The Atmospheric Environment: A Study of Comfort and Performance 9781442656406

Table of contents :
Acknowledgments
Preface
Contents
Tables
Illustrations
Introduction
I. The problem and its background
II. Methods
III. Results and conclusions
Appendices
Bibliography

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THE ATMOSPHERIC ENVIRONMENT A study of comfort and performance

UNIVERSITY OF TORONTO DEPARTMENT OF GEOGRAPHY RESEARCH PUBLICATIONS 1.

THE HYDROLOGIC CYCLE AND THE WISDOM OF GOD: A THEME IN GEOTELEOLOGY by Yi-Tuan

2.

RESIDENTIAL WATER DEMAND AND ECONOMIC DEVELOPMENT by Terence R. Lee

3.

'TOE LOCATION OF SERVICE TOWNS by John U. Marshall

4.

KANT'S CONCEPT OF GEOGRAPHY AND ITS RELATION TO RECENT GEOGRAPHICAL THOUGHT by J. A. May

5.

THE SOVIET WOOD-PROCESSING INDUSTRY: A LINEAR PROGRAMMING ANALYSIS OF THE ROLE OF TRANSPORTATION COSTS IN LOCATION AND FLOW PATTERNS by Brenton M. Barr

6.

THE HAZARDOUSNESS OF A PLACE: A REGIONAL ECOLOGY OF DAMAGING.EVENTS by Kenneth Hewitt and Ian Burton

7.

RESIDENTIAL WATER DEMAND: ALTERNATIVE CHOICES FOR MANAGEMENT by Angelo P. Grima

8.

THE ATMOSPHERIC ENVIRONMENT: A STUDY OF COMFORT AND PERFORMANCE by Andris Auliciems

9.

URBAN SYSTEMS DEVELOPMENT IN CENTRAL CANADA: SELECTED PAPERS edited by L. S. Bourne and R. D. MacKinnon

THE ATMOSPHERIC ENVIRONMENT A study of comfort and performance Andris Auliciems

Published for the University of Toronto Department of Geography by the University of Toronto Press

© University of Toronto Department of Geography Published by University of Toronto Press Toronto and Buffalo, 1972 Printed in Canada ISBN 0-8020-3291-5 Microfiche ISBN 0-8020-0238-2

To Maija

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Acknowledgments

This study would not have been possible without the cooperation of the headmasters, teachers, and especially pupils of a large number of schools. To them, and to the many individuals who contributed by advice, encouragement, and practical assistance, I express my gratitude. Particular thanks is due to Mr. M. Parry, Mr. R. Mead, and Dr. O.G. Edholm. Andris Auliciems Toronto December 1971

vii

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Preface It has become increasingly clear in recent years that climatology has to be brought much closer to man the consumer, and perhaps to man the animal. The study of climate in its own right needs no defenders, but as such it is in the domain of the physical scientist, chiefly the meteorologist. ClimateTs impact on man is something else. If it belongs anywhere, it belongs where human ecology is taught; and one of those places is in geography, Dr. Auliciems' own field of training. Bringing climatology closer to man means, in fact, bringing it back into the geography department, as well as some other places. The history of man-centered climatology is not very distinguished. For many years it consisted of taking from the meteorologist the latter!s prepared digests of statistics of the atmospheric parameters, and then of contemplating them in a sort of environmentalist haze. Climate in regional geography was a few paragraphs, tables, or charts of parameters having no discernible quantitative significance for human activity. It was easy, in such circumstances, to erect vast superstructures of speculation about the impact of climate on man, as did Ellesworth Huntington and Griffith Taylor. Writing of this sort was an exercise in the imagination rather than in scientific logic. After a while we lost interest, and with it a good deal of momentum. When environmental determinism went out nothing very exciting crept in to take its place. ix

But recently there has been an upswing. For one thing climatologists have discovered that they are not simply handmaidens of the weather forecasters. Climate, as a central element in natural ecosystems, is something different from statistics of weather events. It requires methods that the dynamic meteorologist has never heard of. Climatology has become an environmental science, no longer wholly physical, that knows how to take the living worth into account, as well as the atmosphere. For climate has come to be seen as the set of interactions between earth's surface and atmosphere that make up (and are to some extent made by) the environment of living communities. Only by wilful oversimplification can we see this as just a physical science. Andris Auliciems had the foresight to see, when he began his doctoral work at the University of Reading, that this view of climate must apply to man as well as to the biota. Climate touches man in many ways: for example in heavily influencing the plants, animals, soil and geomorphic processes that make up the rest of the natural environment; in thereby defining the set of economic activities he can carry on in any given place; and in affecting his personal comfort and performance. It was the third of these impacts that Dr. Auliciems decided to make his own. He briefed himself very thoroughly on what was known of the effects of climate on human physiology, and on the role of clothing in creating a sort of personal microclimate. He borrowed, and then refined, various testing techniques from the psychologists. Then he carried out various experiments on human comfort and performance, arriving at various interesting and unusually novel conclusions. The present monograph is the record of his work. Like so much of what happens on the margins of geography, it is multi-disciplinary in approach. Dr. Auliciems administers a multi-disciplinary teaching programme in this university. Clearly his research has equipped him to do this with authority and enthusiasm. Toronto, 1971

F. Kenneth Hare

X

Contents ACKNOWLEDGME NTS

vii

PREFACE by F. Kenneth Hare

ix

TABLES

I II III

xiii

ILLUSTRATIONS

xv

INTRODUCTION

3

THE PROBLEM AND ITS BACKGROUND

5

METHODS

46

RESULTS AND CONCLUSIONS

77

APPENDICES

140

BIBLIOGRAPHY

151

XI

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Tables

Table 1.

Correlation between thermal sensations and five thermal measures

18

Thermal comfort for light industrial workers (Bedford 1936)

21

Thermal confort for light industrial workers (Hickish 1955)

22

Thermal confort for children and adults in Canada (Partridge and MacLean 1935)

22

Thermal comfort for light industrial workers in different countries (Whydham 1964)

22

6.

Thermal conditions in Seymour's (1936) experiment

32

7.

Percentage of children and average percentage scores, showing gains and losses per week (Seymour 1936)

33

8.

Scale of thermal sensations

63

9.

Mean boysT group scores (MS), variance (VAR), Teq, and residuals (RES)

79

2. 3. 4. 5.

xiii

10.

Correlation of residuals with meteorological variables

80

11.

Atmospheric variables used in subsequent analysis

80

12.

Range of environmental conditions. Comfort assessments of boys 84

13.

Optimum winter confort conditions (from equations 2-13)

87

Comparison of regression constants and T-values (5% T significance = ± I. 99)

90

14. 15.

Comparison of regression coefficients and T-values of equations 21-33 (5% T significance = ± 1.99, 1%= ± 2 . 6 0 )

91

16.

Comparison of correlation coefficients (R)

94

17.

Monthly mean temperatures (°F)

97

18.

