Board Harvey W. Blanch University of California—Berkele Alan Elzerman Clemson University

W. H. Norton J. T. Baker Chemical Company

John W. Finley Nabisco Brands, Inc.

James C. Randall Exxon Chemical Company

Marye Anne Fox The University of Texas—Austin

E. Reichmanis AT&T Bell Laboratories

Martin L. Gorbaty Exxon Research and Engineering Co.

C. M . Roland U.S. Naval Research Laboratory

Roland F. Hirsch U.S. Department of Energy

W. D. Shults Oak Ridge National Laboratory

G. Wayne Ivie USDA, Agricultural Research Service

Geoffrey K. Smith Rohm & Haas Co.

Rudolph J. Marcus Consultant, Computers & Chemistry Research

Douglas B. Walters National Institute of Environmental Health

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Foreword The ACS S Y M P O S I U M S E R I E S was founded in 1974 to provide a medium for publishin format of the Serie IN C H E M I S T R Y S E R I E S except that, in order to save time, the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable, because symposia may embrace both types of presentation.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Preface T H I S B O O K D E S C R I B E S the assessment of the combined hazards of toxic chemical and explosives facilities. The principal considerations regarding explosive and toxic chemical outputs are blast pressure, fragmentation, thermal parameters, and toxic chemical exposures. The book provides design considerations for protecting workers from these outputs and for protecting property within and away from the facilities. Practical examples and protection principle with practices, training downwind hazard-prediction models, storage methods, and disposal. In addition, methods of measuring and controlling the exposure of workers to toxic chemicals and the development and implementation of engineering and construction features are addressed. RALPH A. SCOTT, JR.

Defense Explosives Safety Board Alexandria, VA 22331 LAURENCE J. DOEMENY

National Institute for Occupational Safety and Health Cincinnati, OH 45226 May 13, 1987

vii In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 1

Blast Pressure Effects: An Overview W. E. Baker Wilfred Baker, Inc., P.O. Box 6477, San Antonio, TX 78209

This keynote paper gives a general discussion of blast waves developed by high explosive detonations, their effects on structures and people, and risk assessment methods. The properties of free-field waves and normally and obliquel reflected reviewed Diffraction aroun is covered next ga pressure explo sions within vented structures are summarized. Simplified methods of estimating damage to structures by blast waves appear next, followed by methods of estimating blast spalling for strong blasts. Prediction curves or graphs are given for external blast wave properties, and internal blast and gas transient pressures. Practical techniques for explosion containment and venting are discussed, and the topic of risk assessment for explosives facilities is reviewed. A selected reference list closes the paper. Blast Pressures Basics of Free-Field B l a s t Waves. The most severe types of energy releases which can occur i n t o x i c chemical and explosives f a c i l i t i e s are explosions of high explosive m a t e r i a l s . When such materials are i n i t i a t e d by some stimulus, they may burn, deflagrate or detonate. Detonation i s by f a r the most severe of these three chemical react i o n s , so i t i s u s u a l l y assumed to occur i n accident s i t u a t i o n s , unless one can prove otherwise quite c o n c l u s i v e l y . A detonation wave i s a very r a p i d wave of chemical r e a c t i o n which, once i t i s i n i t i a t e d , t r a v e l s at a stable supersonic speed, c a l l e d the detonation v e l o c i t y , i n a high explosive. T y p i c a l l y , detonation v e l o c i t i e s f o r pressed or cast high explosives range from 0097-6156/87/0345-0002$ 14.40/0 © 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1.

BAKER

3

Blast Pressure Effects: An Overview

22,000 - 28,000 f t / s e c . As the detonation wave progresses through the condensed explosive, i t converts the explosive w i t h i n a f r a c t i o n of a microsecond i n t o very hot, dense, high pressure gas. Pressures immediately behind the detonation front range from 2,700,000 4,900,000 psi.(These pressures are c a l l e d Chapman-Jouguet, or CJ, pressures.) The most important single parameter f o r determining a i r b l a s t wave c h a r a c t e r i s t i c s of high explosives i s the t o t a l heat of detonat i o n , E . This quantity i s , i n general, d i r e c t l y proportional to the t o t a l weight W or mass M of the explosive. Any given explosive has a s p e c i f i c heat of detonation,AHe per u n i t weight or mass, which can be e i t h e r calculated from chemical reaction formulas or measured c a l o r i m e t r i c a l l y (see References 1 - 3 ) . So E equals W-AH or M ' A H Q , depending on units f o r AHg. Values forAHg f o r many explosives are given i n References 1 and 4. I f the detonating explosive i s bare, the detonation wave propagates out i n t o the surroundin wave, and i s driven by th explosive material. I f i t i s encased, the detonation wave simply overpowers the casing material, and drives i t outward at high v e l o c i t y u n t i l the casing fragments. The high pressure gases then vent out past the casing fragments and again drive a strong b l a s t wave into the surrounding atmosphere. As the b l a s t wave expands, i t decays i n strength, lengthens i n duration, and slows down, both because of spherical divergence and because the chemical reaction i s over, except f o r afterburning as the hot explosion products mix with the surrounding a i r . Good descriptions of the c h a r a c t e r i s t i c s of a i r b l a s t waves appear i n References 5-7. The d e s c r i p t i o n here i s paraphrased from Reference 5. As a b l a s t wave passes through the a i r or interacts with and loads a structure or target, rapid v a r i a t i o n s i n pressure, density, temperature and p a r t i c l e v e l o c i t y occur. The properties of b l a s t waves which are usually defined are r e l a t e d both to the properties which can be e a s i l y measured or observed and to properties which can be correlated with b l a s t damage patterns. I t i s r e l a t i v e l y easy t o measure shock front a r r i v a l times and v e l o c i t i e s and e n t i r e time h i s t o r i e s of overpressures. Measurement of density v a r i a t i o n s and time h i s t o r i e s of p a r t i c l e v e l o c i t y are more d i f f i c u l t , and few r e l i a b l e measurements of temperature v a r i a t i o n s e x i s t . C l a s s i c a l l y , the properties which are usually defined and measured are those of the undisturbed or side-on wave as i t propagates through the a i r . Figure 1 shows g r a p h i c a l l y some of these properties i n an i d e a l wave. P r i o r to shock front a r r i v a l , the pressure i s ambient pressure p . At a r r i v a l time t , the pressure r i s e s q u i t e abruptly (discontinuously, i n an i d e a l wave) to a peak value P + p . The pressure then decays to ambient i n t o t a l time t + drops to a p a r t i a l vacuum and eventually returns to p . The quantity P i s usually termed the peak side-on overpressure, or merely the peak overpressure. The portion of the time h i s t o r y above i n i t i a l ambient pressure i s c a l l e d the p o s i t i v e phase, of duration t ^ . That p o r t i o n below p i s c a l l e d the negative phase. P o s i t i v e spec i f i c impulse, defined by e

Q

a

s

0

a

Q

s

Q

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Time

—Primary

P o s i t i v e Phase S p e c i f i c Impulse, i _

Shock D i r e c t i o n of Movement of the Blast Wave

Figure 1 . Idealized P r o f i l e of a B l a s t Wave from a Condensed High Explosive.(Courtesy Oyez S c i e n t i f i c and Technical Services Ltd.)

Time of •Arrival, t

Ambient Pressure

Peak Overpressure,

1.

5

Blast Pressure Effects: An Overview

BAKER

[p(t) - p ] d t

(1)

Q

i s also a s i g n i f i c a n t b l a s t wave parameter. This impulse i s shown by the cross-hatched area i n Figure 1 . (The units of i are force times time divided by length squared, or pressure times time. They are, therefore s p e c i f i c impulse or impulse per u n i t area, rather than true impulse, which has u n i t s of force times time.) In most b l a s t studies, the negative phase of the b l a s t wave does not a f f e c t damage and i s ignored, and only b l a s t parameters associated with the p o s i t i v e phase are considered or reported. The i d e a l side-on parameter sure loading applied to So a number of other properties are defined to either more c l o s e l y approximate r e a l b l a s t loads or to provide upper l i m i t s f o r such loads. (The processes of r e f l e c t i o n and d i f f r a c t i o n w i l l be d i s cussed l a t e r . ) Properties of f r e e - f i e l d b l a s t waves other than side-on pressure which can be important i n s t r u c t u r a l loading are: s

Density, P Particle velocity, u Shock front v e l o c i t y , U Dynamic pressure q = p u^/2 Because of the importance of the dynamic pressure q i n drag or wind e f f e c t s and target tumbling, i t i s often reported as a b l a s t wave property. In some instances drag s p e c i f i c impulse i , defined as

i s also reported. Although i t i s possible to define the p o t e n t i a l or k i n e t i c energy i n b l a s t waves, i t i s not customary i n a i r b l a s t technology to report or compute these properties. For underwater explosions, the use of "energy f l u x density" i s more common. This quantity i s given approximately by

where p and a the shock. Q

Q

are density and sound v e l o c i t y i n water ahead of

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

6

T O X I C C H E M I C A L A N D E X P L O S I V E S FACILITIES

A t t h e s h o c k f r o n t i n f r e e a i r , a number o f wave p r o p e r t i e s are i n t e r r e l a t e d through the Rankine-Hugoniot equations. These t h r e e e q u a t i o n s are (Reference 5 ) :

P (u -U) = s

P (u -U) s

[\

P (u -U)

s

2

+ p

s

«o

2

u

2

+

e

0

o)

+ e )

s

s

In t h e s e e q u a t i o n s immediately behind th e n e r g y , and Ps

=

p

s

(4)

0

=

s

u

u

P (u -U)2 + p 0

( o" ) (u

s

+

- u)

0

u

Po o

Q

(5)

=

+ p u s

( 6 ) s

,

+

Po

?

( )

S c a l i n g o f t h e p r o p e r t i e s o f b l a s t waves from exp l o s i v e s o u r c e s i s a common p r a c t i c e , a n d a n y o n e who has even a r u d i m e n t a r y knowledge of b l a s t t e c h n o l o g y u t i l i z e s t h e s e laws t o p r e d i c t the p r o p e r t i e s of b l a s t waves f r o m l a r g e - s c a l e e x p l o s i o n s b a s e d on t e s t s on a much s m a l l e r scale. S i m i l a r l y , r e s u l t s of t e s t s conducted at sea l e v e l ambient a t m o s p h e r i c c o n d i t i o n s are r o u t i n e l y used t o p r e d i c t t h e p r o p e r t i e s o f b l a s t waves from e x p l o s i o n s detonated under h i g h a l t i t u d e c o n d i t i o n s . T h e m o s t common f o r m o f b l a s t s c a l i n g i s H o p k i n s o n Cranz or "cube-root" s c a l i n g . T h i s law, f i r s t f o r m u l a t e d b y B. H o p k i n s o n ( R e f e r e n c e 8) a n d i n d e p e n d e n t l y b y C. C r a n z ( R e f e r e n c e 9 ) , s t a t e s t h a t s e l f - s i m i l a r b l a s t waves a r e p r o d u c e d a t i d e n t i c a l s c a l e d d i s t a n c e s when t w o e x p l o s i v e c h a r g e s o f s i m i l a r g e o m e t r y a n d o f t h e same e x p l o s i v e , but of d i f f e r e n t s i z e s , are detonated i n the same a t m o s p h e r e . I t i s c u s t o m a r y t o use as a s c a l e d distance a dimensional parameter, Z

=

R/E!/3

Z

= R/w!/3

(8)

or (9)

where R i s t h e d i s t a n c e from t h e c e n t e r o f t h e e x p l o s i v e source, E i s the t o t a l heat of d e t o n a t i o n of the e x p l o s i v e and W i s t h e t o t a l w e i g h t o f a s t a n d a r d e x p l o s i v e s u c h a s TNT. T h e c o r r e c t e q u a t i o n , E q u a t i o n 8 o r 9, w i l l be a p p a r e n t i n t h e p r o b l e m . F i g u r e 2 shows s c h e m a t i c a l l y t h e i m p l i c a t i o n s o f H o p k i n s o n - C r a n z b l a s t wave scaling. An o b s e r v e r l o c a t e d a t a d i s t a n c e R f r o m t h e

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1.

7

Blast Pressure Effects: An Overview

BAKER

c e n t e r o f an e x p l o s i v e s o u r c e o f c h a r a c t e r i s t i c d i m e n s i o n d w i l l be s u b j e c t e d t o a b l a s t wave w i t h a m p l i t u d e P, d u r a t i o n t ^ , and a c h a r a c t e r i s t i c t i m e h i s t o r y . The i n t e g r a l of the pressure-time h i s t o r y i s the impulse i . The H o p k i n s o n - C r a n z s c a l i n g l a w t h e n s t a t e s t h a t an o b s e r v e r s t a t i o n e d a t a d i s t a n c e AR f r o m t h e c e n t e r o f a s i m i l a r e x p l o s i v e s o u r c e o f c h a r a c t e r i s t i c d i m e n s i o n Ad d e t o n a t e d i n t h e same a t m o s p h e r e w i l l f e e l a b l a s t wave of " s i m i l a r " f o r m w i t h a m p l i t u d e P, d u r a t i o n A t ^ and i m p u l s e A i . A l l c h a r a c t e r i s t i c t i m e s a r e s c a l e d by t h e same f a c t o r as t h e l e n g t h s c a l e f a c t o r A. I n H o p k i n s o n C r a n z s c a l i n g , p r e s s u r e s , t e m p e r a t u r e s , d e n s i t i e s and v e l o c i t i e s a r e unchanged a t homologous t i m e s . T h i s s c a l i n g l a w h a s been t h o r o u g h l y v e r i f i e d by many e x p e r i ­ ments c o n d u c t e d o v e r a l a r g e r a n g e o f e x p l o s i v e c h a r g e energies. A much more c o m p l e t e d i s c u s s i o n o f t h i s l a w and d e m o n s t r a t i o n o 3 o f R e f e r e n c e 5. The b l a s t s c a l i n g y used t o p r e d i c t c h a r a c t e r i s t i c s o f b l a s t waves f r o m e x ­ p l o s i o n s a t h i g h a l t i t u d e i s t h a t o f Sachs ( R e f e r e n c e 1 0 ) . S a c h s l a w s t a t e s t h a t d i m e n s i o n l e s s o v e r p r e s s u r e and d i m e n s i o n l e s s i m p u l s e c a n be e x p r e s s e d as u n i q u e f u n c t i o n s of a d i m e n s i o n l e s s s c a l e d d i s t a n c e , where t h e d i m e n s i o n ­ l e s s p a r a m e t e r s i n c l u d e q u a n t i t i e s w h i c h d e f i n e t h e am­ bient atmospheric conditions p r i o r to the explosion. Sachs scaled pressure i s 1

1

Ρ

= (P/Po)

do)

S a c h s ' s c a l e d i m p u l s e i s d e f i n e d as

ι =

(ID

El/3 p2/3 *o

where a i s a m b i e n t sound v e l o c i t y . These q u a n t i t i e s are a f u n c t i o n o f d i m e n s i o n l e s s s c a l e d d i s t a n c e , d e f i n e d as G

PoW R = R^—

J

3

(12)

B o t h s c a l i n g laws a p p l y t o r e f l e c t e d b l a s t wave p a r a m e t e r s , as w e l l as s i d e - o n p a r a m e t e r s . (Note t h a t , i f c h a r g e w e i g h t W i s used i n s t e a d o f e n e r g y Ε, t h e s e p a r a m e t e r s have d i m e n s i o n s . )

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

8

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Basics

of

Reflection

and

Diffraction

Processes

Normal R e f l e c t i o n . An u p p e r l i m i t t o b l a s t l o a d s i s o b t a i n e d i f one i n t e r p o s e s an i n f i n i t e , r i g i d w a l l i n f r o n t o f t h e wave, and r e f l e c t s t h e wave n o r m a l l y . A l l f l o w b e h i n d t h e wave i s s t o p p e d , and p r e s s u r e s a r e c o n s i d e r a b l y g r e a t e r than side-on. The p r e s s u r e i n n o r m a l l y r e f l e c t e d waves i s u s u a l l y d e s i g n a t e d p ( t ) , and t h e p e a k r e f l e c t e d o v e r p r e s s u r e , P . The integral of o v e r p r e s s u r e o v e r t h e p o s i t i v e p h a s e , d e f i n e d i n Equation (13), i s the r e f l e c t e d s p e c i f i c impulse i . D u r a t i o n s of the p o s i t i v e phase of normally r e f l e c t e d w a v e s a r e a l m o s t t h e same a s f o r s i d e - o n w a v e s , t ^ . The parameter i has been measured c l o s e r t o h i g h e x p l o s i v e b l a s t s o u r c e s t h a n have most b l a s t parameters. r

r

r

r

The H o p k i n s o n - C r a n z s c a l i n g l a w d e s c r i b e d e a r l i e r a p p l i e s t o s c a l i n g o f r e f l e c t e d b l a s t wave parameters j u s t as w e l l as i t does t o s i d e - o n waves. That i s , a l l r e f l e c t e d b l a s t d a t a t a k e n u n d e r t h e same a t m o s p h e r i c c o n d i t i o n s f o r t h e same t y p e o f e x p l o s i v e s o u r c e c a n be r e d u c e d t o a common b a s e f o r c o m p a r i s o n a n d p r e d i c t i o n . Sachs* law f o r r e f l e c t e d waves f a i l s c l o s e t o h i g h ex­ p l o s i v e b l a s t sources but i t does a p p l y beyond about t e n charge r a d i i . F o r s h o c k w a v e s weak e n o u g h t h a t a i r b e h a v e s as a p e r f e c t g a s , t h e r e i s a f i x e d and w e l l - k n o w n r e l a t i o n b e t w e e n p e a k r e f l e c t e d o v e r p r e s s u r e and peak s i d e - o n o v e r p r e s s u r e ( R e f e r e n c e s 5 and 1 1 ) .

p

r

- 2

P

S

+

V

t;; ! 1

(Y-l)

( 1 4 )

P +2 s

1 5

P

s

= P /Po s

( >

P

r

= Pr/Po

( >

1 6

At low i n c i d e n t o v e r p r e s s u r e s ( P - * 0 ) , the r e f l e c t e d overpressure approaches the a c o u s t i c l i m i t of twice the incident overpressure. I f one w e r e t o assume a c o n s t a n t Ύ = 1.4 f o r a i r f o r s t r o n g s h o c k s , t h e u p p e r l i m i t w o u l d a p p e a r t o be P = 8P . B u t , a i r i o n i z e s and d i s s o c i a t e s as s h o c k s t r e n g t h s i n c r e a s e , and Y i s n o t c o n s t a n t . In f a c t , t h e r e a l upper l i m i t r a t i o i s not e x a c t l y known, b u t i s p r e d i c t e d by D o e r i n g and B u r k h a r d t ( R e f e r e n c e 11) t o be as h i g h as 20. B r o d e ( R e f e r e n c e 12) h a s a l s o c a l c u l a t e d t h i s r a t i o f o r normal r e f l e c t i o n of shocks i n s e a l e v e l a i r , a s s u m i n g a i r d i s s o c i a t i o n and ionization. s

r

S

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1.

BAKER

Blast Pressure Effects: An Overview

9

A c u r v e p l o t t e d f r o m an e q u a t i o n i n R e f . 12 i s r e p r o d u c e d h e r e as F i g u r e 3. Above P = 100 p s i and s t a n d a r d atmos­ p h e r i c c o n d i t i o n s , Eq. (14) i s i n c r e a s i n g l y i n e r r o r compared t o t h i s c u r v e , and s h o u l d n o t be u s e d . (Note t h a t , a t t h e s u r f a c e o f a s p h e r i c a l TNT c h a r g e a t s e a l e v e l , R e f . 12 and F i g u r e 3 g i v e P / P = 13.92.) s

r

s

Oblique R e f l e c t i o n . Although normally incident b l a s t wave p r o p e r t i e s u s u a l l y p r o v i d e upper l i m i t s t o b l a s t l o a d s on s t r u c t u r e s , t h e more u s u a l c a s e o f l o a d i n g o f l a r g e , f l a t s u r f a c e s i s r e p r e s e n t e d by waves w h i c h s t r i k e at o b l i q u e i n c i d e n c e . A l s o , as a b l a s t wave f r o m a s o u r c e some d i s t a n c e f r o m t h e g r o u n d r e f l e c t s f r o m t h e g r o u n d , t h e a n g l e o f i n c i d e n c e must change f r o m n o r m a l t o o b l i q u e as t h e shock moves a c r o s s t h e g r o u n d s u r f a c e . O b l i q u e r e f l e c t i o n i s c l a s s e d as e i t h e r r e g u l a r o r Mach r e f l e c t i o n , dependen strength. Geometrie F i g u r e s 4 and 5 f r o m R e f e r e n c e 13. I n r e g u l a r r e f l e c t i o n , t h e i n c i d e n t s h o c k t r a v e l s i n t o s t i l l a i r ( R e g i o n One) a t v e l o c i t y U, w i t h i t s f r o n t making t h e a n g l e o f i n c i ­ dence αj w i t h r e s p e c t t o t h e w a l l . Properties behind t h i s f r o n t ( R e g i o n Two) a r e t h o s e f o r a f r e e a i r s h o c k . On c o n t a c t w i t h the w a l l , the f l o w behind the i n c i d e n t shock i s t u r n e d , b e c a u s e t h e component n o r m a l t o t h e w a l l must be z e r o , and t h e shock i s r e f l e c t e d f r o m t h e w a l l a t a r e f l e c t i o n a n g l e ot t h a t i s d i f f e r e n t f r o m a j . C o n d i ­ t i o n s i n R e g i o n Three i n d i c a t e r e f l e c t e d s h o c k p r o p e r t i e s . A p r e s s u r e t r a n s d u c e r flush-mounted i n t h e w a l l would r e c o r d o n l y t h e ambient and r e f l e c t e d wave p r e s s u r e s ( d i r e c t jump f r o m R e g i o n One t o R e g i o n T h r e e ) as t h e wave p a t t e r n t r a v e l e d a l o n g t h e w a l l ; w h e r e a s , one mounted a t a s h o r t d i s t a n c e f r o m t h e w a l l w o u l d r e c o r d t h e a m b i e n t p r e s s u r e , t h e n t h e i n c i d e n t wave p r e s s u r e , and f i n a l l y t h e r e f l e c t e d wave p r e s s u r e . T h e r e i s some c r i t i c a l a n g l e o f i n c i d e n c e , ^ e x t r e m e dependent on s h o c k s t r e n g t h , above w h i c h r e g u l a r r e f l e c ­ t i o n c a n n o t o c c u r . I n 1877, E r n s t Mach showed t h a t t h e i n c i d e n t and r e f l e c t e d s h o c k s w o u l d c o a l e s c e t o f o r m a t h i r d s h o c k . Because o f t h e g e o m e t r y o f t h e s h o c k f r o n t s , t h e y were t e r m e d t h e Mach V o r Mach Y, w i t h t h e s i n g l e shock formed by t h e c o a l e s c e d i n c i d e n t and r e f l e c t e d s h o c k s n o r m a l l y c a l l e d t h e Mach stem. The g e o m e t r y o f Mach r e f l e c t i o n i s shown i n F i g u r e 5. I n a d d i t i o n t o t h e i n c i d e n t and r e f l e c t e d s h o c k s I and R, we now have t h e Mach s h o c k M; t h e j u n c t i o n Τ o f t h e t h r e e s h o c k s i s c a l l e d the t r i p l e point. In a d d i t i o n , there i s also a s l i p s t r e a m S, a boundary between r e g i o n s o f d i f f e r e n t p a r t i c l e v e l o c i t y and d i f f e r e n t d e n s i t y , b u t t h e same p r e s s u r e . When a j i n F i g u r e 4 e x c e e d s ^ e x t r e m e ' t h e Mach wave M i s formed a t t h e w a l l and grows as t h e s h o c k s y s t e m s move a l o n g t h e w a l l w i t h t h e l o c u s o f t h e t r i p l e p o i n t b e i n g a s t r a i g h t l i n e AB. R

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

10

TOXIC CHEMICAL A N D EXPLOSIVES

FACILITIES

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1.

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Blast Pressure Effects: An Overview

11

H a r l o w and Amsden ( R e f e r e n c e 14) p r e s e n t a resume o f t h e o r y and e x p e r i m e n t on r e g u l a r r e f l e c t i o n and t h e l i m i t of r e g u l a r r e f l e c t i o n (which i s a l s o the s t a r t of Mach r e f l e c t i o n ) . A u s e f u l curve from t h e i r paper i s given here. F i g u r e 6 g i v e s a n g l e o f r e f l e c t i o n a as a f u n c t i o n of angle of i n c i d e n c e a j i n the r e g u l a r regime. The p a r a m e t e r ξ i s d e f i n e d as R

Po ξ

β

? Γ Π *

( 1 7 )

[ H a r l o w and Amsden ( R e f . 14) c a l l ξ t h e s h o c k s t r e n g t h , but i t i s , i n f a c t , the i n v e r s e o f shock s t r e n g t h . ] I n v e r t i n g E q u a t i o n (17) we a l s o have t h e r e l a t i o n

Ps = Po Diffraction. When a b l a s t wave e n c o u n t e r s a f i n i t e o b s t a c l e , i t i s p a r t i a l l y r e f l e c t e d but a l s o d i f f r a c t s around t h e o b s t a c l e . T h i s p r o c e s s i s d e s c r i b e d h e r e . The p r o c e s s o f d i f f r a c t i o n o f a b l a s t wave a r o u n d a r e c t a n g u l a r b l o c k o b j e c t , s u c h as a s i m p l e b u i l d i n g s h a p e , i s w e l l d e s c r i b e d i n R e f . 7, and i s p a r a p h r a s e d here. When t h e f r o n t o f an a i r b l a s t wave s t r i k e s t h e f a c e o f a s t r u c t u r e r e f l e c t i o n o c c u r s . As a r e s u l t t h e o v e r p r e s s u r e b u i l d s up r a p i d l y t o a t l e a s t t w i c e (and g e n e r a l l y s e v e r a l t i m e s ) t h a t i n t h e i n c i d e n t wave f r o n t . The a c t u a l p r e s s u r e a t t a i n e d i s d e t e r m i n e d by v a r i o u s f a c t o r s , s u c h as t h e peak o v e r p r e s s u r e o f t h e i n c i d e n t b l a s t wave and t h e a n g l e between t h e d i r e c t i o n o f m o t i o n o f t h e wave and t h e f a c e o f t h e s t r u c t u r e . The p r e s s u r e i n c r e a s e i s due t o t h e c o n v e r s i o n o f t h e k i n e t i c e n e r g y of t h e a i r b e h i n d the shock front i n t o i n t e r n a l energy as the r a p i d l y moving a i r behind the shock f r o n t i s decelerated at the face of the structure. The high pressure region expands outward towards the surrounding regions of lower pressure. As the wave front moves forward, the r e f l e c t e d overpressure on the face of the structure drops r a p i d l y t o the side-on overpressure, plus an added drag force due t o the wind (dynamic) pressure. At the same time, the a i r pressure wave bends or " d i f f r a c t s " around the structure, so that the structure i s eventually engulfed by the b l a s t , and approximately the same pressure i s exerted on the sides and the roof. The f r o n t face, however, i s s t i l l subjected t o wind pres­ sure, although the back face i s shielded from i t . The developments described above are i l l u s t r a t e d i n a s i m p l i ­ f i e d form i n F i g s . 7a, b, c, d, e; t h i s shows, i n plan, successive stages of a structure without openings which i s being struck by an a i r b l a s t wave moving i n a h o r i z o n t a l d i r e c t i o n . In F i g . 7a the wave front i s seen approaching the structure with the d i r e c t i o n of motion perpendicular t o the face of the structure exposed t o the b l a s t . In F i g . 7b the wave has j u s t reached the front face, producing a high

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

T O X I C C H E M I C A L A N D E X P L O S I V E S FACILITIES

φ (usinoo-O)

°i

/ /'/

R

}

} } ) }

)

/ >/ >ιj Figure 4. Regular Oblique Reflection of a Plane Shock from a Rigid Wall.(Reference 13)

Figure 5.

Mach Reflections From a R i g i d Wall. (Reference 13)

90

jç-yo

'f

^ - ir - - ^ —A' -

?I™7_.

0 95

80*

70*

wv;

60*

50*

40*

30*

20*

Vf 0

#

10*

20"

30*

40*

50*

60*

70*

80*

90*

"I Figure 6. Angle of Incidence Versus Angle of Reflection f o r Shocks of D i f f e r e n t Strengths Undergoing Regular R e f l e c t i o n . (Reference 14)

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1.

BAKER

13

Blast Pressure Effects: An Overview

r e f l e c t e d overpressure. In F i g . 7c the b l a s t wave has proceeded about halfway along the structure. In F i g . 7d the wave f r o n t has j u s t passed the rear of the structure. The pressure on the f r o n t face has dropped t o some extent while the pressure i s b u i l d i n g up on the back face as the b l a s t wave d i f f r a c t s around the structure. F i n a l l y , when the wave front has passed completely, as i n F i g . 7e, approximately equal a i r pressures are exerted on the sides and top of the structure. A pressure difference between front and back faces, due to the wind forces, w i l l p e r s i s t , however, during the whole p o s i t i v e phase of the b l a s t wave ( F i g . 7 f ) . I f the structure i s oriented at an angle t o the b l a s t wave, the pressure would immedi a t e l y be exerted on two faces, instead of one, but the general c h a r a c t e r i s t i c s of the b l a s t loading would be s i m i l a r t o that j u s t described (Figs. 7g, h, and i ) . The pressure d i f f e r e n t i a l between the front and back faces w i l l have i t s maximum value when the b l a s t wave has not yet completel y surrounded the structure a pressure d i f f e r e n t i a l force tending t o cause the structure t o d e f l e c t and thus move b o d i l y , usually i n the same d i r e c t i o n as the b l a s t wave. This force i s known as the " d i f f r a c t i o n loading" because i t operates while the b l a s t wave i s being d i f f r a c t e d around the structure. When the b l a s t wave has engulfed the structure ( F i g . 7e or 7 i ) , the pressure d i f f e r e n t i a l i s small and the loading i s due almost e n t i r e l y t o the drag pressure exerted on the front face. The actual pressures on a l l faces of the structure are i n excess of the ambient atmospheric pressure and w i l l remain so, although decreasing steadi l y , u n t i l the p o s i t i v e phase of the b l a s t wave has ended. Hence, the d i f f r a c t i o n loading on a structure without openings i s eventually replaced by an inwardly directed pressure, i . e . , a compression or squeezing a c t i o n , combined with the dynamic pressure of the b l a s t wave. In a structure with no openings, the loading w i l l cease only when the overpressure drops t o zero. For b l a s t waves from r e l a t i v e l y small explosion sources, the d i f f r a c t i o n phase of the loading may dominate, and the drag phase may be r e l a t i v e l y or e n t i r e l y unimportant, because the d i f f r a c t i o n times may be as long as or greater than drag pressure durations. Reference 7 gives e x p l i c i t procedures f o r c a l c u l a t i n g d i f f r a c ted loads on surfaces of box-shaped structures, and they w i l l not be repeated here. But, we do reproduce several formulas f o r d i f f r a c t i o n times from t h i s reference. These are 4 s (1+R)a

(19) 0

(20)

(21) where S i s the l e s s e r of H or B/2 i n Figure 8, G i s the greater of H or B/2, R i s S/G, L i s block length, and U i s shock f r o n t v e l o c i t y .

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL A N D EXPLOSIVES

Figure 8.

FACILITIES

Representation of a Closed Box-Like Structure.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1.

Blast Pressure Effects: An Overview

BAKER

15

If the structure being loaded by the b l a s t wave i s a slender member or object such as a column/ I-beam, or stack, then the d i f f r a c t i o n times indicated by Equations (19) - (21) give short times because transverse dimensions are small. The d i f f r a c t i o n around such objects i s i l l u s t r a t e d i n Figure 9, with stages s i m i l a r t o those described f o r d i f f r a c t i o n around a block structure. Here, the d i f f r a c t i o n phase i s almost always shorter than the drag phase, and we are interested primarily i n the net transverse pressure loading on the slender structure or object. A s i m p l i f i e d time h i s t o r y of t h i s loading appears i n Figure 10. Methods f o r c a l c u l a t i n g t h i s net pressure loading are given i n Ref. 15, f o r TNT b l a s t sources. Gas Pressures i n Vented and Unvented Enclosures A recent review on the t o p i c of the r e l a t i v e l y long-term gas pressures which develop f o r explosions w i t h i n enclosures appears i n Ref. 16. That materia For explosions i n enclosure propellants, high explosive wit combustible materials contact, or combustible mist, dust, or gaseous explosive mixtures, the longduration gas pressures caused by confinement of the products of the explosions can be the dominant loads causing s t r u c t u r a l f a i l u r e . These q u a s i - s t a t i c pressures are determined by the t o t a l heat energy i n the explosive and/or combustible source, the volume of the enclosure, the vent area and the vent panel configuration, the mass per unit area of vent covers, and the i n i t i a l ambient conditions w i t h i n the enclosure. Here, we concentrate on the gas pressures developed f o r high explosive detonations w i t h i n vented and unvented enclosures, and these explosives plus nearby combustible materials. There i s a voluminous l i t e r a t u r e on pressures and the e f f e c t s of venting f o r confined explosions with only combustible gases and dusts i n a i r , but that t o p i c seems outside the scope of t h i s book, and i s not discussed here. The loading from an explosive charge detonated w i t h i n a s t r u c ture consists of two phases. The i n i t i a l phase consists of several high amplitude, short duration, r e f l e c t e d pressure shocks. This phase of the loading i s very geometry dependent, with the highest loads generally occuring on the surfaces nearest the charge. On each r e f l e c t i o n , the shock strength i s attenuated u n t i l at some point the i n t e r n a l pressure has s e t t l e d t o a slowly decaying l e v e l . This i s the q u a s i - s t a t i c pressure loading phase. This phase i s characterized by e s s e n t i a l l y uniform pressures throughout the structure at any point i n time. The rate of q u a s i - s t a t i c pressure decay i s a function of the vent area, structure volume and the nature of the explosive source (e.g., propellant versus explosive). A t y p i c a l pressure trace obtained during an i n t e r n a l explosion i n a vented structure i s shown i n Figure 11. T r a d i t i o n a l l y (Ref. 17), the peak q u a s i - s t a t i c pressure i s established by f i t t i n g a smooth l i n e through the data beginning at the end of the pressure trace and extending back towards time zero, the time of charge i g n i t i o n . This l i n e i s shown i n Figure 11 as a s o l i d l i n e . The peak P q i s then taken as the i n t e r s e c t i o n of the f i t t e d l i n e and a v e r t i c a l l i n e at time zero (shown as a dotted l i n e i n the f i g u r e ) . This point i s labeled A i n Figure 11. For a vented s t r u c t u r e , a S

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

T O X I C C H E M I C A L A N D E X P L O S I V E S FACILITIES

Figure 9.

Interaction of Blast Wave with Slender Object.

Preβsure

Figure 10. Time History of Net Transverse Pressure on Object during Passage of a Blast Wave.



1—

-

\

:

-

A

1

-25.0

y

:

1

1

0.00

ι

I

-4. . .J

25.0 50.0 TIME (MS)

ι

1

75.0

.

1

100.

Figure 11. Typical Pressure Record from an Internal Explosion i n a Vented Structure.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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17

Blast Pressure Effects: An Overview

more appropriate technique has been suggested (Ref. 13 and 18). This method i s applied by drawing a ramp increase i n pressure extending from time zero, which follows the base of the pressure shocks. This l i n e i s shown as a dashed l i n e i n Figure 11. The i n t e r s e c t i o n of the ramp pressure increase with the l i n e f i t t e d through the pressure decay i s the peak q u a s i - s t a t i c pressure. This point i s labeled Β i n the f i g u r e . For explosions inside sealed enclosures, points A and Β w i l l have nearly the same ordinates, whereas f o r explosions with increasing vent areas, the difference i n ordinates between points A and Β increases. In Ref. 18, a very complete analysis of gas pressures from i n t e r ­ nal explosion data was presented. The authors performed a s i m i l i t u d e analysis t o determine the functional form of the q u a s i - s t a t i c pres­ sure, as a function of the physical parameters pertaining t o the problem of an i n t e r n a l explosion inside a vented structure. This analysis gave the following dimensionless f u n c t i o n a l forms: p

P

=

+

QS P ( 2 2 )

-5T"

5- [i] f

* • (» (m

••

m

In these expressions, ρ Ρ 33 Po W V ffA t a ig f,g,h a

e

Q

= absolute peak gas pressure 9 9 peak gas pressure = atmospheric pressure = charge t o t a l energy (not weight) = enclosure volume = e f f e c t i v e vent area = venting time = sound speed = gas impulse = functional forms

=

a

e

The authors of Ref. 18 f i t t e d data from over 175 experiments t o the scaled vented pressure parameters, using t o t a l heats of explosion for W. Graphs from that paper w i l l be shown l a t e r . Most gas pressure parameters f o r vented HE explosions apply f o r open vents and the special venting configurations developed f o r sup­ pressive shields (Refs. 17 and 19). I f vents are covered with blowout or frangible covers, the peak gas pressures are e s s e n t i a l l y the same as i n unvented structures, but venting times and gas impulses can be altered (increased), depending on the vent area, mass per u n i t

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

18

TOXIC CHEMICAL AND

E X P L O S I V E S FACILITIES

area of the vent cover, and i n i t i a l shock r e f l e c t e d impulse loading of the vent cover. The s t a f f of the Naval C i v i l Engineering Laboratory has conducted a number of a n a l y t i c and experimental studies to determine these e f f e c t s , and has developed methods f o r predicting the r e s u l t i n g gas pressure loads. The methods w i l l be discussed l a t e r . Detailed graphs are too numerous to include. They w i l l appear i n the r e v i s i o n to TM5-1300. Combustion of gas-air mixtures w i t h i n enclosures has long been known to produce s i g n i f i c a n t pressure increases because of a i r heating by a l l or part of the heat of combustion of the gaseous f u e l . So, i t should not be s u r p r i s i n g that combustibles near or i n intimate contact with high explosives detonated i n enclosures can i n many instances r a i s e the gas pressures w e l l above the gas pres­ sures from detonations of only the high explosives. But, i t i s s u r p r i s i n g that there has been l i t t l e t e s t i n g to measure and allow prediction f o r such increase. One of the few such t e s t programs i s reported i n Ref. 20, wit The e f f e c t has been observe but no v a r i a t i o n s i n charge to combustible mass, charge type, s t r u c ture volume, or degree of venting have been tested. The i m p l i c a t i o n s of the data accumulated so f a r are that q u a s i - s t a t i c loading c a l ­ culations should include estimates of contributions from the burning ' of combustible materials whenever such materials are expected to be i n intimate contact with HE sources. Damage Mechanisms The P - i Curve Concept and Applications. We hope that Section I of t h i s chapter demonstrates the Dynamic and transient nature of the b l a s t waves caused by explosives detonations, and the r e s u l t i n g pressure loads they can apply to various structures or objects. Because these loads are usually suddenly applied, and because they l a s t from f r a c t i o n s of a m i l l i s e c o n d to at most seconds, the response of or damage to loaded structures or objects i s almost always dynamic. So, u s u a l l y s t r u c t u r a l response or damage i s dependent not only on the amplitude (peak overpressure) of the applied b l a s t loading, the loaded area and the s t r u c t u r a l strength; but also on the mass or i n e r t i a of the structure, and e i t h e r the duration of the t r a n s i e n t pressure loading or the applied s p e c i f i c impulse. These concepts are probably most simply developed by f i r s t c a l c u l a t i n g the response of very simple dynamic mechanical systems. This has been done i n Refs. 15 and 21, and the reader i s referred to either of these references f o r d e t a i l e d development. Consider the simple e l a s t i c system of F i g . 13. Equations of motion under the applied (simplified) force pulse can be e a s i l y written and solved (see Refs. 15 and 21), and a dimensionless form of the maximum response can be p l o t t e d versus another dimen­ sionless r a t i o which relates loading time Τ to s t r u c t u r a l n a t u r a l period (Figure 14). In these two f i g u r e s , the various symbols represent: P* t Τ m

peak applied force (not pressure) time e f f e c t i v e b l a s t wave duration mass

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1.

BAKER

Blast Pressure Effects: An Overview k χ ω

τ

19

spring constant displacement c i r c u l a r v i b r a t i o n frequencyv i b r a t i o n period

In Figure 14, we see that the scaled maximum response reaches asymptotic r e l a t i o n s f o r both small and large time r a t i o s . The same s o l u t i o n presented i n Fig. 14 can e a s i l y be recast (see Ref. 22) i n t o another form, as i n Fig. 15. Note here that the maximum scaled response curve i s now e s s e n t i a l l y a rectangular hyperbola with one asymptote which depends only on the l e v e l of applied peak force and another asymptote which depends only on the l e v e l of applied t o t a l impulse. In the intermediate loading regime (the "knee" of the hyperbola), response determination requires knowledge of both peak force and t o t a l impulse. This P*-I type of response curve can also be e a s i l y shown to apply to a simple r i g i d - p l a s t i shown i n Figure 16 (see system i s replaced with a pure Coulomb f r i c t i o n element, with r e s i s t i n g force f , which i s independent of displacement once the mass s t a r t s to move. A l l other symbols are defined above. Although the curves i n Figures 13-15 were developed f o r t r a n ­ sient loads defined by t o t a l applied forces and impulses, we could as e a s i l y have developed them by i n i t i a l l y specifying an applied pressure transient loading, with i t s accompanying s p e c i f i c impulse, plus a loaded area. So, the concept c e r t a i n l y applies to simple structures under b l a s t loading. The important inferences to be drawn from the simple» analyses are that structures respond p r i m a r i l y to peak overpressure i f t h e i r v i b r a t i o n periods are much shorter than the b l a s t duration, while they respond p r i m a r i l y to s p e c i f i c impulse i f t h e i r v i b r a t i o n periods are much longer than the b l a s t duration. If these two times are about equal, then both b l a s t loading quan­ t i t i e s are important. Biggs (Ref. 21) discusses responses of simple dynamic systems i n great d e t a i l , including the important intermediate case of e l a s t i c , p e r f e c t l y - p l a s t i c systems. He also presents dimensionless response curves f o r various l e v e l s of e l a s t i c - p l a s t i c response, and f o r several d i f f e r e n t regular pulse shapes. Does t h i s concept of a P - i diagram as a measure of response or damage work f o r complex structures, as w e l l as simple ones? Indeed i t does, as can be shown by the f i t s made i n B r i t a i n f o r bomb damage to houses, following World War I I . These f i t s , i l l u s t r a t e d i n Fig. 17, now form part of the basis f o r the B r i t i s h QuantityDistance tables f o r explosives safety. If one can calculate or measure an "isodamage curve" f o r a structure or s t r u c t u r a l element, i . e . , an hyperbola s i m i l a r to Figure 17, one can p l o t i t as an overlay on those combinations of peak overpressure and s p e c i f i c impulse which r e s u l t from detonating various explosive charge masses or energies at various distances, and graph­ i c a l l y convert the isodamage curve to a set of combinations of charge masses and distances which cause t h i s damage. Figure 18 i s an example f o r a l i g h t structure which i s susceptible to damage from small mass charges. Some s p e c i f i c examples used to c a l c u l a t e

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

2.00

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Figure 13. Linear O s c i l l a t o r Loaded by a Blast Wave. ~i—I

I I I I ll|

1—I

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111111

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Quasi-static asymptote X

1—ι ι ι 11 m

m

1000

Figure 14. Shock Response f o r Blast-Loaded E l a s t i c O s c i l l a t o r .

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Blast Pressure Effects: An Overview

BAKER

1

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4

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P*-I Diagram f o r Blast-Loaded E l a s t i c O s c i l l a t o r . p'(t)

Figure 16.

P*-I Diagram f o r Blast Loaded R i g i d - P l a s t i c System.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

22

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

200h

2000

_J L 4000 6000

Trr

10000

20000

I I I I ITl— 40000 100000 P ( Pa )

IE 200000

I 1 I I 400000 1000000

c

Figure 17. Impulse Versus Pressure Diagram for Constant Levels of Building Damage. (Reprinted with permission from ref. 15. Copyright 1983 Elsevier Science.)

Figure 18. Illustration of Overlays to a P-I Diagram. Incident (Side-On) Overpressure and Impulse from Pentolite Spheres. (Reprinted with permission from ref. 15. Copyright 1983 Elsevier Science.)

