Industrial explosives and their preparation: еducational manual 9786010444270

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Industrial explosives and their preparation: еducational manual
 9786010444270

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AL-FARABI KAZAKH NATIONAL UNIVERSITY

M.I. Tulepov

INDUSTRIAL EXPLOSIVES AND THEIR PREPARATION Educational manual

Almaty «Qazaq University» 2020 1

UDC 66.0 (075) LBC 35.11я73 T 91 Recommended for publication by the decision of the educational-methodical Association of the Republican educational-methodical Council at M. Auezov South Kazakhstan State University (Protocol №1 dated 06.12.2019); and by the Academic Council of the Faculty of Chemistry and Chemical Technology and Environmental Sciences Al-Farabi KazNU (Protocol №2 dated 15.01.2020) Reviewers: Doctor of Chemical Sciences, Professor of al-Farabi Kazakh National University R.G. Abdulkarimova PhD, Head of the Department of engineering physics of Satbayev University R.E. Beisenov PhD, Head of laboratory «SHS new materials», Institute of combustion problems S.M. Fomenko

T 91

Tulepov M.I. Industrial explosives and their preparation: еducational manual / M.I. Tulepov. – Almaty: Qazaq University, 2020. – 159 p. ISBN 978-601-04-4427-0 In the manual the characteristics of explosive process are considered. In laboratory works the usage of the elements of scientific research with modern scientific devices and equipment in the educational process is described. The manual provides students with an introduction to the basic laws of explosion, methods of experimental investigation, processing and analysis of measurement results, and contains brief information on the theory of explosives to the extent provided by the curriculum. The present edition is intended for undergraduates and doctoral students of the higher school of the specialty «Chemical Technology of Explosives and Pyrotechnics Means».

UDC 66.0 (075) LBC 35.11я73 © Tulepov M.I., 2020 © Аl-Farabi KazNU, 2020

ISBN 978-601-04-4427-0

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INTRODUCTION ................................................................................... 5 1. FROM INCENDIARY MIXTURES TO GUNPOWDER  THE MAIN REPRESENTATIVES OF INDUSTRIAL EXPLOSIVES .......................................................................................... 9 1.1. Major industrial explosives ................................................................. 11 1.2. Types and components of industrial explosives .................................. 12 2. MAIN PROPERTIES AND PARAMETERS OF INDUSTRIAL EXPLOSIVES .......................................................... 18 2.1. Basic concepts and definition of an explosion .................................... 18 2.2. Parameters of explosion of industrial explosives ................................ 18 2.3. Main characteristics of industrial explosives ...................................... 19 2.4. Classification of industrial explosives. Physical and chemical properties of industrial explosives ......................... 20 3. EXPLOSIVES ON THE BASE OF AMMONIUM NITRATE ........ 23 3.1. Explosive properties and characteristics of ammonium nitrate ........... 23 3.2. Dynamons and their main characteristics............................................ 27 4. TECHNOLOGY OF PRODUCING AMMONITES ........................ 31 4.1. Composition, physico-chemical and explosive properties of ammonites ............................................................................................. 31 4.2. Suspension explosives and their characteristics .................................. 37 4.3. Emulsion explosives and their characteristics ..................................... 37 4.4. The composition and properties of suspension explosives .................. 39 4.5. Nitroglycerin and perchlorate industrial explosives ............................ 41 4.5.1. Nitroglycerin industrial explosives .................................................. 41 4.5.2. Perchlorate industrial explosives...................................................... 43 5. CHEMICAL REACTIONS AT EXPLOSION AND FORMS OF TRANSFORMATION OF EXPLOSIVES ...................................... 45 5.1. Formation of poisonous gases at explosion......................................... 47 5.2. The heat and temperature of the explosion. The volume and pressure of the gaseous products of explosion .................................... 48 5.3. Detonation and its conditions for explosives ...................................... 51 6. SAFETY EXPLOSIVE SUBSTANCES ............................................. 54 6.1. Atmosphere of underground mine workings, underground gas and dust explosions.............................................................................. 54 6.2. The mechanism of explosion of gas and dust explosions of mine gases. ............................................................................................ 55

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6.3. Explosiveness and flammability of coal dust ...................................... 58 6.4. Ignition by an explosive impulse of combustible mine environments ............................................................................................. 69 7. INDUSTRIAL EXPLOSIVES FOR BLASTING ON THE SURFACE AND IN THE MINES .......................................... 64 7.1. Explosives for blasting only on the earth’s surface ............................. 64 7.2. Explosives for blasting in mines not hazardous on gas and dust explosion, and on the earth’s surface ........................................... 66 7.3. Powdered explosives........................................................................... 69 7.4. Safety Explosives ................................................................................ 71 7.5. Industrial explosives based on recyclable ammunition ....................... 72 8. DETONATION CAPABILITY, DEFLAGRATION OF EXPLOSIVE SUBSTANCES ........................................................... 74 8.1. Flammability and deflagration of safety explosives ............................ 74 8.2. Detonation ability of safety explosives ............................................... 79 8.3. Classification of safety explosives and principles of their composition ................................................................................... 82 9. INDUSTRIAL EXPLOSIVES AND THEIR APPLICATION ........ 91 9.1. Principal components of industrial explosives .................................... 92 10. SAFETY EXPLOSIVES ................................................................... 97 10.1. The use of explosives in mines hazardous on gas and dust ............... 102 10.2. Flame arrestors in the composition of the safety explosives ............. 107 10.3. Detonation of safety explosives ........................................................ 110 10.4. Safety explosives and their combustibility ........................................ 112 10.5. Physico-chemical changes in the properties of explosives over time........ 114 11. ENVIRONMENTAL SAFETY OF INDUSTRIAL EXPLOSIVES .......................................................................................... 123 11.1. Impact of explosives on the environment during their use ................ 123 11.2. Methods of disposal of explosives .................................................... 129 12. LABORATORY WORKS TO THE COURSE «INDUSTRIAL EXPLOSIVES» ............................................................ 131 Lab 1. Determination of the sensitivity of explosives to thermal pulse ..... 131 Lab 2. Determination of the sensitivity of an explosive to impact ............. 135 Lab 3. Determination of the sensitivity of explosives to friction ............... 138 Lab 4. Determination of the heat of explosive transformation ................... 142 Lab 5. Measurement of detonation temperature of condensed explosives ........... 151 TERMS AND ACRONYMS ..................................................................... 157 RECOMMENDED LITERATURE ........................................................... 158

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Efficiency and safety of work often contradict each other in such operations as extraction of solid mineral raw materials in mines, block stones in construction of subways, tunnel construction, laying of various communications and roads, destruction of an asphalt or concrete roadbed, oversized granite blocks, removal of concrete brick buildings in the conditions of dense building development. Thus, an increase in the efficiency of destruction, as a rule, is accompanied by an increase in the intensity of shock air and seismic blast waves, which predetermines the need for the development and production of industrial explosive substances (IES) or industrial explosives (IE). In the area of blasting, a large number of explosives and means of initiation with various properties are used. In modern practice, a very large range of explosives has been developed and is being produced, which are constantly being updated and improved. The unstable political situation at the turn of the nineteenth and twentieth centuries gave impetus to the rapid development of industry and led to the creation and production of powerful explosives: at that time TNT (tetranitropentaerythritol), nitroglycerin, tetrin, picric acid, a detonator (Nobel fuse), explosives based on ammonium nitrate and dynamites were obtained. At the beginning of the XX century TEN and hexogen, which are still very widely applied, were produced. In the 30s of the twentieth century, due to the rapid growth of the mining industry, it became necessary to replace the previously used nitroglycerin dynamites with safer explosives based on ammonium nitrate (ammonites and dynamons). One of the main stages in the history of explosives is the development and production in the early 60s of the twentieth century of the simplest igdanite explosives (mixtures AC-DT) and granular explosives (grammonites and granulites), which made it possible to directly apply mechanized loading, to increase the density of explosives in charges, improve the working conditions of blasting agents. Currently, one of the features of blasting is the use of industrial explosives derived from recyclable ammunition. It is widely applied 5

in production of recyclable shells and bombs TNT, or 2,4,6 trinitrotoluene, C7H5N3O6 (TNT U, TNT UD), nitroglycerin and gunpowder pyroxylin as powerful blasting explosives for crushing hard rock. Competitiveness of the products of the national economy of the Republic of Kazakhstan in the open market is the main technical, economic and scientific problem to be solved by companies of different profiles including research companies. Its solution is especially important for the mining and metallurgical industry, which mainly determines the country’s budget indicators. As is known, the initial process in the mining and metallurgical redistribution of minerals is drilling and blasting. They significantly affect both the cost of the final products of mining and processing plants (up to 15%), and determine the performance of subsequent operations of the mining cycle. The development of new technologies and new methods of blasting operations, the provision of optimal charge parameters, based on the properties of explosives used and their location in the rock mass, operational management of blasting operations and subsequent technological processes in the quarry will significantly improve the efficiency of the mining enterprise. As the statistical analysis of the development of the mining industry and existing technologies for the development of quarries shows, the main means of preparing rocks for excavation is still the energy of the explosion, about 70% of minerals are mined using explosives. Despite seemingly exhausted opportunities, increasing effectiveness of areas for their further improvement remains one of the most important scientific and research tasks. One of the fundamental, but insufficiently studied areas is the analysis and study of the relationship between the processes of dynamic effects, determined mainly by the properties of explosives, on the rock massif and patterns of its destruction to the desired geometric dimensions. Recently, the explosion energy has been widely used in engineering practice for the discovery of new ore deposits of various natural resources, formation and destruction of dams and embankments, laying of highways in the mountains during the construction of roads. 6

The explosive method of processing metals and powders ‒ stamping, welding, cutting, hardening and pressing ‒ is widely used. In addition, the fight against forest fires, laying of routes for gas and oil products, seismic prospecting of minerals, perforation of oil wells and explosive drilling ‒ this is an incomplete list of areas of use of explosive materials in the national economy. At present, destruction and recycling of buildings and structures that have served their term are widespread in large cities. At the same time, research continues to expand the use of this energy source. A new direction of work is devoted to the explosive synthesis of diamonds and valuable artificial minerals. Thus, the reduced explosive energy can be produced by explosives, which, for their distinctiveness, are called industrial explosives (IE). The variety of conditions for the use of IE because of the wide range of technical requirements for IE determines their differences in chemical composition, and accordingly ‒ in physical and explosive properties. The range of IE in many countries is dozens of items. The productivity and efficiency of blasting operations largely depends on the type of IE, which can be correctly chosen only if the properties of IE are known and the preparation technology corresponding to these properties and, most importantly, the relationship between the properties of IE and the effectiveness of the action of the relevant forms of working products of the explosion. A special and distinguishing feature of IE is their chemical and physical heterogeneity. Most of them are a mixture of chemically inhomogeneous materials, produced in the form of powders, granules, suspensions, emulsions, consisting of components that are not identical in physical properties and in the state of aggregation. These characteristics and heterogeneity determine the characteristics of the process of explosion, the initiation and development of detonation of industrial explosive substances, which are in many respects different from the laws of individual explosion ‒ in most of military explosives. The physical and chemical properties of IE when mixed are determined by the physicochemical properties of their components ‒ density, state of aggregation under normal conditions, hygroscopicity, modification, water solubility, colloidal properties. 7

An important task of the science of industrial explosives and the course «Industrial explosives» is, of course, the development of knowledge accumulated in this field for the purpose of further use of this knowledge for creation of modern explosives on the higher technological level by production and safety for application without harmful environmental pressure of products of explosion. Based on this, in accordance with the basic curriculum for undergraduates and doctoral students and the course work program, the following topics are provided.

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In the middle of the 13th century, the well-known Arab scientists Ibn Abi Uzaibia and Ibn Beitar described the properties of the new compound, saltpeter (nitrate) and its cooling effect. At the end of the XIII century, Hassan Al-Rammaya in his book described many ways of coarse and fine purification of natural nitrate under the action of ash liquor on it, followed by recrystallization of the resulting product. The book also contains recipes of incendiary mixtures and pyrotechnic compositions of the so-called «Chinese arrows» or «Chinese fire copies». These names, in a certain sense, are related to the fact that gunpowder was discovered in China and the recipes for its manufacture came through India and the Arab states to Europe. Later in the book on the military art of the Arab scholar Shemseddin Mohammed, ways of use of gunpowder for firing were described. The invention of gunpowder and its application in the military purposes promoted improvement of arms (led to the emergence of cannons and guns). This stimulated the emergence of new chemical crafts: the preparation of nitrate and gunpowder. The proliferation of these crafts had a great influence on the improvement of scientific knowledge, philosophical systems and even the development of civilization. In 1258, the inhabitants of the German city of Cologne, for the first time in Europe, used incendiary compounds. In Freiburg, where the monk Berthold Schwartz, the European inventor of gunpowder, lived for a long time, in 1300 the first gun was cast. In the 14th century, guns and cannons were manufactured in various European countries. The first powder factories appeared in Augsburg in 1340, at Lignitz in 1344, in Spandau in 1348. Originally, saltpeter (nitrate) was imported to European countries. Italian Venice, through which saltpeter got to Europe, had big profits from this trade. And already in the 15th century, due to the growing demand for nitrate and its importance for strengthening 9

defense, many European states organized the production of nitrate from local raw materials. Saltpere suppliers received privileges from the authorities, as evidenced, for example, by orders of the Archbishop of Magdeburg Gunther (1419), decisions of the Frankfurt City Council (1583) and decrees of Brandenburg Elector Johann Georg (1583). The general military significance of firearms grew with its spread throughout the world. The growing production of weapons required more and more mechanics, technicians, and specialists in chemistry and physics. And as a result, the need for gunpowder, metal for cannons and guns, gun carriages and other military equipment and equipment increased. During that period, catapults ‒ stonethrowing machines and various stencils of firearms having more destructive power, considerable firing range, and high mobility were used. The use of firearms had a tremendous impact on the improvement of military technology, which can only be compared with the influence on the development of mankind of the use of iron, which began about three thousand years before. With the help of firearms, seas and continents were conquered, civilizations were destroyed, еру whole nations were destroyed or enslaved. As a result, having learned to use firearms, a man subjugated the mighty forces of nature. Saltpeter (nitrate) in its essence turned out to be also a substance that is very important for chemical crafts. The manufacture of nitrate required a radical improvement in the methods of salt separation and purification; the most important role in this was played by the processses of dissolution and crystallization. The first appearances of fire when burning gunpowder and without air access prompted medieval scholars new ideas about the processes of burning. It was assumed that nitrate contains the «air» necessary for burning. The study of nitrate air subsequently played a huge role in the development of important provisions of chemical science. The results obtained and the improvement of artillery technology, the need for aimed fire of guns and the study of the movement of projectiles led to the emergence of ballistics as a science. Foundry «art» in the XIII-XIV centuries was already quite developed. A new incentive to improve the technology of casting metals appeared after 10

the invention of guns. It was necessary to create special alloys for gun barrels and high-quality metal processing methods. This contributed to the development of chemical knowledge and technical skills of foundry workers. For drilling metals, horse traction or water wheels (to set the drills in motion) were used. The growing demand for saltpeter until the end of the 18th century was mainly satisfied by imports from India and, to a lesser extent, thanks to its own sources. From the 17th century, intensive and systematic searches for nitrate in Europe led to the organization of artificial «deposits» of nitrate. «Saltpeter gardens», or «plantations» were created. Thus, the states were extremely interested in the production of nitrate. In Sweden, for example, the peasants even had to partially pay taxes on nitrate.

1.1. Major industrial explosives In accordance with the Uniform Safety Rules for blasting operations, all industrial explosive materials (explosives, shooting-guns and explosive vehicles) when handling them are classified according to the degree of danger (tab. 1) (storage, transportation, use) and belong to class I. Table 1 Classification of explosive materials according to the degree of danger when handling them Compatibility group (hazard) В С D

F G

Substances, products substances containing initiating explosives deflagrating and throwing explosives smoky gunpowder; products that containing detonating explosives without means of initiation and a propellant powder products containing initiation and propellant charges pyrotechnic compositions and products containing them

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Explosive materials for different compatibility groups must be transported and stored separately. Joint storage is allowed for the following materials: 1. Smoky (D) and deflagrating (C) powders in accordance with the requirements of the most sensitive of them. 2. Group products with explosive materials of groups B, C, and D. 3. Detonating cord (D) with products of group B. According to the conditions of use, Industrial Explosives are divided into 7 classes and class (C), which in turn is divided into 4 groups. This classification divides explosives into: ‒ Explosives for blasting only on the earth’s surface (large negative Kb) (class 1); ‒ Explosives for blasting on the earth’s surface and in mines not hazardous for explosive dust (Кb  0) and for emission of methane (class 2); ‒ safety explosives for blasting in underground workings where there is explosive dust and methane emission (class 3-7); ‒ Explosives and products from them (special class C) intended for special blasting, except for workings in which release of explosive dust and methane is possible (welding, pressing, strengthening of metals, etc.) By physical condition, industrial explosives are divided into granular, powdered, scaly, cast, extruded, flowable, plastic.

1.2. Types and components of industrial explosives The composition of industrial explosives includes a large number of components. Among them are explosives (hexogen, trotyl, TEN-tetranitropentaerythritol, nitroglycerine, octogene) and non-explosive substances (ammonium nitrate, guargam, polyacrylamide, soda, flour presscake, peat, mineral oil, powdered aluminum, water). In general, nitro compounds are explosive components of industrial explosives containing a nitro group -NO2 (aromatic nitro compounds ‒ dinitronaphthalene, trotyl, nitromethane); -O-NO2 (nitrates of alcohols ‒ nitroglycol, nitroglycerine, TEN-tetranitropentaerythritol); -N-NO2 (nitramines-octogen, hexogen). 12

Trotyl (trinitrotoluene) ‒ C6H2(NO2)3CH3 is an insensitive thermally and chemically resistant compound, which is a white powder that turns yellow in light. It is toxic, practically insoluble in water, well detonated in water. It is used for the manufacture of intermediate detonators (T-400G, TG-500), as a component of ammonium nitrate explosives, as an independent explosive (granulotole, granulated trinitrotoluene). Nitroglycerin (nitroglycerine) CH(CH2ONO2)3 is an oily, colorless liquid, which hardens at a temperature of 13.2 °C. It is very sensitive to heat and mechanical stress, very toxic, practically insoluble in water. It is one of the most powerful explosives. It is used in a mixture with nitro-glycol and nitroglycol for the production of explosives based on nitroesters (detonite M, carbonaceous). TEN (tetranitropentaerythritol) C(CH2ONO2)4 is a crystalline white substance with a bulk density of about 1 g/cm3. It is toxic, chemically resistant, practically insoluble in water, sensitive to mechanical stress. TEN when phlegmatized and clean is used in the core of non-thermally resistant detonating cords. Hexogen (cyclotrimethylenetrinitramine) (CH2)3N3(NO2)3 is crystalline white powder. It is thermally and chemically stable, poisonous, long lasting to withstand high temperature, highly sensitive to mechanical stress. It has a small critical diameter of detonation. It is used as a sensitizer in ammonium nitrate explosives. It is applied in a phlegmatized state (up to 6% paraffin or ceresin). Octogen (cyclotetramethylene tetranitramine) (СН2)4N4(NO2)4 is a crystalline white substance with high thermal stability and melting point. It has a small critical diameter and high sensitivity to mechanical stress. Tetryl (trinitrophenylmethylnitramine) С6Н2(NO2)4NCH3 is a pale yellow crystalline powder. It does not interact with metals. When ignited, it burns quickly with the possibility of burning to detonation. It possesses the initiating ability and high sensitivity. Primary initiating explosives are distinguished into a separate group, which are used only to equip the means of initiation. Compared with industrial and other explosives, they have a much higher sensitivity to external influences, capable of exploding in small quantities (tenths of a gram) under the action of a weak pulse (impact, puncture, ray of fire). 13

In terms of sensitivity, initiating explosives are divided into primary (lead azide, explosive mercury, lead trinitroresorcinate or LTNR) explosives and secondary (TEN, tetryl, hexogen) explosives. Explosive mercury (mercury salt of a stinging acid ‒ fulminate) Hg(ONC)2. It is a white crystalline powder with a flashpoint of ≈ 170 °C and a bulk density of ≈ 1.2 g/cm3. It is well pressed to a density of 4 g/cm3, while maintaining the initiating ability and sensitivity. It is very sensitive to moisture (does not detonate at 10% humidity). It is very sensitive to friction, in the wetted state reacts with copper to form copper fulminate. Under the same conditions, it is a porous, non-explosive mass formed with aluminum. The permissible moisture content of the caps is 0.03%, and the cup in which the explosive mercury is pressed is coated with varnish. Lead azide (lead salt of hydrazoic acid) Pb(N3)2. It is a fine white powder. It is insoluble in water, not hygroscopic, does not lose its detonation ability when wet. It does not interact with metals in the dry state. It is pressed into aluminum sleeves. In the wetted state it interacts with copper to form highly sensitive compounds. It is less sensitive to the ray of fire than the explosive mercury, but surpasses the explosive mercury in its initiating ability. LTNR (lead trinitroresorcinate) C6H(NO2)3(OPb)2 is a mercury salt of styphnic acid (stifnat lead). It is a crystal powder, of golden yellow color. It does not enter chemical reactions with metals. It occupies an intermediate position in sensitivity and is weaker than rattling mercury and lead azide in terms of initiation capacity. It is used as an intermediate charge with a mass of 0.1 g to initiate lead azide. Ammonium nitrate NH4NO3 is a white crystalline powder. Several types of ammonium nitrate (AN) are produced: fine-crystalline, powdered, granular, porous, granular, non-porous, waterproof crystal. Ammonium nitrate contains 35% nitrogen, 5% hydrogen, 60% oxygen. 20% of oxygen in an explosive transformation is released in a free state. Melting point 160 °C, at a moisture content of 2.5% the melting temperature decreases to 140 °С. It is thermally stable and chemically resistant (thermal decomposition begins at a temperature of 185–200 °C). It dissolves very well in water (178 g in 100 ml of water at T = 20 °C). It is strongly caking, hygroscopic, especially with increasing temperature and humidity. 14

The main characteristics of primary and secondary initiating substances are presented in tab. 2. Table 2 Characteristics of initiating Explosives

Indicators Heat of explosion, MJ/kg Volume of gases, l/kg Explosion temperature, °C Density, g/cm3 Oxygen balance, % Detonation speed, km/s Operability in a lead bomb, cm3 Flash point, °C Sensitivity to impact (height of the fall of a cargo weighing 2 kg), cm

Explosive mercury 1.49

Primary Lead LTNR azide 1.59 1.64

Tetryl

Secondary TEN Hexogen

4.2

6.2

5.44

316

308

448

412

780

890

4.450

4.300

3.030

3.810

4.000

3.850

3.5 -11.8 5.4

4.6 5.3

2.9 -56.0 5.2

1.0 -47.4 7.2

1.0 -10.1 8.2

1.05 -20.1 8.3

110

115

110

350

500

520

165 2.0

327 4.0

270 11.0

195 30.0

220 30.0

203 30.0

With certain substances (sulfides, sulfur, iron ores) ammonium nitrate enters into chemical reactions with heat, which can lead to spontaneous detonation. The decomposition of ammonium nitrate can occur by several reactions. Under ideal conditions, the maximum amount of heat (384 kcal/kg) and gaseous products (≈ 980 L/kg) is released during the detonation of ammonium nitrate: NH4NO3 → 2H2O↑ + N2↑ + 0.5O2 + Q. Ammonium nitrate is a fire hazard, which is associated with the possibility of transition of combustion into detonation. With an increase in the diameter of the granules and moisture content, the ability of ammonium nitrate to detonate decreases. Admixtures of combustible substances (oil, diesel fuel) with a content of up to 6% 15

dramatically increase the sensitivity of ammonium nitrate to detonation. Among all produced nitrates (potassium, sodium, calcium) the cost of ammonium nitrate is the lowest. As an oxidizing agent, it is used in most industrial explosives. Other types of saltpeter (nitrate) have a higher density; contain significantly more «free» oxygen (2-2.5 times); have a higher sensitivity, however, when explosive transformations form solid oxides and much less gaseous products, they significantly reduce their value as a possible component for industrial explosives. They are used mainly in water-filled explosives to increase plasticity, density, lowering the freezing temperature (especially calcium saltpeter). Diesel oils and fuels. For the manufacture of industrial explosives, all manufactured types of diesel fuel are used (winter, arctic, summer, etc.) with a cetane number of at least 40 or low-viscosity oils (spindle, industrial, instrumentation, solar, transformer). The degree of purification of these oils from various impurities meets the requirements of State Standard (SS) and Technical Conditions (TC) for industrial explosives. Urea H2NCOOH2. It is a non-toxic, loose, non-caking substance. It is used to clean oil from paraffins, as a fertilizer. It is not explosive. It is used in hot explosives (carbatols) for the production of low-melting mixtures (a mixture of urea and AN with 5% water melts at t ≈ 75-80 °C). Thickeners are high-molecular industrial and natural substances intended to increase the physical stability (absence of stratification) of water-filled (water-containing) industrial explosives and impart the explosives a thick (viscous) consistency. PAA (polyacrylamide), CMC (carboxymethylcellulose) and guargam (a natural product) are most often used as a thickener. Thickeners are produced in the form of powders which then, being dissolved in water, considerably increase viscosity of solutions. Guargam has better solubility, CMC dissolves somewhat worse. To dissolve the PAA requires constant mixing and heated water. The solubility of thickeners in water is 98-99%. PAA is used for the manufacture of gel explosives in the factory, CMC is used in water-filled explosives with structure-forming additives. Guargam is a product obtained by grinding the dried beans of some species of tropical acacia. Currently, industrial explosives do not use guargam. 16

Structure-forming additives (crosslinking) are used for crosslinking in aqueous solutions of crosslinking macromolecules thickeners. Chromium nitrate, chromium sulphate, potassium alum chromium (for CMC), borax (for PAA and guargam) are used as crosslinks. The mass of crosslinks introduced into solutions is ≈ 0.01 – 0.05% relative to the mass of thickener. Combustible metal additives. One of the ways to increase the energy of explosion is the introduction of powdered metals into the composition of industrial explosives. Chemical oxidation reactions of metals proceed with a significantly greater heat release than with the oxidation of carbon and hydrogen. With the addition of aluminum powder up to 15% by mass of explosives (aluminotol), the greatest effect is achieved. A further increase in the mass of aluminum leads to an increase in the cost of explosives. Other more economical and less scarce metals and their compounds (iron, silicon, ferrosilicon, silicocalcium) can also be used as additives. These substances also provide a high volumetric concentration of energy (almost the same as aluminum) and can reduce the cost of explosives by 10-15%. Questions for self-control 1. List the first scientists from Arabia who discovered the incendiary mixtures. 2. The history of the development of explosive business in Germany and Europe. 3. The effect of firearms on the improvement of military equipment. 4. List the main representatives of industrial explosives. 5. List the main components of industrial explosives.

