The study of combustion processes of flammable mixtures by Russian and foreign scientists has made it possible to theoretically substantiate many phenomena accompanying the combustion process, including the speed of flame propagation. Studying the speed of flame propagation in gas mixtures makes it possible to determine safe speeds of gas-air flows in ventilation, recovery, aspiration pipelines and in pipelines of other installations through which gas and dust-air mixtures are transported.
In 1889, Russian scientist V.A. Michelson considered two limiting cases of flame propagation during normal or slow combustion and during detonation.
The theory of normal flame and detonation propagation was further developed in the works of N.N. Semenova, K.I. Shchelkina, D.A. Frank-Kamenetsky, L.N. Khitrina, A.S. Sokolika, V.I. Skobelkin and other scientists, as well as foreign scientists B. Lewis, G. Elbe and others. As a result, the theory of ignition of explosive mixtures was created. However, attempts to interpret the phenomena of flame propagation as diffusion of active centers or to explain the limits of flame propagation by circuit breakage conditions are not convincing enough.
In 1942, Soviet scientist Ya.B. Zeldovich formulated the principles of the theory of combustion and detonation of gases. The theory of combustion provides an answer to the main questions: will a mixture of a given composition be flammable, what will be the burning rate of an explosive mixture, what features and forms of flame should be expected. The theory states that the explosion of a gas or steam-air mixture is not an instantaneous phenomenon. When an ignition source is introduced into the combustible mixture, an oxidation reaction of the fuel with the oxidizer begins in the area of effect of the ignition source. The rate of the oxidation reaction in some elementary volume of this zone reaches a maximum - combustion occurs. Combustion at the boundary of an elementary volume with the medium is called a flame front. The flame front has the shape of a sphere. The thickness of the flame front, according to calculations by Ya.B. Zeldovich, equal to 1 – 100 microns. Although the thickness of the combustion zone is small, it is sufficient for the combustion reaction to occur. The temperature of the flame front due to the heat of the combustion reaction is 1000 - 3000 0 C and depends on the composition of the combustible mixture. Near the flame front, the temperature of the mixture also increases, which is due to heat transfer by conduction, diffusion of heated molecules and radiation. On the outer surface of the flame front, this temperature is equal to the self-ignition temperature of the combustible mixture. The change in temperature of the mixture along the pipe axis at moments of time is graphically shown in Fig. 4.1. Gas layer CC 1, in which the temperature of the mixture increases, represents the flame front. As the temperature increases, the flame front expands (up to KK 2) towards the end walls of the pipe A And M, displacing the unburnt mixture towards the wall at a certain speed M, and the burned gas towards the wall A. After ignition of the combustible mixture, the spherical shape of the flame is very quickly distorted and increasingly stretched towards the mixture that has not yet been ignited. Extending the flame front and rapid increase its surface is accompanied by an increase in movement speed
the central part of the flame. This acceleration continues until the flame touches the pipe walls or, in any case, approaches close to the pipe wall. At this moment, the size of the flame decreases sharply, and only a small part of the flame remains, covering the entire cross-section of the pipe. The extension of the flame front and its intense acceleration immediately after ignition by a spark, when the flame has not yet reached the walls of the pipe, are caused by an increase in the volume of combustion products. Thus, at the initial stage of the process of formation of the flame front, regardless of the degree of flammability of the gas mixture, acceleration and subsequent braking of the flame occurs, and this braking will be greater, the higher the flame speed.
Rice. 4.1. Temperature change in front and behind the flame front: 1 – zone
combustion products; 2 – flame front; 3 – self-ignition zone;
4 – preheating zone; 5 – initial mixture
The development of subsequent stages of combustion is influenced by the length of the pipe. Elongation of the pipe leads to the appearance of vibrations and the formation of a cellular structure of the flame, shock and detonation waves.
Let us consider the width of the heating zone in front of the flame front. In this zone chemical reaction does not leak and does not generate heat. Heating zone width l(in cm) can be determined from the dependence:
Where A– thermal diffusivity coefficient; v– flame propagation speed.
