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Classification of explosions depending on the environment. What is an explosion? The concept and classification of explosions

19.01.2022

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1. General characteristics of explosive phenomenany

Explosions represent a particular danger in terms of possible losses and damage.

An explosion is the release of a large amount of energy in a limited amount in a short period of time.

The explosion leads to the formation of a highly heated gas (plasma) with a very high pressure, which, upon instantaneous expansion, exerts a shock mechanical effect (pressure, destruction) on the surrounding bodies.

An explosion in a solid medium is accompanied by its destruction and crushing, in air or water it causes the formation of air or hydraulic shock waves, which have a destructive effect on objects placed in them.

In activities other than intentional industrial explosions, an explosion should be understood as a rapid, uncontrolled release of energy that causes a shock wave traveling at some distance from the source.

As a result of the explosion, the substance that fills the volume in which the energy is released turns into a highly heated gas (plasma) with a very high pressure (up to several hundred thousand atmospheres). This gas, instantly expanding, has a shock mechanical effect on the environment, causing its movement. An explosion in a solid medium causes its crushing and destruction in a hydraulic and air environment - it causes the formation of a hydraulic and air shock (explosive) wave.

Explosive wave - is the movement of the medium generated by the explosion, in which there is a sharp increase in pressure, density and temperature of the medium.

The front (front boundary) of the blast wave propagates through the medium at high speed, as a result of which the area covered by the movement expands rapidly.

By means of a blast wave (or flying explosion products - in a vacuum), the explosion produces a mechanical effect on objects located at various distances from the explosion site. As the distance from the place of explosion increases, the mechanical effect of the blast wave weakens. Thus, the explosion carries a potential danger of hitting people and has a destructive ability.

An explosion can be caused by:

Detonation of condensed explosives (HE);

Rapid combustion of a flammable cloud of gas or dust;

Sudden destruction of a vessel with a compressed gas or superheated liquid;

Mixing superheated solids (melts) with cold liquids, etc.

Depending on the type of energy carriers and the conditions of energy release, the sources of energy during an explosion can be both chemical and physical processes.

The energy source of chemical explosions are fast self-accelerating exothermic reactions of interaction of combustible substances with oxidizers or reactions of thermal decomposition of unstable compounds.

The energy sources of compressed gases (vapors) in closed volumes of equipment (equipment) can be both external (energy used to compress cans, pump liquids; heat carriers that heat liquids and gases in a closed space) and internal (exothermic physical and chemical processes and processes of heat and mass transfer in a closed volume), leading to intensive evaporation of liquids or gas formation, an increase in temperature and pressure without internal explosive phenomena.

The energy source of nuclear explosions are fast chain nuclear reactions of fusion of light nuclei of hydrogen isotopes (deuterium and tritium) or fission of heavy nuclei of uranium and plutonium isotopes. Physical explosions occur when hot and cold liquids are displaced, when the temperature of one of them significantly exceeds the boiling point of the other. Evaporation in this case proceeds in an explosive manner. The resulting physical detonation is accompanied by the appearance of a shock wave with an overpressure reaching hundreds of MPa in some cases.

The energy carriers of chemical explosions can be solid, liquid, gaseous combustible substances, as well as air suspensions of combustible substances (liquid and solid) in an oxidizing environment, incl. and in the air.

explosion energy wave

2. Explosives

Solid and liquid energy carriers in most cases belong to the class of condensed explosives.

Explosives are chemical compounds or mixtures of substances capable of rapid chemical reaction with the release of a large amount of heat and the formation of gas.

The composition of explosives includes reducing agents and oxidizing agents or other chemically unstable compounds. When an explosion is initiated in these substances, exothermic redox reactions or thermal decomposition reactions proceed with great speed with the release of thermal energy and a large amount of gas. This reaction, having arisen at any point of the charge as a result of heating, impact, friction, explosion of another explosive or other external influence, spreads about the charge by heat or mass transfer (combustion), or by a shock wave (detonation).

Explosives have the ability to rapidly decompose, in which the energy of intermolecular bonds is released in the form of heat, and with increasing temperature, the decomposition rate of explosives increases. At a relatively low temperature, the decomposition rate of explosives is low, and explosives may not undergo noticeable changes in their state for a long time. In this case, thermal equilibrium is established between the explosive and the environment.

