The concept and types of explosions and explosives. General characteristics of explosions and their damaging factors Explosion brief definition

Explosion- a fast physical or physicochemical process that takes place with a significant release of energy in a small volume in a short period of time and leads to shock, vibration and thermal effects on the environment due to the high-speed expansion of explosion products.

Deflagration explosion- energy release in the volume of a cloud of combustible gaseous mixtures and aerosols during the propagation of an exothermic chemical reaction with subsonic speed.

Detonation explosion- explosion, in which the ignition of subsequent layers of explosive occurs as a result of compression and heating by a shock wave, characterized by the fact that the shock wave and the chemical reaction zone follow each other inseparably at a constant supersonic speed.

The chemical explosion of non-condensed substances differs from combustion in that combustion occurs when a combustible mixture is formed in the process of combustion itself. : 36

Explosion products are usually gases with high pressure and temperature, which, when expanding, are capable of performing mechanical work and causing destruction of other objects. In addition to gases, explosion products can also contain highly dispersed solid particles. The destructive effect of the explosion is caused by high pressure and the formation of a shock wave. Explosion effects can be enhanced by cumulative effects.

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  The following types of explosions are distinguished by the origin of the released energy:

  • Chemical explosions of explosives - due to the energy of chemical bonds of the initial substances.
  • Explosions of containers under pressure (gas cylinders, steam boilers, pipelines) - due to the energy of compressed gas or superheated liquid. These include, in particular:
    • Explosion of expanding vapors of a boiling liquid (BLEVE).
    • Explosions on depressurization in superheated liquids.
    • Explosions when two liquids are mixed, the temperature of one of which is much higher than the boiling point of the other.
  • Nuclear explosions - due to the energy released in nuclear reactions.
  • Electrical explosions (for example, during a thunderstorm).
  • Volcanic explosions.
  • Explosions in the collision of cosmic bodies, for example, in the fall of meteorites on the surface of the planet.
  • Explosions caused by gravitational collapse (supernova explosions, etc.).

  Chemical explosions

  Unified opinion what chemical processes should be considered an explosion does not exist. This is due to the fact that high-speed processes can proceed in the form of detonation or deflagration (slow combustion). Detonation differs from combustion in that chemical reactions and the process of energy release proceed with the formation of a shock wave in the reacting substance, and the involvement of new portions of an explosive in a chemical reaction occurs at the front of the shock wave, and not through heat conduction and diffusion, as in slow combustion. The difference in the mechanisms of energy and substance transfer affects the rate of the processes and the results of their action on the environment, however, in practice, a variety of combinations of these processes and transitions of combustion to detonation and vice versa are observed. In this regard, various fast processes are usually referred to chemical explosions without specifying their nature.

  There is a more rigid approach to defining a chemical explosion as exclusively detonation. From this condition, it necessarily follows that in a chemical explosion accompanied by a redox reaction (combustion), the combusting substance and the oxidizing agent must be mixed, otherwise the reaction rate will be limited by the rate of the oxidant delivery process, and this process, as a rule, has a diffusional character. For example, natural gas burns slowly in home stove burners as oxygen slowly enters the combustion area by diffusion. However, if you mix gas with air, it will explode from a small spark - a volumetric explosion. There are very few examples of chemical explosions that do not cause oxidation / reduction, for example, the reaction of finely dispersed phosphorus (V) oxide with water, but it can also be considered as a steam explosion.

  Individual explosives usually contain oxygen in their own molecules. These are metastable substances that can be stored more or less long time under normal conditions. However, when an explosion is initiated, sufficient energy is transferred to the substance for spontaneous propagation of a combustion or detonation wave that captures the entire mass of the substance. Nitroglycerin, trinitrotoluene and other substances have similar properties.

  Explosion- this is a very rapid change in the chemical (physical) state of an explosive, accompanied by the release of a large amount of heat and the formation of a large amount of gases, creating a shock wave capable of causing destruction by its pressure.