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2.1. Basic concepts and definition of an explosion By their basic parameters explosions are divided into: 1. Physical ‒ there is a physical transformation of the test substance without changing the chemical nature (explosions of steam boilers, liquefied gas cylinders, etc.). 2. Chemical ‒ in this case, an extremely rapid chemical transformation of the initial substances (the formation of new chemical compounds due to oxidation reactions of carbon, hydrogen, aluminum) occurs with the release of a large amount of heat (up to 6.103 kJ/kg) and gaseous products (up to 1.000 L/kg). 3. Nuclear ‒ reactions of splitting of nuclei with formation of new chemical elements and release of a significant amount of heat (up to 4.1014 kJ/kg). Obviously, chemical explosions are used in mining.

2.2. Parameters of explosion of industrial explosives Typically, the explosives are subjected to transformation by the external pulse (kick, pinned, rapid heating) and can detonate (explode), i.e. enter into a chemical reaction with the release of heat and gases and perform mechanical work (crushing and moving rocks). Energy during an explosion is released when chemical reactions of hydrogen oxidation in water proceed, carbon to oxides of CO and CO2 with oxygen, which are part of the molecules of an explosive (during the explosion of 1 liter of nitroglycerin, ≈ 104 kJ are released, which is significantly less than the energy released during the combustion of the same amount of alcohol or gasoline). However, in an explosion, energy is released for a fraction of a second, which provides more power to the explosion. The heat generated by chemical transformations heats up the resulting explosion products (gases) to a temperature of 2.103 ‒ 5.103 °C. Since the explosion rate is very high, at the initial moment in the 18

explosion zone the gases develop pressure up to 104 MPa, which ensures the destruction and movement of solid rocks. Distinctive signs of explosion of explosive substances are: 1. Supersonic speed of energy release. 2. High volume concentration of energy. 3. Exothermicity of the process. 4. Formation of a large amount of gaseous products. 2.3. Main characteristics of industrial explosives Explosives (or explosive substances) are chemical compounds or mixtures that, under the action of an external impulse, are capable of a rapid self-propagating exothermic process. Explosives are divided by a physical state into: a) solid one-component compounds or mixtures of solids (these include TNT, hexogen, picric acid; a mixture of TNT with ammonium nitrate); b) mixtures of solid and liquid substances (the known ones include ammonium nitrate and diesel fuel, ammonium nitrate and mineral oil); c) gas mixtures (methane in air); d) mixtures of solids and gases (coal dust in the air can also be considered as explosives; e) mixtures of liquid substances (for example, mixtures of nitroesters, nitrogen tetroxide and kerosene). Practical application as industrial explosives have explosives of groups a) and b). The composition of the known industrial explosives may include several components that give each explosive certain properties. All these components are divided into:  oxidizers ‒ compounds containing in their composition excess oxygen consumed for the oxidation of carbon and hydrogen, which are part of all components. Ammonia, potassium and other types of nitrate are oxidizing agents;  combustible additives ‒ substances containing a large amount of carbon and hydrogen (for example, coal, wood flour, liquid hydrocarbons), as well as aluminum; 19

 sensitizers ‒ the most powerful explosives introduced into the mixture to increase sensitivity and detonation transmission (for example, hexogen (RDX), nitroglycerin);  stabilizers ‒ high-molecular substances, such as peat and oil meal, are usually introduced into the explosives to prevent stratification of water-filled and caking powdered explosives;  phlegmatizers ‒ low-melting hydrocarbons that surround explosive particles, which leads to a decrease in sensitivity to thermal and initiating pulses (for example, paraffin, vaseline);  flame arresters ‒ for explosives used in underground work, in which the release of methane and (or) explosive dust is possible, reduce the temperature of the explosion. As flame arresters, NaCl and KCl are most widely used.

2.4. Classification of industrial explosives. Physical and chemical properties of industrial explosives Industrial explosives are classified by chemical composition or physical state, by the most characteristic features of their properties or prescription composition, by area and conditions of use. All explosives on the chemical composition are subdivided into individual chemical compounds and mechanical mixtures. From the individual explosives in industry, only TNT is used independently in blasting operations, mainly in the form of granulotole and detonator checkers. Tetril is used mainly in primers detonators, and pentaerythritol tetranitrate, less often hexogen ‒ in detonating cords. From the mixed explosives in industry, the most widely used mixtures are based on ammonium nitrate, called ammonium nitrate explosives: ammonites, ammonals, detonites, carbonates, etc. A special group consists of water-filled explosives of suspension and emulsion types of different consistency: aquatols, aquanites, aquanals, ifzanites, emulchems, ukrainianites, etc. They are also called water-containing or solution-filled explosives. Water with nitrate in the composition of such explosives forms a saturated solution that makes up the dispersion medium of suspensions and emulsions. 20

Ammonites are a mixture of ammonium nitrate with TNT, less frequently with RDX, dinitronaphthalene and non-explosive combustible components. Safety ammonites contain additionally flame arresters ‒ alkali metal chlorides. Some of them, instead of TNT, contain liquid nitroesters (sulfuric and petroleum ammonites). Grammonites are two-component ammonites in granular form. Ammonals are ammonites containing aluminum, and ammonones in granular form are called grammonals. Dynamons are a mixture of ammonium nitrate with non-explosive combustible components: oils, cellulose, soot, vegetable flour, etc. Dynamons in granular form are called granulites. These also include igdanite, a stoichiometric mixture of granulated ammonium nitrate with diesel fuel. Aquatols are water-filled suspension explosives of fluid consistency, the solid phase of which is granulotole, and the liquid phase is a saturated, thickened solution of ammonium nitrate. Aquanites and aquanals are water-filled suspension explosives of plastic consistency, the active base of which is ammonite and ammonium mixtures with the presence of calcium or sodium nitrate and plasticizing agents. Ifzanites are suspension-containing explosives, the solid phase of which is a mixture of granulated saltpeter and granulote filled with concentrated or thickened solutions of ammonium nitrate at the site of application at the time of loading wells. Carbotols are hardening hot-melting explosives manufactured at the place of use based on a low-melting eutectic mixture of watersoluble components with a low water content. Emulchems are water-based emulsion explosives manufactured usually at the application site, the dispersion medium of which is a saturated aqueous solution of ammonium nitrate, the dispersed phase ‒ mineral oil or diesel fuel. On a physical state explosives can be subdivided into solid ‒ monolithic (cast, pressed), loose (powdery and granulated), plastic and free-flowing suspensions and emulsions. The latter include aquatols, ifzanites, carbotols, emulchems. TNT-hexogen checkers are produced in a form of cast. In the pressed form TNT checkers are produced ‒ ammo-rock cartridges 21

and detonators. Almost all powdered and some plastic explosives for ease of use are made in the form of cartridges. According to the most characteristic properties modern industrial explosives are divided into non-waterproof and waterproof. The hexogen-containing explosives include rock ammonite No.1 and rock ammonal No.3. Powder-type nitroester explosives of the powder type include non-protective detonites and safety uglenites. Industrial explosives are classified according to the conditions, areas and safe use. According to these signs, all explosives allowed for explosive works are divided into six classes. The first two classes are non-protective explosives, approved for open or underground mining in mines that are not hazardous on gas and dust, the other classes are safety explosives of varying degrees of safety. The above classification according to the conditions of application is carried out mainly in relation to the mining industries. Each class of explosives has special requirements and test methods. So, if for explosives approved for open work, the amount of poisonous gases in explosion products is not regulated, then for nonpreventive explosives allowed in mines, the minimum requirement is the formation of poisonous gases and increased detonation ability, and for safety measures, an appropriate degree of anti-blasting. The most important physicochemical properties of explosives, which determine, along with the explosive characteristics, the operational qualities of explosives and their stability, include hygroscopicity, caking, exudation, chemical resistance, water resistance, plasticity and flowability. The last three properties determine the physical stability of explosives. Questions for self-control 1. List distinctive signs of explosion of explosives. 2. What is a part of the known industrial explosives? List the main characteristics of industrial explosives. 3. Requirements imposed on the explosives applied in mining industries 4. Classification of industrial explosives.

22

3.1. Explosive properties and characteristics of ammonium nitrate The main component of ammonium nitrate explosives is ammonium nitrate ‒ the oxidizer most common in industrial explosives. The availability of raw materials, safety and simplicity of technology for the production and processing of ammonium nitrate in the production of explosives led to its wide use. The main factor is the fact that ammonium nitrate itself in its pure form is an explosive: performance (high explosiveness) in a lead bomb of Trauzl is 165-230 cm3, its heat of explosion is 335 kcal/kg, which is about 3 times less than the heat of explosion of TNT. The detonation speed is about 1.5-2.5 km/s, which requires an intermediate detonator from po-werful explosives for its blasting. Ammonium nitrate NH4NO3 according to its physical parameters is a white crystalline substance with a molecular weight of 80, contains 60% oxygen, 5% hydrogen and 35% nitrogen. Ammonium nitrate exists in five stable forms, the areas of existence of which are listed in tab. 3.1. Ammonium nitrate, in addition to these five stable modifications, also has metastable forms, arising under the influence of certain additives and other factors (heat treatment, pressure). This is especially evident in the presence of water. In dry nitrate, only transformations between forms V, IV, II, I occur. However, the conversion of IV ↔ III occurs only in the presence of moisture or in a humid atmosphere, or this period shifts in the temperature range 323328 K. The melting point of ammonium nitrate is within 442.0-443.4 K, the heat of melting is 16.2 cal/g. Evaporation becomes noticeable at a temperature of 403-433 K. Intensive decomposition of ammonium nitrate occurs in the temperature range 483-613 K.

23

Table 3.1. Characteristics and areas of existence of crystalline forms of ammonium nitrate Modification existence area, K

Modification

442.6-398.8 398.8-357.1 357.1-305.3

Density, g/cm3

cubic (i) 1.55-1.57 tetragonal (II) 1.60-1.64 rhombic or monoclinic 1.66 (III) 305.3-256.0 (256 K) rhombic bipyramidal (IV) 1.725 lower than 256.0 tetragonal (V) 1.725

Heat of transformation (at temperature, K), cal/g I ↔II; 13.2 (398.8) II↔ II; I 4.0 (357.1) III↔IV; 5.1 (305.3) IV ↔V; 1.4 (256.0) -

The decomposition of ammonium nitrate, depending on temperature, can occur according to the following main reactions: at 383 К NH4NO3 = НNO3 + NH3 + 41.0 kcal/mol; at 458-473 К NH4NO3 = 2NO2 + 2Н2О + 30.3 ккал/моль; kcal/mol; at 503 К and above 2NH4NO3 = 2N2 +О2 +4Н2О + 30.7 kcal/mol. At temperatures above 673 K, decomposition of ammonium nitrate proceeds with an explosion in one of the following reactions: 4NH4NO3 = 3N2 + 2NО2 + 8Н2О + 29.5 kcal/mol; 8NH4NO3 = 2NО2 + 4NО + 5N2 +16Н2О + 49.5 kcal/mol. The thermal stability of nitrate is reduced by organic substances containing carbohydrates: starch, sugars, and glucose. Cellulose containing substances: paper, cardboard, wood, cotton and flax-containing fabrics also reduce thermal stability. Sulfur and sulfides (sulfide ores), nitric acid and nitrogen oxides, sulfuric and phosphoric acids, many metals (especially in the form of powders) ‒ zinc, copper, cadmium, nickel, magnesium, bismuth easily interact with ammonium nitrate. The thermal stability of ammonium nitrate is particularly affec-ted by nitric acid and nitrite salts. Aluminum, iron, their oxides and salts do not interact with ammonium nitrate.

24

Water is a catalyst for the thermal decomposition of ammonium nitrate. The group of substances that do not affect the thermal stability of ammonium nitrate can also include kieselguhr, kaolin, barium and ammonium sulfates, iron and their oxides and salts. Urea [CO(NH2)2], urotropin, calcium and magnesium carbonates should be attributed to the group of substances stabilizing ammonium nitrate. Ammonium nitrate is very hygroscopic, highly soluble in water, ethyl and methyl alcohols, pyridine, acetone and in liquid ammonia. To impart water resistance, paraffin, fatty acids and iron salts are added simultaneously to ammonium nitrate. In practice, the process of obtaining ammonium nitrate is quite simple. Ammonia gas and diluted nitric acid are used as raw materials for the production of ammonium nitrate. The production of ammonium nitrate technology is conditionally divided into four stages: 1) neutralization (45-50) % of nitric acid with ammonia gas NH3 + HNO3 = NH4NO3 +Q 2) evaporation of ammonium nitrate solutions, 3) crystallization of ammonium nitrate melt, 4) packaging and storage of ammonium nitrate. In industrial production, ammonium nitrate is produced according to State Standard 2-85 of three grades: A ‒ fine-crystalline; B ‒ scaly and crystalline; B ‒ granulated. Ammonium nitrate of grades A and B is used in industry, and of grade C ‒ in agriculture. In addition, ammonium nitrate is also produced according to State Standard 14702-79, which is intended for the production of industrial explosives. In accordance with this standard, waterproof ammonium nitrate is manufactured in two grades: LWC (Liquid Waterproof Crystalline), LWG (Liquid Waterproof Granulated). Water resistance is achieved by introducing hydrophobic additives into the composition of ammonium nitrate: fatty acids (C17-C20 fractions) and paraffin (0.3-0.4% by wt. in a ratio of 1:1) and iron (0.06-0.09) % by wt. 25

The critical diameter for ammonium nitrate charges depends on the degree of grinding, humidity and density. According to A.F. Belyaev, the detonation of dry finely ground nitrate at a density of 0.8 g/cm3 spreads stably in open charges with a diameter of about 100 mm. The explosive transformation of scaly nitrate particles of 1 mm in size with a moisture content of 1% by wt. decays in a charge with a diameter of 300 mm. Ammonium nitrate with a moisture content of 3% by wt. does not explode in charges of even larger diameters. A.F. Belyaev, in a massive shell not subject to destruction and deformation, obtained a stable detonation of ammonium nitrate in a charge of 7 mm in diameter at initiation by a single detonator cap. M.Kuk obtained the following values depending on the charge diameter (Dcharge) of crushed ammonium nitrate and the rate of detonation (D): Dcharge, mm D, m/s

100 refusal

150 1.455

200 1.600

250 1.800

300 2.150

460 2.750

G.Z. Pozdnyakov found that small amounts of hydrophobic additives (up to 0.4% by wt.) in waterproof ammonium nitrate do not significantly increase its hazardousness compared to non-resistant ammonium nitrate. But the dust of waterproof ammonium nitrate in a dry state has a higher explosion hazard. In terms of thermal stability, waterproof ammonium nitrate is inferior to chemically pure ammonium nitrate (ammonium nitrate). The critical detonation diameter of a waterproof ammonium nitrate is slightly less than that of a nonresistant ammonium nitrate. According to G.Z. Pozdnyakov, the detonation speed of nonresistant ammonium nitrate in a metal pipe with a diameter of 40 mm is 1.950 m/s, waterproof ammonium nitrate under the same conditions is 2.570 m/s, and the detonation speed of its dust is 3.400 m/s. Efficiency (high explosiveness) of ammonium nitrate, depending on the mass fraction of the organic impurity in its composition, is defined as: The paraffin content, % wt. Operability, cm 3

1 178

26

2.5 207

4 260

5.5 325

Dry and chemically pure finely ground ammonium nitrate, nonwaterproof, is not sensitive to the detonator cap and detonating cord. Only in a strong metal shell finely ground ammonium nitrate detonates from the primer ‒ detonator and detonating cord. An intermediate detonator in the form of a piece of pressed TNT weighing at least 50 g is needed to excite a continuous detonation in ammonium nitrate of ordinary grinding in a paper shell. The sensitivity to detonation increases with the introduction of organic additives in the nitrate, and the sensitivity to impact also increases.

3.2. Dynamons and their main characteristics Dynamons are mixtures of unexplosive combustible materials and ammonium nitrate. Dynamons contain the most various combustible materials: peat, moss, sawdust, paraffin, solar oil, etc. Critical diameter of a detonation of dynamons can change from several millimeters to tens of centimeters. The impulse depends on dispersion of particles and the cover material initiating it. The explosive properties of dynamons depend on the technology and composition of their manufacture. Dynamons have a strong dependence of detonation capacity on moisture, caking, and degree of compaction due to the absence of an explosive sensitizer in their composition. Table 3.2 Physico-chemical characteristics of dynamons Composition, wt %: 1 Ammonium Nitrate LW Mineral oil Aluminum powder Oxygen balance, % Heat of explosion, kcal/kg Volume of gases, l/kg Operability, cm3 Brisancy, mm Critical diameter, mm in a paper cover in a steel shell

27

AM-8 2 89 3 8 -0.1 1.180 830 420-440 14-16

AM-10 3 87.7 2.3 10 +0.25 1.295 800 425-460 15-17

20-22 10

15-18 10

1 Charge detonation speed, m/s in a paper cover with a diameter of 60 mm in a steel shell with a diameter of 17 mm

2

3

3.400-3.600 3.170

3.400-3.700 3.290

Dynamons based on granulated ammonium nitrate impregnated with 4-6% wt. liquid, hot-melt petroleum products, mainly diesel fuel and paraffin, have recently become widespread. The coarse-dispersed structure of granulated dynamons determines their susceptibility to explosive impulse compared with powdered dynamons and reduced detonation ability. Granulated dynamons stably detonate only from additional detonators: detonite, trotyl drafts, etc.). In the case of the use of microporous granulated ammo-nium nitrate, the detonation ability of granulated dynamons increases markedly, the release of which is of great importance in developed countries. The main advantages of granular dynamons are their low sensitivity to mechanical stress, high flowability, and the absence of dusting. The simplest two-component compositions: granulated saltpeter ‒ diesel oil can be made directly at the mining enterprises, using mobile or stationary mixing and charging units. The first type of granulated dynamon, made directly at the mining enterprises, was igdanite, developed at the A.A. Skochinsky Institute of Mining in Russia. For the manufacture of igdanite several grades of diesel fuel, based on weather conditions are used. In addition to diesel fuel, in some cases it is allowed to use cheap petroleum products and their waste (fuel oil, used oils). Later granulites ‒ prefabricated dynamons are introduced. It is, as a rule, three-component compositions, two-component are called granulites. The most important performance characteristic for factory-made granulites is physical stability, determined by the immobilization ability of ammonium nitrate with respect to liquid fuels and oils. To increase the immobilization capacity of ammonium nitrate, there are two ways: ‒ to increase the porosity of granules in ammonium nitrate (the presence of a developed inner surface of ammonium nitrate granules); ‒ apply oil absorbing combustible surface additives. As a result, a two-component composition is formed: granulite M is made on porous ammonium nitrate of brand P, and three-com28

ponent compositions: granulites АN-8, АN-4, N-2 are made on usual non-porous ammonium nitrate of brand B. As a liquid fuel oils of brand 45 or industrial brand I-40A in three-component formulations are used, oil solar or absorption oil are used in two-component formulations. Aluminum powder and wood flour in granulites of brand N and AN are used as additives. The latter significantly increases the heat of the explosive explosion. The presence of the liquid phase leads to easy compaction of igdanite and granulite. The loading density of boreholes during pneumatic charging reaches 1.2 g/cm3, and that of wells ‒ 1.1 g/cm3, which significantly exceeds the density of charging by patronized and pressed ammonites (0.7-0.8 and 1 g/cm3, respectively). Due to high volumetric energy, the methylized granulites compacted in bore-holes (wells) by efficiency of detonation are not inferior to the most powerful patronized explosives ‒ detonites and rock ammonites. The disadvantages of granulites and igdanite are their low water resistance. Therefore, in the field of view of the industry there are also combustible components: low-melting petroleum products (paraffin, wax, etc.), which increase the water resistance of granulites. Granules, covered with a frozen film of water-insoluble petroleum products, with a relatively long stay in water, retain their explosive properties. Granulite P (a mixture of ammonium nitrate with paraffin) is characterized by the following indicators: the critical diameter of open charges at an intermediate detonator is 100–200 g, TNT is 90 mm, and the detonation velocity at this diameter is 1,880–2,020 m/s. Granulites are insensitive to the detonator caps and detonating cord, but they are reliably detonated from an intermediate detonator ‒ ammonite cartridge No.6 of iron-optics with a mass of 200 g. The composition and properties of granulites are given in tab. 3.3. Table 3.3 The composition and properties of granulites Indicators 1 Composition, % by wt. Ammonium nitrate granulated Industrial oil Instrument oil

AN-8 2 89

Granulites AN-4 N-2 3 4 91.8 92.8

3.0 -

4.2 -

29

4.2 -

M 5 94.5 (porous)

Igdanite 6 94.5

5.5

5.5

1 Aluminum powder Wood flour Oxygen balance,% Heat of explosion, kcal/kg Volume of gases, l/kg Working capacity, cm3 Blasting in steel rings blasting, mm Critical diameter in paper shell, mm Speed of detonation, m/s (charge weighing 50g in a steel shell with a diameter of 38-42 mm, an additional detonator ‒ a piece weighing 102) Sensitiveness to impact, %

2 8.0 +0.34 1,242

3 4.0 +0.41 1,080

4 3.0 +0.06 917

5 +0.14 920

6 +0.14 920

847 410-430 24-28

907 985 980 390-410 320-330 320-330 22-26 15-22 18-22

980 320-330 15-20

80-100

100-120 120-130

70-100

120-150

3,0003,600

2,6003,200

2,4003,200

2,5003,600

2,2002,800

8-12

4-12

0-4

0

0

Questions for self-control 1. Indicate stable modifications and metastable forms of ammonium nitrate. 2. List the organic substances that lower the thermal stability of ammonium nitrate. 3. List the main characteristics of dynamons. 4. What are the disadvantages of granulites and igdanites?