Thermal comfort optima (°F) of schoolchildren in winter: given external temperature (T )

100

19.

Pauli one-hour variables

108

20.

Optimum performance indoor temperatures Pauli one-hour test, ratio score

110

21.

Pauli half-hour variables

120

22.

Cancellation variables

122

23.

Optimum thermal conditions for mental work

134

xiv

Illustrations

Figure 1.

Physiological response to thermal stress

16

2.

Assmann Psychrometer

53

3.

Globe Thermometer

54

4.

Kata Thermometer

54

5.

Chart for estimation of Equivalent Temperature

59

6.

Chart for estimation of Corrected Effective (or Effective) Temperature. Normal scale

62

7.

Boys* mean comfort assessments against Teq

85

1

8.

Girls mean comfort assessments against Teq

85

9.

Flow diagram for boys1 comfort sample

88

10.

Flow diagram for girls' comfort sample

89

11.

Flow diagram for combined comfort sample

92

12.

Chart for estimation of optimum winter indoor air temperatures in schools xv

101

13.

Flow diagram for boysT sample Pauli One-Hour Ratio Score

106

14.

Flow diagram for combined sample Pauli OneHour Ratio Score

110

15.

T

Boys Pauli One-Hour Mean Ratio Scores against Teq

111

T

16.

Girls Pauli One-Hour Mean Ratio Scores against Teq

111

17.

Flow diagram for boys1 sample Pauli One-Hour Total Additions Score

113

18.

!

19. 20.

Flow diagram for girls sample Pauli One-Hour Total Additions Score

114

1

Flow diagram for girls sample Pauli Half-Hour Ratio Score

119

T

Flow diagram for boys sample Cancellation Total Score

xvi

127

THE ATMOSPHERIC ENVIRONMENT A study of comfort and performance

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Introduction Although non-pathological research into the effects of the atmospheric environment on man has gained momentum in recent years, interest has chiefly centred on the relatively stressful climatic conditions encountered in the newly developing areas of the world. It has been pointed out that man f s culture has far outpaced his biological evolution and that his biological fitness has become increasingly dependent upon his technological creations (Sargent 1964a). With rapid progress in the technology of microclimatic regulation and the future possibility of climatic control on a larger scale (Kahn and Wiener 1967), it would seem that more information is needed on the atmospheric influences affecting man, in order that he may capitalize on his innovations and achieve optimum atmospheric conditions . Lambert (1963) regards thermal comfort as the basic requirement of favourable atmospheric environments, which once achieved would also constitute the best working conditions. While this view may appear to be most reasonable, the relationships of comfort not only to work, but also to the thermal and meteorological environments, are by no means clear cut and opinions thereon, often based on mere conjecture, vary considerably. Similarly unclear is the association between work efficiency and the total atmospheric environment. The present study was undertaken to gain more insight into the influence of the atmospheric environment (meteoro3

logical and microclimatic) on man f s comfort and efficiency in the temperate climatic zone. Of necessity any such project must concentrate on only one section of the general population and this study relates in particular to secondary schoolchildren in Southern England. Interdisciplinary investigations such as this, are difficult to focus into a clear perspective within well defined fields of study, and the researcher must borrow techniques from various overlapping sciences. While the problem could be approached from several viewpoints, including those of psychology, physiology, or pedagogy, the essence of any findings should vary only in emphasis, depending upon the field of interest of the investigator. The problem here is approached from the viewpoint of the climatologist, and as such, it must be classed in the general field of Human Biometeorology, or more precisely, into what is defined by the International Society of Biometeorology as *f'Social Biometeorologyn (Tromp 1963a). The essential aspects of biometeorology are elucidated by Tromp (1964, p. 283): The science of biometeorology, dealing with the influence of weather and climate on the living organism, emphasises the continuous interaction between the internal physiological processes in man and the perpetually changing weather and climatic conditions of the atmosphere. As a result, those physiological characteristics known as "adaptational processes" do not represent adaptations to different static environments, but rather to a dynamic, continuously changing physiochemical atmospheric environment.

The unity of the atmosphere has been stressed by Page (1964, p. 75): ". ..the internal and external climates are interrelated and cannot be considered as independent variables. " However, all too frequently microclimatic investigations have totally disregarded the meteorological situation, perhaps partly due to the large number of variables and their attendant complexity. The problem has been greatly simplified by the rapid advances of electronic computer science within the last decade. An essential aim of the study, the attempt to demonstrate the indivisibility of the atmospheric environment in relation to comfort and efficiency, could only be established through the availability of these modern facilities in the processing of multi-variate data. 4

I The problem and its background Atmospheric environments and thermal comfort PHYSIOLOGICAL THERMOREGULATION Since the organism of man is homeothermic, normally its func tions are restricted to the narrow range of temperatures of approximately 97 to 100°F, or 36 to 38°C (Burton and Edholm 1955). This constancy of the internal environment is maintained by means of an equilibrium between metabolic heat production and its dissipation. Almost any particular state of the thermal balance can be represented by the equation introduced by Gagge (1936, p. 656): where M is the metabolic rate, S is the storage rate within the body, E is the rate of heat loss by evaporation, and R and C are the rates of gain or loss of heat by radiation and convection. The physiological processes by which the thermal balance is maintained in equilibrium are very complex, and while much knowledge has been accumulated, large gaps still exist in the under standing of the mechanisms involved (Hardy 1961; Hensel 1959; MacFarlane 1963; Magnes 1964). In conse5

quence, detailed interpretations of thermoregulatory mechanisms may vary with different authors, but in general certain major zones of physiologic response have been recognized. It is assumed that there exists a Mneutral point?T or "set pointTT which the organism attempts to maintain (Hardy 1961). The neutral point would be reached in a thermal environment such that the maintenance of the thermal equilibrium would require no particular action by the body. However, it has been pointed out that due to a time lag in response a completely neutral state is unlikely to be ever achieved (Bartley and Chute 1947; Bedford 1948; Rothman 1954), and instead of a specific temperature, various authors have referred to a zone of thermal neutrality within which only slight alterations in vasomotor tone are required (DuBois, Ebaugh, and Hardy 1952; Gagge, Winslow, and Herrington 1938; Hardy 1961; Ladell 1949). For men in the basal state (resting, nude, and in post-absorptive condition of digestion) this zone appears in still-air conditions to be between air temperatures of approximately 82-86°F, or 28-30°C, (Hardy 1961; Hardy and Soderstrom 1938), but for women the zone has been found to be somewhat wider (DuBois, Ebaugh, and Hardy 1952; Hardy and DuBois 1940). In response to slightly rising or falling temperatures, corresponding changes in vasodilatation take place. These increase or decrease the peripheral blood supply and its associated heat load, thus slightly modifying radiation and convection heat losses. A preliminary step taken by the body to conserve heat is that of progressive reduction of the peripheral blood supply by vasoconstriction (Barcroft and Edholm 1943). This action reduces the thermal gradient to the surroundings and causes the surface tissues to act as an insulating layer. Increased tissue insulation varies in different parts of the body, and, while head temperatures tend to remain relatively constant, insulation in the hands may greatly increase (Day 1949; Froese and Burton 1957). A very minor protective device is the formation of "goose flesh, " a rather "futile" (Cannon 1947) attempt in man to reduce convection heat losses by minimizing air movement next to the skin through the pilomotor action of skin roughening and hair erection. Postural changes may also accompany increasing cold stress with a contraction of the total surface to reduce radiating area (Bruce 1960; Leithead and Lind 1964). 6