If conditions are created under which the heat released by the explosive does not have time to be removed to the environment, then due to an increase in temperature, a process of self-accelerating chemical decomposition of the explosive develops, which is called a thermal explosion.

Another process for the implementation of the explosion is possible, in which the chemical reaction propagates along the explosive charge sequentially from layer to layer in the form of a wave. The leading edge of this wave moving along the charge at a high speed (>9 km/s) is a shock wave - a sharp transition of matter from the initial state to a state with very high pressure and temperature. An explosive compressed by a shock wave is in a state in which chemical decomposition proceeds very quickly.

The process of chemical transformation of B1, which is introduced by a shock wave and is accompanied by a rapid release of energy, is called detonation.

The speed of a chemical reaction during detonation usually reaches several km/sec. A ton of solid explosive can turn into a dense gas with very high pressure in 1*10 -4 sec. The pressure in this case reaches several hundred thousand atmospheres.

The advantage of condensed and water-filled explosives is a significant concentration of energy per unit volume.

Expanding sharply, the compressed gas strikes the surrounding bodies with tremendous force. There is an explosion. Objects located near the charge are subjected to crushing and severe plastic deformation (local or blasting action of the explosion). Objects away from the parade experience less destruction, but the zone in which it occurs is much larger (general or high-explosive blast action). The explosive brisance is determined by the pressure that develops during detonation, which in turn depends on the charge density and detonation velocity. The explosiveness (operability) of explosives is determined by the heat, as well as the volume of gaseous products formed during the explosion.

The main characteristics of explosives are:

Brisance;

Explosiveness (operability);

Chemical and physical resistance (the ability to maintain their properties during storage and handling);

Sensitivity to external influences (the minimum amount of energy required to initiate an explosion);

Detonation ability (critical detonation diameter).

Explosive substances include:

Some substances that do not contain oxygen (azide, acetylene, acetylenide, diazo compounds, hydrazine, nitrogen iodide and chloride, mixtures of combustible substances with halogens, inert gas compounds, etc.).

Of the many explosive compounds, the following are used as explosives:

Nitro compounds (trinitrotoluene, tetryl, hexogen, octogen, nitroglycerin, PETN, nitrocellulose, nitromethane);

Salts of nitric acid (ammonium nitrate).

As a rule, these substances are not used in pure form, but in the form of mixtures.

According to explosive properties (conditions for the transition of combustion to detonation), explosives are divided into:

Initiating (primary);

Brisant (secondary);

Throwing (gunpowder).

Initiating explosives are characterized by a very high rate of explosive transformation, high sensitivity, unstable combustion, and its rapid transition to detonation already at atmospheric pressure. An explosion can be initiated by ignition, impact or friction.

The main representatives of initiating explosives are lead azide, mercury fulminate, tetrazene, lead trinitroresorcinate. Initiating explosives are used to initiate explosions of other explosives.

Brisant explosives are more inert, have less sensitivity to external influences. The combustion of these explosives can turn into detonation only in the presence of a strong shell, or a large amount of explosives. Relatively safe to handle. The main representatives of blasting explosives are nitro compounds and explosive mixtures based on nitrates, chlorates, perchlorates and liquid oxygen: trinitrotoluene, tetryl, hexogen, octogen, etc. They are used in blasting and for equipping ammunition of various types and purposes.

Throwing explosives (gunpowder) have stable combustion, do not detonate in the harshest conditions.

All types of explosions can be classified into the following three groups:

Uncontrolled sudden release of energy in a short period of time and in limited space (explosive processes);

Formation of clouds of fuel-air mixture (FA) or other chemical gaseous, dusty substances, their rapid explosive transformations (volumetric explosion);

Explosions of pipelines, vessels under high pressure or with superheated liquid, especially tanks with reduced carbon gas.

Explosions are due to the release of chemical energy (explosives), intra-nuclear energy (nuclear explosion), electromagnetic anergy (spark discharge, laser spark), compressed gas energy (when the gas pressure in the vessel exceeds the strength limit of this vessel - various cylinders, pipelines, etc. .d.)

Most often, explosions occur at explosive objects (VOO).

An explosive object is an object where substances (products) that acquire the ability to explode under certain conditions are stored, used, produced, transported.