  Explosives (explosives)- special groups of substances capable of explosive transformations as a result of external influences.
  Distinguish explosions :

  1.Physical- the released energy is the internal energy of the compressed or liquefied gas (liquefied steam). The force of the explosion depends on the internal pressure. The resulting destruction can be caused by a shock wave from an expanding gas or by fragments of a ruptured tank (Example: destruction of compressed gas tanks, steam boilers, as well as powerful electrical discharges)

  2.Chemical- an explosion caused by a rapid exothermic chemical reaction that occurs with the formation of highly compressed gaseous or vaporous products. An example is explosion of black powder, in which a rapid chemical reaction occurs between saltpeter, coal and sulfur, accompanied by the release of a significant amount of heat. The resulting gaseous products, heated by the heat of reaction to a high temperature, have high pressure and, expanding, perform mechanical work.

  3.Atomic explosions... Fast nuclear or thermonuclear reactions (fission reactions or the combination of atomic nuclei), in which a very large amount of heat is released. The reaction products, the shell of an atomic or hydrogen bomb and a certain amount of the environment surrounding the bomb are instantly transformed into gases heated to a very high temperature and having a correspondingly high pressure. The phenomenon is accompanied by colossal mechanical work.

  Chemical explosions are classified into condensed and volumetric explosions.

  A) Under condensed explosives are understood chemical compounds and mixtures in a solid or liquid state, which, under the influence of certain external conditions, are capable of rapid self-propagating chemical transformation with the formation of highly heated and high-pressure gases, which, expanding, produce mechanical work. Such a chemical transformation of explosives is usually called explosive transformation.
  

  Excitation of explosive transformation of explosives is called initiation. To excite the explosive transformation of an explosive, it is required to impart to it with a certain intensity the required amount of energy (initial impulse), which can be transferred in one of the following ways:
  - mechanical (impact, prick, friction);
  - thermal (spark, flame, heating);
  - electric (heating, spark discharge);
  - chemical (reactions with intense heat release);
  - explosion of another explosive charge (explosion of a detonator capsule or an adjacent charge).

  Condensed explosives are subdivided into groups :

  	Characteristic. Examples of substance.
  	Extremely hazardous substances Unstable. Explode even in the smallest quantities. Nitrogen trichloride; some organic peroxide compounds; copper acetylenide, formed by contact of acetylene with copper or copper alloy
  	Primary explosives Less hazardous substances. Initiating connections. They have a very high sensitivity to shock and heat. They are mainly used in detonator capsules to excite detonation in explosive charges. Lead azide, mercury fulminate.
  	Secondary explosives (blasting explosives) Detonation is excited in them when exposed to a strong shock wave. The latter can be created during their combustion or with the help of a detonator. As a rule, explosives in this group are relatively safe to handle and can be stored for long periods of time. Dynamites, TNT, RDX, HMX, Centralite.
  	Throwing explosives, gunpowder Shock sensitivity is very low, burn relatively slowly. Ballistic propellants - a mixture of nitrocellulose, nitroglycerin and other technological additives. Ignite from flame, spark or heat. They burn quickly outdoors. Explode in a closed vessel. At the site of the explosion of black powder containing potassium nitrate, sulfur and charcoal in a ratio of 75:15:10, a residue containing carbon remains.

  Explosions can be classified according to the types of chemical reactions:

  1. Decomposition reaction - a decomposition process that produces gaseous products
  2. Redox reaction - a reaction in which air or oxygen reacts with a reducing agent
  3. The reaction of mixtures is an example of such a mixture - gunpowder.

  B) Volumetric explosions are of two types:

  • Dust cloud explosions (dust explosions) are considered dust explosions in mine tunnels and equipment or inside a building. Such explosive mixtures arise during crushing, sieving, filling, moving dusty materials. Explosive dust mixtures have a lower explosive concentration limit (NKPV), determined by the content (in grams per cubic meter) of dust in the air. So for the sulfur powder, the NKPV is 2.3 g / m3. Dust concentration limits are not constant and depend on humidity, degree of grinding, content of combustible substances.