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1. BAKER

Blast Pressure Effects: An Overview

23

effects of medium-sized HE-loaded p r o j e c t i l e s against various types of conventional b u i l d i n g walls appear i n F i g . 19, from Ref. 23. The P - i concept can also be used to collapse the r e s u l t s of a number of dynamic response c a l c u l a t i o n s f o r s t r u c t u r a l elements i n t o compact dimensionless design curves. A number of i l l u s t r a t i o n s are given i n Ref. 15, with one f o r blast-loaded beams with various boundary conditions appearing i n F i g . 20. These curves give p r e d i c t i o n s of maximum dynamic bending s t r a i n s and displacements f o r beams with a variety of boundary conditions. D e t a i l s appear i n Ref. 15, so we do not t r y to define a l l parameters here. This method of presenting the t o p i c of b l a s t damage mechanisms was chosen p r i m a r i l y because i t h i g h l i g h t s the r e l a t i o n s h i p s between blast wave properties and s t r u c t u r a l response or damage. But, we hope that you now also know that the P - i or isodamage curves f o r structures can be useful design t o o l s . To S p a l l or Not to S p a l l sures, of the r e f l e c t e d b l a s close to structures or s t r u c t u r a l elements can be very high. Figure 3 gives as a l i m i t , f o r contact explosions of TNT, a pressure of P = 168,000 p s i , while f o r an incident pressure P of 5000 p s i , P = 61,000 p s i . So, i n addition to applying a very high and l o c a l i z e d impulsive loading to the nearby s t r u c t u r a l surface, the explosion also applies compressive pressure pulses which peak very sharply to pressures w e l l above compressive strengths of concretes, and even strengths of s t r u c t u r a l s t e e l s . Damage caused by the impacts, i n c l u d ing damage from transmission and r e f l e c t i o n s of these intense waves, i s termed " s p a l l i n g " or "scabbing." We should warn you that there i s some confusion i n d e f i n i t i o n of the two terms s p a l l i n g and scabbing. In some c i v i l engineering l i t e r a t u r e (see Ref. 24), s p a l l i n g r e f e r s to scouring and éjecta damage to the loaded face of the structure or slab, while scabbing denotes wave-induced f a i l u r e s at the rear face of the loaded s l a b . But, t h i s i s not the usual physics d e f i n i t i o n , which instead uses the term s p a l l i n g to cover a l l f a i l u r e s induced by intense wave transmission and r e f l e c t i o n s w i t h i n s o l i d s . We use the more general physics d e f i n i t i o n . References 25-27 give good descriptions of the physics of shock transmission through s o l i d s , and s p a l l i n g processes. On the loaded side of a slab subjected to an intense r e f l e c t e d blast wave, a region of the slab w i l l f a i l i f the i n t e n s i t y of the compressive wave transmitted i n t o the s l a b exceeds the dynamic compressive strength of the m a t e r i a l . For an intense wave s t r i k i n g a t h i n concrete s l a b , the f a i l u r e region can extend through the s l a b , and a sizeable area turned to rubble which can f a l l or be ejected from the s l a b . For a thicker s l a b or l o c a l i z e d loaded area, s p h e r i cal divergence of the stress wave can cause i t to decay i n amplitude within the slab so that only part of the loaded face side i s crushed by d i r e c t compression. The more common type of s p a l l i n g f a i l u r e of concrete occurs when (and where) the transmitted compressive wave r e f l e c t s from the free surface back face of the slab as a t e n s i l e wave, and the head of the r e f l e c t e d t e n s i l e wave and t a i l of the transmitted compressive wave combine to produce net t e n s i l e stress exceeding the dynamic t e n s i l e strength of the concrete. This process i s shown schematically i n Figure 21 f o r the s i m p l i f i e d case of a plane, t r i a n g u l a r compressive r

s

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

r

00

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In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1.

BAKER

Blast Pressure Effects: An Overview

Figure 20. Elastic-Plastic Solution for Bending of Blast Loaded Beams. (Reprinted with permission from ref. 15. Copyright 1983 Elsevier Science.)

Figure 21.

Stress Wave R e f l e c t i o n a t a Free Surface i n a S o l i d .

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

25

26

TOXIC CHEMICAL AND

E X P L O S I V E S FACILITIES

stress pulse r e f l e c t e d normally from a plane surface i n a s o l i d . The normal s t r e s s must be zero at the free surface, so a tension wave of a s i m i l a r p r o f i l e but opposite sign must s t a r t propagating i n from the rear surfaces when the compressive front reaches t h i s surface. The actual stress state s h o r t l y thereafter i s shown i n state 2 i n Figure 21. When the t e n s i l e stress exceeds the t e n s i l e strength of the m a t e r i a l , s p a l l occurs on a plane p a r a l l e l to the free surface. The normal s t r e s s then drops to zero again, and the process continues. In b r i t t l e materials weak i n tension (such as concrete), i t i s possible f o r m u l t i p l e s p a l l s to occur before the r e f l e c t e d t e n s i l e waves decay enough to f a l l below the t e n s i l e strength. For t h i s s i m p l i f i e d model of s p a l l i n g , graphical boundaries have been determined f o r i n c i p i e n t s p a l l f o r normally r e f l e c t e d a i r b l a s t loading i n Ref. 28, as shown i n Figure 22. In t h i s f i g u r e , terms not already introduced are defined as follows:

i s the e l a s t i c d i l a t a t i o n a l wave speed i n the s o l i d , H i s w a l l thickness, and a i s ultimate t e n s i l e strength of the w a l l m a t e r i a l . u

In preparing t h i s f i g u r e , the authors of Ref. 28 assumed no wave attenuation through the w a l l thickness H, so P and i are the normally r e f l e c t e d b l a s t loading parameters on the loaded side of the w a l l or s l a b . S p a l l i n g can occur f o r guite strong materials such as s t r u c t u r a l steels and instances are shown i n Refs. 25-27 f o r contact or near contact detonations. But of course i t i s more prevalent f o r weaker materials. For complex composites such as reinforced concrete, the use of simple wave r e f l e c t i o n analyses to predict s p a l l i n g i s guite suspect. So, several investigators have simply studied these thresholds experimentally. One of the most complete such studies i s r e ported i n Ref. 29. The author defined various damage categories f o r explosions near reinforced concrete w a l l s , as i n Figure 23. Then, he conducted a number of experiments and established scaled curves f o r various damage l e v e l s , as i n Figures 24 and 25. The l a t t e r two curves can be used f o r guick estimates f o r both s p a l l i n g and breaching of t y p i c a l reinforced concrete w a l l panels. r

r

Shock Response Versus Quasi-Static Response f o r Internal B l a s t . We noted e a r l i e r that i n t e r n a l detonations of high explosives w i t h i n structures caused both i n i t i a l and r e f l e c t e d shock loadings, plus longer term gas pressure loads c a l l e d g u a s i - s t a t i c pressures. Figure 11 i s a reproduction of a pressure trace showing both phases of the loading. Damage from i n t e r n a l b l a s t i s of course a function of the complete time h i s t o r y of the pressure loading. But, the duration of the shock phase of the loading i s u s u a l l y much shorter than duration of vented gas pressure loading, while the amplitude of the shock phase i s much greater than peak g u a s i - s t a t i c pressure. Quite often, the fundamental periods of walls or roofs are much longer than the shock

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

to

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Co

m jo

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In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Distance of Explosion from Wal

Characteristic Damages

Denned Oemago Category

No relevant damage,

1 1

cracks •v. smel crater

Ο crater, deflections and cracks

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///

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Figure 23. D e f i n i t i o n of Damage Categories. (Ref. 29)

Figure 24. Damage t o Reinforced Concrete W a l l s c a u s e d by Detonation of Uncased Explosives Charges. (Ref. 29) (r/W = Scaled Distance; t/W / = Scaled Wall Thickness) 1/3

1

3

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

BAKER

Blast Pressure Effects: An Overview

Figure 25. Damage to Reinforced Concrete Walls caused by Detonation of Cased Explosives Charges. (Ref. 29) ( r / v / = Scaled Distance; t/W / = Scaled Wall Thickness) 1

3

1

3

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

30

loading phase, but much shorter than the gas loading phase. So, the structure then responds p r i m a r i l y t o shock impulse, and t o peak quasis t a t i c pressure. With good venting, both phases may be s i g n i f i c a n t l y shorter than s t r u c t u r a l periods, i n which case the t o t a l impulse, shock plus gas impulse, governs. As always, dynamics of the response plus these r e l a t i v e times must be considered i n evaluating the r e l a t i v e importance of shock loading versus q u a s i - s t a t i c loading. Prediction of B l a s t Overpressure Outputs A i r Shock Parameters. There are a v a i l a b l e several "Standard" sets of curves of scaled a i r b l a s t parameters f o r high explosive detonations i n a i r . Such curves are always presented i n scaled format using either the Hopkinson-Cranz s c a l i n g (Refs. 6, 15 or 30) or Sachs s c a l ing (Ref. 5) discussed e a r l i e r . When presented i n the more common Hopkinson-Cranz scaled form, i t has been common practice t o use charge weight W or mass also t o key the curves t 6, 15 or 30). I t i s also presumed, but not always stated, that standard (sea l e v e l ) atmospheric conditions e x i s t when the explosions occur. F i n a l assumptions usually employed are that the charges are bare and of s p h e r i c a l geometry. Some sources such as the t r i - s e r v i c e manual (Ref. 30) include sets of b l a s t parameter curves f o r s p h e r i c a l f r e e - a i r explosions and separate sets of curves f o r hemispherical surface burst explosions. This i s superfluous except at very small scaled distances, because the f r e e - a i r curves can be used f o r both s i t u a t i o n s by simply using a higher e f f e c t i v e charge weight f o r surface bursts. We include a set of Hopkinson-Cranz scaled curves f o r b l a s t wave properties versus scaled distance, f o r bare s p h e r i c a l TNT detonated i n free a i r under sea l e v e l ambient conditions, as Figure 26. This set of curves was developed i n Ref. 31 f o r i n c l u s i o n i n the r e v i s i o n t o Ref. 30. When using Figure 26 t o p r e d i c t b l a s t wave properties f o r cond i t i o n s other than bare, s p h e r i c a l TNT detonated away from a r e f l e c t ing surface and a t sea l e v e l ambient conditions, suggested adjustments are as follows: 1)

Account f o r a surface or near-surface burst by f i r s t c a l c u l a t i n g a new e f f e c t i v e f r e e - a i r charge weight, W , as e

W

e

= (1.7 t o 2.0) X W

(27)

The lower value i s used f o r explosions on sand or s o i l , while the upper value i s used f o r explosions which cause no c r a t e r i n g . 2)

Account f o r high a l t i t u d e ambient conditions by using c o r r e c t i o n factors based on Sachs s c a l i n g (Ref. 28). Below 5000 f t . a l t i t u d e , these corrections are n e g l i gible.

3)

Account f o r change i n type of explosion by using a TNT equivalency f a c t o r , unless good t e s t data are a v a i l a b l e

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

BAKER

Blast Pressure Effects: An Overview

Figure 26. A i r b l a s t Parameters vs. Scaled Distance f o r a TNT Spherical A i r Burst. (Ref. 31)

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

32

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

for the explosive. A rough estimate of TNT equivalency can be made based on r e l a t i v e heats of detonation of your explosive and TNT. This procedure i s f a r from exact (see Ref. 6 and 32), but w i l l allow you to at l e a s t e s t i ­ mate b l a s t wave properties f o r other explosives. 4)

See Ref. 28 f o r l i m i t e d methods to predict e f f e c t s of charge shape. For long c y l i n d r i c a l charges, b l a s t i s en­ hanced o f f the charge a x i s and attenuated along the a x i s , compared to equal weight s p h e r i c a l charges. These e f f e c t s can p e r s i s t to about 15 charge diameters.

Wall or C e i l i n g Shock Loads. The shock loads on walls or c e i l i n g f o r explosions w i t h i n structures usually vary appreciably over these surfaces, because the distances of the explosive sources from the surfaces are often l e s s than l a t e r a l dimensions of the surfaces. So, the part of the surface normally r e f l e c t e d shock sweeping over the surface p predicting loading, experimental data f o r such surface loads have been curvef i t t e d , i n preparation f o r r e v i s i o n s to Ref. 30. Figures 27 and 28 present these f i t s . Figure 27 requires knowledge of the angle of incidence of the oblique shock, and the side-on overpressure P . I t then gives a m u l t i p l i e r which y i e l d s the r e f l e c t e d pressure on the surface at t h i s incidence angle, P . Figure 28 gives d i r e c t l y the Hopkinson-Cranz scaled r e f l e c t e d impulse i , also given the i n ­ cidence angle and peak side-on overpressure as inputs. By using these two curves, p l o t s of v a r i a t i o n s of peak pressure and impulse over a w a l l surface can be estimated, f o r the f i r s t shock wave r e f l e c t e d from the surface. Again r e f e r r i n g to Figure 11, we see that the shock loads are, i n general, more complex than t h i s s i n g l e pulse loading, with several r e f l e c t e d pulses. But, study of considerable i n t e r n a l b l a s t data has shown that a good approximation to t o t a l shock loading can be made by assuming only second and t h i r d r e f l e c t e d shocks, with halving of the amplitudes (and impulses) each time (see Figure 29). Times between pulses are assumed to be twice the times of a r r i v a l for shocks c a l c u l a t e d f o r explosive sources centered i n the s t r u c ­ ture. I f the t o t a l loading time t + 4T i s much l e s s than s t r u c ­ t u r a l period, then the three pulses can be combined i n t o a s i n g l e pulse with amplitude 1.75 Ρ and duration T . I t i s also common p r a c t i c e to integrate the pressures and im­ pulses, over the surface areas, to obtain average values, rather than t r y and compute s t r u c t u r a l response to s p a t i a l l y - v a r y i n g , as w e l l as time-varying loads. But, t h i s averaging procedure should be used cautiously f o r long walls or c e i l i n g s , because i t can lead to serious underprediction of shock loads f o r part of the surface. s

rct

r o t

a

r

r

Quasi-Static Parameters. We noted e a r l i e r that the longer-term gas pressures which develop f o r explosions i n vented or unvented s t r u c ­ tures can be characterized by three parameters; the peak quasis t a t i c pressure P Q , the duration t and the gas impulse i g . For uncovered vents, reams of vented gas pressure data have been c o l ­ lapsed i n t o scaled p r e d i c t i o n curves and equations f o r these para­ meters i n Ref. 18. We simply present that material here, as Figures s

m

a

x

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

BAKER

Blast Pressure Effects: An Overview

Figure 27. Incidence.

Reflected Pressure C o e f f i c i e n t Versus Angle of

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1. BAKER

Blast Pressure Effects: An Overview

35

30-32 and Tables I - I I I . Note that l i m i t s of a p p l i c a b i l i t y and stan­ dard deviations appear i n the tables. In most explosives safety structures, completely uncovered vent areas are unacceptable, e i t h e r f o r environmental or security reasons. So, the vent areas have covers which may be quite l i g h t and frangible but have some i n e r t i a . Both analyses and t e s t i n g have shown that even very l i g h t vent covers can s i g n i f i c a n t l y increase the duration and gas impulse f o r the gas pressure phase of i n t e r n a l blast loading. This work has been reduced to prediction curves which w i l l appear i n the r e v i s i o n to Ref. 30, as reported i n Ref. 33. There are too many curves to reproduce here, but one i s shown as Figure 33 to indicate i t s nature. The quantity Ύ i s the s p e c i f i c weight of the vent panel, i n l b / f t , the charge weight i s i n l b TNT equivalent, and room volume V i s i n f t , f o r t h i s f i g u r e . 2

3

Table I .

Summar P

ρ - QS + Po Po W/p Vll00 o

p = 1.336

0

(W/p V) -

6717

0

Correlation C o e f f i c i e n t , r : 0.977 One Standard Deviation, σ W/p Vl350 o

·

0

p = 1.336

1.164 0

(W/p V) 0

Correlation C o e f f i c i e n t , r : 0.977 One Standard Deviation, σ : 0

W/Po

> 700

1.262

ρ = 0.1388 (W/p V) Q

Correlation C o e f f i c i e n t , r: 0.896 One Standard Deviation, a : Q

1.300

Containment and Venting Techniques Containment Structure Concepts. In some types of safety f a c i l i t i e s , i t i s e i t h e r necessary or desirable to completely contain the e f ­ fects of i n t e r n a l explosions. This requirement can a r i s e because personnel, c r i t i c a l equipment, or c r i t i c a l operations must be l o c a ­ ted very near the f a c i l i t y , so one wishes to e n t i r e l y eliminate b l a s t emitted from the safety structure. A more stringent require­ ment requiring complete containment occurs i n f a c i l i t i e s f o r de­ m i l i t a r i z a t i o n of chemical munitions. Here, the extremely t o x i c

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

36

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Figure 30. Reduced Pressure Versus Reduced Energy Density. (Reprinted with permission from r e f . 18. Press.)

Copyright 1983 Pergamon

Figure 31. Reduced Duration Versus Reduced Pressure. (Reprinted with permission from r e f . 18.

Copyright 1983 Pergamon Press.)

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

BAKER

Blast Pressure Effects: An Overview

Figure 32. Reduced S p e c i f i c Impulse Versus Reduced Pressure. (Reprinted with permission from r e f . 18. Pergamon Press.)

Copyright

1983

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

38

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Figure 33. Gas Impulse Inside Structure with Frangible Panel. (W/V = 0.015, i / w V 3 20) (Ref. 33) e

=

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1. BAKER

Blast Pressure Effects: An Overview

39

Table I I . Summary of ~ vs "p (Ref. 18) a

A

/* o \ heff \ \ l / 3 / \ 2/3 / V

v

Po τ = 0.4284 (p)0.3638

Correlation C o e f f i c i e n t , r : 0.799 One Standard Deviation

Table I I I . Summary of i

a

is =

ig o aeff PoV P

Ρ = QS

+

a

1.50

vs ρ (Ref. 18)

g

A

Po

Po i

1

s

= 0.0953 ( ρ ) ·

3 5 1

Correlation C o e f f i c i e n t / r : 0.977 One Standard Deviation:

σ

0

= 1.53

nature of the chemical agents d i c t a t e s the containment i n the event of accidental detonation of explosive bursters during demil opera­ tions. The s i z e , shape and materials of construction depend on the function of the f a c i l i t y , the net explosive weight (NEW) f o r the worst-case accidental explosion i n the f a c i l i t y , and other f a c t o r s . Both reinforced concrete and s t e e l have been used as materials, and shapes range from box (room) shaped, through h o r i z o n t a l and v e r t i c a l c y l i n d e r s to spheres. Generally, the room-shaped s t r u c ­ tures are most economically designed and constructed of reinforced concrete, while c y l i n d r i c a l and s p h e r i c a l shapes are most e f f i c i e n t ­ l y designed when made of s t e e l . In t h i s keynote chapter, we give no d e t a i l s of containment structure configurations and designs. But, we note that Ref. 34

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

40

T O X I C C H E M I C A L A N D E X P L O S I V E S FACILITIES

includes a comparison study f o r d i f f e r e n t c e l l configurations f o r chemical munitions demil operations. Venting Techniques. The majority of explosive safety structures designed t o mitigate or c o n t r o l the e f f e c t s of i n t e r n a l explosions are vented i n some fashion. The structures then attenuate or m i t i gate b l a s t e f f e c t s i n adjacent bays or rooms, but do not completely contain these e f f e c t s . Proper venting can s i g n i f i c a n t l y reduce or even eliminate gas pressure durations and impulses, and thus reduce t o t a l i n t e r n a l b l a s t loads on safety structures. But, you are warned that venting i s e s s e n t i a l l y t o t a l l y i n e f f e c t i v e i n reducing i n t e r n a l shock loads. D i r e c t i o n a l Venting. Most vented explosion safety structures are designed with blowout w a l l panels, e n t i r e w a l l s , e n t i r e r o o f s , o r even the e n t i r e roof and one w a l l . Other walls and roofs i n the structure are designed t catastrophic f a i l u r e . Th provide some c l o s e - i n b l a s protection, hopefully complet pro t e c t i o n from fragments and thermal r a d i a t i o n . But b l a s t i n the venting d i r e c t i o n s i s not always attenuated compared t o f r e e - f i e l d b l a s t and can even be enhanced i n c e r t a i n d i r e c t i o n s . The most complete study of these d i r e c t i o n a l venting e f f e c t s f o r no vent covers i s reported i n Ref. 35. The r e s u l t s of scaled external b l a s t t e s t s i n cubicles with various vent area r a t i o s , A/V / , from 0.020 through 0.77 and a v a r i e t y of "loading d e n s i t i e s " W/V are reported and presented f o r d i f f e r e n t vented c u b i c l e c o n f i g urations, including those with venting of the e n t i r e roof and one w a l l . Highly d i r e c t i o n a l e f f e c t s p e r s i s t f o r some distances from these cubicles f o r some configurations. We have already noted a more recent report (Ref. 33) g i v i n g predictions f o r q u a s i - s t a t i c loading parameters w i t h i n directionally-vented cubicles with covers having various masses per u n i t area. Many explosion safety structures u t i l i z e p a r t i a l l y - b u r i e d designs, t o minimize costs by providing earth support f o r b l a s t r e s i s t a n t walls and t o prevent bay-to-bay propagation. Some of these structures are designed t o vent r e l a t i v e l y slowly through earth-covered or ground-covered roofs. Two such designs have been proof-tested with good i n t e r n a l and external b l a s t instrumentation (Ref. 36 and 37). For i n t e r n a l b l a s t t e s t s of a r e p l i c a of a box-shaped, earth backed bay i n the Pantex Plant a t A m a r i l l o , Texas, as i n Figure 34, some venting occurred through the entranceway (which was not designed f o r containment), but the venting roof opened slowly and a l most completely attenuated external b l a s t waves venting through the roof. A "Gravel Gertie" structure consists p r i m a r i l y of an earthbacked c y l i n d r i c a l reinforced concrete bay, with a deep gravel bed roof supported on a network of s t e e l cables, as i n Figure 35. In an i n t e r n a l b l a s t t e s t of the refurbished prototype f o r t h i s type of s t r u c t u r e , there was no b l a s t venting from the simulated staging bays opening i n t o the main c y l i n d r i c a l bay, and the main bay vented so slowly by upward displacement of the gravel roof that there was no measurable external b l a s t . The slowly-moving gravel bed also 2

3

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Figure 34. Elevation View of Replica of P a r t i a l l y Buried, EarthCovered Bay.(Ref. 36) In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

42

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

2' REINFORCED

Figure 35. Prototype Gravel Gertie Structure at NTS.(Ref. 37)

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

1.

BAKER

43

Blast Pressure Effects: An Overview

proved to be an e f f i c i e n t dynamic f i l t e r f o r small t o x i c p a r t i c l e s from the explosion. Omnidirectional B l a s t Venting. During the period 1973-1977, Edgewood Arsenal sponsored an extensive program t o evaluate the concept of s t e e l explosion safety structures which were vented on a l l sides, or a l l sides plus roof. These structures, intended to be fabricated p r i m a r i l y using standard s t r u c t u r a l s t e e l members, consisted of frameworks supporting multi-layered vent panels. They were termed "suppressive s h i e l d s " . The vent panels were a l l designed to atten­ uate a i r b l a s t f o r explosions w i t h i n the s h i e l d s , and the layers i n the panels were o f f s e t t o prevent d i r e c t passage of fragments. By the conclusion of the program, a number of designs had been b u i l t and tested, and proved quite e f f e c t i v e . Methods f o r p r e d i c t i o n of b l a s t attenuation and fragment arresting c a p a b i l i t y of the designs were developed and v e r i f i e d . There are numerous extensive suppressive shield together with design and analysis methods i n a single design manual, Ref. 38. Seven s h i e l d designs have obtained safety approval from the Department of Defense Explosives Safety Board, and t h e i r s p e c i f i c a ­ tions and construction drawings appear i n an appendix to Ref. 38. Typical sections through vent panels evaluated i n the suppres­ sive shields program are shown i n F i g . 36, together w i t h d e f i n i t i o n s of vent area r a t i o s which were found to correlate with attenuation of transmitted b l a s t waves. The vent area r a t i o f o r a s i n g l e layer structure i s the vent area divided by the t o t a l area of the w a l l . The vent area r a t i o f o r a m u l t i - l a y e r structure i s η a

Z-J

e

ve Set PQint? Steam V a l v e S e t P o i n Steam V a l v e S e t p o i n I n l e t A i r F l a p P o s i t i o n : 100 A i r Volume S e t P o i n t 1: 38. A i r Volume S e t P o i n t 2: 44 A i r Volume S e t P o i n t 3: 38 Atomization A i r Pressure P r e s e l e c t i o n : Atomization A i r Pressure: 4.0 Bar

2.5 b a r s

Glatt Uhit Limit Set Points Jnteruption Mixing: 35 C Operation Cooling 35 C O p e r a t i o n Drying.70 C I n l e t A i r Temperature L i m i t : 90 C Exhaust A i r Temperature L i m i t ( O p e r a t i o n C o o l i n g ) : 35 C Exhaust A i r Temperature L i m i t ( O p e r a t i o n D r y i n g ) : 65 C :

The b i n d e r and f l u i d i z a t i o n a i r parameters a r e i n b a l a n c e w i t h each o t h e r and a l s o e f f e c t t h e p a r t i c l e s i z e d i s t r i b u t i o n . If the b i n d e r a d d i t i o n r a t e o r b i n d e r s p r a y s i z e were i n c r e a s e d , t h e f l u i d i z a t i o n a i r temperature o r f l u i d i z a t i o n a i r r a t e must be increased t o prevent changing the nature o f the f i n a l product. L i k e w i s e i f t h e f l u i d i z a t i o n a i r temperature or r a t e a r e d e c r e a s e d , the b i n d e r a d d i t i o n r a t e o r s p r a y s i z e must be d e c r e a s e d t o m a i n t a i n the same p a r t i c l e s i z e d i s t r i b u t i o n i n t h e f i n a l m i x . The b i n d e r used i n G l a t t g r a n u l a t i o n i s a s i x p e r c e n t ( 6 % ) b y weight s o l u t i o n o f PVA i n w a t e r . The b i n d e r i s a c c u r a t e l y weighed and s l o w l y poured i n t o t h e s t i r r e d non-heated w a t e r . When a l l t h e PVA i s added, heat i s a p p l i e d t o b r i n g t h e temperature o f t h e s l u r r y t o 185 F. T h i s temperature i s m a i n t a i n e d f o r a t l e a s t 30 m i n u t e s , or u n t i l a l l t h e PVA i s i n s o l u t i o n . At t h i s p o i n t t h e a p p l i c a t i o n of heat i s d i s c o n t i n u e d a n d t h e b i n d e r i s a l l o w e d t o c o o l b e f o r e use. F u l l Scale G l a t t Mixing. The f l u i d i z e d bed g r a n u l a t o r i s one o f t h e most important g r a n u l a t i o n methods a v a i l a b l e today, because i t combines t h e u n i t o p e r a t i o n s o f m i x i n g , g r a n u l a t i n g , a n d d r y i n g i n t o

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

9. SHOOK ET AL.

Mixing and Handling of Pyrotechnic Materials

163

one system. The f l u i d i z e d bed m i x e r , w n i c h has long been used by the p h a r m a c e u t i c a l i n d u s t r y , f i t s many p y r o t e c h n i c p r o c e s s i n g r e q u i r e m e n t s s u c h a s m a t e r i a l s containment, e a s e o f c l e a n i n g , homogeneity o f mix. and hygiene. N

Hazards A n a l v s t s - G l a t t . B e f o r e t h e G l a t t c o u l d become a f e a s i b l e a l t e r n a t i v e f o r m i x i n g M18 c o l o r e d smoke mix, i t was n e c e s s a r y t o conduct s a f e t y c l a s s i f i c a t i o n t e s t s [ T a b l e I ) . The c o m p o s i t i o n s were t e s t e d i n t h e G l a t t m a n u f a c t u r i n g p r o c e s s and were found t o g e n e r a t e minimal amounts o f e l e c t r o s t a t i c energy d u r i n g the m i x i n g , g r a n u l a t i n g , and d r y i n g p r o c e s s e s . Full scale simulation tests ut i11 ζ ing 740 and 940 pound b a t c h e s i n d i c a t e d t h a t t h e r e were no mass d e t o n a t i o n h a z a r d s d u r i n g m i x i n g . Based on t h e above e v i d e n c e the Department o f Defense E x p l o s i v e s S a f e t y Board a I lowed an i n - p r o c e s s h a z a r d s c l a s s i f i c a t i o n o f 1.3. T h i s a l l o w e d b a t c h s i z e s to be i n c r e a s e d t c 1000 pounds. A critical differenc pharmaceutical p r o c e s s i n pharmaceutical p r a c t i c e involves p r o c e s s i n g w i t h the operator p h y s i c a l l y p r e s e n t a t t h e u n i t t o make a d j u s t m e n t s a s p r o c e s s i n g d i c t a t e s . S a f e t y requirements i n p y r o t e c h n i c s p r o c e s s i n g f o r c e remote o p e r a t i o n . S i n c e p y r o t e c h n i c p r o c e s s i n g must be p e r f o r m e d w i t h o u t t h e l u x u r y o f an o p e r a t o r p h y s i c a l l y p r e s e n t a t t h e u n i t t o make a d j u s t m e n t s a s t h e p r o c e s s i n g d i c t a t e s , d e t a i l e d o p e r a t i n g parameters were d e v e l o p e d f o r each p y r o m i x t u r e . Product Loading. P r o d u c t i o n o f mixes w i t h c o n t r o l l e d p a r t i c l e s i z e d i s t r i b u t i o n s ( F i g u r e 4 ) c a n be a c c o m p l i s h e d i n t h e G l a t t , a n d t h i s c o n t r o l o f p a r t i c l e s i z e i s e s s e n t i a l f o r s u c c e s s f u l automated v o l u m e t r i c feeding of a Stokes r o t a r y press. S l u g production r a t e s exceed 80 s l u g s p e r m i n u t e . T h e r e f o r e a f r e e - f l o w i n g p r o d u c t i s e s s e n t i a l to obtain consistent s l u g q u a l i t y . After production, the s l u g s t r a v e l f l a t on a c o n d u c t i v e rubber conveyor ( F i g u r e 5) t o a g r a v i t y t r a c k where they a r e t u r n e d on edge. Next they r o i I down t o an a u t o m a t i c s l u g placement machine. Four s l u g s a r e f e d i n t o each of two r o t a r y c y l i n d e r s w h i c h r o t a t e t h e s l u g s 90 degrees t o a v e r t i c a l p o s i t i o n . The e i g h t s l u g s f a l l four each i n t o two cans on f l o a t i n g p a l l e t s on t h e conveyor beneath. Proper i n s e r t i o n o f t h e s l u g s i s a s s u r e d by t h e passage o f rods through t h e r o t a r y c y l i n d e r s . The s l u g f i I l e d cans t r a v e l t o an automated c o n s o l i d a t i o n p r e s s where t h e s l u g s a r e c o n s o l i d a t e d i n t o an i n t e g r a l mass (9,JO). Equipment s u r v e y s l e d t o t h e p u r c h a s e o f a t w i n f e e d , 11 s t a t i o n , r o t a r y s l u g g i n g p r e s s (Pennwalt S t o k e s 523 PBX). The p r e s s has a v a r i a b l e p r o d u c t i o n r a t e o f from 60 t o 180 s l u g s p e r m i n u t e . Seme f e a t u r e s o f t h i s p r e s s a r e : d o u b l e a c t i o n compression, 30,000 pound c a p a c i t y , remote pneumatic f i l l weight a d j u s t m e n t , 7.6 cm maximum s l u g diameter p r e s s , vacuum dust c o l l e c t o r s , and e x p l o s i o n p r o o f e l e c t r i c a l c o n t r o l s . The p r e s s i s c a p a b l e o f c o n s i s t e n t l y p r o d u c i n g s l u g s o f u n i f o r m d e n s i t y and s i z e a t a compaction p r e s s u r e of 5000 l b s . V a r i a t i o n s i n t h e p a r t i c l e s i z e d i s t r i b u t i o n o f t h e smoke m i x wi11 o c c u r i n any m i x i n g p r o c e s s . T h e r e f o r e s t u d i e s were made u s i n g t h r e e mixes o f d i f f e r e n t p a r t i c l e s i z e d i s t r i b u t i o n from t h e G l a t t p r o c e s s . The p a r t i c l e s i z e d i s t r i b u t i o n s were i d e n t i f i e d a s "Dusty"

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

164

PLOTS

OF

SLUG

THICKNESS

2.46

W > A ^

2.39 (CM) IF OUTLET AIR TEMP - 45 C MIX WILL BE DUSTY

I1 1

6- 4 0 20 100 10

35 C IDEAL

75% 50% 25% 0%

SIEVE SIZE

1 1 SIEVE

25 C COARSE %

THRU SIEVE

SIZE

1 11

1

SIEVE SIZE

ADDITION OF: MASS (WATER) AND ENERGY (HEAT) MUST B E BALLANCED AT SPECIFIC LEVELS (OUTLET AIR TEMP) FOR PROPER GRANULATION F i g u r e 4.

R e l a t i o n s h i p Between G l a t t Particle

F i g u r e 5.

S i z e and R e s u l t a n t

Operating Slug

Parameter,

Thickness

S l u g Placement Machine

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

9.

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(many p a r t i c l e s s m a l l e r than 100 mesh), "Idea!" (most p a r t i c l e s 60-100 mesh), and "Coarse" (many p a r t i c l e s i n 12-40 mesh r a n g e ) . S l u g s were produced u s i n g the t h r e e d i f f e r e n t m i x e s w i t h samples taken at one m i n u t e i n t e r v a l s f o r s l u g t h i c k n e s s checks. Figure 4 shows the g e n e r a l e f f e c t of p a r t i c l e s i z e d i s t r i b u t i o n on s l u g thickness. As was shown above ( F i g u r e 4), a u n i f o r m p a r t i c l e s i z e d i s t r i b u t i o n i s important t o a c h i e v e c o n s i s t e n t p r e s s f e e d i n g . A change i n p a r t i c l e s i z e d i s t r i b u t i o n changes the r a t e a t w h i c h the p a r t i c l e s f l o w and t h e r e f o r e a f f e c t s s l u g p r e s s l o a d i n g . Two v a r i a b l e s t h a t a f f e c t the s l u g q u a l i t y a r e the r a t e of mix f e e d i n t o the s l u g p r e s s d i e and the d i e f i l l v o i u r e . The mix f e e d r a t e v a r i e s d i r e c t l y w i t h m a t e r i a l hopper d i s c h a r g e h e i g h t above the f e e d e r . S l u g d e n s i t y v a r i e s d i r e c t l y w i t h d i e f i 1 1 volume. The d i e f i l l volume i s a d j u s t e d by r a i s i n g or l o w e r i n g the lower punch on the s l u g p r o d u c t i o n p r e s s . If the mix d e n s i t y changes from " i d e a l " to " c o a r s e " , the hoppe die f i l l volume i s i n c r e a s e dens ιty. Jet

A i r m i x Mixer Smoke Mix

Batches.

H e x a c h l p r o e t h a n e ( H Q smoke mix p r o d u c t i o n . E v a l u a t i o n of the Sprout Waldron 35 c u b i c f o o t J e t A i r m i x U n i t ( F i g u r e 3) f o r M i x i n g 2,200 pounds of w h i t e HC smoke mix ( c o n s i s t i n g of HC, z i n c o x i d e , and aluminum) was conducted ( H ) . The m i x e r was s e l e c t e d t o r e p l a c e the 340 pound r o t a r y M c C l e l l a n d B l e n d e r . T e s t i n g revealed that improved m i x i n g was acccrrpl i s h e d i n about 2 m i n u t e s w i t h v e r y few r e j e c t e d batches. The J e t A i r m i x u n i t uses d r y , h i g h p r e s s u r e (250-300 p s i ) a i r p u l s e s d i s c h a r g e d through a n g u l a r n o z z l e s t o l i f t , s w i r l , and b l e n d the m a t e r i a l through a t i i r b l i n g a c t i o n . F i v e t o twenty s h o r t (2-5 sec.) p u l s e s spaced w i t h s i m i l a r l y timed pauses represented a ccmplete m i x i n g c y c l e . S a f e t y t e s t i n g i n d i c a t e d low e l e c t r o s t a t i c charge g e n e r a t i o n d u r i n g m i x i n g . P a r a m e t r i c s t u d i e s r e p o r t e d the m a t e r i a l was d i f f i c u l t to i g n i t e . In-process c l a s s i f i c a t i o n of 1.4 was approved. Four m i x e r s have been i n o p e r a t i o n a t PBA f o r s e v e r a l y e a r s . Loading i s from the t o p , u s i n g weigh f e e d e r s and a i r t r a n s f e r equipment. M i x i n g a i r i s d i s c h a r g e d t o a bag house d i r e c t l y above the m i x e r and then through a HEPA f i I t e r . The bag house f i n e s d i s c h a r g e back i n t o the mix and a r e r e c y c l e d . Red Phosphorus smoke mix p r o d u c t i o n . E v a l u a t i o n of t h e Sprout Waldron 35 c u b i c f o o t J e t A i r m i x u n i t f o r p r o d u c t i o n of Red Phosphorus (RP) M8E1 Smoke M i x t u r e s was conducted ( 1 2 ) . R e s u l t s i n d i c a t e d t h e mix was s t a b i l e and not e a s i l y i n i t i a t e d by h e a t , but s e n s i t i v e t o f r i c t i o n and spark s t i m u l i . The b u r n i n g time was slow w i t h dense smoke e m i s s i o n . F u l l s c a l e m i x i n g s t u d i e s were conducted w i t h o u t i n c i d e n t u s i n g 100, 250, 500, and 1,000 pound b a t c h s i z e s . E l e c t r o s t a t i c charge g e n e r a t i o n d u r i n g the b l e n d i n g c y c l e was s e v e r a l o r d e r s of magnitude below t h a t r e q u i r e d f o r i n i t i a t i o n . To f u r t h e r e v a l u a t e the mix an e l e c t r i c match was used t o i n i t i a t e t h e r e a c t i o n of a 1,000 pound b a t c h o f smoke c o m p o s i t i o n . Al I t e s t s were conducted w i t h the b l e n d e r e q u i p p e d w i t h a 16 i n c h

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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diameter r u p t u r e d i s c r a t e d a t 4 p s i and an i n t e r n a ! I y mounted UV d e c t e c t o r and water d e l u g e . Without the use of t h e rapid f i r e d e t e c t i o n and water d e l u g e , a m a s s i v e " f i r e b a l l " was r e l e a s e d . W i t h the use of the r a p i d f i r e d e t e c t i o n and water d e l u g e , t h e r e was no mass f i r e and the mix was dtmped i n t o water f o r c o n t i n u e d f i r e s u p p r e s s i o n . Any f i r e w i t h RP r e s u l t s i n the f o r m a t i o n of w h i t e phosphorus (wP). wP must be c o v e r e d w i t h water s i n c e i t i g n i t e s s p o n t a n e o u s l y when exposed to a i r . P r o c e s s i n g s t u d i e s were conducted t o d e t e r m i n e the b e s t methods f o r p o l l u t i o n abatement s i n c e WP/water m i x t u r e s a r e t o x i c a t 29 ppb f o r b l u e gi11 bream and s i n c e h i g h l e v e l s of phosphorus C r e p o r t e d as t o t a l phosphorus) may not be dumped i n t o the environment. There was no s i g n i f i c a n t damage t o equipment i n the f i r e t e s t s , and i t was demonstrated t h a t a J e t A i r m i x mixer may s a f e l y h a n d l e the m i x i n g of RP f o r m u l a t i o n s on a r o u t i n e b a s i s . S i n c e a h i g h r i s k of f i r e i s always a s s o c i a t e d w i t h any method of t r a n s f e r of RP, a p n a m a t i c conveying syste t r a n s f e r system) was e v a l u a t e E l e c t r o s t a t i c c h a r g e measurements were minimal and i n d i c a t e d the system was s a t i s f a c t o r y t o l o a d the b l e n d e r . Al I work was conducted w i t h "οι l e d " RP as s u p p l l e d by ERGO L i m i t e d , Canada. The " o i l e d " RP i s much l e s s s e n s i t i v e than " n o n - o i l e d " RP. Conclusion. Proper s a f e t y t e s t i n g and c l a s s i f i c a t i o n of p y r o t e c h n i c e n e r g e t i c c a p a c i t y w i l l a l l o w the s e l e c t i o n of a p p r o p r i a t e , remotely o p e r a t e d , corrmercial l y a v a i l a b l e equipment. T h i s eouicment can be i n s t a l l e d i n l e s s c o s t l y s t r u c t u r e s and p l a n t s i t e s f o r the m a n u f a c t u r e of p y r o t e c h n i c m a t e r i a l s i n a s a f e and economical manner. O f t e n , c o n s i d e r a b l e problems a r i s e i n c o s t and s a f e t y when p y r o t e c h n i c formulas a r e s e l e c t e d frcm the l i t e r a t u r e and used w i t h o u t r e g a r d f o r t h e e n e r g e t i c requirements o f the task t o be acccmpl i s h e d . For example s t a r t e r mix formulas mav be too r e a c t i v e f o r t h e i r intended use, but they c o u l d be used i f they were m o d i f i e d and t e s t e d r e l a t i v e t o p e r c e n t c o m p o s i t i o n , p a r t i c l e s i z e , c o n s o l i d a t i o n p r e s s u r e , p u r i t y , e t c . t o g a i n a 1.3 or 1.4 UNO classification. The c o n t i n u e d a d d i t i o n of i n g r e d i e n t s over the y e a r s f o r h e a t i n g or c o o l i n g o f a f o r m u l a t i o n w i t h o u t r e g a r d t o the b a s i c c h e m i s t r y o f the m i x t u r e was a p r o b l e m t h a t was n o t e d through r e v i e w of many f o r m u l a t i o n s i n the l i t e r a t u r e . Thus many examples may be found where " e x t r a " i n g r e d i e n t s have been i n c l u d e d w h i c h tend to negate each o t h e r and r a i s e p r o d u c t i o n c o s t s . The American P y r o t e c h n i c s A s s o c i a t i o n , P.O. Box 213, C h e s t e r t o w n , M a r y l a n d 21620, an i n d u s t r y a s s o c i a t i o n , p r o v i d e s a s s i s t a n c e t o m a n u f a c t u r e r s t h a t r e q u i r e more i n f o r m a t i o n . Annual Summer Symposia i n P y r o t e c h n i c C h e m i s t r y a r e a l s o o f f e r e d by Washington Col l e g e , C h e s t e r t o w n , M a r y l a n d 21620. The I n t e r n a t i o n a l P y r o t e c h n i c s Seminar on E x p l o s i v e s and P y r o t e c h n i c s i s o f f e r e d on a b i e n n i a l b a s i s . A d d i t i o n a l i n f o r m a t i o n on t h e s e seminars may be o b t a i n e d from I IT R e s e a r c h I n s t i t u t e , Chicago, I l l i n o i s 60616.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

9. SHOOK ET AL.

Mixing and Handling of Pyrotechnic Materials

Literature Cited 1.