Explosive objects include:

Enterprises of the defense, oil-producing, oil-refining, petrochemical, chemical, gas industries;

Enterprises of the bakery, textile and pharmaceutical industries

Warehouses for flammable and combustible liquids and liquefied gases.

The main damaging factors of the explosion are:

1. air shock wave arising from nuclear explosions, explosions of initiating and detonating explosives, explosive transformations of fuel-air mixtures (FA), gas-air mixtures (GVS), explosions of tanks with superheated liquid and tanks under pressure,

2. fragmentation fields created by flying fragments of various kinds of objects of technological equipment, building parts.

During the explosion of the gas-air environment, three hemispherical regions (zones) are formed:

I - zone of direct blasting action of a gas-air explosion near the ground (zone of complete destruction);

II - zone of action of explosion products;

III - zone of action of an air shock wave.

Effective impact in zone I is characterized by destruction that occurs as a result of a sharp impact of detonation products located inside the gas-air mixture of surrounding objects. The radius of this zone is determined by the tables or by the formula H I \u003d 1.7 H 0.

In hydrocarbon, propane and methane explosions, P0 has a value of 8.

The main parameters of damaging factors are:

1. - air shock wave - excess pressure in its front.

2. - fragmentation field - the number of fragments, their kinetic energy and radius of expansion.

The shock wave of any explosions causes large casualties and destruction of building elements. The size of the affected areas from explosions increases with the increase in their power. The action of a shock wave on the elements of a structure is characterized by a complex set of loads:

direct pressure;

reflection pressure;

Flow pressure;

leakage pressure;

The resistance of elements of structures to the action of a shock wave is usually characterized by the amount of excess pressure in the front of the shock wave, in Rf. Excess pressure in Pf is used as a universal characteristic of the resistance of building elements to the action of a shock wave and to determine the degree of their destruction and damage.

The degree and nature of damage to structures during explosions during industrial accidents depend on:

1. - power (TNT equivalent) of the explosion;

2. - technical characteristics of the structure (design, strength, size, shape - capital, temporary, ground, underground, etc.);

3. - layout of the object (dispersion of structures), the nature of development, the landscape of the area (relief, soil, drift);

5. - weather conditions (direction and strength of the explosion, humidity, temperature, precipitation).

Consequences of the explosions

As a result of the action of the damaging factors of the explosion, buildings, structures, technological equipment, vehicles, communication elements and other objects are destroyed or damaged, and people die.

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General information about the explosion

An explosion is a fast-flowing process of physical and chemical transformations of substances, accompanied by the release of a significant amount of energy in a limited volume, as a result of which a shock wave is formed and propagates, which has a shock mechanical effect on surrounding objects.

CHARACTERISTIC FEATURES OF THE EXPLOSION:

High rate of chemical transformation of explosives;
a large number of gaseous explosion products;
strong sound effect (rumble, loud sound, noise, strong bang);
powerful crushing action.

Depending on the environment in which explosions occur, they are underground, ground, air, underwater and surface.

The scale of the consequences of explosions depends on their power and the environment in which they occur. The radii of the affected zones during explosions can reach up to several kilometers.

There are three blast zones.

3she I- zone of action of the detonation wave. It is characterized by an intense crushing action, as a result of which the structures are destroyed into separate fragments, flying away at high speeds from the center of the explosion.

Zone II- the area of action of the products of the explosion. In it, the complete destruction of buildings and structures occurs under the action of expanding explosion products. At the outer boundary of this zone, the resulting shock wave separates from the explosion products and moves independently from the center of the explosion. Having exhausted their energy, the products of the explosion, having expanded to a density corresponding to atmospheric pressure, no longer produce a destructive effect.

Zone III- zone of action of an air shock wave - includes three subzones: III a - strong destruction, III b - medium destruction, III c - weak destruction. At the outer boundary of zone 111, the shock wave degenerates into a sound wave, which is still audible at considerable distances.

EXPLOSION EFFECTS ON BUILDINGS, STRUCTURES, EQUIPMENT .

Buildings and structures of large sizes with light load-bearing structures, which rise significantly above the earth's surface, are subjected to the greatest destruction by explosion products and a shock wave. Underground and underground structures with rigid structures have significant resistance to destruction.

Damage is divided into full, strong, medium and weak.