30

4.1. Composition, physico-chemical and explosive properties of ammonites Ammonites are industrial explosives consisting of ammonium nitrate and nitro compounds, mainly TNT. Ammonites can be finely divided and coarsely dispersed, depending on the degree of grinding of the components. Coarse grammonites are used for loading wells of increased diameter (80 mm and more). They consist of granulated nitrate and granulated or flaked TNT. The addition of combustible components (wood or peat flour) is provided to reduce production costs and reduce caking. TNT in ammonites plays the role of an active fuel, being a sensitizer, since it decomposes much faster and easier than ammonium nitrate in a detonation wave. Ammonites have a higher detonation ability than dynamones. To obtain explosives with a very small critical diameter and high critical density and to further increase the detonation ability, an additional sensitizer is introduced into them ‒ nitroglycerin, hexogen or tan. The detonation properties of ammonites are regulated by the content of trotyl and the dispersity of the components. The increase in the content of TNT in ammonites at a given density reduces the diameters of detonation (dcritical, dlimit); for a given charge diameter, the critical density (corresponding to the boundary of stable detonation) and optimal density (corresponding to the maximum detonation velocity) of the explosive increase. When the content of trotyl is more than 50% by wt., ammonite acquires detonation properties close to those of trotyl in a rather wide range. With an increase in the density dcritical does not increase, as is typical of low-percent ammonium on trotyl, but decreases, as in trotyl. The energy characteristics of ammonites (bulk and without water) are highest with a stoichiometric ratio of components. The stoichiometric ratio corresponds to a mixture containing 79% by wt. of ammonium nitrate and 21% by wt. of TNT. This mixture in powder form is often used as a reference for comparative assessments 31

(QV = 1,030 kcal/kg) of explosive properties of industrial explosives. A mixture of scaly trotyl and granulated ammonium nitrate of the same composition is called grammonite 79/21. The main purpose of powdered ammonites is to load wells and holes during underground mining with cartridges with a diameter of 32 to 90 mm. For the manufacture of ammonites, waterproof ammonium nitrate LW (liquid waterproof) is mainly used. For underground works, ammonite No. 6 LW is the most common ammonite. When carrying out cleaning works in some underground mines, dinaphthalite is used, produced according to the runner technology. Ammonite No. 7 LW, previously used in underground explosions of rocks of small and medium strength (in the extraction of brown coal, potash ore, etc.), is currently not produced due to the high labor intensity of production. Ammonals are mixtures of aluminum and ammonium nitrate in energy significantly higher than the mixture of nitrate with TNT. The maximum amount of heat (Q = 2,330 kcal/kg) is released during the explosion of a mixture containing 40% by wt. of aluminum, according to the reaction: NH4NO3 + 2 Al → Al2O3 + 2H2 + N2. In the explosion of a mixture containing 18.5% by wt. of aluminum, water is present in the reaction products: 3NH4NO3 + 2 Al → Al2O3 + 6H2О + 3N2. The amount of heat released (QV) is about 1,600 kcal/kg. Ammonals, due to their low detonation ability in their pure form, are rarely used in blasting operations (large critical diameter, low susceptibility to detonation impulse). With the introduction of aluminum in the amount of 4-10% by wt., the heat of ammonite explosion increases by 100-300 kcal/kg (ammonal WA-4 (W-waterproof) and rock ammonites ‒ ammonals). Rock Ammonite No. 1 (ammonal No. 1) is intended for blasting particularly hard rock and is produced mainly in a pressed form. Rock Ammonal No. 3 is produced in a powdered, patronized form with a reduced diameter in cartridges of normal diameter (32-36 mm and 60-90 mm). 32

The use of powdered ammonites is currently unpromising: they do not meet the requirements of mechanized methods of loading, they are dusting, compressed and poorly transported. They remain promising only as ammunition fighters. They remain promising only as live ammunition. These negative properties of powdered ammonites are partially eliminated in grammonites, in which ammonium nitrate is presented in the form of granules of 2-3 mm in size, and trotyl in the form of scales in grammonites of 79/21 and 79/21 HM (Hot Mix), in the form of granules in grammonite 30/70, in the form of a film of TNT, covering the granules of ammonium nitrate during its crystallization from the melt in grammonites 50/50-W (W-waterproof) and 30/70-W. In grammonals (aluminum powder in molten TNT and granulated hardened suspensions of ground ammonium nitrate), in addition to TNT, aluminum is included. Grammonals and grammonites in industry are represented with both zero and negative oxygen balance. The first are used on the surface as well as underground, the second is intended only for open work. The most common during blasting is ammonite 79/21, it is less compacted than granulites and has no water resistance. In grammonite 30/70 ammonium nitrate relatively quickly goes into solution and does not have hydrophobic protection. However, in the solution, it participates in the explosion process as an oxidizing agent until its volume (in solution) exceeds the charge volume; in practice, the energy of explosives (immobilized with water) corresponds to the energy of water-filled TNT. If the amount of water becomes limiting, the participation of dissolved ammonium nitrate will not be complete in the chemical processes of the explosion. Grammonite is more effective in partially watered wells where there is no running water. TNT in grammonite 30/70 is used in the form of granules of 5 mm in size. Granules with such dimensions drown in water better and are less phlegmatized by water due to a decrease in the contact surface of TNT with water. Waterproof grammonite of brand W is prepared by spraying molten TNT (melting temperature ~ 82 °C) into granules of ammonium nitrate in the apparatus «fluidized» bed, grammonals – by mixing the aluminum powder and the ammonium nitrate with the molten TNT in the paddle mixer. 33

Grammonites 30/70-W and 50/50-W, as well as Grammonal A-45 are used in open works, the first two are close to TNT in power, and the third is much higher than TNT. Their water resistance in-creases with an increase in the content of trotyl, the most resistant to water is the composition 30/70-W. Grammonal A-8 is designed for underground works, with little moisture it is not dusty and is well compacted in the wells during pneumatic charging and in wet holes. The detonation rate of grammonites strongly depends on the diameter of the charge. The dependence becomes weaker for blasting in wells drilled in hard rock. Grammonites detonate on a mode which is close to ideal, corresponding to the maximum velocity of detonation at minimal chemical losses in the rock wells with a diameter greater than 200 mm. For a complete detonation of grammonites, a rather powerful initial impulse is required; therefore, trotyl pieces are used as intermediate detonators, and ammonite charges are also used for dry charges. Gramomonals detonate from the blasting cap, but more reliably they detonate from the intermediate detonator. The tables show the basic properties of ammonites (tab. 4.1), grammonals and grammonites (tab. 4.2). Table 4.1 Physico-chemical and explosive properties of ammonites Ammonites Indicators

1 Composition, % by wt: Ammonium nitrate waterproof Ammonium nitrate TNT (trotyl) Dinitronaphthalene Wood flour Aluminum powder Paraffin

AmmoDinal naphNo. 6 No. 7 No. 9 No. 10 WA-4 thalite LW LW LW LW 2 3 4 5 6 7

Ammonal rock (powdered) No. 1 No. 3 8

9

79

81.5

87

85

80,5

35(15*)

66

72

-

-

-

-

-

53(73*)

-

-

21 -

16 2.5 -

5 8 -

8 7 -

15 4.5

11.6 -

5 5

5 8

-

-

-

-

-

0,4

-

-

34

1 2 3 4 5 Hexogen Oxygen balance, -0.42 +0.34 +2.74 +1.53 % Heat of explosion, 1,030 995 857 908 kcal/kg Volume of gases, 895 905 933 924 l/kg Efficiency (high explosiveness) by 360- 350- 300- 300Trauzl sample, 380 370 320 320 cm3 Brisancy, mm 10.015-18 15-17 11-13 12.5 Critical diameter of open charge, 10-13 11-13 20-25 15-20 mm Detonation speed, 3.63.53.03.2km/s 4.8 4.0 3.5 3.6 Density, g/cm3 Sensitivity to impact, %

1.01.2

0.951.1

0.951.1

6 -

7 -

8 24

9 15

+0.18

+0.3

-0.79

-0.78

1,180

975

1,292 1,360

845

920

830

810

410430

320340

450480

450470

18-20

15-16

18.518-20 22.5

12-14

13-14

5-6

8-10

4.04.5

3.54.6

4.85.3

4.04.5

1.01.1

1.01.15

0.950.95-1.1 1.0-1.15 1.1

16-32 16-28 12-24 12-24

24-36

12-24

40-60 40-44

Table 4.2 Physico-chemical and explosive properties of grammonites and grammonals Indicators 1 Composition, % by wt. TNT Ammonium nitrate Aluminum powder Oxygen balance, % Heat of explosion, kcal/kg Volume of gases, l/kg Efficiency (high explosiveness) by Trauzl sample, cm3 Brisancy in charges in a steel shell, mm Critical diameter of open charge without water, mm

Grammonites 79/21 30/70 50/50-B 30/70-B 2 3 4 5

Grammonals A-8 A-45 6 7

21 70 79 30 +0.02 -45.9 1,030 950 895 800

50 50 -27.15 985 810

70 30 -45.9 950 800

12 80 8 -0.24 1,285 860

45 40 15 -38.65 1,490 752

330340

340350

330340

420440

440460

20-25 24-27

23-25

24-27

-

30-32

50-60 40-60

40-50

40-60

30-40

60-80

360370

35

1 Detonation speed, km/s in a waterless state in a water-filled state Bulk density, g/cm3 Sensitivity to impact of crushed dry explosive, %

2

3

4

5

6

7

3.0-3.6 0.800.85

-

3.6-4.2 5.2-5.6 0.850.90

3.8-4.5 5.5-6.0 0.850.90

3.8-4.0 0.850.90

5.8-6.3 0.900.95

12-24

12-16

24-36

24-36

-

12-24 12-24

For loading the wells with running water in the open mine workings, granular mixture of TNT and aluminum (15% by wt.) ‒ alumotol (alumotrinitrotoluene) and granulated trotyl (granulotol) are widely used. Alyumotol is prepared by the method of aqueous granulation of aluminum powder suspension in the molten trotyl. Alumotol and granulotol retain the ability to detonate in clean water for a long time. In alkaline waters, their chemical stability is reduced. It is economically advantageous to use alumotol and granulotole only in wells filled with water. In addition, the water charge of the charges leads to an increase in their density, which increases the explosion pressure, and with a negative oxygen balance of explosives, the reaction gas of the generator gas 2CO ↔ CO2 + C + Q shifts to the right and additional heat is generated. For alumotol and granulotol, a secondary flame is characteristic due to burning of hydrogen and carbon monoxide in the air, which is negative for such explosives. The explosive characteristics of alumotol and granulotol are given in Table 4.3. Table 4.3 Explosive properties of granulotol and alumotol Indicators Heat of explosion, kcal/kg Volume of gases, l/kg Efficiency (high explosiveness) by Trauzl sample, cm3 Brisancy in charges in a steel shell, mm Critical diameter of open charge without water, mm Detonation speed, km/s Bulk density, g/cm3 The density of the granules, g/cm3

Granulotol Alumotol dry water filled dry water filled 825-870 1,000* 1,130-1,260 1,340* 745 895 635 815 285-295

320

420-440

-

24-26

32-34

28-30

-

60-80

-

70-80

-

4.5-5.0 0.95-1.0 1.48-1.54

5.5-6.7 -

4.3-4.8 0.95-1.0 1.52-1.68

5.5-6.0 -

Note. * ‒ experimental results without water evaporation

36

4.2. Suspension explosives and their characteristics There are the following types of suspension explosives, which are solid particles containing continuous liquids in the form: 1) non-condensed solution of the oxidizing agent (water + oxidizing agent); 2) thickened oxidant solution (water + oxidizer + thickener); 3) thickened and structured oxidant solution (water + oxidizer + thickener + structurant). In the first case, the oxidizer solution is a crystalline solution containing solid particles, in the second case ‒ a colloidal solution, in the third case ‒ a gel-like solution, which contains two continuous phases ‒ a crystalline solution and «thick» colloidal particles connected to each other (cross-linked) by hydrogen bonds and particulate matter. The combination of the bulk rigidity of the structure of solid particles with the two interpenetrating phases that fill it gives such an explosiveness to their gel-like character. As gelling agents, guargam and polyacrylamide are often used, for which a crosslinking agent in the form of other salts or borax is necessary. Carboxymethylcellulose salts (sodium, ammonium) form less stable gels with lower water resistance. But they are able to quickly dissolve in cold water, so that they are used for the manufacture of dry semi-finished products to be filled with water in mixing-charging machines. The content of the thickener in suspension explosives is usually from 0.7 to 1.5% by wt., water ‒ 5-15% by wt. For aluminum-containing water-filled explosives, it is necessary to ensure their physical stability in addition to chemical resistance, taking into account the ability of aluminum to interact with water, especially in the presence of alkalis. Two effective methods were found for the internal stabilization of aluminum-containing water-filled explosives ‒ passivation of aluminum particles and waterproofing. External stabilization is achieved by the use of a polymer shell (cartridges). 4.3. Emulsion explosives and their characteristics Emulsion explosives are a new stage in the development of industrial explosives. Emulsion explosives consist of two liquids that 37

do not dissolve in each other, one of which (the dispersed phase) is distributed in the other (dispersion medium) and belongs to disperse systems. For emulsion explosives, the dispersion medium is a mixture of mineral oil (sometimes diesel fuel) and wax (reverse emulsions ‒ water/oil) and the dispersed phase is the smallest droplets of an aqueous solution of ammonium nitrate. At high magnification under a microscope, the structure of an emulsion explosive resembles a honeycomb. The thickness of the membranes of oil and wax separating droplets of an aqueous solution of nitrate is less than one ten-thousandth of a millimeter. This creates a colossal area of contact between the oxidizing agent (ammonium, sodium, calcium nitrates) and fuel (oil, wax, diesel, etc.). The result is a very complete and rapid explosive combustion. Oil and wax membranes make emulsion explosives very waterproof and protect every drop of aqueous nitrate.

a

b

Figure 4.1. Structure under a scanning electron microscope: a ‒ emulsion matrix, b ‒ emulsion explosive

The degree of sensitivity of emulsion explosives varies by adding sensitizing additives, which are gas-generating additives (chemicals that generate gas when they enter the emulsion) or microballs (hollow glass balls). Air inclusions or microballs are destroyed under the action of the shock wave from the action of the blasting cap. Thus, a rapid explosive burning of the emulsion begins and the destruction intensifies the shock wave. 38

Emulsion explosives acquire explosive properties only at the final stage of production, when a sensitizing additive is introduced, and do not contain raw materials classified as explosives. Emulsion explosives are not sensitive to impact, friction and fire.

4.4. The composition and properties of suspension explosives Carbotols is a mechanical mixture of carbamide, ammonium nitrate with TNT and aluminum, which maintains fluidity to 65 °C and forms high-density castings during curing in the well. The optimal content of Na-CMC (carboxymethylcellulose) –2.0%, guargam ‒ 0.8%, PAA (polyacrylamide) –1% with a structurant ‒ for Na-CMC and PAA: chromium-potassium alum, chromium sulphate, for guargam ‒ potassium bichromate. Component composition: the ratio of water: carbamide and trotyl is 4.10.15% by wt., the compositions contain aluminum powder from 15 to 35% by wt. Charges density is from 1.55 to 1.63 g/cm3, detonation speed is 4.5-5.3 km/s, heat of explosion is 820-1,360 kcal/kg, critical detonation diameter is 230260 mm. The composition of the suspension of explosives may include perchlorates, ammonium nitrate and other nitrates. Perchlorates are characterized by their lower solubility in water than in nitrates. At the same time, a positive fact for perchlorates is the fact that the solubility is less dependent on temperature. Perchlorates are more energy-intensive than nitrates, due to which the energy characteristics of the explosives themselves are higher compared with analogues containing ammonium nitrate. Gelexes contain ammonium perchlorate as a satellite of recyclable solid rocket fuel. Calcium nitrate and urea are used in suspension (emulsion) explosives as an additive that lowers the crystallization temperature of ammonium nitrate from solution. Water-filled explosives, which, in addition to ammonium nitrate, contain sodium nitrate, have a higher detonation rate and density. The optimum ratio between sodium and ammonium nitrate is the ratio of 0.185:0.815. The production technology of aquatols M-15 and 65/35 consists of the following operations: 39

1. In the factory, dry semi-finished product is made by mixing flaked TNT, granulated ammonium nitrate, sodium salt of aluminum powder and carboxymethylcellulose (if necessary according to the recipe). 2. In the quarries and mines just before filling the wells, water filling is carried out on stationary installations or semi-finished products of factory production in self-propelled mixing and charging machines of the type «Aqual». Water filling is carried out with hot water heated to 85-95 °C so that the temperature of the finished explosive is not lower than 30 °C, at which fluidity is maintained, allowing the mass to flow out of the machine under the action of compressed air. All operations of the technological process can also be carried out at blasting sites: 1. Preparation of a hot (75 °C) saturated ammonium nitrate solution with a concentration of 30.8% by wt. 2. Mixing the solution of TNT and ammonium nitrate in heated stationary mixing plants. Other components are added together with TNT (additional amount of solid ammonium nitrate, aluminum powder, etc.). 3. The introduction of a thickener in the composition of the prepared explosives in the process of mixing with TNT or in the process of preparing a saturated solution of nitrate. 4. Delivery of explosives to the place of loading and blasting wells. As the explosives cool down in the well, a portion of the nitrate crystallizes out of solution and the mass acquires a solid-like consistency. In this way (directly at the blasting sites), the so-called hot-running ones are made: ifzanites and aquatols. In aquatols, ammonium nitrate content is 66-74% by wt., TNT is 20% by wt., and water is 6-14% by wt. The high fluidity of ifzanites and aquatols at the moment of loading water-filled wells causes physical stability and reduced water resistance. These deficiencies are devoid of gel (plastic) water-filled aquatols AW and MH, produced by factories in cartridges of the required diameter in polyethylene shells. Guargam with a crosslinking additive and polyacrylamide are used as thickeners. Thanks to antifreezes, gel-like aquatols retain 40

plasticity up to -18-20 °C in winter. Gel-like aquatols do not lose their explosive properties for several days after being under water. For underground works, the following suspension explosives are used, manufactured at factories in the form of cartridges of different diameters (aqual No.1 and aquanites No. 2, 3, 16). Aquanit 3L, with high fluidity, is designed for loading inclined and horizontal holes and wells using injection pumps.

4.5. Nitroglycerin and perchlorate industrial explosives 4.5.1. Nitroglycerin industrial explosives Nitroglycerin explosives are industrial explosives that contain nitroglycerin in their composition, regardless of the nature and content of other components. They are classified according to the consistency of explosives, according to the content of nitroglycerin (or other nitroesters close to it) and other features. The explosives of this type by the content of nitroesters are divided into: ‒ low-percentage (15% by wt.); ‒ medium-percentage (60% by wt.); ‒ high-percentage (more than 60% by wt.). According to the second sign, explosives of this type are divided into: ‒ plastic, ‒ powdered, ‒ semi-plastic; Plastic and semi-plastic are called dynamites. Powdered explosives include compounds containing not more than 15% by wt. of nitroesters. Due to the fact that nitroglycerin has a high crystallization temperature (+10 – +13 °C), the compositions on its basis become solid (plasticity is lost) at temperatures below those indicated. The compositions in this state become very sensitive to various mechanical impulses, lose flowability. In practice, a mixture of nitroglycerin with other nitroesters-diethylene glycol and ethylene glycol, is usually used to prevent this behavior of nitroglycerin. A mixture of nitro 41

diglycol and nitroglycerin in a 1:1 ratio turns into a solid state at a temperature of –19.5 °C. To prevent leakage of nitroesters and nitroglycerin from the composition of the explosives they are usually thickened by dissolving pyroxylin containing 12.0-12.5% by wt. of nitrogen. Non-concentrated nitroesters are used if their content in explosives does not exceed 5-6% by wt. Currently, only nitroglycerin powdered explosives are used: ‒ non-protective detonites; ‒ safety ammonites sulfur and oil, uglenites, pobedites, et al. Chemical composition of detonites is close to ammonal, but they additionally contain from 6% to 15% by wt. of a mixture of nitroglycol and nitroglycerin. In terms of their mass energy characteristics, they belong to powerful industrial explosives. Detonites are more sensitive to mechanical stress than ammonites, so their use in bulk is not allowed. At temperatures below –20 °C, they do not lose their flowability, although they harden, especially detonite 15A, which contains 15% by wt. of nitroesters. With a decrease in temperature, the sensitivity to the initiating pulse somewhat decreases, which is manifested in a decrease in the detonation transfer distance between the cartridges, but remains at a sufficiently high level to ensure reliable detonation of blast-hole charges. Powdered detonites have a high detonation ability (small dcritical). Therefore, detonites are produced in cartridges of reduced diameter ‒ 24-28 mm and the standard diameter – 32-36 mm. To ensure reliable water resistance, 0.7% by wt. of calcium stearate or zinc stearate is additionally introduced into the composition of detonites. The properties of detonites are presented in tab. 4.4. Table 4.4 Physico-chemical and explosive properties of detonites Indicators 1 Composition, % by wt.: Nitroesters (hard-freezing) Ammonium Nitrate TNT

6A 2 6 77 11

42

Detonites 10A 15A 3 4 10 76 8

14.7 74 -

M 5 10 78 -

1 Aluminum powder Calcium Stearate (Zinc) Pyroxylin Soda (in excess of 100% by weight) Engine oil Oxygen balance, % Heat of explosion, kcal/kg Volume of gases, l/kg Performance on Trauzl, cm3 Brisancy, mm Critical diameter of open charge, mm Speed of detonation in cartridges with a diameter of 24 mm, km/s Transfer of detonation at a distance (cm) between cartridges with a diameter of 24 mm Density of explosives in cartridges, g/cm3 Sensitivity to impact, %

2 3 5.3 5.2 0.7 0.7 0.1 0.2-0.3 0.2-0.3 -1.00 +0.51 1,218 1,200 837 828 425-440 430-450 17-18.5 17-20 8-10 6-8 4.0-4.3 4.2-4.5

4 10 1.0 0.3 0.2-0.3 -0.75 1,407 778 470-520 18-23 4-9 4.3-5.0

5 10,7 1.0 0.3 0.2-0.3 0.2 +0.18 1,382 832 460-500 18-22 8-10 3.9-4.3

10-15

6-12

1.1-1.2 1.15-1.25

1.2-1.3

1.1-1.3

32-56

48-88

40-60

5-8

6-10

40-78

The detonation parameters make it possible to use detonites as ammunition fighters to initiate low-sensitive granulites, igdanites and 3L aquanites. The disadvantages of detonites include their high toxicity, which is characteristic of all powders and nitroglycerin explosives. Of the detonites, the most perfect in explosive and physicochemical properties is M detonite. Its production has good profitability.

4.5.2. Perchlorate industrial explosives Perchlorate explosives are mixtures in which perchloric acid salts, sodium, potassium and ammonium perchlorates, are used as an oxidizing agent. Ammonium perchlorate decomposes according to the following equation: 2NH4 ClО4 → Cl2 + 4 H2O +2 NO + O2 + q. The heat of formation of ammonium perchlorate Qformation (298) = = +70.69 kcal/mol. 43

Potassium perchlorate decomposes according to the following equation: КClО4 → КCl +2О2 ± q. The heat effect (q) of this reaction ranges from –38.9 to +9.6 kJ/mol. Sodium perchlorate is decomposed by a similar equation: NaClО4 → Na Cl +2О2 + q. The heat of formation of sodium perchlorate is taken as Qformation (298) = = ‒92.2 kcal/ mol. Perchlorates as oxidizing agents give a large energy gain compared to ammonium nitrate. Thus, stoichiometric mixtures of nitrate with TNT have an explosion heat of about 1,000 kcal/kg, with aluminum ‒ 1,600 kcal/kg, with paraffins ‒ about 900 kcal/kg, the same mixtures with ammonium perchlorate give the following heat of explosion – 1,326, 1,250 and 2,150 kcal/kg, respectively. Perchlorate mixtures are very sensitive to friction and impact; therefore, the use of such mixtures is problematic. A promising direction should be considered the use of water-filled perchlorate explosives. Potassium perchlorate as the flame arrester is a part of some safety explosives. Questions for self-control 1. Production and main purpose of powdered ammonites. 2. List the main characteristics of suspension (slurry) explosives. 3. Production technology of aquatols M-15 and 65/35. 4. Classification of nitroglycerin industrial substances. 5. The main characteristics of perchlorate explosives.

44

There are four main characteristic forms of chemical transformation of explosives:  thermal decomposition ‒ occurs when the explosive is heated below the flash point. The balance between the heat output and the input heat is important (an explosion may occur);  combustion ‒ occurs during strong heating of individual foci, which leads to the movement of this zone due to the heat released throughout the explosives. The reaction rate of propagation is up to several meters per minute;  detonation ‒ an explosive transformation that is little dependent on external pressure and temperature and maintained due to a sharp jump in temperature and pressure in the zone of chemical reactions;  explosive combustion ‒ an intermediate mode between detonation and combustion; it propagates through the explosive at a speed of up to several hundred meters per second. An important characteristic of industrial explosives is the oxygen balance, indicating a lack or excess of oxygen to the amount necessary for the oxidation of combustible elements to higher oxides. Virtually any explosive substance consists of four basic elements, the general chemical formula of which can be represented as СaНвNсOd. Then the oxygen balance can be calculated by the formula (in %): Kδ = ([d-(2a+0.5b)]16/Mexplosive)·100%,

(5.1)

where M is the molecular mass of the explosive, 16 is the atomic mass of oxygen. There are positive, negative and zero oxygen balances. At Kδ = 0, oxygen is sufficient for the oxidation of H and C to higher oxides; when Kδ < 0, CO is released and oxygen is insufficient; at Kδ > 0, the excess of oxygen goes to the formation of poisonous gases NO2 and NO. The amount of heat released decreases with 45

a lack of oxygen, because the reaction of formation of CO comes with less heat than the reaction of the formation of CO2. When explosives explode with Kδ = 0, the minimum amount of poisonous gases and the maximum possible amount of energy are released. In underground explosions it is allowed to use explosives only with Kδ close to zero, in quarries and with a negative Kδ value. Oxygen balance of some industrial explosives: Grammonite 79/21 ≈ 0 Igdanite + 1.4% Granulotol – 74% Granulite AN-4 + 0.4% Grammonite 30/70 – 45.9% Granulite AN-8 + 0.3% Grammonite 50/50 – 27.5% Granulite M + 0.1% The composition of the products of the explosion, which stand out as a result of the chemical reactions of the explosive transformation of the explosive, is important for calculating the heat of explosion, the volume of the explosion gases, the complete ideal operation of the explosion (design characteristics of explosives). All explosives are conventionally divided into 3 groups: 1. Explosives with oxygen sufficient to oxidize combustible elements to higher oxides (Kδ ≥ 0). When preparing the reaction, nitrogen is released as a molecular gas (nitroglycerin reaction), first of all, hydrogen is oxidized, then carbon: 4С3Н5(ОNО2)3 → 10Н2О + 12СО2 + О2 + 6N2 + Q. 2. Explosives with oxygen sufficient for complete gassing (gas formation). When preparing the reaction, hydrogen is first oxidized to water, carbon is oxidized to carbon monoxide. The remaining oxygen with a part of carbon monoxide forms carbon dioxide (the reaction of TEN and hexogen): С5Н8N4О12 → 4Н2О + 3СО2 + 2СО + 2N2 + Q C3Н6N6О6 → 3Н2О + 3СО + 3N2 + Q. 3. Explosives with insufficient oxygen to form gaseous products. To compose reactions of this type, hydrogen is first oxidized to 46

water. The remaining oxygen carbon is oxidized to carbon monoxide and free carbon is released (the reaction of TNT): 2С7Н5N3O6 = 5H2O + 7CO + 7C + 3N2 + Q. These reactions give an approximate characteristic of explosives and are possible only under ideal conditions. In real conditions, the composition of the products depends on the specific conditions of use of explosives and is more diverse.

5.1. Formation of poisonous gases at explosion In quarries, blasting operations are accompanied by the release of a large amount of gaseous products, some of which are poisonous. In the composition of the explosion products one can isolate nitrogen oxides NO, NO2, N2O4; carbon monoxide CO; H2S hydrogen sulfide; sulfur dioxide SO2; as well as lead compounds and mercury vapors, formed during the electric and firing methods of blasting. Carbon monoxide CO is a colorless gas, almost odorless. It is well dissolved in water, its density is equal to the density of air. In small quantities causes dizziness, severe headaches, nausea. At high concentrations, convulsions and poisoning occur with loss of consciousness. At poisoning it is necessary to take out the victim to fresh air immediately and whenever possible to give oxygen. Threshold limit value at long stay of people should not exceed 0.02 mg/l (0.0016% of volume of air). Nitrogen oxides are more dangerous, than carbon oxide. They have a pungent smell, yellow-brown color. At explosions NO nitrogen oxide which in air passes into NO2 or N2O4 is usually formed. When combined with water vapors in air, nitrogen oxides form nitric or nitrous acids, which at inhalation of air are deposited on mucous membranes and in lungs, causing hypostasis. Threshold limit value of nitrogen oxides of 0.005 mg/l (0.0001%), concentration of 0.02% is deadly even at short inhalation. Sulfur dioxide is a colorless gas with a strong irritating odor and sour taste. Sulfurous acid is formed in the air with water vapor. The maximum permissible concentration is 0.0007% of the volume. 47

Hydrogen sulfide is a colorless gas with the smell of rotten eggs. In combination with air hydrogen sulphide is explosive. The maximum permissible concentration is 0.00066%. Mercury vapors have no color, smell or taste. Mercury vapors damage the kidneys and the central nervous system. The maximum permissible concentration in the atmosphere is 0.00001 mg/L. To calculate the total amount of toxic gases released, the formula in which the volume of gases is converted to the volume of CO is used: V = VCO + 6.5(VNO + VNO2 + VN2O4).