For a methane-air mixture, the width of the heating zone is 0.0006 m; for a hydrogen-air mixture it is much smaller (3 microns). Subsequent combustion occurs in a mixture whose state has already changed as a result of thermal conductivity and diffusion of components from adjacent layers. The addition of reaction products does not have any specific catalytic effect on the speed of flame movement.
Let us now consider the speed of movement of the flame front through the gas mixture. Linear speed of movement v(in m/s) can be determined by the formula
where is the mass combustion rate, g/(cm×m 2), p is the density of the initial combustible mixture, kg/m 3.
Linear speed the movement of the flame front is not constant, it changes depending on the composition of the mixture and the admixture of inert (non-flammable) gases, the temperature of the mixture, the diameter of the pipes, etc. The maximum speed of flame propagation is observed not at the stoichiometric concentration of the mixture, but in a mixture with an excess of fuel. When inert gases are introduced into a flammable mixture, the speed of flame propagation decreases. This is explained by a decrease in the combustion temperature of the mixture, since part of the heat is spent on heating inert impurities not participating in the reaction. The speed of flame propagation is affected by heat capacity inert gas. The greater the heat capacity of an inert gas, the more it reduces the combustion temperature and the more it reduces the speed of flame propagation. Thus, in a mixture of methane with air diluted with carbon dioxide, the flame propagation speed is approximately three times less than in a mixture diluted with argon.
When the mixture is preheated, the speed of flame propagation increases. It has been established that the speed of flame propagation is proportional to the square of the initial temperature of the mixture.
As the diameter of the pipes increases, the speed of flame propagation increases unevenly.
When the pipe diameter increases to 0.10 - 0.15 m, the speed increases quite quickly; with a further increase in the diameter of the pipes, it continues to increase, but to a lesser extent. The temperature increases until the diameter reaches a certain limiting diameter, above which the speed does not increase. As the diameter of the pipe decreases, the speed of flame propagation decreases, and at a certain small diameter the flame does not propagate in the pipe. This phenomenon can be explained by an increase in heat loss through the pipe walls.
Therefore, in order to stop the spread of flame in a combustible mixture, it is necessary to lower the temperature of the mixture in one way or another, by cooling the vessel (in our example, a pipe) from the outside or diluting the mixture with cold inert gas.
The normal speed of flame propagation is relatively low (no more than tens of meters per second), but in some conditions the flame in pipes spreads at a tremendous speed (from 2 to 5 km/s), exceeding the speed of sound in a given environment. This phenomenon was called detonation. Distinctive features detonations are as follows:
1) constant burning rate regardless of the pipe diameter;
2) high pressure flame caused by a detonation wave, which can exceed 50 MPa depending on chemical nature combustible mixture and initial pressure; Moreover, due to the high burning rate, the developed pressure does not depend on the shape, capacity and tightness of the vessel (or pipe).
Let us consider the transition of rapid combustion to detonation in a long pipe of constant cross-section when the mixture is ignited at the closed end. Under the pressure of the flame front, compression waves – shock waves – appear in the combustible mixture. In the shock wave, the gas temperature rises to values at which self-ignition of the mixture occurs far ahead of the flame front. This combustion mode is called detonation. As the flame front moves, the movement of the layers adjacent to the wall is slowed down and, accordingly, the movement of the mixture in the center of the pipe is accelerated; distribution
The growth across the cross section becomes uneven. Jets of gas mixtures appear, the speed of which is less than the average speed of the gas mixture during normal combustion, and jets moving faster. Under these conditions, the speed of the flame relative to the mixture increases, the amount of gas burned per unit time increases, and the movement of the flame front is determined by the maximum speed of the gas jet.
As the flame accelerates, the amplitude of the shock wave also increases, and the compression temperature reaches the self-ignition temperature of the mixture.