Complete destruction. Ceilings in buildings and structures collapsed and all the main load-bearing structures were destroyed. Recovery is not possible. Equipment, means of mechanization and other equipment are not subject to restoration. In utility and energy networks, there are breaks in cables, destruction of sections of pipelines, supports of overhead power lines, etc.

Strong destruction. There are significant deformations of load-bearing structures in buildings and structures, most of the ceilings and walls are destroyed. Restoration is possible, but impractical, as it practically boils down to new construction using some of the surviving structures. The equipment and mechanisms are mostly destroyed and deformed.

In communal and energy networks, there are breaks and deformations in certain sections of underground networks, deformations of overhead power lines and communications, breaks in technological pipelines.

Medium destruction. In buildings and structures, it was mainly not load-bearing, but secondary structures (light walls, partitions, roofs, windows, doors) that were destroyed. Possible cracks in the outer walls and falls in some places. Ceilings and cellars are not destroyed, part of the structures is suitable for operation. In utility and energy networks, destruction and deformation of elements are significant, which can be eliminated by major repairs.

Weak destruction. Part of the internal partitions, windows and doors were destroyed in buildings and structures. The equipment has significant deformations. There are minor damages and breakdowns of structural elements in utility and energy networks.

General information about the fire

FIRE AND ITS BEGINNING .

A fire is an uncontrolled burning that causes material damage, harm to the life and health of citizens, the interests of society and the state.

Essence of burning was discovered in 1756 by the great Russian scientist M. V. Lomonosov. By his experiments, he proved that combustion is a chemical reaction of the combination of a combustible substance with oxygen in the air. Therefore, in order for the combustion process to proceed, the following are necessary conditions:

The presence of a combustible substance (in addition to combustible substances used in production processes and combustible materials used in the interior of residential and public buildings, a significant amount of combustible substances and combustible materials is contained in building structures);
the presence of an oxidizing agent (usually, oxygen in the air is an oxidizing agent during combustion of substances; in addition to it, chemical compounds containing oxygen in the composition of molecules can be oxidizing agents: nitrates, perchlorates, nitric acid, nitrogen oxides and chemical elements: fluorine, bromine, chlorine);
the presence of an ignition source (open flame candles, matches, lighters, fires or sparks).

It follows that the fire can be stopped if one of the first two conditions is excluded from the combustion zone.

The possibility of fires in buildings and structures, and in particular the spread of fire in them, depends on what parts, structures and materials they are made of, what are their sizes and layout. As can be seen from Scheme 2, substances and materials are divided into flammability groups:

On non-combustible substances, unable to burn;
for slow-burning substances capable of burning under the influence of an ignition source, but unable to burn independently after its removal;
for combustible substances capable of burning after the ignition source is removed:
a) hardly flammable, capable of igniting only under the influence of a powerful ignition source;
b) flammable, capable of igniting from short-term exposure to low-energy ignition sources (flames, sparks).

1.3. Rights and obligations of citizens of the Russian Federation and heads of organizations in the field of fire safety

Chapter 2. Types of combustion and fires

2.1. Fundamentals of the theory of combustion. Types of combustion, their characteristics

2.2. Types of fires. Parameters characterizing the fire. Damaging fire factors

2.3. Classification of fires and recommended extinguishing media

Chapter 3. Fire_technical classification of building materials, structures, premises and buildings

3.1. Fire-technical classification of building materials

3.2. Fire-technical classification of building structures for fire safety, and buildings for fire resistance

3.3. Categories of premises by explosion and fire hazard

Chapter 4

4.2. Requirements for methods of ensuring fire safety of a fire protection system

4.3. Anti-explosion and fire-prevention requirements for the layout of industrial buildings and premises

4.4. Appointment and arrangement of fire breaks, walls, doors, gates, zones, ceilings, lsk, cut-offs, fire arresters and smoke protection of buildings