With increased cold stress the organism must resort to metabolic heat increase to maintain the heat balance. Although the time of appearance of elevated metabolism is determined by the environmental temperature and the duration of exposure, 79-82°F (26-28°C) air temperature (Burton and Edholm 1955; Hardy, Milhorat, and DuBois 1941) has been recognized as the "critical temperature" at which this would initiate in basal man (Andersen and Hellstrom 1960; Enger 1957). Increased thermogenesis is recognised in two forms, non-shivering, or muscular tension (Burton and Edholm 1955; Davis and Johnston 1961; Hardy, Milhorat, and DuBois 1941; Hemingway and Stuart 1963) and subsequent shivering, during which groups of muscles discharge in accord. These processes release large amounts of chemical and mechanical energy (Bazett 1949; Burton and Edholm 1955) and consequently the zone of increased metabolic activity is relatively wide, with uncontrollable heat loss occurring only at approximately 50°F air temperature (Ladell 1949). In concurrence with the muscular activity, complex interactions take place between muscles, various organs, the central nervous system, and glands (Bruce 1960; Hardy 1961). In relatively warm conditions the body involuntarily tends to reduce heat production and facilitate heat exchange by increasing its surface area through the relaxation of muscles, assumption of a limp posture, and spreading of the limbs (Bazett 1949; Bruce 1960; Leithead and Lind 1964; Winslow and Herrington 1949). With increasing temperature, insensible perspiration—a continuous osmotic process under all temperatures—begins to accelerate (Bazett 1949; Kuno 1934; Ladell 1949). With environmental temperature such that bodily heat losses by radiation and convection fail to eliminate the metabolic heat load due to the reduced temperature gradient, equilibrium is maintained by evaporative heat losses. In this zone of evaporative regulation, active sweating shows rapid and progressive increases. Evaporative heat losses have been found to increase significantly in basal man above ambient temperatures of approximately 86-90°F, or 30-32°C (Gagge, Winslow, and Herrington 1938; Hardy and Soderstrom 1938; Kuno 1934; Rothman 1954; Woodcock 1964), with the threshold value for women being slightly higher (Hardy, et al. 1941; Sargent and Weinman 1964). It appears that equilibrium within this 7

zone is established sooner than in conditions of cold stress (Hardy 1961). The process of heat loss by radiation and convection requires a positive thermal gradient between the body and the environment, but above ambient temperature of approximately 98°F, or 36.5°C (the maximum possible skin temperature), the gradient and heat transfer is reversed. In such conditions the body can only resort to cooling by evaporation (Edholm 1954). In conditions hotter than those in which the skin becomes completely covered with sweat, the body possesses no further cooling mechanism. Heat gains exceed heat losses and a state of uncontrolled body temperature rise is reached (Brody 1945). BEHAVIOURAL THERMOREGULATION Apart from physiological regulation, man also adapts to the thermal environment by behavioural, conscious processes (Burton and Edholm 1955; Glaser 1963). This maybe manifest in the simple action of seeking less stressful surroundings, or in the complex technological creations of culture in the form of clothing and shelter. These provide what Burton and Edholm (1955) call a nprivate climate"—a modification of the existing natural environment. This affords protection against direct exposure to the hydrometeors, wind, solar radiation, and excess thermal gradients between the body and the environment. Moreover, the mechanical devices of dwellings enable the artificial adjustment of the atmospheric microclimate by heating, ventilation, and recently by air conditioning. Through the combined and individual action of both types of nprivate climate, " the range of climatic regions within which homeothermy is possible has been widely extended, and the achievement of environments producing least strain greatly facilitated. Clothing entraps pockets of "dead air" thus interposing an insulating layer between the body and the environment, thereby modifying radiation and convection heat losses. Depending upon the type and amount of clothing, the effect is one of widening and lowering the zone of vasomotor control in relation to ambient temperatures. For example, a comparison of nude and normally clothed men (in business suits) in a semi-reclining position, revealed that in an environment of equal temperatures of air and surroundings with 15 ft/min (8 cm/sec) air move8

ment, the zones of vasomotor regulation were 84-88°F (2931°C) and 77-84°F (25-29°C) air temperature respectively. It was also noted that in the nude state convection heat losses exceeded radiation losses, while the converse was true for clothed men (Gagge, Winslow, and Herrington 1938). While thermal neutrality can be maintained at much lower temperatures with increased amounts of clothing, the law of diminishing returns operates so that a limit of thickness is reached beyond which the increased insulation value becomes negligible (Burton and Edholm 1955; Winslow and Herrington 1949). In circumstances of intense radiation or high air temperatures, clothing may serve as a shielding device. It may also aid evaporation heat losses due to increased surface area and, given suitable texture, its "wick" action (Bruce 1960; Burton and Edholm 1955). Since the zone of vasomotor control shows large variation between individuals, the private climate of clothing permits quite simple adjustment according to individual needs. Although additional clothing may achieve thermal neutrality in relatively cold conditions, limitations are imposed not only by the inconvenience of weight and bulk, but also by the pressures of social customs which may run contrary to physiological needs. Indeed, customs may often exert the greater influence (Flugel 1940; Fourt and Harris 1949; Schreider 1963). Moreover from the point of view of hygiene, it would seem that light garments are more desirable. It has been pointed out by Burton and Edholm (1955) that clothing tends to produce even temperature distribution over the covered surfaces of the skin which is not in accord with the great variation of naked skin temperatures, nor with the distribution of thermal receptors in "normal" relations with environmental factors. "The integrated regulatory mechanism is evidently adjusted for dealing with environmental temperature in the TtemperateT range when light clothing only is worn" (Burton and Edholm 1955, p. 104). It is pertinent to note that with the progress of the technology of heating and ventilation, resulting in relatively easily achieved equable thermal conditions, the insulating importance of indoor garments has progressively decreased and people tend to wear less and lighter clothing. This trend is reflected particularly in the USA where over a period of only thirty years a rise in preferred temperatures of more than 5°F (3°C) air 9

temperature has been observed in successive surveys (Koch et al. 1960). The degree of privacy offered by the microclimate of dwellings may be questioned when considered in the light of the great physiological variability of individuals. Since most housing caters to a number of people, its thermal adjustment can at best serve only the majority of the occupants. Bedford (1936, p. 36) points out that As the environment becomes warmer or cooler than a certain desirable condition, an increasing number of persons tend to feel too warm or too cold. It is clearly desirable that conditions should be maintained which will be found comfortable by as many people as possible, and a narrow zone is desirable for practical purposes.