(5.2)

5.2. The heat and temperature of the explosion. The volume and pressure of the gaseous products of explosion The volume of the gaseous products of the explosion can be determined experimentally (Dolgov’s bomb) or calculated analytically. Based on the Avogadro law, an analytical determination is made of the volume of the explosion products, according to which the volume occupied by a gram-molecule of gas at a temperature of 0 °C and a pressure of 9.8.104 Pa is equal to 22.4 L. The volume of gas formed at the explosion of 1 kg of explosive is calculated by the formula: V 

22,42( n1  n2  n3  ...  nn )  1000, m1 M 1  m2 M 2  m3 M 3  ...  mn M n

(5.3)

where n1, n2, n3,., nn are the amounts of gram-molecules of the gaseous products of the explosion; M1, M2, M3, ..., Mn are the molecular weights of the components of the composite explosive; m1, m2, m3, ..., mn are the numbers of gram-molecules of the components of the composite explosive. As an example we will consider calculation of the volume of gaseous products at hexogen explosion: 48

С3Н6N6O6 → 3H2O + 3CO + 3N2, V = (22.42·(3 + 3 + 3)·1,000)/222 ≈ 909 L/kg To determine the volume of gaseous explosion products in the Dolgov’s bomb (a steel vessel with a capacity of up to 50 liters with a massive lid and valves for pumping air and measuring the pressure of the explosion gases), up to 100 g of explosive are exploded. After an explosion for 30 minutes, the bomb is aged in air to equalize the temperature outside and inside and the pressure inside the bomb is measured. The volume of gases Vg, reduced to normal conditions, is calculated by the formula:

Vg=[Vb(P-W)T·1,000]/760Tbq,

(5.4)

where Vb is the volume of the bomb, l; P is the pressure in the bomb after the explosion; Tb is the temperature of the bomb at the time of pressure measurement, °C; q is the mass of explosive explosives, T = 273K. The specific energy or heat of explosion is the amount of heat that is released during the explosion of 1 kg of explosives and is expressed in kJ/kg. The heat of the explosion is one of the most important characteristics of explosives. If the heat of the explosion is multiplied by the density of the explosive in the charge, then we obtain the volume concentration of energy (kJ/m3). The heat of the explosion is calculated on the basis of the Hess law, according to which the thermal effect of the chemical transformation of the system depends only on the final and initial states and does not depend on the intermediate ones. The heat of explosion can be calculated at constant pressure or at constant volume: Q1 + Q2 = Q3, 49

(5.5)

where Q1 is the heat of formation of the components of a mixed explosive, kJ/kg; Q2 is the heat of explosion, kJ/kg; Q3 is the heat of formation of explosion products, kJ/kg. Thus, the heat of the explosion is determined from the equation Q2 = Q3 – Q1.

(5.6)

The heat of formation of the components and products of the explosion that are part of the explosive is determined by reference books (reference books on thermodynamics). Experimental determination of the heat of explosion is carried out in calorimetric installations with bombs with a capacity of 5-50 liters, in which explosives weighing up to 100 g explode. The explosion temperature is the maximum temperature to which the explosion products are heated. The temperature of the explosion is usually determined on the basis of the calculated heat of explosion and the heat capacity of all products of the explosion by calculation using the formula t

Q2 , CV

(5.7)

where Q2 is the heat of explosion, j/mol; СV is the average heat capacity of all explosion products at a constant volume in the temperature range from 0 to T °C, J/(mol °C). The value of heat capacity depending on the temperature is determined from the expression CV = a + bt, where a and b are the temperature coefficients. Having solved together equations (5.6) and (5.7) we get: t

 a  a 2  4Qb . 2b 50

(5.8)

When determining the heat capacity of a mixture of gases, it is necessary to take into account the fraction of each of them. The calculation formula takes the form: t

  a  (  a )2  4(  b )  Q  1000 2 b

.

(5.9)

The pressure of gases generated during the explosion of explosives is determined by the law of Boyle-Mariotte and Gay-Lussac: P

P0V0T , 273V

(5.10)

where Po is the atmospheric gas pressure at a temperature of 0°C equal 1,01.105 Pa; Vо is the volume of explosion gases at zero temperature and pressure Po, m3; T is the explosion temperature, K; V is the volume of the charging chamber, m3. With the actual charging densities, the volume of explosion molecules (co-volume) plays an important role, which is assumed to be α = 0.001Vо (for ρ = 0.5-1 t/m3) and α = 0.0006Vо (for ρ > 1 t/m3). Taking into account co-volume the pressure is calculated by the formula: P

PoV0T . 273( V   )

(5.11)

5.3. Detonation and its conditions for explosives In accordance with the hydrodynamic theory, the detonation of explosives is the displacement of a shock wave through explosives, which in a certain layer causes an abrupt change in all thermodynamic parameters: temperature, pressure, density. Behind the wave front there is a sharp heating of gases and explosive particles. As a result, an intensive chemical reaction begins 51

with the release of heat, the energy of which supports the further propagation of the shock wave. Distinctive features of the shock wave are: a) the medium moves after the shock wave front; b) the speed of propagation is higher than the speed of sound in this environment; c) an abrupt increase in pressure, temperature and density occurs at the wave front; d) the velocity of the shock wave depends on the pressure (amplitude) at the wave front. A detonation wave is a shock wave passing through the explosive and causing it to detonate. Detonation is a stationary process, i.e. it spreads with a constant pressure, amplitude and velocity (fig. 5.1 a, b).

ρ1 T1 P1

ρ0 T0 P0

Figure 5.1. The process of detonation of explosives: 1 ‒ explosion products; 2 ‒ detonation wave front; 3 ‒ the front of the expansion of the explosion products; 4 ‒ not expanded gases (ρ1, T1, P1); 5 ‒ rarefaction wave front; 6 ‒ shock wave

The theory of detonation is designed for gas mixtures. For solid condensed explosives, it is not yet fully developed. It is established that the velocity of the gases behind the detonation wave front (v w), the pressure at the detonation wave front (P) and the detonation velocity (vd) are related by the following relations: P = (ρ v2d)/4

(5.12)

vw= vd/4

(5.13)

52

vd = vw + c,

(5.14)

where c is the speed of sound in detonation products, km / s. The speed of detonation can be determined by the following formula: 𝑣𝑑 = √2𝑄2 (𝑘 2 − 1),

(5.15)

where k is a coefficient, the value of which is taken depending on the heat of explosion at a constant volume (Qv) and explosive density (ρ). In theory, it is assumed that the detonation wave front causes chemical reactions and compresses the layers of the explosive in the front. This mechanism is possible only with the explosion of onecomponent powerful explosives (tetryl, hexogen or RDX, TEN or PETN) and is considered homogeneous. Industrial explosives are multicomponent mixtures, i.e. physically and chemically they are heterogeneous. For such explosives, explosive transformation is multistage (primary and secondary chemical reactions). First, the bonds in the explosive molecules or their gasification break, then they interact with substances that have not undergone changes in the first stage (aluminum oxidation) or between themselves. The uniform distribution of the components in the mixture and the particle size distribution have a significant impact on the detonation process of industrial explosives. Chemical reactions first proceed in separate granules and only then the decomposition products interact with each other. Questions for self-control 1. List the chemical conversion forms of explosives. 2. Classification of explosives according to oxygen balance. 3. Poisonous gases during explosive transformations. 4. Theoretical determination of the volume and pressure of the gaseous products of the explosion. 5. Detonation wave and its main stages.

53

6.1. Mine atmosphere of underground mine workings, underground gas and dust explosions The main characteristic of the atmosphere of coal mines is the presence of coal dust and methane. Along with methane in the atmosphere of mines, other unsaturated and saturated hydrocarbons (ethane, propane, ethylene), carbon dioxide, nitrogen, carbon monoxide, hydrogen sulfide, sulfur dioxide, hydrogen are contained in small amounts. On average, natural gas produced in coal mines contains 1– 4% of heavy hydrocarbons, 80–83% of methane, about 10% of nitrogen, 5% of carbon dioxide and less than 1% of other gases. There are bonded (associated) and free state of gases in the rock. Associated gas is gas adsorbed by rock. Free gas accumulates in cracks, voids and pores of the rock. The ratio of free gas to associated gas is approximately 1:3. The release of gas from the massif into the atmosphere of mines is of three types: ordinary ‒ from cracks and pores that are not visible to the eye, suflyar ‒ visible to the eye from the cracks, sudden, when the gas is ejected from the mass of the massif, with simultaneous ejection of coal, usually within a short time. The gas pressure in coal seams reaches 60 kg·s/cm2, depending on the depth. Fossil coals are characterized by gas content, which is determined by the gas content (m3) per 1 ton (or m3) of coal. Coking coals and anthracites are the most gas-bearing, brown coals containing a large amount of volatile substances are the least gas-bearing. Coal mines by the amount of gas emitted into the atmosphere per unit time (gas content) are divided into four categories: 1 category – gas content no more than 5 m3/t, 2 category ‒ from 5 to 10 m3/t, 3 category ‒ from 10 to 15 m3/t, super-categorial ‒ more than 15 m3/t. Dust in mines is formed especially intensively when machinery and machines are working, when coal is transported, and when blasting operations are in progress. Weighted dust (or «particulate matter», PM) accumulates on the surface and accumulates in significant 54

quantities. During blasting operations, settled dust rises into the atmosphere with a shock wave, as a result of which an explosive dust cloud is formed. The explosiveness of coal dust is usually assessed by the content of gasification products in coal ‒ volatile substances formed by heating coal without oxygen at a temperature of 850 °C. The content of volatile substances in coal minus the ash content is expressed in% by wt., referred to anhydrous coal. Coal mines are dangerous for dust, if the content of volatile substances in the coal by mass exceeds 10%. Dangerous because of gas content: ‒ potash mines; methane and hydrogen is contained in their mine atmosphere; ‒ ozokerite and oil mines; methane and other unsaturated and saturated hydrocarbons are contained in their mine atmosphere (the special danger is constituted by vapors of gasolines). Sulfuric mines are classified as dangerous due to dust, in the atmosphere of which high-explosive sulfur aerosols are located. The explosiveness of sulfur aerosols is enhanced by the presence of methane and flammable hydrogen sulfide in the atmosphere. Mines that develop other sulfide ores and pyrites are less dangerous in underground dust explosions than sulfur mines. The presence of dust and combustible gases in the atmosphere of underground mine workings creates the danger of dust and gas explosions. An explosion can occur under the influence of a spark, a ray of fire and other sources of heat. During blasting operations, explosive mine environment can be affected by solid and gaseous explosion products heated to a high temperature, incandescent metal slags of electric detonators and fragments, and air shock waves. Analysis of the causes of accidents during blasting in the mines of Donbass for the 1957-1967 period shows that about 50% of accidents are associated with the use of explosives of insufficient detonation ability and anti-crushiness (burnout). 6.2. The mechanism of gas and dust explosions of mine gases The basis of dust and gas explosions is self-accelerating exothermic oxidation reactions of sprayed solid (liquid) substances or combustible gases. 55

Oxidation of methane by air oxygen is described by the reaction with the release of a large amount of heat [2·57.49+94.51–17.7 = = 191.79 (kcal/mol)] and can occur as an explosion under certain conditions (a sufficient initial impulse and vessel diameter): СН4 + 2О2 → СО2 + 2Н2О. At the same time, hydrocarbon molecules interact with oxygen with great difficulty. This is explained by the fact that in the initial reactants for the rearrangement of atoms it is necessary to break the primary bonds with an energy expenditure of 50–100 kcal/mol. In nature, there are less stable systems that contain atoms (free radicals) or valence unsaturated compounds. Free valence facilitates the interaction of reagents, in this case, the activation energy decreeses to 0–20 kcal/mol. An important feature of radical reactions is that in some cases more than one radical is formed, and at least one of its products is also valencely unsaturated. In general, the oxidation of hydrocarbons is a radical chain reaction with degenerate chain branching and includes the following main stages: a) chain generation (formation), which proceeds as a mono, bi and trimolecular reaction: Ко СН 3 Н  СН 3  Н  /

Ко СН 3 Н  О2  СН 3  НО2



Ко 2СН 3 Н  О2  2СН 3  Н 2О2 ; //

b) continuation (development) of the chain: К1 СН 3  О2  СН 3 О2



К2 СН 3 О2  СН 3  Н  СН 3 ООН  СН 3 ;

c) chain branching as a result of monomolecular decomposition of hydroperoxide, the reaction of two hydroperoxide groups with each other or hydroperoxide with a hydrocarbon: 56

К4 СН 3ООН  СН 3O ОН /

К4 СН 3ООН  СН 3 Н  СН 3O   СН 3  Н 2О 

//

К4 2СН 3ООН  СН 3O2  СН 3О   Н 2О .

It is assumed that the radicals ОН and СН3О quickly react with the surrounding substance (CH4), turning into methyl radicals:

СН 3О  СН 4  СН 3ОН  СН 3 ОН   СН 4  СН 3  Н 2О ; d) the break of a chain occurs as a result of disproportionation or a recombination of any two free radicals participating in the oxidetion reaction: 

К6 2СН 3  СН 3  СН 3 

/

К6 СН 3  СН 3О2  СН 3ООСН 3 //

К6 2СН 3О2  СН 3ООСН 3  О2 .

It follows from the laws of chemical kinetics that the oxidation of hydrocarbons passes through a chain of the above-described elementary acts involving radicals, with lower energy costs compared with the direct reaction of the interaction of oxidant molecules and fuel. Self-acceleration of chain reactions leading to a thermal explosion occurs under the condition of transition to a non-stationary selfaccelerating regime with prevailing or equal branching over a chain break, with a sufficiently high heat release (chain-thermal explosion) and a sufficiently large number of initial centers of radical formation. Many substances affect the kinetics of chain reactions, slowing down or speeding them up. Positive catalysts contribute to the branching and nucleation (formation) of chains. Inhibitors ‒ catalysts bind or destroy the active centers, which contribute to the chain breakage. In practice, in addition to homogeneous catalysis, which

57

takes place entirely in the gas phase, heterogeneous catalysis is carried out at the interface. Hydroxyl radicals are destroyed on alkali metal salts. Since the OH• radical during the oxidation of methane is one of the leading active centers, its recombination on the surface of alkali metals leads to a change in the kinetics of the reaction, all other things being equal, this is expressed by an increase in Tignition. By blowing inhibitor powders into a vessel heated with a gas, it was shown that the flame-retarding ability of a series of salts with respect to methane-air mixtures fit in a row in decreasing efficiency: KF, KI, NaAlF4, KCl, NaSiF4, NaCl. The effectiveness of salts is increased by increasing the dispersion and with a decrease in their melting temperature.

6.3. Explosiveness and flammability of coal dust The flammability of suspended particles of coal dust suggests that gasification is preceded by heating ‒ under the action of a heat source there is a release of combustible gaseous products. Coals of all grades emit flammable gases when heated to several hundred degrees, which mix with air and form a two-phase (dust+gases) explosive dust-gas-air mixture. The induction period of the flash of the dust-air mixture consists of the induction period of the flash of the dust-gas-air mixture formed and the gasification time. Based on this mechanism, the flammability of suspended coal dust is strongly dependent on the chemical composition and size of dust particles and on the content of volatile substances in the coal. Typically, gasification products are: carbon monoxide, hydrogen, methane, etc. The explosive mixture can form from the underlying on the walls and soil dust generation layer under the action of the primary shock wave caused by explosion in the array of the explosive charge. The ignition temperature of coal dust ranges from 750 to 1,105 °C, contained in the mine atmosphere, methane increases the danger of coal dust explosion: 0.3-0.5% of methane makes explosive mixtures that are not capable of exploding in their pure form and facilitate the ignition of dust. 58

With an increase in the ash content in coal dust, its explosiveness decreases. Moisture coating particles, make it unable to exposure. The best flame extinguishing effect has dust of chalk, carbonates, limestone, dolomite. The most explosive is sulfuric dust, the temperature of flash of an aero suspension of sulfuric dust is 260-290 °C. Ignition of sulfuric dust is preceded by the expressed induction period at which the first stage is sulfur evaporation, the second – its oxidation in vapor. Oxidation of sulfur has the chain character by the mechanism:

S  O2  SO  O ;

SO  SO  SO2  S ;

O   S  2  SO  S ; SO  O2  SO2  O and so on. Effective flame arresters of sulfur dust suspension are materials that can cool the products of the explosion due to the absorption of heat by evaporation, decomposition, dehydration: water, sodium sulfate (crystalline hydrate), ammonium carbonate, ammonium chloride. Sulphidic dust by inflammability holds average position between coal and sulfuric dust. The mechanism of oxidation of sulphidic dust assumes that the reaction has the chain mechanism and proceeds according to the following scheme: FeS2  O2  FeS  SO  O ; SО  O2  SO2  O  ;

FeS  O2  FeO  SO ; SO  SO  SO2  S ; 2FeO  O  Fe2O3 ; S  O2  SO  O .

The active centers in these reactions are atomic oxygen (O•) and the radical SO•. The most typical flash point temperature of sulfides is 400500 °C. For sulfide dust, flame arresters with inhibitory properties were not detected. 59

6.4. Ignition by an explosive impulse of combustible mine environments The mechanism of initiation of dust and gas explosions at a detonation of charges of explosives has a complex character. At the explosion the ignition of the mine environment is determined by the shape and the amount of energy imparted to the medium, by the explosion conditions and the nature of the interaction of carriers with the energy medium. This energy should be sufficient to start a selfaccelerating oxidation reaction and to overcome the thermodynamic barrier in a certain volume of the medium, resulting in an explosion. The initial center in which there is a flash should be sufficient for distribution of the flame throughout the environment. As explosive oxidation develops in time and has the chain and thermal nature, its course is influenced by catalytic properties of the gaseous and solid products of detonation, kinetic characteristics of the mixture, which is mixing up with the medium, the character and conditions of the mixture of gases, conditions of reflection of shock waves, the mode of burning of particles. The minimum amount of energy released during the explosion of an explosive material, i.e. the critical value of the explosive impulse, sufficient for ignition of the combustible medium, can be calculated only for specific conditions of interaction of the explosion with the medium in a specific space. Any of the listed igniting agents (red-hot solids, gaseous products of the explosion, shock waves, etc.) can ignite a hot environment. Different hypotheses, mainly of a qualitative nature (E. Audibert, K. Beiling, etc.), were developed to explain the mechanism of ignition of combustible mine environments under the influence of an explosion of explosive materials. W. Shefferd suggested that the methane-air mixture ignites when collision of shock waves is reflected from the drift walls. Subsequently, other researchers (K. Beiling and others) assigned to the shock wave the role of an indirect factor contributing to ignition. E. Audibert continued the research, and K. Beiling confirmed that the ignition of the methane-air mixture is caused by solid heated particles, with the main role being assigned to deflagrating particles. 60

These burning particles have a high temperature at which the flash delay is so small that it has time to occur at even a high particle velocity. E. Audibert offered the mechanism of the process of methane ignition at explosion of a charge of explosive material: «ignition mechanism by mixture». At explosion of a charge of an explosive, the methane-air mixture mixes up with explosion products. If the flash point is reached during the process of diluting of the explosion products with a methane-air mixture, the methane-air mixture will ignite. The impossibility of obtaining ignition according to E. Audibert when blasting in coal is determined by the following inequality: q < 21.5-0.94n,

(6.1)

where q is the specific energy per unit volume of explosion products (kcal/mol), n is the oxygen content in the explosion products in % by wt. Experiments of E. Audibert showed that explosives with negative and positive oxygen balance are dangerous in relation to the ignition of methane. The least dangerous are the compositions, the oxygen balance of which is close to zero. In order for explosives to meet the criterion of E. Audibert, to reduce the specific heat of explosion, they have to contain a large number of inert additives. In the 60-70s of the 20th century a research of the process of ignition showed that ignition of methane-air mixture is caused by a complex of factors, i.e. a joint influence of several igniting agents, at the same time calculation of such a combined influence in specific conditions presents great difficulties. Nevertheless, according to the ignition mechanism, the experimental material makes it possible to predetermine safe conditions for blasting operations in mines and to create special safety explosives. The major qualitative safe conditions are the following: 1. The ignition effect of an explosion relative to combustible mine environments is defined as the specific thermal characteristics of explosives, expressed, for example, by the temperature of the explosion products ‒ T1 = Q/nc or the heat of explosive transformation ‒ Q (kcal/kg), and by the total charge energy ‒ E = GQ (kcal, where 61

G is the mass of the charge), with each of these characteristics may have an independent value. This means that the equality of the total energy of charges consisting of explosives with different temperatures or heat of explosion does not determine their identical igniting ability. As a rule, explosives have a higher flammable ability with a higher specific heat energy. And, on the contrary, at any specific characteristics, such mass of the charge can be found at which the combustible medium can ignite. It is explained by the existence of various mechanisms of ignition in which the defining factors are either the total or specific heat of explosion. Thus, at ignition by gaseous explosion products in a stream with red-hot solid particles, their temperature or their heat content per unit volume of gases is decisive, and when ignited by reflected shock waves, the total explosion energy with which the the wave is incident on the obstacle are important. The total energy can be a defining characteristic in the case of ignition with a limited volume of the mine environment with homogeneous mixing of the explosion products. Specific thermal characteristics are the basis for the selection and classification of explosives according to the degree of anti-grisonity and reflect the individual properties of the safety explosives. The total energy underlies the limitations of mass charges, which are different for safety explosives of various degrees of anti-grisonity. 2. The critical values of the thermal characteristics of an explosion depend on the interaction of the products of the explosion (shock-air waves) with the medium (explosives, charges) and on the conditions of the blasting of charges, which cause ignition of the mine environment. As a result, it is advisable to limit the safety of explosives to the degree of anti-grisonity and power characteristics. The higher the probability of ignition of gas or dust in the mine development and dangerous conditions of blasting, the higher should be the class of explosives by safety. 3. The critical values of the energy characteristics of the safety explosives of all classes, i.e. regardless of the ignition mechanism and the conditions of interaction of the explosion products with a combustible medium, they increase if the inhibitors are evenly distributed in the medium. The higher the concentration of the inhibitor in the medium and the higher its catalytical activity, the higher the 62

ignition parameters of the combustible medium (induction period and flash point) and, accordingly, the higher the allowable energy level of the explosive (specific energy) or charge (total energy). Experimental studies of E. Audibert, K. Beiling of the effect of energy characteristics of explosives, density and brisance of explosives, mass, diameter and loading density, combustible shell of cartridges and composition of explosion products, moisture of explosives on the detonation speed of ignition showed that of all the properties of explosives, the ignition of the methane-air mixture during the explosion of explosives is most strongly influenced by the catalytic (inhibitory) properties of explosives contained in the composition salts ‒ flame arresters and energy (heat of explosion) of explosives. Gasoline blends with air are set on fire with explosives with lower energy costs. Gasoline-methane-air mixtures occupy an intermediate position between gasoline-air and methane-air mixtures by flammability. The hydrogen-air mixture is significantly more sensitive to an explosive impulse than the methane-air mixture. Some explosives containing alkaline-earth and alkaline nitrates will be anti-blasting relative to methane-air mixture, while at the same time not safe enough against coal dust. It is assumed that the increased igniting ability of explosives containing metal nitrates is associated with a two-stage process of igniting a suspension of dust, where the first stage is the gasification of coal particles. The burning particles of thermally resistant nitrates of metals, scattering during the explosion, fall into the gasified cloud of dust and ignite it. The most effective flame arresters with respect to coal dust are NaF and KCl, and less effective are NH4Cl and NaCl. Questions for self-control 1. Classify the mine atmosphere of underground mine workings, underground gas and dust explosions. 2. Describe the mechanism of explosion of gas and dust explosions of mine gases. 3. What is the oxidation of hydrocarbons in a radical chain reaction with degenerate branching of the chain? 4. Explain the mechanism, flammability of suspended coal dust, depending on the chemical composition and size of dust particles 5. List the energy parameters of the explosion and ignition of the mine environment.

63

7.1. Explosives for blasting only on the earth’s surface The main characteristics of explosives are presented in Table 7.1. Table 7.1. Prescribed composition and characteristics of explosives Components and indicators

Explosives Granulotol*

Composition, % Trotyl (TNT) 100 Ammonium nitrate Aluminum Water Specifications: Oxygen balance, % -74 Volume of explosion 1.045 gases, l/kg Detonation speed, km/s 5.5-6.0 Critical diameter, mm 5-10 Components and Explosives indicators Alumotol* T-20 Composition, % Trotyl (TNT) Ammonium nitrate Aluminum Water Specifications: Oxygen balance, % Volume of explosion gases, l/kg Detonation speed, km/s Critical diameter, mm

Grammonites 30/70 30/70W

50/50

70 30 -

70 30 -

50 50 -

-45.9 800

-45.9 800

-27.15 810

5.3-5.8** 10-15**

5.3-5.8** 10-15**

5.0-5.6 15-20

T-80

Carbatol GL-10V

Ifzanites T-60

85 15 -

20 66 14

20 72 8

20 74 6

-76.25 1.340

-1.6 937

-0.4 920

0 913

-21.4 8.44

5.5-6.0 5-10

4.2-4.5 100-120

4.5-5.0 100-110

4.5-5.0 90-100

4.5-5.1 35-40**

Note: * ‒ for water-filled condition; ** ‒ for water filled condition in steel pipe ø 40 mm.