  The mechanism of dust explosions in mines is based on relatively weak explosions of a gas-air mixture of air and methane. Such mixtures are considered already explosive at a 5% concentration of methane in the mixture. Explosions of the gas-air mixture cause turbulence of air flows sufficient to form a dust cloud. The dust ignites and creates a shockwave that raises more dust, and then a powerful destructive explosion can occur.

  Measures used to prevent dust explosions:

  1. ventilation of premises, objects
  2. wetting surfaces
  3. dilution with inert gases (CO 2, N2) or silicate powders

  Dust explosions inside buildings and equipment most often occur on elevators, where, due to the friction of the grains during their movement, a large amount of fine dust is formed.

  • Explosions of steam clouds- processes of rapid transformation, accompanied by the appearance of a blast wave, occurring in open air as a result of the ignition of a cloud containing combustible vapor.

  Such phenomena occur when a liquefied gas leaks, as a rule, in confined spaces (rooms), where the limiting concentration of combustible elements at which the cloud ignites is rapidly increasing.
  Measures used to prevent vapor cloud explosions:

  1. minimizing the use of flammable gas or steam
  2. lack of ignition sources
  3. location of units in an open, well-ventilated area

  The most common emergencies associated with with gas explosions, arise during the operation of a communal gas equipment.

  To prevent such explosions, preventive maintenance of gas equipment is carried out annually. Buildings of explosive workshops, structures, some of the panels in the walls are made easily destructible, and the roofs are easily removable.

  BASIC INFORMATION ABOUT INTERNAL AND EXTERNAL BALLISTICS.

  The science that studies the movement of a bullet (projectile) is called ballistics (ballistics from the Greek word BALLO - throw). By the nature of the forces acting on the bullet, ballistics is divided into internal and external.

  Explosives (explosives) unstable mixtures and chemical compounds are called, which are capable, under the influence of insignificant external influences (impact, friction, prick, heating, etc.), to make a rapid transformation into a gaseous state.

  Explosion is called the phenomenon of an extremely rapid physical or chemical change in a substance, accompanied by the same rapid transformation of its potential (latent) energy into mechanical work.

  A chemical reaction accompanied by an explosion is called explosive transformation.

  The characteristic signs of an explosion are as follows: short duration of the process- the rapidity of the transition of explosives from a solid or liquid state to a gaseous state, i.e. into the final system of transformation products. Depending on the chemical composition and the conditions under which the explosion occurs, explosive transformations proceed at different speeds - from hundredths to millionths of a second. So, a charge of smokeless powder burns out in a rifle in 0.0012 sec., 1 kg. dynamite explodes within 0.00002 seconds; gas formation - the presence of a large amount of gaseous explosion products capable of expansion. The amount of gaseous products released during an explosion is expressed approximately in the following figures: 1 liter. pyroxylin gives 994 liters. gaseous explosion products; 1 l. nitroglycerin gives 1121 liters. gaseous explosion products; heat generation during an explosive transformation reaction, which increases the elasticity of gas products.

  Types of explosive transformations

  Depending on the chemical composition of the explosive and the conditions of the explosion, explosive transformations proceed at different rates at which they can occur: rapid combustion, explosion itself, detonation.

  Fast combustionExplosive is called the process of explosive transformation, spreading throughout the entire mass of explosive at a speed of no more than a FEW meters per second. An example is the combustion of black powder grains in the open air at a speed of 10-12 mm / sec.

  In a closed volume, the combustion of explosives proceeds more vigorously than in air, and the combustion is accompanied by a sharp sound. An example is the burning of a charge of smokeless powder in the bore (speed up to about 10 m / s). The sequential rapid combustion of explosives is accompanied by a more or less rapid increase in the gas pressure in the barrel bore, which, as it is formed, spreads towards the least resistance, while performing the work of moving, pushing a bullet or projectile out of the barrel bore.

  The explosion itself- the process of decomposition of explosives, which proceeds at a tremendous speed, measured in hundreds of meters per second. Such an explosion is accompanied by a sharp increase in the pressure of gases at the explosion site, the impact of gases on the environment, which entails the splitting and crushing of objects in the immediate vicinity of the explosion site.