McLain, Joseph H. Pyrotechnics; The Franklin Institute Press Philadelphia, Pennsylvania. (1980). 2. Conkling, John A. Chemistry of Pyrotechnics: Marcel Dekker, Inc. New York (1985). 3. Meyer, Rudolf. Explosives; Verlag Chemie, New York (1977). 4. Safety Regulation (AMC-R 385-100, Chapter 17), U.S. Army Material Command, Alexandria, Virginia 22333-0001 (1985). 5. Armour, Carl; and Smith, Lloyd A.; "The Invention of a New Type of Friction Sensitivity Apparatus," RDTR No. 60, 11 June 1965, U.S. Naval Ammunition Depot, Crane. IN 6. McIntyre, F.L. Safety Enhancement Program for MIGRAD Mixer Study; U.S. Army Armament, Munitions, and Chemical Command, Aberdee (1985). 7. Aikman, Loy; Shook, Thomas E.; Lehr, Robert; Robinson, Eddie; and McIntyre, F.L.; Improved Mixing, Granulation and Drying of Highly Energetic Pyromixtures; Pine Bluff Arsenal, Pine Bluff, Arkansas 71602-9500 (1986). 8. Garcia, David; Aikman, Loy; Abies, Larry; McIntyre, Fred; and Shook, Thomas; Smoke Mix Facility (Glatt); Pine Bluff Arsenal, Arkansas 71611 (1983). 9. Garcia, David J.; Aikman, Loy M.; McIntyre, F.L.; and Shook, Thomas E.; Rapid Plant Scale Mixing Granulation and Loading of Dry Materials During the Manufacture of Colored Smoke Munitions; Pine Bluff Arsenal, Pine Bluff, Arkansas 71602-9500 (1981). 10. Aikman, Loy; Garcia, David; and Shook, Thomas E.; New Fill and Press Technology for Production of Colored Smoke Grenades; Pine Bluff Arsenal, Pine Bluff, Arkansas 71602-9500 (1982). 11. Fortner, Wendell; Yeldell, Steven L; and Shook, Thomas E.; HC Product Improvement Studies: Pine Bluff Arsenal, Ρine Bluff, Arkansas 71602-9500 (1977). 12. McIntyre, Fred; Amend, R.J.; and Smith, M.; Blending Technology for Red Phorphuros Smoke Compositions, U.S. Army Armament, Munition and Chemical Command. Aberdeen Proving Ground, Maryland 21010-5423 (1985). RECEIVED May 1, 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

16

Chapter 10

Engineering Design for White Phosphorus Filling Operations and Facilities Harold D. McKinney Pine Bluff Arsenal, Pine Bluff, AR 71602-9500

This paper describes the development of a system and facilities for safe, efficient, and accurate filling of white phosphorus (WP) munitions Thi replaces dip-fil over thirty years, a productio method that was hazardous to operating personnel and generated unacceptable quantities of phosphorus contaminated water and gas. The new development, Volumetric Filling, is relatively pollution free and exceeds the U.S. Army's standards for filling of white phosphorus munitions. Since World War II, Pine Bluff Arsenal has produced m i l l i o n s of white phosphorus (WP) munitions for the United States Department of Defense. White phosphorus has a s p e c i f i c gravity of 1.728 at 145 F (the temperature that i s normally used for WP f i l l i n g operations) and melts at 111.4 F; i t ignites spontaneously i n atmospheric a i r and generates a dense white smoke, phosphorus pentoxide (P^O,.). Phosphorus pentoxide reacts with moisture i n the a i r to form phosphoric acid. WP munitions were used by U.S. m i l i t a r y forces and their a l l i e s to mark targets and to provide smoke screen coverage for troops and equipment i n combat zones. These munitions were produced primarily by the d i p - f i l l or w e t - f i l l method i l l u s t r a t e d by Figure 1. The method i s c a l l e d d i p - f i l l because empty munition bodies are dipped below the molten phosphorus l e v e l i n an open tank u n t i l the munitions are f i l l e d with l i q u i d phosphorus. The method i s also c a l l e d w e t - f i l l because a water overlay i s maintained over the l i q u i d phosphorus ( i n the f i l l tank) to prevent spontaneous combustion of the chemical element and because the f i l l e d munition w i l l have a slight water overlay (up to 1/8" column height allowed). Contamination of line equipment on a d i p - f i l l line i s a constant problem. During f i l l i n g operations, WP contamination i s transferred from f i l l e d munitions and pallets to surfaces of accessory equipment u n t i l the f i l l e d munition enters the cleaning station. Large quantities of water and gas are contaminated from: Q

This chapter not subject to US. copyright Published 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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169

a. p a r t i a l aspiration of f i l l e d munitions to the correct height fill b. necessary f i r e control action of spraying water on munitions and pallets on the f i l l i n g line c. munition cleaning station Because of the disadvantages of the d i p - f i l l method, the U.S. Army began e f f o r t s to provide a more acceptable method to f i l l and close white phosphorus munitions. This effort included design and i n s t a l l a t i o n of a small prototype WP "Height of F i l l " (HF) production line at Rocky Mountain Arsenal for 105mm, H60 rounds, and fabrication and test of a two nozzle HF line at Edgewood Arsenal. After the Edgewood Arsenal HF line was successfully demonstrated i n Maryland, the equipment was moved and r e i n s t a l l e d at Pine Bluff Arsenal where approximately 30,000, 2.75", MK67 WP rockets were f i l l e d for the U.S. Navy and 750, 175mm, XM510 WP rounds for the U.S. Army. After satisfactory Arsenal prepared a t o t a munition HF production l i n e . The s p e c i f i e d production rate was 8,000 munitions per eight hour s h i f t . A contract (Project No. 5680242) to design, fabricate, i n s t a l l , and de-bug the system at Pine Bluff Arsenal was awarded i n June of 1969. The new HF line was i n s t a l l e d at Pine Bluff Arsenal i n 1971. After numerous attempts to operate the f a c i l i t y ended i n f a i l u r e , the contract was terminated i n late 1972. Serious problems with the HF f i l l i n g system was the primary reason for f a i l u r e of the new production l i n e . Shortly after termination of the contract, Pine Bluff Arsenal conceived and developed a "volumetric dry f i l l " concept that proved to be an outstanding method for production of WP munitions. A project (No. 5751274) was approved and funded by the Army's Production Base Modernization and Expansion Project Management Office to prove out the Pine Bluff Arsenal volumetric f i l l i n g concept on a production basis. Some of the contractor-furnished equipment for the o r i g i n a l dry f i l l production line (conveyors, munition p a l l e t s , f i l l i n g station framework and f i l l tank, hydraulic units and e l e c t r i c a l power c i r c u i t s ) was modified and used during early development work. of

Description of the Pine Bluff Arsenal Volumetric F i l l i n g , Concept The Pine Bluff Arsenal white phosphorus volumetric f i l l i n g system (U.S. Patents 4,002,268, 11 January 1976, and 4,043,490, dated 23 August 1977) was conceived and developed by Pine Bluff Arsenal i n 1973 and has been used i n f i l l i n g WP munitions since early 1974. This development has provided a safe, clean and e f f i c i e n t method for processing WP munitions (30% reduction i n manpower requirements and a 90% reduction i n a i r and water p o l l u t i o n ) . The system i s an extremely accurate production f i l l i n g method. This accuracy i s very important i n WP operations since any adjustment i n munition volume i s hazardous and i n e f f i c i e n t . The line changeover from one munition to another i s accomplished by two experienced men i n one day. The f i l l i n g method (See Figure 2) i s e s s e n t i a l l y a f a i l - s a f e system i n that controls are designed to prevent double-cycling. The f i l l i n g valve and the reservoir valve are e l e c t r i c a l l y interlocked so

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Figure 2. Pine B l u f f Arsenal WP volumetric f i l l i n g system.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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171

that only one of the two valves can be open at any given time and the other must be completely closed and remain so u n t i l the other valve closes* This direct control feature prevents an operator error " s p i l l " from occurring i n the f i l l station* Also, a l l WP f i l l i n g , reservoir, and control valves are pneumatically-operated (spring-return closure), f i r e - s a f e b a l l valves that close immediately upon interruption of e l e c t r i c a l power or a i r supply. The automatic f i l l i n g cycle begins when an empty munition moves into position under a f i l l i n g nozzle (the volumetric chamber has been previously charged). The f i l l i n g nozzle (See Figure 3) i s inserted into the munition (the nozzle spring i s compressed and opens the f i l l port) and the f i l l i n g valve opens for a timed i n t e r v a l , dispensing a fixed, repeatable volume into each munition presented. After the f i l l i n g time i s terminated, the f i l l i n g valve closes, the nozzle retracts (the nozzle spring expands and closes the f i l l port) and the reservoir valve (See Figure 4) i s opened for a timed i n t e r v a l , allowing molten WP to flo reservoir valve into th of the adjustable vent tub y , ga trapped i n the volumetric chamber i s s l i g h t l y compressed. The molten WP then flows through the path of least resistance, which i s through the adjustable vent tube. WP flows through the vent tube u n t i l the l i q u i d height i n the vent tube i s equal to that i n the reservoir tank. The reservoir valve closes, and a preset and repeatable volume of WP i s ready for dispensing into the next munition presented. The f i l l i n g volume can be changed by a simple adjustment of the vent tube. The volume i s decreased when the bottom of the vent tube penetrates further into the volumetric chamber and i s increased when i t i s raised to a higher l e v e l i n the chamber. Figure 4 shows the o r i g i n a l volumetric chamber used under Phase I of this development and an improved volume chamber that was used for Phase II work. Figure 5 shows the accuracy of the volumetric chamber used during Phase I of t h i s development. The improved chamber provided increased accuracy (See Figure 6) required for smaller munitions such as the 60mm M302. The small diameter i n the vent tube adjustment area prevents any serious volume variations caused by changes i n gas compression. Design Considerations for Development of the Pine Bluff Arsenal Automatic Volumetric WP F i l l i n g F a c i l i t y Design Considerations. For t h i s new f a c i l i t y requirements were set as follows: a. Meet or exceed the f i l l i n g accuracy requirements for a l l WP munitions f i l l e d by the U.S. Army. b. Have the capability to f i l l a l l WP munition bodies up to 18" i n height. c. Provide safe working conditions for operators. d. Reduce manpower requirements and increase e f f i c i e n c y . e. Production rate of 24 munitions per minute. f. Reduce s i g n i f i c a n t l y a i r and water p o l l u t i o n associated with d i p - f i l l operations. g. Provide f a i l - s a f e , automatic operation where possible.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES 1. PNEUMATIC AIR CYLINDER ROD CONNECTION POINT 2. WHITE PHOSPHOROUS FILLING TUBE 3. FILLING NOZZLE TUBE 4 . FILLING NOZZLE SLIP TUBE ANO TIP SEAL CHEVRON TUBE SEALS CHEVRON PRESSURE ADAPTER 7. NOZZLE CLOSURE SPRING 8. FILLING NOZZLE SPRING ADAPTER 9. FILLING NOZZLE PORT 10. TAPERED TEFLON TUBE SEAL 11. "0" RING TUBE SEAL A2. NOZZLE TIP SEAL 13. MUNITION CAVITY

NOZZLE CLOSED POSITION] Figure 3.

NOZZLE OPEN POSITION

Pine Bluff Arsenal WP f i l l i n g nozzle -RESERVOIR VALVE

THREADED PRESSURE PLUG .-ADJUSTABLE VOLUME VENT TUBE ASSEMBLY

Figure 4.

Volumetric cylinder development.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987. 1060 1003 111

ml

1.27 ml

PROCESS AVERAGE (ml)

Figure 5. Pine B l u f f Arsenal phase 1 WP volumetric f i l l i n g accuracy.

A

1003 { 1000+

• 99* CONFIDENT THAT AT LEAST 99% OF MUNITIONS FILLED BY ••"THIS SYSTEM WILL BE WITHIN THE SPECIFICATION LIMITS AS LONG AS PROCESS AVERA6E IS BETWEEN 1006.3 ml - 1056.7 ml

ASSUME: PROCESS STANDARD OEVIATION

SAMPLE SIZE2991 PROCESS AVERAGE: 1030.7 ml PROCESS STANDARD DEVIATION: 1.27 ml 99/99 TOLERANCE LIMITS: UPPER: 1034.0 ml LOWER: 1027.4 ml

PRELIMINARY DATA- jj

6IVEN: SPECIFICATION LIMITSUPPER: LOWER:

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2

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m

2 η

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TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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McKINNEY

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175

The major e f f o r t for the Pine Bluff Arsenal development work was concentrated on the f i l l i n g system with other work stations receiving as much attention as time and funding allowed. The f a c i l i t y i s l i s t e d as WP Line No. 3, Building 34-110, at Pine Bluff Arsenal. A p a r t i a l l i s t i n g of major material and equipment requirements and components for the f a c i l i t y i s as follows: Materials Specifications. A l l piping, valves, tanks and other metal parts which are i n direct contact with WP are constructed of 316 low-carbon ( L ) , stainless steel (SS) for welded connections and 316 SS for screwed connections. Hot water jackets are fabricated from Schedule 40 black iron pipe. A i l WP f l e x i b l e f i l l i n g , drain, and vent lines are fabricated from SS braided Teflon hoses. A l l automatic valves for WP service, including f i l l i n g and reservoir valves, are pneumatically-operated, f a i l - s a f e , spring-return, f i r e - s a f e b a l l valves. These automatic valve units include a waterproof limit switch double-throw switches. A l are made with quick-clamp compression-typ fitting gaskets. Automatic White Phosphorus F i l l i n g Station. The f i l l i n g station has eight complete f i l l i n g units and consists of the following items: (See Figure 2) a. Pallet stop systems with alignment shot pins for accurate alignment of a munition and p a l l e t under the f i l l i n g nozzle. b. An automatically-operated drip pan (for a l l eight f i l l i n g units) that retracts when a munition i s i n f i l l i n g position and extends horizontally after f i l l i n g i s completed and the f i l l i n g nozzles are retracted i n the v e r t i c a l plane. c. A f i l l i n g nozzle with guide system for accurate alignment with m u n i t i o n - f i l l i n g openings. The m u n i t i o n - f i l l i n g nozzle ( i l l u s t r a t e d by Figure 3) i s spring loaded with Teflon chevron seals i n the body between moving parts to prevent external contamination of metal parts of the nozzle. A nozzle t i p seal (including an "0" r i n g and a Teflon t i p seal) reduces drippage of WP after the nozzle closes. The nozzle serves as a valve with the primary function to reduce drippage after each f i l l i n g operation. The nozzle i s moved i n the v e r t i c a l d i r e c t i o n (See Figure 2) by a pneumatically-operated cylinder. The f i l l i n g nozzle i s connected to the f i l l i n g valve by a f l e x i b l e f i l l i n g hose. The framework on which the nozzle, cylinder, and alignment guide are mounted i s adjustable i n the v e r t i c a l d i r e c t i o n i n order to accommodate large or small munitions. A clean-up f i x t u r e i s furnished to drain WP from above the reservoir valve after the f i l l i n g tank has been drained of WP and replaced with phossy water. The clean-up f i x t u r e i s used at the end of a s h i f t and prior to start up. At the end of the s h i f t (after the f i l l tank has been drained of WP and replaced with phossy water), the WP above the f i l l i n g valve i s flushed through the f i l l i n g system into the clean-up f i x t u r e and back to the WP operating tank; the f i l l i n g system i s then operated through several cycles to clean the reservoir and f i l l i n g valves, volumetric chamber, vent assembly, f i l l i n g nozzles, and f i l l i n g hoses. The system i s then secured at the f i l l i n g station.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

176

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

The clean-up fixture i s part of the d r i p pan* The clean-up fixture and the drip pan are drained by gravity to the VP operating tank* The f i x t u r e i s connected by a hose to a drain pipe that connects to the WP operating tank* The f i x t u r e i s operated i n the horizontal plane by a cushioned-stroke pneumatic cylinder for smooth operation* The f i x t u r e travel i s two-position travel* The f i r s t travel or shorter distance i s for drip pan function during normal operation and the greater or over travel i s for clean-up operations* The clean-up f i x t u r e opening i s such that the f i l l i n g nozzle seats on the clean-up f i x t u r e as i t would on a munition* F i l l i n g Conveyor* F i l l i n g line transfer system i s an automatic, noneynchronus, variable-speed drive unit complete with f i l l i n g pallets and nests for the f i v e different munitions f i l l e d and closed on the l i n e * This unique system moves work p a l l e t s from station to station and provides accurate shot pin alignment for the work piece as various operations ar acceleration and deceleratio unusually smooth, quiet Inert Gas Cabinet System. The cabinet system encloses an automatic WP f i l l i n g system and a weighing station and contains an atmosphere that i s maintained at 3% 0~ or less to reduce the occurrence of smoke generation or f i r e should any WP become exposed inside the cabinet area. The cabinet has a temperature controlled steam heating system that maintains the cabinet space at 145°F, and an inert gas d i s t r i b u t i o n system for maintaining the inert (CO^ and Nj) atmosphere, and an entry and exit a i r lock to reduce the inflow of a i r during f i l l i n g operations. Flexible rubber s t r i p s are used at the a i r lock s i t e s . Small exhaust fans (150 CFM) are used at the a i r lock locations to prevent inert gas from discharging to the work area. The exhaust fans are vented to the outside atmosphere. The cabinet enclosure has hot water wash hoses with nozzles for any clean-up necessary, and contains both a manual and an automatic f i r e control system. Lexan plexiglass doors and windows are provided at the front or operating face of the enclosure for observation and access. A l l doors and enclosures are essentially a i r tight. Adequate l i g h t i n g i s provided for the i n t e r i o r of the housing* Sequence of Operation of the Pine Bluff Arsenal WP Volumetric Line.

Filling

An operator (See Figure 7) l i f t s empty munitions from a standard wooden pallet (elevated for operator access) and places munitions into the f i l l i n g line p a l l e t s . The pallets are released automatically when the munitions are dropped into p a l l e t s . The items are conveyed to an empty munition weigh station and are weighed simultaneously and the weights recorded i n the programmable logic controller (PLC) for l a t e r use i n matching and interface with the data from a f i n a l weighing of the munitions after the rounds have been f i l l e d . After weighing, the munitions are released to a four-unit vacuum purge station. Automatic vacuum/purge nozzles make a vacuum/pressure seal on top of the empty munitions, and a three-way automatic valve

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

ι * ι

Γι

UNLOAD CONV.. PLACE IN OVEN TEST PALLETS FOR φTRANSFER TO OVEN

#

TEMPORARY STORAGE

ROTATE HOT SHELLS. — — BEFORE

WEI6H-Z0NE SCALE

OA CERTIFICATION OF ACCEPTANCE. VISUAL LEAK INSPECTION ^

Figure 7. Schematic flow diagram of Pine B l u f f Arsenal WP volumetric f i l l i n g f a c i l i t y .

STER CASING DROP

, PARATION OF 'COMPONENT PARTS,

-TRUCK TO LONG TERM STORAGE

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opens and connects the a i r - f i l l e d empty munitions to a vacuum surge tank. The empty munitions are evacuated to 29" Hg. The three-way valve then closes the vacuum port and opens up to an inert gas port which breaks the vacuum i n munition cavities with low pressure inert gas (C(>2 and N^). This station reduces the amount of burning and smoke generation during WP f i l l i n g operations. The vacuum/purge nozzle retracts from the munition and the pallet stops drop allowing the four munitions and pallets to move into an eight-munition accumulator. From t h i s accumulator, eight munitions move into the f i l l i n g station containing eight f i l l i n g heads. After f i l l i n g , the munitions leave the station and arrive at an eight-unit accumulator which releases four pallets/munitions at a time into the net weight station where the f i l l e d items are weighed. The data for the empty weight i n memory and the f i l l e d weight collected by the PLC i s used by the PLC to calculate the amount of WP i n the munition bodies and to determine i f the munitions are acceptabl munitions for removal an automatically printed for record purposes. From the weight station, the munitions move into a burster casing station where an operator drops burster casings into the f i l l e d and accepted rounds. The operator then presses a release button and the munitions travel to the hydraulic press accumulator. The accumulator automatically releases four munitions with bursters into the press station where the burster casings are hydraulically pressed (metal interference f i t ) into the munition. After pressing, the munitions are released and t r a v e l to a manually-operated stop where an operator removes the f i l l e d and closed munitions and transfers them to the degreaser (cleaning) unit. The empty pallets are automatically released from this station and t r a v e l back to the front of the line to accept empty munitions for another cycle. After cleaning of munition bodies, the rounds are sampled for Quality Assurance l o t acceptance, painted, weighed and zoned ( i f required), and then placed i n oven test p a l l e t s . The f i l l e d oven test p a l l e t s are loaded into a hot a i r oven and the munitions are heated to 210 F and then maintained at that temperature for 15 minutes. The munitions are then returned to the WP plant for leak inspection, p a l l e t i z a t i o n and storage or transfer to an ammunition loading plant. Status and Plans for WP Operations The Pine B l u f f Arsenal volumetric WP dry f i l l system development work has resulted i n the i n s t a l l a t i o n of two production lines and one small experimental production f a c i l i t y . These f a c i l i t i e s are used to produce WP b u l k - f i l l e d munitions, wick loaded canisters, and experimental munitions. Figure 8 i s a photograph of the o r i g i n a l single-station prototype f i l l i n g station used to prove out the Pine Bluff Arsenal volumetric concept. Figure 9 shows the f i r s t production line fabricated and operated at Pine Bluff Arsenal using the concepts proven on the prototype unit. Figure 10 i s a photograph of the f i l l i n g s t a t i o n of the production line for 155mm, M825 wicktype munitions. This f a c i l i t y uses the Pine Bluff Arsenal concept

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

10.

McKINNEY

Design for White Phosphorus Filling Operations

Figure 8. O r i g i n a l Pine B l u f f Arsenal WP prototype f i l l i n g s t a t i o n . Photo courtesy of the U.S. Army.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Figure 9. Front view of the f i r s t WP production f a c i l i t y using the PBA volumetric f i l l i n g concept. Photo courtesy of the U.S. Army.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Mc KINNEY

Design for White Phosphorus Filling Operations

Figure 10. Front view of the second WP production f a c i l i t y (PBA concept with vacuum a s s i s t ) f o r f i l l i n g of the 155mm, M825 wick canister.Photo courtesy of the U.S. Army.

Figure 11. Most recent f a c i l i t y using the PBA concept f o r l i m i t e d production/experimental f i l l i n g of standard and new munitions and canisters. Photo courtesy of the U.S. Army.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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but d i f f e r s i n that vacuum i s used i n the f i l l i n g cycle. Figure 11 is a photograph of the most recent WP dry f i l l line i n s t a l l e d at Pine Bluff Arsenal (19S6). The capacity of t h i s small f a c i l i t y i s only six munitions per minute; however, the purpose of this experimental unit i s to provide limited production of b u l k - f i l l e d or wicked-type munitions and canisters, and fast set up for f i l l i n g of new experimental WP items. Future plans for our WP operations include the replacement of two remaining WP d i p - f i l l production lines with the more accurate, e f f i c i e n t , and safer volumetric f i l l i n g method described i n t h i s paper. Acknowledgments : I l l u s t r a t i o n s provided by James Palmer, Pine Bluff Arsenal. The contributions of severa contributed to the succes Pine Bluff Arsenal volumetric f i l l i n g production l i n e . support was provided by the following i n d i v i d u a l s :

Noteworthy

Pine Bluff Arsenal: B.T. Armstrong - Senior Electronic Engineer W i l l Bradford - Senior Project Engineer/120mm Wick Round B i l l M i l l e r - Senior Electronic Engineer Lonnie Witham - Project Engineer/155mm M825 Wick Round Jackie Smedley - Electronic Technician Larry Davenport - Mechanical Technician Earle Mustachia - Mechanical Technician Tom Woolley - Senior Tool & Die Maker Elmer 0. Woods - Equipment Mechanic Hubert Gates - Welder O.B. Summerford - WP Pumper Foreman William A. Cook - WP Pumper Edgewood Arsenal: Frank Stewart - Phase I Project Manager Merlin Erickson - Phase II Project Manager

U.S. Patents: 1. McKinney, H.D. 2. McKinney, H.D. RECEIVED April

U.S. Patent 4 002 268 - 1976 U.S. Patent 4 043 490 - 1977

23, 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 11

Design and Use of High-Speed Detection Systems for Explosives Operations Kenneth M. Klapmeier and Bernhard G. Stinger Detector Electronics Corporation, 6901 West 100th Street, Minneapolis, MN 55438

A properly designed fire or explosion suppression system can provide satisfactory protection for applications involving the presence of explosive materials by respondin matter of milliseconds only the fastest equipment and techniques are adequate. A successful system includes an optical detector that responds to the electromagnetic radiation produced by a flame. The detector generates a signal that is used to open a high speed electrically actuated valve. Opening the valve initiates immediate flow of water through the nozzles of a carefully designed piping system to extinguish or contain the fire or explosion. When considering the use of equipment f o r detecting and suppressing f i r e s and explosions, munitions manufacturing processes are among the most hazardous. In these a p p l i c a t i o n s , l i t t l e time i s a v a i l a b l e f o r the system to respond. A reaction time that i s only a few milliseconds too slow could r e s u l t i n extensive property damage and even loss of l i f e . By combining r a d i a t i o n detectors with an u l t r a high speed water deluge system, response times that are short enough to prevent a catastrophe can be achieved. The high speed deluge system i s designed to detect a flame or i g n i t i o n source and respond by applying large volumes of water i n an extremely short period of time (milliseconds). The system consists of the following basic components: - Flame detectors - Controllers - Source of water - Valve (squib or solenoid operated) - Piping system with nozzles. The flame detector i s an o p t i c a l device that responds to the radiant energy that i s given o f f by a flame. When a flame or explosion occurs within the f i e l d of view of the detector, the r e s u l t i n g electromagnetic r a d i a t i o n t r a v e l s toward the detector at 0097-6156/87/0345-0183$06.00/0 © 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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the speed of l i g h t . The detector responds to the radiant energy i n milliseconds, sending a f i r e s i g n a l to the c o n t r o l l e r , which i n turn generates the s i g n a l that opens the valve. When the valve opens, l i n e water pressure i s applied to the priming water that i s i n the pipe behind the nozzles. This causes water to flow from the nozzles, extinguishing the f i r e . Simultaneously, the c o n t r o l l e r sends alarm signals to audibly and/or v i s u a l l y indicate a f i r e occurrence and shut down the associated process equipment. U l t r a v i o l e t Detectors The u l t r a v i o l e t (UV) detector (see Figure 1) consists of a gasf i l l e d cold cathode sensor tube that i s mounted i n s i d e an explosion proof housing. The sensor tube i s designed to respond to a narrow band of r a d i a t i o n t y p i c a l l y between 1850 and 2450 angstroms. Figure 2 i l l u s t r a t e s the general r e l a t i o n s h i p between solar r a d i a t i o n at the surface of the eart typical gas-filled ultraviole r a d i a t i o n spectrum extend approximately 30,00 angstroms. Therefore, the sensor tube does not respond to solar r a d i a t i o n or normal ambient l i g h t . Radiation i s not emitted continuously, but i s emitted i n small bundles c a l l e d photons. The energy of a photon i s dependent on the wavelength of the r a d i a t i o n . When a photon of r a d i a t i o n i s absorbed into a metal such as the cathode (negative plate) of the UV tube, the energy of the photon i s imparted to an electron w i t h i n the metal, causing i t to leave the surface of the metal and be drawn toward the anode (positive p l a t e ) . The energy that the electron must have to leave the metal i s c a l l e d the work function of the metal. The s e n s i t i v i t y range of the r a d i a t i o n detector i s dependent upon the work function of the metal used i n the cathode. The sensor tube i s f i l l e d with an ionizable gas, such that when an electron i s emitted from the cathode and i s rapidly drawn to the anode as shown i n Figure 3, i t s t r i k e s a gas molecule with enough energy to cause electrons to be emitted from the gas molecule. These electrons s t r i k e other gas molecules releasing more electrons. The t o t a l number of electrons generated i n t h i s manner i s t y p i c a l l y several m i l l i o n times more than were emitted from the cathode. This current of electron flow i s known as the avalanche e f f e c t . The current can be stopped by reducing the applied voltage to the tube so that the emitted electron does not have s u f f i c i e n t energy to cause other electrons to be emitted when i t c o l l i d e s with gas molecules. In a t y p i c a l UV detector, the current i s allowed to flow f o r a very short period of time before the voltage i s reduced and the current stopped. Thus the output of the sensor tube i s a series of voltage pulses, the frequency of which i s proportional to the i n t e n s i t y of the UV sensed by the detector. The closer a f i r e i s to the detector, the higher the output frequency, and the smaller the flame s i z e that i s needed to actuate the system. In the past, the c i r c u i t r y i n the c o n t r o l l e r that was used f o r counting the voltage pulses would amplify and square the pulses, and then use the pulses to charge a capacitor. When the capacitor was charged to a pre-calibrated threshold voltage, the c o n t r o l l e r

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

KLAPMEIER AND STINGER

Figure 1.

Detection Systems for Explosives Operations

UV Detector and Controller

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

m 00

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In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

11.

KLAPMEIER AND STINGER

Detection Systems for Explosives Operations

187

generated an output s i g n a l that energized the alarm relays and deluge systems. The use of microprocessors now makes i t possible to count and process the d i g i t a l pulses from the UV detectors. Pulses no longer need to be stored i n c a p a c i t o r s , but can be i n d i v i d u a l l y counted, entered into the r e g i s t e r s of the microprocessor, stored i n memory and manipulated l i k e any type of data processing information. This allows the design of f l e x i b l e u l t r a v i o l e t f i r e detectors using programmable memories and switches to provide an i n f i n i t e number of combinations. Thus we now have a marriage of extremely high gain g a s - f i l l e d vacuum tube UV detection devices that have existed f o r many years with state-of-the-art microprocessors. Since the UV detector requires no s i g n a l processing other than comparing the r a d i a t i o n l e v e l to a preset threshold, a very fast response time i s achieved. Applications. U l t r a v i o l e applications where r a p i d l open area. UV detector y l i n e s , gunpowder troughs, or open areas that are stocked with hazardous materials. These detectors are not t y p i c a l l y affected by extremes of temperature or pressure, adverse weather conditions, high humidity, nor are they s e n s i t i v e to solar r a d i a t i o n . In a t y p i c a l a p p l i c a t i o n , UV detectors are used i n general or spot coverage locations. General coverage detectors are usually mounted i n the corners and along the walls of a hazardous area. They are normally positioned for overlapping f i e l d s of view. Their purpose i s to detect a f i r e that occurs anywhere w i t h i n the hazardous area. Spot coverage detectors are normally mounted as close as possible to the point of p o t e n t i a l i g n i t i o n . Examples are the extruder/cutter i n a high explosives machining operation or the compression point i n a s h e l l loading machine. Spot detectors assure the fastest possible detection time by p h y s i c a l l y being mounted the closest to the point of i g n i t i o n . Limitations. Although UV f i r e detectors have many advantages, they also have t h e i r l i m i t a t i o n s . They w i l l respond to r a d i a t i o n sources besides f i r e such as l i g h t n i n g or e l e c t r i c arc welding, as w e l l as x- and gamma rays. In some a p p l i c a t i o n s , the system may have to be shut down to prevent f a l s e alarms when these sources of interference are present. In a p p l i c a t i o n s where the presence of x- and gamma r a d i a t i o n i s a continuous problem the use of a s p e c i a l nuclear surveillance system i s recommended. This system uses dual detectors. One responds to both nuclear r a d i a t i o n and UV from f i r e . The other i s blinded to UV produced by f i r e and detects only nuclear r a d i a t i o n . The microprocessor based c o n t r o l l e r uses a s p e c i a l program that u t i l i z e s a "count subtraction" technique. By subtracting the output count of the detector that sees only nuclear r a d i a t i o n from the count of the other detector, r e l i a b l e protection can be assured i n a p p l i c a t i o n s that normally would be d i f f i c u l t or impossible to supervise. I t must be noted, however, that the a d d i t i o n a l s i g n a l processing that i s required w i l l increase the response time of the detection system.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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188

It must also be noted that since the u l t r a v i o l e t detector i s an o p t i c a l device, objects that are able to block i t s view cannot be allowed to come between the detector and the area to be protected. In addition, smoke and various vapors can s i g n i f i c a n t l y absorb UV, making i t d i f f i c u l t or impossible for the detector to "see" a f i r e . It i s recommended that the detectors be positioned so that any point within the area to be protected i s covered by more than one detector. This w i l l assure r e l i a b l e protection i f a given detector should f a i l or i f i t s view i s suddenly blocked. Self-checking Feature. UV absorbing contaminants that are present i n the environment can accumulate on the o p t i c a l surfaces of the detector. An accumulation of c e r t a i n materials, sometimes barely v i s i b l e to the naked eye, can cause a s i g n i f i c a n t reduction i n the l e v e l of UV that reaches the sensor tube of the detector. This could make the detector nearly "blind to UV r a d i a t i o n . An electronic s e l f - t e s t i n g Integrity, has been designe The system generates a c a l i b r a t e that i s located inside the detector housing beside the UV sensor tube. The test beam passes outside the viewing window of the detector and i s then reflected back through the window and into the UV sensor. See Figure 4. The sensor tube then generates an output signal that i s sent to the c o n t r o l l e r , where the intensity i s evaluated to determine the r e l a t i v e cleanliness of the viewing window. The test signal does not i n t e r f e r e with the normal functioning of the detector, since i t i s considerably weaker than a UV f i r e s i g n a l . Therefore, no danger of a f a l s e alarm e x i s t s . In addition, i f a f i r e should occur during an Optical Integrity t e s t , a f i r e s i g n a l w i l l immediately be generated. The system continuously checks the o p t i c a l surfaces, electronic components, and inter-connecting wiring of the detector. Any malfunction i s detected i n a matter of seconds. The c o n t r o l l e r responds by r e g i s t e r i n g a f a u l t output to a l e r t personnel that a problem has occurred. When properly applied, u l t r a v i o l e t detectors can serve as excellent f i r e detectors i n munitions manufacturing. Detection times as fast as 10 milliseconds can be achieved while e f f e c t i v e l y r e s i s t i n g f a l s e alarms. 11

Infrared Detectors The infrared (IR) detector i s an extremely fast device that i s capable of detection times as short as f i v e milliseconds. In the past, infrared detectors have been unsuitable for general applications because of the large number of f a l s e alarm sources found i n the work place. However, when properly applied i n controlled surroundings, they can provide r e l i a b l e and e f f e c t i v e protection. A t y p i c a l high speed IR detector consists of a cadmium selenide sensing element that i s contained i n a stainless s t e e l housing. See Figure 5. By using a narrow bandpass infrared f i l t e r that i s designed to minimize extraneous and ambient l i g h t sources, response i s confined to the 0.75 to 0.85 micron range. This i s the range that provides the fastest detector response. Figure 6 i l l u s t r a t e s

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

KLAPMEIER AND STINGER

Detection Systems for Explosives Operations

CURRENT METER

Figure 3.

U l t r a v i o l e t Detector

SNAP-IN oj R I N G .

1 Figure 4.

M

Optical

Integrity

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Figure 5. High Speed IR Detector and Controller

WAVELENGTH (MICRONS)

Figure 6.

Response Range of Typical IR Detector

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

11.

KLAPMEIER AND STINGER

Detection Systems for Explosives Operations

the general relationship between solar radiation at the surface of the earth and the spectral response range of a t y p i c a l high speed IR detector. Note that this spectral response range includes f a l s e alarm sources such as the sun and a r t i f i c i a l l i g h t . The detector also contains an infrared source within the enclosure. When a test signal i s applied to the source, IR radiation i s generated for testing the detector. Like the UV detector test, this test also checks the sensor and i t s wiring without r e s u l t i n g i n a f a l s e alarm. The IR detectors are usually connected to a c o n t r o l l e r that supplies power to the detectors and acts as a signal processor and output device. A t y p i c a l c o n t r o l l e r monitors up to four detectors and energizes an output when any one of the detectors senses IR radiation that exceeds the alarm threshold l e v e l . The c o n t r o l l e r also contains the c i r c u i t r y that checks the detectors and e l e c t r i c a l l y supervises the interconnecting wiring to the explosive squibs or solenoid valves by t r i c k l i n g a small current through the external c i r c u i t s . Advantages. Like u l t r a v i o l e t detectors, infrared detectors have t h e i r advantages and l i m i t a t i o n s . Several advantages of IR units make them valuable i n c e r t a i n i n s t a l l a t i o n s : 1. They do not respond to the strong u l t r a v i o l e t radiation from e l e c t r i c arc welding and lightning. 2. X-ray and gamma radiation do not extend to the infrared region, and single band IR units are not affected by them. 3. Smoke and/or vapors do not absorb radiation as s i g n i f i c a n t l y i n the IR spectrum as i n the UV spectrum. This makes devices of this type p a r t i c u l a r l y useful when heavy smoke concentrations may accompany a f i r e . However, care must be taken that thick IR absorbing dusts are not part of the hazard. 4. An IR detector can "see" through substantially more contamination on i t s viewing window than a UV detector. 5. They are able to see hot ember-like f i r e s t y p i c a l of oxygen depleted areas. Limitations. I t i s important to remember that the signal processing techniques necessary for r e l i a b l e and stable detector operation may slow down the response time. In contrast, the requirements of the munitions industry have become more c r i t i c a l , requiring faster o v e r a l l response times. The IR spectrum i s broad and there are many sources of IR that radiate over the entire IR band. Typical are hot manifolds, b o i l e r s , processing vessels, engines and the sun i t s e l f . With some types of IR detectors the background radiation from a heat source can a c t u a l l y mask the presence of a f i r e and result i n f a i l u r e to respond. Attempts to use the well known f l i c k e r p r i n c i p l e cannot be r e l i e d on to discriminate flame from background because of the amount of time needed for signal processing. To achieve the fast detection times needed, the IR detector cannot afford the luxury of the signal processing required to d i f f e r e n t i a t e between the radiation emitted by f i r e and that emitted by blackbody radiation and ambient l i g h t . Therefore, high speed infrared sensors must be c a r e f u l l y isolated from possible f a l s e alarm sources. Such sources include the sun and other blackbody radiation sources, high intensity l i g h t s , flashbulbs, fluorescent and normal incandescent lighting.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Applications. The munitions industry has several applications suited f o r infrared detectors. Conveyor belts passing through large covered ducts and explosive and propellant mixers are examples of the controlled environment necessary f o r proper application. Typical applications f o r these high speed IR detectors are characterized by s t r i c t l y controlled, dark environments where a f l a s h f i r e could originate. While simple high speed infrared systems have been available for several years, modern sensor and f i l t e r developments, coupled with state-of-the-art e l e c t r o n i c s , have resulted i n systems t a i l o r e d for the munitions industry. These systems are more selective within the electromagnetic spectrum, fast i n response, and extremely f l e x i b l e i n application to suppression systems. T y p i c a l l y , these systems are recommended to be used i n combination with the appropriate u l t r a v i o l e t systems, combining the advantages of u l t r a v i o l e t for space protection with infrared for enclosed areas, as i l l u s t r a t e Response time of suc type of material, ambient a i r , fumes or vapor composition, distance and orientation of the f i r e source. When discussing the response times for detectors, i t must be recognized that a far more important measurement i s the speed of response for the entire detection and suppression system. For example, a high speed UV detector can detect a rapidly developing f i r e i n approximately ten milliseconds under i d e a l conditions. In addition, however, the water extinguishing agent can require one hundred milliseconds or more to t r a v e l through the piping to the nozzle, and from the nozzle through the a i r to the f i r e . Thus i t i s important to r e a l i z e that the speed of response of the detector i s a small part of the t o t a l response time of the system. Detonator Module The Detonator Module i s a control unit that i s used with the UV and/or IR detection system to activate the water deluge system. When dealing with an entire f i r e detection system that u t i l i z e s more than one type of detector, a Detonator Module greatly expands the f l e x i b i l i t y and c a p a b i l i t y of the system. An i n d i v i d u a l Detonator Module can accept multiple inputs from UV and IR c o n t r o l l e r s , other Detonator Modules, manual alarm stations, heat sensors, smoke detectors or any contact closure device. In the event of a f i r e , any of these devices w i l l cause the i n t e r n a l f i r e c i r c u i t r y of the module to activate the detonator c i r c u i t , sound alarms, and i d e n t i f y the zone that detected the f i r e . When properly used, a Detonator Module w i l l add only one millisecond to the t o t a l system response time. See Figure 8 for an i l l u s t r a t i o n of a f i r e detection system with a Detonator Module. Reliable operation of the system i s ensured by the a b i l i t y of the Detonator Module to continuously monitor the input c i r c u i t s and the detonator output c i r c u i t s , to supervise the c o i l and wiring of the solenoid valve or squib, as well as to perform a s e l f - t e s t procedure to allow v e r i f i c a t i o n of other c r i t i c a l c i r c u i t s .

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

KLAPMEIER AND

STINGER

J

Detection Systems for Explosives Operations

j

VERTICAL MIXING B O W L

j

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DARK, DUSTY ENVIRONMENT

Figure 7.

Typical Application Characteristics of UV and IR Detectors

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

UV DETECTOR

Figure 8.

RELAY OUTPUT H H MODULE H h

F i r e Detection System with Detonator Module

PRESSURE DETECTOR

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SUPPLY (AT SYSTEM PRESSURE)

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Figure 4.

Pilotex Valve Cutaway (Closed)

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

204

Figure 5. P i l o t e x Valve Cutaway (Open)

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V PILOTEX VALUES WITH NOZZLES • •SOLENOID *: OPTIONAL OR AIR VENT NUMBER OF SOLENOIDS DEPENDANT ON SYSTEM LAYOUT AND SPEED REQUIREMENTS. Figure 6.

BOTH PILOT AND SUPPLY AT HIGH PRESSURE. (SUPPLY PRESSURE UP TO 175 PSI )

Typical Pilotex Configuration

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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p r o p e l i a n t f i r e by s u p p r e s s i n g t h e oxygen s u p p l y * Why w a t e r ? I t i s g e n e r a l l y agreed t h a t c o o l i n g i s a p r i n c i p a l f a c t o r because i t p r e v e n t s feedback o f s u f f i c i e n t heat energy t o m a i n t a i n combustion. I t i s o f course d e s i r a b l e t o g e t t h e water t o t h e a c t u a l b u r n i n g s u r f a c e . However, i t i s n o t enough t o wet t h e p a r t o f the s u r f a c e , as t h e f i r e w i l l burrow i n t o t h e m i x t u r e and c o n t i n u e t o burn, b e i n g s h i e l d e d from t h e w a t e r by an o u t e r l a y e r o f water soaked m a t e r i a l . T h i s makes i t h i g h l y d e s i r a b l e t o be a b l e t o a p p l y t h e w a t e r r a p i d l y b e f o r e burrowing c a n o c c u r . Another f a c t o r w h i c h makes r a p i d o p e r a t i o n e s s e n t i a l i s t h a t water must r e a c h t h e b u r n i n g s u r f a c e b e f o r e t h e p r e s s u r e o f combustion gases i s s u f f i c i e n t l y h i g h t o prevent w a t e r from r e a c h i n g t h e source o f t h e f i r e . T h i s r e q u i r e s t h a t t h e system o p e r a t e i n a mater o f m i l l i s e c o n d s . I n some c a s e s , e s p e c i a l l y w i t h l a r g e b u l k q u a n t i t i e s o f e x p l o s i v e s , i t my be n e c e s s a r y t o f l o o d the c o n t a i n e r from the bottom and the t o p o r add a w e t t i n g agent t o t h e water i n the e x p l o s i v e . To summarize to c o o l down and d i s p e r s e t h e e x p l o s i v e s o r p r o p e l l a n t . A p p l i c a t i o n s f o r u l t r a - h i g h speed s u p p r e s s i o n i s a s many and a s v a r i e d as t h e r e a r e h i g h energy p r o d u c t s . Deluge systems have been used i n primary h i g h e x p l o s i v e s such as mercury f u l m i n a t e , l e a d a z i d e , and DDNP. Secondary h i g h e x p l o s i v e s such as TNT, T e t r y l , RDX, n i t r o g l y c e r i n , b l a s t i n g g e l a t i n and C4. B l a c k powder i s another v e r y common a p p l i c a t i o n . Note t h a t S p r i n k l e r c o n t r a c t o r s s h o u l d be n o t i f i e d n o t t o use copper o r b r a s s f i t t i n g s o r components when p r o t e c t i n g l e a d a z i d e , due t o t h e f a c t t h a t l e a d a z i d e i n the presence o f copper and m o i s t u r e c a n become e x t r e m e l y s e n s i t i v e copper a z i d e . U l t r a High Speed s u p p r e s s i o n i s a l s o w e l l s u i t e d f o r the p y r o t e c h n i c s and fireworks f i e l d . F o r example, magnesium t e f l o n f l a r e s , c o l o r e d s t a r s , and smoke g e n e r a t i n g d e v i c e s . I n the case o f magnesium t e f l o n f l a r e s , t h e system c o u l d be used a l s o t o p r o p e l t h e b u r n i n g f l a r e away from the person t o prevent burns. The o p e r a t i o n s i n an e x p l o s i v e f a c i l i t y a l s o v a r y g r e a t l y and the system s h o u l d be c u s t o m i z e d and geared towards t h e o p e r a t i o n . The t y p e s o f o p e r a t i o n s commonly seen i n e x p l o s i v e f a c i l i t i e s are weighing, pressing, p e l l e t i z i n g , p r o p e l l a n t l o a d i n g , m e l t i n g , e x t r u s i o n , m i x i n g , b l e n d i n g , s c r e e n i n g , sawing, g r a n u l a t i n g , d r y i n g , p o u r i n g , and machining. Each p r e s e n t s i t s own s p e c i f i c h a z a r d and a t t e n t i o n s h o u l d be g i v e n t o a r e a s o f i g n i t i o n such as p i n c h - p o i n t s , f r i c t i o n p o i n t s , and a r e a s where t h e r e i s an o p e r a t o r w o r k i n g . The f i r e d e t e c t o r s and n o z z l e s s h o u l d be p u t as c l o s e t o t h e h a z a r d as p o s s i b l e . I n many cases use d e d i c a t e d n o z z l e s t o key-on s p e c i f i c problem a r e a s , such as m i x i n g b i n s , machining p r o c e s s e s , e x t r u d e r d i e s , e t c . As mentioned b e f o r e , determine what i s r e q u i r e d o f your system. I s i t t o s t o p p r o p a g a t i o n , p r o t e c t p e r s o n n e l , p r o t e c t maohinery? With t h i s i n mind, one can d e s i g n a system t h a t w i l l e f f e c t i v e l y meet the needs. Each o p e r a t i o n r e q u i r e s s p e c i a l c o n s i d e r a t i o n . For i n s t a n c e , d u r i n g w e i g h i n g , o f t e n w i t h d r y m a t e r i a l , t r a n s f e r and p o u r i n g o f m a t e r i a l can c r e a t e d u s t and

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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i g n i t i o n , t h i s i s a good a p p l i c a t i o n for u l t r a - v i o l e t detection and high speed water spray. In the case of pressing and p e l l e t i z i n g , usually the goal here would be to prevent propagation. During the pressing and p e l l e t i z i n g operation, there i s a good chance of explosion or i g n i t i o n and the best bet would be to stop propagation to the bulk propellant. With propellant loading the t r a n s i t i o n of material from one vessel to another i s a potential hazard. I t i s a good idea to have u l t r a - v i o l e t detection here and directed water spray. In the process of melting, usually these are closed melt k e t t l e s using steam for heat and often i n t h i s case i n f r a - r e d detection with high speed nozzles directed i n t o the k e t t l e i s a common configuration. With extrusion, the most l i k e l y point of i g n i t i o n i s where the material leaves the die. Again, keying the nozzles and detection at t h i s point would help stop propagation. Mixing and blending are usually done i n one of two (2) ways; within an open type mix or blendin on the type of machine u t i l i z e d , pressure detectio option would be positioned accordingly. With screening, sawing and granulating, there i s a good p o s s i b i l i t y for dust and sparks, key on the action. System response time i s a controversial issue that i s often discussed but seldom s e t t l e d . Probably the best and only concise way to determine i f the deluge system i s adequate i s to run an actual f i r e test with the explosive or high energy material u t i l i z i n g proposed detection and suppression system. Often t h i s i s not f e a s i b l e for obvious reasons. The second most accurate method of time t e s t i n g would be using high speed video cameras. Commonly these cameras record approximately one frame every eight (8) milliseconds, so what one does i s record the event, play i t back, count the frames and e s t a b l i s h the response time. The advantage of t h i s system i s that you are able to see the propagation of the flame to the point of detection, the start of flow at the nozzle, and water spray as i t progresses to the hazard, spray patterns can also be observed. This system i s f i n e for a laboratory type evaluation but usually i s not f e a s i b l e f o r " i n - f i e l d " a p p l i c a t i o n . Reasons being, the equipment runs from F i f t y to Eighty thousand d o l l a r s ($50,000.00 to $80,000.00). Also, i t i s very bulky, often l i g h t i n g i s not adequate within the areas, the expense of providing the technicians and shipping the equipment i s often p r o h i b i t i v e . So f a r , the most economical and r e l i a b l e system for i n - f i e l d time t e s t i n g i s a d i g i t a l timer. Reaction time being defined as: beginning at instant of detection and stopping at flow from nozzle. The timer i s started by a signal from detection control and i s stopped by a flow switch connected at the nozzle. This seems to be acceptable by most a u t h o r i t i e s for t e s t i n g deluge systems " i n - f i e l d " and also for periodic maintenance t e s t i n g . n

n

Table I i s a b r i e f overview of available fast action deluge. The Priraac i s a squib actuated deluge valve. The system

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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uses one l a r g e v a l v e connected t o a pre-primed p i p i n g system u t i l i z i n g n o z z l e s w i t h end caps o r r u p t u r e d i s c s . I n Primac Systems u s i n g r u p t u r e d i s c s a t t h e n o z z l e , t h e r u p t u r e d i s c s a r e b u r s t by w a t e r p r e s s u r e n o t an e x p l o s i v e charge. The body o f t h e Primac v a l v e i s t h a t o f a s t a n d a r d " g l o b e " v a l v e . The w a t e r s e a l i s a c h i e v e d by a p i s t o n e n t e r i n g t h e t h r o a t o f t h e v a l v e body. An "0" r i n g i n s e r t e d i n t h e same manner as a p i s t o n r i n g makes the p i s t o n w a t e r t i g h t . The stem a t t a c h e d t o t h e p i s t o n e x t e n d s through t h e t o p o f t h e v a l v e . A s w i n g i n g l a t c h c o n n e c t i n g t h i s stem h o l d s t h e v a l v e i n a c l o s e d p o s i t i o n . The yoke s u p p o r t i n g the l a t c h i s d e s i g n e d t o accommodate a p r i m e r so p o s i t i o n e d t h a t when the p r i m e r d e t o n a t e s , t h e l a t c h i s f o r c e d o f f t h e stem and the water p r e s s u r e under t h e p i s t o n opens t h e v a l v e . NOTE: Be s u r e t o keep stem 0 " r i n g s i n good c o n d i t i o n ; a l e a k a t t h i s p o i n t may cause submersion o f s q u i b . The e x p l o s i v e r u p t u r e d i s c system i n c o r p o r a t e s t h e same p r i n c i p l e a s H a l o n typ i s used a s t h e e x t i n g u i s h i n a p p l i c a t i o n s , t h e r e i s a s q u i b and r u p t u r e d i s c a t each n o z z l e . The P i l o t e x s o l e n o i d o p e r a t e d system does n o t use e x p l o s i v e s q u i b s . I t ' s p r i n c i p a l o f o p e r a t i o n v a r i e s g r e a t l y from t h e p r e v i o u s two. When p i l o t p r e s s u r e i s r e l i e v e d , a l l P i l o t e x v a l v e s connected t o t h e one p i l o t l i g h t opens i n s t a n t a n e o u s l y and s i m u l t a n e o u s l y . When t h e p i l o t p r e s s u r e i s r e s t o r e d , t h e n o z z l e s c l o s e . A P i l o t e x v a l v e c o n s i s t s o f a two p i e c e body threaded t o g e t h e r and s e a l e d w i t h an 0 r i n g . The upper body h a s a h a l f (1/2) i n c h NPT male c o n n e c t i o n f o r i n s t a l l a t i o n and s t a n d a r d p i p e l i n e f i t t i n g s and a q u a r t e r (1/4) i n c h NPT female c o n n e c t i o n from t h e p i l o t l i n e . I t i s through t h i s p i l o t l i n e c o n n e c t i o n t h a t t h e c y l i n d e r and t h e poppet, t h a t make up the d i f f e r e n t i a l v a l v e , r e c e i v e p i l o t p r e s s u r e . The poppet has a t e f l o n f a c e w h i c h s e a t s a g a i n s t t h e o r i f i c e l o c a t e d i n t h e l o w e r body h a l f o f the v a l v e . The l o w e r body i s i n t e r c h a n g e a b l e t o accommodate v a r i o u s t y p e s o f d i s c h a r g e d e v i c e s . Male a d a p t e r s a r e o f t e n used where t h e r e i s a need f o r f l a n g e mount o r t o d i r e c t l y f l o o d a melt k e t t l e o r m i x e r . The female a d a p t e r i s most o f t e n used w i t h t h e Autospray n o z z l e s . When t h e P i l o t e x v a l v e i s i n i t s n o r m a l l y c l o s e d p o s i t i o n , t h e poppet i s h e l d a g a i n s t t h e d i s c h a r g e o r i f i c e by t h e p r e s s u r e w i t h i n t h e poppet c y l i n d e r . When t h e p i l o t p r e s s u r e d r o p s , t h e main f i r e p r e s s u r e overcomes the d i f f e r e n t i a l and f o r c e s t h e poppet up and i n s t a n t l y s t a r t s f u l l d i s c h a r g e . When p i l o t p r e s s u r e i s r e s t o r e d , t h e poppet r e s e a t s , even a g a i n s t f i r e main p r e s s u r e . Speed o f t h e P i l o t e x system i s n o t dependent on system s i z e . W e l l under F i f t y ( 5 0 ) m i l l i s e c o n d s o p e r a t i o n i s guaranteed o n a l l P i l o t e x system where s u c h speeds a r e r e q u i r e d . W i t h t h e v a r i o u s system a v a i l a b l e f o r t h e s u p p r e s s i o n h i g h energy c h e m i c a l f i r e s , t h e r e i s , i n most cases a c o n f i g u r a t i o n s u i t a b l e f o r almost any e x p l o s i v e s , p y r o t e c h n i c o r m u n i t i o n s facility. n

n

n

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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FACILITIES

Table I. Comparison of Ultra-High-Speed Deluge Features

X

COMPLETE ELECTRICAL SUPERVISION RESPONSE TIME NOT AFFECTE PIPE EXTRA PIPING FOR PILOT NOT NEEDED

X

WIRING TO EACH SQUIB/SOLENOID NOT NEEDED

X

X

NO RE-OCCURING COST OR REPLACEMENT PARTS NEEDED FOR RESET AFTER EACH FIRING

X

AUTOMATIC RESET FEATURE AVAILABLE

X

SYSTEM DOES NOT REQUIRE EXPLOSIVES FOR OPERATION

X

SYSTEM CAN BE SUPERVISED FOR HIGH PRESSURE PRIME SYSTEM CAN BE RESET AND BACK ON LINE IN LESS

X

X

THAN 30 SECONDS

X

INDEFINITE SHELF LIFE OF COMPONENTS

X

MECHANICAL MANUAL OPERATION AVAILABLE

X

ELECTRICAL PUSH-BUTTON RESET

X

EACH HEAD ACTS AS AN INDIVIDUAL DELUGE VALVE (SAFETY THRU REDUNDANCY)

X

X

RESPONSE TIME NOT AFFECTED BY SYSTEM SIZE

X

X

EXPLOSIVE SQUIBS NOT REQUIRED IN HAZARD AREA

X

COMPATIBLE WITH ALL FORMS OF DETECTION

X

SYSTEM CAN BE ΡRE-PRIMED WITH HIGH PRESSURE

X X

X

X

X

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Ultra-High-Speed Fire Suppression for Explosives Facilities

NOTE A;

Due to innovations with P i l o t e x , Spectronic system was obsoleted by manufacturer.

