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Most of the elements of the economic complex of the country are classified as fire and explosion hazardous OE. Sources of fires and explosions are: containers with flammable, combustible or poisonous substances; warehouses of explosive and highly fuming compounds; explosive technological installations, communications, the destruction of which leads to fires, explosions and gas contamination of the territory; railways, etc.

The predicted consequences are:

• gas leaks and the spread of toxic fumes;
• fires and explosions in wells, cisterns and other containers;
• violations of technological processes, especially those associated with harmful substances or hazardous processing methods;
• impact of ball lightning, static electricity;
• explosions of flammable liquids vapors;
• heating and evaporation of liquids from containers and pallets;
• dispersion of combustion products in the interior;
• toxic effects of combustion products and other reactions;
• thermal radiation during fires;
• distribution of flame and fire flow in buildings, depending on the location of the walls and the internal layout.

When assessing the layout of the MA territory, the influence of the density and type of development on the possibility of the occurrence and spread of fires and on the formation of blockages is determined.

Particular attention is paid to areas where secondary damaging factors may occur: first of all, the possibility of air-blast formation during the explosion of pressure vessels is taken into account. In this case, the total effect of the impact of dynamic head and static overpressure is considered.

Most fires are associated with the burning of solid materials, although the initial stage of a fire is usually associated with the combustion of liquid and gaseous combustible substances, which are abundant in modern production. The formation of a flame is associated with the gaseous state of matter. Even when burning solid or liquid substances, they pass into a gaseous state. This transition process for liquid substances consists in simple boiling with evaporation near the surface, and for solid substances, with the formation of products of a sufficiently low molecular weight that can volatilize from the surface of a solid material and enter the flame region (pyrolysis phenomenon).

Due to the influence of the so-called "light pulse" there is a fire or a steady combustion of specific materials. A possible fire situation is assessed in a comprehensive manner, taking into account the impact of the shock wave and the magnitude of the "light pulse", the fire resistance of structures, the category of their fire and explosion hazard.

In accordance with the requirements of building codes and regulations (SNiP 2.09.01-85), all building materials and structures are divided into groups according to flammability:

• fireproof, which, under the influence of fire or high temperature, do not ignite, do not smolder or char (stone, reinforced concrete, metal);
• hard-to-combustible materials that are difficult to ignite under the action of fire and high temperature; smolder or char only in the presence of a source of fire, and in its absence, combustion or smoldering stops (clay-straw mixtures, asphalt concrete);
• combustible materials that ignite or smolder under the influence of fire or high temperature (wood, cardboard).

Fire resistance is understood as the resistance of a structure to fire, which is characterized by a combustibility group and a fire resistance limit (SNiP 2.01.02-85). The most dangerous are structures made of combustible materials. But even if the structure is made of non-combustible materials, it can withstand the effects of fire for a certain time. The fire resistance limit of a structure is determined by the time (in hours) during which through cracks do not appear, the structure itself does not lose its bearing capacity, does not collapse and does not heat up to a temperature above 200 ° C on the side opposite from the fire.

According to the degree of fire resistance buildings are:

• I and II degrees of fire resistance - the main structures of such structures are made of fireproof materials;
• III degree of fire resistance - buildings with stone walls and wooden plastered ceilings;
• IV degree of fire resistance - wooden plastered houses;
• V degree of fire resistance - wooden buildings.

According to accepted standards, all objects - in accordance with the nature of the technological process for fire and explosion hazard - divided into categories (GOST 12.1.004-91, ONTP 24-96):

• category A (explosive and flammable) - combustible gases, flammable liquids with a flash point below 28 ° C in an amount sufficient to form fuel assemblies and air-blasts with an overpressure of more than 5 kPa;
• category B (explosive and flammable) - combustible dusts, fibers, flammable liquids with a flash point above 28 ° C in an amount sufficient to form explosive hot water and air-blasts with an overpressure of more than 5 kPa;
• categories B1 ... B4 (fire hazardous) - combustible and slow-burning materials that can only burn when interacting with water, oxygen in the air or other substances;
• category G - non-combustible materials in a hot state, during the processing of which light energy, sparks or flames are released;
• category D - enterprises for cold processing and storage of metal and other non-combustible materials.

Combustion - a chemical oxidation reaction with the release of a large amount of heat and light. Combustion requires the presence of a combustible substance, an oxidizing agent (oxygen, chlorine, fluorine, nitrogen oxides, bromine) and an ignition source (impulse).