The increase in the total amount of gas burned per unit time is explained by the fact that in a jet with a variable cross-sectional speed, the flame front bends; as a result of this, its surface increases and the amount of combustion material increases proportionally.
One of the ways to reduce the burning rate of flammable mixtures is the action of inert gases on the flame, but due to their low efficiency Currently, chemical combustion inhibition is used by adding halogenated hydrocarbons to the mixture.
Combustible gas mixtures have two theoretical combustion temperatures - at constant volume and at constant pressure, and the first is always higher than the second.
The method for calculating the calorimetric combustion temperature at constant pressure is discussed in Section 1. Let us consider the method for calculating the theoretical combustion temperature of gas mixtures at constant volume, which corresponds to an explosion in a closed vessel. The basis for calculating the theoretical combustion temperature at constant volume is the same conditions as indicated in subsection. 1.7.
When gas mixtures burn in a closed volume, the combustion products do not perform work; The explosion energy is spent only on heating the explosion products. In this case, the total energy is defined as the sum of the internal energy of the explosive mixture Q ext.en.cm and the heat of combustion of the given substance. The value of Q int.en.cm is equal to the sum of the products of the heat capacities of the components of the explosive mixture at constant volume and the initial temperature of the mixture
Q int.en.cm = s 1 T + s 2 T +… + s n T,
where с 1, с 2, с n – specific heat capacities components making up the explosive mixture, kJ/(kg × K); T is the initial temperature of the mixture, K.
The value of Q ext.en.cm can be found in reference tables. The explosion temperature of gas mixtures at constant volume is calculated using the same method as the combustion temperature of the mixture at constant pressure.
The explosion temperature is used to determine the explosion pressure. The pressure during the explosion of a gas-air mixture in a closed volume depends on the temperature of the explosion and the ratio of the number of molecules of combustion products to the number of molecules in the explosive mixture. When a gas-air mixture explodes, the pressure usually does not exceed 1.0 MPa if the initial pressure of the mixture was normal. When replacing air in an explosive mixture with oxygen, the explosion pressure increases sharply as the combustion temperature increases.
During the explosion of even a stoichiometric gas-air mixture, a significant amount of heat is spent on heating the nitrogen in the mixture, so the explosion temperature of such mixtures is much lower than the explosion temperature of mixtures with oxygen. Thus, the explosion pressure of a stoichiometric mixture of methane, ethylene, acetone and methyl ether
ra with oxygen is 1.5 – 1.9 MPa, and their stoichiometric mixtures with air are 1.0 MPa.
The maximum explosion pressure is used in calculations of the explosion resistance of equipment, as well as in calculations safety valves, explosive membranes and enclosures of explosion-proof electrical equipment.
The explosion pressure P adult (in MPa) of gas-air mixtures is calculated using the formula
,
where P 0 – initial pressure of the explosive mixture, MPa; T0 and Texp – initial temperature of the explosive mixture and explosion temperature, K; – the number of molecules of combustion product gases after the explosion; – the number of molecules of gases in the mixture before the explosion.
Example 4.1 . Calculate the pressure during the explosion of a mixture of ethyl alcohol vapor and air.
.
P 0 = 0.1 MPa; T adult = 2933 K; T 0 = 273 + 27 = 300 K; = 2 + 3 + 11.28 = 16.28 mol; = 1 + 3 + 11.28 = 15.28 mol.
The theory states that the explosion of a gas or steam-air mixture is not an instantaneous phenomenon. When an ignition source is introduced into the combustible mixture, an oxidation reaction of the fuel with the oxidizer begins in the area of effect of the ignition source. The rate of the oxidation reaction in some elementary volume of this zone reaches a maximum - combustion occurs. Combustion at the boundary of an elementary volume with the medium is called a flame front. The flame front has the shape of a sphere. The thickness of the flame front, according to calculations by Ya.B. Zeldovich , equal to 1-100 microns. Although the thickness of the combustion zone is small, it is sufficient for the combustion reaction to occur. The temperature of the flame front due to the heat of the combustion reaction is 1000-3000°C and depends on the composition of the combustible mixture.