64

Granulotol is a granulated trotyl with an average size of spherical granules of 2-4 mm. The granules are from light yellow to brown color, compactly fit and well drown in water, providing a charge density of 1 g/cm3. Granulotol is not dusty, free-flowing, nonhygroscopic, non-caking, practically insoluble in water. It is not sensitive enough to explosives, especially in the water-filled state. The greatest explosion effect for granulotol is observed in a waterfilled state, especially in a saturated solution of ammonium nitrate, which allows the loading density to reach 1.4 g/cm3. Alumotol is a granulated alloy of aluminum powder (15%) and TNT (85%). The granules are gray. Alumotol is sensitive to alkaline water, because aluminum is converted into hydroxide by interacting with alkali, which leads to some reduction in explosive power. It is designed for crushing hard, hard-to-explosive rocks of any watering. Alumotol is effective when used in the lower part of borehole charges, because a good development of the scarp foot and crushing quality is achieved. The use of alumotol reduces the amount of drilling by 30-40%. All other properties are the same as those of granulotol. Grammonite 30/70V is a granular explosive in which the graules of ammonium nitrate (30%) are coated with TNT (70%). The aveage granule size is 2-4 mm. Grammonite water resistance and hygrocopicity depends on the uniformity of the TNT layer on the surface of ammonium nitrate granules. It is free-flowing, it does not clog, it is practically dustless. In the wells with running water it can be up to 15 days, with non-flowing water ‒ up to 30 days. When blasting, its highest efficiency is achieved for rocks of medium and high strength. Under these conditions, it can replace the granulotol, since gramonite is cheaper than granulotol. Grammonite 30/70 is a mechanical mixture of granulated TNT (70%) and granulated ammonium nitrate (30%). In terms of its physical and explosive characteristics, it practically does not differ from 30/70 W grammonite. It is intended for use in wells with water, which should have enough water to dissolve ammonium nitrate and to fill the intergranular gaps of TNT with the solution. In dry wells this explosive is 20-30% more efficient than granulotol, it can be used in flooded wells with non-flowing water where there are moolithic rocks. 65

Grammonite 50/50 is a mechanical mixture of granulotol and granulated nitrate. It retains all the properties of grammonite 30/70 with the same application area except for flooded wells. Previously, it was produced in a waterproof form, but due to cracking of the film, TNT lost its water resistance when loading. The water filled explosives Ifzanites are not stratified suspensions from a mixture of TNT, granulated ammonium nitrate and a saturated solution of ammonium nitrate, filling the intergranular space in the charge of explosive. Perhaps, additional structuring with stitches and thickener. In open pit mining, ifzanites T-80, T-60, T-20 are approved for permanent use. The number in the name of the explosive indicates the tempeature of the saturated solution of ammonium nitrate. Ifzanites are intended for dry and watered wells with strong, hard-to-explosive rocks, they are classified as powerful explosives with an increased volumetric concentration of energy. Carbatols (HF-10W, HF-15T) are hot-flowing explosives that solidify after cooling in wells. They are made on a low-melting (alost anhydrous) mixture of ammonium nitrate and carbamide and mixed with granulotol when loaded into the well. Until hardening, the resuling suspension does not stratify, because the melt density is equal to the density of trotyl granules. In order to increase the explosion enery, an additional aluminum powder is introduced into the carbatols. The use of carbatol for crushing hard rock is 20-30% more efficient and more economical than the use of alumotol or granulotol.

7.2. Explosives for blasting in mines not hazardous on gas and dust, and on the earth’s surface It is the most representative class of explosives, including powdery and granular non-water-resistant and waterproof explosives, granulated without trotyl explosives, hexogen-sensitized and nitroether-containing. Many of them are produced in patronized form. Grammonite 79/21B is a granular explosive from light to dark yellow, well-flowing, in which ammonium nitrate granules are slightly oiled and covered with melted TNT. Grammonite is suitable 66

for mechanized loading and does not cake during storage. It is issued in paper bags. It is most effective in crushing rocks of medium strength. Granulites AN-4W, AN-8W are granular explosives with steelgray color, they are free-flowing. They are physically stable, do not clothe. Ammonium nitrate granules are covered with a thin layer of hydrophobic wax composition and sprinkled with aluminum powder, which is well kept on the surface. In wells with stagnant water and boreholes, granulites can be up to 4 hours. АN-8W is designed for blasting hard rock, АN-4W ‒ for blasting rocks of medium strength (equals to grammonite 79/21B). Grammonite 79/21 is a mechanical mixture of granulated ammonium nitrate and flaked or granulated powder. It is not caking, rather loose, non-resistant explosive, practically does not dust with manual loading. Grammonite 79/21 is approved for mechanized charging with injection of 3-5% water. It is effective in combined charges with granulotol and aluminotol when loading partially watered wells and for crushing rocks of medium strength. Granulites АN-4, АN-8 are silver-gray granulated metallized explosives. They are loose, greasy to the touch, do not clot, suitable for mechanized and manual loading, almost no dust. AN-8 is used for crushing hard rock, recommended for use mainly in underground works. AN-4 is recommended in combined well charges at open-pit and for crushing rocks of medium strength in open and underground work. Granulite M in appearance does not differ from the usual granulated ammonium nitrate and it is the simplest factory-made granular explosive. It is not caked, free-flowing, physically stable, practically dustless. Since the oil is uniformly absorbed by porous granules of ammonium nitrate, it is characterized by excellent detonation ability. Granulite M can be used for crushing hard rock, it is well compacted in borehole and blast-hole charges during pneumatic charging. It is most effective for crushing rocks of medium strength. Igdanite (or igdanit) is a safe, simplest explosive at the enterprises leading the blasting. It is a stoichiometric mixture of diesel fuel and ammonium nitrate. It is well loose, practically does not dust, pneumotransportable, it is well condensed in charges. Igdanite prepa67

red should be used within 4 to 6 hours (diesel fuel flows to the bottom of the charge and phlegmatizes it). The field of application of igdanite is the fragmentation of rocks of medium and weak strength in blast-hole and borehole charges. The calculated and experimental characteristics of the explosives are presented in Table 7.2. Table 7.2 Characteristics of granular explosives Components and indicators Composition, % 1 Ammonium nitrate granulated Trotyl (TNT) Aluminum powder Mineral oil Diesel fuel Indicators: Oxygen balance, %

Grammonites 79/21B 79/21

Volume of gases, l/kg Heat of explosion, kJ/kg Detonation speed, km/s Efficiency, cm3 Brisancy, mm (in the steel ring) Components and indicators Composition, % Ammonium nitrate granulated Trotyl (TNT) Aluminum powder Mineral oil Diesel fuel Indicators: Oxygen balance, % Volume of gases, l/kg Heat of explosion, kJ/kg Detonation speed, km/s

Igdanite

2 79

3 79

4 94.5**

21 -

21 -

5.5

0.02

0.02

0.12

895 1,030 3.8-4.2 360-380 22-26

895 1,030 3.2-4.0 360-370 20-25

980 920 2.2-2.8 320-330 15-20

AN-4 92 4

Granulite AN-4W AN-8 AN-8W

M

89

94.5*

4 -

-

8 3

-

5.5

0.41 907 1,080

0.35 907 1,080

0.34 847 1,248

-3.3 850 1,250

0.14 980 920

2.6-3.5

2.8-3.5

3.0-3.6

3.0-3.6

2.5-3.6

68

1 Efficiency, cm3 Brisancy, mm (in the steel ring)

2 390-410 22-26

3 4 1 2 390-410 410-430 400-420 320-330 22-24 22-28 22-26

Note: * ‒ porous ** ‒ nonporous crystalline, liquid water resistant (LW) is allowed.

7.3. Powdered explosives Ammonite No.6 LW (Liquid Waterproof) is the simplest mechanical mixture of powdered TNT and powdered waterproof AN (Ammonium Nitrate) of the LW (Liquid Waterproof) brand. It is produced in patronized form (ø 32 mm, m = 200 and 250 g) and in bags. It is used for the manufacture of cartridges, intermediate detonators, blasting (mainly blast-hole charges). It is relatively waterproof in running water (1 ‒ 2 hours). It is allowed for loading only manually, it is intended for crushing rocks of medium strength. Dinaphthalite is a half-grained little dusting light yellow powder. It is insensitive to mechanical stress, not caking, allowed to be loaded manually. It is designed for crushing rocks of medium strength. It is available in ø 32 mm cartridges. Detonite M is a dusting powder of explosive gray-steel color, powerful industrial explosive, greasy to the touch. It steadily detonates in charges of small diameter and after a long stay in water. It is issued only in patronized form. Detonite M is approved for manual loading. It is sensitive to sudden temperature changes (possible exudation). It is designed for crushing hard rock of any degree of watering. Rock Ammonite No.1 is produced in pressed or powdered form in a patronized state. When pressed, it detonates well in a wet state, waterproof. To mechanical stress Rock Ammonite No.1 has a heightened sensitivity. It is designed for crushing hard rock of any degree of watering with manual loading. Ammonal rock No. 3 is a steel-gray powder. It is not compressed, waterproof, well detonated in small-diameter cartridges. This is the most powerful of powdered explosives. It is intended for cru69

shing of strong and very strong rocks with blast-hole charges of any degree of watering. Ammonal Rock No. 3 is allowed only for manual loading. The calculated and experimental characteristics and composition of explosives are presented in Table 7.3. Table 7.3 Characteristics of powdered explosives Components and indicators

1 Composition, % Ammonium nitrate LW Ammonium nitrate crystalline Trotyl (TNT) Nitroesters Hexogen Aluminum powder Calcium Stearate Colloidal cotton Soda (over 100%) Engine oil (over 100%) Dinitronaphthalene

AmmoDinanite No. 6 phthalite LW

Detonite M

Rock Ammonite No. 1 pressed powdery

2

3

4

5

6

Ammonal rock No. 3 7

79

35

78

66

66

72

21

53

-

5

5

6

-

-

10 10.7

24 5

24 5

1.5 8

-

-

1

-

-

-

-

-

0.3 0.2

-

-

-

-

-

0.2

-

-

-

-

11.6

-

-

-

-

-

0.4

-

-

-

-

Indicators: Oxygen balance, % Volume of gases, l/kg Heat of explosion, kJ/kg Detonation speed, km/s Efficiency, cm3 Brisancy, mm

-0.53

+0.3

+0.18

-0.79

-0.79

-0.78

895

920

780

830

830

810

1,030

975

1.382

1.292

1.292

1.360

3.6-4.8

3.5-4.6

4.2-5.2

4.8-5.3

6.0-6.5

4.2-4.6

365-380 14-18

320-350 15-16

450 18-22

450-460 450-500 22 18

450-470 18-20

70

7.4. Safety Explosives Ammonite AS-5 LW (Ammonite Safety-5 Liquid Waterproof), with low protective properties, is a rather powerful explosive, which is a fine powder of light yellow color with separate large particles of salt. It is produced only in the patronized form for crushing rocks of any degree of watering with blast-hole charges. Ammonites PLW-20, T-19 are fine powders of light yellow color with separate large particles of salt. They are well detonated in water-filled blast-hole charges. With a strong compaction (up to 1.7 g/cm3) these are explosives of average power and safety have higher detonation characteristics, because they are technologically better processed and contain more sensitizer. Uglenite E6 is an explosive that selectively detonates depending on the blasting conditions. It is a fat white powder, almost nondusting. Its good detonation ability is ensured by the introduction of nitroesters. The process of exudation in the composition of the uglenite E-6 is hampered by wood flour. It refers to ion-exchange explosives – AN (Ammonium Nitrate) and flame arrester are formed as a result of ion-exchange reaction: NaNO3 + NH4Cl → NH4NO3 + NaCl. Table 7.4 Characteristics of safety explosives Components and indicators 1 Composition, % Nitroesters Sodium Nitrate AN brand LW (liquid waterproof) Ammonium chloride Sodium chloride Potassium chloride Trotyl (TNT) Wood flour Calcium Stearate

Ammonite AS-5 LW 2

Ammonite SLW-20 3

Ammonite T-19 4

Uglenite E6 5

70

64

61

14.0 -

12 18

20 16

20 19

71

46.3 7.0 2.5 1.0

1 Colloidal cotton Indicators: Oxygen balance, % Heat of explosion, kJ / kg Volume of gases, l / kg Brisancy, mm Efficiency, cm3 Detonation speed, km / s

2

3

4

5 0.2

-0.002 907 787 15-17 320-330 3.6-4.6

+0.32 813 717 14-16 265-280 3.5-4.0

-2.47 805 724 15-17 270-280 3.6-4.3

+0.53 640 560 8-11 130-170 1.1-2.2

7.5. Industrial explosives based on recyclable ammunition A large number of various ammunition and explosives are currently stored in the warehouses of the Ministry of Defense of the CIS countries, the warranty period of which has long expired or the ammunition itself is morally obsolete. Disposal of explosives and ammunition covers a limited list of products, so the bulk of such products is destroyed by blasting or burning. The release of harmful components into the earth’s atmosphere reaches enormous values. At the same time, a number of explosives and ammunition can be used in the national economy without complicated demilitarization and processing. These explosives can be divided into four classes:  solid rocket fuels;  engineering ammunition;  gunpowder;  ammunition combat units. The most widely used explosives are explosives based on smoky and colloidal powders (pyroxylin, ballistic, cordite). Colloidal powders are used for blasting operations using borehole, boiler, overhead, chamber and elongated (trench) charges. To separate the blocks of the stone rock from the massif using the method of blasthole charges, smoky powders are used. Currently, on the basis of pyroxylin powders phlegmatized with oil products, granipores are produced (PZF, FM, B1, B2, B3, VS). Granipores are produced in the form of particles ranging in size from 5 to 20 mm industrial grade I explosives, made on the basis of obsolete brands of ballistic powders. They are intended for blasting only 72

on the earth’s surface in flooded wells of rocks with a coefficient of strength up to 20. They are intended only for manual loading and are available in bags weighing 40-42 kg. In recent years, trotyl (TNT) has received widespread use in blasting operations, which is recycled from ammunition and is produced under the trademark TNT Y and is used to produce intermediate detonators, grammonites, and also as an independent explosive. The characteristics of some explosives based on recyclable ammunition are presented in Table 7.5. Table 7.5 Characteristics of industrial explosives from recyclable ammunition Explosive

TNT Granipor FM Granipor PZF Granipor B1 Granipor B3

Heat of explosion, kJ/kg 3,900 3,500 3,500 3,450 3,450

Oxygen balance, %

Detonation speed, km/s

Bulk density, kg/m3

-74 -(42-45) -(42-45) -(50-60) -(50-70)

5.0-5.5 5.5-6.3 5.5-6.3 4.5-5.0 5.0-5.2

800 850-900 850-900 750-850 700-800

Questions for self-control 1. Physico-chemical characteristics of explosives for blasting only on the earth’s surface. 2. What are the features of water filled explosives? 3. Explosives for blasting in mines not dangerous on gas and dust and on the earth’s surface. 4. The main types of powdered and safety explosives. 5. Industrial explosives based on recyclable ammunition.

73

8.1. Flammability and deflagration of safety explosives Detonation is not the only possible form of explosive transformation of explosives. Depending on the type and power of the initial impulse, the physical state of explosives and some other factors, such forms of explosive transformation as slow normal burning with speeds of the order of several millimeters per second are possible, as well as unstable explosive burning at speeds of tens and hundreds of meters per second. In mines, such an explosive transformation is called burnout or deflagration of explosives. The danger of burning safety explosives is that a slower interaction of the combustion products with an explosive environment at a sufficiently high temperature (800–1.000 °C) compared with detonation facilitates the conditions for the ignition of the medium. Studies of the flammability of the methane-air environment have shown that the higher the flame temperature and its magnitude, the less is its ignition delay. Based on this, the first criterion of anti-grisonity (or flameproofness) of explosives was the magnitude of the explosion flame. This ban was the first to get black powder, as fast explosive burning, which is the predominant form of explosive transformation. Another danger of burnout is related to the duration of the burning of the coal ignited in the hole or the duration of the very process of burning the explosives. The process in the mine environment becomes uncontrollable due to the violation of the blasting mode, leading to the possible achievement of explosive concentrations (for methane-air mixture ‒ 5%) and an increase in time. The possibility of sustained propagation of the transformation of explosives depends on the diameter of the charge, its character depends on the magnitude of the pulse. Each transformation regime corresponds to a certain critical diameter, depending on the physical state of the explosive and the chemical nature, size and properties of the shell of the charge and environmental properties. In addition, the combustion temperature to a greater extent than detonation is in74

fluenced by the temperature of explosives and ambient pressure. With an increase in these parameters, the ability to sustainably burn at a given diameter decreases and the critical diameter of a cylindrical charge capable of burning increases. This is postulated in the general form: with increasing pressure, the rate of combustion of explosives (Ucombustion) and powders increases based on the expression: Ucombustion = а Р,

(8.1)

where a and  are coefficients, P is pressure. An increase in the number of collisions of reacting particles depends on an increase in temperature and leads to an increase in the rate of combustion of the explosive. If a passive charge is capable of both detonation and burning, then at each fixed distance between the passive and active charges, one of the three events is possible with some probability: ignition, failure or excitation in the passive detonation charge. With an increase in the distance, the probability of burning and failure increases, the probability of detonation decreases and, starting from a certain distance, the probability of burning also decreases. The heated explosion products of an active explosive charge ignite a passive explosive charge. A mechanism of ignition of the failed part of the passive charge by the explosion products heated to a high temperature of the detonated part of the passive charge is possible if the integrity of the charging chamber (hole) is not impaired and the part of the charge detonated is relatively small. In this case, the gases are in contact with the unexploded part of the charge at a relatively high pressure for a sufficiently long time and the pressure drop of the heated explosion products is slow. Ignition of explosive passive charge by the above two mechanisms is known, but is not the only possible. A number of authors recommend the possibility of ignition of explosives by shock waves. The theoretical possibility of ignition of explosives by shock waves is indicated by the mechanism of shock excitation, the first stage of which is the ignition of a certain boundary layer regardless of the subsequent development of combustion or detonation and adiabatic heating. 75

In this case, the zone of ignition can be both discrete (focal heating) and continuous (homogeneous heating). Since warming up occurs as a result of adiabatic compression in a shock wave, each explosive, on the basis of its physical state and chemical nature, corresponds to a certain critical pressure Pcritical of the initiating wave, sufficient to heat explosives or individual sources in it (hot spots) to a flash point Tflash. In this case, the absolute value Tflash is weakly dependent on pressure. The nature of the heating determines the critical pressure of the initiating wave. For continuous (homogeneous) heating characteristic of physically homogeneous substances to flash point, for example, explosive liquids, single crystals or close to them low-porous systems: such as gels, emulsions, high-density pressings or castings, pressures of the order of tens of thousands of atmospheres are required. For focal heating typical of powdered explosives (when air is compressed between solid particles of explosives to a flash point, when rubbing between particles of a substance), emulsion explosives (when compressing air between liquid drops), much less pressure is required ‒ thousands of atmospheres. If the temperature itself (equal to the flash point) lasts in the substance for the duration of the induction period, the flash is realized, which corresponds to the state parameters of the compressed substance Tflash and Pcritical, i.e. the time of compression of the substance in the shock wave (or its stay in the compression phase) must be longer than the flash delay period: τcompression  τ (Tflash, Pcritical). A flash may not be realized if the reaction zone before the flash is captured by a discharge wave. For the initiation of a stable combustion in the explosive charge, the second condition is also necessary, which states: «the initiation of stable combustion in the charge is possible if the primary zone of ignition (a) created by the shock wave during steady-state combustion is not less than the heated layer ()»:

  .

(8.2)

The described model relates to the initiation of combustion by dynamic compression of explosives in a shock wave entering a 76

substance from a dense low-compressible medium. If the wave hits an explosive in the air, then in this case the ignition of the explosive by air heated in the shock wave reflected from the charge surface acquires priority significance. Due to the fact that the air has a high compactibility, even waves of low parameters cause its strong warming up. In addition, due to the difference between the densities of explosives and air, the pressure in the reflected wave is about 8 times higher than the pressure of the incident wave, which leads to an increase in the air heating. The development of detonation, in contrast to burning, is determined by the impact of the shock front and the intense reaction zone behind it. As previously mentioned, detonation repeatedly propagates if the dissipative energy losses of the shock wave are compensated by the energy coming from the chemical reaction zone behind the wave. In cases of burning, detonations, the initiating wave must be able to ignite explosives; for detonation, the reaction rate in the zone is more important, since it is necessary that the heat generated during a chemical reaction has time to feed the shock front, but some minimum heating layer is required to initiate the burning. Burning of the explosive material with a blast wave is possible: 1) as a result of contact with the products of the explosion of a passive explosive active charge; 2) surface ignition of the air heated in the reflected shock wave; 3) heating and adiabatic compression of the explosive itself by the shock wave. The combustibility of explosives is their ability to burn. The steady propagation of combustion in explosives is analogous to the propagation of detonation, starting from a certain charge diameter, which is called the critical burning diameter dcritical burning. In physical terms, this value does not fully coincide, although it is close to the critical detonation diameter dcritical. If dcritical is due to the introduction of a discharge wave into the zone or a radial spread of the substance from the reaction zone in the detonation wave, then dcritical combustion is associated with the removal of heat from the combustion zone into the environment due to thermal conductivity. Uniform spread of the flame on explosives i.e. the stability of burning is determined by the dynamic equilibrium of the heat flow. The amount of heat emitted from the combustion zone in front of the 77

underlying layers should be sufficient for evaporation (gasification) or heating of these layers to the ignition temperature, since most components of industrial explosives, such as ammonium nitrate, nitroglycerin, trotyl, etc., first heat up when heated and then react in the gas phase. It can be calculated from the overall dynamic heat balance of the system: qо = q1 + q2 + q3,

(8.3)

qо = Ucombustion Qcombustion,

(8.4)

or through mass speed:

where q1 is the rate of heat flow into the substance, q2 is the rate of heat removal to the environment through the side surface, q3 is the rate of heat removal by combustion products, Ucombustion is the mass combustion rate (g/cm2·s), Qcombustion is the heat of combustion (cal/g). The rate of heat removal to the environment through the side surface can be calculated: q2 = a S (Тcz ‒ Тb),

(8.5)

where a is the heat transfer coefficient to the environment, S is the heat transfer surface, Tcz is the temperature in the combustion zone, Tb is the temperature at the boundary with the environment. Since a significant proportion of heat generation relates to the reactions of evaporation or gasification of explosives, the burning rate becomes a function of pressure: Ucombustion = А + ВР,

(8.6)

where A and B are empirical coefficients determined by Po. The burning rate also depends on the initial temperature (To) of explosives: 78

Ucombustion 

1 , А1  В1Т о

(8.7)

where A1 and B1 are empirical coefficients. Between the values of dcritical combustion, T0 and P0 a certain relationship can be established. For a given T0 and P0, a certain value dcritical combustion will be determined under other constant conditions. And with a constant charge diameter, the value of P or T can be found, starting from which a stable distribution of burning is possible. It is accepted to call these values either critical temperature Tcritical combustion or critical pressure Pcritical. Any of these values can be taken as a criterion for the combustibility of explosives. The less dcritical combustion or Pcritical or Tcritical, the more combustible explosives. On this principle, various methods of experimental evaluation of the combustibility of explosives are based. Most industrial explosives have a relatively low flammability. Potassium chloride, sodium and ammonium, when their content in the composition of safety explosives is more than 10% by wt., lower the combustibility of the explosive, and when their content in the composition of safety explosives is less than 10% by wt. increase the combustibility of the explosive. The flammability of explosives increases dramatically when nitroglycerin is added to ammonium nitrate explosives (and nitroglycols) to 6% by wt. With the introduction of wood flour in ammonium nitrate explosives, the critical ignition pressure first increases (flammability decreases), reaches a maximum at a mass content of wood flour of about 1%, and then decreases to zero (when the content of wood flour is about 5% by wt.). Amines, crystalline hydrates, fluorine compounds, and water inhibit the flammability of protective explosives.

8.2. Detonation ability of safety explosives «Burnout» of safety explosives occurs in case that the explosion is incomplete and disrupts the normal mode of detonation in a blasthole charge. It turns out that the more reliable the detonation of the 79

pre-charge safety explosive charges is, the less likely they will «burn out». The reliability of the detonation of a multi-cartridge protective explosive (fig. 8.1) is mainly determined by three factors: ‒ the susceptibility of the action block (position 3) to the detonator capsule pulse (position 2), ‒ detonation ability of explosives in charge (position 4), ‒ the ability to transmit detonation from cartridge to cartridge.

Figure 8.1. The scheme of placement of the charge in the hole: 1 ‒ detonation cord, 2 ‒ detonator capsule, 3 ‒ cartridge-primed blasting, 4 ‒ the main charge of 4 cartridge, 5 ‒ stemming

The measures to evaluate these factors are the minimum initiating impulse (the charge of the initiating charge or the parameters of the initiating shock wave), the transmission distance of the detonation and the critical diameter of the detonation. These indicators depend on the physical state of the explosives laid down by the parameters of the production process (density, grinding degree, recipe). These initial physical properties of explosives may change during the preparation, storage and blasting in boreholes. The formation of jumpers from drilling mud and dust between the cartridges in case of poor cleaning of bore-holes and wetting of explosives in watered bore-holes causes incomplete explosions of multi-cartridge explosive charges. The resulting high pressure in the bore-holes during the explosion may contribute to the formation of large gaps between the cartridges and the ejection of the stem. 80

The more complex causes of burnout of explosives associated with the dynamics of blasting include: violation of the integrity and shape of the charge, which will affect the detonation mode along the length of the charge, compaction of explosives. Earlier, it was already noted that the detonation regime of an explosive is determined by the nature of the shell; the stronger it is, the more stable is the detonation regime. When loading holes between the cartridges and the walls of the hole, there is always some air gap that will affect the detonation mode in the direction of its attenuation and instability, especially for explosives of low detonation ability, which include ammonia-nitrate safety explosives. This effect on the detonation mode of the radial gap is called «the channel effect». Experimental studies have shown that the channel effect depends on the properties of explosives, increases with increasing pipe strength and mass, the length of the charge, the presence of bridges between the parts of the charge. It disappears at very small (less than 0.12 charge diameter) and very large gaps (more than 3 charge diameters) and reaches a maximum with a certain optimal gap (about 0.2 charge diameter). The surface roughness of the charge and the walls of the hole, as well as the overlap of the gap with cardboard or paper partitions, weaken the channel effect. The smaller the diameter of the charge, the more likely the detonation of the detonation of the charge from the channel effect. The radial clearance should be completely eliminated to prevent the channel effect, which is facilitated by the use of emulsion explosives in recent years. As a result of the use of short-delay blasting (after 15–25 s) or a variation in the response time of instantaneous electric detonators during group blasting, the interaction of adjacent blast-hole charges leads to compaction of individual charges. Previously exploded charges produce compression waves in the exploding coal mass that act on neighboring unexploded blast-hole charges, which are manifested in filling the free space of the hole with coal dust that has broken away from the walls of the hole and compaction of the explosive charge. Dust can form inert bridges between the ends of explosive cartridges and get between them, which can lead to an unstable detonation of such charges, affected by compression waves. 81

With group non-simultaneous blasting, the very fact of compaction of explosives is a negative phenomenon, since it leads to a change in the detonation mode. If we also take into account the fact that compaction of explosives in dynamic conditions (when exploded in mines) and in static conditions (on the press during manufacture) are essentially different processes, then throughout the explosives, compaction on the press leads to uniformity of density. In group explosions, compression with compression waves leads to uneven density across the entire explosive volume; according to the explosive charge, alternation of less dense with more dense areas occurs. This leads to a deterioration of the detonation ability of dynamically compacted safety explosives and may cause the explosives to burn out. Some researchers see a possible cause of burnout of protective explosive charges as the effect of explosion products of an exploding charge that spread through cracks and reached charges that have not yet exploded. The products of an explosion of a previously exploded blast-hole charge can reach the neighboring hole, spreading through the cracks, compact the charge, break the continuity, and in some cases, set it on fire.