Combustion can be homogeneous (source substances have the same state of aggregation: combustion of gases) or heterogeneous (source substances have different states of aggregation: solid or liquid combustible substances). Depending on the speed of flame propagation, combustion is divided into deflagration (several meters per second), explosive (tens of meters per second) or detonation (thousands of meters per second). Fires are characterized by deflagration combustion.

There are three types of self-acceleration of the chemical reaction of combustion: thermal, chain and combined. Real combustion processes follow a combined self-acceleration mechanism (chain-thermal).

The combustion process has several stages:

• flash - rapid combustion of a combustible mixture without the formation of compressed gases;
• ignition - the occurrence of combustion under the influence of a source of ignition;
• ignition - ignition with the appearance of a flame;
• spontaneous combustion - the phenomenon of a sharp increase in the rate of an exothermic reaction, leading to combustion in the absence of a source of ignition;
• self-ignition - spontaneous combustion with the appearance of a flame;
• explosion - an extremely rapid chemical transformation, accompanied by the release of energy and the formation of compressed gases capable of producing mechanical work.

Depending on the source of ignition (impulse), spontaneous combustion processes can be divided into thermal, microbiological and chemical.

The main indicators of fire and explosion hazard:

Flash point - the lowest temperature of a combustible substance at which vapors (gases) are formed above its surface that can flare up from an ignition source. But the rate of their formation is still insufficient for subsequent combustion. Flash point of vapors: carbon disulphide -45°С, gasoline -ZGS, oil -2GS, acetone -20°С, dichloroethane +8°С, turpentine +32°С, alcohol +35°С, kerosene +45°С, glycerin + 17°C. Liquids with a flash point below + 45 ° C are called flammable, and above - combustible.

The auto-ignition temperature is the lowest temperature at which there is a sharp increase in the rate of an exothermic reaction in the absence of an ignition source, which ends in stable combustion.

Ignition temperature. At this temperature, the combustible substance releases combustible vapors (gases) at a rate sufficient (after ignition of the substance) for stable combustion. The temperature limits of ignition are the temperatures at which saturated vapors of a substance form concentrations in a given oxidizing environment equal to the lower or upper limit of ignition, respectively.

Flashpoints, self-ignition and ignition temperatures of combustible substances are determined experimentally or by calculation (GOST 12.1.044-89); the lower and upper concentration limits - experimentally or guided by the "Calculation of the main indicators of fire and explosion hazard of substances and materials."

The fire and explosion hazard of OE is determined by the fire hazard parameters and the amount of materials used in technological processes, the design features and operating modes of the equipment, the presence of ignition sources and the conditions for the rapid spread of fire. The spread of fires and their transformation into continuous fires depends on the building density, destruction and other factors.

The fire hazard of substances is characterized by linear (cm / s) or mass (g / s) burning rates, as well as the limiting oxygen content. During the combustion of solid substances, the rate of entry of volatile components is directly related to the intensity of heat transfer in the zone of contact between the flame and the solid surface. Mass Burn Rate (g/m²*c) depends on the heat flux from the surface, the physicochemical properties of solid fuel and is expressed by the formula:

where V is the mass burn-out rate of the material, g/m²*With; - heat flow from the combustion zone to solid fuel, kW/m²; Q- heat loss of solid fuel to the environment, kW/m²; is the amount of heat for the formation of volatile substances, kJ/g.

The heat flow coming from the combustion zone to the solid fuel depends on the energy released in the combustion process and the heat exchange conditions at the combustion boundary and in the contact zone of the solid fuel and the environment.

The fire situation and the dynamics of its development depend on:

• ignition impulse;
• fire hazard OE;
• fire resistance of the structure and its elements;
• building density in the fire area;
• weather conditions, especially the strength and direction of the wind.

At OE, many technological processes take place at temperatures that are significantly higher than the ambient temperature. Heated surfaces radiate streams of radiant energy that can cause negative consequences. The duration of thermal exposure of a person without tangible consequences depends on the amount of heat release (J / s) of his body. In order for physiological processes in a person to proceed normally, the heat released in it must be completely removed to the environment. Excess external heat radiation can lead to overheating of the body, loss of consciousness, burns or death. The temperature of the skin reflects the body's reaction to the influence of the thermal factor. If the heat transfer is insufficient, then the temperature of the internal organs rises (characterized by the concept of "hot"). Thermal energy, turning on a hot surface (seat of fire) into radiant energy, is transferred - like light - to another body that has a lower temperature. Here, radiant energy is absorbed and again converted into heat.