4.5. Fire safety of technological processes

4.6. Organizational and technical measures to prevent the spread of fires and explosions

4.7. Fire alarm (give diagrams). Heat, smoke and light detectors

4.8. Fire safety signs. Fire fighting briefings

Chapter 5

5.1. Fire extinguishing methods. Classification, characteristics and selection of fire extinguishing agents

5.2. Types of fire extinguishers

5.3. Classification of fire extinguishers

5.4. Choice of fire extinguishers. The effectiveness of their use, depending on the class of fire and charged resp.

5.5. Device, operation procedure, characteristics and scope of carbon dioxide fire extinguishers OU.

5.6. Device, operating procedure, characteristics and scope of air-foam fire extinguishers ovp

5.7. Device, operating procedure, characteristics and scope of powder fire extinguishers op.

5.8. Standards for equipping premises with portable fire extinguishers

5.9. Device and principle of operation of sprinkler and deluge automatic fire extinguishing systems

Chapter 6. Fire prevention on the territory and premises of educational institutions

6.1. Evacuation of people in case of fire

6.2. Basic fire prevention measures on the territory, in industrial and educational premises

Chapter 7. Fire safety system

7.1. Concept, main elements and functions of the fire safety system in the Russian Federation

7.2. Types and main tasks of fire protection in the Russian Federation. Rights of the state fire inspector

7.3. Organization of fire fighting and rescue operations

7.4. Organization of fire protection at the enterprise. Duties and tasks of the fire-technical commission

Chapter 8. Classification and characteristics of explosions

8.1. Characteristics of the explosive state of objects of the economy of the Russian Federation

8.2. Classification of explosions

8.3. Characterization and classification of condensed explosives

8.4. Dusty air mixtures and features of their combustion

8.5. Features of the physical explosion. Causes of explosions of pressure vessels

Chapter 9. Explosion protection of pressurized systems

9.1. Measures to prevent explosions of high-pressure systems

9.2. Classification of hazardous areas and premises

9.3. Classification of the severity of injury to people and destruction of buildings, depending on the pressure in the shock wave

9.4. State supervision of explosive objects: permission to work, testing of vessels. Rights of Rostekhnadzor

9.5. First aid for fires and burns

Sample list of questions for the exam

Bibliographic list

8.2. Classification of explosions

At explosive sites, the following are possible: types of explosions:

1. Explosions of condensed explosives (CEE). In this case, an uncontrolled sharp release of energy occurs in a short period of time in a limited space. These explosives include TNT, dynamite, plastid, nitroglycerin, etc.

2. Explosions of air-fuel mixtures or other gaseous, dusty-air substances (PLVS). These explosions are also called volumetric explosions.

3. Explosions of vessels operating under excessive pressure (cylinders with compressed and liquefied gases, boiler plants, gas pipelines, etc.). These are the so-called physical explosions.

Main damaging factors of the explosion are: air shock wave, fragments.

Primary consequences of the explosion: destruction of buildings, structures, equipment, communications (pipelines, cables, railways), injury and death of people.

Secondary consequences of the explosion: collapse of structures of buildings and structures, injury and burial under their debris of people in the building, poisoning of people with toxic substances that were in destroyed tanks, equipment, pipelines.

In explosions, people will receive thermal, mechanical, chemical or radiation damage.

To prevent explosions at enterprises, a set of measures is taken, depending on the nature of production. Many measures are specific, characteristic only for one or several types of production. However, there are measures that must be observed in any production. These include:

1) placement of explosive production facilities, storage facilities, explosive depots in uninhabited or sparsely populated areas;

2) if the first condition cannot be met, then such facilities may be built at safe distances from populated areas;

3) for the reliable supply of explosive industries with electricity (in this case, the technological regime is violated), it is necessary to have autonomous sources of power supply (generators, batteries);

4) on long oil and gas pipelines, it is recommended to have emergency teams every 100 km.

8.3. Characterization and classification of condensed explosives

KVV means chemical compounds located in solid or liquid state, which, under the influence of external conditions, are capable of a rapid self-propagating chemical transformation with the formation of highly heated and high-pressure gases, which expand to produce mechanical work. Such chemical transformation of explosives is called explosive transformation.

Explosive transformation, depending on the properties of the explosive and the type of impact on it, can proceed in the form of an explosion or combustion. The explosion propagates through the explosive at a high variable speed measured in hundreds or thousands of meters per second. The process of explosive transformation, caused by the passage of a shock wave through an explosive and proceeding at a constant (for a given substance in a given state) supersonic speed, is called detonation. In the event of a decrease in the quality of explosives (humidification, caking) or an insufficient initial impulse, detonation can turn into combustion or completely die out.