NOTE B;

Solenoids are supervised f o r short, opens and grounds. On a Squib operated system, the i g n i t e r wire can be supervised but condition of explosive i s not known.

NOTE C:

A f t e r f i r i n g of the squib operated systems d i s c or caps must be replaced/squibs must be replaced.

NOTE D;

Squibs have a shelf l i f e and should be p e r i o d i c a l l y replaced.

NOTE E:

Mechanical manual release i s possible even i n the event of t o t a l power f a i l u r e (including loss of primary power and battery back-up).

NOTE F;

Pushing rese s e t t i n g system.

209

Literature Cited (1) Pyrotechnics;, George W. Weingart (2) Chemistry of Pyrotechnics, Basic Principles and Theory;, John A. Conkling (3) Survey of Sensitivity Characteristics of Typical Delay Ignitor Flash and Signal-Type Pyrotechnic Compounds; Joseph Kristal and Seymour M. Kaye; Picatinny Arsenal, Dover New Jersey;439383 (4) Fireworks from a Physical Standpoint;Dr.Takeο Shimizu, Kawagoe-Shi, Japan (5) The Chemistry of Powder and Explosives;, Tenney L Davis (6) The Safe Practices Manual for Manufacturing, Transportation, Storage and Use of Pyrotechnics;publication of The Department of Health,Education and Welfare,bulletin #PB-297807 (7) Fire Extinguishing Devices in Propellent Plants;, Peter R. Weibel, Swiss Federal Propellant Plant, Wimmis, Switzerland (8) The Minutes of the Rapid Action Fire Protection Seminar, AMCA , MCCOM Safety Office; 23rd and 24th,October, 1984 (9) Pilotex Ultra High Speed Deluge Fire Protection for Munitions Explosives Pyrotechnics ; Gary A. Fadorsen, "Automatic" Sprinkler Corporation of America (10) The Loading, Assemblying and Packing of M42 Grenades;"Are We Doing It Right?";Donald R. Kennedy (11) Recent Developments in High Speed Optical Detection Systems for Pyrotechnic and Munitions Processing from the In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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International Pyrotechnic Society Seminar in Vail, Colorado; July 6 thru 11, 1986; Ken M. Klapmeier of Detector Electronics Corporation, Minneapolis, Minnesota (12) Ultra High Speed Deluge System for the DDESΡ Seminar; Bob Lloyd,AMCCOM, Rock Island, Illinois (13) False Alarm Reduction in Industrial Flame Detection; Roger A. Wendt, Armteck Industries, Manchester, New Hampshire (14) Ultra-Violet Deluge Study XX-61; Day & Zimmerman (15) Explosives and Demolitions,Department of the Army Field Manual,FM5-25 (16) Engineering Guide for Fire Protection and Detection Systems at Army Amuunition Plants, Vol. 1;Lewis Joblove, Manuel Avelar and Norval Dobbs, of Ammann and Whitney RECEIVED

March 6, 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 13

Systematic Approach for Safely Designing a Chemical Surety Materiel Laboratory George E. Collins, Jr. Chemical Research Development and Engineering Center, Attn: SMCCR-SFC, Aberdeen Proving Ground, MD 21010-5423

This article shows, through example, how established system safety concepts can be used to develop safety criteria for th laboratory. Thi as described in this article, results in a laboratory dedicated to achieve mission objectives in an environment relatively free of inherent hazards for the least number of dollars.

F a c i l i t y System Safety (FSS), which i s the a p p l i c a t i o n of system safety concepts t o the f a c i l i t y a c q u i s i t i o n process, has recently gained acceptance throughout the Department of Defense and most recently w i t h i n the Department of Army with the conception of SAFEARMY 1990. The Army's goal i s to: f u l l y integrate the t o t a l system safety, human f a c t o r s , and health hazard assessments i n t o continuous comprehensive evaluation of selected systems and f a c i l i t i e s . The Chemical Research Development and Engineering Center (CRDEC) has mandated appropriate l e v e l s of system safety throughout the l i f e c y c l e of f a c i l i t y development f o r many reasons. These include: 1. Optimum safety and health are required to prevent personal i n j u r y to chemical surety agents. F a c i l i t y System Safety i s one avenue used to achieve optimum safety and health i n operations that deal with these agents. 2. FSS i s a proactive approach which w i l l reduce inconsistencies during the f a c i l i t y a c q u i s i t i o n process. This r e s u l t s i n a more mission responsive f a c i l i t y that i s less expensive. The intended purpose of t h i s a r t i c l e i s to demonstrate, through s p e c i f i c examples, how FSS can be applied to the design/construction/operation of a chemical surety materiel laboratory. The laboratory under study i s a 32 m i l l i o n d o l l a r M i l i t a r y Construction, Army (MCA) project designed to replace aging f a c i l i t i e s which are c u r r e n t l y u t i l i z e d to perform d a i l y Chemical Surety M a t e r i e l (CSM) operations. For the purpose of t h i s a r t i c l e , CSM i s defined as a This chapter not subject to U.S. copyright Published 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

13.

COLLINS

Designing a Chemical Surety Materiel Laboratory

213

chemical compound used i n m i l i t a r y operations to k i l l , s e r i o u s l y i n j u r e or incapacitate a person through chemical properties. This a r t i c l e demonstrates the methods used i n i d e n t i f y i n g , analyzing and u l t i m a t e l y eliminating or reducing the e f f e c t of a hazard on the f a c i l i t y , equipment and personnel. F a c i l i t y System Safety Overview. The process of applying system safety to the f a c i l i t y a c q u i s i t i o n process can be divided i n t o the following tasks: 1. 2. 3. 4.

Risk Categorization Preliminary Hazard L i s t Preliminary Hazard Analysis Design Considerations

The remainder of t h i s a r t i c l e w i l l involve a d e s c r i p t i o n of each of these tasks followe applied to the design o Risk Categorization. The f i r s t step i n t h i s process i s to c l e a r l y define the r i s k associated with the operation of t h i s laboratory. This step includes a b r i e f d e s c r i p t i o n of the operation followed by a r i s k assessment and a recommendation on the l e v e l of system safety required. Laboratory Description. The laboratory under consideration w i l l conduct d i v e r s i f i e d chemical surety materiel laboratory operations. These materials are a n t i c h o l i n e r g i c agents and are extremely l e t h a l i n small concentrations. The recommended permissible airborne exposure concentration f o r some of these agents i s 0.0001 mg/m3 (2 χ 10-5 ppm). Two personnel are required, as a minimum, to per­ form t h i s operation. Assessment. An analysis of the hazards present i n t h i s laboratory show the most s i g n i f i c a n t hazard to be the release of vapor CSM from engineering controls and into the workplace. The s i g n i f i c a n c e of t h i s hazard mandates further e f f o r t s i n system safety i n the form of a Preliminary Hazard L i s t (PHL) and a Preliminary Hazard Analysis (PHA). The user must i n t h i s instance take an a c t i v e r o l e i n the design review process. Preliminary Hazard L i s t . Once the r i s k categorization i s completed, the next step i s to develop a PHL. The PHL i s a user generated l i s t i n g of hazards which must be c o n t r o l l e d . The user must, at t h i s stage, assign a r i s k assessment code to each hazard and e s t a b l i s h any further requirements f o r analyses (the methodology used i n the development of r i s k assessment codes i n t h i s a r t i c l e i s shown as Figure 1). As a minimum the user should use the following sources of information f o r PHL development: 1. 2. 3. 4. 5.

M a t e r i a l Safety Data Sheets F e a s i b i l i t y Studies Project Development Brochures Standing Operating Procedures Operator Interviews

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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214

Hazard Severity (1) Category I - Catastrophic: May cause death or loss of a f a c i l i t y . (2) Category I I - C r i t i c a l : May cause severe i n j u r y , severe occupa­ t i o n a l i l l n e s s , or major property damage. (3) Category I I I - Marginal: May cause minor i n j u r y , minor occupa­ t i o n a l i l l n e s s , or minor property damage. (4) Category IV - N e g l i g i b l e : Probably would not a f f e c t personnel safety or health, but i s nevertheless i n v i o l a t i o n of s p e c i f i c standards. Mishap P r o b a b i l i t y (1) (2) (3) (4)

Subcategory Subcategory Subcateogry Subcategory

A Β C D

-

L i k e l y to occur immediately. Probably w i l l occur i n time. Ma Unlikel

Risk Assessment Code

Hazard Severity

I II III IV

Mishap Probability A Β C 1 1 2 1 2 3 2 3 4 3 4 5

D 3 4 5 5

Figure 1. Risk Assessment

Preliminary Hazard L i s t Description. The incorporation of t h i s information into a PHL entry i s shown as Table I . This entry describes; the nature of the hazardous event (column 1), why or how the hazard may r e s u l t i n a mishap (column 2), the e f f e c t s on operating personnel, equipment, and the f a c i l i t y (column 3), the r i s k assessment code assigned t o the uncontrolled hazard (column 4) and any comments the o r i g i n a t o r may have (column 5). Preliminary Hazard Analysis. The next step i n the process i s the development of a PHA. This analysis i s the core of the FSS program and as such i s v i t a l i n eliminating or reducing the inherent hazards associated with t h i s laboratory operation. The PHA i s used to further analyze the data i d e n t i f i e d i n the PHL. This enhances the hazard control data base and provides s p e c i f i c recommended correc­ t i v e action f o r the r e s o l u t i o n of hazardous conditions. A combina­ t i o n of the informational sources used i n the PHL development and any a d d i t i o n a l design information should be used i n PHA development.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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215

Designing a Chemical Surety Materiel Laboratory Table I .

COLUMN 1

COLUMN 2

HAZARDOUS EVENTS

CAUSAL FACTORS

Release of vapor CSM from lab hood and into workplace or atmosphere.

1. Power failure

P r e l i m i n a r y Hazard

List

COLUMN 3

COLUMN 4

COLUMN 5

EFFECTS

RISK ASS. CODE

COMMENTS

I A1

None

1. Loss or lab hood capture. Release of CSM into workplace. Personnel injury or death, System/f acuity damage minimal.

2. Mech exhaust fa failure 3. Poor lab hood capture design)

3. Turbulence may IΒ 1 result in small re­ lease of CSM into workplace. Personnel injury or death could result. System/facility damage minimal.

None

4. Operator error

4. Judgement errors could result in an inadvertent release of CSM into the work­ place. Personnel injury or death could result. System/facil­ ity damage minimal.

None

5. Filters do not remove CSM from exhaust

5. Personnel injury II C 3 to people surrounding the facility. System/ facility damage minimal Adverse publicity.

Scenario less likely and severe due to dilu­ tion factor.

6. Exhaust ductwork not properly sealed

6. Small concentra­ tions CSM in the workplace possible in the event the exhaust system were to go positive. Personnel injury or death possi­ ble. System/facility damage minimal.

Scenario less likely due to addi­ tional require­ ment for system to go posi­ tive.

IΒ1

I C2

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

216

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES Table I I .

Preliminary Hazard Analysis

COLUMN 6

RECOMMENDED ACTIONS

COLUMN 7

COLUMN 8

CONTROLLED RISK ASS. CODE

STANDARDS

Causal Factor / / l ; IV D 5 a.) Emergency generator system shall be installed to automatically initiate in the event of a power failure, system phasing shall be accomplished in a manner which will not permit the occurrence of a hazardous condition.

DOD 6055.9-STD AMCR 385-102 CRDECR 385-1

b. ) Laboratory hoods mus a mechanism to warn operator power status and hood function. c. ) Standing Opeating Procedures should contain provisions for the curtailment of operations, immediate masking and evacuation from areas that experience power failures. Causal Factor //2; a. ) Two alternatives are available to prevent a hazardous condition from occurring in the event of a mechanical failure. These include: (1) Redundant exhaust fan units, (2) Procedural controls which require curtailment of operations, donning of protective masks and immediate evacuation during ventilation loss.

IV D 5

DOD 6055.9-STD AMCR 385-102 CRDECR 385-1 LOCAL SOPs

IV D 5

AMCR 385-102 AEHA Technical Guide y/30 CRDECR 385-1

b. ) Laboratory hoods shall be equipped with a means to warn operators of improper ventilation system functioning. Causal Factor //3: a.) Laboratory hoods must be located away from: - Main traffic aisles and doorways - Adjacent walls and operable windows - Cross drafts exceeding 30 lfpm - Heating Units - Exits.

b.) Laboratory hoods must perform as follows: - Average inward face velocity of 100 lfpm +/- 10% with the velocity at any point not deviating from the average face velocity by more than 20%.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

13.

COLLINS

Table I I .

Designing a Chemical Surety Materiel Laboratory

Continued COLUMN 6

RECOMMENDED ACTIONS

COLUMN 7

COLUMN 8

CONTROLLED RISK ASS. CODE

STANDARDS

IV D 5

CRDECR 385-1

Causal Factor //3 (Continued): c.) Operators must be trained in proper operation within a laboratory hood. Causal Factor /M: a. ) Operating personnel must be properly trained. b. ) Operating personnel priate protective clothing. c. ) Operating personnel must work under a properly approved SOP. Causal Factor //5: a.) Exhaust filtration system shall meet CSL SOP 70-18.

IV D 5

CSL SOP 70-18 CRDECR 385-1

Causal Factor //6: a.) Ductwork shall be sealed to preclude leakage.

IV D 5

DOD 6055.9-STD CRDECR 385-1

b. ) A l l joints shall be seamless welded. c. ) Ductwork shall be capable of withstanding 16 inches water column vacuum and 25 inches water column positive pressure.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

217

218

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES Table I I I . COLUMN 9

ACTION TAKEN CAUSAL FACTOR //It a. ) Emergency generator installed and properly phased b. ) Laboratory hoods equipped with warning devices to notify operator of power loss c. ) Installation notified of finding

CAUSAL FACTOR //2; a. ) Installation safety office determines need to go with procedural controls. SOPs will be developed accordingly. b. ) Laboratories equipped with warning devices to notify operators of ventilation system failure

Hazard Tracking Log

COLUMN 1 0

COLUMN 11

COLUMN 1 2

DESIGN CERTIFICATION

CONSTRUCTION CERTIFICATION

Drawing //:099 Specification Section //09991

Mr. Smith

Mr. Jones

Drawing //:061 Specification Section #08001

Mr. Smith

Mr. Jones

TRANSFER

sent 6 Jan 86 to safety office

Disposition Form 10 Jan 86

Drawing //:061 Specification Section #08001

CAUSAL FACTOR //3: a.) Lab hoods meet the Drawing #:045 following: Away from: - Main traffic aisles - Doorways and windows - Adjacent walls - Cross drafts > 30 lfpm - Heating units - Exits

Mr. Smith

Mr. Jones

Mr. Smith

Mr. Jones

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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219

Designing a Chemical Surety Materiel Laboratory

Table I I I . Continued COLUMN 9

ACTION TAKEN

COLUMN 10

TRANSFER

CAUSAL FACTOR //3; (Continued) Drawing //:046 b.) Lab hoods perform as Specification follows: Section //07010 - Average face velocity 100 lfpm +/- 10%. No single reading deviating from average by 20% - Smoke testing did not result in a release of visible smoke c.) Installation notifed of requirement for proper training of operators

COLUMN 11

COLUMN 12

DESIGN CERTIFICATION

CONSTRUCTION CERTIFICATION

Mr. Smith

Mr. Jones

Disposition Form dated 25 Mar 86

CAUSAL FACTOR //4: Installation responsibility

Installation notified 25 Mar 86

CAUSAL FACTOR //5; Exhaust system complies with CSL SOP 70-18

Specification Section //01001

Mr. Smith

Mr. Jones

CAUSAL FACTOR //6: Ductwork properly sealed and tested

Specification Section //02000

Mr. Smith

Mr. Jones

Disposition Form dated 25 Mar 86

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

220

Preliminary Hazard Analysis Description. The incorporation of t h i s information into a PHA entry i s shown as Table I I . This entry describes; the proposed actions needed to eliminate or c o n t r o l the hazard (column 6), the r i s k assessment code assigned a f t e r controls (column 7), and the i d e n t i f i c a t i o n of applicable codes and standards (column 8). Hazard Tracking Log. In a d d i t i o n to the above a n a l y s i s , a hazard tracking l o g (HTL) should be maintained. This log i s to ensure a l l open loops are closed and ensures the appropriate l e v e l of management i s i d e n t i f i e d as being involved i n the acceptance of r i s k . This log should be i n i t i a t e d during the design phase and maintained throughout construction. As t h i s f a c i l i t y i s not at the design stage at the time of p u b l i c a t i o n , a simulated HTL was used and i s shown at Table I I I . This entry describes: the s p e c i f i c action taken to eliminate, c o n t r o l or accept the hazard (column 9), the reference of the blueprint/drawin number othe document tha addres th action taken (column 10) on design (column 11), an g the action during construction (column 12). The information contained i n t h i s l o g i s proposed because the laboratory i s i n the design stage of development. Laboratory Design Considerations. As a r e s u l t of t h i s e f f o r t , d e t a i l e d safety design considerations can be developed to preclude the release of l e t h a l concentrations of vapor CSM into the workplace. This w i l l minimize the p o t e n t i a l f o r death or serious i n j u r y to our research s c i e n t i s t s . A summary of these requirements i s shown i n Appendix A. Conclusions. The e f f o r t put f o r t h i n FSS f o r t h i s laboratory has many b e n e f i t s . Most noteworthy are: 1. Safest possible laboratory 2. More mission responsive f a c i l i t y 3. Less expensive f a c i l i t y This a r t i c l e i s a step i n the d i r e c t i o n we must a l l head toward and that i s t o t a l system safety f o r f a c i l i t i e s to reduce inherent hazards associated with t h e i r operation. Literature Cited 1. 2. 3. 4.

Chemical Systems Laboratory Standing Operating Procedure (CSL SOP) 70-18, 10 Nov 82, Exhaust Ventilating Systems. Department of Defense (DOD) 6055.9 - STD, July 1984, Ammunition and Explosives Safety Standards. Army Materiel Command Regulation (AMCR) 385-102, 6 May 1982, Safety Regulations for Chemical Agents GB and VX. Chemical Research Development and Engineering Center Regulation (CRDECR) 385-1, 15 Aug 1986, Chemical and Occupational Safety and Health Program.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

COLLINS

Designing a Chemical Surety Materiel Laboratory

221

APPENDIX A Laboratory Design Considerations for Protection Against Vapor Chemical Surety M a t e r i e l Exposure E l e c t r i c a l Design Considerations (Causal Factor / / l ) : 1. Emergency generator systems w i l l be i n s t a l l e d to service the f o l l o w i n g : -

Exhaust v e n t i l a t i o n fans Make-up a i r handling u n i t s C r i t i c a l operating equipment Emergency l i g h t i n g A l l emergency alarm systems

2.

Diesel-powered generator erator w i l l be size emergency load.

3.

Start-up of the exhaust v e n t i l a t i o n system and c r i t i c a l equipment must be sequenced to prevent a hazardous condition. In a d d i t i o n , the s t a r t i n g of the supply a i r handling u n i t and the exhaust fan services each room s h a l l i n i t i a t e simultaneously to avoid placing the room under p o s i t i v e pressure. Automatic t r a n s f e r switching w i l l be used.

Warning Systems (Causal Factor 111 & 2): 1. F a c i l i t y w i l l be equipped with a master c o n t r o l panel and alarms which permits f u n c t i o n a l v e r i f i c a t i o n of the exhaust blowers, f i l t e r s , make-up a i r supply systems, f i r e c o n t r o l systems and waste treatment processes. 2.

Laboratory hoods w i l l be equipped with audible and v i s u a l alarms which w i l l be designed to i n i t i a t e when the average inward face v e l o c i t y f a l l s below 90 l i n e a r feet per minute.

3.

V i s i b l e alarms must be located so they can be r e a d i l y seen by personnel while working at the exhaust hood.

4.

A t e s t switch must be i n s t a l l e d on a l l alarms which w i l l permit the operator to v e r i f y that the l i g h t has not burned out and the sound alarm w i l l function. This t e s t must be performed while v e n t i l a t i o n system i s i n f u l l operation.

Laboratory Hood Location (Causal Factor //3): 1. Laboratory hoods must be located away from: - Heavy t r a f f i c a i s l e s - Doorways

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

222

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

- Adjacent walls - Crossdrafts that exceed 30 lfpm - Heating u n i t s 2.

Sidewall r e g i s t e r s and conventional c e i l i n g d i f f u s e r s s h a l l not be used f o r laboratory a i r supply.

3.

Perforated c e i l i n g panels s h a l l be used so that d i s t r i b u t i o n of supply a i r i s three feet minimum from the front face of the hood. The e x i t v e l o c i t y from these panels s h a l l not exceed 35 lfpm.

D. Laboratory Hood Performance (Causal Factor #3): 1. Laboratory hoods s h a l l have an average inward face v e l o c i t y of 100 lfpm +/- 10% with the v e l o c i t y at any point not deviating from the average face v e l o c i t y by more than 20% 2.

Leakage t e s t i n smoke candles place approximately the hood. Any v i s i b l e escape of smoke should be considered i n d i c a t i v e of unacceptable performance.

3.

Laboratory hoods s h a l l be designed as deep and low i n height as p r a c t i c a l . Rough w a l l surfaces and recesses i n walls and work surfaces are unacceptable.

4.

The l o c a t i o n of sash tracks and the number of b a f f l e s and s l o t s provided are i n t e g r a l to the proper containment of materials.

5.

Laboratory hoods w i l l be equipped with a 20 centimeter l i n e taken from the face of the hood. No CSM contaminated equipment should be placed i n front of t h i s l i n e during operations.

E. Exhaust V e n t i l a t i o n / F i l t r a t i o n System (Causal Factor #5): 1. A l l laboratory exhaust a i r s h a l l be exhausted through a f i l t r a t i o n system which complies with CSL SOP 70-18. These systems have been proven to be e f f e c t i v e i n removing CSM vapor from an e x i t i n g airstream. 2.

V e n t i l a t i o n exhaust s h a l l not be r e c i r c u l a t e d .

3.

Instrumentation s h a l l be required to monitor and control the a i r f l o w through the f i l t e r system. Instrumentation s h a l l provide a means to monitor o v e r a l l pressure drop as w e l l as the pressure drop between each f i l t e r element.

4.

The f i l t e r system s h a l l include a series redundant-parallel Chemical B i o l o g i c a l R a d i o l o g i c a l (CBR) f i l t e r assembly with a c a p a b i l i t y of placing a detector between the adsorber banks to warn of "breakthrough". The system s h a l l provide a c c e s s i b i l i t y to f i l t e r s f o r r e p a i r s , maintenance and leak testing.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

13.

COLLINS 5.

Designing a Chemical Surety Materiel Laboratory

223

The f i l t e r system s h a l l be as follows:

Hood - P r e f i l t e r - HEPA - Adsorber - Adsorber - HEPA - Exhaust 6.

Exhaust stacks s h a l l be designed and constructed to ensure good dispersion of exhaust a i r to the atmosphere thereby preventing r e c i r c u l a t i o n .

F. Exhaust Ductwork (Causal Factor #6): 1. A l l ductwork s h a l l be round, and welded with flange connections. 2.

Ductwork s h a l l be designed to f a c i l i t a t e dismantling and to minimize the release of contamination to adjacent areas with bagging or other approved means.

RECEIVED March 6,1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 14

Laboratory Design Frances H. Cohen Oneil M. Banks, Bel Air, MD 21014

Research laboratories are very unique facilities which require a great deal of preparation and coordination to produce a proper design. Much like the research that will be performed in the facility, each laborator ha specifi need d requirements Th primary considerations i the ventilation system, type equipment, and safety and health of the work environment. Each of these primary consideration are of equal importance to the development of a successful design. A safe and healthful work environment is a crucial requirement of a research laboratory. This consideration is the most often overlooked, yet it is intertwined with all aspects of building design and operation. Protection of the buildings occupants includes not only fire safety aspects as defined in the National Fire Protection Association Life Safety Code, but in the breathing air quality. Therefore, the materials of design, means of egress, and ventilation system should be the first subjects considered during the design process. Just their

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0097-6156/87 0345-0224$06.00/0 © 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

act

Laboratory Design

14. COHEN

225

as a mediator when disagreements a r i s e . Representation i s limited to a few s c i e n t i s t s . They, i n turn, usually develop t h e i r own research program subcommittee. The extent of t h i s subcommittee i s dependent of the size of the building and the number of d i f f e r e n t research programs that w i l l occupy the b u i l d i n g . Health and safety considerations are addressed j o i n t l y by an i n d u s t r i a l hygienist and a safety s p e c i a l i s t . These are the individuals that are "the authority having j u r i s d i c t i o n " as referenced by the National F i r e Protection Association. Because of the unique nature of many research laboratories, i t i s not always possible to adhere s t r i c t l y to the NFPA Codes and these i n d i v i d u a l must use t h e i r professional judgement i n applying the intent of the Codes. Once the team i s assembled, i t i s important to have a " k i c k - o f f " or pre-design meeting so that each representative i s given the opportunity to present t h e i r needs and requirements. The remainder of t h i s chapter w i l l be devote the design of a research DEFINITION There i s probably nothing more confusing than the d e f i n i t i o n of a laboratory. For the sake of consistency i n t h i s chapter a laboratory i s defined as a b u i l d i n g , space, room, equipment, or operation used for t e s t i n g , analysis, research, i n s t r u c t i o n , or s i m i l a r a c t i v i t i e s . To further explain t h i s d e f i n i t i o n , a room i s considered a laboratory i f any of the following e x i s t : 1. 2. 3. properties;

4. 5. 6. CODES AND

fume hood/biosafety cabinet gas cylinders use or storage of chemicals with any of the following a. flammable b. combustible c. explosive d. water sensitive e. caustic f. corrosive g. high or unknown t o x i c i t y h. carcinogen/mutagen/teratogen biohazardous material grinding operations radioisotopes/radioactive sources

SPECIAL REQUIREMENTS

At the outset of involvement i n laboratory design i t i s incumbent for the health and safety s p e c i a l i s t s to designate those codes, regulations, and s p e c i a l requirements they consider e s s e n t i a l to produce a safe and h e a l t h f u l work environment. A l l to often the A/E w i l l choose a standard building code to follow. These codes, while appropriate for o f f i c e buildings, do not address the necessary l i f e safety requirements necessary for laboratories. T y p i c a l l y , the codes and regulations required for proper health and safety i n laboratory design are the National F i r e Protection

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Association Code, Occupational Safety and Health Administration Standards, Environmental Protection Agency Regulations, National I n s t i t u t e s of Health/Centers f o r Disease Control Biosafety Guidelines, Nuclear Regulatory Commission Regulations, American National Standards I n s t i t u t e Standards, American Conference of Governmental I n d u s t r i a l Hygienists Manual on I n d u s t r i a l V e n t i l a t i o n , and s p e c i f i c w r i t t e n p o l i c y of the agency/company planning the design. I t i s becoming more commonplace for i n d i v i d u a l companies to develop s p e c i f i c requirements for v e n t i l a t i o n systems, biosafety f a c i l i t i e s , r a d i o l o g i c a l safety, animal f a c i l i t i e s , and performance standards for equipment. Under the NFPA L i f e Safety Code each b u i l d i n g i s given an occupancy c l a s s i f i c a t i o n . Laboratory structures are usually c l a s s i f i e d as " i n d u s t r i a l " with "high hazard contents." When a b u i l d i n g i s designed for mixed occupancies such as o f f i c e s and c l i n i c a l areas, separate c l a s s i f i c a t i o n s con be assigned i f separate safeguards are provided of a buildings occupanc of b u i l d i n g materials, placement of the mechanical room, and egress design, l o c a t i o n and number. VENTILATION SYSTEMS There are two main types of v e n t i l a t i o n systems; constant volume and v a r i a b l e volume. Both systems can be either 100% fresh a i r or r e c i r c u l a t i n g . The type of system that i s selected should be c a r e f u l l y chosen with safety and health as the primary consideration. Constant volume systems d e l i v e r a preset volume of a i r over a s p e c i f i e d temperature and humidity range. Variable volume systems d e l i v e r variable amounts of a i r which are determined by temperature change, a i r needed ( i . e . , use of fume hoods), and by pressure d i f f e r e n t i a l s . Constant volume systems are dependable and require l i t t l e maintenance, but are not energy e f f i c i e n t . Variable volume systems are usually energy e f f i c i e n t , but require sophisticated technology and scheduled preventive maintenance. Only recently has the technology been developed to properly implement v a r i a b l e volume systems. There are numerous pros and cons for s e l e c t i o n of either system which w i l l not be discussed at t h i s time. However, the team must consider funds available for the project, maintenance provisions, and current and future research needs before making a selection. In a mixed occupancy b u i l d i n g i t i s wise to consider the design of separate v e n t i l a t i o n systems f o r laboratory areas, areas s e r v i c i n g the p u b l i c , animal holding areas, and administrative o f f i c e s . Although t h i s approach adds a d d i t i o n a l cost to both the design and construction of the b u i l d i n g , i t allows for s e l e c t i o n of d i f f e r e n t systems i n each area and increases the f l e x i b i l i t y of the research functions. Also, the use of separate v e n t i l a t i o n systems allows for the use of more energy e f f i c i e n t systems i n those areas where a i r r e c i r c u l a t i o n can be employed safely. For example, i f the v e n t i l a t i o n system f o r the laboratory area i s properly designed, the addition of another fume hood can be achieved without redesign or any e f f e c t to other areas of the b u i l d i n g . Animal holding areas create t h e i r own unique requirements depending on the species and type of research to be performed. A separate v e n t i l a t i o n system allows the

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

14.

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f l e x i b i l i t y to change for these requirements as they a r i s e without e f f e c t i n g other areas of the b u i l d i n g . Requirements f o r animal holding areas w i l l be discussed further under Animal F a c i l i t i e s . Further, the use of variable a i r volume r e c i r c u l a t i n g systems i n o f f i c e s i s an e f f e c t i v e way to save energy and provide a h e a l t h f u l work environment i f , using a moderate flow rate, 20% fresh a i r i s introduced into the system. Design of laboratory v e n t i l a t i o n systems should be approached with the r e a l i z a t i o n that the laboratory can be the single most dangerous workplace. S t r i c t adherence to NFPA 45 - F i r e Protection for Laboratories Using Chemicals i s advised. R e c i r c u l a t i o n of laboratory a i r should be prohibited as i t poses both a f i r e safety problem and a p o t e n t i a l health hazard. R e c i r c u l a t i n g systems allow for more rapid spread of f i r e to other areas. More importantly, i n the event of a t o x i c chemical s p i l l , r e c i r c u l a t i n g systems spread the contamination throughout the laboratory and do not provide the necessary exhausting capacit environment that a 100% Although room changes of a i r per hour i s not a very technical means of determining that enough a i r i s supplied to a laboratory area, i t i s a term which i s e a s i l y understandable. For most laboratory a p p l i c a t i o n s , eight to twelve room changes per hour are adequate to provide proper d i l u t i o n v e n t i l a t i o n . Laboratories designed for biocontainment require a minimum of ten room changes of a i r per hour. For both f i r e safety, health considerations, and proper functioning of fume hoods the a i r pressure of laboratory areas must be negative r e l a t i v e to surrounding areas. The only exception to t h i s i s for c e r t a i n biocontainment applications. These applications usually require very s p e c i f i c v e n t i l a t i o n requirements which w i l l not be addressed. Also, a l l laboratory v e n t i l a t i o n systems, e s p e c i a l l y fume hoods, should incorporate low flow warning devices. As stated e a r l i e r , the laboratory chemical fume hood i s the single most important engineering control i n the laboratory f o r the protection of workers from exposures to t o x i c substances. While t h i s statement usually receives widespread approval, the lack of attention paid to fume hood design s p e c i f i c a t i o n s and l o c a t i o n w i t h i n the laboratory i s t r u l y amazing. While a fume hood i s a very substantial piece of equipment i t ' s proper functioning i s dependent on d e l i c a t e placement and balancing. Recent developments i n research on fume hood face v e l o c i t i e s has shown that face v e l o c i t i e s as low as 75 feet per minute (fpm) are s u f f i c i e n t for the handling of v o l a t i l e materials. With t h i s reduction of face v e l o c i t i e s i t becomes more important than ever to place fume hood away from t r a f f i c areas and supply a i r d i f f u s e r s . When walking, the average person creates turbulence of approximately 250-300 fpm. S l i g h t movement, such as breathing can create turbulence as high as 25 fpm. A i r supply d i f f u s e r s generally supply a i r at 100 fpm or higher. Therefore, i t i s easy to see how these otherwise i n s i g n i f i c a n t events can t o t a l l y disrupt the proper operation of fume hoods. I d e a l l y , each fume hood should be i n d i v i d u a l l y exhausted from the b u i l d i n g . This allows for the greatest f l e x i b i l i t y w i t h i n the hood as to s e l e c t i o n of chemicals that can be used. I t also provides the most safety i n case of an accidental s p i l l , f i r e , or explosion. In an i n d i v i d u a l l y exhausted system an accident can be contained

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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within one fume hood, whereas, i n a manifolded system the s i t u a t i o n can spread. However, manifolded systems are more the rule than the exception. From a health and safety perspective, these systems require careful planning to avoid the use of incompatibles within the system. This requires the researchers involved with the project to develop a l i s t of chemicals which may be used i n t h e i r research. After this l i s t i s reviewed for i n c o m p a t i b i l i t i e s , i n d i v i d u a l fume hoods need to be assigned for use with s p e c i f i c chemical classes. A hidden aspect to this s i t u a t i o n i s the administrative controls which the project leader must enforce i n order to keep incompatibles separate. Balancing of manifolded systems i s often very d i f f i c u l t . The use of damper within the system was the generally accepted method u n t i l f a i r l y recently. The use of dampers has not proven to be e f f e c t i v e because they tend to f a i l for a variety of reasons and are d i f f i c u l t to keep adjusted. More recently, balancing of manifolded systems has been accomplishe d i f f e r e n t i a l s . This metho limitations. The placement of fume hood exhaust motors i s an important f i r e protection consideration. Fume hood exhaust motors should be placed on the roof of the building or i n a f i r e secured penthouse. Placement of the exhaust motor d i r e c t l y on top of the fume hood i s a f i r e and explosion hazard as, except for s p e c i a l l y order motors, these motors are not sealed and are thus exposed to the chemicals they are exhausting. Fume hood exhaust stack heights are another area of concern to health and safety s p e c i a l i s t s . Stack heights should be determined by the height of the building (building envelope), proximity to other buildings, prevailing winds, weather conditions, and location of the building's a i r intake. Ignoring these parameters can cause entrainment of exhaust a i r into the supply system, thus creating an indoor a i r p o l l u t i o n problem. As a general rule of thumb, 10 foot stack heights for single story buildings and 15 foot stacks for multi-story buildings are reasonable, provided the exhaust v e l o c i t y i s at least 2,500 fpm. It i s important to remember that the exhaust v e l o c i t y i s a c r u c i a l element i n the o v e r a l l exhaust design. The stacks are an aesthetic problem, but the use of decorative facades can e a s i l y hide the stacks. ANIMAL FACILITIES Animal f a c i l i t i e s have t r a d i t i o n a l l y been under the purview of the s c i e n t i s t . However, there are special safety and health considerations which should be involved i n the design of i n d i v i d u a l animal rooms. These f a c i l i t i e s may, also, include housing for insects, parasites, etc. Most often consideration i s given only to keeping odors from reaching other parts of the building. From a health and safety perspective, this i s the l a s t of many reasons for the use of a separate v e n t i l a t i o n system. In some research applications the animals i n use or the diseases under study are zoonotic (animal diseases transferable to humans). Under these conditions special precautions must be taken to prevent exposure to humans. For example, sheep carry a zoonotic disease c a l l e d Q Fever which i s

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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usually manifested i n humans as a f l u - l i k e disease. Sheep rooms should be kept negative to the surrounding area, and exhaust a i r c i t h e r incinerated or HEPA f i l t e r e d . This disease i s also transmissible to other animals such as c a t t l e . Contamination from room to room i s usually accomplished by designing each room with independent supply and exhaust ducts. The converse s i t u a t i o n i s the housing of primates. They are extremely susceptible to human diseases such as measles and tuberculosis. I t i s sometimes advisable to design t h e i r holding f a c i l i t i e s under p o s i t i v e pressure with l i m i t e d access. A t y p i c a l design i s s i m i l a r to containment laboratories with an ante room for clothes change and showering. Rodents present a very d i f f e r e n t problem. They are perhaps the greatest escape a r t i s t s i n the world. Many experiments have been ruined because the controls and treated animals have " v i s i t e d each other or t o t a l l y "disappeared." Rodent f a c i l i t i e s need to be "escape proofed." In p r a c t i c a l orderly technology. Ther i n the w a l l s , c e i l i n g , an penetration c a r e f u l l y sealed, i n a fashion s i m i l a r to a biocontainment f a c i l i t y . A i r vents and drains should be screened. Care must be taken not to use too small mesh as i t w i l l i n t e r f e r e with a i r f l o w . The w a l l material should be smooth. Another problem encountered with rodents, p r i m a r i l y r a t s , i s t h e i r s u s c e p t i b i l i t y to respiratory diseases. C o n t r o l l i n g temperature, humidity, and the day/night cycle are necessary to maintain the health of these animals. The answer to t h i s problem i s to incorporate of i n d i v i d u a l controls i n each rodent holding area. Insectories present another problem. Many species of insects pose a l l e r g y problems for humans. The exact nature of the a l l e r g e n has not yet been characterized. However, i t has been shown that continuous exposure to insect scales and fras (insect debris) can create a l l e r g i c responses i n s e n s i t i v e i n d i v i d u a l s . Also associated with the r a i s i n g of insects, are exposures to various molds, b a c t e r i a , and formaldehyde. There i s no single s o l u t i o n to t h i s problem, but there are good engineering controls available an s p e c i f i c design considerations. V e n t i l a t i o n systems f o r i n s e c t o r i e s should be designed with d i r e c t i o n a l a i r flow. The supply a i r can be directed from the front (entrance) of each room down and toward the back. Return a i r ducts are than placed near the f l o o r . The supply discharge v e l o c i t y should approach laminar to approximate an a i r c u r t a i n around workers when i n the room. A l l surfaces should be washable, as good housekeeping i s a key to a l l e r g y prevention. Often insect screening i s placed over a l l openings. This practice i s u s u a l l y detrimental to the effectiveness of the v e n t i l a t i o n system. Replaceable f i l t e r s can be used which w i l l prevent the escape of f l y i n g insects. As i n the design of rodent f a c i l i t i e s , care should be taken to seal a l l penetrations. Self-contained incubation chambers are commercially a v a i l a b l e which can be used as either negative or p o s i t i v e pressure u n i t s . These chambers employ d i r e c t i o n a l a i r flow so that insect scales and fras are c o l l e c t e d on the bottom where cleaning i s easier and worker exposure i s minimized. The key to design of animal f a c i l i t i e s i s s i m p l i c i t y . A l l surfaces should be washable and a water source available i n each 11

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room. Each room should have i n d i v i d u a l temperature, humidity, and l i g h t i n g controls. The v e n t i l a t i o n system should be given primary consideration p r i o r to room layouts so that the most f l e x i b i l i t y can be designed into the f a c i l i t y . This becomes e s p e c i a l l y important i f future research w i l l require the separation of "clean and " d i r t y " areas. Actual room layout should consider the c o m p a t i b i l i t y of animal species e s p e c i a l l y with respect to cross-contamination. In a m u l t i p l e occupancy b u i l d i n g a separate means of egress i s advisable for transportation of animals to and from the b u i l d i n g . Aside from the obvious odor containment, t h i s egress provides protection to the animals. 11

FIRE SAFETY Each i n d i v i d u a l laboratory room should have a second means of e x i t . Adjacent laboratory rooms may share t h i s remote e x i t , v i a a common separation w a l l . The usua s c i e n t i s t ' s need for a argument i s understandable i t i s not as important as the safe escape of workers i n the event of a f i r e or t o x i c release. The storage of flammable/combustible materials should be considered during i n i t i a l laboratory design. The use of the cabinets under fume hoods, although a common p r a c t i c e , i s not acceptable under NFPA Codes, unless the cabinets have been designed f o r t h i s purpose. I t i s important to note that unless t h i s type of cabinet i s s p e c i f i c a l l y required i n the t e c h n i c a l s p e c i f i c a t i o n s , a t y p i c a l nonflammable storage cabinet w i l l be provided. Therefore, each laboratory should be designed to store flammable/combustible materials i n a segregated, vented storage cabinet i n accordance with NFPA 30 - Flammable and Combustible Liquids Code and NFPA 45. The amount of chemicals stored i n each laboratory should be l i m i t e d to a short term supply (e.g., enough for one week or month). This supply by i t ' s nature w i l l be f a c i l i t y dependent. In order to allow for the storage of larger amounts of chemicals, a s p e c i f i c a l l y designed area should be used. The size and b u i l d i n g materials are s p e c i f i e d i n the OSHA Standards, NFPA 30, and NFPA 45. Compressed gas cylinders are commonly used i n laboratories. Where compressed gases are to be used which are common to several laboratories i t i s advisable to manifold these gases i n a c e n t r a l location. Sprinklers and f i r e protection systems are required by NFPA Codes, but are often dependent on the o v e r a l l size of the f a c i l i t y and quantity of stored flammable/combustible m a t e r i a l . The wisest course of action i s to provide heat and smoke detectors i n each laboratory and provide a s p r i n k l e r system at least i n the hallways. Each laboratory should have at l e a s t one ABC portable f i r e extinguisher. Computers have become more important to l a b o r a t o r i e s than ever. Halon f i r e extinguishing systems are a v a i l a b l e which are nondestructive to both e l e c t r o n i c equipment and human l i f e . These should be employed for f i r e protection. MISCELLANEOUS Each laboratory should have an emergency eye/face wash and shower s t a t i o n . The minimum c r i t e r i a f o r these systems are:

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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1. 2.

independently plumbed potable water supply control valve designed to remain open without operator

3. 4. 5.

control valve to remain open u n t i l manually shut off a c t i v a t i o n foot or hand treadles water flow rate to meet ANSI Z358.1-81

assistance

There are numerous portable units and hand held single head eyewash devices commercially a v a i l a b l e . Some of these are good a d d i t i o n a l support, but none of them are acceptable i n l i e u of stationary dual head eye/face washes. Laboratory f u r n i t u r e i s prefabricated or custom designed for every purpose. Wood f u r n i t u r e i s often used because of i t ' s a v a i l a b i l i t y and attractiveness. The are several drawbacks to the use of wood f u r n i t u r e : i t adds to the f i r e load of the b u i l d i n g ; and i t i s e a s i l y contaminated. In general, laboratory f u r n i t u r e should be constructed such that 1. 2. 3.