The limiting temperature of inhaled air, at which a person is still able to breathe for several minutes without special protective equipment, is 110 ° C. A person's tolerance for high temperature depends on humidity and air velocity: the greater the humidity, the less sweat evaporates per unit time, that is, the body overheats faster. At an ambient temperature above 30°C, sweat does not evaporate, but flows down in drops, which sharply reduces heat transfer.

Effect of high temperature on wood:

• 110°С - moisture is removed (wood is drying);
• 150°C - the release of volatile products of thermal decomposition begins, its color changes (it darkens);
• 200°C - the same as at 150°C, but the wood becomes brown;
• 300°C - significant release of gaseous products capable of self-ignition, wood begins to smolder;
• 400°C - the same as at 300°C, but self-ignition of the wood occurs.

With self-burning under fire conditions, the linear rate of wood burnout for thin objects (up to 20 mm) is about 1 mm / min, for thicker ones - 0,63 mm / min.

Heavy concrete at a temperature of about 300°C takes on a pink hue, at 600°C - reddish with the appearance of microcracks, and at a temperature of 1000°C the color turns into pale gray, the particles burn out. Due to the difference in the expansion coefficients of its components, the width of cracks in concrete reaches 1 mm. Explosive destruction of concrete during a fire is observed in prestressed and thin-walled elements, especially with high moisture content, at a temperature of 700...900°C.

Steel structures at a temperature of 650°C lose their bearing capacity, deform, change their physical and chemical properties, and melt at a temperature of 1400...1500°C.

If the temperature of the heated surface is below 500°C, then thermal (infrared) radiation predominates, and at temperatures above 500°C, infrared radiation of visible and ultraviolet light is present. Infrared rays have a mainly thermal effect on a person, which leads to a decrease in the oxygen saturation of the blood, a decrease in venous pressure, and disruption of the cardiovascular and nervous systems. The total amount of heat absorbed by the body depends on the area and properties of the irradiated surface, the temperature of the radiation source, and the distance to it.

To characterize thermal radiation, the concept of "intensity of thermal exposure" is used. This is the power of the radiant flux per unit of the irradiated surface. Irradiation with intensity up to 350 W/m² does not cause discomfort, up to 1050 W / m² - after a few minutes, it feels like a burning sensation at the site of irradiation, and the temperature of the skin in this area may rise by 10 ° C. When irradiated with intensity up to 1400 W/m² the pulse rate increases, and up to 3500 W / m² - burns are already possible. Pain sensations appear at a skin temperature of about 45 ° C.

The main parameter characterizing the damaging effect of light radiation is light pulse "AND". This is the amount of light energy falling for the entire time of the fiery glow by 1 m² illuminated surface perpendicular to the direction of radiation. Light pulse is measured in J/m² or kcal/cm². Light radiation causes burns to open areas of the body, damage to the eyes (temporary or complete), fires.

Depending on the magnitude of the light pulse, there are burns of varying degrees.

1st degree burns are caused by a light pulse equal to 2...4 kcal/cm² (84...168 kJ/m²). In this case, redness of the skin is observed. Treatment is usually not required.

2st degree burns are caused by a light pulse equal to 5...8 kcal/cm² (210...336 kJ/m²). Blisters form on the skin filled with a clear white liquid. If the area of ​​the burn is significant, then the person may lose his ability to work and need treatment. Recovery can occur even with a burn area of ​​up to 60% of the skin surface.

Burns of the 3rd degree are observed when the magnitude of the light pulse is 9 ... 15 kcal / cm². (368...630 kJ/m²). Then there is necrosis of the skin with damage to the germ layer and the formation of ulcers. Long-term treatment is required.

4th degree burns occur with a light pulse over 15 kcal/cm² (630 kJ/m²). There is a necrosis of deeper layers of tissue (subcutaneous tissue, muscles, tendons, bones).

When a large area of ​​the body is affected, death occurs. The degree of burns of body parts depends on the nature of the clothing: its color, density, thickness and density of fit to the body.