  Detonationis called a process propagating through an explosive with the maximum possible speed of explosive transformation for it, usually measured in thousands of meters per second (the detonation speed of pyroxylin is up to 6800 m / s, nitroglycerin is 8200 m / s). By the end of the explosion, i.e. By the time the entire charge has decomposed, the gases have not yet had time to expand and occupy the initial volume of the explosive, in connection with which an enormous gas pressure immediately develops in all directions. Such a sharp jump in pressure and the impact of gases lead to crushing the obstacle into smallest pieces.

  release of a large amount of energy in a limited amount in a short period of time. V. leads to the formation of a highly heated gas (plasma) with a very high pressure, which, upon expansion, exerts a mechanical effect (pressure, destruction) on the surrounding bodies. In a solid environment, it is accompanied by its destruction and crushing. V. is carried out most often due to the release of the chemical energy of explosives.

  Excellent definition

  Incomplete definition ↓

  Explosion

  rapid transformation of matter (explosive combustion), accompanied by the release of energy and the formation of compressed gases capable of performing work. A blast wave spreads in the environment. The amount released at v. Energy determines the scale (volume, area) of destruction. The value of the concentration of energy per unit volume determines the intensity of destruction in the focus of the explosion. Explosion pressure, kp-scale of damage to buildings 100 Complete destruction of buildings 5350% destruction of buildings 28 Average damage to buildings 12 Moderate damage to buildings (damage to internal partitions, frames, doors, etc.) 3 Minor damage to buildings (part of the Glazing is broken) damage to a person, taken as a boundary value when determining the category of premises and buildings, outdoor installations. At pressure in. Below 5 kPa, the room, building, outdoor installation does not belong to category a or b in terms of explosion and fire hazard. In the case of diffusion combustion of solid and liquid substances (materials) under fire conditions c. Not implemented. However, when the products of thermal and thermooxidative destruction (hydrogen, methane, carbon monoxide, etc.) accumulate in a closed volume, V. can occur. An example is c. Silos and bunkers at elevators, feed mills. During self-heating and subsequent spontaneous combustion of plant raw materials, decomposition products accumulate in the burned-out cavities and, when the arches collapse, ignite from the vault. Projects V. They are used in military affairs, mining, construction, etc.

  EXPLOSION - an extremely rapid release of energy associated with a sudden change in the state of a substance, as a rule, accompanied by the same rapid transformation of energy into mechanical work, destruction environment, the formation and propagation of a shock or blast wave in the medium.

  The explosion site is a set of traces of an explosive action displayed in a specific situation, the identification and fixation of which is impossible without highlighting the main signs of the manifestation of an explosion in general and an explosive device of a certain design in particular.

  The classifications of the explosions themselves are varied and numerous, the criteria of which are the environment in which they are produced (ground, non-contact, underwater, etc.), the presence of concentration of explosion products in a certain direction (cumulative), and other factors. Detailed list varieties of explosions are cited by R.A. Strehlow and W.E. Bacer (1976):

  1) natural explosions (lightning, volcanoes, meteorites, etc.);

  2) deliberate explosions (nuclear; explosions of military, industrial and pyrotechnic explosives; explosions of fuel-air mixtures; explosions at a cannon or weapon muzzle; electrical and laser explosions; explosions in the cylinders of internal combustion engines; research explosions, etc.);

  3) accidental explosions (explosions of condensed explosives; explosions of containers under pressure, containers with superheated liquid, containers with substances that have undergone uncontrolled chemical transformations, etc.).

  In the forensic literature, the nature of the explosion is most often considered as a criterion for systematization. So, A.M. Larin et al. Distinguish between explosions: 1) physical (explosion of a steam boiler); 2) electrical (lightning); 3) atomic (explosion of a nuclear charge); 4) chemical (explosions of high explosives).