THERMAL COMFORT

Subjective Interpretation of Physiological Responses Although the actions of the complex physiological mechanisms of thermoregulation may overlap, broadly speaking the zone of vasomotor regulation, or zone of thermal neutrality, can be regarded as one of minor physiological adjustment (Bazett 1949; Bruce 1960), within which "the organism has no need to struggle against heat or cold" (Lambert 1963, p. 260). Hendler and Hardy (1958) found that an individual exposed for a prolonged period to a thermally neutral environment experiences slight and equally alternating sensations of warmth, coolness, and an absence of sensation. In these circumstances, the blood flow and skin temperatures fluctuated irregularly over the body surface, and slight environmental temperature rises caused slight vasodilatation and a reversal with small temperature falls. Within the zone of vasomotor regulation, thermal stimuli of low intensity are subjectively interpreted as varying degrees of comfort or pleasantness. Above and below, the individual perceives various sensations of discomfort (Bruce 1960; Lambert 1963). Macpherson (1962) points out that discomfort may be regarded as subjective impressions of the physiological strain imposed by the thermal environment. Webb (1962, p. 23) makes a similar point. 10

Thermal discomfort arises when the thermal senses are excited, whether by the temperature of the environment or by the internal processes of the body to the extent of becoming subjectively disagreeable. It is perhaps unimportant in itself, but it serves as a warning of associated objective physiological changes and events, which may be of considerable importance to the individual and to the society of which he is a part.

While recognising the complexity of not only physiological but also psychological factors involved in thermal sensations, Yaglou (1949, p. 282) defined comfortable conditions as those TT . . .under which a person can maintain a normal balance between production and loss of heat at normal body temperature and without sweating.Tt This range of thermal conditions inducing subjective comfort is referred to as the comfort zone. Desirability of Thermal Comfort In general, indoor environments requiring minimum action by the thermoregulatory mechanism, or subjectively those inducing maximum comfort, have been identified as optimum for the human habitat. Broadly, the argument presented in support could well be typified by Seyle's generalization (Culver 1959, p. 140): .. .adaptation to any stimulus is acquired at the cost of adaptation energy of which the organism possesses only a limited amount so that its use for adaptation to a certain stimulus of necessity involves a decrease for the use in resistance to other stimuli.

Blackfan and Yaglou (1933, p. 1191) categorically state: The essential factor in determining the fitness of air... is the maintenance of the physical conditions of air which favour the normal loss of body heat with the minimum strain on the part of the heat regulating mechanism of the body.

Bartley and Chute (1947, p. 99) regard comfort as an end in itself and point out that .. .since human beings are homeothermic, continuous active adjustment is necessary to maintain the required constancy of temperature. ... In the course of maintenance of temperature constancy, discomfort and fatigue often develop. 11

Herrington (1949, p. 263) states that it seems probable that thermal adaptations which are frequently required of human workers constitute a dishygienic factor of very considerable proportion.

And Markham (1947, p. 28) says that ... whilst the complicated human mechanism of heat elimination, adjusts itself to a considerable range of external temperature..., it adjusts at the expense of energy and efficiency.

Modern heating and ventilating practice appears to be mainly concerned with the attainment of maximum comfort, but it must be noted that the above arguments are largely theoretical and the benefits of thermal neutrality have practically no evidence in support. Indeed, from the point of view of hygiene, a number of authors have expressed disquiet at absolute thermal neutrality. While agreeing that comfort corresponds to the principle of least action, Missenard (1937a, p. 606) gives warning that the T f . . . equable warmth that one actually gets in houses is prejudicial to the health of the occupants.TT He argues that the flexibility of the heat regulating mechanism and the adaptation speed of the body may become atrophied and that its susceptibility to respiratory diseases may be increased. Burton and Edholm (1955, p. 243) suggest that the prolonged daily exposure to the warmth of houses may adversely affect the facility for cold acclimatization. Similar views were earlier held by Hill et al. (1913), who stressed the need for the variability of temperature and strongly emphasized the "invigorating" benefits of fresh air. Vernon (1923) and later Bedford and Warner (1939) pointed out that in practice, environmental warmth is only one aspect of comfort which cannot be divorced from the need of "invigorating and refreshing air" (p. 509). They originally specified the often reiterated (Bedford 1948, 1954, 1961; Bruce 1960; Dufton 1939; Manning 1965) optimum requirements for pleasant thermal environments and prescribed that temperatures should be as "cool as is compatible with comfort," implying that the ideal conditions may be those at the lower limit of the thermal comfort zone. Houghten and Yagloglou (1923b) also suggested that temperatures lower than those inducing maximum comfort should be adopted as

12

standard practice. They believed that the cooler conditions would be beneficial to health, comfort, and human activity. Assessment of Thermal Environments A basic problem in the prediction of subjective sensations of warmth is that of the estimation of the thermal microclimate. Any assessment of the environment must consider the factors that contribute to the rate of heat exchange, as illustrated by various generalized and specific equations experimentally derived for radiation (R), convection (C) and evaporation (E) heat losses. Generalized (Bruce 1960)

where 6 T and T

- Stefan-Boltzmann constant = absolute temperature of body and surroundings respectively e and e = emissivities of surface of body and of envi2 ronment A = effective radiating area of body K

where A K

\~> C

v t s t a

= exposed surface area of body = convection constant

= velocity of air = average surface temperature of body = air temperature

E = (W M )A(P - RH x P ) s a

where W = fraction of body area completely wet M = coefficient of heat transfer by evaporation (constant only for given air velocity and direction) A = total body area P = saturated vapour pressure of skin s

RH = relative humidity P = saturated vapour pressure at air temperaa ture 13

Specific

R = 5. 7 (t - t )

(Nelson et al. 1947)

C = 0.5\/v~(t - t ) s a

(Nelson et al. 1947)

E = 0.45v°- 63 (P - P ) (Clifford, Kerslake, and Waddell S a 1959) where R, C, E are heat losses of naked man (Kcal/m2 of body surface area/hour) v = velocity of air (ft/min) t = skin temperature (°C) t t

= globe thermometer temperature (° C) o

P P

= air temperature (°C) = vapour pressure of skin (mm Hg)

a

= vapour pressure of air (mm Hg)

It is apparent that four atmospheric parameters must be considered in the assessment of the thermal environment: air temperature, thermal radiation, rate of air movement, and humidity. Since the description of conditions in terms of only one of these factors would leave a wide margin for error, and in terms of all four individually would become too complex, various attempts have been made to devise methods which would enable measurement by a single value index. Macpherson (1962) recognises three types of indices: 1. Indices based on measurement of physical factors (dry and wet bulb temperatures, Kata cooling power, globe thermometer temperature, and equivalent temperature [Teq]). 2. Indices based on physiological strain (effective temperature [ET] and its derivatives, corrected effective temperature [GET], index of physiological effect, predicted four-hour sweat rate and wet-bulb-globe temperature). 3. Indices based on calculations of heat exchange (operative temperature, Belding and Hatch index, wind chill, and equivalent still-shade temperature). However, as pointed out by Yaglou (1949), there is no entirely satisfactory or complete method of estimating thermal conditions and the choice of index must fit the particular circumstances in question. A number of the above indices will be examined in greater detail in Part II. 14