The process of combustion of CVV proceeds relatively slowly at a speed of several meters per second. The burning rate depends on the pressure in the surrounding space: with increasing pressure, the burning rate increases and sometimes combustion can turn into an explosion.

The excitation of explosive transformation of explosives is called initiation. It occurs if you inform the explosives of the required amount of energy (initial impulse). It can be passed in one of the following ways:

Mechanical (impact, prick, friction);

Thermal (spark, flame, heating);

Electrical (heating, spark discharge);

Chemical (reactions with intense heat release);

An explosion of another explosive charge (explosion of a detonator cap or an adjacent charge).

All KVV used in production are classified into three groups:

- initiating(primary), they have a very high sensitivity to impact and thermal effects and are mainly used in detonator caps to detonate the main explosive charge (mercury fulminate, nitroglycerin);

- secondary explosives. Their explosion occurs when they are exposed to a strong shock wave, which can be created in the process of their combustion or with the help of an external detonator. Explosives of this group are relatively safe to handle and can be stored for a long time (TNT, dynamite, hexogen, plastid);

- gunpowder. Sensitivity to impact is very small, slowly burning. Ignite from a flame, spark or heat, burn faster in the open air. They explode in a closed container. The composition of gunpowder includes: charcoal, sulfur, potassium nitrate.

In the national economy, CVVs are used for laying roads, tunnels in the mountains, breaking ice jams during the period of ice drift on rivers, in quarries during the extraction of minerals, during the demolition of old buildings, etc.

Explosions most commonly encountered in practice can be divided into two main groups: physical and chemical(see figure 7.2).

Physical explosions include processes that lead to an explosion and are not accompanied by a chemical transformation of matter.

Chemical explosions include processes of chemical transformation of matter, manifested by combustion and characterized by the release of thermal energy in a short period of time and in such volume that pressure waves are formed that propagate from the source of the explosion.

The most common cause of accidental explosions are combustion processes. Explosions of this kind most often occur during storage, transportation and manufacture of explosives. They occur when handling explosives and explosive substances in the chemical and petrochemical industries; in case of natural gas leaks in residential buildings; in the manufacture, transportation and storage of volatile or liquefied combustible substances; when flushing storage tanks for liquid fuels; in the manufacture, storage and use of combustible dust systems and some spontaneously combustible solid and liquid substances.

Rice. 7.2. Classification of explosions most frequently encountered in practice

At physical explosion the released energy is the internal energy of the compressed or liquefied gas (more strictly, liquefied steam). The strength of such explosions depends on the internal pressure, and destruction can be caused by a shock wave from an expanding gas or fragments of a ruptured tank. In a number of accidents, physical explosions were noted, arising from the complete destruction of tankers. Depending on the circumstances, parts of such a reservoir scattered hundreds of meters.

The same thing can happen (on a smaller scale) to portable gas bottles if the bottle falls and the pressure-reducing valve breaks. Numerous cases of such purely physical explosions of vessels with liquefied gases under pressure not exceeding 4 MPa are known.

Physical explosions should also include the phenomenon of so-called physical (or thermal) detonation, which occurs when hot and cold liquids are mixed, when the temperature of one of them significantly exceeds the boiling point of the other (for example, when pouring molten iron into water). In the resulting vapor-liquid mixture, evaporation can proceed explosively due to the developing processes of fine fragmentation of melt droplets, rapid removal from them, and overheating of the cold liquid. Physical detonation is accompanied by the formation of a shock wave with excess pressure in the liquid phase, reaching hundreds of megapascals in some cases. This phenomenon can cause major accidents in nuclear reactors and at industrial enterprises in the metallurgical, chemical and paper industries.

Energy sources of compressed gases (vapors) in closed volumes of equipment can be both external and internal. External - this is electrical energy used to compress gases and pump liquids; heat carriers, including electrical ones, providing heating of liquids and gases in closed volumes of equipment. Internal sources include the energy of exothermic physicochemical and heat and mass transfer processes in a closed volume of equipment, leading to intensive evaporation of liquid media or gas formation, an increase in temperature and pressure without internal explosive phenomena.

chemical explosions are divided into volumetric (see Fig. 7.3) and explosions of condensed explosives. The source of a chemical explosion is a rapidly flowing self-accelerating exothermic reaction of the interaction of combustible substances with oxidizing agents or thermal decomposition of unstable compounds. Under some circumstances, uncontrolled reactions are possible, accompanied by an increase in pressure in the reaction vessel, which can completely collapse if there is no safety valve. In this case, a shock wave and a fragmentation field can form.