As the flame front moves, the temperature of the unburnt part of the combustible mixture increases as the pressure of the mixture increases. Near the flame front, the temperature of the mixture also increases, which is due to
heat transfer by conduction, diffusion of heated molecules and radiation. On the outer surface of the flame front, this temperature is equal to the self-ignition temperature of the combustible mixture.
After ignition of the combustible mixture, the spherical shape of the flame is very quickly distorted and increasingly stretched towards the mixture that has not yet been ignited. The elongation of the flame front and the rapid increase in its surface is accompanied by an increase in the speed of movement of the central part of the flame. This acceleration continues until the flame touches the pipe walls or, in any case, approaches close to the pipe wall. At this moment, the size of the flame decreases sharply, and only a small part of the flame remains, covering the entire cross-section of the pipe. Extending the flame front
and its intense acceleration immediately after ignition by a spark, when the flame has not yet reached the walls of the pipe, are caused by an increase in the volume of combustion products. Thus, at the initial stage of the process of formation of the flame front, regardless of the degree of flammability of the gas mixture, acceleration and subsequent braking of the flame occurs, and this braking will be greater, the higher the flame speed.
The development of subsequent stages of combustion is influenced by the length of the pipe. Elongation of the pipe leads to the appearance of vibrations and the formation of a cellular structure of the flame, shock and detonation waves.
The width of the heating zone (in cm) can be determined from the dependence
1 = a/ v
Where A- thermal diffusivity coefficient; v- flame propagation speed.
Linear speed of movement v(in m/s) can be determined by the formula
V = V t /
Where V t- mass combustion rate, g/(s m3); - density of the initial combustible mixture, kg/m 3.
The linear speed of movement of the flame front is not constant; it varies depending on the compositions. Mixtures and admixtures of inert (non-flammable) gases, mixture temperature, pipe diameter, etc. The maximum flame propagation speed is observed not at the stoichiometric concentration of the mixture, but in a mixture with an excess of fuel. When inert gases are introduced into a flammable mixture, the speed of flame propagation decreases. This is explained by a decrease in the combustion temperature of the mixture, since part of the heat is spent on heating inert impurities not participating in the reaction.
As the diameter of the pipes increases, the speed of flame propagation increases unevenly. When the pipe diameter increases to 0.1-0.15 m, the speed increases quite quickly. The temperature increases until the diameter reaches a certain maximum diameter,
above which no increase in speed occurs. As the diameter of the pipe decreases, the speed of flame propagation decreases, and at a certain small diameter the flame does not propagate in the pipe. This phenomenon can be explained by an increase in heat losses through the walls
pipes.
Therefore, in order to stop the spread of flame in a combustible mixture, it is necessary to lower the temperature of the mixture in one way or another, by cooling the vessel (in our example, a pipe) from the outside or diluting the mixture with cold inert gas.
The normal speed of flame propagation is relatively low (no more than tens of meters per second), but in some conditions the flame in pipes spreads at a tremendous speed (from 2 to 5 km/s), exceeding the speed of sound in a given environment. This phenomenon was called detonation. The distinctive features of detonation are as follows:
1) constant burning rate regardless of the pipe diameter;
2) high flame pressure caused by the detonation wave, which can exceed 50 MPa depending on the chemical nature of the combustible mixture and the initial pressure; Moreover, due to the high burning rate, the developed pressure does not depend on the shape, capacity and tightness of the vessel (or pipe).
As the flame accelerates, the amplitude of the shock wave also increases, and the compression temperature reaches the self-ignition temperature of the mixture.
The increase in the total amount of gas burned per unit time is explained by the fact that in a jet with a variable cross-sectional speed, the flame front bends, as a result of which its surface increases and the amount of combustion substance increases proportionally.