In the atmosphere, radiant energy is attenuated due to the absorption or scattering of light by particles of smoke, dust, moisture drops, so the degree of transparency of the atmosphere is taken into account. Light falling on an object is partially absorbed or reflected. Part of the radiation passes through transparent objects: window glass transmits up to 90% of the energy of light radiation, which can cause a fire inside the room due to the conversion of light energy into heat. Thus, in the cities and on the MA there are combustion centers. The rate of spread of fires in the city depends on the nature of buildings and wind speed. With a wind speed of about 6 m / s in a city with brick houses, a fire spreads at a speed of about 100 m / h; in combustible buildings - up to 300 m / h, and in rural areas over 900 m / h. In this case, it is necessary to take into account the presence of combustible materials around buildings (roofing, paper, straw, peat, reeds, wood, oil products), their thickness, moisture content.

Fires are the most dangerous and widespread disaster. They can flare up in settlements, forests, OE, peat extraction, gas and oil production areas, energy communications, transport, but most often they arise due to the careless handling of fire by people.

Of paramount importance is the ability to competently implement when extinguishing a fire fire extinguishing principles:

• isolation of the combustion source from oxidants, reduction of their concentration by dilution with non-combustible gases to a value at which the combustion process cannot proceed;
• cooling of the combustion center;
• inhibition (deceleration) of the reaction rate in the flame;
• mechanical breakdown of the flame by the impact of an explosion, a jet of gas or water;
• creating conditions for a fire barrier: for example, you can make the flame spread through narrow channels.

Water is the main extinguishing agent. It is cheap, cools the place of combustion, and the steam formed during the evaporation of water dilutes the burning medium. Water also mechanically affects the burning substance, that is, breaks the flame. The volume of steam generated is 1700 times the volume of water used. It is not advisable to extinguish flammable liquids with water, as this can significantly increase the area of ​​the fire and cause contamination of water bodies. It is dangerous to use water when extinguishing energized equipment - to avoid electric shock.

To extinguish fires, water fire extinguishing installations, fire trucks or water guns are used. Water is supplied to them from water pipes through fire hydrants or taps, while constant and sufficient water pressure in the water supply network must be ensured. When extinguishing fires inside buildings, internal fire hydrants are used, to which fire hoses are connected. Sprinkler and deluge installations are used for automatic water fire extinguishing.

sprinkler installations is a branched, water-filled pipe system that is equipped with sprinkler heads whose outlets are sealed with a fusible compound (designed for a temperature of 72, 93, 141 or! 182 ° C). In the event of a fire, these holes open up on their own and irrigate the protected area with water.

Deluge installations - this is a system of pipelines inside the building, on which special heads (drenchers) are installed with a diameter of outlet holes of 8, 10 and 13 mm of a paddle or rosette type, capable of irrigating up to 12 m² gender. The deluge sprayer with screw slots makes it possible to obtain sprayed water with a finer dispersion, and at a height of 5,2 m it can irrigate up to 210 m² sex.

Used to extinguish solid and liquid substances foam. Their extinguishing properties are determined by the multiplicity (the ratio of the foam volume to the volume of its liquid phase), resistance, dispersion and viscosity. Depending on the conditions and method of obtaining foam can be:

• chemical is a concentrated emulsion of carbon monoxide in an aqueous solution of mineral salts;
• air-mechanical (multiplicity 5 ... 10), which is obtained from 5% aqueous solutions of foaming agents.

When extinguishing fires with gases, carbon dioxide, nitrogen, argon, flue or exhaust gases, steam are used. Their extinguishing effect is based on the dilution of air, that is, on the reduction of oxygen concentration. At zero temperature and pressure of 36 atm. 1 liter of liquid carbon dioxide produces 500 liters of carbon dioxide. When extinguishing fires, carbon dioxide fire extinguishers (OU-5, OU-8, UP-2m) are used if oxygen, alkali and alkaline earth metals are included in the molecules of the burning substance. The gas in the fire extinguisher is under pressure up to 60 atm. To extinguish electrical installations, it is necessary to use powder fire extinguishers (OP-1, OP-10), the charge of which consists of sodium bicarbonate, talc and iron and aluminum stearators.

Steam extinguishing is used to eliminate small fires in open areas, in closed apparatus and with limited air exchange. The concentration of water vapor in the air should be about 35% by volume.

Fire-extinguishing compositions-inhibitors based on saturated hydrocarbons, in which one or more atoms are replaced by halogen atoms, have found wide application in fire fighting. They effectively inhibit reactions in the flame, penetrating into it in the form of droplets. Low freezing point allows the use of these compounds at sub-zero temperatures. Powder compositions based on inorganic salts of alkali metals are also used.

Explosives - these are chemical compounds or mixtures capable of rapid chemical transformation with the formation of highly heated gases, which, due to expansion and enormous pressure, are capable of producing mechanical work.