Variability in Thermal Perception Apart from the problem of microclimatic assessment, prediction is further complicated by a host of factors which affect rates of metabolic heat production and rates of heat loss. These may differ in individual variability of basal metabolism, body build, state of nutrition, time of day, and state of acclimatization (Bruce 1960; Buskirk, Thompson, and Whedon 1963; Lambert 1963; Leithead and Lind 1964; Siple'l949; Winslow and Herrington 1949). Age and sex also appear to contribute greatly to variability and from figures of basal metabolic rates it can be seen that a progressive decrease occurs with age and that females have lower values than males (Bruce 1960). It has therefore been argued that thermal neutrality of children (Hill 1919; Seymour 1939) and of males (Black 1954) should be at lower temperatures. However, certain investigations based on subjective sensations have failed to reveal differences between children in comparison to adults (Partridge and Mac Lean 1935) and between the sexes (Yaglou and Messer 1941). Moreover, even the slightest muscular activity may lead to the generation of additional heat above that of the basal rate (Hardy 1961). This additional load needs to be dissipated and in effect, the position of thermal neutrality on the temperature scale is depressed as muscular activity increases. Assessment of Comfort Following the First World War research into the environments of factory workers, the formation of the Industrial Fatigue Research Board in 1918 gave stimulus to a large number of investigations into the thermal conditions in industry (Bedford 1923; Bedford and Angus 1923; Hambly and Bedford 1921; Vernon and Bedford 1923; Vernon, Bedford, and Warner 1926a, 1926b, 1930). At this time inquiries in the USA into air conditioning equipment led to the development of the first index of physiological effect, the Effective temperature" scale and the determination of the earliest comfort zones (Houghten and Yagloglou 1923a, 1924; Yaglou 1926; Yaglou and Drinker 1928; Yagloglou and Miller 1925). In the search for an objective method of assessing the thermal effect on comfort, results from a number of laboratory experiments showed strong association between skin temperatures—measured at various parts of the body—and comfort 15

Figure 1.

Physiological response to thermal stress

sensations (Gagge, Winslow, and Herrington 1938; Hardy and DuBois 1940; Ward 1930; Yaglou and Messer 1941). These results suggested that measurement of skin temperatures could be used as an index of comfort, but the more extensive field study of Bedford (1936) had indicated that subjective sensations were not only more easily ascertained, but were also more reliable. This finding received subsequent support (Glickman et al. 1950) and the more recent investigations into thermal requirements have almost invariably used the more practicable "comfort vote" technique in line with Bedford!s (1954, p. 88) common sense approach: M . . .the only way to find out how a man feels is to ask him, and the only sound way to establish comfort zones is by the careful questioning of large numbers of people. Tf The relationship between physiological responses and BedfordTs (1936) thermal scale is illustrated in Figure 1, which specifically refers to a resting nude male. After a preliminary investigation into ventilation, methods of heating and sensations of warmth of factory workers (Vernon, Bedford, and Warner 1926a), Bedford (1936) carried out the now classic winter field study into the thermal comfort of factory workers. He enlarged the previously used comfort scale and, by quantifying the subjective sensations of a large number of people, he was able to establish a linear scale and predict thermal comfort through regression analysis (see Part II). In subsequent years, linear scales have been used in many studies (Angus and Brown 1957; Black 1954; Davis, McMillan, and Webb 1965; Glickman et al. 1950; Hasan 1965; Hickish 1951, 1955; Koch et al. 1960; Munro and Chrenko 1949; Roberts 1959; Webb 1959). While the use of the quantified scale has enabled statistical treatment and fairly accurate prediction of mean sensations of groups, the prediction of an individuals comfort needs is highly unreliable. The correlation coefficients as found by Bedford (1936) and Hickish (1955) have been fairly low (Table 1), since in both studies over 2, 000 subjects participated from whom usually only one assessment was obtained. Some recent experiments at the Building Research Station have avoided this contamination and utilized responses from only single subjects thus obtaining much migher correlation (Davis, McMillan, and Webb 1965; Hasan 1965). These results have prompted the conclusion that n .. .the thermal ex17

TABLE 1. CORRELATION BETWEEN THERMAL SENSATIONS AND FIVE THERMAL MEASURES (7 POINT SCALE)

Thermal Sensation correlated with

Correlation Coefficient r* (Bedford 1936)

Correlation Coefficient r* (Hickish 1955)

air temperature (dry bulb)

.48

.38

globe temperature

.51

.37

equivalent temperature (Teq)

.52

.37

effective temperature (ET)

.48

-

-

.34

corrected effective temperature (GET) *signs ignored

periences. . .are closely correlated with environmental variation, to an extent previously unsuspected1' (Davis, McMillan, and Webb 1965, p. 7). However, in spite of Hasan!s (1965) criticism of Bedford1 s methods, it is obvious that the value of a single-subject experiment is restricted to the prediction of that person's sensations only, and the determination of practical optimum conditions must still resort to studies of large samples. The system of linear interpolation of thermal sensations, i.e., the sensation number really representing a rank position equidistantly spaced on temperature scales, oversimplifies the much more complex response to thermal stimulus (Chrenko 1955; Koch, Jennings, and Humphreys 1960; Webb 1962). Bedford (1936, p. 19) himself expressed caution: It is realized that any statistical treatment using such a numerical scale of comfort must be carried out with the full recognition that the scale is an arbitrary one. We cannot say that in one environment we feel twice as warm as in another, nor can it be assumed that the steps in a comfort scale necessarily indicate equal values of sensation.

However, on comparison of the results with a scale which assumed a normal distribution of sensations, he could find no significant differences. More recently Koch, Jennings, and Humphreys (1960, p. 275) found in support that n ... within the 18

comfort range, ranks may be treated as numbers without appreciable error." Unfortunately scales have varied greatly with investigators and the validity of comparison of the findings may be questioned. Webb (1962, p. 26) points out that "the wording of the scale is important and unconsidered variations are apt to make it less definite. TT More specifically, Hickish (1951) having used the words "warm" and TT cool TT found them to be ambiguous, yet these words appear in a number of later studies (Angus and Brown 1957; Black 1954; Givoni and Rim 1962; Koch, Jennings, and Humphreys 1960; Roberts 1959; Webb 1959). The resulting confusion is evident when it is realized that "warm" and "cool" signify undesirable sensations outside the comfort range to Hickish (1951), Roberts (1959), and Webb (1959), while to Black (1954) and under certain circumstances to Angus and Brown (1957) the same term describes conditions of comfort. Moreover, apart from the two parallel investigations of Bedford (1936) and Hickish (1955), and that on radiant heat by Munro and Chrenko (1949), all other studies in Britain have employed sensation scales differing greatly in wording and sensitivity, as indicated by the number of available responses. While the former three studies employed Bedford!s seven point scale, Black (1954) used only five points, Roberts (1959) and Hickish (1951) nine and Angus and Brown (1957) no less than fifteen. In view of the above shortcomings and the differing criteria in choice of comfort limits, comfort zones are hardly comparable and applicability is purely arbitrary. Of more value are the optimum figures, either obtained by regression analysis (Bedford 1936; Hickish 1955), mean (Black 1954; Roberts 1959), or modal values (Angus and Brown 1957). These values are more reliable since they tend to indicate thermal neutrality or the state of being "comfortable, " the latter term being identical in position and meaning in all studies. Comfort Zones In the early investigations on normally clothed American adults engaged in sedentary activities in winter (Houghten and Yagloglou 1923a and b) and summer (Yaglou and Drinker 1928), the investigators decided that the comfort zones lay between 19