When gas mixtures burn in a closed volume, the combustion products do not perform work; The explosion energy is spent only on heating the explosion products. In this case, the total energy is defined as the sum of the internal energy of the explosive mixture Q ext.en.cm. and heat of combustion of a given substance ΔQ g. Value Q ext.en.cm. equal to the sum of the products of the heat capacities of the components of the explosive mixture at constant volume by the initial temperature
mixture temperature
Q ext.en.cm. = C 1 T + C 2 T + …+ C p T
where C 1, C 2, C p are the specific heat capacities of the components that make up
explosive mixture, kJ/(kg K); T - initial temperature of the mixture, K.
The explosion temperature of gas mixtures at constant volume is calculated using the same method as the combustion temperature of the mixture at constant pressure.
The explosion temperature is used to determine the explosion pressure. The pressure during the explosion of a gas-air mixture in a closed volume depends on the temperature of the explosion and the ratio of the number of molecules of combustion products to the number of molecules in the explosive mixture. When gas-air mixtures explode, the pressure usually does not exceed 1.0 MPa if the initial pressure of the mixture was normal. When replacing air in an explosive mixture with oxygen, the explosion pressure increases sharply as the combustion temperature increases.
Explosion pressure of stoichiometric mixtures of methane, ethylene, acetone and
methyl ether with oxygen is 1.5 - 1.9 MPa, and stoichiometric mixtures with air is 1.0 MPa.
The maximum explosion pressure is used in calculations of explosion resistance of equipment, as well as in calculations of safety valves, explosion membranes and enclosures of explosion-proof electrical equipment. Explosion pressure R adult (in MPa) gas-air mixtures are calculated using the formula
R adult =
Where p 0- initial pressure of the explosive mixture, MPa; T 0 And T adult- initial temperature of the explosive mixture and explosion temperature, K;
The number of molecules of combustion product gases after the explosion;
- the number of molecules of gases in the mixture before the explosion.
1 The method consists in determining the upper limits for the maximum and average rate of increase in the pressure of the explosion of gas and steam-air mixtures in a spherical reaction vessel of constant volume.
The upper limit for the maximum rate of pressure rise in kPa s -1 is calculated using the formula
Where p i-initial pressure, kPa;
S And. i- normal flame propagation speed at initial pressure and temperature, m s -1;
a-radius of the spherical reaction vessel, m;
Dimensionless maximum explosion pressure;
R -maximum absolute explosion pressure, kPa;
And-adiabatic index for the mixture under study;
-thermokinetic exponent depending on the normal speed of flame propagation on pressure and temperature. If the value unknown, it is taken equal to 0.4.
The upper limit for the average rate of pressure increase in kPa s -1 is calculated using the formula
,
(98)
where is a function of parameters e , And , , the values of which are found using nomograms shown in Fig. 26 and 27.
Values e And And are found by thermodynamic calculation or, if calculation is impossible, are taken equal to 9.0 and 1.4, respectively.
The relative root mean square error of calculation using formulas (97) and (98) does not exceed 20%.
2. The maximum rate of increase in pressure of explosion of gas and steam-air mixtures for substances consisting of atoms C, H, O, N, S, F, Cl is calculated by the formula
,
(99)
Where V-volume of the reaction vessel, m3.
The relative root mean square error of the calculation using formula (99) does not exceed 30%.
Method for experimental determination of conditions for thermal spontaneous combustion of solids and materials
1. Equipment.
Equipment for determining the conditions of thermal spontaneous combustion includes the following elements.
1.1. A thermostat with a working chamber capacity of at least 40 dm 3 with a thermostat that allows you to maintain a constant temperature from 60 to 250 °C with an error of no more than 3 °C.
1.2. Baskets made of corrosion-resistant metal of cubic or cylindrical shape with a height of 35, 50, 70, 100, 140 and 200 mm (10 pieces of each size) with lids. The diameter of the cylindrical basket should be equal to its height. The wall thickness of the basket is (1.0±0.1) mm.