Rice. 7.3. Classification of volumetric explosions

Energy carriers of chemical explosions can be solid, liquid, gaseous substances, as well as air suspensions of combustible substances (liquid and solid) in an oxidizing environment (often in air). Explosions of gas mixtures and air suspensions of combustible substances are sometimes called bulk explosions. Solid and liquid energy carriers in most cases belong to the class condensed explosives. These substances or their mixtures contain reducing and oxidizing agents or other chemically unstable compounds. When an explosion is initiated in these substances, exothermic redox reactions or thermal decomposition reactions proceed with the release of thermal energy (during explosions of a condensed explosive, carbon and hydrogen atoms in the substance molecules are replaced by nitrogen atoms).

Gaseous energy carriers are homogeneous mixtures of combustible gases (vapours) with gaseous oxidants such as air, oxygen, chlorine, etc., or unstable gaseous compounds such as acetylene, ethylene (prone to thermal decomposition in the absence of oxidizing agents). The source of explosions of gas mixtures are exothermic reactions of oxidation of a combustible substance or reactions of decomposition of unstable compounds.

Two-phase explosive air suspension consist of finely dispersed combustible liquids (“fogs”) or solids (dust) in an oxidizing environment, mainly in air. The source of energy for their explosions is also the heat of combustion of these substances.

A technological system is explosive if it has a store of potential energy released at such a high rate that it can generate an air shock wave (ASW) capable of causing crashes or injury to people. The amount of potential energy is determined by the corresponding physical and chemical laws of energy release.

The energy of the explosion of gas-vapor media is determined by the heat of combustion of combustible substances in a mixture with air (oxidizer); condensed explosives - according to the heat released during their detonation (decomposition reactions); in physical explosions of systems with compressed gases and superheated liquids - according to the energy of adiabatic expansion of vapor-gas media and liquid overheating.

The rate of energy release is generally expressed as power density, i.e., the amount of energy released per unit time per unit volume. In chemical explosions, the rate of energy release can be determined from the speed of propagation of detonation or flame in a gaseous medium. The velocity of detonation propagation in a solid or liquid explosive approximately corresponds to the speed of sound in a substance and is in the range 2 . 10 3 -9 . 10 3 m/s; during gas physical and chemical explosions, compression waves move at a speed close to the speed of sound in air.

Chemical explosions caused by exothermic decomposition reactions in condensed explosives or unstable compounds in the gas phase are accompanied by the formation (increase) in the number of moles of gases. For example, in the explosion of 1 kg of trinitrotoluene (TNT), which is a substance with a negative oxygen balance, approximately 20 mol of gases (vapors) are formed (0.6 - CO; 10.0 - CO 2; 0.8 - H 2 O; 6, 0 - N 2; 0.4 - NH 3; 4.7 -CH 3 OH; 1.0 - HCN) and 15 mol of carbon. Most other blasting explosives (with the exception of nitroglycerin) are also substances with a negative oxygen balance, i.e. the number of oxygen atoms in their molecules is not enough to completely convert the existing carbon atoms into CO 2 and hydrogen into H 2 O. The ability of a substance to an explosive process is subject to the laws of thermochemistry, according to which, if in a given reaction the sum of the heats of formation of products is less than the heat of formation of the initial compound, then this substance is potentially explosive. For example, if substance A, which decomposes according to the reaction A → B + C + D, is explosive, then the condition must be met:

q(A) ≥ q(B) + q(C) + q(D),

where q is the enthalpy (heat) of formation; q is positive for compounds formed with heat absorption (endothermic processes) and negative for compounds formed with heat release (exothermic processes).

Thus, it is only possible to evaluate the ability of a substance to an explosive process, and the energy and power of an explosion are determined by the reaction rate.

Energy sources of explosions can be redox chemical reactions, in which
air or oxygen interact with the reducing agent.
Along with combustible gases, reducing agents can be
fine combustible solids (dusts) or
dispersed liquids. Redox reactions under these conditions can proceed both in closed and open volumes at sufficiently high rates at which shock waves are generated that can cause significant damage.