60-74°F (15.5-23.5°C) ET and 64-79°F (18-26°C) ET respectively. The difference between the two zones has been largely explained by the lighter clothing worn in summer and seasonal acclimatization (Bedford 1936; Bruce 1960; Pepler 1964). These zones are wide because the figures chosen as comfortable in winter were those within which 50 per cent of the responses were "comfortably warm" to "comfortably cool." In summer, any temperature scoring one of these votes was considered as compatible with comfort requirements. Hickish (1955) analysing this winter zone, showed that temperatures required to produce 80 per cent comfort votes would lie between 65 and 69°F (18.5 and 20.5°C) ET and on the same basis he indicated that summer comfort would lie between 69-74°F (20. 5-23. 5°C) ET. In Great Britain, Bedford (1936) obtained some 3, 000 winter assessments and took the comfort zone to be those conditions which elicited at least 70 per cent votes claiming "comfortably warm, " "comfortable, " and "comfortably cool. " However, as pointed out by Hickish (1955), the zone actually included over 85 per cent comfort votes and could be extended upwards by some 4°F (2°C) and still retain 80 per cent of the sample. The zone is shown in Table 2 in which corrected effective temperature (GET) values as calculated by Hickish are included. Chrenko (1955) also suggested modifications and showed that 90 per cent of the sample would have felt comfortable if the range between 62 and 68°F air temperature had been chosen.

1 The effective temperature (ET) of an environment is the temperature of still air, saturated with water vapour which induces an equivalent sensation of warmth (Houghten and Yagloglou 1923a and b). As such, effective temperature is a sensory scale of warmth and not a temperature (Yaglou 1949), and Macpherson (1954) advised that it should not be referred to as "°F" nor should it be converted to a Centigrade scale. While this is valid on theoretical grounds, in practice the effective temperature scale is not reduced in significance or accuracy by a mathematical conversion and converted scales have been used by Pepler (1963), Buettner (1962), Lind (1964), Landsberg (1964), and even Yaglou himself (1949). Moreover, as illustrated by the cases of Terjung (1966, 1967) and Hentschel (1964), both of whom simply used °ET but implied different scales, it has become necessary to refer to "°F ET" and "°C ET" to avoid confusion. In the present report, indices have been converted and are given in terms of both, °F and °C in the text—whole degrees Fahrenheit being correct to the nearest half degree Centigrade.

20

TABLE 2. THERMAL COMFORT FOR LIGHT INDUSTRIAL WORKERS (BEDFORD 1936)

Thermal Measure °F

Upper to include 80 per cent comfort

Lower

Optimum

Upper

air temperature (dry bulb)

60

65 (64.7)

68

72

globe temperature

62

65 (65.1)

68

74

equivalent temperature (Teq)

58

62 (62.3)

66

70

effective temperature (ET)

57

61 (60.8)

63

66

corrected effective temperature (GET)

-

62 (61.7)

-

68

The winter comfort zone for office workers was investigated by Black (1954) who gained a huge number of assessments (over 10,000) from men and women, and found that 85 per cent of the occupants of offices considered themselves to be comfortable between 64 and 72°F (18 and 22°C) air temperature. She found some evidence that women preferred slightly higher temperatures (optimum 66.7°F, or 19.3°C) than men (optimum 65.9°F, or!8.8°C). Roberts (1959), satisfied with a 70 per cent comfort basis, determined the comfort zone for students as that between 60-76°F (15. 5-24. 5°C) dry bulb temperature—a range of 16°F (9°C). Angus and Brown (1957) investigating the atmospheric requirements in lecture halls, found that approximately 70°F (21°C) air temperature and 65°F (18.5°C) ET provided the greatest comfort for multi-racial audiences. The summer comfort zone in Great Britain for light industrial workers was established by HicMsh (1955), whose investigation was designed to parallel Bedford's (1936) winter study. Although no data were available for lower limits, the optimum and upper limits based on 80 per cent comfort are given in Table 3. Comparing with Bedford!s (1936) winter optimum values, these summer temperatures were 2.1°F (1.2°C) air temperature, 3.4°F(1.9°C) globe temperature, 3.6°F (2.0°C) Teq, and 2.7°F (1.5°C) ET higher. From theoretical considerations of metabolic rates, Billington (1953) suggested various comfort zones suitable for 21

TABLE 3. THERMAL COMFORT FOR LIGHT INDUSTRIAL WORKERS (HICKISH 1955) Thermal Measure °F

Optimum

Upper

air temperature

66.8

75

globe temperature

68.5

75

Teq

65.9

73

ET

62.9

70

GET

64.4

71

TABLE 4. THERMAL COMFORT FOR CHILDREN AND ADULTS IN CANADA (PARTRIDGE AND MacLEAN 1935) Lower

Optimum

Upper

Range

Subjects

°F, ET

°F, ET

°F, ET

°F, ET

Boys

56

66

73

17

Girls

58

67.5

72.5

14.5

Boys and Girls

57

66.5

73

16

Adults

61.5

66.5

71.5

10

TABLE 5. THERMAL COMFORT FOR LIGHT INDUSTRIAL WORKERS IN DIFFERENT COUNTRIES (WYDHAM 1964) Country

Upper Limit (°F ET)

United Kingdom

68

United States of America

76

Iran

77

India (Calcutta)

77

Singapore

78

Malaya

81

Australia (Weipa)

81.5

different types of work. For sedentary occupations he chose 65-72°F (18.5-22.0°C) ET and 68-76°F (20. 0-24.5°C) air temperature with approximately 20 ft/min (10 cm/sec) air movement and 50 per cent relative humidity, and for general office work 60-70°F (15. 5-21. 0°C) air temperature. 22