  K.V. Vishnevetsky, A.I. Gaeva, A.V. Gusev, V.N. Mikhailoshin propose the following classification of the explosion:

  ■ depending on the type of explosive: 1) explosion of gases and vapors of liquids mixed with air (for example, propane, methane, oil products, etc.), as well as flammable dust of some materials suspended in the air (for example, coal, flour, tobacco, wood, plastic); 2) explosions of solid explosives;

  ■ depending on the method of propagation of explosive energy: 1) volumetric (explosion, in which damage is inflicted by a shock wave arising from the explosion of a cloud); 2) directional (the environment moves mainly in a given direction and at a calculated distance (cumulative explosion).

  M.A. Mikhailov rightly recognizes the most universal and laconic classification of explosions proposed by Yu.M. Dildin, V.V. Martynov, A. Yu. Semenov, A.A. Shmyrev, on explosions of physical and chemical nature.

  Physical explosions (physical transformations of the system) can occur with a rapid transition of a substance into a vapor state when heated from the outside, a powerful spark discharge, mixing two substances in a liquid state with a large temperature difference (for example, when water enters molten metal).

  Examples of deliberate unlawful use of a physical explosion are placing a compressed gas cylinder in the furnace of a furnace, making an improvised explosive device.

  For criminal purposes, chemical explosions are more often carried out, in which the energy of explosives is converted into the energy of compressed gases as a result of a chemical reaction. Persons conducting a preliminary investigation into an explosion, in most cases, have to deal with the consequences of chemical explosions, characterized by the following factors:

  1) exothermicity (the release of heat, due to which the gaseous products are heated to a high temperature and their subsequent expansion; the greater the heat and the rate of propagation of the reaction, the greater the destructive effect of the explosion);

  2) the high speed of propagation of the explosive reaction (in the form of explosive combustion or detonation; determined based on minimum quantity the time required for the reaction);

  3) the release of a large amount of gaseous products of a chemical reaction (gives an explosion a destructive force by a shock wave arising from a pressure drop).

  The process of the reaction of a chemical explosion consists of three stages. It:

  1) initiation - the excitation of the explosion process caused by an external impulse (friction, heating, impact, etc.);

  2) detonation - the passage of the reaction of transformation of an explosive inside the mass of the charge into gas at a speed exceeding the speed of sound;

  3) the formation and propagation of a shock wave - carried out as a result of a sharp expansion gas mixture, which leads to a sharp jump in pressure in the external environment, as a result of which the air around the explosive charge is displaced. The overpressure phase lasts for a fraction of a second, gradually decreasing to the value of the ambient pressure; in this case, the displaced compressed air begins to move in the opposite direction, seeking to fill the vacuum formed in the epicenter of the explosion, which leads to additional destruction of objects and the movement of individual objects.

  Explosion damaging factors. A chemical explosion is accompanied by the formation of a large number of products heated to high temperatures and compressed to high pressures, which, expanding, form a shock wave that has a strong dynamic effect on the environment and objects of material furnishings. The damaging effect of the explosion is to cause damage to objects of material environment and people. These manifestations in the external environment of a number of signs indicating the effects produced by the explosion are called explosion factors. The main factors of a chemical explosion are:

  1) thermal (incendiary) action, expressed in the occurrence of foci of ignition of objects of material situation, causing burns on open areas of the surface of the body of a person who was at a distance of up to 7 radii of the charge of explosives; the main signs of the thermal action of the explosion: a) traces of entrenchment; b) traces of melting;

  2) cumulative effect, manifested in the defeat of the target by a concentrated and directed jet of explosion products of the charge and lining materials, which leads to a significant increase in the penetration depth of the obstacle;

  3) fragmentation action that occurs during the explosion of charges placed in a strong metal shell, when, as a result of the blasting action, the shell is crushed and the resulting fragments (primary) are thrown at a high speed; signs of fragmentation: a) craters and tracks (scratches) on objects; b) through holes and "blind" from the introduction of fragments into the materials of obstacles; c) characteristic (multiple and different localization) damage to the human body;

  4) impact action, manifested in the defeat of the target due to the kinetic energy of a moving projectile, the material traces of which are traces characteristic of the fragmentation, high-explosive, high-explosive fragmentation action of the explosion;