I t i s corrosion r e s i s t a n t . Contamination i s e a s i l y removed. I t can be arranged not to impede egress i n an

4.

The working surface i s free from cracks and j o i n t s .

emergency.

BIOCONTAINMENT LABORATORIES Biocontainment laboratories are s p e c i a l work environments which often require s p e c i a l design and equipment to protect the workers and the experiments. U n t i l a few years ago the biocontainment l e v e l or l e v e l of protection was designated with a "P" symbol followed by a number. The "P" has been replaced with "BSL" or Biosafety Level. There are four biosafety l e v e l s which are defined according to a combination of f a c i l i t y design, laboratory practices and techniques, equipment and health and safety controls. I t i s not p r a c t i c a l to t r y to completely describe a l l of the features and d e f i n i t i o n s pertaining to biocontainment laboratories i n a chapter dedicated to an overview of design. Therefore, we w i l l concentrate on the elements of b u i l d i n g design for "maximum containment" or BSL-4 f a c i l i t i e s . A maximum containment laboratory i s usually a separate b u i l d i n g , although i t can be part of another b u i l d i n g . To maintain the required security and necessary engineering features, including v e n t i l a t i o n and b u i l d i n g materials, i t i s usually more p r a c t i c a l to b u i l d a separate f a c i l i t y . In the simplest of terms, the primary design difference between a BSL-4 laboratory and any other laboratory i s the use of "secondary b a r r i e r s . " Secondary b a r r i e r s include b u i l d i n g materials, v e n t i l a t i o n systems, equipment (e.g., biosafety cabinets, space s u i t s ) , a i r l o c k s , change rooms, sealed openings, and decontamination systems. A BSL-4 laboratory has four " l a y e r s " between the hazardous agent and the outside environment. These layers or b a r r i e r s can be achieved by using a v a r i e t y of secondary b a r r i e r s . There are a number of BSL-4 applications i n the United States, but only one actual laboratory b u i l d i n g . The primary considerations i n deciding

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to use an application or b u i l d a laboratory are the hazard l e v e l of the research and the cost of the b u i l d i n g . Although from the outside a BSL-4 building can look l i k e any other laboratory the b a r r i e r s required a quite d i f f e r e n t . The structure must be a i r t i g h t . A l l a i r from within the f a c i l i t y must be f i l t e r e d through HEPA f i l t e r s before release to the outside. Therefore, at the outset of the design process the v e n t i l a t i o n system and the s t r u c t u r a l materials become the primary concerns. From the outer structure i t i s not evident that between the walls are foam materials not for i n s u l a t i o n , but for sealing porous building materials. The use of t i l i n g i s kept to a minimum as grout i s porous and allows penetration of bacteria/viruses. High quality epoxy paints are used instead as they afford the same washability and often help seal the walls. V e n t i l a t i o n systems are usually designed to maintain pressure d i f f e r e n t i a l s between d i f f e r e n t ares of the building and to provide d i r e c t i o n a l airflow from the "cleanest" to the " d i r t i e s t sophisticated i n design an follow the same general p r i n c i p a l previously V i r t u a l l y everything that goes into a BSL-4 laboratory does not come out again without being s t e r i l i z e d , with the exception of workers. Workers are required to change clothing before entering the containment area and completely shower p r i o r to leaving. There are some applications that require workers to shower p r i o r to entering and again before leaving. The change area i s usually located d i r e c t l y off of the main entrance. It should consist of a disrobe area with lockers and t o i l e t f a c i l i t i e s , showers, and a rerobe area. A l l clothing used within the containment area i s s t e r i l i z e d between uses. Decontamination i s required for a l l l i q u i d effluents from within the containment area. This includes the waste from laboratory sinks, biosafety cabinets, autoclaves, t o i l e t f a c i l i t i e s , etc. High pressure heating vessels are usually used for treatment of l i q u i d wastes. Even a f t e r s t e r i l i z a t i o n , the processing must be tested to ensure safety p r i o r to discharge outside of the f a c i l i t y . A l l s o l i d waste must be incinerated or s t e r i l i z e d and buried. Sometimes i n the design of a BSL-4 f a c i l i t y , the f u l l l e t t e r of health and safety codes/requirements for the protection of workers can not be met. This i s where health and safety s p e c i a l i s t s must compromise and use their ingenuity to meet the intent of the requirements. For example, i t i s not always possible to provide a secondary means of egress from each area. Two change f a c i l i t i e s are not cost e f f e c t i v e or p r a c t i c a l . A viable alternative i s the use of airlocks with b u i l t - i n l i q u i d d i s i n f e c t i o n systems which are not hazardous to humans, but destroy the biohazard. These a i r l o c k s must be c l e a r l y i d e n t i f i e d as others are often used for transportation of equipment and other materials and contain hazardous d i s i n f e c t i o n systems. The above elements of BSL-4 design are only the basics. P a r t i c i p a t i o n i n the design of such a f a c i l i t y i s extremely fascinating and d i f f i c u l t . Upon a n t i c i p a t i o n of such a design i t i s advisable to contact at least two biosafety experts who have had extensive experience i n the development of maximum containment applications. The f i e l d of biosafety i s rapidly growing with new applications and design c r i t e r i a developing continually.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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SUMMARY The success of a laboratory design depends on many f a c t o r s , not the least of which are health and safety considerations. When the team approach i s implemented, each member brings to the design s p e c i f i c expertise e s s e n t i a l to the element of proper design.

LITERATURE CITED

1.

Occupational Safety and Health Administration Standards, Occupational Safety and Health Administration, U.S. Government Printing Office: Washington, DC, 1986. 2. National Fire Protection Association Codes, National Fire Protection Association, 1986. 3. Biosafety in Microbiologica Edition, U.S. Departmen Health Service Centers for Disease Control and National Institutes of Health, U.S. Government Printing Office: Washington, DC, March, 1984. 4. American National Standards Institute Standards, American National Standards Institute, 1986. 5. Construction Policy Design Manual, U.S. Department Of Agriculture, Agricultural Research Service, 1986. 6. Laboratory Chemical Fume Hoods- Manual, U.S. Department Of Agriculture Agricultural Research Service, 1981. 7. Industrial Ventilation, 17th edition, American Conference of Governmental Industrial Hygienists: Cincinnati, OH, 1986. 8. Guide for the Care and Use of Laboratory Animals, DHEW, National Institutes of Health (out of print). 9. Health Research Laboratory Design, National Institutes of Health (out of print). 10. Midwest Plan Service, Livestock Facilities, Iowa State University: Ames, IA, 1986. 11. Comfortable Quarters for Laboratory Animals, Animal Welfare Institute (undated). 12. Chlad, F. L. Professional Safety; March, 1982. RECEIVED

March 6, 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 15

Design Considerations for Toxic Laboratories William J. Maurits Department of Army, Aberdeen Proving Ground, MD 21010-5423

Those elements of conventional laboratory design that must be refined for facilities in which toxic chemicals will be handled are presented. Alarms, communications, construction materials, containment cabinets, filter systems, floor plans waste disposal ar design considerations dictated by the use of large numbers of fume hoods.

A successful designer of a t o x i c l a b o r a t o r y w i l l f i n d i t necessary t o r e f i n e most o f the elements o f the t r a d i t i o n a l c h e m i c a l l a b o r a tory. Many d e t a i l s which a r e n ' t d i r e c t l y a s s o c i a t e d w i t h the t o x i c o p e r a t i o n s w i l l impact on the s a f e t y o f these o p e r a t i o n s . Because common l a b o r a t o r y mishaps w i l l be f a r more s e r i o u s where t o x i c s are used, i t makes sense t o i n v e s t e v e r y e f f o r t to p r e c l u d e such a c c i dents through c a r e f u l d e s i g n . Floor

Plan

The flow of personnel i n and out o f t o x i c areas can spread c o n t a m i n a t i o n , so the l a y o u t o f a l a b o r a t o r y s h o u l d f a c i l i t a t e r o u t i n e movement o f workers as w e l l as emergency e v a c u a t i o n s . S t a f f s h o u l d not have to walk through one l a b o r a t o r y t o get to another nor s h o u l d an o f f i c e be l o c a t e d where the o n l y e x i t i s through a l a b o r a t o r y . The p r o v i s i o n o f s e p a r a t e a d m i n i s t r a t i v e areas w i l l a v o i d l o c a t i n g s c i e n t i s t ' s desks i n rooms where t o x i c s are used. V i s i t o r s are s a f e r and more e a s i l y s u f f e r e d i f they can view the l a b o r a t o r y rooms through windows. L a b o r a t o r y a i s l e s must be no l e s s than 5 f e e t wide and benches s h o u l d have s u f f i c i e n t u n o b s t r u c t e d w i d t h t o accommodate modern a n a l y t i c a l i n s t r u m e n t a t i o n . An overhead ( f i l t e r e d ) exhaust system would p e r m i t s m a l l canopy hoods t o be connected as n e c e s s a r y to scavenge fumes from areas near i n j e c t i o n and exhaust p o r t s o f anal y z e r s not l o c a t e d i n hoods. Each room s h o u l d have i t s own s u p p l y

This chapter not subject to US. copyright Published 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

15.

MAURITS

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of a i r f o r v e n t i l a t i o n . S e l f c l o s i n g doors w i l l h e l p m a i n t a i n required s t a t i c pressure d i f f e r e n t i a l s . Emergency s t a t i o n s s h o u l d be l o c a t e d near e x i t s and s h o u l d i n c l u d e emergency shower ( w i t h d r a i n ) , and s t o r a g e f o r b l a n k e t s , t o w e l s , soap and l i g h t c l o t h i n g . Eyewashes must be a v a i l a b l e i n each l a b o r a t o r y , and s h o u l d f e a t u r e p o s i t i v e temperature c o n t r o l , s i n c e i t i s i m p o s s i b l e to wash ones eyes f o r 15 minutes i n i c y water. Alarm p u l l boxes s h o u l d be near each door f o r c o n v e n i e n t use on the way o u t . Each l a b o r a t o r y or storeroom s h o u l d have two e x i t s ( w i t h doors t h a t swing o u t ) p l a c e d so t h a t no c r e d i b l e event can b l o c k emergency e g r e s s . Workers must be assured an unimpeded path out o f the b u i l d i n g i n the event o f e m e r g e n c i e s , so i t i s i n a p p r o p r i a t e t o secure b u i l d i n g doors w i t h l o c k s t h a t cannot be opened from the i n s i d e . Any p e r i m e t e r f e n c i n g s h o u l d i n c l u d e gates w i t h l o c k s t h a t can be opened from the i n s i d e . L a b o r a t o r y rooms i n t e n d e d f o r t o x i c work s h o u l d be p r o v i d e d w i t h adjacent shower an r e q u i r e f r e s h l y showere t h a t they might have j u s t c o n t a m i n a t e d . A l l drains, including those i n l a b o r a t o r y f l o o r s , s h o u l d have deep t r a p s and be d i r e c t e d t o a t o x i c sump. A i r l o c k s w i l l help prevent t o x i c fumes from s p r e a d i n g t o n o n - t o x i c areas i n the event of a f a i l u r e of a p r i m a r y containment c a b i n e t . Check v a l v e s i n the incoming water l i n e s w i l l prevent c o n t a m i n a t i o n o f p o t a b l e water s u p p l i e s when p r e s s u r e i s lost. Secure d o c k a b l e ) s t o r a g e f o r s m a l l q u a n t i t i e s o f t o x i c c h e m i c a l s s h o u l d be a v a i l a b l e i n each room. A c e n t r a l s t o r a g e p o i n t f a c i l i t a t e s i n v e n t o r y i n g , but must accommodate c o m p a t i b i l i t y r e q u i r e m e n t s f o r the s t o r e d i t e m s . P r i m a r y Containment C a b i n e t s The n a t u r e o f the work t o be done, s t a t u t o r y r e q u i r e m e n t s , and the p r e f e r e n c e s o f the s t a f f w i l l d i c t a t e the s e l e c t i o n o f l a b o r a t o r y containment c a b i n e t s , but the f o l l o w i n g c o n s i d e r a t i o n s s h o u l d be taken i n t o account by the d e c i s i o n makers. Glove boxes ( i n c l u d i n g C l a s s I I I c a b i n e t s ) may be n e c e s s a r y f o r most t o x i c o p e r a t i o n s or where a e r o s o l s are i n v o l v e d . Glove boxes p e r m i t the use o f i n e r t or o t h e r w i s e c o n t r o l l e d atmospheres. They s h i e l d the o p e r a t o r d u r i n g use, r e q u i r e l e s s v e n t i l a t i o n than fume hoods, and d o n ' t cease t o p r o t e c t when house power i s l o s t , though t h e y may l o s e t h e i r n e g a t i v e p r e s s u r e . However, c l o s e d g l o v e boxes are i n c o n v e n i e n t . M a t e r i a l s must be passed i n or out through an a i r l o c k or dunk tank and the o p e r a t o r i s a f f o r d e d o n l y l i m i t e d movement by v i r t u e o f the arm l e n g t h g l o v e s being i n a f i x e d l o c a t i o n . S e a l s and g l o v e s w i l l be exposed t o h i g h e r c o n c e n t r a t i o n s o f c h e m i c a l s than would be generated i n a hood, so o r g a n i c s may permeate over a p e r i o d o f t i m e . Glove boxes o f f e r l e s s p r o t e c t i o n w h i l e s e a l s or g l o v e s are b e i n g changed. A l l work i n a c l o s e d g l o v e box i s viewed through g l a s s which seems t o a t t r a c t d i r t on both s u r f a c e s . Fume hoods are o f t e n s e l e c t e d f o r t h e i r convenience o f use though t h e y g r e a t l y c o m p l i c a t e the d e s i g n o f a l a b o r a t o r y . O p e r a t o r s can work c o m f o r t a b l y anywhere i n the hood and m a t e r i a l s

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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can be brought i n or out e a s i l y . Gloves can be changed c o n v e n i e n t l y w i t h o u t r i s k i n g o p e r a t o r exposure t o the hood's c o n t e n t s . U n f o r t u n a t e l y , fumes can d r i f t out of a hood f o r a v a r i e t y o f reasons and a e r o s o l s w i l l d r i f t o u t . Hoods s t r a i n h e a t i n g and a i r c o n d i t i o n i n g systems by consuming v a s t q u a n t i t i e s o f room a i r , t h e y are i n c o m p a t i b l e w i t h c o n t r o l l e d atmospheres, t h e y p r o v i d e no s h i e l d i n g w i t h the sash up, and t h e i r p r o t e c t i o n i s degraded by t u r b u l e n t flows i f t h e y are l o c a t e d near doors or i n areas t h a t have heavy p e d e s t r i a n t r a f f i c . Flow at the hood f a c e i s o b s t r u c t e d by workers s t a n d i n g i n f r o n t o f the hood and a l l p r o t e c t i o n i s l o s t when power f a i l u r e s are e x p e r i e n c e d . The l a r g e fans a s s o c i a t e d w i t h hoods may cause severe v i b r a t i o n problems u n l e s s t h e y are a p p r o p r i a t e l y mounted at some c o n s i d e r a b l e d i s t a n c e . The mounting o f blower motors behind the b u i l d i n g can reduce unwanted v i b r a t i o n s i n the l a b o r a t o r i e s , but c a r e must then be taken to a v o i d i r r i t a t i n g l o w - f r e q u e n c y n o i s e from the l e n g t h y duct work p e r f o r a t e d dropped c e i l i n g lowered v e l o c i t i e s to reduce t u r b u l e n t f l o w s . Each hood i n t e n d e d f o r t o x i c work must have a face v e l o c i t y o f 100 l i n e a r f e e t per m i n u t e . When many hoods are employed, the volume o f tempered a i r t h a t must be s u p p l i e d (summer and w i n t e r ) i s q u i t e l a r g e . The r e q u i r e d a i r h a n d l i n g equipment i s so massive t h a t minor misadjustments may make i t d i f f i c u l t t o get out of a room because o f a i r p r e s s u r e on a d o o r . One way t o deal w i t h t h i s i s to vent the doors and keep the h a l l w a y s at a s l i g h t l y h i g h e r p r e s s u r e than the l a b s . When an a i r h a n d l i n g ( s u p p l y ) u n i t f a l l s s h o r t , the h a l l w a y p r o v i d e s needed makeup a i r . Computers can o p e r a t e a i r h a n d l i n g systems more p r e c i s e l y than can t r a d i t i o n a l systems and an alarm system t h a t p i n p o i n t s d e f e c t i v e elements f o r e a r l y r e p a i r can h e l p a v o i d g r o s s i m b a l a n c e s . Hoods f o r t o x i c work s h o u l d be e a s i l y decontaminatable w i t h a c a t c h b a s i n l e a d i n g t o a t o x i c sump. The hoods s h o u l d be made o f s t a i n l e s s s t e e l and be c o n v e n i e n t l y l o c k e d . P r o v i s i o n s h o u l d be made f o r l i m i t i n g t r a v e l o f the hood door t o t h a t opening which can be supported by the hood fans and the a i r h a n d l i n g s y s t e m . These s t o p s s h o u l d be s t u r d y but a d j u s t a b l e . Hoods may be r e q u i r e d t o c o n t a i n c o n s i d e r a b l e amounts o f equipment w h i l e m a i n t a i n i n g a s p e c i f i e d range o f a i r f l o w at the face. T h e r e f o r e , the hoods must f e a t u r e s e v e r a l i n t e r n a l a i r f l o w adjustments to accommodate the l o c a l i z e d e f f e c t s o f equipment p l a c e d i n the a i r p a t h . The hoods s h o u l d be l a r g e enough t o s e t a l l work back 20 c e n t i m e t e r s or more from the face o f the hood. Access through the r e a r panel makes the r e p a i r o f contaminated equipment much s a f e r . L a b o r a t o r i e s designed f o r the h a n d l i n g o f t o x i c m a t e r i a l s n o r m a l l y m a i n t a i n reduced p r e s s u r e s i n the rooms and h a l l w a y s , r e l a t i v e t o the p r e s s u r e o u t s i d e the b u i l d i n g s . Hoods s h o u l d t h e r e f o r e be f i t t e d w i t h a n t i b a c k f l o w v a l v e s t o a v o i d s u c k i n g the c o n t e n t s o f the ductwork i n t o the l a b o r a t o r y i n the event o f a power f a i l u r e . Backup power p r o v i d e d i n 15 seconds does not p r e v e n t t h i s phenomenon, even i f the hoods and a i r h a n d l e r s are designed to r e s t a r t a u t o m a t i c a l l y . The f l o o r s o f hoods s h o u l d have l i p s f o r c o n t a i n i n g s p i l l s .

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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D r a i n s s h o u l d be f i t t e d w i t h d r a i n plugs when not i n use t o ensure t h a t t o x i c s w i l l not be a l l o w e d to go down the d r a i n i n an accident. I t i s advantageous to decontaminate t o x i c m a t e r i a l before i t i s mixed w i t h many g a l l o n s o f d i l u e n t i n a t o x i c sump so the t o x i c d r a i n s h o u l d be r e l i e d upon as a f a l l b a c k s a m p l i n g and treatment p o i n t . O p e r a t i o n s t h a t i n v o l v e t r a n s f e r s o f t o x i c s between c o n t a i n ment c a b i n e t s can be conducted most s a f e l y i f the c a b i n e t s are l o c a t e d adjacent t o one another and f e a t u r e i n t e r c o n n e c t i n g p a s s ageways. C a b i n e t f l o o r s can be equipped w i t h steam baths or s t o r a g e compartments t o m i n i m i z e the frequency w i t h which t o x i c m a t e r i a l s must be packaged up f o r t r a n s f e r t o another safe a r e a . The c l a s s I b i o l o g i c a l s a f e t y c a b i n e t i s i n t e r m e d i a t e between a fume hood and a c l o s e d g l o v e box. T h i s c a b i n e t can be used w i t h the f r o n t open or be f i t t e d w i t h g l o v e s . S i n c e the f r o n t access opening i s n o r m a l l y o n l y 8 inches h i g h , the c a b i n e t r e q u i r e s l e s s v e n t i l a t i o n than a fume a i r f l o w at the face o f 10 Filter

Systems

F i l t e r systems f o r t o x i c c h e m i c a l o p e r a t i o n s u s u a l l y employ a rough p r e f i l t e r f o l l o w e d by a h i g h e f f i c i e n c y p a r t i c u l a t e a i r (HEPA) f i l t e r , i n t u r n f o l l o w e d by c h a r c o a l bed f i l t e r s to remove the c h e m i c a l s . P a i r s o f c h a r c o a l f i l t e r s s h o u l d be connected i n s e r i e s w i t h a sampling p o r t between f i l t e r s so t h a t breakthrough from the f i r s t f i l t e r can be d e t e c t e d w h i l e the excess i s s t i l l being c a p t u r e d by the s e c o n d . Influent f i l t e r i n g of a l l laboratory a i r i s n e c e s s a r y t o reduce the frequency w i t h which replacement o f the contaminated f i l t e r s i s r e q u i r e d . Hood f i l t e r systems s h o u l d be d e s i g n e d t o reduce the hazards o f change out p r o c e d u r e s . One such system has been d e s c r i b e d . ^ ) The f i l t e r e d e f f l u e n t from hoods must never be d i r e c t e d back i n t o the l a b o r a t o r y . I t s h o u l d be r e l e a s e d above the b u i l d i n g at a h i g h enough v e l o c i t y t o ensure t h a t i t w i l l not be p u l l e d i n t o the i n t a k e v e n t s . Waste D i s p o s a l A l l d r a i n s i n a t o x i c l a b o r a t o r y w i t h e x c e p t i o n o f those from the t o i l e t s s h o u l d l e a d t o a t o x i c sump. The t o x i c sump s h o u l d be f i t t e d w i t h the w h e r e w i t h a l t o p e r m i t a d d i t i o n o f r e a g e n t s , a g i t a t i o n , and s a m p l i n g , as w e l l as adequate i n d i c a t o r s and alarms t o h i g h l i g h t m a l f u n c t i o n s . V a l v i n g s h o u l d be c o n v e n i e n t t o o p e r a t e and the system s h o u l d f e a t u r e p a r a l l e l tanks so one batch can be t r e a t e d w h i l e the lab c o n t i n u e s to d i s c h a r g e to the o t h e r t a n k . P r o v i s i o n s h o u l d be p r o v i d e d t o pump out c o n t e n t s when u n t r e a t a b l e . The s t o r a g e o f s o l i d or l i q u i d t o x i c waste r e s i d u e s must be c o n s i d e r e d i n the d e s i g n o f the l a b o r a t o r y complex. Whatever temporary s t o r a g e i s s e l e c t e d , such as berms, s h e d s , e t c . , i t i s i m p e r a t i v e t h a t a l e a k i n g drum not r e s u l t i n c h e m i c a l s being d i s c h a r g e d toward the a q u i f e r . Wastes must not be s t o r e d on s i t e f o r more than 90 days a f t e r c o l l e c t i o n , so the l a b o r a t o r y s t o r a g e

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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space may not need to be l a r g e as long as room e x i s t s s e g r e g a t i o n o f c h e m i c a l s as n e c e s s a r y .

for

Compressed Gases When such equipment as chromatographs or atomic a b s o r p t i o n s p e c t r o p h o t o m e t e r s are used, compressed gas tanks p r o l i f e r a t e to the p o i n t where the q u a n t i t i e s o f e n e r g e t i c s are too l a r g e t o be s a f e l y l o c a t e d i n a l a b o r a t o r y i n which t o x i c s are u s e d . Two alternatives exist. Hydrogen can be generated e l e c t r o l y t i c a l l y on s i t e as needed, or i t can be p i p e d from compressed gas c y l i n d e r s through m a n i f o l d s . M a n i f o l d s p e r m i t the c y l i n d e r s to be kept i n a p l a c e more c o n v e n i e n t t o the bulk s t o r a g e p o i n t and reduce the amount of such m a t e r i a l i n a t o x i c l a b o r a t o r y . The m a n i f o l d s s h o u l d be l o c a t e d where t h e y can be checked w i t h a soap s o l u t i o n r e g u l a r l y to f i n d any l e a k s t h a t might have d e v e l o p e d . Manifolds s h o u l d be c o l o r c o d e d . Construction Materials C o n s t r u c t i o n m a t e r i a l s must be nonabsorbent and e a s i l y c l e a n e d or decontaminated. Seamless f l o o r i n g a v o i d s c r a c k s from which s p i l l e d c h e m i c a l s can c o n t r i b u t e a s i g n i f i c a n t p o l l u t i o n burden t o the l a b o r a t o r y a i r . Epoxy p a i n t s h o u l d be used f o r i n t e r i o r w a l l s . Dropped c e i l i n g s s h o u l d be made o f nonabsorbent m a t e r i a l such as enameled m e t a l . Hoods and s i n k s s h o u l d be f a b r i c a t e d o f s t a i n l e s s steel. Wood or o t h e r porous s u r f a c e s must be a v o i d e d . C o n s t r u c t i o n and l a n d s c a p i n g s h o u l d p r o v i d e a p p r o p r i a t e earthquake and storm r e s i s t a n c e as w e l l as good p h y s i c a l s e c u r i t y . Communications T o x i c o p e r a t i o n s must be supported by a good communications s y s t e m . In l a b o r a t o r i e s where communications are i n a d e q u a t e , workers w i l l n a t u r a l l y use " r u n n e r s " f o r communication needs. T h i s p r a c t i c e r e s u l t s i n a v o i d a b l e t r a f f i c i n and out o f t o x i c areas which i n c r e a s e s the o p p o r t u n i t i e s f o r c o n t a m i n a t i o n t o s p r e a d . In e m e r g e n c i e s , a phone or i n t e r c o m can h e l p ensure t h a t a s s i s t a n c e i s t a i l o r e d t o the a c t u a l need. An " a l l purpose" response t o an alarm w i l l n o r m a l l y be l e s s r a p i d at a time when speed may be of the essence. V i d e o cameras t r a i n e d on c r i t i c a l o p e r a t i o n s add a measure o f s a f e t y , but annoy the workers who may f e e l t h a t the p u r pose o f the system i s to "spy" on them. As a minimum, the l a b o r a t o r y doors s h o u l d have windows so t h a t e n t e r i n g personnel d o n ' t blunder i n t o a r a p i d l y d e v e l o p i n g s c e n a r i o . Alarm Systems A g e n e r a l alarm system f o r a t o x i c l a b o r a t o r y s h o u l d f e a t u r e coded p u l l boxes to a i d emergency response p e r s o n n e l i n l o c a t i n g the s p e c i f i c a r e a where the emergency e x i s t s . S u f f i c i e n t audible and v i s i b l e alarms s h o u l d be p r o v i d e d to ensure t h a t a l l personnel are a l e r t e d . The f a c t t h a t maintenance personnel may be caught working at n o i s y l o c a t i o n s above c e i l i n g s , on the r o o f , i n s e r v i c e t u n n e l s or o u t s i d e the b u i l d i n g s h o u l d be c o n s i d e r e d . When

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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a c t i v a t e d , the alarms s h o u l d c o n t i n u e to sound u n t i l they are t u r n e d o f f by human i n t e r v e n t i o n . Alarm systems s h o u l d be p r o v i d e d w i t h r e l i a b l e back up power, and s h o u l d f e a t u r e t e s t c i r c u i t s . Klaxons and o t h e r components s h o u l d be c o n t i n u o u s d u t y r a t e d and a l l w i r i n g s h o u l d be encased i n d e d i c a t e d metal c o n d u i t s . Power surges or f a i l u r e s may leave the best designed a i r h a n d l i n g equipment i n v a r i o u s s t a t e s o f d i s a r r a y . It is v a l u a b l e i n such c i r c u m s t a n c e s t o be able to assess the s t a t u s o f the hoods from o u t s i d e the b u i l d i n g . An easy t o read s t a t u s board can be p l a c e d so as to be v i s i b l e from the o u t s i d e through a window and/or remote outputs can be made a v a i l a b l e at o t h e r l o c a t i o n s . Mechanisms f o r r e s e t t i n g the hoods s h o u l d a l s o be c o n v e n i e n t l y located. The exhaust duct o f each v e n t i l a t e d containment c a b i n e t must be f i t t e d w i t h an a d j u s t a b l e low flow s e n s o r . A u d i b l e and v i s i b l e alarms must be l o c a t e d near the c a b i n e t , and the s i l e n c e s w i t c h s h o u l d e n e r g i z e an i n d i c a t o alarms which s h o u l d not a u t o m a t i c a l l response p e r s o n n e l . An alarm system s h o u l d be p r o v i d e d t o warn workers o f power i n t e r r u p t i o n s t h a t have o c c u r r e d d u r i n g non-duty h o u r s . Such e v i d e n c e t h a t e n g i n e e r i n g c o n t r o l s have been compromised a l e r t s incoming personnel t o the n e c e s s i t y f o r f i r s t e n t r y m o n i t o r i n g o f l a b o r a t o r y rooms. Power Ground f a u l t i n t e r r u p t e r s s h o u l d be i n c l u d e d i n a l l c i r c u i t s used t o power l a b o r a t o r y i n s t r u m e n t a t i o n . C i r c u i t b r e a k e r s s h o u l d be near the areas they s e r v e . Emergency l i g h t i n g must be p r o v i d e d i n each room, h a l l w a y and s t a i r c a s e . I t i s common p r a c t i c e to u t i l i z e b a t t e r y powered l i g h t s f o r t h i s p u r p o s e . House power i s used t o keep the b a t t e r i e s c h a r g e d . Security The use o f t o x i c s c a r r i e s w i t h i t a r e s p o n s i b i l i t y t o m a i n t a i n an e f f e c t i v e system t o ensure t h a t dangerous c h e m i c a l s are not r e l e a s e d to u n a u t h o r i z e d p e r s o n s . The e n t i r e b u i l d i n g s h o u l d be w i t h i n a secure p e r i m e t e r and/or i n d i v i d u a l l a b o r a t o r i e s or s u i t e s of l a b o r a t o r i e s s h o u l d be s e c u r a b l e . W i t h i n l a b o r a t o r i e s and stockrooms t h e r e s h o u l d be secure s t o r a g e f o r any t o x i c s and o t h e r c o n t r o l l e d substances t h a t are u s e d . S e c u r i t y systems are a v a i l a b l e f e a t u r i n g magnetic badges, p e r s o n n e l i d e n t i f i c a t i o n numbers, p a s s p h r a s e s , or even d i g i t a l or r e t i n a l scanners t h a t unlock those s p e c i f i c areas t o which the i n d i v i d u a l employee has been granted a c c e s s . S i n c e these systems are computer c o n t r o l l e d , the access a u t h o r i z a t i o n f o r any i n d i v i d u a l can be c o n v e n i e n t l y and q u i c k l y adjusted as circumstances warrant. Logging of t r a f f i c i n the v a r i o u s areas can be accomplished a u t o m a t i c a l l y . I t s h o u l d be understood t h a t c o m p u t e r i z e d systems are s u s c e p t i b l e t o i n t r u s i o n and may t h e r e f o r e l a c k the p o s i t i v e c o n t r o l o f a w e l l o r g a n i z e d and m o n i t o r e d system o f secure keys or c o m b i n a t i o n s .

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Literature Cited 1. Barberto, M. S. In Toxic Chemical and Explosive Facilities; Scott, R. Α., Ed.; ACS Symposium Series No. 96; American Chemical Society: Washington, DC, 1979; pp 192-214. RECEIVED May 13, 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 16

Design of Blast-Containment Rooms for Toxic Chemical Ammunition Disposal Paul M. LaHoud Huntsville Division, U.S. Army Corps of Engineers, P.O. Box 1600, Huntsville, AL 35807

Environmentally safe destruction of obsolete chemical weapons must be performed in facilities which assure total containment of blast effects and toxic gas i detonation. Functiona recommended structural design procedures for containment rooms to accomplish this purpose are presented. The requirements presented are consistent with Department of the Army and Department of Defense Explosive Safety Board requirements.

A variety of chemical warfare (CW) munitions have been manufactured by the United States ending i n the l a t e I960's. Large quantities of these CW munitions remain stored at several U*S. Army i n s t a l l a t i o n s . The CW agents contained i n these munitions are extremely toxic compounds that produce l e t h a l or incapacitating e f f e c t s on man. The two general categories of concern are nerve agent and mustard-blister agents. The nerve agents are organophosphate chemicals. The mustard-blister agents, also c a l l e d vesicants, are systemic poisons. A wide v a r i e t y of weapon configurations were designed to dispense these agents. These included bombs, rockets, mines, spray-tanks, cartridges, mortars and p r o j e c t i l e s . The U.S. stockpile of these munitions ranges from 18 to 32 years o l d . The agent contained i n the munitions i s even older and has begun to deteriorate i n storage. In many cases, weapon systems to d e l i v e r these munitions are no longer i n service. Many of these munitions pose an additional hazard resulting from the presence of explosive bursters, fuses and propellant. None of these munitions were designed to f a c i l i t a t e disassembly at the end of their useful l i f e . Figure 1 i l l u s t r a t e s a t y p i c a l explosively configured weapon. Rising concern over the deterioration of these munitions i n storage and the related safety and environmental r i s k s , led to Public Law 99-145, which d i r e c t s the Secretary of Defense to carry

This chapter not subject to U.S. copyright Published 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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out the destruction of the U.S. stockpile of CW munitions by September 30, 1994. Responsibility f o r implementation of the requirements of t h i s law rests with the Office of the Program Manager for Chemical Munitions (OPMCM), Aberdeen proving Ground, Maryland. The Huntsville D i v i s i o n of the U.S. Army Corps of Engineers, Huntsville, Alabama i s providing engineering and contracting i n support of the execution of t h i s program. Functional Process

Requirements

The Army terminology f o r destruction of obsolete weapons i s " d e m i l i t a r i z a t i o n " . This term encompasses a l l the steps required to disassemble and safely destroy or decontaminate the component materials of which the munition was constructed. National Academy of Sciences and Department of the Army Guidance for d e m i l i t a r i z a t i o n of obsolete chemical weapons (1) requires absolute safety and security, assurance of maximum protection of operatin evidence v e r i f y i n g the destruction of the toxic wastes. The functional steps i n the destruction of explosive chemical munitions include: 1. 2. 3. 4. 5. 6.

Safe disassembly of the munition and removal of the explosive components and propellant. Disposal of the explosive components and propellant. Accessing the agent cavity of the munition. Disposal of the CW agent. Disposal of the munition bodies. Disposal of the process generated waste streams.

The approved method for disposal of chemical agent and decontamination of other munition components i s incineration (2^). Figure 2 presents the functional disposal process selected f o r this program. The dominant process c r i t e r i a i s agent containment. Overall containment within the process f a c i l i t y i s accomplished by maintenance of negative pressures within the b u i l d i n g . The negative pressures increase progressively as v e n t i l a t i o n a i r passes from low r i s k areas into higher r i s k areas. A l l v e n t i l a t i o n a i r i s "once through" and then treated using high e f f i c i e n c y charcoal f i l t e r s before release to the environment. Assurance of agent containment i n areas where explosives are removed from munitions requires t o t a l blast and fragment containment and the c a p a b i l i t y to confine the residual toxic gas products i n the event of an accidental detonation during processing. Explosive Containment

Requirements

The design requirements for the explosive containment rooms i n the f a c i l i t y are defined using the detailed process operating requirements and safety and environmental factors: 1.

Total containment of blast and fragmentation e f f e c t s i n the event of a detonation.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

16.

LAHOUD

Blast-Containment Rooms for Toxic Ammunition Disposal

-31.18 MAX-

GB FILLER PROPELLING CHARGE

PRIMER

PROJECTILE

FIGURE 1:

CARTRIDGE, 105 MILLIMETER:

AGENT CONTAINMENT

AGENT GB, M360

Ί EXPLOSIVES INCINERATION

1 I

RESIDUE

TOTAL STORAGE YARD

RECEIPT INSPECTION

II 1J

SEPARATE AGENT & EXPLOSIVES!^

DECON METAL PARTS

;

1

I

SCRAP METAL

CONTAINMENT \

DEMIL ACCOUNT 1

FIGURE 2:

AGENT INCINERATION

DRY L BRINEf^SALTS

CHEMICAL MUNITION DEMILITARIZATION SCHEMATIC

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

243

244 2. 3. 4. 5.

6.

T O X I C C H E M I C A L A N D E X P L O S I V E S FACILITIES

Total containment of post-detonation toxic hot gas products u n t i l safe for processing. Protection of the v e n t i l a t i o n supply and exhaust ducts from blast pressures. Blast resistant doors and conveyor gates to seal material handling penetrations during hazardous operations. Non-combustible agent-resistant i n t e r i o r surface f i n i s h e s . Note that combustion and/or vaporization of materials i n the containment room may add s i g n i f i c a n t l y to hot gas pressures i n the event of an accidental detonation; therefore, the quantity of these kinds of materials i n the containment room must be kept to an absolute minimium. Capability f o r repair and reuse with minimum e f f o r t i n the event of an accidental detonation.

Each of these requirements i s considered i n d i v i d u a l l y and then as an integrated system requiremen configuration. Blast and Fragmentation. The optimum s t r u c t u r a l system for confinement of explosive shock and residual gas pressures would i n t u i t i v e l y appear to be some form of a s h e l l of revolution such as a sphere, or cylinder with hemispherical heads. A s t r u c t u r a l material such as s t e e l with good t e n s i l e strength can be used with great e f f i c i e n c y i n this fashion. However, as the t o t a l system requirement i s considered, t h i s i n i t i a l economy i s rapidly eroded by other factors. S t i f f e n e r s , doubler plates and other d e t a i l s are required to r e d i s t r i b u t e stesses whenever penetrations are necessary i n a stressed skin structure. The r e s u l t i n g material and labor cost penalties o f f s e t much of the i n i t i a l advantage for a s h e l l . Another s i g n i f i c a n t factor detrimentally a f f e c t i n g a thin walled containment was found to be the fragmentation hazard. Chemical weapons munitions generally have a burster tube surrounded by a cavity f i l l e d with l i q u i d agent. In many cases, the burster casing materials are s i g n i f i c a n t l y d i f f e r e n t from normal munitions and prediction methods for fragmentation of these type munitions are not a v a i l a b l e . There i s a high degree of uncertainty regarding application of standard fragment prediction methodologies to these weapons. To resolve t h i s problem, a special fragmentation test (3) was conducted to develop applicable data. Based on t h i s test data, a manual (4) was then developed f o r prediction of chemical weapon c r i t i c a l fragments. The r e s u l t i n g c r i t i c a l design fragment requires a s i g n i f i c a n t l y thicker wall f o r the containment rooms than i s required to confine the blast pressures alone. The f i n a l element which influenced the room shape selection was volumetric e f f i c i e n c y . To provide a given room f l o o r area and overhead clearance requires a much larger volume for a s h e l l of revolution than i s required by a more t y p i c a l rectangular-shaped room. The unusable extra f l o o r space and volume to be ventilated i n a spherical or c y l i n d r i c a l s h e l l are s i g n i f i c a n t penalties. The r e s u l t s of t h i s evaluation lead to the conclusion that a rectangular-based cubicle i s the preferred room configuration. Additional parameter studies concluded that i n the rectangular cubicle configuration, reinforced concrete i s the preferred construction material over s t r u c t u r a l s t e e l . Design of reinforced

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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245

concrete structures to r e s i s t blast forces i s based on well proven procedures ( J 5 ) . Recent experimental data from a model structure similar i n configuration was also available to validate the design methods. À detailed discussion and design example of t h i s model i s presented elsewhere i n this Handbook under the t i t l e of "Structural Design for Blast Containment." Containment of Gas Pressure. In the event of an accidental explosion during munition disassembly, the highly toxic agent i n the munition would be released. The t o t a l containment c r i t e r i a dictates that any such release be confined i n the process f a c i l i t y containment room. The energy released by the explosion would vaporize the agent and heat the a i r i n the room to a high temperature. Because the a i r cannot be vented, a substantial gas pressure w i l l develop and exist after the blast shock waves have dissipated. The containment room must safely confine t h i s pressure u n t i l i t decays throug As the gas cools the i n t e r n a reaches a l e v e l suitable f o r processing through the v e n t i l a t i o n system. In practice, t o t a l containment i s d i f f i c u l t to achieve since there w i l l be some leakage around door seals, conveyor gate seals and through the concrete i t s e l f . Consideration was given to providing a vapor tight l i n e r plate to minimize r i s k of leakage through the concrete. Such a l i n e r plate would have to be s u f f i c i e n t l y thick to assure that no fragment penetration occurred. In addition the l i n e r plate would have to be erected i n segments, seal welded and then have concrete cast against i t . The p r a c t i c a l d i f f i c u l t i e s i n accomplishing these actions r e l i a b l y are s i g n i f i c a n t . In addition, there was concern that voids could exist between the l i n e r and the concrete. Leaks i n welds could allow agent migration into these voids, and these dangerous pockets of contamination would be undetectable. It was preferred that the concrete be exposed to allow v e r i f i a b l e decontamination i f required. To assure confinement i n the f a c i l i t y of the t o t a l leakage from a l l possible sources, the explosive containment rooms are surrounded by a plenum area which i s maintained at negative pressure. The v e n t i l a t i o n rate of t h i s plenum area i s designed to e a s i l y accommodate the projected leakage from the containment room after an incident. Live explosive model tests (6) were used to predict vapor leakage through the concrete. The rate of leakage i s a d i r e c t function of the i n t e r n a l pressure after an incident. Testing confirmed that the confined gas cools r a p i d l y , with proportional decrease i n i n t e r n a l pressure. Thus, the leakage rate also decreases at the same rate. Figure 3 presents graphically t h i s mechanism. Information shown i n the figure i s c l o s e l y representative of the expected performance of the actual design. Pneumatic pressure testing w i l l be performed after construction to v e r i f y design leak rates are not exceeded. V e n t i l a t i o n System Blast Protection. The explosive containment rooms have the highest potential contamination l e v e l i n the process f a c i l i t y . The punching and shearing that are part of the remote controlled disassembly operation r e s u l t i n the release of

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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s i g n i f i c a n t agent vapor i n the rooms. For this reason the containment rooms are maintained at the highest negative pressure i n the f a c i l i t y and a high rate of a i r change i s maintained continuously. A l l v e n t i l a t i o n a i r passing through the containment rooms leaves the f a c i l i t y and goes d i r e c t l y to the f i l t e r s . It i s c r i t i c a l that the containment rooms have the c a p a b i l i t y to quickly i s o l a t e the v e n t i l a t i o n supply and exhaust ducts i n the event of an explosion. This i s o l a t i o n i s achieved by providing a quick response blast-actuated valve i n series with a c o n t r o l l a b l e gas tight valve for both the supply and exhaust ducts. The blast-actuated valve provides protection from the explosive shock pressures and the gas valve provides p o s i t i v e gas leakage control thereafter. Figure 4 shows the f i n a l v e n t i l a t i o n system protection scheme. It should be noted that even with a blast valve that closes i n a few milliseconds there w i l l be some reduced shock pulse that "leaks through" during closure of the valve. The peak value of t h i s shock i s a function of losse valve and the duration was predicted using th Figures 5a and 5b, respectively, show representative values for the incident shock and the leakage shock passing the blast valve. This loading was then used to analyze the v e n t i l a t i o n ducting to assure no damage would occur. Blast Resistant Penetrations. A l l doors, conveyor penetrations, feed chutes and u t i l i t y penetrations must be designed to assure the t o t a l containment requirement i s not compromised. They must be operationally r e l i a b l e and well sealed to minimize leakage to the plenum area surrounding the containment rooms. Design of these elements revealed that the fragmentation threat was the governing factor and required 2.5-inch s t e e l plate. Obviously doors and conveyor gates made of plate t h i s size required powered operators* Compression seals were also used for leak tightness. The door, conveyor gates and feed chute doors are remotely controlled by the process control system. These assemblies are factory tested to assure that they operate and meet the minimum leak rate requirements. Frames for these closures are cast into the concrete at the time of construction. Surface F i n i s h Materials. The explosive containment rooms w i l l be exposed to a harsh environment during the l i f e t i m e of the f a c i l i t y . The toxic agent exposure l e v e l i s high. The surface coating system for walls, roof and f l o o r must be non-reactive and impermeable to these exposures. Decontamination during maintenance or equipment changeout w i l l require room washdown with highly caustic decontamination solutions. The surface coating system must also survive i n t h i s environment. An epoxy coating system has been tested and approved which does not absorb or react with the chemical agents and i s f u n c t i o n a l l y r e s i s t a n t to the washdown solutions. A secondary benefit of the surface coating system i s i t s sealing of the concrete which improves i t s vapor tightness. The presence of the coating system as well as other materials which were p o t e n t i a l l y combustible raised the r i s k of causing additional increases i n the post-detonation gas pressure. Recent experimental work (7) has confirmed the significance of t h i s

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

16.