8.3. Classification of safety explosives and principles of their composition The basic laws of ignition of aerosols and combustible gases by explosive impulse and the thermodynamics of an explosion modeled on the conditions of underground workings, outlined earlier, indicate the following ways to prevent ignition of a combustible mine environment and to ensure the reliability of detonation of explosive explosives: 1) control of the explosion energy depending on the conditions of blasting; 2) introduce inhibitors into the safety explosives, so that at a given level of anti-grisonity effects, it is possible to increase the level of energy characteristics of the safety explosives; 3) reduce the amount of solids in the explosion products, an increase in thermodynamic efficiency the blast. 82

Currently, the introduction of inhibitors in the safety explosives is a common method of creating safety explosives. By changing the content of such salts, it is possible to simultaneously adjust the surface of negative catalysis and the thermal parameters of the explosion. The protective properties of such explosives with increasing salt content increase due to the increase in the inhibitory effect and due to the decrease in the temperature of the explosion. During the first development of anti-grisonity explosives, inert salts were introduced into explosives to reduce the temperature of the explosion products. If the inert salts contained crystallization water and were still fusible, the effect of lowering the temperature of the explosion products was high. After publication of papers, in which the inhibitory effect of many oxides and salts was unambiguously revealed in the oxidation reactions of methane and other suspensions of combustible and gases, their introduction into the composition of explosives became targeted. Given that each inhibitor has its inhibitory activity, it became possible to use the inhibition effect when creating safety explosives. This makes it possible, with a constant mass content in explosives, by replacing a less effective inhibitor with a more effective inhibitor to increase the degree of anti-grisonity of safety explosives without altering the energy characteristics. In formulations of explosives, fluoride salts are the most effective inhibitors, but they are toxic. Of the chloride salts, the most acceptable are the sodium and potassium salts. Potassium chloride is more effective, but it is hygroscopic to a greater extent and the composition based on KCl is less waterproof than sodium chloride. Increasing the specific surface area of explosives or reducing the particle size can increase the inhibitory effect of salts, since the rate of heterogeneous catalysis is directly proportional to the surface of the catalyst. If it is assumed that the crushing ratio in an explosion is constant, then in the process of explosion after crushing the inhibitor with larger initial particles will have a larger particle size, and in the process of explosion after crushing, the inhibitor with smaller initial particles will have a smaller particle size. Phlegmatizing effect of non-explosive salt is enhanced by extremely fine grinding of the inhibitor. To neutralize the phlegmatizing effect of finely divided inhibitors, nitroglycerin or, more rarely, 83

RDX, PETN (Pentaerythritol Tetranitrate) sensitizers are often introduced into the safety explosives. To the greatest extent, in safety explosives, ultrafine spraying of the inhibitor containing ionic salts, for example, sodium or potassium nitrate and ammonium chloride, is used. These salts in the explosion interact by the reaction with the formation of ammonium nitrate, which further decomposes into nitrogen, water and oxygen, and sodium or potassium chloride, which is an inhibitor: NH 4 Cl  NaNO3  NaCl  NH NO  q . 4 3  2 H 2O  N 2  0.5O2

One of the reasons for the high protective properties of explosives containing an ion exchange pair of salts (NaNO3 + NH4Cl) is the formation of an ultrafine inhibitor (NaCl) during the explosion. The idea is realized in the combined cartridge of explosives, similar to the ion-exchange pair, when the salt aqueous solution of the inhibitor is brought to the periphery of the main explosive charge in the form of a shell. In the PVP-1 cartridges created at the MSRI, the main charge filled with saline solution is placed in a plastic sheath. It is possible to increase the effectiveness of safety explosives, depending on the conditions of blasting, by controlling the energy of the explosion. Such a problem is solved by the so-called selective detonation. The mode of such detonation can be created using a mixture of explosives containing components of different kinetic abilities: they detonate either all components or part of the most active components. For example, a mixture consisting of ammonium chloride, nitroglycerin and sodium nitrate of type of uglenit, explodes with a complete release of energy only in a closed chamber with strong walls. When such a mixture is blasting in air, low-active salts are scattered as inert substances since they do not have time to react in the detonation wave created by nitroglycerin, only nitroglycerin is detonated. Intermediate mode is also possible. A pronounced selectivity of detonation also has a mixture of nitroglycerin, pentaerythritol tetranitrate and hexogen with ammonium nitrate, with an increase in the size of the particles of nitrate the degree of selectivity of this mixture 84

increases. Water-filled explosives may also have selectivity, in which a part remains in a solid state, and a part of the oxidizer passes into an aqueous solution. The most dangerous for the ignition of gas and dust are the conditions in which the energy of the explosion is mainly concentrated in the explosion products heated to a high temperature and the mechanical work of the explosion is minimal. These conditions are met by an explosion of a partially or completely «naked» charge. Under these conditions, the heat release is minimal, which is not dangerous in terms of ignition of combustible gases and dust and the detonation of selective explosives does not occur completely. One of the effective methods to improve the safety of explosives can be to reduce the amount of solid phase in the explosion products, while their protective properties should not be reduced. It is possible to lower the temperature and heat of the explosion products if the oxidizer and fuel components with a high heat of formation are used. Based on the foregoing, it is necessary to be guided by the following when making the compositions of modern safety explosives: ‒ safety explosives should form or contain the most catalytically active inhibitors with particles of the minimum size during the explosion, ‒ experimentally or by calculation, determine the limit for this class of explosive energy levels of the safety explosives, regulated by the test conditions, ‒ provide the set energy level with the known thermochemical constants with the corresponding selection of active components of explosives, and if necessary – also include cooling explosion products into the composition of the substance, ‒ take into account heat when calculating the heat balance of the explosion, absorbed by the inhibitor, ‒ the minimum mass content of the inhibitor, provided a large specific surface of the inhibitor dispersible by the explosion, will contribute to an increase in thermodynamic efficiency of explosion, ‒ there are such preferable safety explosives which form explosion products with the minimum quantity of a solid phase at explosion of a fine suspension of highly active inhibitors, and also the explosives having ability to a selective detonation thanks to what de85

pending on the conditions of detonation they can have the properties corresponding to various classes of safety explosives. For safety explosives when solving the above problems, the general requirements for industrial explosives cannot be ignored: ‒ frost resistance; ‒ physical and chemical stability; ‒ manufacturability and safety of production; ‒ sensitivity to the initiating pulse; ‒ environmental safety. When classifying safety explosives according to their composition and properties according to the field of application, it is necessary to take into account that they are closely interrelated, since the conditions and field of application determine the properties and composition of the explosives. By application, safety explosives are divided into the following groups: ‒ explosives for sulfur and pyrite mines and other mining operations, hazardous of sulfur compounds and sulfur dust; ‒ explosives for coal mines and other mining operations dangerous of coal dust or methane; ‒ explosives for oil, ozocerite mines and other mining operations dangerous of heavy hydrocarbons and gasoline fumes. In each group, safety explosives are distinguished by the danger of mine workings for gas and dust and the conditions of use. In accordance with the accepted classification, safety explosives are subdivided into classes. Safety explosives for rock faces dangerous of methane and for special purposes ‒ Explosives of Class III. Explosives of this class should not ignite the methane-air mixture during the direct initiation and when blasting in the channel of the mortar. Typical representatives of explosives of this class are «Pobedit WP-4» and ammonite AP-5 LW (liquid waterproof). Explosives of Class III also include explosives intended for pyritic, sulfuric, petroleum and ozocerite mines, as well as other mining operations dangerous of heavy hydrocarbons and gasoline fumes. Currently, explosives of class III in coal mines are of limited use. 86

Explosives of Class IV are safety explosives for mixed faces of mines, hazardous of gas or dust and coal. These explosives are used in mine workings carried out on coal and rock on non-gas formations dangerous of dust explosion, as well as on formations with a small outgassing when explosive methane-air mixture is excluded in the process of blasting. The typical representative of explosives of this class is ammonite PLW-20 (liquid waterproof). When tested in the experimental drift, explosives of class IV should not ignite: ‒ dust-air mixture with its direct initiation by blasting in the channel of the mortar without tamping with a mass of 0.7 kg; ‒ methane-air mixture when it explodes in the channel of the mortar with a stemming (10 cm) charge of mass 0.6 kg with direct initiation. Currently, explosives of class IV are widely used in coal mines. Explosives of class V are explosives of increased safety for mixed and coal faces and special works in mines of all categories. These explosives are used in mine workings carried out on coal and rock or on coal with one outcrop surface, in which the formation of an explosive methane-air mixture is possible during blasting operations. Representatives of this class of explosives are uglenit-5, uglenitE-6 and cartridges PVP-1-U and PVP-1-A. When tested in the experimental drift, explosives of this class should not ignite the dust-air and methane-air mixtures when exploding in the channel of the mortar without tamping down a charge of 0.6 kg in reverse initiation and charge of 1.0 kg in direct initiation. Explosives of this class are widely used in coal mines. Explosives of class VI are high-safety explosives for special work in mines, especially dangerous on gas and coal breaking. Explosives of this class are used in mine workings carried out on coal or on coal and rock with two or more outcrop surfaces, where formation of explosive methane-air mixture is possible during blasting operations, and explosive charges can be exposed from the side surface through cracks or directly. When tested in the test drift, explosives of this class should not ignite: 87

‒ dusty and methane-air mixtures when exploding in a corner mortar (with a reflected wall at a distance of 0.6 m) of a charge weighing 1.4 kg. ‒ dusty and methane-air mixtures when exploding in the channel of a mortar without tamping up with a mass of 1 kg with direct and reverse initiation. Cartridges in solution-filled polyethylene shells ‒ SP-1 cartridges meet these conditions. The emergence of new knowledge in the study of the causes of accidents in mines during blasting led to practical results: the development of new formulations using components that enhanced the safety properties of used explosives. The following explosive mixtures appeared chronologically: ‒ explosive mixtures based on ammonium nitrate, having a large negative oxygen balance (due to the low temperature of the explosion products) or a large positive one; ‒ explosive mixtures containing inert additives in relation to explosive transformation, as the endothermic decomposition or heating of these additives consumes part of the thermal energy released during the explosion; ‒ explosive mixtures in protective shells of inert substances, which simultaneously provide high anti-crush resistance and high detonation ability; ‒ the inhibitor is directly introduced into the composition of explosives; explosive mixtures with catalytically active substancesinhibitors, flame arresters ‒ equivalent safety explosives; ‒ explosive mixtures, which, depending on the conditions of explosion, have selective detonation, selective safety explosives; ‒ explosive mixtures containing an exchange pair (NaNO3 + + NH4Cl), called ion exchange explosives. The explosive and physicochemical properties of modern safety explosives are presented in Table 8.1. All of them are produced on waterproof ammonium nitrate LW, have relatively high resistance to water, are stable during storage and can be used in all climatic zones. In the technological process of production of safety explosives for increasing their detonation ability the phase of intensive crushing of active components (TNT, ammonium nitrate) is used. 88

Table 8.1 Physico-chemical properties of safety explosives Composition,% by weight

TNT

Wood flour

Nitroesters

Sodium Chloride (Potassium)

Sodium Nitrate

Ammonium chloride

Stearates

68

17

-

-

(15)

-

-

-

70

18

-

-

12

-

-

-

65.5

12

1.5

9

12

-

-

-

64

16

-

-

20

-

-

-

61

19

-

-

20

-

-

-

Uglenit E-6

-

-

2.5 14.2

(7)

Selektit (granular)

66.5

-

8.5

10

15

-

-

Uglenit No. 5

14

-

1

10

75

-

-

Uglenit No. 7

-

-

Class

Ammonium Nitrate Liquid Waterproof

Explosive

III

IV

Ammonite AP-4 LW (Liquid Waterproof) Ammonite AP-5 LW (Liquid Waterproof) Pobedit WP-4 (Waterproof) Ammonite PLW-20 Ammonite T-19

V

VI

V

1 2

46.3 29

2 10 (57) 30 Cartridges SP-1 The core is uglenit E-6. The shell is an aqueous solution of ammonium nitrate Cartridges PVP-1-U The core is ammonite PLW (Liquid Waterproof) -20 The shell is an aqueous solution of ammonium nitrate Industrial explosives for special purposes Sulfur ammonite 52 1.5 1.5 5 30 No. 1 LW Petroleum ammonite 52.2 7 9 (30) No. 3

1 1*

1.5

Note: * – diatomite may be replaced by polyvinyl chloride

Many safety explosives contain nitroglycerines, nitroglycol and liquid nitroesters in the composition. 89

Questions for self-control 1. Combustibility and deflagration of safety industrial explosives. 2. Measure of assessment of detonation ability of safety explosives. 3. Inhibitors and principles of configuration of their structures. 4. List safety explosives for rock faces dangerous on methane, and for special purposes. 5. Characteristics and physical and chemical properties of modern safety explosives.

90

Industrial explosives are called explosives intended for blasting in the national economy. They are issued in cartridges, packages, bags and boxes, each of which differs in color of covers of cartridges and diagonal strips on boxes and bags. Recently explosives are also produced in special containers. Explosive cartridges are usually cylindrical. Paraffin-impregnated paper is used as a shell. The diameter and weight of the cartridges is taken depending on the diameter of the holes or boreholes. For ease of transportation and storage, cartridges are packaged in packs, and then placed in wooden cases. Polyethylene ampoules can be used as shells for flowing explosives. Only those industrial explosives that have State Standards or technical specifications approved in the prescribed manner, as well as journal resolutions of the State Mining Technical Inspectorate, are allowed for use in exploration and development of deposits. Industrial explosives should have a reduced sensitivity to external influences, be safe in handling, transportation and storage, have a relatively low cost, should not have a harmful effect on the human body. At the same time, industrial explosives should have sufficient power, smoothly detonate from modern means of initiation, ensure stable detonation throughout the entire mass of explosives, maintain their properties during the warranty period of storage, as well as for a long time in charging tanks. Industrial explosives must be suitable for mechanized charging and have a sufficiently high resistance to water in case of their use in flooded wells. Industrial explosives used in underground conditions should not form a lot of poisonous gases, and in mines that are dangerous due to the explosion of gas or dust, they additionally still have a lower explosion temperature. The variety of conditions of use and high technical requirements for industrial explosives have caused the need to have a wide range of them, numbering dozens of items. 91

Special properties of industrial explosives are supplied by such components as oxidizers, phlegmatizers, sensitizers, structured, hydrophobic, and combustible additives and others. Oxidizers are substances that contain excess oxygen, consumed by exploding the oxidation of combustible elements (ammonium nitrate ‒ AN, potassium nitrate ‒ PN, sodium nitrate ‒ SN, etc.). Flammable additives are solid or liquid substances, which, as a rule, are not explosives – finely ground coal, wood flour, solar oil. Flammable additives are introduced into the explosive composition to increase the amount of energy released during explosion. The role of flammable additives is also performed by explosives (tropyl, hexogen, and others), which in their composition have an inadequate amount of oxygen to completely oxidize the burning elements in them. The flame arresters are introduced into the composition of the explosives to reduce the temperature of the explosion and the likelyhood of ignition of methane and dusty air mixtures in the mines. NaCl and KCl are often introduced as flame arresters. Flame extinguishers do not elapse in an explosion when exploding, they only get hot and run down, thus lowering the temperature of explosive gases. Sensitizers are substances that are introduced into the explosives to increase their sensitivity to the formation and transfer of detonation. They are generally powerful explosives (e.g., TNT, hexogen, nitroethers) sensitive to the initiating impulse, which in a mixture of low-sensitive explosives (ammonium nitrate, etc.) with non-explosive substances (wood or cotton flour) provide a normal sensitivity of such a mixed explosive to initiation. The role of the sensitizer can also be performed by non-explosive substances (combustible additives): solar oil, wood flour or coal. At the same time, the best composite mixture explosives are formed: dynamons, igdanites, gra-nulites.

9.1. Principal components of industrial explosives Stabilizers (wood, peat flour, etc.) are introduced to improve the chemical and physical resistance of explosives. Phlegmatizers are fusible substances, oils with high heat capacity and high flash point, enveloping the particles of explosives and 92

not reacting with them. The introduction of phlegmatizers reduces the sensitivity of explosives to mechanical stress and provides safer conditions for their use. Vaseline, paraffin and various oils are often applied. For mines and quarries the powder-shaped explosives on the basis of dry powdered components, and also with additives of liquid substances are used. From multicomponent mixes the most application the following main groups of explosives have: a) ammonites – mixtures of ammonium nitrate, TNT and nonexplosive combustible additives; Hexogen additive is a part of rocky ammonite; safety ammonites for mines are produced with additive of flame arresters ‒ ammonite No. 6LW (iron nitrate LW grade), AP-5LW ammonite, ammonite PLW-20, ammonite T-19 and etc.). b) ammonals ‒ ammonites with an additive of aluminium powder; c) detonites ‒ a mixture of ammonium nitrate, nitroesters and aluminum peroxide; d) dynamons ‒ a mixture of ammonium nitrate and non-explosive flammable additives; e) grained explosives ‒ mixtures on the basis of dry graded, flaked components or graded alloys of the components; g) grammonites ‒ a mixture of granulated ammonium nitrate with granulated TNT (trotyl) or crumbled trotyl; f) granulites – mixtures of granulated ammonium nitrate with liquid and powder non-explosive combustible additives; h) igdanites ‒ a mixture of granulated ammonium nitrate with a liquid, flammable additive; i) granylotol ‒ a granular TNT; l) alumotol (alumotrinitrotoluene) ‒ granulated crushed alloy with aluminum powder; m) hydrogen-containing explosives ‒ on the basis of dry granular or flaky components or granulated alloys of components with additives of cold or hot ammonium nitrate, NaCl or KCl, thickening of the stabilizer and stabilizing charge; n) aquatol ‒ a mixture of granulated ammonium nitrate and granulated TNT with a solution of nitrous, wrinkling and stabilizing additives. 93

o) emulsion explosives ‒ mixtures of cold or hot saturated solvent, salt with liquid non-explosive combustible additive and emulsifier, which, when processed in the distributor, turns into water resistant, waterproof movable explosive. When cooling hot emulsion explosive it hardens. The most important characteristics of industrial explosives (other than explosive characteristics, explosive qualities of explosives, stability) are: ‒ hygroscopicity; ‒ caking; ‒ flowability; ‒ compactibility; ‒ flowability; ‒ aging; ‒ volatility; ‒ exudation. Hygroscopicity is the ability of industrial explosives to absorb moisture from the surrounding atmosphere. The ability to moisten ammonia-selective explosives is due to the high hygroscopic nature of the main component (ammonium nitrate). This leads to weakening and complete loss of explosives. The accumulated moisture phlegmatizes the explosive. Caking is the ability of some powdered substances to lose flowability during storage and turn into a solid mass. Caked explosives have increased danger. In such cartridges the introduction of the detonator is hampered. Caked ammonites (especially in small-diameter patrons) are not very susceptible to primary initiating agents, they are characterized by low detonation capacity. Chemical stability characterizes the speed of decomposition of explosives when stored. If explosives have a low stability, then as a result of storing large quantities of it, a self-destructive decomposition and explosion can occur. In this case, the primary decomposition products catalyze a further reaction, which accelerates the decomposition procedure. Water resistance is the ability of explosives to maintain explosive properties when immersed in water. Different methods are used to improve water resistance of explosives, one of which is introduction of calcium or zinc stearate in powdered nitroglycerin explosives 94

– detonites, uglenites. To reduce the wetting ability of liquid nitroethers in these explosives, they are weakly gelatinized with colloidal cotton. Plastic explosives are explosives of a highly viscous structure, the ability to easily be deformed at minor loads and to fill the full cavities. These explosives include dynamites and aquanites. Flowing (pouring) explosives are low-viscosity aquatols, ifzanites and some aquanites containing up to 30% of aqueous gelatins. Such explosives can be transported through hoses. Compaction is the quality of the explosive, which determines the density of the charge capacity. The density increases with the presence of a liquid phase in explosives. Flowability is the ability to be easily transported through pipes and hoses to the place of loading, free to pour out, to fill up the wellbore. Flowability is sometimes characterized by the angle of the natural slope. The granulites, grain-granulites, granulotol are industrial explosives, characterized by good flowability. Aging is an irreducible increase in explosive properties of explosives when stored, which is caused by physical and chemical changes in the substance due to internal processes or interaction with the external environment. For all industrial explosives, a guarantee period of storage is established, and the main indicators of technical conditions are guaranteed to be not lower than those regulated by the standards. Volatility is the ability of some liquid components of industrial explosives to evaporate. Such components include nitroglycerol, dinitroethylene glycol, nitroglycol. The loss of the weight of such explosives leads to an extremely noticeable change in their explosive characteristics. Exudation is the process of separating the liquid phase from a solid multicomponent system. This phenomenon is observed in the aging of dynamites, as a result of which droplets of pure nitroglycerin appear on the surface of the charges, while the explosive characteristics change, the danger in handling of such explosives increases. Delamination of system components, recrystallization of components, etc. can lead to violation of the physical resistance of explosives. 95

For open works, explosives are used, which are not subject to the composition of explosive items. They do not impose any special requirements on detonation ability. For explosives designed to conduct explosive works in underground mining, except for mines that are hazardous on dust and gas, there are requirements for the minimum formation of toxic gases (CO, CO2, NO, NO2, SO2) when exploding. Compressed and not amenable to spreading powdered explosives that do not contain hexogen or liquid nitroesters, should be crushed in accordance with the requirements of «unified safety rules for explosive works». After that, they can be used only in open-air mines that are not hazardous by gas or developing plates (ore bodies), that are not hazardous by dust explosions, as well as by working on the earth’s surface. Compacted powdered explosives containing hexogen or liquid nitroesters should be used without kneading or grinding only during explosive works on the earth’s surface. When loading it is forbidden to cut the cover of cartridges in the coal and slate mines dangerous on gas or dust. Questions for self-control 1. Industrial explosives in the national economy. 2. Physico-chemical characteristics of powder explosives.