What is an explosion? This is a process of instantaneous transformation of the state in which a significant amount of thermal energy and gases are released, forming a shock wave.

Explosives are compounds that have the ability to undergo changes in the physical and chemical state as a result of external influences with the formation of an explosion.

Classification of explosion types

1. Physical - the energy of an explosion is the potential energy of a compressed gas or steam. Depending on the magnitude of the internal energy pressure, an explosion of different power is obtained. The mechanical impact of the explosion is due to the action of the shock wave. Fragments of the shell cause an additional damaging effect.

2. Chemical - in this case, the explosion is due to the almost instantaneous chemical interaction of the substances that make up the composition, with the release of a large amount of heat, as well as gases and steam with a high degree of compression. Explosions of these types are typical, for example, for gunpowder. Substances arising as a result of a chemical reaction acquire high pressure when heated. The explosion of pyrotechnics also belongs to this species.

3. Nuclear explosions are lightning-fast reactions of nuclear fission or fusion, characterized by a huge power of released energy, including heat. The colossal temperature at the epicenter of the explosion leads to the formation of a zone of very high pressure. The expansion of the gas leads to the appearance of a shock wave, which is the cause of mechanical damage.

The concept and classification of explosions allow you to act correctly in an emergency.

Action type

Distinctive features

Explosions differ depending on the chemical reactions taking place:

Decomposition is characteristic of a gaseous medium.
Redox processes imply the presence of a reducing agent with which the oxygen in the air will react.
Reaction of mixtures.

Volumetric explosions include dust explosions, as well as explosions of steam clouds.

dust explosions

They are typical for closed dusty structures, such as mines. A dangerous concentration of explosive dust appears during mechanical work with bulk materials that give a large amount of dust. Working with explosives requires full knowledge of what an explosion is.

For each type of dust, there is a so-called maximum permissible concentration, above which there is a danger of spontaneous explosion, and this amount of dust is measured in grams per cubic meter of air. The calculated concentration values are not constant values and must be corrected depending on humidity, temperature and other environmental conditions.

Of particular danger is the presence of methane. In this case, there is an increased probability of detonation of dust mixtures. Already a five percent content of methane vapor in the air threatens with an explosion, due to which the ignition of a dust cloud follows and an increase in turbulence. A positive feedback occurs, leading to an explosion of great energy. Scientists are attracted by such reactions, the explosion theory still haunts many.

Safety when working in confined spaces

When working in closed rooms with a high content of dust in the air, it is imperative to adhere to the following safety rules:

Dust removal by ventilation;

Fight against excessive dryness of air;

Dilution of the air mixture to reduce the concentration of explosives.

Dust explosions are typical not only for mines, but also for buildings and granaries.

Steam cloud explosions

They are reactions of a lightning-fast change of state, generating the formation of a blast wave. Occur outdoors, in a confined space due to the ignition of a combustible vapor cloud. This usually happens when there is a leak.

Refusal to work with combustible gas or steam;

Refusal of ignition sources that can cause a spark;

Avoiding closed spaces.

You need to have a sound understanding of what an explosion is, what danger it carries. Failure to comply with safety rules and the illiterate use of some items leads to disaster.

Gas explosions

The most common accidents in which a gas explosion occurs occur as a result of improper handling of gas equipment. Timely elimination and characteristic definition are important. What does gas explosion mean? It occurs due to improper operation.

In order to prevent such explosions, all gas equipment must undergo regular preventive technical inspection. All residents of private households, as well as apartment buildings, are recommended an annual maintenance of the VDGO.

To reduce the consequences of an explosion, the structures of the premises in which gas equipment is installed are made not capital, but, on the contrary, lightweight. In the event of an explosion, there is no major damage and blockages. Now you imagine what an explosion is.

In order to make it easier to determine the leakage of household gas, the aromatic additive ethyl mercaptan is added to it, which causes a characteristic smell. If there is such a smell in the room, it is necessary to open the windows to ensure the supply of fresh air. Then you should call the gas service. At this time, it is better not to use electrical switches that can cause a spark. It is strictly forbidden to smoke!

The explosion of pyrotechnics can also become a threat. The storage of such items must be equipped in accordance with the standards. Poor quality products can harm the person who uses it. All this should definitely be taken into account.

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