Blast-Containment Rooms for Toxic Ammunition Disposal

LAHOUD

r-THIS AREA DENOTES LEAKAGE - PRESSURE DECAY WITH COOLING AND NO .LEAKAGE

20- - M

ACTUAL LEAKAGE

TIME (MINUTES) FIGURE 3:

INTERNAL PRESSURE DECAY WITH TIME

18" DIA.-^ ΟΙ

GAS TIGHT VALVE

VnV

I ^BLAST 3000 VALVE CFM EXPLOSIVE CONTAINMENT ROOM

.

r-18"DIA.

A

4 ^-BLASTr ' VALVE Π 3000 CFM 0

EXPLOSIVE CONTAINMENT ROOM

3000 CFM

3000 CFM BLAST VALVE-^f^ BLAST VALVE J/-BLA5

3000 CFM / 18" DIA.^

PJ

GAS TIGHT VALVE EXPL EXPLOSIVE CONTAINMENT VESTIBULE

3000 CFM 8" DIA.

FIGURE 4: EXPLOSIVE CONTAINMENT ROOM VENTILATION SYSTEM BLAST PROTECTION

American Chemical Society Library 1155 16th and St.,Explosives M.W. Facilities; Scott, R., et al.; In Design Considerations for Toxic Chemical ACS Symposium Series;Washington. American Chemical Society: Washington, DC, 1987. B.C. 20036

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FIGURE 5a:

SHOCK PULSE AT INLET SIDE OF BLAST VALVE

110 PSI

2.4 M S

FIGURE

5b:

SHOCK PULSE PASSING THROUGH BLAST VALVE

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

LAHOUD

Blast-Containment Rooms for Toxic Ammunition Disposal

FIGURE 6a: EXPECTED PRESSURE-TIME HISTORY FOR DETONATION IN CONTAINMENT ROOM WITH NO COMBUSTIBLES PRESENT

TIME

FIGURE 6b: EXPECTED PRESSURE-TIME HISTORY FOR DETONATION IN CONTAINMENT ROOM WITH THE BURNING OF COMBUSTIBLES

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

250

phenomena. Figure 6a shows the expected pressure time history for a detonation i n a containment room. Figure 6b shows a similar event except the burning of combustible materials present i n the test caused a dramatic increase i n the subsequent gas pressure. To assure no such r i s k s were present, an explosive test program (8) was conducted on a model containment room using the proposed surface coating system. This test v e r i f i e d that the coating was not combustible for the conditions expected and would not, therefore, contribute to the gas pressure. Other combustibles expected to be i n the rooms w i l l be monitored c a r e f u l l y during operations. Repair and Reuse After Explosion. Although the r i s k of a high order detonation of a munition during disassembly i s low, t h i s hazard does e x i s t . In the event of such an incident, i t i s a design requirement for the containment rooms to suffer only minimal damage and allow rapid refurbishment. To assure this c a p a b i l i t y , the containment room s t r u c t u r a l design Department of Defense Explosiv require. This i s considere appropriat vapo so c r i t i c a l i n t h i s f a c i l i t y . During the transient load phase of an accidental explosion, when the shock duration i s less than the time of maximum response of the s t r u c t u r a l elements, member end rotations are limited to one degree. Maximum i n e l a s t i c deformation i s limited to three times the member e l a s t i c l i m i t d e f l e c t i o n . Since this loading phase i s suddenly applied, use of material dynamic increase factors based on s t r a i n rate of loading are also used. After the transient shock load phase has damped out, the subsequent confined hot gas pressure can be considered as a steady state load from a s t r u c t u r a l dynamics point of view. Therefore the design c r i t e r i a requires that these loadings do not exceed the e l a s t i c l i m i t of the structure. Dynamic increase factors are not applicable since loading rate i s no longer a consideration. Summary Integration of explosive containment rooms into a process f a c i l i t y requires consideration of o v e r a l l process system performance not simply the s t r u c t u r a l design elements. Use of reinforced concrete for containment design i s a v i a b l e and economical choice of material for the f a c i l i t y requirements of t h i s process. Design procedures for reinforced concrete subjected to blast loads are well documented and tested and are suitable for containment design. Additional considerations are present i n containment structure design which are neglected during design of vented structures. These include long term gas pressure, additional pressures from combustion products and v a l i d i t y of material allowables and deformation l i m i t s . Safety dictates that these elements be considered c a r e f u l l y .

Literature Cited 1.

Report of the Disposal Hazards of Certain Chemical Warfare Agents and Munitions, prepared by an Ad Hoc Advisory Committee of the National Academy of Sciences, Washington, DC, June 24, 1969.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

16. LaHOUD

Blast-Containment Rooms for Toxic Ammunition Disposal

2. Technical Paper Defining the Operating Conditions for the Incineration of the Chemical Agents GB, H, and VX, U.S. Army Toxic and Hazardous Materials Agency, 7 May 1984. 3. Powell, J.G. Fragmentation Characterization Profile for Chemical Filled Munitions-M23 Land Mine, 115MM Rocket Warheads and 8-inch Projectiles, Naval Surface Weapons Center, April 1983. 4. Whitney M.G.; Friesenhahn, G.J.; Baker, W.E.; Vargas, L.M. A Manual To Predict Blast and Fragment Loadings from Accidental Explosions of Chemical Munitions Inside An Explosive Containment Structure, U.S. Army Toxic and Hazardous Materials Agency, April 1983. 5. Structures to Resist the Effects of Accidental Explosions, U.S. Army Technical Manual, TM 5-1300, Washington, DC, June 1969. 6. Kirtland Underground Munitions Storage Complex Model Designs, Construction, and Test Data, Technical Report SL-84-14, U.S. Army Waterways Experimen Nuclear Agency, Washington 7. Hokanson, J.C.; Esparza, E.D.; Baker, W.E.; Sandoval, N.R.; Anderson, C.E. Determination of Blast Loads in the Damaged Weapons Facility, Volume 1, Final Report for Phase II, Southwest Research Institute Project 06-6578, Pantex Plant, July 1982. 8. JACADS Explosive Containment Room Model Test, Southwest Research Institute Project 06-8069, prepared for the U.S. Army Corps of Engineers, Huntsville Division, Huntsville, Alabama, July 1984. RECEIVED March

6, 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

25

Chapter 17

Intrinsically Safe Electrical Circuits in Explosives Facilities Kenneth W. Proper U.S. Army Defense Ammunition Center & School, Equipment Division, Savanna, IL 61074-9639

During design of explosive facilities, one of the major concerns is limiting the electrica the ofte due to sparks or thermal effects. Intrinsically Safe Circuits provide a means of accomplishing this. However, the successful utilization of intrinsically safe electrical circuits depends upon a complete understanding of not only its construction requirements, but also its concept. Therefore, in order to provide this understanding, a presentation of its history, definition, application, and general construction requirements are presented. More importantly, its virtues and disadvantages are discussed. In the design of explosive f a c i l i t i e s , two major c o n s i d e r a t i o n s are of paramount importance: c o n t r o l l i n g the conditions which can lead to a premature i n i t i a t i o n of energetic m a t e r i a l s , and p r o v i d i n g the maximum degree of personnel and property protection. C o n t r o l l i n g the c o n d i t i o n s which can lead to a premature i n i t i a t i o n of energetic materials can be accomplished through the e l i m i n a t i o n of energy sources w i t h i n the hazardous environment. However, i n doing so, the c a p a b i l i t y to accomplish the m i s s i o n i s a l s o e l i m i n a t e d . T h e r e f o r e , the goal i s to provide the amount of energy which w i l l accomplish the m i s s i o n ; yet, do so i n such a way as not to provide energy which can cause i n i t i a t i o n of the energetic material. One method of l i m i t i n g the amount of energy capable of causing i n i t i a t i o n has been through the use of pneumatic and

This chapter not subject to U.S. copyright Published 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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h y d r a u l i c equipment. However, the major disadvantages of this approach are the complicated logic systems required and the slow response times, especially for sensing and metering equipment. Another approach has been through the use of explosion-proof e l e c t r i c a l i n s t a l l a t i o n s to p r o v i d e the energy r e q u i r e d to accomplish the mission. This method does not l i m i t the amount of energy, r a t h e r i t s philosophy i s i f an explosion occurs, to contain that explosion within i t s heavy w a l l c o n s t r u c t i o n and prevent i t s propagation to the outside environment. An additional approach, which permits the use of e l e c t r i c a l energy i n the hazardous environment, i s the use of purged and pressurized enclosures for e l e c t r i c a l equipment. Once again, t h i s approach r a t h e r than l i m i t i n g the energy depends on not allowing the hazardous environment to come i n c o n t a c t with the e l e c t r i c a l energy, thereby e l i m i n a t i n g the probability of an explosion. T h i s i s accomplished through purging of the e l e c t r i c a l installation in them so that the environmen non-hazardous. A f i n a l approach, which permits the use of e l e c t r i c a l energy w i t h i n a hazardous environment, i s through the use of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s . Rather than r e s t r i c t i n g the propagation of an explosion or maintaining a non-hazardous environment, i t reduces the amount of e l e c t r i c a l energy within the hazardous environment to l e v e l s which are i n c a p a b l e of i g n i t i n g that environment. This concept i s not new; due to new advances i n technology, i t s application has greatly increased i n scope. History of I n t r i n s i c a l l y Safe E l e c t r i c a l C i r c u i t s At the turn of the century i n Germany, research was begun on the e f f e c t of an e l e c t r i c a l spark on methane-air mixtures. This work would p l a y an important r o l e s e v e r a l years l a t e r i n Britain. In B r i t a i n i n 1912 and 1913, a rash of mine explosions lead to a formal court inquiry. I t was found that at t h i s time the p r a c t i c e of s i g n a l i n g was accomplished by the rubbing together of two bare wires connected to a battery to form a c i r c u i t . As a r e s u l t of the court f i n d i n g s , t e s t i n g became required for signaling equipment i n B r i t i s h mines. T h i s task was assigned to what i s now called the Safety i n Mines Research Establishment. I t was at this organization where the concept of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s was f i r s t d e f i n e d a f t e r continued r e s e a r c h i n t o the i g n i t i o n of methane-air mixtures. In 1936, the f i r s t c e r t i f i c a t e was issued i n Great B r i t a i n for an i n t r i n s i c a l l y safe e l e c t r i c a l d e v i c e which was not designed for application i n mining operations. In 1938, the United States Bureau of Mines began development of r u l e s r e l a t i n g to the use of e l e c t r i c i t y for telephone and signaling equipment, which included application of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s .

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U n t i l the 1950 s , the use of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s had l i t t l e a p p l i c a t i o n i n other than j u s t b a t t e r y operated s i g n a l i n g d e v i c e s . At t h i s time due to advances i n technology and an increase i n the use of e l e c t r i c a l equipment i n hazardous locations, a new world-wide interest developed in the application of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s beyond what had been i t s t r a d i t i o n a l r o l e . In the United States, this new interest was recognized, and i n 1956, the N a t i o n a l E l e c t r i c a l Code (NEC) introduced the use of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s . "Equipment and a s s o c i a t e d w i r i n g approved as i n t r i n s i c a l l y safe may be i n s t a l l e d in any hazardous location for which i t i s approved, and the provisions of A r t i c l e 500 and 510 w i l l not apply to such i n s t a l l a t i o n s . " ( 1 ) However, no guide was give the c i r c u i t s . In 1967, the N a t i o n a l F i r e P r o t e c t i o n Association (NFPA) i s s u e d NFPA 493-1967 which d e f i n e d specific tests and c o n s t r u c t i o n techniques to be employed. Today, the current standard i s NFPA 493-1978. World-Wide Acceptance I n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s are now recognized around the world as an additional technique f o r p r o v i d i n g e l e c t r i c a l energy i n hazardous locations. However, the standard used i n the United States and the standards used i n Europe do not coincide. The d i s s i m i l a r i t i e s are due to a d i f f e r e n c e i n the manner i n which hazardous environments are c l a s s i f i e d and to a divergence i n philosophy over the safety factor employed. NFPA 493 uses a safety of 1.5 p e r t a i n i n g to the t o t a l energy, while the I n t e r n a t i o n a l E l e c t r o t e c h n i c a l Commission (IEC) and European Committee for E l e c t r o t e c h n i c a l S t a n d a r d i z a t i o n (CENELEC) r e q u i r e a s a f e t y f a c t o r of 1.5 f o r the v o l t a g e or c u r r e n t , which relates to a 2.25 factor of safety for the energy. What Are I n t r i n s i c a l l y Safe E l e c t r i c a l C i r c u i t s ? Definition: Webster's d e f i n e s i n t r i n s i c as " n a t u r a l l y , e s s e n t i a l l y , or i n h e r e n t l y " and further defines safe as "free from damage, danger, or i n j u r y ; unable to cause t r o u b l e or damage" ( 2 ) . From these d e f i n i t i o n s , a d e f i n i t i o n of i n t r i n s i c a l l y safe can be d e r i v e d to mean: i n h e r e n t l y and naturally unable to cause trouble, damage, or injury. Due to t h i s d e r i v e d d e f i n i t i o n , c i r c u i t s are m i s t a k e n l y considered as i n t r i n s i c a l l y safe due to the c i r c u i t u t i l i z i n g low energy. However, i n r e a l i t y , the c i r c u i t may not q u a l i f y as i n t r i n s i c a l l y safe because the d e f i n i t i o n as s t a t e d in NFPA 493-1978 q u a l i f i e s the above d e f i n i t i o n .

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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" I n t r i n s i c a l l y Safe C i r c u i t s : A c i r c u i t which any spark or thermal e f f e c t , produced e i t h e r normally or i n specified fault conditions, is i n c a p a b l e , under the t e s t c o n d i t i o n s prescribed i n this standard, of causing i g n i t i o n of a mixture of flammable or combustible material i n a i r i n i t s most e a s i l y ignited concentrât ion. ( 3 ) The q u a l i f i c a t i o n being that i t must f a i l safe not only i n i t s normal mode of operation, but, also, under s p e c i f i c modes of f a i l u r e . Therefore, i t i s not enough to state that the c i r c u i t i s of low v o l t a g e , and because of this i s i n t r i n s i c a l l y safe. T h i s i s only h a l f of the requirement. To q u a l i f y as i n t r i n s i c a l l y safe, the c i r c u i t must also f a i l i n such a way as to be incapable of causing i g n i t i o n , and f u r t h e r , i t must be either tested or analyze 11

Evaluation of I n t r i n s i c a l l y Safe C i r c u i t s NFPA 493-1978 i s very e x p l i c i t i n Chapter 2 as to b a s i c requirements which must be met i n order f o r a c i r c u i t to be considered i n t r i n s i c a l l y safe. They are: 1. The normal o p e r a t i o n s h a l l not be capable of i g n i t i n g the hazardous environment when adjusted for i t s worst o p e r a t i n g conditions and an additional energy factor of 1.5 i s introduced; 2. The c i r c u i t must be incapable of i g n i t i n g the hazardous environment when operated at 1.5 i t s energy r a t i n g and the inducement of one fault and i t s related f a i l u r e s . F u r t h e r , the c i r c u i t must be incapable of i g n i t i n g the hazardous environment at i t s normal energy rating when two f a u l t s and their associated f a i l u r e s are introduced; 3. I n t r i n s i c a l l y safe c i r c u i t s s h a l l conform to the construction requirements contained i n Chapter 3 and 4 of the standard. Defining the Hazardous Environment The f i r s t task, which should be completed before considering the d e s i g n of any f a c i l i t y or equipment i n v o l v i n g e n e r g e t i c m a t e r i a l , i s to d e f i n e e x a c t l y what type of hazardous environment w i l l be i n v o l v e d i n each room, s e c t i o n or area. This i s a prerequisite, whether selecting i n t r i n s i c a l l y safe or any other technique to provide e l e c t r i c a l protection. The c l a s s i f i c a t i o n of hazardous l o c a t i o n s i n v o l v e s the determination of four factors: 1. What are the hazardous elements i n the process? 2. Are the hazardous elements vapors or dusts? 3. What are the explosive and/or e l e c t r i c a l c h a r a c t e r i s t i c s of the hazardous elements? 4. Are the hazardous elements constantly present or only present under special circumstances?

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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The Hazardous Element. To o f t e n i t i s automatically assumed that i n an explosive f a c i l i t y the e x p l o s i v e item i s the most hazardous item and, t h e r e f o r e , the e l e c t r i c a l p r o t e c t i o n i s designed based on i t s requirements. However, t h i s assumption can lead to i n s t a l l i n g the wrong type of e l e c t r i c a l protection. A l l the processes being performed, i n each room, section, or area, must be c a r e f u l l y reviewed to determine i f other elements being used pose a greater hazard. The f o l l o w i n g q u e s t i o n s can serve as a guide i n reviewing the processes to determine a l l the hazardous elements involved: 1. Are elements given o f f which are more hazardous, i . e . gases from chemical reactions? 2. Are elements introduced into the process which are more hazardous, i . e . l a r g e volumes of flammable s o l v e n t s d u r i n g rework processes? Vapor or Dust. Once within the f a c i l i t y hav determine whether they constitute a hazard due to being a vapor or a dust. Vapor and dust represent two d i f f e r e n t types of explosion hazards. E x p l o s i o n s from vapors occur due to the rapid transfer of heat from one molecule to the next molecule. A d d i t i o n a l l y , vapors can only i g n i t e when present i n c e r t a i n concentration ranges - known as their lower and upper explosive l i m i t s . Also, vapors disperse due to d i f f u s i o n and convection; therefore, i f a vapor cloud i s released and i s not ignited, the hazard i s soon gone. Dust p r e s e n t s a d i f f e r e n t type of hazard, because while i t has a lower explosive l i m i t , i t does not have an upper explosive l i m i t . T h i s can r e s u l t i n a primary e x p l o s i o n , followed by secondary explosions as new a i r i s p r o v i d e d . Secondly, dust does not diffuse away from i t s point of release, but settles out of the a i r and accumulates into layers. Unlike vapor, the dust e x p l o s i o n i s caused by the r a d i a n t heat from one p a r t i c l e i g n i t i n g the next. Because of t h i s , the lower e x p l o s i v e l i m i t s for dusts are g r e a t l y h i g h e r than for vapors. Also, the size and shape of the dust p a r t i c l e s are important f a c t o r s i n e f f e c t i n g i t s lower explosive l i m i t . Due to the d i f f e r e n c e s i n b e h a v i o r a l c h a r a c t e r i s t i c s , d i f f e r e n t approaches are used to prevent t h e i r a c c i d e n t a l i g n i t i o n due to the presence of e l e c t r i c a l energy. The National E l e c t r i c a l Code (NEC) r e c o g n i z e s three c l a s s e s of hazardous environment. C l a s s I b e i n g f o r hazardous environments c o n s i s t i n g of flammable vapors or gases; Class II for hazardous environments r e s u l t i n g from the presence of combustible d u s t s ; and C l a s s I I I f o r f i b e r s and f l y i n g s , usually associated with the t e x t i l e industry. I t i s important to note that each class employs a d i f f e r e n t type of p h i l o s o p h y to prevent i g n i t i o n . Therefore, Class I r a t e d p r o t e c t i o n may not provide protection when used i n Class II or Class I I I environments or vice versa.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Type of Vapor or Dust: The NEC further subdivides Class I and II into groups. Groups A through D are used to denote groups of equivalent types of gases or vapors present. While Groups Ε and G are used to denote groups of equivalent types of dust hazards based on t h e i r c o n d u c t i v i t y . Group F i s used to denote carbonaceous dusts. Likelihood of Hazard. The NEC recognizes two d i s t i n c t levels of hazard p r o b a b i l i t y . D i v i s i o n 1 denotes an environment i n which the p r o b a b i l i t y exists that s u f f i c i e n t levels of the hazardous element may always e x i s t , under normal operating c o n d i t i o n , as to warrant extreme protections. Whereas, D i v i s i o n 2 denotes an environment where the p r o b a b i l i t y for s u f f i c i e n t l e v e l s of the hazardous element to e x i s t , under normal operating conditions, i s less l i k e l y , and t h e r e f o r e , the extreme p r o t e c t i o n i s not j u s t i f i a b l e . F u r t h e r areas adjacent to D i v i s i o n 1 areas can often constitute c l a s s i f i c a t i o 1

The E x p l o s i v e s Environment. The Army Materiel Command (AMC), which has the primary r e s p o n s i b l i t y for manufacture and storage of e x p l o s i v e s f o r the Department of Defense, c l a r i f i e d i t s d e f i n i t i o n of the type of hazardous l o c a t i o n i n v o l v e d with e x p l o s i v e s , p r o p e l l a n t s , and pyrotechnics i n i t s most recently r e v i s e d s a f e t y manual ( 4 ) . When the only c o n s i d e r a t i o n for hazardous environment i s the presence of explosive m a t e r i a l , i t recommends that the environment be c l a s s i f i e d as Class I I , Group G, with the appropriate d i v i s i o n based on the p r o b a b i l i t y of the hazardous element being present i n the environment. I t further states that consideration must be given to vapors which might be present or to the presence of metallic dust. NOTE For complete d e f i n i t i o n s and c l a s s i f i c a t i o n of hazardous e l e c t r i c a l environments, consult A r t i c l e 500 of the NEC. Completing the E v a l u a t i o n . Once the hazardous environment has been c l a s s i f i e d , the design of the e l e c t r i c a l protection can be completed. I t may require only f u l f i l l i n g the requirements for one class and group, or several groups within one c l a s s , or even two c l a s s e s and several groups. Whatever the r e s u l t , the cost of the i n s t a l l a t i o n can be greatly reduced by this a c t i o n w h i l e ensuring the maximum degree of p r o t e c t i o n i s being provided. T h i s i s p o s s i b l e s i n c e equipment can be s e l e c t e d which was designed to f u l f i l l the requirements e x p l i c i t l y f o r that environment, rather than a wide spectrum of requirements for a l l possible hazardous environments. I n t r i n s i c a l l y Safe and the E x p l o s i v e Environment. I f the evaluation concludes that the environment i s i n fact a Class I I , Group G, D i v i s i o n 1 l o c a t i o n , then the i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s must be designed as dust-tight and meet the

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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requirements f o r Class I, Group D as defined in NFPA 493. For other types of hazardous environments, the i n t r i n s i c a l l y s a f e e l e c t r i c a l c i r c u i t s must be designed to meet the requirements of NFPA 493 for that type of environment. How

i t works

I n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s i n a sense are usually composed of two d i f f e r e n t c i r c u i t s . One of which i s l o c a t e d i n the hazardous area, while the second i s l o c a t e d i n the non-hazardous a r e a . The former being a low energy c i r c u i t connected to a metering, sensing, or an enabling device, while the l a t t e r being connected to a c o n t r o l l i n g , i n d i c a t i n g , or instrumentation device. Electrical Isolation. These two c i r c u i t s are integrated to create one c i r c u i t throug this safety barrier electrical isolatio highe energy available i n the non-hazardous c i r c u i t s cannot be transmitted to and through the c i r c u i t s i n the hazardous area. C i r c u i t s Not Device. During design, when considering the use of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s , the whole e l e c t r i c a l c i r c u i t must be considered. It i s not enough just to consider the e l e c t r i c a l apparatus employed i n the hazardous environment. C o n s i d e r a t i o n must be given to i t s associated apparatus located i n the non-hazardous a r e a . T h e r e f o r e , i t i s not j u s t the apparatuses which must be c o n s i d e r e d , but the whole c i r c u i t , both i n the hazardous area and the non-hazardous area. S a f e t y B a r r i e r s . Figure 1 i l l u s t r a t e s an a p p l i c a t i o n employing i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s for the d e m i l i t a r i z a t i o n of ammunition. Three separate areas are r e q u i r e d f o r t h i s application - one area, c l a s s i f i e d as non-hazardous, to serve as the c o n t r o l and l o a d i n g area; a second area, c l a s s i f i e d as hazardous, where the actual d e m i l i t a r i z a t i o n i s accomplished; and a t h i r d area, c l a s s i f i e d as non-hazardous, i s required for the hydraulic pump due to the l e v e l of noise produced. The hazardous area was c l a s s i f i e d as C l a s s I I , Group G, D i v i s i o n 1 due to the p r o j e c t i l e s being separated from the c a r t r i d g e s and the p r o p e l l a n t being dumped i n t o a vacuum c o l l e c t i o n system. The operation of the machine's pneumatic and h y d r a u l i c systems are controlled and v e r i f i e d by the use of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s . The c o n t r o l c a b i n e t l o c a t e d i n the non-hazardous area c o n s i s t s of a programmable c o n t r o l l o r , other e l e c t r i c a l equipment, and safety b a r r i e r s . A l l s i g n a l s passed to or r e c e i v e d from the hazardous area by the c o n t r o l l o r are conducted through safety b a r r i e r s . T h i s ensures that any faults occurring i n the n o n - i n t r i n s i c a l l y safe c i r c u i t s could not r e s u l t i n dangerous energy l e v e l s being passed to the hazardous l o c a t i o n .

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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For this application, Zener safety barriers were selected as the protective interface. Further, every c i r c u i t going into the hazardous area i s connected to a separate Zener safety b a r r i e r . Zener safety barriers are probably the most widely used and a c c e p t a b l e method of l i m i t i n g the energy (5). A Zener safety b a r r i e r consists of Zener diodes and r e s i s t o r s i n a network. The r e s i s t o r s l i m i t the c u r r e n t and protect the diodes, while the diodes l i m i t the v o l t a g e and allow grounding of the c i r c u i t . The working rating of the Zener diodes i s chosen to be above the peak value of the normal working v o l t a g e of the c i r c u i t . S e v e r a l companies manufacture modular forms (6) which o f f e r f l e x i b i l i t y of d e s i g n and at the same time are t e s t e d and approved for use. However, other type of p r o t e c t i v e devices are a v a i l a b l e which can be used. They are: 1. Transformers, three d i f f e r e n t types are discussed i n NFPA 493; 2. Current-limitin 3. Blocking capacitors; 4. Shunt diodes; 5. Relays; 6. Self contained apparatus, i . e . battery operated. The construction requirements which must be met by each of the above are contained i n Chapter 3 of the standard. Physical Separation. In a d d i t i o n to p r o v i d i n g e l e c t r i c a l i s o l a t i o n , i t i s necessary to provide p h y s i c a l s e p a r a t i o n to ensure the non-hazardous c i r c u i t s can not degrade the i n t r i n s i c a l l y safe p o r t i o n of the c i r c u i t s . T h i s can be accomplished by planning the physical layout to incorporate the use of distance, enclosures, p a r t i t i o n s , separate raceways, and insulation. The f i n a l physical layout selected should meet or exceed the requirements of Chapter 3, Sections 1, 2, 3, and 4 of NFPA 493. Additional Requirements. In addition to e l e c t r i c a l and physical i s o l a t i o n requirements, the surface temperature of a l l equipment and w i r i n g located i n the hazardous environment must not exceed the values indicated i n the standard. F u r t h e r , the apparatus must be marked a c c o r d i n g to the requirements of Section 2 of Chapter 4 of the standard. Demonstration of Requirements. The use of e l e c t r i c a l , physical separation i s demonstrated i n Figure 2. The safety b a r r i e r s are contained i n a separated compartment w i t h i n the e l e c t r i c a l control cabinet. Each of the safety b a r r i e r s are p o s i t i o n e d so that the i n t r i n s i c a l l y safe t e r m i n a l s are f a c i n g each other (Figure 2). This allows easier segregation of the n o n - i n t r i n s i c a l l y safe wires from the i n t r i n s i c a l l y safe wire. For added protection, the wiring i s enclosed i n grounded, metal raceways f o r support and a d d i t i o n a l i s o l a t i o n . Each safety b a r r i e r i s grounded, and t h i s common ground i s earthed

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Figure 2.

E l e c t r i c a l and physical separation.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

17. PROPER

Safe Electrical Circuits in Explosives Facilities

s e p a r a t e l y from n o n - i n t r i n s i c a l l y safe c i r c u i t s (Figure 2). To provide additional protection, the s a f e t y b a r r i e r s are b r i g h t blue i n c o l o r and marked as r e q u i r e d . Following a l o c a l requirement, blue tape i s wrapped around i n t r i n s i c a l l y s a f e wiring every few inches for easy recognition. Demanding

Requirements

The d e s i g n requirements for i n t r i n s i c a l l y safe would seem to be demanding, and a review of NFPA 493 enforces this f a c t . Today's i n d u s t r i a l environment imposes additional requirements not only on the use of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s , but other hazardous e l e c t r i c a l techniques as well. These requirements are due to the Occupational Safety and Health Act and the employer's increasing v u l n e r a b i l i t y for l i a b i l i t y . OSHA Requirements. OSH options must be f u l f i l l e equipment for locations c l a s s i f i e d as hazardous (7). The f i r s t option permits the s e l e c t i o n of i n s t r i n s i c a l l y safe equipment and associated wiring. The equipment and wiring must be approved for the hazardous location i n which i t w i l l be used. The second o p t i o n permits selection of approved equipment. However, not only must i t be approved for the hazardous c l a s s , but, a l s o , f o r the s p e c i f i c type of vapor, dust, or f i b e r involved. The l a s t o p t i o n allows the employer to s e l e c t equipment which i s safe for the hazardous location. While the equipment does not have to be approved, the employer must be able to demonstrate that the d e s i g n w i l l p r o v i d e the p r o t e c t i o n necessary to prevent the i g n i t i o n of the vapors, l i q u i d s , gases, dusts or fibers i n the hazardous location. Employer L i a b i l i t y . Today more than ever before, employers are being challenged by their employees to prove that a l l p o s s i b l e e f f o r t was employed to reduce hazards i n their work place. Many employers had not been able to prove they had done t h i s , and, t h e r e f o r e , they have suffered costly settlements and increased l i a b i l i t y insurance expenses. Certification. I t i s a benefit to the employer to ensure that the i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t i s c e r t i f i e d . C e r t i f i c a t i o n can be achieved through the use of a t h i r d party, such as Underwriters Laboratories or F a c t o r y Mutual Research. Both of these o r g a n i z a t i o n s have t h e i r own standards f o r approval which are based on NFPA 493. The c e r t i f i c a t i o n i s accomplished i n three steps: 1. The c i r c u i t i s analyzed to determine f a u l t s and operating c h a r a c t e r i s t i c s ; 2. The c i r c u i t i s reviewed to ensure c o n s t r u c t i o n and temperature requirements are met;

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

3, The p e r f o r m a n c e c h a r a c t e r i s t i c s are v e r i f i e d by e i t h e r the a c t u a l t e s t i n g o f the c i r c u i t i n i t s i n t e n d e d environment o r comparing c a l c u l a t e d or a c u t a l measured v a l u e s a g a i n s t the graphs i n C h a p t e r 5 o f the s t a n d a r d . B e n e f i t s of I n t r i n s i c a l l y

Safe E l e c t r i c a l

Circuits

I n s p i t e of the r i g o r o u s d e s i g n r e q u i r e m e n t s and t h e n e e d f o r c e r t i f i c a t i o n , i n s t r i n s i c a l l y safe e l e c t r i c a l circuits offer many advantages which the o t h e r h a z a r d o u s l o c a t i o n e l e c t r i c a l t e c h n i q u e s do n o t . F i r s t , o n c e d e s i g n e d , e v a l u a t e d , and i n s t a l l e d , the s a f e t y o f the system cannot e a s i l y be degraded because the s a f e t y i s i n t h e d e s i g n , n o t p r o t e c t i o n added a f t e r w a r d . In f a c t , the i n t r i n s i c a l l y s a f e e l e c t r i c a l c i r c u i t w i l l cease t o f u l f i l l the f u n c t i o n f o r w h i c h i t was d e s i g n e d l o n g b e f o r e i t can become a hazard. T h i s i s due t fault conditions. Th become h a z a r d o u s i s i f unapprove componen i s s u b s t i t u t e d i n t o the c i r c u i t . Secondly, the circuits do n o t require the additional e x p e n d i t u r e o f money f o r added p r o t e c t i o n t o e n s u r e t h e s a f e t y o f the d e s i g n e d system as do o t h e r t e c h n i q u e s used f o r hazardous wiring. T h i r d l y , t h e c o s t and time f o r i n s t a l l a t i o n i s l e s s , a g a i n due t o s a f e t y b e i n g i n t h e d e s i g n and n o t a d d e d p r o t e c t i o n , w h i c h must c a r e f u l l y be i n s t a l l e d t o e n s u r e i t p r o v i d e s the degree o f s a f e t y r e q u i r e d . F o u r t h l y , i n t r i n s i c a l l y s a f e e l e c t r i c a l c i r c u i t s are the e a s i e s t to maintain. S i n c e i n t r i n s i c a l l y s a f e c i r c u i t s by t h e i r n a t u r e are i n c a p a b l e o f c a u s i n g i g n i t i o n , they can be m a i n t a i n e d w i t h o u t r e g a r d to s h u t t i n g down o p e r a t i o n s , nor a r e h o t p e r m i t s required, or is lengthly disassembly, assembly and r e c e r t i f i c a t i o n o f added p r o t e c t i o n r e q u i r e d . F i n a l l y , due t o t h e r e q u i r e m e n t s f o r i n t r i n s i c a l l y s a f e c i r c u i t s b e i n g t h e most c o n s e r v a t i v e o f h a z a r d o u s l o c a t i o n c i r c u i t s r e q u i r e m e n t s , i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s o f f e r t h e maximum i n s a f e t y . Not o n l y do t h e y c o n t r o l t h e c o n d i t i o n s which can l e a d to i n i t i a t i o n o f e n e r g e t i c m a t e r i a l s , by t h e i r v e r y n a t u r e - t h e y e l i m i n a t e i t . Intrinsically

S a f e C i r c u i t s The

Easy

Way

The s i m p l e s t m e t h o d o f u s i n g i n t r i n s i c a l l y s a f e electrical c i r c u i t s i s not to d e s i g n and c e r t i f y them y o u r s e l f , but r a t h e r to take advantage of a c l a u s e c o n t a i n e d i n NFPA 493 which states : "One o f t h e s e r i o u s problems which has f a c e d b o t h m a n u f a c t u r e r s and u s e r s i n a p p l y i n g the i n t r i n s i c s a f e t y concept has been the i n a b i l i t y t o interconnect a p p a r a t u s o f d i f f e r e n t m a n u f a c t u r e r s and

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

17. PROPER

Safe Electrical Circuits in Explosives Facilities

265

be assured that the combination i s s t i l l i n t r i n s i c a l l y safe. The marking scheme below . . . . ( e x p l a i n s the marking system and requirements)... The above (marking system) information and cable characteristics are a l l that are necessary to determine that independently c e r t i f i e d i n t r i n s i c a l l y safe and a s s o c i a t e d apparatus may be interconnected, without loss of intrinsic safety. I t should be recognized that t h i s procedure r e s u l t s i n systems which are evaluated with as many as four independent faults."(8) Through the use of this clause, the design time can be reduced and the problem of c e r t i f i c a t i o n can be e l i m i n a t e d . I t now becomes a matter of definin the environment, s e l e c t i n which i s r a t e d as compatibl , g manufacturer's i n s t r u c t i o n f o r i n s t a l l a t i o n and v e r i f y i n g the cable c h a r a c t e r i s t i c s . Availability. Both Underwriters Labatories and Factory Mutual Research publish y e a r l y guides to e l e c t r i c a l equipment which they have c e r t i f i e d and continue to c e r t i f y as being rated for use i n hazardous environments. Many of the items contained i n these guides are r a t e d as i n t r i n s i c a l l y safe or as associated equipment for use with i n t r i n s i c a l l y safe equipment. F u r t h e r , the amount of equipment available should increase each year as the demand increases f o r i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s . Real World Application Due to the concept of low energy, i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s do not provide the energy necessary to drive motors or high powered e l e c t r i c a l equipment. Nevertheless, this does not l i m i t or r e s t r i c t their application i n the r e a l world. As mentioned e a r l i e r , pneumatic and hydraulic systems have been extensively used i n hazardous environments to p r o v i d e the power necessary to move and drive machinery to complete needed tasks. T h e i r use has demanded development of complex l o g i c systems which involve the addition of valves and piping. These l o g i c c o n t r o l systems are o f t e n hard to d e s i g n , debug, construct, and maintain. The advent of the programmable c o n t r o l l o r has allowed complex logic systems to be e a s i l y developed and permits greater c o n t r o l over processes than ever b e f o r e . They can interpret both d i g i t a l and analog s i g n a l s . They are capable of m u l t i - t a s k i n g , permitting one unit to control several d i f f e r e n t processes at the same time. They can be connected to main frame computers, e n a b l i n g process data to be c e n t r a l l y collected for both coordination of processes and report generation.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

266

Another new important tool for use i n hazardous locations i s robotics. This tool allows the operator to be removed from the hazardous environment to a l o c a t i o n away from the danger, affording the operator maximum safety. Intrinsically safe e l e c t r i c a l circuits provide the c a p a b i l i t y to combine the strengths of pneumatic and h y d r a u l i c systems with the s o p h i s t i c a t i o n of the programmable controllor and r o b o t i c s , and to do so with the maximum s a f e t y and flexibility. The U.S. Army Defense Ammunition Center and School i s employing the use of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s i n equipment designed to d e m i l i t a r i z e and renovate munitions - from small arms to large p r o j e c t i l e s . This i s accomplished by u s i n g pneumatics and h y d r a u l i c s to provide the power, while using position switches and s o l e n o i d v a l v e s l i n k e d to programmable controllors to direct the total machine process. In one a p p l i c a t i o n c o o r d i n a t i n g the a c t i o n control over an i n t r i n s i c a l l y safe robotic arm which loads and unloads the heavy p r o j e c t i l e s being processed. In this way, the maximum protection i s a f f o r d e d not only to the o p e r a t o r , but also to the f a c i l i t y . Conclusion The u t i l i z a t i o n of i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s when p o s s i b l e during the d e s i g n of e x p l o s i v e f a c i l i t i e s , can accomplish one of the paramount o b j e c t i v e s - c o n t r o l l i n g the conditions which can lead to a premature i n i t i a t i o n of energetic m a t e r i a l s i n the environment. This i s p o s s i b l e because i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s are designed to be i n c a p a b l e of i g n i t i n g the hazardous environment, not only when operating correctly, but even when malfunctioning. The i d e a l way to accomplish t h i s u t i l i z a t i o n i s through purchasing c e r t i f i e d apparatuses and combining them to arrive at the c i r c u i t d e s i r e d , r a t h e r than d e s i g n i n g the apparatus and circuit. T h i s s i m p l i f i e s the d e s i g n process and, f u r t h e r , provides documentation for OSHA requirements. F i n a l l y , i n t r i n s i c a l l y safe e l e c t r i c a l c i r c u i t s are an o l d idea, whose time has just begun. Tomorrow's world w i l l see ever greater uses of programmable c o n t r o l l o r s , robotics, s o l i d s t a t e c i r c u i t s , and other low energy devices. This i s the world i n which i n t r i n s i c a l l y safe c i r c u i t s belong. Acknowledgments The author wishes to acknowledge the assistance of Ms. Flanagan, Ms. Miatke, Mrs. LaShelle and the USADACS Equipment D i v i s i o n .

Literature Cited 1. Article 500, National Electrical Code, National Fire Protection Association, Quincy, MA, 1956

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

17. PROPER

Safe Electrical Circuits in Explosives Facilities 267

2. Webster's Twentieth Century Dictionary, 2nd Ed., Unabridged, William Collins + World Publishing Co., Inc. 3. Section 1-4.1. Reprinted with permission from NFPA 493-1978, Standard for Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Division 1 Hazardous Locations, Copyright 1979, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and offical position of the NFPA on the referenced subject, which is represented only by the standard in its entirety. 4. Chaper 6, "Electrical Equipment and Wiring", AMC Regulation 385-100, U.S. Army Materiel Command, 1984 5. Garside, Robin, Intrinsically Safe Instrumentation, A Guide, North American Edition, Instrument Society of American, Research Triangle Park, NC, 1978, has good discussion of Zener barriers. 6. Garside, Robin, "Modular Zener Barrier Design Simplifies IS Installations", page 45, Control and Instrumentation, Vol II, No. 1, Jan 1979 7. 1910.307(b)(1)-(3) 1900 to 1910, Revise y , , Register, National Archives and Records Service, General Services Administration, U.S. Government Printing Office: Washington, DC, 1984 8. Appendix A-4.2. Reprinted with permission from NFPA 493-1978, Standard for Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II and III, Division 1 Hazardous Locations, Copyright 1978, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the complete and offical position of the NFPA on the referenced subject, which is represented only by the standard in its entirety. Other Standards Manufacture, T r a n s p o r t a t i o n , Storage, and Use o f Explosive M a t e r i a l s , NFPA 495, N a t i o n a l F i r e P r o t e c t i o n A s s o c i a t i o n , Quincy, MA, 1985 Purged and Pressurized Enclosures for E l e c t r i c a l Equipment, NFPA 496, National F i r e P r o t e c t i o n Association, Quincy, MA, 1982 A p p r o v a l Standard I n t r i n s i c a l l y Safe Apparatus and Associated Apparatus for Use i n Class I , I I and I I I , D i v i s i o n 1, Hazardous Locations, Class No. 3610, Factory Mutual Research, Norwood, MA, Oct. 1979 I n t r i n s i c a l l y Safe Apparatus and Associated Apparatus for Use i n C l a s s I , I I and I I I , D i v i s i o n 1, Hazardous Locations, UL 913, Underwriters Laboratories, Inc., Northbrook, I L , J u l y 1979 I n s t a l l a t i o n of I n t r i n s i c a l l y Safe Instrument Systems i n Class I Hazardous Locations, ISA-RP12.6, Instrument Society of America, Research Triangle Park, NC

Other References Bartkus, Albert Α., "Intrinsically Safe Equipment For Use in Class I, Division 1 Hazardous Locations", Lab Data, Winter/Spring, 1982

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Capp, B. and Widginton, D.W., "The Intrinsic Safety of Resistive Circuits", 2nd International Conference on Electrical Safety in Hazardous Environments, 9-11 Dec 1975, pages 43-47 Electrical Equipment for Hazardous Locations, Underwriters Laboratories, Inc., Northbrook, IL Magison, Ernest C., Electrical Instruments in Hazardous Locations, 3rd Ed., Instrument Society of America, Research Triangle Park, 1978 Magison, Ernest C., Intrinsic Safety, Instrument Society of America, Research Triangle Park, 1984 Redding, R.J., "The Use of Solid State Circuitry Within Hazardous Areas", 3rd International Conference on Electrical Safety in Hazardous Environments, 1-3 Dec 1982, pages 219-233 Weatherhead, D., "Intrinsic Safety", Measurement and Control, Vol 10 No. 9, Sept 1977, pages 341-349 Zborovszky, Zsuzsanna and Louise A. Cotugino, A Comprehensive Study of Intrinsic Safet Criteria Burea f Mines Ope Fil Report 23-73, March 197 RECEIVED

March 6, 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 18

Electrostatic Studies in Army Ammunition Plants 1

2

3

William O. Seals , James Hokenson , and George Petino 1

Army Research, Development and Engineering Center, Dover, NJ 07801-5001 Southwest Research Institute, San Antonio, TX 78284 Hazards Research Corporation, Denville, NJ 07834 2

3

One of the greatest hazards that exist in the manufacture of solid propellants, explosives, and pyrotechnic materials is dust explosions. At the differen quantities of dust can b dust are produced during the screening, drilling and packaging operations. In addition to posing a fire/explosive hazard, health problems for plant personnel can be serious. It is essential that the dust be removed safely from each operation. To accomplish this removal, exhaust fans are used to extract dust from the surrounding atmosphere and deposit it in transport ducts. The dust is then air carried through the ducts to a dry dust collector or passed through a water blanket for removal. The collision of dust particles with each other and the frictional forces upon each particle as it contacts the air can produce hazardous levels of electrostatic energy. Dusts which do not contain an oxidizer have an upper explosive limit. When these dust concentrations are s u f f i c i e n t l y high enough, the f u e l - a i r r a t i o of the cloud can produce an energetic reaction; therefore, dust concentration levels under dynamic flow i n a dust c o l l e c t i o n system were d e s i r a b l e . The i n t e r r e l a t i o n s of duct s i z e , dust concentration l e v e l s , and flow conditions that can produce hazardous i n i t i a t i n g and propagating reactions within the ducts needed to be addressed. This chapter w i l l discuss the evaluation of dust explosion potent i a l at various manufacturing operations i n three Army Ammunition Plants. The assessment of data from each plant w i l l be presented in detail.