More than 30 years ago, Partridge and MacLean (1935) determined the comfort zone for Canadian children (aged 7-14 years) and compared this with adult requirements. The same 25 children, engaged in quiet activity, and 6 adults, were presented with a five point scale of thermal sensations. The summer comfort zone based on 600 observations and 50 per cent comfort showed the same 66-75°F (19-24°C) ET for boys, girls, and adults. In winter, 860 observations were obtained and the advocated zone appears in Table 4. Although the optimum values can be seen to be very nearly identical for all groups, the width of the zones is much greater for children, especially in the case of boys. In Great Britain no comparable investigation has been conducted into the comfort requirements of children, nor are the Canadian results applicable for British conditions since North American temperatures invariably show higher values. This has been explained by the differences in clothing, habits of heating and ventilation, and acclimatization (Bedford 1948; Page 1963). Some approximate upper limits in summer for light industrial workers are given by Wyndham (1964) in Table 5, and while the validity and reliability of these generalized figures must be viewed with certain suspicion, they serve as a rough illustration of the varying standards of comfort in different climatic and cultural areas. The differences are probably attributable to acclimatization and clothing (Macpherson 1964). Although the various recommended temperatures have been frequently quoted, particularly those of Bedford (1936), the legally required standards fall appreciably below those advocated by research workers. Manning (1965) has pointed out that in most modern buildings the standards prescribed in the UK Offices, Shops and Railway Premises Act (1963) are usually exceeded. However, the legal specifications are ambiguous and M . . .couched in very general terms n (Manning 1965, p. 62). An example of this is the statement: Effective provision shall be made for securing and maintaining a reasonable temperature... T f (Offices, Shops and Railway Premises Act 1963, p. 1187) which goes on to stipulate a minimum 16°C (60.8°F) air temperature for activities which do not require a severe physical effort. Specifying lowest permissable temperatures does not provide for optimum comfort conditions and the Insti23

tute of Heating and Ventilating Engineers (1959, p. 41) makes more specific recommendations with 65°F (18.5°C) as desirable for sedentary occupations. In support of this, a Second World War report is quoted: "For individuals doing light work in winter the air temperature should be nearly as possible 65°F. It is undesirable that it should fall below 60°F or rise above 68°F. " The origins of these figures can be seen as Bedford's (1936) optimum and comfort limits.

Comfort of Children Neither optimum values, nor comfort zones have been established in Great Britain for schoolchildren. This omission seems surprising when it is realized that Young people attending schools of various educational levels constitute in developed countries by far the largest population group doing very similar work in similar conditions. It consists of almost a fourth of the total population of the country. [Karvonen, Kokela, and Nord 1962, p. 471.]

It is interesting that Bedford (1936) did not discriminate between age groups and used "women and girls" as a homogeneous sample, and although no data were given, it may be assumed that some subjects at least would have been of school age. Recommendations for school temperatures, invariably lower than those recommended for adults, have been largely based on theoretical grounds as postulated by Hill (1919, p. 78): "The young have a greater metabolism per unit body surface than the older. " Seymour (1939, p. 26) argues that "children have a much smaller body surface from which to dissipate heat, usually eat more, in proportion to body weight than adults and.. .the heat produced by tissue activity is related to the food consumed. " In 1885 air temperatures of 56-60°F (13. 5-15. 5°C) were suggested for schools (Oliver 1957). Similar figures were advocated in 1929 (Clay 1929) and in 1936 (Board of Education 1936). The range was somewhat modified by Vernon, Bedford, and Warner (1930, p. 57) who advised that for manual tasks, writing and drawing, air temperatures should not be "much below 60°F and in -any case not below 55°F, whilst the air 24

should not have a cooling power much above 7 and in any case not above 8 or 9. " A cooling power (CP) of 7 indicates wind velocity of approximately 25-30 ft/min (13-15 cm/sec).2 Although the latter temperatures were based on measurement of skin temperatures of children at school and certain tasks of manual dexterity, the reasons for their choice are not altogether clear. Vernon, Bedford, and Warner (1930) found that with hand temperatures at 70°F (21°C) ".. .we felt so cold that it needed some mental effort in order to keep our attention on our work" (p. 23), but regarded hand temperatures at 75°F (24°C) "probably warm enough" (p. 30). This temperature was registered in only 50 per cent of the children at 60°F (15. 5°C) air temperature with 27 ft/min (14 cm/sec) air motion, but in these conditions the authors themselves indicated, by their subjective sensation votes, that they felt too cold. In the light of subsequent research, this is not surprising, since optimum comfort occurs at average skin temperature of the fingers at approximately 85°F, or 29.5°C (Bedford 1936; van Dilla, Day, and Siple 1949). There are other indications which suggest the insufficiency of the recommended temperatures. On examining records of absenteeism and estimating the prevalent temperatures in school, it was found that least absence was evident in schools with temperatures regularly exceeding 60°F (15.5°C), even though the others had temperatures only a few degrees below. It was pointed out that the thermal measurements were only rough estimates and Vernon and his colleagues agreed that no evidence existed to show ill effects of lower temperatures on health. The increased absenteeism was attributed to the restraining action of parents due to the low temperatures of schools. It must therefore be concluded that in schools with temperatures below 60°F (15.5°C), children had experienced such discomfort as to complain to their parents. ^The "cooling power" of atmosphere is determined by a Kata thermometer (described in detail in Part II) and indicates the rate of heat loss of the atmosphere. Cooling power is related to air temperature and air movement. Wind velocity may be calculated from the CP and dry bulb temperature by the general formula given by Bedford (1948):

where V is the air velocity, t is the air temperature, H is the cooling power, T, a, and b are constants depending upon the type of instruments used.

25

It is regrettable that no comfort votes were gained from the children in the study, but the results indicate that the skin temperature of adults appears to react similarly at the same temperature. The authors made no reference to higher metabolic rates but expressed surprise that "the hand temperature of the children was no higher than that of the investigators in spite of their acclimatization" (p. 60). From the point of view of thermal comfort, neither this nor the study of Partridge and MacLean (1935) revealed significant differences between the needs of adults and children. The latter investigation actually found that girls apparently preferred higher temperatures than the six adults participating in the experiment. In previous years (in the USA) Houghten and Yagloglou (1923b, p. 373) had recommended the 64. 5°F (18.1°C)ET optimum comfort line as equally suitable for ".. .schools, theatres, residences and other places where mental work and light activities are carried out. n Of interest are the recommended American comfort requirements, as quoted by Page (1963) which show school temperatures, 70-72°F (21-22°C) air temperature, actually higher than those in offices, 68-72°F (2022°C), while the comparative British standards (Institution of Heating and Ventilating Engineers 1959) are completely reversed with schools at 62°F (16.5°C) and offices 65°F (18.5°C) air temperature. On the basis of the work of Vernon, Bedford, and Warner (1930) and that of A.H. Seymour (1936), D.W. Seymour (1939) suggested 55. 3-57. 3°F (12. 9-14.1°C) Teq, or 58-60°F air temperature with CP of 8 (35-40 ft/min, 18-20 cm/sec air movement), as optimum for schools. In Postwar Building Studies Heating and Ventilating of Schools (Ministry of Works 1947) the importance of lowered temperatures for children, due to their higher metabolic rates, was again stressed and 5760°F (14.0-15.5°C) Teq with a minimum of 55°F (13°C) air temperature were advocated. In 1954, the air temperature prescribed in Statutory Instruments (Statutory Publications Office 1954) was somewhat higher at 62°F (16.5°C) at a height of 3 feet (92 cm), and the classrooms required six air changes per hour. The latter would presuppose air velocity of 20-40 ft/ min (10-20 cm/sec) which is regarded as tolerable for children who are unlikely to feel draughts up to 60 ft/min or 31 cm/sec (Godfrey and Cleary 1953). However, the origins of 26