1.3. Thermoelectric converters (at least 3) with a maximum working junction diameter of no more than 0.8 mm.
2. Preparation for the test.
2.1. Carry out a calibration test to determine the correction ( t T) to the readings of thermoelectric converters 2 And 3 . To do this, place a basket with a non-flammable substance (for example, calcined sand) in a thermostat heated to a given temperature. Thermoelectric converters (Fig. 2) are installed in such a way that the working junction of one thermoelectric converter is in contact with the sample and located in its center, the second is in contact with the outer side of the basket, and the third is at a distance of (30±1) mm from the wall of the basket. The working junctions of all three thermoelectric converters must be located at the same horizontal level, corresponding to the center line of the thermostat.
1 , 2 , 3 -working junctions of thermoelectric converters.
The basket with a non-flammable substance is kept in a thermostat until a stationary mode is established, in which the readings of all thermoelectric
converters remain unchanged for 10 minutes or fluctuate with a constant amplitude around average temperatures t 1 , t 2 , t 3 . Amendment t T is calculated using the formula
,
(100)
2.2. Test samples must characterize the average properties of the substance (material) being tested. When testing sheet material, it is collected in a stack corresponding to the internal dimensions of the basket. In samples of monolithic materials, a hole with a diameter of (7.0 ± 0.5) mm for a thermoelectric converter is pre-drilled to the center.
Federal Agency for Education of the Russian Federation
State educational institution higher professional education
"Ufa State Petroleum Technical University"
Department of Industrial Safety and Labor Protection
Test on the subject:
Theory of combustion and explosion
1. Theoretical questions on explosion
In technological processes associated with the extraction, transportation, processing, production, storage and use of flammable gases (GG) and flammable liquids (FLL), there is always a danger of the formation of explosive gas and steam-air mixtures.
An explosive environment can be formed by mixtures of substances (gases, vapors, dusts) with air and other oxidizing agents (oxygen, ozone, chlorine, nitrogen oxides, etc.) and substances prone to explosive transformation (acetylene, ozone, hydrazine, etc.).
The most common causes of explosions are violations of the rules for the safe operation of equipment, gas leaks through leaks in connections, overheating of devices, excessive pressure increases, lack of proper control over technological process, rupture or breakdown of equipment parts, etc.
The source of initiation of the explosion are:
open flame, burning and hot bodies;
electrical discharges;
Thermal manifestations of chemical reactions and mechanical effects;
sparks from impact and friction:
shock waves;
Electromagnetic and other radiation.
According to PB 09-540-03 Explosion is:
I. The process of rapid release of potential energy associated with a sudden change in the state of a substance and accompanied by a pressure surge or shock wave.
2. Short-term release of internal energy, creating excess pressure
An explosion can occur with or without combustion (oxidation process).
Parameters and properties characterizing the explosiveness of the environment:
Flash point;
Concentration and temperature limits of ignition;
Auto-ignition temperature;
Normal flame propagation speed;
Minimum explosive content of oxygen (oxidizing agent);
Minimum ignition energy;
Sensitivity to mechanical stress (shock and friction). Dangerous and harmful factors affecting workers
as a result of the explosion are:
A shock wave in the front of which the pressure exceeds the permissible value;
Collapsed structures, equipment, communications, buildings and structures and their flying parts;
Formed during an explosion and (or) released from damaged equipment harmful substances, the content of which in the air working area exceeds the maximum permissible concentrations.
The main factors characterizing the danger of explosion:
Maximum pressure and explosion temperature;
Rate of pressure rise during explosion;
Pressure at the front of the shock wave;
Crushing and high-explosive properties of explosive environments.
During an explosion, the initial potential energy of a substance is converted, as a rule, into the energy of heated compressed gases, which in turn, when they expand, turns into the energy of motion, compression, and heating of the medium. Part of the energy remains in the form of internal (thermal) energy of the expanded gases.