Army Ammunition Plant Dust Evaluation Three Army Ammunition Plants were selected to evaluate whether dust explosions could occur i n their explosive materials manufacturing operations:

0097-6156/87/0345-0269$06.00/0 © 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

270 1.

Louisiana ΑΑΡ, Shreveport, La.



Longhorn ΑΑΡ, Marshall, Texas

3.

Lone Star ΑΑΡ, Texarkana, Texas

In each of these p l a n t s , the characterization of the dust ex­ p l o s i o n p o t e n t i a l was carried out by sampling transport ducts for explosive dust concentrations during an actual plant operation. The c r i t i c a l measurements taken were the q u a n t i f i c a t i o n of explo­ s i v e dust concentrations and l e v e l of e l e c t r i c energy generated from the e l e c t r o s t a t i c charge accumulations found i n the duct. In order to characterize the concentration of dust flowing i n s i d e a duct, a measured amount of dust must be extracted over a known period of time. This c o l l e c t i o n v e l o c i t y must be the same as the i n t e r n a l duct flow v e l o c i t y to avoid a l t e r i n g the d i s t r i b u ­ t i o n of dust p a r t i c l e s i z e s points over the e n t i r e duc define the o v e r a l l dust concentration. This method of sampling, known as gravimetric sampling under i s o k i n e t i c conditions, was used to determine the dust concentrations at the various manufac­ turing areas i n the Army Ammunition P l a n t s .

Duct V e l o c i t y and Flow Rate To measure the i n t e r n a l flow v e l o c i t y i n the duct, dust samp­ l i n g was taken at various points along the v e r t i c a l diameter. A p i t o t s t a t i c tube and magnehelic gauge, shown i n Figure 1, was the equipment used f o r these measurements. The duct humidity, tempertaure, and s t a t i c pressure were measured to calculate the gas density. In determining the humidity, the wet and dry bulb temperature of a continuous sample stream was used. To prevent dust buildup on the wet bulb thermometer, an i n l i n e metal f i l t e r was inserted into the l i n e . Dust Concentration Dust samples were c o l l e c t e d by the p r o b e / f i l t e r configuration shown i n Figure 2. The f i l t e r used to trap the explosive dust was a 37mm p l a s t i c f i l t e r cassette. To monitor the actual flow r a t e , a rotometer was used. The c a l c u l a t i o n f o r each traverse point dust concentration was obtained from Ci

β

"ru Qsi t Qsi t s i

8

i

where : C^ « Di Qsi si subscript w

58 β

t

Note:

β

dust concentration i n the duct. weight of dust collected on f i l t e r cassette. P °be sample flow r a t e . sampling time. i = value at the i traverse point. r

t

n

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

18.

Electrostatic Studies in Army Ammunition Plants

SEALS ET AL.

Κ 1

T 0 T A L

PRESSURE LEAD LOW OR HIGH VELOCITY PRESSURE GAGES ON PANEL BOARD

STATIC PRESSURE

DUCT PENETRATION

\/

/

/



/

/

/ /

//

TYPICAL DUCT SURFACE

AIR

FLOW

Figure 1. Pitot-static velocity probe.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

271

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

272

INLET DRILLED TO MATCH 1/4" T U B I N G

ACETATE FILTER WITH BACKING PAD

TO MEASUREMENT PANEL BOARD ROTAMETER

DUCT

Figure 2. Dust sampling probe.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

18.

SEALS ET AL.

Electrostatic Studies in Army Ammunition Plants

273

E l e c t r o s t a t i c Instrumentation The charge density of dust transported through ducts and the resultant e l e c t r i c f i e l d s at the duct inner walls was monitored by a Monroe Electronics Inc., Model 171 e l e c t r i c fieldmeter. A l l the e l e c t r o s t a t i c sampling i n the f i e l d was performed i n c i r c u l a r crosssection ducts. Thus, the e l e c t r o s t a t i c f i e l d i n t e n s i t y , f o r t h i s geometry, can be determined from Poisson's equation using the c y l i n d r i c a l coordinate system. Calibrations The Monroe E l e c t r i c F i e l d Meter was calibrated by using a v o l ­ tage standard and a large p a r a l l e l plate capacitor. The e l e c t r i c f i e l d between the two p a r a l l e l plates i s calculated as a function of voltage across the plates. The calculated f i e l d i s used to deter­ mine the c a l i b r a t i o n constants meter, simultaneous e l e c t r o s t a t i the charge density meter and e l e c t r i c f i e l d meter. By comparing the simultaneous measurements under uniform space charge condi­ t i o n s , the transfer function f o r the charge density meter was determined from the e l e c t r i c f i e l d meter as the standard. The transfer function accounts f o r flow conditions, e f f e c t s of the medium being measured, and the c h a r a c t e r i s t i c s of the sampling hose. The transfer function determined was based upon Composition Β explosive dust flowing through 305m (100 f t . ) of 2.54cm (1 i n . ) diameter conductive hose at 9.4 1/s (20 cfm)

36.9 QlOpJ y

3

Q

η C/m

where C ~ gain of charge density instrument V = output voltage 3

η C/m

= 1.0 χ 10~

9

coulombs

Charge Density Measurements A charge density meter, shown i n Figure 3, designed and b u i l t by Southwest Research I n s t i t u t e was used to record the charge den­ s i t y measurements. This meter consisted of a sensor u n i t , control readout u n i t , and power supply. B a s i c a l l y , t h i s instrument operates by extracting a dust sample from a duct and then passing through the sensor u n i t . Here, a series of s t e e l screens trap the charge laden dust p a r t i c l e s . To avoid hazardous charge buildups i n the sensor, the charge i s removed from the s t e e l screens to ground. This creates a current flow that can be converted to voltages. I t i s t h i s voltage that i s recorded. Plant Sampling and Results Louisiana ΑΑΡ Two d i f f e r e n t process areas were selected at the Louisiana ΑΑΡ

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

274

for dust concentration and e l e c t r o s t a t i c charge accumulation determination. These areas were (1) the Composition Β screening and bin loading i n b u i l d i n g 1611 and (2) the 155mm s h e l l d r i l l i n g oper­ ation i n b u i l d i n g 1619. Building 1611 Bulk Composition Β explosive i s received i n 27.4 kg (60 lb) boxes and conveyed to the second f l o o r . The explosive i s dumped on a shaker and screened to remove foreign matter. In t h i s opera­ t i o n , a considerable amount of dust i s generated. The dust i s contained by vented hoods above the shaker and transferred into 30.5 cm (12.0 i n . ) ducts. The screened material then drops through a duct to a loading hopper on the f i r s t f l o o r . The explosive dust generated by t h i s process i s removed through a 10.2 cm (4.0 i n ) duct. The 12 inch and 4 inch ducts are connected i n a Y configuration tha c o l l e c t o r . This c o l l e c t i o cleanout openings i n the ducts that f a c i l i t a t e the removal of dust accumulations were used as the sample c o l l e c t i o n areas. To record the dust v e l o c i t y , probes were i n s t a l l e d i n the duct. One of the most e s s e n t i a l features of t h i s probe was i t s round bottom which prevented disturbances i n the flow during normal operations· B u i l d i n g 1619 The d r i l l i n g operation, which provides a recess f o r the i n s t a l ­ l a t i o n of a fuze i n a 155mm s h e l l , was performed i n b u i l d i n g 1619. An a i r driven d r i l l i s used to put a recess i n the Composi­ t i o n Β that has been encased i n the nose. The dust generated from t h i s operation i s removed by suction through a 5.1 cm (2.0 in) l i n e to a Hoffman primary dust c o l l e c t o r . Downstream of the primary c o l l e c t o r i s a secondary c o l l e c t o r used to take any excess not trapped i n the primary c o l l e c t o r . Two sample areas were selected f o r study as shown i n Figure 5. Dust Concentration Measurements In both b u i l d i n g l o c a t i o n s , the v e l o c i t y p r o f i l e indicated duct f l o e turbulence. The d r i l l i n g operation o f b u i l d i n g 1619 had flow v e l o c i t i e s and negative s t a t i c pressures that were s i g n i f i c a n t ­ l y higher than the operations i n b u i l d i n g 1611. These differences can be attributed to the duct diameters, s i z e s , and number of dust cleanouts found i n the two removal systems. Sampling of the dust concentration was made at the centerline and one point above and one point below the c e n t e r l i n e . A close inspection of the data indicated that a higher dust concentration was observed at the bottom of the duct with e s s e n t i a l l y constant l e v e l s from the top of the duct to the centerline. Dust concentrations were three orders of magnitude higher f o r the d r i l l i n g operation i n 1619 than obtained i n the hopper loading operation of 1611. This was to be anticipated when one analyzed the two types of a c t i v i t y . I t had been found that the d r i l l i n g of 48 s h e l l s would accumulate 11.34 kg (25 l b s ) of explosive dust.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

SEALS ET AL.

Electrostatic Studies in Army Ammunition Plants

Figure 3. Charge density sensor.

SHAKER TABLE

HOPPER LOADING

SAMPLE LOCATION No. 1

30.5CM DUCT

Φ .

ELBOW DOWN ELBOW HORIZONTAL 30.5CM DUCT

SAMPLE LOCATION No. 2

SECOND FLOOR DUCTING FIRST FLOOR DUCTING

t SAMPLENo.LOCATION 3 WET DUST COLLECTOR

Figure 4. Dust and electrostatic sampling location in the Composition Β screening and bin loading operation of Building 1611, Louisiana ΑΑΡ.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

276

TOXIC C H E M I C A L A N D EXPLOSIVES FACILITIES E l e c t r o s t a t i c Measurements

B u i l d i n g 1611 E l e c t r i c f i e l d and charge d e n s i t y measurements were r e c o r d e d at e a c h sample l o c a t i o n i n b u i l d i n g 1611. T y p i c a l measurements a r e shown i n the F i g u r e 6. I n t h e s t r i p c h a r t r e c o r d i n g s , e a c h peak i n t h e e l e c t r i c f i e l d t r a c e s , c o r r e s p o n d s to when C o m p o s i t i o n Β was dumped on the s h a k e r . The l a g c o r r e s p o n d s t o the l e n g t h o f time t a k e n f o r t h e d u s t t o be t r a n s p o r t e d t h r o u g h 30.5m (100 f t . ) o f sampling hose. I n s p i t e o f t h i s d e l a y , one can see t h a t t h e r e i s e x c e l l a n t agreement between t h e two i n s t r u m e n t s f o r t h e d u r a t i o n of e a c h p u l s e and a r r i v a l t i m e . B u i l d i n g 1619 The d u c t d i a m e t e r s was l i m i t e d t o t h e c h a r g low d r i l l i n g charge d e n s i t y measurements were made a t l o c a t i o n s 4 and 5 i n F i g u r e 5. The magnitude o f t h e c h a r g e a t e i t h e r o f t h e s e p o i n t s showed no s i g n i f i c a n t d i f f e r e n c e s . S i n c e the charge d e n s i t y s i g n a l was dependent upon t h e o p e r a t o r , no p r e d i c a b l e c h a r a c t e r i s ­ t i c s c o u l d be r e n d e r e d from one s i g n a l t o another from the random loadings. Charge

and Energy L e v e l s

A l t h o u g h t h e c h a r g e d e n s i t y l e v e l s i n b u i l d i n g 1619 a r e two o r d e r s o f magnitude g r e a t e r than found i n b u i l d i n g 1611, t h e e n e r g y l e v e l s a r e a l l a p p r o x i m a t e l y o f t h e same magnitude. T h i s i s based upon t h e energy l e v e l dependent upon t h e d u c t d i a m e t e r . The l e v e l s l e v e l s o f e n e r g i e s found a t t h e s e l o c a t i o n s were many o r d e r s o f magnitude s m a l l e r t h a n t h e r e p o r t e d i g n i t i o n e n e r g i e s f o r Compo­ s i t i o n B. Longhorn ΑΑΡ Longhorn ΑΑΡ i s i n v o l v e d i n t h e manufacuture o f t h e 4.2 i l l u m ­ inating flares. Two s i t e s , b u i l d i n g s B-7 and 34Y, were s e l e c t e d f o r d u s t and e l e c t r o s t a t i c measurements. I n b u i l d i n g B-7, 4.2 aluminum c a n d l e s a r e p r o c e s s e d ; w h i l e , i n B u i l d i n g 34-Y, w h i t e s i g n a l f l a r e s a r e manufactured. P r o c e s s i n g o f 4.2 i l l u m i n a t e c o n s i s t s o f m i x i n g t h e composi­ t i o n , w e i g h i n g , c o n s o l i d a t i o n , removal o f a c a r b o a r d p l u g , a d d i n g a p r i m e r s t a g e , and p a c k a g i n g . A s c h e m a t i c o f t h i s p r o c e s s i n g o p e r a t i o n i n B u i l d i n g B-7 i s i l l u s t r a t e d i n F i g u r e 7. The same m a n u f a c t u r i n g p r o c e s s s t e p s f o l l o w e d i n b u i l d i n g B-7 a r e found i n B u i l d i n g 34-Y. The s a m p l i n g a r e a s f o r B u i l d i n g 34-Y are shown i n F i g u r e 8.

Duct V e l o c i t y , F l o w R a t e s , and Dust C o n c e n t r a t i o n Measurements The p r o c e s s e s m o n i t o r e d were n o t c o n t i n u o u s ; t h e r e f o r e , t h e

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

18.

SEALS ET AL.

Electrostatic Studies in Army Ammunition Plants

277

DRILL CUBICLES

if

PALLET OF 155mm SHELLS

ru SAMPLE LOCATION No. 4

VACUUM PUMP

Figure 5. Dust and electrostatic sample locations in the drilling operation of Building 1619, Louisiana ΑΑΡ.

(a) ELECTRIC FIELDMETER OUTPUT

-**| |-*-5SEC

UJ CO

Û S -120 LU

Ο

Ο

S

0 (b) CHARGE DENSITY METER OUTPUT

-H

h*-5SEC

Figure 6. Electrostatic measurements at Building 1611 in 30.5-cmdiameter duct at Location 1.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

278

TYPICAL VACUUM EXHAUST INLETS

NOTE: CONSOLIDATIO INLET ALWAY INLETS INTERMITTENTL AND CLOSED DURIN

CARDBOARD DISK REMOVAL

ΛΑ/" Figure 7. Dust and electrostatic sampling locations in 4.2 aluminum candle production process in Building B-7, Longhorn ΑΑΡ.

SAMPLE LOCATION^

10 HP HOFFMAN WET DUST COLLECTOR

^SAMPLE LOCATION

Ô

Ό

20 HP HOFFMAN WET DUST COLLECTOR

Figure 8. Dust and electrostatic sampling locations in the signal flare production process in Building 34-Y, Longhorn ΑΑΡ.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

18.

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AL.

Electrostatic Studies in Army Ammunition Plants

279

consistency i n the measured values was poor. This was attributed to intermittent vacuuming performed at the d i s c r e t i o n of the oper­ ator. Only the i n l e t s on the consolidation press had i t s dust vacuumed continuously. E l e c t r o s t a t i c Measurements The small 2.0 i n . ducts i n buildings B-7 and 34-Y l i m i t e d the instrumentation studies to the charge density meter. The same locations cited f o r dust v e l o c i t y and flow rate sampling points were used f o r these measurements. At t h i s l o c a t i o n , pyrotechnic materials are processed. These materials d i f f e r from the Composi­ t i o n Β that was used i n the o r i g i n a l c a l i b r a t i o n of the charge density meter. As a consequence of not using the pyrotechnic material with the e l e c t r i c fieldmeter to c a l i b r a t e the charge den­ s i t y meter, only r e l a t i v data. While these small diameter ducts produced high charge l e v e l s , the energy l e v e l s i n the transport system were small. P o s i t i v e and negatively charge species were found to co-exist. The p o s i t i v e charges occured from the intermittent vacuum at the weigh s t a t i o n and the negative charges from the continuous vacuuming at the consolidation presses. Building B-7 A t y p i c a l charge density waveform from the sample 6 l o c a t i o n r e f l e c t s the dust taken during the vacuum operation at the d i s k removal s t a t i o n . As seen i n Figure 9, the charge can be e i t h e r p o s i t i v e or negative. Typical p o l a r i t y charge reversals can be attributed to the transfer of image charges. Building 34-Y Sampling points i n Building 34-Y were selected near two wet c o l l e c t o r s of two independent vacuum c o l l e c t i o n systems. I t was i n t e r e s t i n g to note that the dust c o l l e c t e d at these points were granular and larger i n size than dusts collected at any of the other plants analyzed. Apparently there i s s u f f i c i e n t moisture or v o l a t i l e content to cause the f i n e magnesium and aluminum p a r t i c l e s to agglomerate i n t o large p a r t i c l e s . The charge magni­ tudes were observed to be higher i n the morning. As the tempera­ ture increased i n the afternoon, t h i s charge magnitude was seen to decrease. Moisture condensate formed on the duct surfaces as the temperature changed. These moisture and temperature v a r i a t i o n s may have contributed to the decreased charge l e v e l s . The dust from the weighing and pressing s t a t i o n s of Bay 103 were sampled at l o c a t i o n 8. Again, the sampling of dust was per­ formed by the operator i n a random fashion. This random operation produced unpredictable charge density waveforms. The charge density l e v e l s are quite high, but the energy l e v e l s are low. These low l e v e l s are attributed to the small duct diameters and dependency of the energy upon the duct radius to the f i f t h power. The energy l e v e l s at b u i l d i n g 34-Y are approximately an order of

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

280

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

magnitude lower than those observed at building B-7. This lower order was due to the agglomeration of the aluminum composition that occurred i n building 34-Y.

Lonestar ΑΑΡ The burster facing operation (building 04-M-40) and a grenade pressing operation (building B-46) were sampled at Lonestar ΑΑΡ for dust and e l e c t r o s t a t i c s * These operations were s i m i l a r i n nature as those performed i n Building 1619 at Louisiana ΑΑΡ and the press­ ing operation at Longhorn ΑΑΡ. The vacuum exhaust and dust c o l l e c t i o n system i s i l l u s t r a t e d for buildings 04-M-40 and B-46 i n Figure 10 and 11 respectively. In building B-46, three separate operations are performed: c o n s o l i ­ dation, demachining, and cone swagging. A rotary press i s used to consolidate A-5 explosiv dust from t h i s pressin are used. These l i n e s are then connected to a s t a i n l e s s steel l i n e that runs into a wet c o l l e c t o r .

Dust Measurements The flow rates and s t a t i c processes are approximately the same for a l l vacuum l i n e s . The v e l o c i t y p r o f i l e does show turbulence i n both processes. Except f o r the d r i l l i n g operation i n the Louis­ iana ΑΑΡ, the dust concentrations at location 10 and 11 were the highest recorded. In location 10, the dust concentration was more concentrated at the bottom, while the top and centerline concentrations were f a i r l y uniform. Of the three operations i n building B-46, higher dust concen­ trations were generated by the demachining operation. F a i r l y constant concentrations were found across the duct. This can be attributed to the high duct flow v e l o c i t i e s .

E l e c t r o s t a t i c Measurements The operations studied were limited to the charge density meter because of the small ducts. The dust collected from the rotary d r i l l and facing machine at location 10 had the highest charge l e v e l s measured i n the entire testing program. I t soon became apparent i n the i n i t i a l start up of the sampling that the s t e a d i l y increasing charge l e v e l s would exceed the measurement range of the charge density meter. At t h i s point, the flow rates through the charge density meter were reduced from 9.4 /s (20 cfm) to 7.1 / s ( 1 5 cfm). The peak measurements for the two flow rates were than compared. The charge density meter transfer function at a flow rate of 7.1 /s (15 cfm) was found to be - 156.8

V _100 I V

0

nC/nr

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

18.

SEALS ET AL.

g_ LU t*i

û |

Electrostatic Studies in Army Ammunition Plants

+4000 0

(a) CHARGE DOUBLET

LU «

+3600 0

(b) POSITIVE PULSE

- H h*-5 SEC

Figure 9. Charge density measurements at Building B-7 at Sample Location 6.

Figure 10. Vacuum exhaust ducting and dust collection system for burster facing operation in Building 04-M-40.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

281

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

282

CONSOLIDATION ROTARY PRESS

CONE SWAGGING PRESS

DEMACHINING AREA

Φ

SAMPLE LOCATION No. 12

\

g)

SAMPLE LOCATION No. 13

."Y"CONNECTION

SAMPLE LOCATION No. 14

L WET DUST COLLECTORS

Figure 11. Vacuum exhaust and dust collection system for grenade press operation in Building B-46.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

18.

Electrostatic Studies in Army Ammunition Plants

SEALS ET AL.

283

B u i l d i n g B-46: D i s t i n c t and unusual waveforms were observed from A-5 explosive dust c o l l e c t e d at l o c a t i o n 14 when the explosive m a t e r i a l i s dumped from a bucket i n t o a rotary press hopper. P o s i t i v e and negative charge species were found with the predominance of charge being negative i n p o l a r i t y . D i s t i n c t charge doublets r e s u l t each time a bucket i s emptied. With the deposition of a negative charge i n the press hopper, the opposite image charge i s retained by the pow­ der remaining i n the bucket. As the bucket i s completely emptied, the negative charge reaches i t s maximum and then begins to diminish. As a r e s u l t of t h i s a c t i o n , the charge reverses i t s p o l a r i t y · This phenomenon i s completed when the image charge doublet of the opposite p o l a r i t y i s formed and returns to zero when the bucket i s empty. Charg Building 04-M-40 recorded the highest density l e v e l s of any of the sample locations measured. In a d d i t i o n , the highest readings were also always obtained when the sample was withdrawn from the bottom of the duct. Summary of Plant Sampling A summarization of a l l the data c o l l e c t e d at the three Army Ammunition Plants i s given i n Table 1· The maximum values obtained at each sample l o c a t i o n have been l i s t e d i n t h i s t a b l e . Although the r e s u l t s from the d i f f e r e n t processes are d i f f i c u l t to compare, these q u a l i t a t i v e observations can be made. ° Sampling i n small diameter vacuum ducts resulted i n higher vacuum pressures, flow v e l o c i t i e s , dust concentrations and charge d e n s i t i e s , but lower flow r a t e s . ° Higher charge d e n s i t i e s , dust concentrations, and energy l e v e l s were found i n processes involving d r i l l i n g , and facing operations of explosive. 0

Low flow v e l o c i t i e s prevented uniform dust concentrations i n the ducts. (This was r e f l e c t e d i n the dust buildup at duct cleanouts)· 0

Batch operations have periods of high and low loading densi­ t i e s . This indicates that the gravimetric method of sampling, dependent on the t o t a l mass of dust c o l l e c t e d over a given period, can only r e f l e c t average concentrations. Instantaneous concentra­ tions may be s i g n i f i c a n t l y higher. ° Minimum explosive concentration f o r explosive and pyrotechnic dusts have been reported* i n the range of 40 to 1000 gm/mm, (40 to 1000 o z / f t ) . With the exception of l o c a t i o n 5 i n B u i l d i n g 1619 at Louisiana ΑΑΡ, a l l the dust concentrations determined f o r the various plants were below the maximum average concentrations. 3

3

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

SAMPLED

ALUMINATE

ALUMINATE

B L D G 34-Y: 8

9

A-5

A-5

13

14

COMP Β

11

A-5

COMP Β

10

B L D G B-46: 12

BUILDING 04-M-40:

LONESTAR Α Α Ρ

ALUMINATE

ALUMINATE

6

7

B L D G B-7:

LONGHORN Α Α Ρ

COMP Β

5

5.1

5.1

5.1

7.6

5.1

5.1

5.1

5.1

5.1

5.1

5.1

30.5

COMP Β

COMP Β

3

B L D G 1619: 4

10.2

COMP Β

COMP Β

2

30.5

(CM)

DUCTDIA

B L D G 1611: 1

LOUISIANA Α Α Ρ

MATERIAL

SAMPLING

LOCATION

6.30

5.80

4.70

8.90

3.30

4.20

3.00

4.90

0.47

3.80

-

68.00

4.90

63.00

3

(M /MIN)

FLOW R A T E

-50.80

-50.80

-50.80

-76.20

-50.80

-101.60

-88.90

-108.00

-127.00

-152.40

-

-2.29

-2.29

-2.29

80

80

75

80

79

89

89

89

88

-

75

72

63

62

(°F)

TEMP

63

63

82

70

67

50

36

42

6

35

-

36

50

41

(%)

REL HUMIDITY

0.180

0.660

0.820

13.800

26.000

1.400

12.100

6.300

0.900

330.000

-

0.115

1.610

0.093

3

DUST CONCENTRATION (GM/M )

+19.600

-5,170

-4.890

94,000

140,000

+1,030

+3,500

-11,100

+7,750

+11.100

+14,800

-287

+184

-232

3

CHANGE DENSITY (nC/M )

1.790

0.125

0.112

315.000

698.000

0.005

0.057

0.570

0.280

0.570

1.020

3.000

0.005

2.430

(pJ)

ENERGY

•MAXIMUM V A L U E S MEASURED DURING THE PLANT SAMPLING

STATIC PRESSURE (MM Hg)

Table 1. Summary of Measurements Taken During the Plant Sampling*

Κ) 00

18.

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Electrostatic Studies in Army Ammunition Plants

285

° Minimum i g n i t i o n energies for explosive and pyrotechnic dusts were reported i n the range of 0.2 and 8.0 j o u l e s . Maximum energy l e v e l s calculated from the charge density measurements were a l l very low. (maximum energy l e v e l of 7 0 0 ^ * J ) . This was an unusually high reading f o r Building 04M-40. The highest maximum energy l e v e l was i n Building 1611 at Louisiana ΑΑΡ which read 3.0 M J . ° The charge density appears to be approximately proportional to the peak mass flow rate (duct flow r a t e , Q, times the maximum dust concentration) i n the duct. R E C E I V E D May 1 5 , 1 9 8 7

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 19

Ionizing Air for Static Charge Neutralization While Processing Sensitive Materials Β. V. Diercks Morton Thiokol, Longhorn Division, P.O. Box 1149, Marshall, TX 75671

Ionized air can be safely and effectively utilized for neutralizing static charges which are generated while processing sensitiv horn Division of incorporated systems, in which electrically generated ions are used to neutralize charges which accumulate on infrared energy generating compositions consisting of magnesium powder, polytetrafluoroethylene (PTFE) and a binder. Ignitions sporadically occurred as pressed pellets of the composition were removed from the consolidation press. The ionizing air systems enhanced the safety of this and other infrared compo­ sition processing operations. Morton Thiokol, Inc. i s the operating contractor of the Government owned f a c i l i t i e s at Longhorn Army Ammunition Plant. The plant i s physically located i n Karnack, Texas. The Longhorn Division i s the Government's primary production f a c i l i t y for illuminating ammuni­ t i o n , signals, pyrotechnic simulators (gun flash, a r t i l l e r y burst, hand grenade, etc.) and infrared decoy f l a r e s . An e l e c t r o s t a t i c problem encountered i n 1983 while processing infrared flare compos­ i t i o n resulted in the u t i l i z a t i o n of ionizing a i r for neutralizing s t a t i c charges while processing these compositions. Although the use of ionized a i r to date has been limited to infrared composi­ tions, the techniques employed are applicable to any s i t u a t i o n wherein the processing of energetic compositions are susceptible to i g n i t i o n from e l e c t r o s t a t i c discharge. Compositions whose products of combustion produce energy i n the infrared wave band are generally composed of magnesium powder, poly­ t e t r a f luoroethylene (PTFE) and a binder. For e f f i c i e n t t a c t i c a l u t i l i z a t i o n of the energy developed by the combustion process the composition i s normally formed into p e l l e t s either by press c o n s o l i ­ dation or by press extrusion. The process being used at Longhorn at the time the e l e c t r o s t a t i c problem was encountered was press consol­ idation. The composition was being consolidated into a pellet

0097-6156/87/0345-0286$06.00/0 © 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

19. DIERCKS

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287

approximately 2"x3"x5" which weighed approximately 600 grams. The consolidation load was applied to the 2"x5" surface. Grooves were pressed into the top and bottom of the pellet by the upper and lower punches. Additionally, a cavity, into which a Safe and Igniting (S&I) device i s i n s t a l l e d , was formed during the consolidation process by using a side punch. Figure 1 depicts the consolidation press which was being used. As depicted, the punches are a l l r e tracted and ready to receive composition. Upon charging the cavity with material the press sequenced by moving the upper and side punches into position. The lower punch then raised, pressing the composition against the die walls and other punches to form the pellet to the f i n a l configuration. After a predetermined dwell time, the lower punch relaxed and the other two punches retracted to their load positions. The lower punch then raised to push the consolidated pellet completely above the die (Figure 2). Ignitions occurred when the pellet was physically removed from the lower punch. E l e c t r o s t a t i c charge ed. At least one of the surfaces has to be a poor conductor a l though both can be. These charges can then be inductively transferred to and delivered by conductors, or can be transferred to conductors i n the form of a spark. The Magnesium/PTFE/Binder p e l l e t is a poor or non-conductive material. As the pellet i s removed from the die of the press, electrons are stripped from the walls of the steel die and fluted upper punch and accumulate on the p e l l e t surfaces. At the completion of pellet ejection from the die cavity the pellet contains a negative charge on a l l exposed surfaces (Figure 2). The magnitude of this charge i s not the same on each exposed surface. Because the pellet i s a poor conductor, the charge can not dissipate through the grounded lower punch. The situation i s one i n which a charged pellet i s being removed by a grounded and conductive press operator. Although investigation of the incidents revealed the actual pellet ignitions resulted from e l e c t r o s t a t i c discharge between the pellet and the lower punch created by the physical act of separating the pellet from the lower punch (corrected by using a surfactant to improve the conductivity between the lower pellet surface and the punch), the potential for pellet i g n i t i o n existed through e l e c t r o s t a t i c discharge between the charged pellet and the press operator. To remove or neutralize an e l e c t r o s t a t i c charge from a poor or nonconductive surface, a l l points on the surface must be physically addressed. This can be accomplished by sparklessly grounding the entire surface and neutralizing the charge or by "washing the surface with ionized a i r . The l a t t e r i s by far the faster and more positive approach. Figure 3 i s a generalized depiction of a voltage versus time p r o f i l e of a charged pellet exposed to the atmosphere and of one exposed to ionized a i r . The use of radioactive ionization sources i n areas subject to explosion or f i r e i s undesirable because of the potential for area contamination with radioactive material which could be disseminated in the event of an explosion or f i r e . With proper precautions, however, e l e c t r i c a l ionizing systems can be safely and e f f e c t i v e l y u t i l i z e d while processing e l e c t r o s t a t i c a l l y sensitive energetic materials. Ions are generated e l e c t r i c a l l y by corona discharge 11

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Figure 1. Consolidation Press (Reproduced with permission from Réf. 1. Copyright 1986 E l s e v i e r Science Publishers.)

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Figure 3.

Generalized Voltage/Time P r o f i l e

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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using a needle capacitively coupled to approximately 7500 v o l t s . These corona generators are made in the form of nozzles i n which a i r i s forced through the annular space between the high voltage needle and the c y l i n d r i c a l nozzle body. By arranging nozzles in manifolds and coupling them to a common power and a i r supply, large e l e c t r o s t a t i c a l l y charged surface areas can be e f f e c t i v e l y neutralized. Such a system was developed for use on the infrared flare pellet consolidation system described above. Figure 4 depicts the locations and general connections of the nozzle system employed to neutralize the infrared flare pellet as i t rests on the lower punch awaiting removal by the operator. The high voltage supply i s located in a non-hazardous area and high voltage is cabled to the nozzles. Various interlocks are used to insure that ionized a i r i s proper and present during operations. Contact type interlocks are provided to assure regulated power i s delivered to the high voltage power supply. Current to the power supply i s metered through relay points. I f for any reaso or goes above the high se point, de-energiz press operating controls and the press ceases to function. Furthermore, pressure switches interlocked with the press operating cont r o l s (PS# 1,2,3 Figure 4) are i n s t a l l e d in the a i r lines upstream and downstream of the ionizing a i r nozzles which assures the presence of high pressure a i r at the ionizing nozzles. Low pressure a i r is l e f t on the system at a l l times preventing dust or particulate matter from s e t t l i n g around or on the ionizing electrodes. Since u t i l i z i n g the ionizing a i r system on the infrared f l a r e consolidation press, we have provided for s t a t i c charge n e u t r a l i z a tion in other processing areas used for manufacture and handling infrared compositions. Figure 5 shows a horizontal mixer i n which flare composition i s mixed and masticated. The serai-dry and granular material i s dumped from the mixer bowl into a transfer hopper. The dump chute located i n the area between the t i l t e d mixer bowl and the open hopper i s "washed" with ionized a i r neutralizing any charge which tends to accumulate on the material as a result of granular attrition. Composition i n the transfer hopper i s later dispensed into blender buckets for ease of handling in subsequent operations (Figure 6 ) . Material i s fed from the hopper by a star valve, through a ring of six ionizing nozzles located i n a c i r c u l a r pattern at 60° i n t e r v a l s , into the blender bucket. The blender bucket of material i s then dispensed into an o s c i l l a t i n g granulator which forces the material through a screen to arrive at a p a r t i c l e size suitable for charging the consolidation dies on the press (Figure 7). The material as i t exits the granulator screen f a l l s through a ring of ionizing a i r nozzles similar to that used on the hopper to blender bucket transfer system. Safety interlocks employed i n these systems are e s s e n t i a l l y the same as used for the consolidation press. A l l of the ionizing a i r systems at Longhorn are located in areas where u l t r a v i o l e t sensors are used in conjunction with deluge systems for f i r e protection. Care must be taken to shield the u l t r a v i o l e t detectors from the ion generating corona source. The systems used at Longhorn are i n d i v i d u a l l y shielded with PVC tubing or with hoods.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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PS #3

Power Supply

291

v

Ionizing Nozzle

PLAN VIEW Consolidated Pellet

^

Consolidation Die

Lower Punch-^fj^-w-V-^i.

SIDE VIEW

Figure 4. Ionizing A i r Nozzles (Reproduced with permission from Réf. 1. Copyright 1986 E l s e v i e r Science Publishers.)

Mixer Bowl Ionizer

Figure 5. Horizontal Mixer

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

TOXC I CHEMC IAL AND EXPLOSV IES FACILITIES Π

Ionizing Nozzles Blender Bucket Figure 6.

Transfer Hopper to Blender Bucket

Figure 7.

Material Granulation

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Ionized a i r i s p a r t i c u l a r l y b e n e f i c i a l i n preventing the buildup o f e l e c t r o s t a t i c charges on materials susceptible to the generation of these charges when processing can be r e a d i l y accom­ plished i n an ionized atmosphere. I t i s equally e f f e c t i v e i n quick­ l y n e u t r a l i z i n g a charged item or material when the processing en­ vironment i s not d i r e c t l y accessible with ionized a i r , but where subsequent processing environments allow i t to be subjected to an ionized atmosphere before i t must be moved or handled. Caution must be exercised, however, i n the i n s t a l l a t i o n of these systems to assure that they i n themselves do not create a hazardous s i t u a t i o n .

Literature Cited 1. Diercks, Β. V. Journal of Hazardous Materials, 13 (1986) 3-15. RECEIVED April 16, 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 20

Design and Use of Ammunition Peculiar Equipment To Protect Workers Mark M. Zaugg Tooele Army Depot, Tooele, UT 84074

Discusses the use of Ammunition Peculiar Equipment (APE) used by the military community to perform various operations on ammunition items. Ways in which operators are protecte Specifically, th to contain effects of an explosion is explained. Ammunition Peculiar Equipment, commonly referred to as APE, i s specialized equipment f o r use i n the maintenance, modification, renovation, surveillance and d e m i l i t a r i z a t i o n of ammunition items. This equipment i s used a t world wide m i l i t a r y i n s t a l l a t i o n s with ammunition missions that require any of the above mentioned activities. Whenever the operation to be performed involves the p o t e n t i a l to cause the i n i t i a t i o n of the propellant, explosive or pyrotechnic (PEP) component(s) of a munition item, the APE i s either operated by remote c o n t r o l , with the operator behind a protection w a l l or b a r r i e r , or i t i s enclosed i n a protective barricade or operational s h i e l d . Barricades or operational shields are designed to protect personnel and assets from the effects of b l a s t overpressures, thermal effects or f i r e b a l l , and fragments r e s u l t from the i n i t i a t i o n of PEP components, such as the fuze, primer, p r o p e l l i n g charge, burster, e t c . Operational shields are designed and tested i n accordance with MIL-STD 398, Shields, Operational f o r Ammunition Operations, C r i t e r i a f o r Design of and Tests for Acceptance, dated 5 November 1976 (see reference 1). This m i l i t a r y standard provides c r i t e r i a for the protection of personnel and assets from the effects of accidental or i n t e n t i o n a l detonation and deflagrations, considering the maximum c r e d i b l e incident (MCI) involving the maximum amount of ammunition and explosives within or adjacent to an operational s h i e l d , that w i l l detonate or deflagrate as a r e s u l t of the functioning of a single item.

This chapter not subject to U.S. copyright Published 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Operational shields are to be designed to conform to the following requirements: BLAST ATTENTION. Shields used to provide protection from accidental detonation, are to be designed to prevent exposure of operating personnel to peak p o s i t i v e incident pressures above 2.3 psi or peak p o s i t i v e normal r e f l e c t e d pressure above 5.0 p s i . Shields used to provide protection from i n t e n t i o n a l detonation of ammunition are to be designed to prevent exposure of operating personnel to impulse noise l e v e l s exceeding 140 decibels. FRAGMENT CONFINEMENT. Shields are to be designed to contain a l l fragmentation, or d i r e c t fragmentation away from areas requiring protection. They are also to prevent generation of secondary fragmentation within area movement, overturning, r e s u l t i n personnel injury. THERMAL EFFECTS ATTENUATION. Shield designs are to also l i m i t exposure of personnel to a c r i t i c a l heat f l u x value based on the t o t a l time of exposure. This value of heat f l u x i s determined by the following equation: 7423

9 = 0.62t-°' where: 0 = heat f l u x i n cal/cm2-sec t = t o t a l time i n seconds that a person i s exposed to the radiant heat Operating personnel are to be located a t a distance from the s h i e l d that assures their exposure i s less than the heat f l u x determined by the above equation. In a d d i t i o n , the upper torso of an operator's body s h a l l not be subjected to any v i s i b l e f i r e or flame. Flame impingement upon the lower portion of the body may be permitted provided that the heat f l u x specified above i s not exceeded. ASSET PROTECTION. Shields intended f o r i n t e n t i o n a l detonation are to be designed to prevent damage to buildings, equipment, and other assets i n the area. Damage prevention i s considered adequate i f normal operations are i n no way interrupted or hindered as a r e s u l t of any change to the operational environment from explosions i n this type of s h i e l d , and the s h i e l d may be expected to remain operational throughout i t s designed l i f e cycle. Shields designed f o r accidental explosions only are designed to provide personnel protection from the MCI at that operation and may not, i n a l l cases provide asset protection. SHIELD DESIGN. In the i n i t i a l approach to operational s h i e l d design, the hydrostatic pressure that would r e s u l t from the MCI in the s h i e l d i s determined. For a high explosive detonated i n a

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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closed a i r space, a hydrostatic pressure develops w i t h i n the space subsequent to the shock wave propagation. This pressure can be found from the equation: ΔΡ - 4000 hw/v where: h = heat of combustion (kcal/gm) (Table I) w = charge weight ( l b ) ν =• volume of a i r ( f t 3 ) Po = S t a t i c pressure above ambient ( p s i ) β

This equation i s derived from the energy equation of state for gas Ε = P V ( f - l ) , which b a s i c a l l y gives the hydrostatic pressure produced by the burning of a substance i n a f i x e d volume of a i r without a heat l o s s , (see reference 2). I t should be noted that the above r e l a t i o n s h i p applies to bare explosive charges. S t a t i c pressure from case predicted by the equatio case fragments. The s t a t i pressur decay function of the heat conduction and convection v a r i a b l e s of the s h i e l d , and the degree of pressure venting provided. Table I. Heats of Combustion f o r Several Explosives are Contained

Explosives PETN RDX P e n t o l i t e 50/50 Comp Β Tetryl TNT HBX-1 H-6 T r i t o n a l 80/20 HBX-3

Heat of Combustion kcal/gm 1.95 2.28 2.79 2.82 2.93 3.62 3.73 3.84 4.38 4.56

Once the s t a t i c pressure has been determined, the i n i t i a l s h i e l d design can be done using standard unfired pressure vessel design methods. The geometric shape of the s h i e l d i s of course driven by the shape of the machine to be contained and the a v a i l a b l e space i n the operating area where the machine and operational s h i e l d are to be located. Once the i n i t i a l design has been made, the dynamic response of the designed s h i e l d members to the dynamic pressure i s checked. This i s necessary to ensure that deflections of s t r u c t u r a l members due to loading from dynamic pressure produced by the MCI, namely the peak p o s i t i v e incident and r e f l e c t e d pressures, does not permit the escape of fragments or heat f l u x that would endanger personnel.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Unless s p e c i f i c a l l y designed to do so, operational shields do not t o t a l l y contain and hold the pressures generated from an explosion. Venting of pressures occurs through j o i n t s , flanges, and openings i n the s h i e l d , and may be enhanced by providing large vented openings that exhaust through the roof or w a l l of the b u i l d i n g i n which the s h i e l d i s located. The next f a c t o r i n the s h i e l d design i s to design for prevention of fragment penetration of the s h i e l d material. Fragment penetration can not only be a d i r e c t hazard to operating personnel, but p a r t i a l penetration can weaken the s h i e l d causing subsequent f a i l u r e from the overpressures. Fragment data and c r i t e r i a for s h i e l d design to prevent penetration are contained i n chapter 2 of reference 3 and i n reference 4. Knowing that the pressure and f i r e b a l l w i t h i n the s h i e l d from an MCI w i l l be vented throug design should provide fo c i r c u i t o u s routes for the pressure and f i r e b a l l to t r a v e l . This w i l l help eliminate passage of fragments outside the s h i e l d through openings caused by deflections of s h i e l d members. I t also provides for quenching of the f i r e b a l l by heat transfer from the hot gases to the passageway. SHIELD TESTING. After the design of the s h i e l d has s a t i s f i e d the requirements, and the prototype s h i e l d has been fabricated, reference 1 s p e c i f i e s the t e s t i n g to which i t must be subjected. The prototype operational s h i e l d must be tested by creating an MCI i n a simulated operational environment. The MCI i s created by detonating or i g n i t i n g a t e s t round(s), or item(s) with a l l items i n the operational configuration i n the s h i e l d , including the equipment or reasonable simulation thereof, that performs the intended function on the munitions. I f the s h i e l d i s intended to be used for a v a r i e t y of rounds, the one(s) having the most severe e f f e c t s for overpressure, fragmentation, thermal emissions and shape charge e f f e c t s i s to be tested. For each test the s h i e l d must be repaired to the equivalent of new condition or a new s h i e l d used, except f o r shields intended for i n t e n t i o n a l detonations. A d d i t i o n a l explosives equivalent to 25 percent of the explosive f i l l e r i s added to the test round, i f i t can be applied i n a manner as not to diminish the normal e f f e c t and response of the ammunition. The t e s t should also be conducted i n a l o c a t i o n that simulates the l o c a t i o n when i t w i l l be s p e c i f i c a l l y used. For example, shields to be used i n an operational bay should be tested i n a simulation of an operational bay.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Table I I . L i s t of Instrumentation 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

1 1 4 4 1 1 1 7 1 1

ea ea ea ea ea ea ea ea ea ea

11. 12. 13. 14. 15. 16.

1 1 1 1 1 1

ea ea ea ea ea ea

1. 1 ea 2. 1 ea 3. 1 ea 4. 1 ea 5. 1 ea 6. 1 ea 7. 2 ea 8. 1 ea 9. 1 ea 10. 1 ea 11. 1 ea

Honeywell 7610 Instrumentation Tape Recorder A r t i s a n EPC 19061 D i g i t a l Programmer K i s t l e r 504E Dual Mode Amplifiers K i s t l e r 201B4 Pressure Transducers Medtherm 64 Series Heat Flux Sensor (Schmidt-Boelter type) Systron Donner 8120 Time Code Generator Tektronix 184 Time Mark Generator Honeywell 117 Accudata Amplifiers Krohn-Hite 320 Honeywell 185 Amplifiers ERA TR36-8M Power Supply Newport 60-3 Amplifier HyCam Model 41—0004 High Speed Movie Camera M i l l i k e n DSB-5A High Speed Movie Camera Polaroid SX-70 Camera Canon A - l Reflex Camera Support and C a l i b r a t i o n Equipment Cohu 335 DC Voltage Standard Dana 5600 D i g i t a l Voltmeter B e l l & Howell TD 2903-4B Tape Degausser HP 5300A Measuring System HP 3311 Function Generator Beckman 905 WWV Receiver David Clark 10SB-A Sound Powered Head Sets 40 f t . Instrumentation T r a i l e r w/instailed equipment, racks, patch paneling, l i g h t i n g systems, heating system, and i s o l a t i o n transformer K i s t l e r 563 A Charge Calibrator Tektronix 561A Oscilloscope with 3A6 A m p l i f i e r and 3B4 Time Base Plug-Ins. Pressure Transducer Pulse C a l i b r a t i o n Systems

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Tests must be properly instrumented to meet the c r i t e r i a s p e c i f i e d e a r l i e r i n this chapter. A l l instrumentation should be selected to have the necessary response time and bandwidth equivalent to the anticipated overpressures and heat f l u x e s . Instrumentation must also be properly calibrated to ensure v a l i d i t y of the data. B l a s t pressure gages, heat f l u x transducers, and sound l e v e l meters are to be located a t the probable head l o c a t i o n of the operator and a t representative positions where transient personnel may be located. Documentation of the tests should a l s o be provided by s t i l l photography, video camera/recorder systems, and high speed photography. The high speed photography with a minimum speed of 500 frames per second i s necessary to be able to see any flame front e x i t i n g a s h i e l d on an operational s h i e l 4). INDUSTRIAL SAFETY PROVISIONS. In the design of the APE and associated operational s h i e l d , conventional machine design practices are used to protect operators from hazards associated with moving parts. Proper techniques f o r guarding of hazardous machine areas are used, including the use of i n t e r l o c k s i n the control system to prevent movements u n t i l c e r t a i n conditions are s a t i s f i e d , or to stop movements i n emergency s i t u a t i o n s SUMMARY. The safety record associated with the use of APE operated remotely or w i t h i n operational shields i s excellent. Operational shields that are properly designed, fabricated, and tested do provide operators with adequate protection, and ensures t h e i r safety during hazardous operations.