Explosives can be divided into groups:

• initiating, which have great sensitivity to external influences (impact, prick, heat) and are used to undermine the main explosive charge;
• blasting - less sensitive to external influences. They have increased power, are undermined as a result of detonation;
• propellant - this is gunpowder, the main form of chemical transformation of which is combustion. Can be used for demolition work.

Characteristics of explosives:

• sensitivity to external influences (shock, light, prick);
• heat of transformation during explosion;
• detonation speed;
• brisance (power), which depends on the speed of detonation;
• explosiveness (operability).

Often the cause of fires and explosions is the formation of fuel-, steam- or dust-air mixtures. Such explosions occur as a result of the destruction of gas containers, communications, units, pipelines or technological lines. Enterprises with a high fire and explosion hazard of categories A and B can be especially dangerous potential sources of explosions [46]. When units or communications are destroyed, the outflow of gases or liquefied hydrocarbon products is not excluded, which leads to the formation of an explosive or flammable mixture. The explosion of such a mixture occurs at a certain concentration of gas in the air. For example, if in 1 m³ air contains 21 liters of propane, then an explosion is possible, if 95 liters - ignition.

A significant number of accidents are associated with discharges of static electricity. One of the reasons for this is the electrification of liquids and bulk substances during their transportation through pipelines, when the electric field strength can reach a value of 30 kV/cm. It must be taken into account that the potential difference between the human body and the metal parts of the equipment can reach tens of kilovolts.

Strong explosions of a dust-air mixture (DAM) are usually preceded by local pops inside the equipment, in which the dust passes into a suspended state with the formation of an explosive concentration. Therefore, in closed vehicles, it is necessary to create an inert environment, to ensure sufficient strength of the apparatus and the availability of emergency protection. Up to 90% of accidents are associated with the explosion of vapor-gas mixtures (VGM), while up to 60% of such explosions occur in closed equipment and pipelines.

Acetylene under certain conditions is capable of explosive decomposition in the absence of oxidizing agents. The energy released in this case (8,7 MJ/kg) is sufficient to heat the reaction products to a temperature of 2800°C. During the explosion, the flame propagation speed reaches several meters per second. But for acetylene, a variant is possible when part of the gases burns out, and the rest is compressed and detonated. In this case, the pressure can increase hundreds of times. The autoignition temperature of acetylene depends on its pressure (Table 3.1).

Table 3.1. Autoignition temperature of acetylene

The most dangerous in operation are high-pressure apparatuses and pipelines of acetylene (0,15-2,5 MPa), since in case of accidental overheating, an explosion can occur, turning into detonation with a long pipeline length. The maximum flame propagation speed during the combustion of an acetylene-air mixture containing acetylene 9,4% (vol) is 1,69 m/s. A mixture of acetylene with chlorine and other oxidizing agents can explode under the influence of a light source. Therefore, it is forbidden to make extensions for the production of chlorine, liquefaction and air separation to buildings where acetylene is used.

Often, when iron drums with calcium carbide are opened manually, sparks occur, which leads to explosions. In addition, one must always take into account the possibility of the presence of moisture in the drum.

During the explosion of fuel assemblies, a lesion center is formed with a shock wave and light radiation ("fireball"). Three spherical zones can be distinguished in the FA explosion site (Fig. 3.1).

Rice. 3.1. Zones in the lesion focus during the explosion of fuel assemblies. R₁, R₂, R₃, are the radii of the outer boundaries of the corresponding zones

Rice. 3.2. Dependence of the radius of the outer boundary of the overpressure zone on the amount of explosive gas-air mixture

Zone I - detonation wave zone. Located within the explosion cloud. The zone radius is determined by the formula:

where R₁ - radius of zone I, m; - mass of liquefied gas, m.

Within zone I, the excess pressure can be considered constant and equal to 1700 kPa.

Zone II - the area of ​​action of the explosion products, which covers the entire area of ​​the explosion products of the fuel assembly as a result of its detonation. The radius of zone II is 1,7 times the radius of zone I, i.e. R₂= 1,7R₁, and the excess pressure decreases to 300 kPa as it is removed.