the prescribed 62°F (16.5°C) are difficult to trace. The first reference to this temperature seems to occur in the Building Bulletin No. 2 (Ministry of Education 1950) which only refers to secondary schools. Further reference can be found in the Heating and Ventilation of Schools (Institution of Heating and Ventilating Engineers 1954) which states that 62°F (16.5°C) is also acceptable to primary schoolchildren, but no reasons are advanced for this particular temperature. It is also pertinent to note that this recommendation becomes questionable (Weston 1953, p. 491) when heating and ventilating engineers themselves can be found to debate not only the origins, but also the desirability of 62°F (16.5°C) air temperature. More disturbing still is the completely fallaceous argument presented by Weston (1953, p. 492) who explained that the reason for the reduced temperature could be found in the lower metabolic rate (!) of children. This of course is nonsense, but if so, children would require higher temperatures to maintain the thermal balance. Effect of External Meteorological Conditions While thermal comfort has been shown to be largely dependent on thermal levels, other atmospheric factors, apart from temperature acclimatization to prolonged exposure, have been ignored in comfort studies. However, Humphreys, Imalis, and Gutberlet (1946) recognised possible effects and kept their subjects in a control room prior to testing ... to eliminate the effect of varying exertion or weather en route to the laboratory, and thus to make sure that all the subjects were at equilibrium with a common environment. [P. 155.]

While recently Edholm (1966) has emphasized the need for further correlation between meteorological events and biological activity, Petersen suggested earlier (1938) that changes take place in skin blood vessel dilatation and constriction, muscular tone, and blood pressure levels in response to warm and cold air masses. Tromp (1964a) pointed out the probability that the hypothalamus, the extremely sensitive organ controlling central processes of thermoregulation (Benzinger 1962), may also regulate physiological responses to meteorological changes. The functions of the skin, lungs, throat, nose, eyes, and the peripheral nervous system have been recognised as primary registration centres of the meteorological environment 27

(Tromp 1963a). The degree of excitation of these receptors cannot be reasonably expected to be the exclusive result of the impingement of indoor thermal environments without at least some contributary stimulation of exposure to outdoor weather. Tromp (1936b) presents a long, well-documented list of physiological functions which have been observed to be influenced by various meteorological phenomena. Among these, complicated chemical and physical changes have been observed in the blood composition and volume, circulatory system, skin, muscles, and the endocrinal system, all of which are involved to some degree in thermoregulation. In view of the reasonably strong theoretical grounds for suggesting that weather influences on indoor thermal sensations may be quite considerable, it seems very surprising that no investigation has been carried out to test this hypothesis.

Atmospheric environments and working efficiency THERMAL CONDITIONS AND WORK Field and Experimental Studies While no direct proof exists to show the benefits of maximum comfort, evidence that more extreme thermal conditions may be detrimental to work was first presented in field studies in industry. Accident rates in ammunition factories appeared to increase by some 30 per cent in temperatures above 75°F (24°C) and below 50°F, or 13°C (Osborne, Vernon and Muscio 1922; Vernon 1918). In coal mines absences due to accidents showed a substantially higher incidence in hot seams (Vernon, Bedford, and Warner 1928, 1931) and at 81°F (27°C) ET less coal tubs were filled and more frequent rest pauses taken than at 66°F (19°C) ET (Vernon, Bedford, and Warner 1927). Production in heavy glass and metalurgical industries (Vernon 1919, 1920; Farmer, Brooke, and Chambers 1923) showed a marked decrease during the hottest months of the year, and in textile in28

dustries (Weston 1922; Wyatt, Fraser, and Stock 1926) linen and cotton weaving production decreased above wet bulb temperatures of 70-73°F (21-23°C). Although certain experimental investigations have reported no loss of performance at very high temperatures (Pepler 1963), decreases have been observed in a number of others. The earliest controlled laboratory experiments designed to compare performances under various thermal conditions, appear to be those conducted by the New York State Commission on Ventilation (1923). In a weight-lifting experiment a number of different scores were obtained, one of which showed that 15 per cent less work was done at 75°F (24°C) air temperature than at 68°F (20°C). In the inquiry into thermal conditions of schools by Vernon, Bedford, and Warner (1930), a chain link assembly task took some 12 per cent longer to complete by both men and boys at 50°F (10°C) than at 62°F (16.5°C) air temperature. An experiment on heat-acclimatized men at a manipulative coordination task showed a 62 per cent loss of accuracy and a 14 per cent increase in performance time with 91°F (33°C) ET compared with 65-68°F (18. 5-20. 0°C) ET (Weiner and Hutchinson 1945). Viteles and Smith (1946) used artificially acclimatized subjects, apparently fully clothed, and at three temperature levels found that on a long battery of tests of psychomotor and mental performance output at 87°F (30.5°C) ETwas reduced when compared to that at 80 and 73°F (26.5 and 23°C) ET. Mackworth (1946, 1950) applied various extended vigilance and physical effort tasks to artificially acclimatized servicemen and found that all performances showed deterioration at 86°F (30°C) ET. 3 He concluded: There is a critical region on the atmospheric temperature scale above which most acclimatized men dressed in shorts will not work effectively indoors. This region lies between the effective temperature readings of 83 °F and 87.5°F, i.e., between the dry bulb/wet bulb readings of 90/80°F and 95/85°F when the air movement is 100 feet per minute. This conclusion applies to all forms of intensive work, both physical and mental. [Mackworth 1950, p. 151.]

3

Mackworth actually reported 87.5°F (30.8°C) ET having erroneously used the normal scale of effective temperature, and not the appropriate basic scale, as his subjects were stripped to the waist (Pepler 1958; Watkins 1956).

29

Confirmation of a critical temperature zone has also come from Carpenter (1950), Pepler (1956, 1958), and Watkins (1956). These three investigators conducted what may be considered a series of experiments comparable to those of Mackworth^, but Pepler employed naturally acclimatized British servicemen in Singapore and Watkins used indigenous West African soldiers. In both the latter experiments performance decrement was observed at 86°F (30°C) ET, but neither experiment could support MackworthTs earlier conclusions that performance decrement is a logarithmic function of thermal levels, nor could it be shown that performance was independent of incentives. Pepler (1958) found that the best performance with no incentives was worse than the worst performance with incentives. Of particular interest is PeplerTs (1958) discovery of a statistically significant decrement (P