Literature Cited 1. Mil-STD 398; Shields, Operational for Ammunition Operations, Criteria for Design of and Test for Acceptance; 5 November 1976. 2. "Explosives in Enclosed Spaces", U.S. Naval Ordnance Laboratory NavOrd Reports 2934 and 3890; Sixth Symposium on Combustion, Reinhold Publishers, Inc. N.Y., 1957 p. 648 3. CPIA Publication 394, Hazards of Chemical Rockest and Propellants, Volume I, Safety, Health, and the Environment: September 1984, Healy, J., Weissman, S., Werner, H., and Dobbs, N. 4. Priming Fragment Characteristics and Impact Effects on Protective Barriers, Picatinny Arsenal, Dover, New Jersey, Technical Report 4903, December 1975. 5. Miller, J., APE 1011M6 Operational Shield Tests MK39 Primer in Empty 6 Inch/47 Cartridge Case (1340 Grains Black Powder), Ammunition Equipment Directorate, Tooele Army Depot, Tooele, Utah, D/AE Report 05-82, 22 February 1982. RECEIVED April 21, 1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Chapter 21

Cleaning Process Lines in the Explosives Industry Roy W. Wheeler 715 Connie Road, Baraboo, WI 53913

Many hazardous operations require the use of pipelines to convey product material from one location to another. In time, these pipelines become lined with the hazardous product to the extent they could serve as a media to station. Therefore hazardous residue is important to operational safety. Additionally, removing accumulations of residue in the pipelines will increase flow volume, operating efficiency, and will minimize the possibility of product contamination. The necessity to clean these process pipelines varies from desirable to imperative, and the frequency of cleaning may range from weekly to annually or less often. Even though flanged joints are used to connect sections of pipelines that convey hazardous materials, there is a slight risk of initiating the product when disassembling these connections to gain access to the interior for cleaning the sections. Circulating a cleaning fluid, or flushing these pipelines with water or fluid is often not effective in removing residual material. The r i s k s can be s u b s t a n t i a l l y reduced and residual material can be e f f e c t i v e l y removed by a method used at an ordnance plant which was placed i n an inactive status. After shutdown, thousands of feet of product lines were found to contain hazardous accumulations of residual product, and were thoroughly cleaned i n a f r a c t i o n of the time i t would have taken to dismantle these p i p e l i n e s and clean them by sections. A d d i t i o n a l l y , the r i s k of dismantling was p r a c t i c a l l y eliminated. Cleaning waterlines and fuel pipelines with pipe pigs has been an acceptable practice for many years. However, cleaning pipelines that conveyed explosives with a pipe pig i s innovative, and proved to be very e f f e c t i v e and economical. Many v a r i e t i e s of pigs are a v a i l a b l e , some of which are quite sophisticated. However, very simple pigs are s u f f i c i e n t for most pipe cleaning operations i n the explosives industry.

0097-6156/87/0345-0300$06.00/0 © 1987 American Chemical Society

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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A system can e a s i l y be navigated by these pigs, which are prop e l l e d h y d r a u l i c a l l y , at pressures usually substantially less than operating pressures of the system. The pig c o l l e c t s debris and pushes i t out of the system and also puts into suspension, material that can be combined into the flow that i s propelling the p i g . Pigs may be obtained that are made of metal, rubber or urethanes, or i n combination of these materials. The type chosen for use w i l l depend on i t s compatibility with the product i n the pipel i n e and i t s d u r a b i l i t y . Simply flushing a system, even with f u l l bore flow, and at maximum v e l o c i t y , i s only marginally successful and an unacceptable way to clean many of the pipeline systems i n the explosives industry. The carrying a b i l i t y of the f l u i d can be r e l i e d upon only i f the flow can keep everything i n suspension or moving. But simple flow cannot loosen and remove encrustations or tuberculation that may be i n residence, and that contribute to the p o s s i b i l i t y of propagation, contamination, or decrease pig i s highly successfu Pipe pigs can be obtained that negotiate turns and pass through f u l l y opened valves, which eliminates the need to dismantle the pipel i n e at these locations. Polyurethane foam pipeline pigs, which were used at the ordnance plant, can be obtained i n diameters from 1/2 to 108 inches i n increments of 1/8 inch. The most common sizes used at this plant were 8", 10". 12" and 16". The pipes to be cleaned may be of almost any length. A means of ingress and egress for the pig must be provided, a l l valves i n the l i n e to be cleaned must be f u l l y open. (Valves i n any branch l i n e should be kept closed, to insure the p i g follows the path of least resistance - the main l i n e . ) Using a p i g approximately 1/4 - 1/2 inch larger i n diameter than the pipe to be cleaned, the p i g i s inserted into a larger spool attached to the ingress end of the p i p e l i n e . The spool end would then be capped with a plate that has been provided with a f i t t i n g to attach the hydraulic l i n e to be used to propel the pig through the pipeline (Figure The ordnance plant used a s p e c i a l l y fabricated tapered pipe section that could be attached to the pipeline and be removed after use (Figure 2). Pipelines that require frequent cleaning can be provided with a permanently i n s t a l l e d "y" section at the ingress end of the pipe for launching the p i g (Figure 3 ) . The speed of the pig i s controlled by regulating the discharge pressure of the hydraulic f l u i d pressure l i n e . This can be determined and monitored by i n s t a l l i n g a pressure gauge on the system. The most e f f e c t i v e cleaning i s obtained when the linear speed of the p i g i n the pipeline i s controlled within 1 to 5 fps (0.3 to 1.5 m/g). At the egress (discharge) end of the p i p e l i n e , provisions should be made to handle the f l u i d and product being emitted. Explosive products that are insoluble i n the hydraulic f l u i d being used can be discharged into a sump where they can be removed l a t e r and destroyed, or through a fine mesh screen that w i l l r e t a i n the explosive products for l a t e r d i s p o s i t i o n . Soluble products w i l l require c o l l e c t i o n and d i s p o s i t i o n of both the product and the hydraulic f l u i d .

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Figure 1. Straight Line Spool Launcher.

Figure 2. Straight Line Tapered Launcher.

Figure 3. Permanently Installed "Y" Launcher.

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

21.

WHEELER

303

Cleaning Process Lines in the Explosives Industry

It may be desirable to f i r s t clean the pipeline with a polyurethane foam swab. This material can be purchased commercially either i n s p e c i f i c cut s i z e s , or i n bulk, which can be cut to the desired s i z e . Swabs w i l l e f f e c t i v e l y remove soft scales and loose material. Their method of use i s i d e n t i c a l to that of the pig* While cleaning the p i p e l i n e , the swab or p i g may encounter a heavy build-up of encrustation, and i t s progress be interrupted. This would be evidenced by an increase on the pressure gauge. In most cases the swab or pig w i l l progress past the interuption and regain i t s normal progression. However, i f i t d i d not, and the pressure continued to r i s e without f l u c t u a t i o n , the hydraulic pressure should be allowed to drop and then the p i p e l i n e re-pressurized i n an attempt to force the p i g past the obstacle. In the worst case, where the p i g or swab became lodged, i t would be necessary to reverse the flow by applying hydraulic pressure on the egress end of the p i p e l i n e . Before adopting t h i pipelines were chosen f o pig method would s a t i s f a c t o r i l y clean these contaminated pipes. One half the sections were cleaned by t h i s method and the other half was thoroughly flushed with water. They were allowed to dry and then were subjected to i n i t i a t i o n by f i r e s . The sections that had been flushed with water ignited and burned vigorously. The sections that had been subjected to cleaning with the swab and p i g had no product remaining that would support combustion. In keeping with the cardinal p r i n c i p a l of safety i n the explosives industry, cleaning product pipelines by the p i g method exposes personnel to the least amount of hazardous material f o r the shortest period of time and reduces p o t e n t i a l l y hazardous disassembly operations to the minimum. Every explosive operation that requires conveying hazardous material by enclosed pipelines should be considered a candidate for cleaning the pipes by t h i s method.

RECEIVED March 6,1987

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Author Index Aikman, Loy M , 152 Baker, W. E., 2 Cohen, Frances H., 224 Collins, George E., Jr., 212 Diercks, Β. V., 286 Fadorsen, Gary Α., 200 Frauenthal, Max, 152 Garcia, David, 152 Herrera, W. R. 147 Hokenson, James Janski, Joe G., 15 Klapmeier, Kenneth M , 183 LaHoud, Paul M , 241 Maurits, William J., 234 Mclntyre, F. L., 152

McKinney, Harold D., 168 Meyers, Gerald E., 107,130 Petino, George, 269 Powell, Joseph G., Jr., 58 Proper, Kenneth W., 254 Seals, William O., 269 Shook, Thomas E., 152 Sime, Richard W., 68 Stinger Bernhard G. 183

Vargas, L . M , 147 Wheeler, Roy W., 300 Wight, Richard L., 85 Zaugg, Mark M , 294

Affiliation Index N A S A National Space Technology Laboratories, 152 Naval Civil Engineering Laboratory, 92,107,130 Oneil M Banks, 224 Pine Bluff Arsenal, 152,168 Southwest Research Institute, 147,269 Tooele Army Depot, 294 U.S. Army Corps of Engineers, 85,241 U.S. Army Defense Ammunition Center & School, 254 U.S. Naval Surface Weapons Center, 58 Wilfred Baker, 2

Army Research, Development and Engineering Center, 269 Automatic Sprinkler Corporation of America, 200 Black & Veatch, Engineers-Architects, 68 Chemical Research Development and Engineering Center, 212 Department of Army, 234 Detector Electronics Corporation, 183 Hazards Research Corporation, 269 Morton Thiokol, 286

Subject Index A Accident probability design goals, U.S. Army production base modernization program, 48/ Accumulator, white phosphorus filling facilities, 178

Accuracy, volumetric filling of white phosphorus munitions, 171,173-174/ Air, ionized—See Ionized air Air blast waves, description, 3 Air locks biocontainment laboratories, 232

306

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Author Index Aikman, Loy M , 152 Baker, W. E., 2 Cohen, Frances H., 224 Collins, George E., Jr., 212 Diercks, Β. V., 286 Fadorsen, Gary Α., 200 Frauenthal, Max, 152 Garcia, David, 152 Herrera, W. R. 147 Hokenson, James Janski, Joe G., 15 Klapmeier, Kenneth M , 183 LaHoud, Paul M , 241 Maurits, William J., 234 Mclntyre, F. L., 152

McKinney, Harold D., 168 Meyers, Gerald E., 107,130 Petino, George, 269 Powell, Joseph G., Jr., 58 Proper, Kenneth W., 254 Seals, William O., 269 Shook, Thomas E., 152 Sime, Richard W., 68 Stinger Bernhard G. 183

Vargas, L . M , 147 Wheeler, Roy W., 300 Wight, Richard L., 85 Zaugg, Mark M , 294

Affiliation Index N A S A National Space Technology Laboratories, 152 Naval Civil Engineering Laboratory, 92,107,130 Oneil M Banks, 224 Pine Bluff Arsenal, 152,168 Southwest Research Institute, 147,269 Tooele Army Depot, 294 U.S. Army Corps of Engineers, 85,241 U.S. Army Defense Ammunition Center & School, 254 U.S. Naval Surface Weapons Center, 58 Wilfred Baker, 2

Army Research, Development and Engineering Center, 269 Automatic Sprinkler Corporation of America, 200 Black & Veatch, Engineers-Architects, 68 Chemical Research Development and Engineering Center, 212 Department of Army, 234 Detector Electronics Corporation, 183 Hazards Research Corporation, 269 Morton Thiokol, 286

Subject Index A Accident probability design goals, U.S. Army production base modernization program, 48/ Accumulator, white phosphorus filling facilities, 178

Accuracy, volumetric filling of white phosphorus munitions, 171,173-174/ Air, ionized—See Ionized air Air blast waves, description, 3 Air locks biocontainment laboratories, 232

306

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

INDEX

307

Air locks—Continued toxic laboratories, 235 Air shock parameters, prediction of blast overpressure outputs, 30-32 Alarm pull boxes, toxic laboratories, 235 Alarm systems, toxic laboratories, 238-239 Ammunition disposal, toxic chemical, design of blast-containment rooms, 241-250 Ammunition peculiar equipment definition, 294 design and use to protect workers, 294-303 Ammunition plants, Army—See Army ammunition plants Animal research laboratories, design considerations, 228-230 Annealed glass, description, 108 Architectural standard details for Army ammunition plants, 68-84 Areal density, hazardous fragment definition, 64 Army ammunition plants architectural standard details, 68-84 electrostatic studies, 269-285 Army Materiel Command, definitions and classification of hazardous electrical environments, 259 Asset protection, operational shield, 295 Automatic filling station, white phosphorus filling facilities, 175 Avalanche effect, U V fire detectors, 184

Β Barricades—See Operational shields Barriers biocontainment laboratories, 231-232 description, 92 Beads, window frames, design criteria, 109 Beams, blast-loaded, elastic-plastic solution for bending, 23,25/ Behavioral modes, reinforced concrete, 93-98 Bending element, reinforced concrete, deflection, 95/ Binders, fluidized-bed granulators, 157,160-162 Biocontainment laboratories, design requirements, 231-232 Biodynamics of blasts, 48,50-54 Biological safety cabinets, toxic laboratories, 237 Biosafety levels, description, 231 Bite requirements, window frames, 122/, 123/, 143 Blast attention, operational shields, 295 Blast biodynamics, 48,50-54 Blast-containment rooms, design for toxic chemical ammunition disposal, 241-250

Blast-hardened structures, use of reinforced concrete, 92-106 Blast injuries, humans, 48,50-54 Blast load(s) considerations for concrete reinforcement, 101,102/ effect of duration on blast capacity of polycarbonate glazing, 142 modeling, polycarbonate glazing, 133 Blast-loaded elastic oscillator, shock response, 18-19,20/ Blast loading, repeated, schematic, 34/ Blast overpressure outputs, prediction, 30-39 Blast pressure, effects on structures and people, 2-54 Blast pressure capacities

Blast-resistant glazing guidelines, 107-129 polycarbonate, design criteria, 130-144 Blast valves, ventilation system blast protection, 246,248/ Blast waves damage mechanisms, 18-30 diffraction, 11,13-14,16/ free-field, 2-7 idealized profile, 4/ prediction of properties, 6-7 properties, 3-6 reflection, 8-11 scaling laws, 6-7 spalling, 23,25/,26-29 Blender bucket, use in preparing flare composition, 290,292/ Blowout walls and roofs, explosives facilities, 40 Breeching, reinforced concrete, 99,105 Brittle behavior, reinforced concrete, 99 Building codes, design of research laboratories, 225-226 Burster casing station, white phosphorus filling facilities, 178

C Cadmium selenide sensing element, IR fire detectors, 188 Calibrations, electric field meter, 273 Catastrophic hazard, definition, 46/ Catch basin leading to a toxic sump, fume hoods, 236 Ceiling design considerations, Army ammunition plants, 71,73,74/ Ceiling shock loads, explosions in enclosures, 32

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

308

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Certification, intrinsically safe electrical circuits, 263-264 Chapman-Jouget pressures, definition, 3 Charge density measurements, Army ammunition plants, 273-283 Charge density meter, transfer function, 280 Charge levels, Army ammunition plants, 276,283 Charge neutralization—See Static charge neutralization Charged pellet, voltage versus time profile, 289/ Charts glazing design, UV-stabilized polycarbonate, 133-142 glazing survival of prescribed blast loads, 110-121 Chemical Research, Development Engineering Center, requirement system safety, 212 Chemical surety materiel, definition, 212-213 Chemical surety materiel laboratories, systematic approach for safely designing, 212-223 Chemical warfare munitions containment, 35,39 destruction of U.S. stockpile, 241-250 storage at U.S. Army installations, 241 Cleaning of process lines, explosives industry, 300-303 Clothing, protective, toxic chemical and explosives facilities, 151 Coating of surfaces, blast-containment rooms, 246,249/,250 Codes, building, design of research laboratories, 225-226 Coefficients for frame loading, 127/, 143/ Collection systems, dust, Army ammunition plants, 274,275/,280,282/ Collective risk, definition, 47 Combustible materials containment rooms, effect on gas pressure during an explosion, 246,249/,250 effective charge weight multiplier, 20/ storage in research laboratories, 230 Combustion heats, explosives, 296/ Communications, toxic laboratories, 238 Compressed gas cylinders, placement in research laboratories, 230,238 Compression failure, reinforced concrete, 99 Concentration measurements, dust, Army ammunition plants, 270,272/,274,280 Concrete, reinforced—See Reinforced concrete Consolidation press development of static charges, 286-287 schematic, 288/

Constant-volume ventilation systems, research laboratories, 226 Construction materials statement regarding use in Army ammunition plants, 70 toxic laboratories, 238 Containment cabinets, primary, toxic laboratories, 235-237 Containment structural concepts, explosives, 35,39-40 Contamination, white phosphorus munitions, 168-169 Cooling, fluidized-bed granulators, 161 Corner concentrated load, window frames, produced by design load, 127,143 Critical hazard, definition, 46/ Critical loading density effect on mass

magazine, 90/ trial, reinforced concrete, 101 Cube-root scaling law, blast waves, 6-7 Current, U V fire detectors, 184 Cylinder, Gurney equation, 61 Cylinder development, volumetric filling of white phosphorus munitions, 171,172/ Cylindrical structures, construction for containment, 39

D Damage categories, explosions near reinforced concrete walls, 28/ Damage mechanisms blast waves, 18-30 fire in a facility, 149 Damage prevention, operational shield, 295 Deflection allowable, determination for reinforced concrete, 103-104 bending element of reinforced concrete, 95/ maximum, determination for reinforced concrete, 103 maximum allowable limits for window frames, 123 Deflection-resistance curve, flexural response of concrete elements, 94/ Deflection-resistance functions, reinforced concrete, 96,98/, 101,103 Degradation, environmental, polycarbonate, 131 Deluge fire suppression, ultra-high-speed, 200-210 Deluge systems comparison of features, 208-209 piping configurations, 200-204

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

INDEX Demilitarization chemical munitions,schematic, 243/ definition, 242 use of intrinsically safe electrical circuits, 266 Density, blast waves, 5-6 Department of Defense Explosives Safety Board, fragment hazard criteria, 64-65 safety classification tests for pyrotechnic materials, 153/ Design charts, glazing, UV-stabilized polycarbonate, 133-142 Design considerations research laboratories, 224-233 toxic chemical and explosives facilities, 148-151 toxic laboratories, 234-239 white phosphorus filling facilities, 171,175-176 Design criteria glazing, 108-121 magazines, 86 polycarbonate blast-resistant glazing, 130-144 window frames, 109,122-129 Destruction of chemical warfare munitions containment requirements, 242,244-250 functional process requirements, 242,243/ Detection systems, high-speed, design and use for explosives operations, 183-199 Detection time, U V and IR fire detection systems, 195,198 Deterministic methods, risk assessment, 46 Detonation of energetic materials, fragmentation effects, 58-65 Detonation velocities, description, 2-3 Detonation wave, description, 2-3 Detonator modules, use with U V and IR fire detection systems, 192-195 Diagonal tension, reinforced concrete, 104 Diffraction, blast waves, 11,13-15,16/ Diffraction loading, structure being struck by a blast wave, 13 Digital timers, use to determine response times of deluge systems, 206 Dip fill method, white phosphorus munitions, 168,170/ Direct shear, reinforced concrete, 105 Directional venting, explosives facilities, 40-45 Disinfection systems, biocontainment laboratories, 232 Documentation, operational shield tests, 299 Door(s) design for blast-containment rooms, 246 equipment, Army ammunition plants, 75/ escape, Army ammunition plants, 76-80/

309 Door latch bar, Army ammunition plants, 77-79/ Door sill, Army ammunition plants, 80/ Drag coefficients, fragments, 60-61 Drag specific impulse, blast waves, 5 Drains fume hoods, 237 toxic laboratories, 235 Drying fluidized-bed granulators, 161 pyrotechnic materials in mixers, 155-158 Duct velocity and flow rate, dust, Army ammunition plants, 270,271/,276,279 Ductile behavior, reinforced concrete, 93-98 Ductwork, exhaust, chemical surety material laboratories, 223 Dust

concentration measurements, 270-274,280 duct velocity and flow rate, 270-271,276,279 evaluation, 269-270 explosion potential, 269-285 explosives facilities, hazards, 258-259 Dynamic increase factors, reinforced concrete, 100/ Dynamic pressure blast waves, 5-6 produced by a maximum credible incident, 296 Dynamic strength reinforced concrete, 99-100 steel reinforcing, 99-100 Ε Ear damage to humans, caused by blast waves, 52/ Earth-backed bay, venting of explosives facilities, 40-43 Edge requirements, window frames, 122/, 123/ Elastic dilatational wave speed, definition, 26 Electric field meter, calibrations, 273 Electrical circuits, intrinsically safe—See Intrinsically safe electrical circuits Electrical installations, explosion-proof, 255 Electron flow, U V fire detectors, 184 Electrostatic charges generation, 165-166,287 removal from a surface, 287 Electrostatic instrumentation, to determine dust explosion potential, 273 Electrostatic studies, Army ammunition plants, 269-285

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

310

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Emergency stations, toxic laboratories, 235 Enclosed areas, use of IR fire detectors, 192 Energetic capacity, pyrotechnic materials, 153 Energetic materials detonation, fragmentation effects, 58-65 exothermic decomposition, 150 Energy flux density, blast waves, 5 Energy levels, Army ammunition plants, 276,283 Escape chute, Army ammunition plants, 82/ Escape door, reinforced plastic, Army ammunition plants, 76-80/ European Committee for Electrotechnical Standardization, standard for intrinsically safe electrical circuits, 256 Exhaust ductwork, chemical suret laboratories, 223 Exhaust motors, fume hoods, placement, 228,236 Exhaust systems chemical surety materiel laboratories, 222-223 fume hoods, 227-228 toxic laboratories, 234-235 Exits Army ammunition plants, 73,75-76/ research laboratories, 230 toxic laboratories, 235 Explosions caused by vapors or dust, 258-259 in enclosures gas pressures, 15-18,20/ shock response versus quasi-static response, 26,30 near reinforced concrete walls, damage categories, 28/ Explosives cooling and dispersion with water, 205 Gurney constants, 61/ hazard class and division designation, 154/ heats of combustion, 296/ Explosives facilities design considerations, 148-151 high-speed fire detection systems, 183-199 ultra-high-speed fire suppression, 200-210 Explosives industry, cleaning of process lines, 300-303 Explosives Safety Board, Department of Defense, fragment hazard criteria, 64-65 Explosives storage structures—See Magazines Exterior wall at concrete floor slab, Army ammunition plants, 72/

Exterior wall—Continued at second floor and roof, Army ammunition plants, 74/ Extrusion processes in explosives facilities, use of fire detection systems, 206 Eye wash stations research laboratories, 230-231 toxic laboratories, 235

F Face requirements, window frames, 122/, 123/ Face velocities, fume hoods, 227,236 Face wash stations, research laboratories, 230-231

description, 212 Factory mutual research, certification of intrinsically safe electrical circuits, 263 Failure modes, reinforced concrete, 99 False-alarm sources IRfire detectors, 191 U V fire detectors, 187-188 Fasteners, maximum allowable limits for window frames, 123 Feed chutes, design for blast-containment rooms, 246 Fiberglass reinforced plastic chute, Army ammunition plants, 82/ Filling conveyor, white phosphorus filling facilities, 176 Filling nozzle, volumetric filling of white phosphorus munitions, 171,172/ Filling operations and facilities, white phosphorus munitions, 168-182 Filling station, automatic, white phosphorus filling facilities, 175 Filtration systems chemical surety materiel laboratories, 222-223 toxic laboratories, 237 Fire detection, red phosphorus smoke mix production, 166 Fire detection-suppression system, mixers for pyrotechnic materials, 155 Fire detection systems for explosives operations, requirements for good design, 198-199 Fire detectors IR, explosives operations, 188-193 U V , explosives operations, 184-188 Fire safety research laboratories, 230

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

311

INDEX

Fire safety—Continued toxic chemical and explosives facilities, 148-151 Fire severity parameters, to characterize real-world fires, 149-150 Fire testing, deluge systems, 206 Flame detectors, description, 183-184 Flammable materials, storage in research laboratories, 230 Flexural design, reinforced concrete, 100-104 Flexural response, concrete elements, resistance-deflection curve, 94/ Flexural stress, polycarbonate glazing, 131 Floor design considerations, Army ammunition plants, 70 Floor gutter design considerations, Army ammunition plants, 81,82/ Floor plan, toxic laboratories, 234-23 Fluidized-bed granulators, pyrotechnic materials, 157-165 Flushing of pipelines, to remove hazardous residues, 300 Fragment(s) confinement by operational shields, 295 drag coefficients, 60-61 hazard criteria, 64-65 hit probabilities, 64 penetration of reinforced concrete, 99,105-106 sizes, 63 velocities, 59-62 Fragmentation effects, detonation of energetic materials, 58-65 Fragmentation phenomenon, description, 58-59 Frames, window design criteria, 109,122-129 loading coefficients, 127/ polycarbonate glazing, 142-143 Free-field blast waves, 2-7 Fume hoods research laboratories, 227-228 toxic laboratories, 235-237 Functional process requirements, destruction of chemical warfare munitions, 242,243/ Furniture, requirements for research laboratories, 231

G Gas cylinders research laboratories, 230 toxic laboratories, 238 Gas impulse inside structure containing vent panel, 35,38/

Gas pressures containment during a munition disassembly explosion, 245 explosions in enclosures, 15-18,20/ prediction for explosions in enclosures, 32,35-39 Gaskets, window frames, design criteria, 109 Glass descriptions of various types, 108 tempered blast pressure capacities, 110-121 static design strength, 124-126/ Glazing blast-resistant—See Blast-resistant glazing polycarbonate—See Polycarbonate glazing Glazing setting, design criteria, 109,122/, 123

advantages of using fluidized-bed granulators, 162-163 flare composition, 290,292/ pyrotechnic materials in mixers, 155-158 Gravimetric sampling under isokinetic conditions, use to determine dust concentrations, 270 Ground-covered roofs, venting of explosives facilities, 40-43 Gurney constants, explosives, 61/ Gurney equation, prediction of fragment initial velocity, 61 Gutter design considerations, Army ammunition plants, 81,82/ H Handling procedures, remote, pyrotechnic materials, 152-166 Hardware considerations, Army ammunition plants, 73,76,82 Hazard analysis chemical surety materiel laboratories, 213-220 fluidized-bed granulators, 163 toxic chemical and explosives facilities, 149 Hazard probability ranking, qualitative, 47 Hazard severity catégories chemical surety materiel laboratories, 214 definitions, 46/ Hazard tracking log, chemical surety materiel laboratories, 218-219/,220 Hazardous environment, defining for explosives facilities, 257-260 Hazardous fragment areal density, definition, 64 Hazardous residues, removal from pipelines, 300-303

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

312

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Health requirements, research laboratories, 224-233 Heat flux, determination, 295 Heat of combustion, explosives, 296/ Heat of detonation, definition, 3 Height of fill production line, white phosphorus munitions, 168-169 Hexachloroethane smoke mix production, 165 High-speed detection systems, design and use for explosives operations, 183-199 Hit probabilities, ejected fragments, 64 Hoods, fume chemical surety materiel laboratories, 222 research laboratories, 227-228 toxic laboratories, 235-237 Hopkinson-Cranz scaling law, blast waves, 6-7,10/,30 Humans, blast injuries, 48,50-5 Hydraulic equipment, use in explosives facilities, 254-255 Hydrostatic pressure determination, 296 produced by a maximum credible incident, 296

International Electrotechnical Commission, standard for intrinsically safe electrical circuits, 256 Intrinsically safe electrical circuits applications, 265-266 availability, 265 benefits, 264 components and construction, 260 definition, 256-257 design based on type of hazardous environment, 259-260 evaluation, 257 history, 255-256 methods of using, 264-265 requirements, 263-264 standards, 256 i explosive facilities 254-266

Ionized air, use for static charge neutralization, 286-293 Ionizing air nozzles, neutralization of charged surfaces, 290,291/ Irregular fragments, drag coefficients, 60/ Isodamage, walls, 24/

I Illuminate, processing in Army ammunition plants, 276,278/ Impulse blast waves drag-specific, 5 reflected-specific, 8 incident positive phase, outside a suppressive shield, 45 versus pressure diagram, constant levels of building damage, 22/ Individual risk, definition, 47 Industrial safety provisions, ammunition peculiar equipment, 299 Inert gas cabinet system, white phosphorus filling facilities, 176 Infrared fire detectors, explosives operations, 188-193 Infrared flare consolidation press, use of ionized air for static charge neutralization, 290,291/ Initial velocity of a fragment, detonation of energetic materials, 59-62 Instrumentation, operational shield tests, 298/ Interference sources IR fire detectors, 191 U V fire detectors, 187-188 Interior surfaces of walls, roofs, and ceilings, design considerations for Army ammunition plants, 71,73,74/

L Laboratory chemical surety materiel, description, 213 definition, 225 design considerations, 224-239 protection against vapor chemical surety materiel exposure, 220-223 Lacing steel, use for concrete reinforcement, 96,97/ Latch bar, door, Army ammunition plants, 77-79/ Lateral load transmitted by a glass pane to a window frame, 127,128/ Lead conductive floor, Army ammunition plants, 82/ Lighting details, Army ammunition plants, 76/ Line shear, window frames, produced by design load, 123,127,142-143 Load criteria, blast-resistant glazing, 107-129 Loading applied by a pane to a frame, 144/ explosions in enclosures, 15-17 product, fluidized-bed granulators, 163-165 Lung damage to humans, caused by blast waves, 51/

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

313

INDEX

M Mach reflection, plane shock from a rigid wall, 9,12/ Magazines cross sections, 90/ design requirements, 86 explosives storage, 85-91 purpose, 85 security features, 89/ standardization, 86-91 structural features, 86,87/ threats to structure, 85 worst-case test condition, 88/ Magnesium powder-poly(tetrafluoroethylene) pellets, static charge generation, 286-287 Manifolded exhaust systems, fum Marginal hazard, definition, 46 Mass burning rate, effect of critical loading density, 150 Mass effects tests, pyrotechnic materials, 153-154 Materials specifications, white phosphorus filling facilities, 175 Materiel, chemical surety, safety criteria for laboratories, 212-223 Maximum credible incident creation in a simulated operational environment, 297 operational shields, 294-297 Melting processes in explosives facilities, use of fire detection systems, 206 Membrane resistance, tensile, reinforced concrete, 96,103-104 Microprocessors, use with U V fire detectors, 187 Mishap probability categories, chemical surety materiel laboratories, 214 Mixed-occupancy building, design of ventilation systems, 226-227 Mixers fluidized-bed granulators, 160-162 mixing, granulation, and vacuum drying of pyrotechnic powders, 155-158 safety classification for pyrotechnic materials, 154 Mixing procedures, remote, pyrotechnic materials, 152-166 Monolithic action between adjoining polycarbonated layers, 133 Mullions, use with window frames, 127,143 Multibase propellants, architectural standard details for manufacturing facilities, 68-84 Multiple debris missile impact simulation, determination of debris, 62

Munitions chemical warfare—See Chemical warfare munitions white phosphorus—See White phosphorus munitions Mustard blister agents, storage at U.S. Army installations, 241

Ν

National Electrical Code classification of hazardous environments, 258-259 introduction of intrinsically safe electrical circuits, 256 levels of hazard probability, 259

standard for intrinsically safe electrical circuits, 256 Negligible hazard, definition, 46/ Nerve agents, storage at U.S. Army installations, 241 Neutralization, static charge, use of ionized air, 286-293 Nitrocellulose, architectural standard details for manufacturing facilities, 68-84 Normal reflection, blast waves, 8-9 Number, fragment, detonation of energetic materials, 63-64

Ο

Oblique reflection, blast waves, 9,11,12/ Occupational Safety and Health Act, electrical equipment requirements for hazardous locations, 263 Omnidirectional venting, explosives facilities, 43-45 Operating parameters, mixers for pyrotechnic materials, 157,158/ Operation, white phosphorus filling facilities, 176-178 Operation time, U V and IR fire detection systems, 195,198 Operational shields design requirements, 295-297 standard governing design and testing, 294 testing, 297-299 Optical integrity test, U V fire detectors, 188,189/ Oscillator, linear, loaded by a blast wave, 18-19,20/ Overpressure, peak—See Peak overpressure

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

314

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Ρ Pane design theory, polycarbonate glazing, 131-133 Particle size distribution, pyrotechnic materials, fluidized-bed granulators, 162-165 Particle velocity, blast waves, 5-6 Peak applied force-total impulse diagram blast-loaded elastic oscillator, 21/ blast-loaded rigid plastic system, 21/ Peak blast pressure capacities polycarbonate glazing, 133-142 tempered glass panes, 110-121 Peak overpressure blast waves, 3 outside a suppressive shield, 45 Peak overpressure-specific impuls concept, damage mechanism waves, 18-25 Peak reflected overpressure, relation to peak side-on overpressure, 8,10/ Pellet, charged, voltage versus time profile, 289/ Pellet formation, development of static charges, 286-287 Penetrating flux, fires in facilities, 149-150 Penetration by fragments blast-containment rooms, 246 operational shields, 297 Personnel protection requirements, toxic chemical and explosives facilities, 151 Phosphoric acid, formation from white phosphorus, 168 Phosphorus red—See Red phosphorus white—See White phosphorus Phosphorus pentoxide, formation from white phosphorus, 168 Photography, use in operational shield tests, 299 Photons, U V fire detectors, 184 Physical separation, intrinsically safe electrical circuits, 261 Pigs, pipe—See Pipe pigs Pine Bluff Arsenal, volumetric filling of white phosphorus munitions, 168-182 Pipe pigs construction materials, 301 sizes, 301 speed through pipes, 301 use to clean pipelines in the explosives industry, 300-303 Pipeline cleaning, explosives industry, 300-303 Piping configuration rupture-disk deluge system, 202,203/

Piping configuration—Continued solenoid-actuated deluge system, 202,204/ squib-actuated deluge system, 200,201/ Plenum areas, surrounding blast-containment rooms, 245,247/ Pneumatic equipment, use in explosives facilities, 254-255 Poisson's ratio, polycarbonate, 131 Polycarbonate, characteristics, 131 Polycarbonate blast-resistant glazing design criteria, 130-144 frame requirements, 142-143 pane design theory, 131-133 Poly(tetrafluoroethylene)-magnesium powder pellets, static charge generation, 286-287 Polyurethane foam pipe pigs, sizes, 301

industry, 303 Poly(vinyl alcohol), use as a binder in fluidized-bed granulators, 161-162 Polyvinylpyrrolidone, use as a binder in fluidized-bed granulators, 161 Postfailure fragmentation, reinforced concrete, 99 Power, toxic laboratories, 239 Prediction of blast overpressure outputs, 30-39 Preliminary hazard analysis, chemical surety materiel laboratories, 214,216-217/,220 Preliminary hazard list, chemical surety materiel laboratories, 213 Pressing and pelletizing operations in explosives facilities, use of fire detection systems, 206 Pressure(s) blast—See Blast pressure explosions in enclosures, 15-18,20/ generated by an explosion, 295-297 prediction for explosions in enclosures, 32,35-39 Pressure containment munition disassembly explosion, 245 operational shields, 295-297 Pressure differential fluidized-bed granulators, 160 structure being struck by a blast wave, 11,13,14/ Primary containment cabinets, toxic laboratories, 235-237 Primary fragments, description, 58 Primate research laboratories, design considerations, 229 Probabilistic methods, risk assessment, 46 Probability, hit, ejected fragments, 64 Process line cleaning, explosives industry, 300-303

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

315

N I DEX Product loading, fluidized-bed granulators, 163-165 Programmable logic controller, white phosphorusfillingfacilities, 176,178 Propellants architectural standard details for manufacturing facilities, 68-84 cooling and dispersion with water, 205 exothermic decomposition, 150 Protection requirements for personnel, toxic chemical and explosives facilities, 151 Protective devices, intrinsically safe electrical circuits, 261 Purged and pressurized enclosures for electrical equipment, 255 Pyrotechnic materials exothermic decomposition, 150 fluidized-bed granulators, 157-16 general discussion, 152-154 mixing, granulation, and vacuum drying, 155-158 remote mixing and handling procedures, 152-166 safety classification in mixers, 154 smoke mix production, 165-166

Reinforced concrete behavioral modes, 93-98 blast-containment rooms, 244-245 blast-hardened structures, 92-106 damage caused by detonation of explosives charges, 28-29/ dynamic strength, 99-100 failure modes, 99 flexural design, 100-104 properties, 92-93 shear design, 104-106 static strength, 100 tensile membrane resistance, 96,103-104 Remote mixing and handling procedures, pyrotechnic materials, 152-166 Repair and reuse, blast-containment room after an explosion, 250

Residues, removal from pipelines, 300-303 Resistance-deflection curve, flexural response of concrete elements, 94/ Resistance-deflection functions, reinforced concrete, 96,98/101,103 Resistance function, polycarbonate glazing, 131-133 Response times deluge systems, determination, 206 Q UV and IRfiredetection systems, 192 Risk assessment Qualitative hazard probability ranking, 47 chemical surety materiel Quasi-static parameters, prediction of blast laboratories, 214,216-217/,220 overpressure outputs, 32,35-39 Swiss methods, 47-48,49/ Quasi-static pressure loading, explosions in toxic chemical and explosives enclosures, 15-17 facilities, 46,49,149 Quasi-static response versus shock response, Rodent research laboratories, design explosions in enclosures, 26,30 considerations, 229 Roof design considerations, Army ammunition R plants, 71,73,74/ Room changes of air per hour, requirements Radiation detector requirements, fire for research laboratories, 227 detection systems, 198 Room-shaped structures, construction for Range standards for fragment hazards, containment, 39 detonation of energetic materials, 65 Rupture-disk deluge system Rankine-Hugoniot equations, interrelation of description, 207 blast wave properties, 6 piping configuration, 202,203/ Rebound, consideration in designing blastresistant glazing, 127,129,143 S Recirculation of laboratory air, dangers, 227 Sachs's scaling law, blast waves, 7,30 Red phosphorus smoke mix Safety barriers, intrinsically safe production, 165-166 electrical circuits, 260-261,262/ Reflected specific impulse, blast waves, 8 Safety chute design considerations, Army Reflection, blast waves, 8-11 ammunition plants, 81 Regular oblique reflection, plane shock from Safety classification, pyrotechnic a rigid wall, 9,12/ materials, 153/, 154 Regulation considerations, design of research Safety design considerations, toxic chemical laboratories, 225-226 and explosives facilities, 148-151

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

316

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Safety provisions, ammunition peculiar equipment, 299 Safety requirements chemical surety materiel laboratories, 212-223 research laboratories, 224-233 Sampling, Army ammunition plants, 273-274,283-285 Scabbing, reinforced concrete, 99 Scaling laws, blast waves, 6-7 Sealants, window frames, design criteria, 109 Secondary barriers, biocontainment laboratories, 231-232 Secondary fragments description, 58 prediction of initial velocity, 62 Security features magazines, 89/ toxic laboratories, 239 Semitempered glass, description, 108 Sensitive materials processing, neutralization of static charges, 286-293 Sensors fluidized-bed granulators, 160-161,162/ IRfire detectors, 188 U V fire detectors, 184,186/ Shear reinforced concrete, 97/99,104-106 window frames, produced by design load, 123,127 Sheep research laboratories, design considerations, 228-229 Shelters, description, 92 Shields, operational—See Operational shields Shock front velocity, blast waves, 5-6 Shock loads, ceiling and wall, explosions in enclosures, 32,33-34/ Shock response blast-loaded elastic oscillator, 18-19,20/ versus quasi-static response, explosions in enclosures, 26,30 Shock strength, inverse, definition, 11 Showers research laboratories, 230-231 toxic laboratories, 235 Side-on overpressure, blast wave, 3,5 Sill, door, Army ammunition plants, 80/ Similitude analysis, gas pressures during explosions in enclosures, 17 Single-base propellants, architectural standard details for manufacturing facilities, 68-84 Single degree of freedom blast analysis, 133

Single degree of freedom spring-mass system, determination of deflection of reinforced concrete, 103 Siting criteria for thermal protection, toxic chemical and explosives facilities, 150 Size, fragment, detonation of energetic materials, 63 Slipstream, reflection of blast waves, 9 Slugs, fluidized-bed granulators, 163-165 Smoke mix production, pyrotechnic materials, 165-166 Solenoid-actuated deluge system description, 207 piping configuration, 202,204/ Spalling blast waves, 23,25/,26-29

Sphere, Gurney equation, 61 Spherical structures, construction for containment, 39 Spot-coverage detection, use of U V fire detectors, 187 Spraying, fluidized-bed granulators, 161 Sprinklers, research laboratories, 230 Squib-actuated deluge system description, 207 piping configuration, 200,201/ Stack heights, exhaust from fume hoods, 228 Standard details, architectural, Army ammunition plants, 68-84 Standardization, magazines, 86-91 Static charge neutralization, use of ionized air, 286-293 Static pressure, produced by cased charges, 296 Static strength reinforced concrete, 100 tempered glass, 124-126/ Steel, lacing, use for concrete reinforcement, 96,97/ Steel reinforcing, dynamic strength, 99-100 Sterilization, biocontainment laboratories, 232 Storage flammable-combustible materials, research laboratories, 230 wastes, toxic laboratories, 235,237-238 Stress, maximum allowable limits for window frames, 123 Stress wave reflection at a free surface of a solid, 23,25/26 Structural features, magazines, 86,87/ Sumps, toxic, requirements for toxic laboratories, 237

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

317

INDEX Support rotations, allowable, reinforced concrete, 104/ Suppressive shields, explosives facilities, 43-45 Surface finish materials, blast-containment rooms, 246,249/,250 Survival curves, blast injuries, 50-51/ Swiss risk assessment methods risk analysis, 48,49/ risk matrix, 47,49/ Τ

Team design of research laboratories, 223-224 Temperature requirements, intrinsically safe electrical circuits, 261 Tempered glass blast pressure capacities, 110-121 description, 108 static design strength, 124-126/ Tensile membrane resistance, reinforced concrete, 96,103-104 Tensile stress, structures struck by blast waves, 23,25/26 Testing, operational shields, 297-299 Thermal effects attenuation, operational shields, 295 Thermal exposure magnitude, prediction, 149-150 Thermal safety design considerations, toxic chemical and explosives facilities, 148-151 Thermally tempered glazing, peak blast overpressure capacities, 110-121/ Toxic chemical ammunition disposal, design of blast-containment rooms, 241-250 Toxic chemical facilities, design considerations, 148-151,234-239 Toxic sumps, requirements for toxic laboratories, 237 Tracking log, hazard, chemical surety materiel laboratories, 218-219/,220 Transfer hopper, use in preparing flare composition, 290,292/ Transverse pressure on an object during passage of a blast wave, 15,16/ Triple point, reflection of blast waves, 9

Ultraviolet fire detectors, explosives operations, 184-188 Ultraviolet-stabilized polycarbonate, glazing design charts, 133-142 Underwriters laboratories, certification of intrinsically safe electrical circuits, 263 V Vacuum exhaust systems, Army ammunition plants, 280,281/ Valves, blast, ventilation system blast protection, 246,248/ Vapor hazards, explosives facilities 258-259

Velocity, fragment, detonation of energetic materials, 59-62 Vent area ratios, suppressive shield structural configurations, 43,44/ Vent panel, gas impulse inside structure containing, 35,38/ Vented and unvented enclosures, gas pressures during explosions, 15-18,20/ Ventilation animal laboratories, 228-230 biocontainment laboratories, 232 chemical surety materiel laboratories, 222-223 explosives facilities, 40-45 research laboratories, 226-228 toxic laboratories, 234-235 Ventilation system blast protection during a munition disassembly explosion, 245-248 Video cameras use in operational shield tests, 299 use to determine response times of deluge systems, 206 Volumetric efficiency, blast-containment rooms, 244 Volumetricfilling,white phosphorus munitions, 169-182 W

Walls exterior at concretefloorslab, Army ammunition plants, 72/ Ultra-high-speed deluge systems, comparison at secondfloorand roof, Army of features, 208-209 ammunition plants, 74/ Ultra-high-speedfiresuppression isodamage, 24/ applications, 205 shock loads, explosions in explosives facilities, 200-210 enclosures, 32 justification, 202 U

In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

318

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES

Warning systems, chemical surety materiel laboratories, 221 Waste disposal, toxic laboratories, 237-238 Water, use for ultra-high-speed fire suppression, 202,205 Water delivery time, fire detection systems, 195,198 Water deluge systems activation by detonator modules, 192-195 red phosphorus smoke mix production, 166 Water supply requirements, fire detection systems, 198 Waves, blast—See Blast waves Weapon, explosively configured, 243/ Weighing processes in explosives facilities, use of fire detection systems Wet fill method, white phosphoru munitions, 168,170/

White phosphorus, properties and uses, 168 White phosphorus munitions contamination, 169-182 volumetric tilling, 169-182 Window(s), design considerations for Army ammunition plants, 73,75-76/ Window frames, design criteria, 109,122/, 123/ Wire-reinforced glass, description, 108 Wiring requirements, fire detection systems, 198 Wood cup detail, Army ammunition plants, 72/ Wood equipment door, Army ammunition plants, 75/ Wood frame construction, Army ammunition plants, 71,72/ Worst-case tests

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In Design Considerations for Toxic Chemical and Explosives Facilities; Scott, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.