  5) high-explosive action, characterized by the defeat (destruction) of the target by the explosion products of the explosive charge and the resulting shock wave, which manifests itself in a much larger space from the center of the explosion and produces irreversible changes in the environment; its signs: a) the defeat of people; b) moving objects of the environment; c) destruction, damage and deformation of individual elements and objects in the area of ​​the explosion; d) high-speed dispersal of elements of objects destroyed by the explosion, followed by impact interaction with other objects of the environment;

  6) blasting (crushing) effect, manifested in the ability of explosives to destroy (crush) the medium in direct contact with the charge during an explosion; the main signs of the blasting action of the explosion: a) a funnel in the soil and other materials; b) local deformation of the zone of plastic flow of the metal; c) destruction in the form of dents, funnels, chips on high-strength elements of metal, reinforced concrete, bricks, etc .; d) local areas of complete destruction on low-strength objects made of wood, glass, polymeric materials, etc .; e) the formation of grievous bodily harm on the human body;

  7) special-purpose action (lighting, signaling, jamming, etc.).

  The damaging effect of an explosion on a body is shown in Figure 3.3.

  Figure 3.3 - Damage to open areas of the body during an explosion.

  Thus, in an explosion, detonation products, explosives, a shock wave of the environment, fragments of an explosive device, special damaging elements and substances, and secondary effects have a damaging effect. Their combination is denoted by the damaging factors of the explosion, given in Scheme 3.4.

  

  Scheme 3.4 - Classification of the damaging factors of the explosion.

  The traumatic effect of the damaging factors of the explosion is ambiguous. Explosion damage is extremely diverse: from single shrapnel wounds to complete destruction of the body of an adult. The traumatic effect of damaging factors is shown in Diagram 3.5.

  Since explosive devices differ in their constructive and power variety, the distances from the center of the explosion are considered, based on several conditional qualitative distances:

  a) direct contact (close, "contact", "zero" distance), when the victim's body is in the zone of combined action of explosive gases;

  b) a relatively close distance (within the range of the shock wave, but outside the range of explosive gases);

  c) not a short distance, when only shell fragments or components of an explosive device act.
  

  Comparative characteristics of explosive damage at all distances are shown in Table 3.1.

  

  Scheme 3.5 - The nature of the traumatic effect of the damaging factors of the explosion.

  Table 3.1 - The nature of damage depending on the distance of the explosion (according to V.L. Popov, 2002) 62

  Blast distance	Damaging	The nature of the damage
  1. Contact of the projectile with the body or a very close distance (within the range of explosive gases)	- a wave of explosive gases Pieces of explosives Shock wave Shell fragments, fuse, secondary shells	Combined lesions: Destruction and detachment of body parts Scorching -Smoking Closed bone injuries and internal organs Shrapnel wounds
  2. Relatively close (within the range of the shock wave)	- shock wave Throwing and dropping the body Shell shards Secondary projectiles	- closed and open fractures and injuries of internal organs Shrapnel wounds
  3. Close in the presence of destructive barriers	- destruction of the barrier Shards	- closed and open injuries of bones and internal organs Shrapnel wounds
  4. Not close	- single fragments	- one or more shrapnel wounds

  62 Popov, V.L. Forensic medicine: textbook / V.L. Popov. - SPb .: Peter, 2002 .-- S. 214-215.

  Thus, the general characteristics of explosives, explosive devices, explosions and their traces allow us to determine the range of objects under study, directions of their research, to reasonably build investigative and expert versions regarding the circumstances associated with the specifics of the device and the operation of explosives and explosive devices, as well as possible sources. the origin of the objects of study on the fact of the explosion.

  Explosive injury is the only type of injury, as a result of which, simultaneously, within a very short period of time, mechanical, thermal and chemical factors act on the human body. It is this combination that determines its originality, makes it possible to differentiate different kinds explosions based on the results of forensic medical examination.

  More on the topic General characteristics of explosions and their damaging factors:

  1. Characteristics of bodily injuries and their description during the initial examination of the corpse at the place of its discovery
  2. Inspection of gunshot injuries on a corpse, visually detected during inspection of the scene
  3. General characteristics of explosions and their damaging factors

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