Zone III - air-blast coverage zone. An air-blast front is formed here. The value of excess pressure is determined according to the graph, fig. 3.2.

shock wave (UVV) - the most powerful damaging factor in an explosion. It is formed due to the colossal energy released in the center of the explosion, which leads to the emergence of enormous temperature and pressure here. The incandescent products of the explosion, during rapid expansion, produce a sharp blow to the surrounding layers of air, compress them to a significant pressure and density, heating to a high temperature. Such compression occurs in all directions from the center of the explosion, forming an air-blast front. Near the center of the explosion, air-blast propagation velocity is several times higher than the speed of sound. But as it moves, the speed of its propagation decreases. The pressure in the front also decreases. In the layer of compressed air, called the air-blast compression phase (Fig. 3.3), the greatest destructive effects are observed. As the air-blast front moves, the pressure drops and at some point reaches atmospheric pressure, but will continue to decrease due to a decrease in temperature. In this case, the air will begin to move in the opposite direction, that is, towards the center of the explosion. This zone of low pressure is called the zone of rarefaction.

Air-blast parameters

1. Overpressure (see fig. 3.2). It is determined by the difference between the actual air pressure at a given point and atmospheric pressure (P_huts = P_ф - R_atm,). Measured in kg/cm² or Pascals (1 kg/cm² = 100 kPa). When the air-blast front passes, excess pressure affects a person from all sides.

2. Velocity air pressure (dynamic load). It has a throwing action. Measured in kg/cm² or Pascals. The combined effect of these two air-blast parameters leads to the destruction of objects and human casualties.

3. Air-blast propagation time (T_р, With).

4. The duration of the compression phase on the object (T_р, With). Excessive pressure in air-blast front (Р_huts, kPa) can be determined by the formula

where is the TNT equivalent of explosives, kg; R is the distance from the explosion center, m.

Velocity air pressure depends on the air velocity and density behind the air-blast front and is equal to:

where V is the speed of air particles behind the air-blast front, m/s; ρ - air density behind air-blast front, kg/m³.

Rice. 3.3. Phases and air-blast front

The impact of air-blast on a person can be indirect or direct. In case of indirect damage, air-blast, destroying buildings, involves in the movement a huge amount of solid particles, glass fragments and other objects weighing up to 1,5 g at a speed of up to 35 m/s. So, with an overpressure of about 60 kPa, the density of such hazardous particles reaches 4500 pieces/m². The largest number of victims are victims of the indirect impact of air-blast.

With direct damage, air-blast causes extremely severe, severe, moderate or light injuries to people.

Extremely severe injuries (usually incompatible with life) occur when exposed to excess pressure of more than 100 kPa.

Severe injuries (severe contusion of the body, damage to internal organs, loss of limbs, severe bleeding from the nose and ears) occur with an excess pressure of 100 ... 60 kPa.

Moderate injuries (concussions, damage to the hearing organs, bleeding from the nose and ears, dislocations) occur at an overpressure of 60...40 kPa.

Minor injuries (bruises, dislocations, temporary hearing loss, general contusion) are observed at an excess pressure of 40 ... 20 kPa.

The same air-blast parameters lead to destruction, the nature of which depends on the load created by the air-blast and the reaction of the object to the actions of this load. Damage to objects caused by air-blast can be characterized by the degree of their destruction.

A zone of complete destruction. It is impossible to restore destroyed objects. Mass destruction of all living things. It occupies up to 13% of the entire area of ​​the lesion. Here, buildings are completely destroyed, up to 50% of anti-radiation shelters (PRS), up to 5% of shelters and underground utilities. The streets are full of rubble. Continuous fires do not occur due to severe destruction, flame failure by a shock wave, scattering of ignited debris and filling them with soil. This zone is characterized by overpressure over 50 kPa.

Zone of severe destruction covers an area of ​​up to 10% of the lesion. Buildings are badly damaged, shelters and utilities are preserved, 75% of shelters retain their protective properties. There are local blockages, areas of continuous fires. The zone is characterized by an overpressure of 0,3...0,5 kg/cm² (30...50 kPa).

Medium damage zone observed at an excess pressure of 0,2 ... 0,3 kg / cm² (20...30 kPa) and covers an area of ​​up to 15% of the lesion. Buildings receive moderate damage, while defenses and utility networks are preserved. There may be local blockages, areas of continuous fires, massive sanitary losses among the unprotected population.

Zone of weak damage characterized by overpressure 0,1...0,2 kg/cm² (10...20 kPa) and occupies up to 62% of the area of ​​the lesion. Buildings receive minor damage (destruction of partitions, doors, windows), there may be individual blockages, fires, and people may be injured.

Authors: Grinin A.S., Novikov V.N.

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