96

Safety explosives are intended for performing explosive works in the mines with a danger of gas and dust explosions. The main representatives of the considered explosives are, for example, safety ammonites which belong to explosives of III and IV classes. The safety properties of these explosives are achieved by the introduction of flame arresters (usually sodium or potassium chlorides) into the composition of explosive mixtures. With the introduction of flame arresters into explosives, the content of active components in the unit mass of the explosive decreases, which reduces the specific heat of the explosion. During the explosion, flame arresters with high heat capacity absorb heat from the explosion products. As a result of the decrease in the specific heat of the explosion and the absorption of heat to the heating of the flame arresters, the temperature of the explosion is significantly reduced. This circumstance significantly reduces the risk of ignition of methane- or dusty air mixtures. In addition, flame arresters in relation to explosive mine atmosphere are anti-catalysts (inhibitors). They significantly decrease the lower limit of the flash point and lengthen the flash delay. The content of flame arresters in safety ammonites is 12–20%. The increase in the content of the flame arrester in the composition of the safety of explosives contributes to the improvement of their safety properties, however, this reduces the detonation ability. Therefore, with a high content of flame arrester, incomplete explosions, burnout of explosives is possible, which not only drastically reduces the effectiveness of explosions, but can also lead to the ignition of the methane-air mixture. Improving the detonation ability of explosives is achieved by introducing additives of liquid nitroesters into their composition, as well as using special designs of protective cartridges for explosivescartridges with protective shells. The core of these cartridges is a safety explosive with a small content of flame arrester. The main part of the flame arrester is located in the shell. In this case, high safety properties of explosives and their good detonation ability are provided. 97

In the classification of industrial explosives, protective explosives are classified as class III-IV. The basis of this classification is the danger of underground explosions of gas or dust during blasting. The chemical composition of the mine atmosphere, gas-bearing formations, the possibility of sudden outbursts of gas, the nature of blasting, mining and geological features of the workings, etc., contribute to the occurrence of explosive situations. Let’s give as examples some safety explosives of the III–VII-th classes. Safety explosives (short-flame explosives) of class III. This class is represented by ammonite AP-5 LW, which contains waterproof ammonium nitrate, trotyl and sodium chloride. Powerful explosives of limited use are applied in pure-face coal mines, with hazard of gas or dust explosion, under the following conditions: the implementation of measures that prevent the ingress of coal dust from other mines or open formations, the use of water-spray curtains with methane content in the bottom to 1.0 %. With a higher methane content, the use of ammonite is not allowed, it is also not allowed to apply it in rock faces up to 5 m from coal seams. Safety explosive of class IV. At present, this class is represented by ammonite T-19, which also contains a triple mixture: waterproof ammonium nitrate ‒ trotyl ‒ sodium chloride, but in a different ratio than ammonite AP-5 LW, in particular, contains more flame arrester. Explosives of average power and safety have a high detonation ability and detonate with significant compaction (1.65-1.7 g/cm3). This reduces the likelihood of partial failures and burnout charges with short-delay blasting. Safety explosives of class V. This class is represented by uglenit E-6. This is an ion exchange explosive sensitized with liquid nitroethers. As a result of the exchange reaction between ammonium chloride and sodium nitrate during the explosion of uglenit E-6 sodium chloride is formed in the ultrafine state. In addition to the ion-exchange pair, uglenit E-6 contains a small amount of potassium chloride in the composition as an additional flame arrester. Uglenit E-6 is characterized by a fairly high detonation ability, which is provided by a significant content of nitroesters. Water resistance is achieved by dusting the components of the composition with a hydrophobic additive such as stearates and weakly 98

gelatinizing nitroesters with colloidal cotton. In terms of water resistance, uglenit E-6 is inferior to ammonite T-19, the holding time of cartridges in water before the test for detonation transmission is 30 minutes. Explosives of class V are recommended for blasting coal of any strength and for weak and medium strength rocks only if there are two open surfaces in the bottomhole, in the soft and medium hard coals with one open surface. The safety explosives of class VI include uglenit 12CB, selectively detonating explosive sensitized with nitroethers. Uglenit 12CB contains a mixture of urea and sodium nitrate, which is during the explosion in the closed chamber is reacted to form carbon dioxide, water and nitrogen. To enhance the protective properties of the uglenit a small amount of sodium chloride is additionally introduced. Sodium carboxymethylcellulose is used as a gelatiniser. Safety explosives of class VI are intended for blasting in especially dangerous conditions of coal mines. Uglenit 12CB is used for blasting coal and rock by the borehole method in the mines with a hazard of gas explosions of all categories and danger of dust explosions, except for especially dangerous rising faces on coal and especially dangerous combine niches with one outcrop plane. The safety explosives of class VII ‒ ion exchanger is a typical ion exchange explosive consisting of a mixture of sodium nitrate, ammonium chloride and a sensitizer. As with the explosion of uglenit E-6, finely dispersed sodium chloride is formed as a result of the ion-exchange reaction. Collodion cotton is used as a gelatinizing agent. Ionite is allowed to explode in the form of overhead charges: when passing coal (rock) stuck in coal mines and crushing oversized pieces of rock (and fuel shale), weighing no more than 600 g; with the destruction of wooden poles, as well as for the explosive method of spraying water in polyethylene vessels, weighing 150 g (for vessels with a capacity of 20 L) and 300 g (for vessels with a capacity of 40 L). The safety explosives of classes VI-VII are characterized by a rather high detonation ability, which is ensured by the presence of liquid nitroesters in the composition. Water resistance is achieved by 99

dusting the components with stearates, as well as by weak gelatinizetion of nitroesters. Nitroether-containing safety explosives (uglenit E-6, 12CB, ionite) are made in two phases. In the first phase, the bulk components (ion-exchange pair) are mixed and they are hydrophobized with stearates. The final mixing of bulk components with weakly gelatinized nitroethers is carried out in mechanical blade mixers of the Werner-Pfleider type. Table 10.1 presents the properties of safety explosives. Table 10.1 Properties of safety explosives No

1 1 2

Indicators

2 Oxygen balance, % Heat of explosion, kJ/kg 3 Full perfect blast performance, kJ/kg 4 Explosion temperature, °С 5 Volume of explosion gases, L/kg 6 Cartridge density, g/cm3 7 Efficiency in lead bomb, cm3 8 Operability on the ballistic pendulum 9 Brisance, mm 10 Detonation velocity, km/s 11 Critical diameter, mm 12 Transmission of detonation, cm: between cartridges after exposure in water, cm

Ammonite AmmoAP-5 LW nite (Liquid T-19 Waterproof) 3 4 -0.02 -2.47 3,500 3,410

Uglenites E-6 12 CB

Ionite

5 +0.5 2,680

6 0 2,300

7 +6.47 1,930

3,000

2,600

1,950

-

1,440

2,520

2,230

1,790

-

-

787

724

560

520

580

1-1.15

1.05-1.2 1.1-1.25 1.1-1.3

1-1.2

320-330

265-280 130-170 95-120

95-125

0.74

0.7

0.58

0.8

-

14-17 3.6-4.6

15-17 3.6-4.3

7-11 1.9-2.2

1.9-2.0

5-6 1.6-1.8

10-12

10-12

7-9

-

-

5-10 2-7

7-12 4-8

5-12 3-10

4-5 2-3

-

100

1 2 15 Sensitivity to: impact, % friction without sand, MPa friction with impurity of 5% of sand, MPa

3

4

5

6

7

12-32 -

12-24 -

40-70 230

50-60 -

24-32 300

190

190

-

-

-

Protective explosives of VI-VII-th classes, such as nitroethercontaining explosives, are characterized by increased sensitivity to mechanical stress, are more toxic, and therefore require more careful handling than ammonites. They are suitable for use in various climatic regions of the country. Cartridges stored in surface storage at temperatures below ‒20 °С should be warmed up in an underground storage warehouse before use. Ammonite type protective explosives are manufactured in ball mills with preliminary ball treatment of the ammonite mass and subsequent mixing with a flame arrester (sodium chloride) of a certain dispersion, providing the necessary anti-grisonity properties to the composition. Granulite NM is used for ore mines of the Krivoy Rog basin. At the coal mines of the Republic of Kazakhstan and Russia explosives with protective properties of granulite AN-S and emulsolite P are widely used. Granulite АN-S contains АN (ammonium nitrate) ‒ 84%, liquid oil product ‒ 3%, table salt ‒ 10% and coal powder ‒ 3%. Emulsolite P in appearance is a plastic substance from light yellow to dark brown in color, containing 99% emulsion and 1% gasgenerating additive of sodium nitrate solution. Table 10.2 The properties of explosives used in fire hazardous areas of coal mines Indicators

Emulsolite P

1 Density of composition, g/cm3 not more than The fullness of detonation of 6 turns of detonating cord, DCA, DCE-12 Specific heat of explosion, kJ

2 1.3 total

Granulite АN-С 3 1.0 –

2,710

3,340

101

1 Specific volume of gases, l Oxygen balance,% Detonation rate of a charge with a diameter of 120 mm in a polyethylene shell, km/s Sensitivity to impact, % Sensitivity to friction, MPa not less Initial temperature of thermal decomposition by the DTA method, °С more

2 910 -7.1

3 940 0

3.6 – 4.0 0 294

3.1 – 3.5 0 –

170 – 190

170 – 190

According to the safety properties ammonite AP-5LW should not ignite the methane-air mixture in the test drift when exploded in a cylindrical mortar with a charge of 600 g. Ammonite T-19, in addition to this test, should not ignite coal dust in the explosion of a charge weighing 700 g. Uglenit E-6 withstands the tests when an open, freely suspended charge weighing 200 g is exploded in the chamber of an experimental drift in an atmosphere of methane-air mixture and coal dust. Uglenit CB should not ignite methane and coal dust in the explosion of a charge weighing 1,000 g in a cylindrical mortar without tamping. In addition, uglenit CB should not ignite a methane-air and dust-air mixture in the explosion of the charge weight of 800 g angular mortar. Ionite withstands tests when an explosive charge weighing 600 g is exploded in an angle mortar of an experimental drift with a reflective wall located 200 m from the mortar.

10.1. The use of explosives in mines with a hazard of gas and dust explosion Coal mines. Presence of methane and coal dust is the main characteristic of the atmosphere of coal mines. The natural gas which is released in coal mines contains 80‒83% of methane, 1-4% of its heavier homologs, about 10% of nitrogen, 5% of carbon dioxide and less than I % of other gases. There are free and associated (bound) states of gases in the rock. A bound gas is a gas adsorbed by a rock. Free gas accumulates in the cavities, cracks and pores of the rock. Due to the high sorption ca102

pacity of coal seams, due to the highly developed surface, reaching 200 m2 per 1 g, about 3/4 of the gas is in a bound state, 1 t of fossil coal can absorb up to 100 m3 of methane. Methane is emitted into the atmosphere of coal mines from the array, as well as from coal loosened by explosion or mechanically. There are three types of gas emission from an array: ordinary ‒ from pores and cracks that are not visible to the eye, souffar ‒ from cracks that are visible to the eye, sudden ‒ when gas is ejected from the mass of the massif, usually within a short time, with simultaneous ejection of rock (coal). The gas pressure in coal seams reaches 5.9 MPa and depends on the depth. Experiments on the flammability of methane-air mixtures with different methane content in the mixture and different heating temperature of the vessel are given in Table10.3. Table 10.3 Flammability of methane-air mixtures with different methane content in a mixture with different heating temperatures The methane content in the mixture, % 6 7 8 9 10 12

775 1.08 1.15 1.23 1.3 1.4 1.64

Delay of ignition (sec.) depending on vessel temperature, °С 825 875 925 975 1,075 1,175 0.58 0.35 0.2 0.122 0.039  0.6 0.36 0.21 0.13 0.041 0.01 0.62 0.37 0.22 0.138 0.042 0.012 0.65 0.39 0.23 0.141 0.044 0.015 0.68 0.41 0.24 0.148 0.049 0.018 0.74 0.44 0.25 0.16 0.055 0.02

Thus, hot surfaces most easily cause ignition of methane-air mixtures containing 6–7% methane. At a temperature of 1,770 °C, a 9.1% methane-air mixture has the shortest ignition delay (1.9 millisec.). Under normal conditions of pressure and temperature, methane-air mixtures containing 5-14% methane are explosive. Preheating or precompression expands the indicated explosion limits of the methane-air mixture. In the presence of suspended explosive coal dust in the air, the danger of ignition of methane-air mixtures increases. Theoretically, the most explosive is a mixture containing 9.46% methane and 90.54% air, in which methane is completely oxidized. 103

The combustion of methane-air mixtures occurs with the release of heat due to the oxidation reaction of methane with atmospheric oxygen. In the final form, this reaction can be expressed by the following equation: СН4 + 2О2 + 8N2 = СО2 + 2Н2О + 8N2 + 198.4 kcal/mol. Fossil coals are divided by gas content, which is determined by the gas content (m3) per 1 t or 1 m3 of coal. Anthracites and coked coals are the most gas-bearing, coals with a high volatile content are the least gas-bearing. Gas abundance depends on the amount of gas released into the atmosphere per unit of time. Usually, gas mobility is expressed in relative units ‒ the amount of gas released per day, referred to 1 ton of daily coal production. By gas content coal mines are classified into the following categories:  Category I ‒ relative gas content no more than 5 m3/t;  Category II ‒ from 5 to 10 m3/t;  Category III ‒ from 10 to 15 m3/t;  Super-altitude mines, the relative gas content of which is more than 15 m3/t, as well as mines developing reservoirs that are dangerous due to emissions of coal and gas and souffly emissions. Coal dust is especially intensively formed when machines and mechanisms are operating in the process of drilling faces and mechanized coal blasting, during blasting operations and transportation of battered coal. The dust settles and accumulates in large quantities on the walls and soil excavation. Research has established that coal dust is practically nonexplosive when the content of volatiles in the coal is less than 10%, blows weak at a content of volatile of 10 to 15%, if they contain more than 15% volatile coal dust explosiveness grows rapidly. In the explosion, dust particles of sizes from 0.1 to 1 mm take part. However, the dust fractions of 75-100 microns in size (dust passing through sieve No.80) are considered the most explosive. Coal dust can explode only when its concentration in the air is within certain limits. The lower explosive limit of airborne coal dust 104

from layers containing more than 30% volatile is in the range of 12– 20 g/m3, depending on the ash content in coal, and in the presence of 0.5–1.5% methane in the air, this limit decreases 2 -3 times. The most destructive effect has an explosion of a dust-air mixture containing 300–600 g of dust per 1 m3 of air. The flash point of the dust-air mixture is in the range of 750–900 °C. The ignition of dust-air mixtures, as well as the ignition of methane-air mixtures, is preceded by an ignition delay. The duration of this delay is somewhat less than that of the methane-air mixture, since volatile, flammable gases are emitted when the coal dust is heated. The ignition and explosion of suspended coal dust in the air occurs by a mechanism similar to the explosion of the gas-air mixture. So, if a mixture of coal dust with air ignites as a result of an explosion of an explosive or a methane-air mixture, from a part of the coal dust enveloped in a flame, combustible gases (hydrogen, methane) and small amounts of other combustible gases are emitted, which, mixing with oxygen, form an explosive gas-dust mixture. This mixture explodes and, with its flame, covers adjacent particles of coal dust, from which again flammable gases are emitted, etc. At the same time, fine coal dust is more explosive than coarse dust, since it passes into suspended state more easily. Moreover, its surface is much greater, therefore, all reactions proceed faster and more completely with fine dust explosion. The explosiveness of coal dust depends on its ash content. Ash, i.e., inert dust, during an explosion absorbs a significant amount of heat and thereby reduces the temperature of the explosion flame. The moisture content of dust also affects its explosiveness, since it hampers the formation of a dust cloud and absorbs a significant portion of the heat. Potash mines. The mine atmosphere contains hydrogen and methane, which are part of natural gas. The ratio of hydrogen to methane in natural gas ranges from 3:1 to 8:1. For example, the gas released from the carnallite layers of the Solikamsk Deposit contains 2045 % hydrogen, 15 % methane and 40-65 % nitrogen. It is assumed that methane was formed as a result of decomposition of plant and animal residues brought into the dried pond during the formation of salts. 105

The formation of hydrogen is associated with the processes of decomposition of water under the influence of radioactive salts, crystallized simultaneously with salt minerals. The most intense gassing occurs during blasting. The volume of combustible gases reaches 70 m3 (in terms of methane), and the relative gas-richness is 2 m3 per 1 m3 of rock mass repulsed in one blasting. Sulfur and pyrite mines. Sulfuric mines are among the most dangerous in terms of dust explosions, sulfur ignition in the reservoir and underground fires. This is due to the especially high explosiveness of sulfuric aerosols aggravated by the combustible and easily flammable hydrogen sulfide, methane, ethane, arsenic hydrogen, organic compounds of selenium, phosphorus, arsenic, carbon monoxide in the atmosphere of the mines. Mines that develop pyrites and other sulphide ores are less dangerous in underground dust explosions and fires than sulfur mines due to the lower explosiveness of sulphide aerosols. Their gas atmosphere is qualitatively close to the atmosphere of sulfur mines. Oil and ozocerite mines. In many countries, oil is extracted by mining method. The atmosphere of oil and ozocerite mines contains methane and other saturated and unsaturated hydrocarbons in the form of gases and vapors. Hydrogen sulfide and carbon dioxide are found in smaller quantities. Combustible gases and vapors are released both from the rocks and during the evaporation of the light fractions of oil (gasolines, etc.), which run onto the ground from the overlying horizons. Especially dangerous are gasoline vapors. The concentration limits of the explosiveness of some flammable gases and liquids (vapors) are given in Table 10.4. Table 10.4 The concentration limits of explosiveness of some flammable gases and liquids (vapors) Gas, liquid fuel vapor 1 Methane Ethane Propane

Explosion concentration limits in admixture with air, % Lower limit Upper limit 2 3 5.0 15.0 3.22 12.45 2.37 7.35

106

1 Butane Pentane Hexane Heptane Gasolines Benzene Toluene Ethanol Acetylene Hydrogen Ammonia Hydrogen sulphide Carbon monoxide

2 1.86 1.4 1.25 1.0 0.3-1.3 1.41 1.27 3.28 2.5 4.0 15.5 4.3 15.5

3 8.41 6.0 6.9 6.0 7.0 6.75 6.75 18.95 80.0 74.2 27.0 45.5 74.2

10.2. Flame arrestors in the composition of safety explosives The composition of safety explosives includes mineral supplements, usually alkali metal salts, which on the one hand, play the role of an inert impurity, lowering the flame temperature in the explosion, and on the other hand ‒ the role of inhibitors of inflammation reactions of methane-air mixtures. The choice of flame arrester is determined by its inhibitory ability, compatibility with other components of explosives, the effect on explosive and physicochemical properties of explosives, the toxicity of the flame arrester itself or its decomposition products, as well as its availability and commercial value. For example, fluoride salts, although they are characterized by a high inhibitory ability, are used in safety explosives with great care due to toxicity. Highly active lithium salts are not used because of the high cost. Chlorides of sodium and potassium due to their low cost, availability and at the same time, a sufficiently high inhibitory ability are the most widely used. The inhibitory effect of the salts of the flame arresters largely depends on the specific surface of the particles forming the suspension in the detonation products, and, consequently, on their size. The total surface of the particles is approximately calculated by the formula: 107

S  ns  

G

d  0 / 6

d 2 k  k

6G , d 0

where n is the number of salt particles dispersed in the medium; s' is the particle surface; G is the mass of salt in the explosive charge; d is the average particle diameter; p0 is the salt density; k is the crushing factor of salt in the explosion. According to the experimental data, during the explosion of explosives, a flame arrester is crushed. The degree of fragmentation depends on the surface defects of the original crystals and does not require large loads. With an initial salt particle size of 0.1–2 mm, the largest number of particles after the explosion had an average size of about 8 microns. At the same time introduction of the fine flame arrester to the composition of safety explosives has negative sides: the caking of the ammonite mass increases, the detonation ability of the explosive decreases. Therefore, in compositions containing a finely dispersed flame arrester, sensitizers are usually introduced in an amount of 5–15%, most often nitroglycerin or its mixtures with nitroglycols, less often solid hexogen or PETN sensitizers (Fig. 10.1). Figure 10.2 shows the dependence of the protective properties of the ammonium nitrate mixture (79% ammonium nitrate and 21 % TNT) on the dispersion of the flame arrester. With a decrease in the particle size of the sodium chloride in the flame arrester, the efficiency of the explosive somewhat decreases. When the particle size decreases by an order of magnitude, the efficiency decreases by 13 % (see Fig. 10.2). Many researchers tried to obtain a suspension of ultra-dispersed flame arrester by introducing organic or mineral metal compounds into explosives, which would decompose in the explosion to form salts or metal oxides. As such, picrate of potassium (IV), potassium or sodium perchlorate (oxidizing agent), etc. have been proposed. However, the tested salts were not applied, because in addition to inhibiting the flame the arrester must reduce the temperature of detonation products. Ultrafine sputtering of the flame arrester is achieved 108

by the explosion of selective-detonating explosives containing the so-called ion-exchange or reverse salt (ammonium chloride and sodium or potassium nitrate).

Figure 10.1. Dependence of the critical diameter of the charge of protective explosives (dcritical, mm) with 20% of the flame arrester at a density of 1.6-1.7 g/cm3 on the amount of sensitizer (n): 1 ‒ TNT; 2 ‒ mixture of nitroesters 60/40; 3 ‒ hexogen; 4 – nitroglycerin.

The product of their interaction in the explosion is ultra dispersed sodium chloride or potassium.

Figure 10.2. Dependence of the probability of ignition of the methane-air mixture («omega») on the particle size of the flame arrester (s) with its content of 35% (curve 1) and 40% (curve 2)

Figure 10.3 shows the dependence of efficiency on the dispersion of salt. 109

Figure 10.3. The dependence of the safety of explosives (F) on the particle size of the flame arrester (S) with its content of 35% (curve 1) and 40% (curve 2)

10.3. Detonation of safety explosives Strong influence on the properties of selective detonating safety explosives has a particle size distribution. For compositions containing the same amount of sensitizer and ion-exchange pair of salts (53% sodium nitrate and 35% ammonium chloride), but differing in particle size components, the deviation of the ballistic pendulum, characterizing the performance of explosives, was determined. The charge in all cases was 100 g, diameter 36 mm, distance to the toe of the pendulum 40 mm, weight of the pendulum 160 kg. All compositions in which not too thin powders of the ion-exchange pair were used gave a deflection of the pendulum that is 2 to 3 times greater than the deviation in the explosion of the composition with sodium chloride, taken as the reference explosive. This indicates a different degree of completeness of the reaction of the ion-exchange pair or, which is the same, selectivity. The reaction is slowed down only with very fine dispersion of powders (less than 100 microns). High and stable detonation ability is the most important requirement for safety explosives, especially due to the extensive use of short-delay blasting and the increased danger of burnout of safety explosives due to the non-simultaneous explosion of charges and their compression in the holes by compression waves. The most effective way to increase the detonation ability of safety explosives is the introduction of sensitizers. For almost all the history of the safety explosives, in most cases nitroglycerin, nitrogly110

cols, or mixtures have been used as sensitizers. The latter are contained in domestic protective explosives such as uglenit. It is known that nitroether-containing explosives in the compacted state are characterized by high detonation ability. The critical diameter of these explosives is 5-10 mm, in the compacted state (pressure 50 MPa) 15–17 mm. The compactibility of nitroether-containing explosives is lower than that of ammonites. The density of these explosives quickly reaches a maximum value, but with increasing pressure it increases a little. The relative density in this case does not exceed 0.94, while ammonite is compacted to a relative density of 0.965. The stabilizing effect on nitroether-containing explosives is exerted by disintegrating agents (wood flour, etc.). The best can be considered the content of baking powder 4%. To increase the detonation ability of the protective ammonites that do not contain nitroglycerin, more intensive grinding of the ammonite mass is used, an increase in the content of TNT (ammonite T-19). According to the detonation ability determined by the explosive tests in coal-cement blocks, the shortest reduced distance, at which stable explosive detonation is maintained in the compacted state, in ammonite T-19 with 19% of trotyl R < 7.5 and in ammonite T-19 with 16% of trotyl R = 9.0. The smaller the value of R, the higher the detonation stability. A radical solution to the problem of eliminating burnout safety explosives is the use of sustainably detonating explosives in the form of solid charges (mono-charges). The use of single charges eliminates the possibility of gaps and bridges between the cartridges, thereby reducing the likelihood of interrupting detonation. One of the ways to increase the detonation ability of protective explosives is to increase the diameter of cartridges, for example, from 32 to 36 mm. To improve the efficiency of blasting when using low-power high-safety explosives, it is necessary to increase the diameter of blast-hole charges. Experimental explosions in coal mines showed that when using safety explosives of class VI in cartridges with a diameter of 43 mm, it was possible to obtain the same efficiency of blasting operations as when exploding a more powerful explosive of class V – Uglenit E-6. Even greater efficiency is ensured with mechanized loading of bore-holes at full cross-section. With properly 111

selected technology and rational organization of work, record rates of preparatory workings (more than 1,000 m/month) are achieved for the rocks, the destruction of which by combines is not yet possible.

10.4. Safety explosives and their combustibility It is well known that the transition of detonation of safety explosives into combustion is a very undesirable phenomenon, since may cause ignition or even an explosion of methane-air mixture. One of the reasons leading to the burnout of safety explosives may be the compaction of explosives in the borehole both during the preparatory work and at the time of detonation as a result of the channel effect. The compression mechanism of powdered explosive in this case is described in detail by K.K. Andreyev. The propagation of detonation at low speeds leads to its transition to combustion. To prevent burnout of safety explosives, it is necessary that, along with high detonation ability with possible seals, safety explosives are also characterized by low flammability. Most ammonium nitrate explosive mixtures are characterized by relatively low flammability. Sodium chloride, potassium and ammonium with their content in the safety explosives up to 10%, increase the combustibility of explosives (Fig. 10.4). The introduction of nitro-glycerin into these mixtures also increases the flammability of explosives (Fig. 10.5). When wood flour is added, the critical ignition pressure first increases, the flammability decreases, reaches a maximum when the wood flour content is about 1%, and then decreases to atmospheric pressure when the wood flour content is about 5%. Additives of small amounts of ammonium fluoride or sodium (about 3%) reduce the flammability of safety explosives signifycantly, by 2-2.5 times. Ammonite combustibility is also reduced in the presence of diammonium phosphate in combination with fluorides. Other phosphoric acid salts, as well as ammonium oxalate, calcium oxide hydrate, calcium and potassium formate, etc., were studied to reduce the flammability. 112

Figure 10.4. Dependence of the critical pressure (pcritical) of ignition of ammonite 6 LW on the content of the flame arrester (FA): 1 ‒ sodium chloride; 2 ‒ potassium chloride; 3 ‒ ammonium chloride

1,4

1,0

0,6 2

4

6

8

n, %

Figure 10.5. Dependence of the critical ignition pressure (pcritical) for ammonite on the content of nitroglycerin in it (n)

In the Table 10.5 the data on the effect of different flame retardants on the flammability of ammonium nitrate explosive mixtures are presented. The best results are obtained on samples with the addition of formates. Low-flammability have safety explosives, which contain calcium nitrate, as well as samples of water-containing explosives. Other performance characteristics, such as the stability of physicochemical properties, water resistance and others, are provided by well-known methods common to industrial explosives. To ensure the safety of protective explosives containing liquid nitroesters, in addi113

tion to the hydrophobization of the composition, weak gelatinization of nitroesters with collodion cotton (0.2%) is also necessary to reduce the mobility (increase in viscosity) of the liquid component. Table 10.5 Effect of various antipyrenes (fire-retarding agents, flame retardants) on the flammability of ammonium nitrate explosive mixtures The name of the flame retardant

The content of the flame retardant in ammonite, % Ammonium oxalate Ammonium oxalate 5.0 Ammonium oxalate 10.0 The hydrate of calcium oxide 40.0 The hydrate of calcium oxide 4.0 Calcium Formate 6.0 Calcium Formate 4.0 Calcium Formate 5.0 Calcium Formate 6.0 Potassium Phosphate 10.0 Ammonium phosphate 10.0 Ammonium phosphate 10.0 Calcium Phosphate 10.0 Asbestos 2.0 Asbestos 6.0

pcritical, MPa Ammonite Ammonite 6 LW 6 LW+18% NaCl 1.8 3.2 4.6 10 2.0 3.9 2.6 1.8 1.5 1.8 1.5 1.4 0.4

1.3 1.7 2.0 3.0 2.7 3.4 1.8 1.8 1.3 -

An even higher water resistance of safety explosives with liquid nitroesters can be obtained if, along with the hydrophobization of the composition, additives are added to explosives in water. In this case, upon contact with water, a gel-like layer is formed on the periphery of the cartridge, which prevents water from penetrating deep into the cartridge.

10.5. Physico-chemical changes in the properties of explosives over time The physical characteristics of explosives are determined by the following characteristics: wettability, caking, compaction, separation (disintegration, stratifying), volatility. 114

Wettability is the ability of hydrophilic material to absorb moisture from the surrounding atmosphere (hygroscopicity). Hygroscopicity is determined by the value of the hygroscopic point, i.e. the ratio of the water vapor pressure over the saturated solution of a given substance to the water vapor pressure saturating the air at the same temperature. Hygroscopic point is expressed as a percentage of relative humidity and characterizes a state of matter in which it does not dry out and does not moisten. The higher the hygroscopic point of a substance, the less hygroscopic it is. Of the salts used in the production of industrial explosives, calcium nitrate (hygroscopic point at 25 °C 44%) and ammonium nitrate (62.7%) are highly hygroscopic; sodium nitrate (74.5%), so-dium chloride (75.5%), ammonium chloride (78.5%) are moderately hygroscopic, potassium nitrate (92%) and potassium chloride (83.4%) are poorly hygroscopic. They mainly determine the hygros-copicity of the mixed explosive itself. The hygroscopic point of most explosives based on ammonium nitrate at a temperature of 15–20 °C is 60–68%. Therefore, in most climatic regions of the CIS, they can be moistened in the absence of moisture-proof packaging. Moisturizing disrupts the physical stability of the explosive: promotes caking, reduces flowability, water resistance and degrades detonation. Various methods of coating ammonium nitrate crystals with a moisture-proof film or changes in the crystal lattice did not give positive results in reducing wetting. Therefore, the main measure to prevent the humidification of the explosives on the basis of ammonium nitrate is the external protection of charges by various moisture-proof materials. Caking is the ability of some powdery substances to lose their flowability during storage and to turn into a dense solid mass. Sometimes this phenomenon is also called «sintering». However, for the most part, sintering is understood as loss of flowability caused by heating. Compressed explosives are inconvenient to handle: it is impossible to crush cartridges in boreholes, the danger increases and the introduction of a detonator into the cartridge action makes it difficult, the loaded ammonites have to be crushed before loading wells 115

in place, etc. In addition, packed ammonites are characterized by low detonation ability. One of the causes of caking is the recrystallization of watersoluble components. When moistening explosives, some of the salts (ammonium nitrates, sodium chloride, etc.) go into solution. Then, when drying or lowering the temperature, new crystals are released from the saturated solution, which cement the mass into a solid conglomerate. This process is facilitated by capillary forces that bring wet particles together. Therefore, when caking, in addition to loss of flowability, the powder often self-compacts, i.e., bulk shrinkage occurs. The described process takes place with a moderate wetting of hydrophilic materials. With a high moisture content, a decrease in solubility with decreasing temperature may not be sufficient for the cementation of the mass to form new crystals from the solution. The caking mechanism increases with external pressure, for example, when stacking material is packed in soft containers (paper, plastic bags), or when internal stresses are caused by polymorphic transformations of ammonium nitrate. In this respect, heating of ammonium nitrate above the temperature of +32 °C is particularly dangerous, as at this temperature it passes from β-form to γ-form with an increase in volume by 2.5%. Some researchers found caking as a result of polymorphic transformations at a temperature of +32 °C only in wet ammonium nitrate, in the absence of moisture caking during heating did not occur. Other things being equal, the caking capacity of ammonium nitrate mixtures increases with the degree of grinding. Enveloping, insoluble oils, paraffin, kerosene and other impurities reduce the caking of the hygroscopic explosive, covering its particles with a non-hygroscopic film. As a result, the rate of moisture absorption by this explosive decreases. In addition, the hydrophobic film isolates the particles of the substance from each other and the new crystals formed less strongly bind the mass of the substance. In the theory of crystallization, the principle of changing the size and shape of crystals by active impurities is known, for example, by the addition of surface-active substances (0.01 ‒ 0.1%), including dyes. Accordingly, these additives can influence the caking process. 116

It has been experimentally proven that the dye acts by changing the shape of the crystals, as a result of which they become mechanically fragile and caking decreases. Common to the structural characteristics of dyes that effectively change the size of crystals is the presence in them of sulfo groups and a cationic group in the form NH2 or OH. The caking of ammonium nitrate is most effectively reduced by acid fuchsin from the class of triphenylmethane dyes and acid red amaranth from the class of azo dyes. Substances with average hygroscopic point of 50-70%, which can periodically wet and dry with a change in humidity, have the highest caking. These are the main components of industrial explosives ‒ ammonium nitrate, as well as sodium chloride or potassium chlorides that are part of safety explosives. When capping a hygroscopic substance in an unpressurized container due to alternating moistening and drying of the substance, as well as cyclic heating and cooling during storage, variable caking and loosening of the substance is possible. However, caking may be irreversible, if the process was too deep and there are very strong bonds between the particles. Irreversible caking is often observed when packing insufficiently dried up and cooled ammonite. For this cause in technological processes of production the humidity and temperature of ammonites and other explosives on the basis of ammonium nitrate are strictly regulated. At storage of these explosives it is necessary to avoid conditions when strong heating of substance, for example, under the influence of sunshine is possible. The size and shape of explosive particles can influence caking. With increasing sizes, the specific surface of the powder decreases, and consequently, the number of possible adhesion sites decreases. For the same reason, a powder consisting of spherical particles is less caking than powders containing particles with flat surfaces. The nature of the particles also affects caking. A smooth surface creates less caking than a rough surface. Ways to eliminate or weaken caking of industrial explosives are as follows: 1) minimum moisture content and cooling of ammonium mass before assembling cartridges and capping (to a temperature below 117

32 °C), reliable moisture insulation of the finished product with an air-tight plastic film (bags), moisture-proof mastics, etc.; 2) storage under conditions that exclude external compressive loads and sharp temperature fluctuations with the transition through a temperature of +32 °C, corresponding to the polymorphism of the conversion of ammonium nitrate; 3) introduction of the additives reducing caking to saltpeter (nitrate) or in the composition of explosives: the porous substances which are characterized by good sorption moisture capacity, for example, silica gel, wood, peat flour, etc.; hydrophobic substances, insulating particles of hydrophilic substances in the composition; additives that reduce the thickness and mechanical strength of intercrystalline binding bridges, such as fuchsin, amaranth, and other dyes; surface active additives (0.03 ‒ 0.05%); 4) enlargement of the size of particles in explosives or their individual components by granulation or other technological methods. Such methods of caking reduction are also practiced, such as the shift of polyformal transformations of ammonium nitrate to higher temperatures. This is achieved, in particular, by introducing potassium chloride and potassium nitrate into the ammonium nitrate crystals. Caking is determined by the resistance to crushing checkers on a laboratory press. The most accurate method is the method for determining the degree of caking in a ball mill. It is determined by the amount of residue on the corresponding sieve after crushing the compacted substance in the mill for a given mode of operation. The comparative effectiveness of the recommended anti-caking agents can be judged by the following test results of a number of ammonites containing various additives, according to the Pestov method. The simplest binary mixture of nitrate with TNT with zero oxygen balance was adopted as a reference. Ammonite 6 LW contains an additive of salts of fatty acids. As can be seen from the above data, disintegrating additives interfere with the greatest degree of caking (Table 10.6). Compaction is an important operational quality of bulk explosives. The ability of industrial explosives to condense under external loads can be of double practical importance ‒ both positive and negative. 118

Table 10.6 Ammonite

Without With With fatty additives amaranth acids Crushing pressure (MPa) at humidity, %: 0.1 0.23 0.08 0.06 0.1-0.5 0.37 0.23 0.14 Ammonite Wood Wood With flour and flour asphaltite fatty acids (8%) and paraffin (1.5%) Crushing pressure (MPa) at humidity, %: 0.1 0.02 (not 0.18 caked) 0.1-0.5 0.065 0.045 0.38

With fuchsin

With wood flour (3%)

0.04 0.12 With aluminum (powder)

0.03 0.08 PLW-20 (Powder Liquid Waterproof ‒ 20)

0.04

0.009

0.16

0.13

For granular explosives charged using air chargers, this property contributes to an increase in the density of loading. Compaction increases with the presence of a liquid phase in explosives. So, granulites and igdanit with bulk density of 0.85 ‒ 0.9 g/cm3, containing liquid petroleum oils, are compacted to 1.2 g/cm3 during pneumatic charging in boreholes. Moistening before pneumatic charging of grammonite 79/21, which does not contain liquid petroleum products, has a similar effect. For packaged powdered explosives, especially safety explosives, compaction can lead to loss or reduction of detonation ability and, as a result, to burnout charges. Moreover, the compaction itself can be caused by the impact of shock air waves with non-simultaneous group blasting. For this reason, strive to reduce the compactibility of safety explosives. The results of pressing the moistened samples at a specific pressure of 3 MPa are given in Table 10.7. From the compared samples of saltpeter slightly less sealing is characterized by waterproof ammonium nitrate brand LWC (liquid waterproof crystalline). Ammonite, containing an elastic fibrous additive – wood flour, is less compacted compared to ammonite PLW-20 (powder liquid waterproof), which consists of two hygroscopic salts (ammonium nitrate and sodium chloride).

119

Table 10.7 Duration Crystalline of ammonium moisnitrate ture, h

0

ω, % 0.04

ρ, g/ml 1.44

6 24 48 72

0.15 0.45 0.64 0.97

1.5 1.52 1.49 1.65

Ammonium Ammo-nite Ammonite nitrate, PLW-20 with the crystalline (Powder addition of brand LWC Liquid wood flour (Liquid Waterproof (4%) Waterproof – 20) Crystal) ω, ρ, ω, ρ, ω, ρ, % g/ml % g/ml % g/ml 0.038 1.47 0.5 1.5 0.15 Not compacted 0.09 1.42 0.25 1.45 0.27 1.0 0.53 1.41 1.08 1.73 0.54 1.25 0.94 1.42 1.18 1.59 0.6 1.0 1.44 1.43 1.9 1.65 0.92 1.31

Ammonite with mipora (microporous rubber) (2%) ω, % 0.11

0.34 1.23 1.45 2.10

ρ, g/ml Not compacted -»-»-»-»-

Note: ω ‒ humidity, ρ – density

Ammonium nitrate explosives containing an elastic, highly porous additive, mipora, are practically not compacted under the experimental conditions. Delamination is spontaneous or under the influence of external forces, separation of explosives into its component parts or individual components. Delamination is typical for mixed bulk explosives, the components of which differ significantly in density, shape and particle size, state of aggregation. So, igdanite (or igdanit) has a runoff of diesel fuel to the lower layers of explosives. In water-containing explosives, with a high content of the liquid phase and its insufficient thickening, constant sedimentation and accumulation of solid components in the lower layers occurs. Industrial explosives, factory fabricated, at observance of normal conditions of transportation and application are stratified slightly. The introduction of certain surfactants into granulated nitrate helps to reduce or prevent the separation of components. In such cases, the absorption capacity of the liquid component (diesel fuel, oil, etc.) nitrate increases. Increased absorbency with respect to die120

sel fuel is characterized by waterproof nitrate of the brand LWC, containing salts of fatty acids. Absorbent (retaining) ability of the granules of nitrate depends on their porosity and humidity. Below we present the data on the absorbency of granulated nitrate of grade B (numerator) and granulated porous nitrate of grade P with a porosity of 0.45 cm2/g (denominator of the fraction) relative to solar oil. 1 Humidity of saltpeter (nitrate), % 2 Absorption of oil by nitrate, %

0.3/0.13

0.73/0.4

1.08/1.0

1.66/1.4

8.21/15.8

9.55/15.46

7.18/14.1

4.68/12.08

In mixtures of igdanites made on low-porous saltpeter with a smooth surface of the granules and on low-viscosity fuel, such as diesel fuel, there is a flow of fuel into the lower layers of the charge. Delamination of water-containing explosives is inversely related to their viscosity. To prevent delamination, the aqueous component is thickened with so-called gelling agents that swell in water (polyacrylamide, sodium carboxymethyl cellulose, some vegetable polysaccharides, for example, guargam, etc.). In addition, in water-containing explosives, structuring or so-called «crosslinking» agents is used, among which the most common are borax, bichromates, etc. One of the forms of delamination is exudation of the liquid phase due to its migration to the surface of the charge due to capillary forces. Exudation is usually observed in the packaged explosives containing free or thickened with liquid polymers. The destruction of the gels (water for water-containing explosives and nitroglycerine for nitroether-containing explosives) leads to the appearance of a liquid phase, which can migrate to the surface of the cartridges. Exudation is especially dangerous for plastic dynamites, since the appearance of liquid nitroether or nitroglycol on paper-wrapped cartridges increases the danger of handling. Therefore, when developing formulations, it is necessary to provide the prevention of exudation of liquid nitroesters. To prevent exudation, liquid nitroesters are gelatinated with nitrocellulose or special absorbing additives are introduced. 121

The exudation is determined visually by the fatty band of the exuded nitroether when the cartridge paper is unfolded, and it can also be quantified. It is usually expressed relative to the content of nitroesters in the composition of explosives. Volatility is the ability of some components of the explosive to partially or completely volatilize (evaporate, sublimate) during storage or use. The higher the vapor pressure and temperature of the evaporated component, the higher the volatility of the explosive. Nitroesters partially volatilize from nitroether-containing industrial explosives, by which their toxic effect is caused, as well as water from water-containing explosives and diesel fuel from igdanite evaporates. At +40 °C nitroglycerin noticeably evaporates. The vapor pressure of nitroglycerin, according to G. Caste, increases at elevated temperatures from 0.027 Pa at 20 °C to 0.32 Pa at 40 °C and 2.67 Pa at 60 °C. The volatility of nitroglycol at a temperature of +35 ‒ +38 °C is 13 times higher than that of nitroglycerin. From powdered explosives with a content of 5% liquid nitroglycol in waxed cartridges at room temperature in 12 days ‒ 2%, in 2 months ‒ 12%, for 6 months ‒ 50% of nitroglycol is evaporated. Such a mass loss of nitroesters during storage may affect the explosive properties of explosives. Questions for self-control 1. Explosive works in the mines dangerous of gas and dust explosion. 2. Classes and properties of safety explosives. 3. Properties of flame arresters as a part of safety explosives. 4. Detonation of safety explosives. 5. Conditions of combustibility of safety explosives. 6. Physical stability and change of properties of explosives over time.

122

11.1. Impact of explosives on the environment during their use The action of an explosion, usually associated with the detonation of explosives, extends far beyond the zone in which useful work is performed. Seismic waves from explosions retain significant, sometimes destructive force. Under the seismic waves we understand oscillations of rock mass and soil propagating from the explosion. An array of rock near the marginal contours of quarries, slopes of quarries, structures and buildings of industrial sites of enterprises with open and underground mining methods, mining, residential, industrial and public buildings and structures in towns and cities are exposed to seismic waves. M.A. Sadovsky made a fundamental conclusion: the speed of ground oscillations exceeds a certain critical value typical for a given structure if the same type of structures are damaged by seismic waves from explosions. Experimental studies have confirmed the correctness of this conclusion. At a speed of fluctuations of soil more than 10 cm/sec in buildings violations are possible. The power of explosions at the mining enterprises of the country conducted in recent years has increased. According to the perception of urban dwellers and the results of instrumental observations in a number of quarries, the explosions are comparable in effect to earthquakes. The consequences of such explosions are manifested in the fall of chimneys, floor beams of buildings, delamination of plaster. In underground conditions, the main object of harmful effects of explosion seismic waves is structures located within the area of seismic explosion. They are subjected to residual deformations. Insufficient attention to measures to ensure the sustainability of workings, the lack of proper control and the ineffectiveness of such measures lead to detachment of slaughter and collapse of workings. In addition, underground mass explosions can have a seismic effect on industrial and cultural facilities located on the surface of the 123

building and underground workings outside the seismic sources for a long period of operation. During massive explosions in underground mines, workers have repeatedly been poisoned. When combined mining of mineral deposits by open and underground methods, poisonous gases from explosions in quarries can fall into underground mines, which can lead to serious consequences. Mine dust absorbs carbon monoxide and nitrogen oxides and retains them for a month or more. Dust, adsorbed toxic gases, enhances the development of silicosis in 2 ‒ 3 times. When explosions are made on the earth’s surface at a speed of 150 m/s or more, the spread of pieces of rock mass periodically leads to accidents, including group accidents. During blasting operations in water areas, the underwater structures are often destroyed, and there is a massive loss of marine animals and fish. Such cases are the result of hazardous manifestations of hydrostatic waves produced during the explosions. In the layer of water adjacent to the charge during the explosion of the charge of TNT, the pressure at the front of the hydroshock wave exceeds 100 kPa and the density of water increases dramatically. In the case of explosions in wells and on rocky foundations in the water, part of the energy is reflected, increasing the intensity of the wave. In modern conditions, the sound effect of an explosion, in addition to the negative effect on people, also negatively affects the habitat of animals, which is especially unacceptable near environmental protection complexes. In the practice of explosive business, it is required to determine the safe mass of charges and safe distances. According to the expression 

u  K u QЭn  K u RЭ n , 

where u is a ground oscillation rate, Q is a reduced charge mass 

equal to Q 

3

Q , r 124

Кu is a proportionality coefficient equal to 6.5 / 3 0,4  0,6nB3 and 2.0 / 3 0,4  0,6nB3 accordingly, in the following ranges of distances; nВ is the ratio of the radius of the discharge funnel to the depth of charge or indicator of the explosion, n is the effective attenuation of oscillations with a distance equal to 2 and 1.5 in the range of reduced distances, R

3

r , Q

where r is the distance to the explosion site, Q is the mass of the explosive charge up to 12.0 and over 12.0 m/kg 1/3. In specific conditions it is very important when the mass of the charge varies in proportion to the third degree. Modern engineering methods of explosion control allow us to increase or decrease its seismic action several times. The mass of the charge will change by 8-27 times when changing the speed of ground movement by 2-3 times. The seismic action of an explosion depends on the deformation properties of the rocks being destroyed under various loading conditions and not only on the charge mass. The deformation properties of rocks are determined by their ability to change the shape and size under the action of mechanical loads, and then partially or fully restore the size and original shape after removing the loads. The energy accumulated by the medium as a result of the propagation of compression-expansion waves is converted into the kinetic energy of the elements of the medium and the energy of formation of cracks. This kinetic energy leads to the scattering of individual pieces of rock, because with some delay in time the piston effect of gases that have remained in the expanded cracks manifests. The uncontrolled scattering of individual pieces of rock as a result of action of the kinetic energy of explosions is a dangerous phenomenon. Moreover, if the piston effect of detonation products of an explosive charge is regulated and relatively simply predicted, the degree of transfer of 125

kinetic energy by voltage waves is hardly predictable and more difficult to adjust. The forecast of the range of dispersion of pieces of rock can be made according to the laws of atmospheric ballistics. However, in this case, it is necessary to know the air resistance to their expansion, the shapes of the flying pieces, the nature of movement of pieces ‒ translational with rotation or translational, etc. Such calculations can be performed only when the properties of explosive rocks and specific explosion technologies are studied. In this case, with a slight overestimate, the radius of the longest range of expansion of pieces can be calculated without taking into account the air resistance using the formula

rk 

u k2 sin 2a , g

(11.1)

where uk is the rate of departure of pieces of rock, m/s; a is their departure angle, degree; g is acceleration of gravity, m/s2. The maximum range of expansion, obviously, will be when the piece flies at an angle of 45° to the horizon:

rk  u k2 / g .

(11.2)

G.I. Pokrovsky and I.S. Fedorov recommended to determine the maximum possible departure speed taking into account the value of the specific consumption of explosives (q) and density of rocks (ρ) by the formula uк= 72000 q /ρ.

(11.3)

Breaking out of wells and expanding, the mass of explosive gases displaces the surrounding air and forms around it a zone of heated and compacted air. This zone acts on the surrounding, not yet disturbed air and compresses it. Compression is transmitted further and further. 126

Shock air waves from industrial explosions can have different amplitudes and frequencies. The source of shock air waves can be explosive gases escaping during an explosion from wells, cracks or boreholes, a detonating cord used to transmit detonation, a mountain mass flying away during an explosion. By nature, the disturbance propagating from explosions in the air is referred to as weak air shock waves. According to the frequency of air oscillations, shock air waves can be infrasonic and sound. They pose a danger to the glazing of buildings, can create uncomfortable conditions for a person or surroundding natural complexes and exceed the permissible limits of oscillations in the sound range, and in some cases can be the source of unacceptable vibrations of elements of engineering structures or other buildings. The duration of its action and overpressure are the most important characteristics of the shock air waves that determine their impact. The hydro-shock waves formed during the explosions of industrial explosives are characterized by a relatively short duration of the compression period and large pressure values. This determines the risk of explosions for living organisms. At the same time, water shock waves do not pose a significant danger to people and animals on the shore, near the water with a sufficiently deep placement of charges. Investigations of B.V. Vyskrebentsev, L.N. Solodilov and others identified the dependencies of the sizes of the safe and lethal radii rlethal and rsafe and determined the coefficients and safe distances depending on the types and design of explosive charges, the mass of charges, and the nature of the impact loads. Experiments have shown that this dependence can be expressed as rlethal = Klethal √ Q rsafe = Ksafe √ Q. According to the experimental data Klethal = 8-27 and Ksafe = 12-45. As can be seen from the formulas, they do not take into account the parameters of explosions, which until recently, in many cases are determined by R. Cole. If we use the dependence proposed by 127

R. Cole, the pressure at the front of the shock wave (MPa) is expressed by the formula:

Pmax  53,3(3 Q / r )1,13 . Among the main toxic compounds and oxides formed during explosions, the most toxic are: oxide and nitrogen dioxide, carbon monoxide. If sulfur or sulfur compounds are present in the rocks being destroyed, hydrogen sulfide and sulfur dioxide are formed during explosions. The volume percentage (mg/l) for carbon monoxide (CO), nitrogen oxides (+2), sulfur dioxide (SO2) and hydrogen sulfide (H2S), the maximum permissible concentration (MPC) have the following values: 0.0016 (0.02); 0.0001 (0.005); 0.00035 (0.01) and 0.00066 (0.01). Calculation of poisonous gases in connection with their varying degrees of toxicity in the atmosphere is carried out by reference to the conditional carbon monoxide with the introduction of appropriate coefficients. The total amount of conditional carbon monoxide (L/kg) is determined by the formula V = NCO + 6.5 NNO + NO2 + 2.5N (SO2 +H2S),

(11.4)

where N is an amount of the corresponding gases. The poisonous products formed during explosive explosions are absorbed by the broken rock mass mixed with air, by dust filling pores and cracks of the rocks, niches and voids of workings. The main measure of protection of animals and people at explosive works from poisonings by poisonous gases is their removal out of the zones with a gas hazard. To reduce the concentration of gases released into the atmosphere, in addition to the selection of appropriate explosives, gases are bound with water and special compositions and intensive ventilation of explosion sites is used. Water can be used for irrigation of places of explosions and in the form of tamping. Great harm to the environment and human health is caused by spreading over long distances of the dust generated during blasting operations. 128

A harmful effect on the health of animals and people also has dust of other rocks. A system of measures, mainly the same as in the fight against poisonous gases, is carried out to combat dust in enterprises that carry out the blasting operations.

11.2. Methods of disposal of explosives All explosive materials (EM), which for one reason or another have become unfit for blasting, are to be destroyed. Common safety rules permit destruction by blasting, dissolving or burning and drowning in water. The applicability of these methods depends on the abilities and properties of explosive materials. Do not detonate explosives that are not capable of detonation or have lost it. It is impossible to sink water-insoluble explosives, do not burn explosives that can detonate during combustion. Blasting is considered the easiest way to destroy explosives. Explosives capable of explosion should be destroyed in this way. Overmoistened and poorly detonating explosives are to be mixed with other sensitive to detonation in open explosive charges. Only by detonation the electric detonators, blasting caps, detonating checkers and cords ‒ detonators are destroyed. Charges of the destroyed explosives are initiated by electrical and benign means of ignition or, in extreme cases, by fire. On charges of poorly concreted explosives, the bulk of the firing charge is recommended to be placed on top. Beyond the blasting means or fire, explosives are allowed to be destroyed only by incineration. The destruction of detonators is thus prohibited. Detonating cords not capable of detonation are burned separately from explosives. In combustion during destruction, measures against possible transition of combustion into detonation must be used. To do this, limit the amount of simultaneously burned explosives, produce dispersion and its closure over the soil surface, do not allow the presence of a capsule detonator (CD), electric detonator (ED), detonating cord (DC), detonator checkers and other highly sensitive explosives capable of burning causing detonation. When burning, explo129

sive cartridges must be unpacked, and explosives must be discharged. It is recommended to burn the explosives in separate tracks 0.5-0.6 m wide, scattered around. The thickness of the track is chosen from the ability of the explosive to burn and the tendency to transition to detonation and should not exceed 20 cm. You can simultaneously burn several tracks that are separated from one another at a distance that is safe to transfer detonation. To ignite explosives in the tracks, you can use container waste or add petroleum oil or small amounts of diesel fuel. Every means of ignition or explosives is destroyed on a separate site. Containers for explosives are also burnt separately. The safest method of destroying explosives is to drown them in water or to dissolve them. However, due to the introduction of toxic substances, it leads to pollution of water bodies and makes them unsuitable for other purposes. Rules allow us to destroy by dissolving only explosives dissolved in water. Questions for self-control 1. Influence of explosives on the environment at their application. 2. Influence of seismic waves on explosions. 3. List conditions of formation of hydroshock waves. 4. List ways of utilization of explosives.

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Lab 1. Determination of sensitivity of explosives to thermal pulse The purpose of the work is to study the delay period and flash point of the explosive flash with the different heating modes of the explosive. General information The study of sensitivity of explosives to the heat pulse is of great practical importance, as in the process of application and production, explosives are exposed to high temperatures. In most cases, the explosives must be sufficiently resistant to the heat pulse, and only for initiating explosives and gunpowder high susceptibility to heat is desirable. Thermal effects are divided into: ‒ homogeneous heating, uniform at a certain critical temperature for the entire mass of explosives (with a slight change in the temperature field from the center of the explosive mass to the periphery), at which the decomposition of explosives develops according to the laws of thermal explosion; ‒ local heating ‒ ignition with a significant temperature gradient. In this connection, sensitivity of the explosive to heating and ignition are determined, i.e. flammability. In solid and liquid explosives when they are heated, an explosion may develop by a thermal or chain mechanism. The most important is the thermal mechanism. The peculiarity of the thermal explosion is that the acceleration of the decomposition reaction of an explosive is possible if the heat input due to the reaction exceeds the heat sink in the reaction center. The chemical reaction starts when the explosive is heated, the speed of which depends on the temperature. When the temperature of the explosive is above the temperature of the walls of the vessel with 131

which the explosive is in contact, the rate of chemical reaction increases dramatically. The magnitude of pre-explosion heating is determined by the formula ΔT = Tcritical ‒ T0 = RT0 2/E