The total amount of energy released during the explosion determines the general parameters (volume, area) of destruction. The energy concentration (energy per unit volume) determines the intensity of destruction at the source of the explosion. These characteristics, in turn, depend on the rate of energy release by the explosive system, causing the blast wave.
Explosions, which are most often encountered in investigative practice, can be divided into two main groups: chemical and physical explosions.
Chemical explosions include processes of chemical transformation of a substance, manifested by combustion and characterized by the release of thermal energy in a short period of time and in such a volume that pressure waves are formed, propagating from the source of the explosion.
Physical explosions include processes that lead to an explosion and are not associated with chemical transformations of the substance.
Accidental explosions are most often caused by combustion processes. Explosions of this kind most often occur during the storage, transportation and manufacture of explosives. They take place:
When handling explosives and explosive substances of the chemical and petrochemical industry;
For leaks natural gas in residential buildings;
during the production, transportation and storage of highly volatile or liquefied flammable substances;
when washing liquid fuel storage tanks;
in the manufacture, storage and use of flammable dust systems and some spontaneously combustible solid and liquid substances.
Features of a chemical explosion
There are two main types of explosions: an explosion of condensed explosives and a volumetric explosion (explosion of vapors of dust and gas mixtures). Explosions of condensed explosives are caused by all solid explosives and a relatively small number of liquid explosives, including nitroglycerin. Such explosives usually have a density of 1300-1800 kg/m3, but primary explosives containing lead or mercury have much higher densities.
Decomposition reactions:
The simplest case of an explosion is the process of decomposition with the formation of gaseous products. For example, the decomposition of hydrogen peroxide with a large thermal effect and the formation of water vapor and oxygen:
2H2O2 → 2H2O2 + O2 + 106 kJ/mol
Hydrogen peroxide is dangerous starting at a concentration of 60%.
Decomposition by friction or impact of lead azide:
Pb(N3)2 → Pb -ь 3N2 + 474 kJ/mol.
Trinitrotoluene (TNT) is an “oxygen-deficient” substance and therefore one of its main breakdown products is carbon, which contributes to the formation of smoke during TNT explosions.
Substances prone to explosive decomposition almost always contain one or more characteristic chemical structures responsible for the sudden development of the process with the release large quantity energy. These structures include the following groups:
NO2 and NO3 - in organic and inorganic substances;
N=N-N - in organic and inorganic azides;
NX3, where X is a halogen,
N=C in fulminates.
Based on the laws of thermochemistry, it seems possible to identify compounds whose decomposition process may be explosive. One of the decisive factors determining the potential danger of a system is the prevalence of its internal energy in the initial state compared to the final state. This condition is met when heat is absorbed (endothermic reaction) during the formation of a substance. An example of a corresponding process is the formation of acetylene from the elements:
2C + H2 → CH=CH - 242 kJ/mol.
Non-explosive substances that lose heat during formation (exothermic reaction) include, for example, carbon dioxide
C + O2 → CO2 + 394 kJ/mol.
It should be taken into account that the application of the laws of thermochemistry only allows us to identify the possibility of an explosive process. Its implementation depends on the reaction rate and the formation of volatile products. For example, the reaction of candle paraffin with oxygen, despite its high exothermicity, does not lead to an explosion due to its low speed.
The reaction 2Al+ 4AC2O2 → Al2O3 + 2Fe by itself, despite its high exothermicity, also does not lead to an explosion, since no gaseous products are formed.
Redox reactions, which form the basis of combustion reactions, for this reason can lead to an explosion only under conditions favorable to achieving high speeds reaction and pressure increase. Combustion of highly dispersed solids and liquids can lead, under closed volume conditions, to an increase in excess pressure of up to 8 bar. Relatively rare, for example in liquid air systems, where the aerosol is a mist of oil droplets.
In exothermic polymerization reactions and the presence of a volatile monomer, a stage is often reached at which a dangerous increase in pressure can occur; for some substances such as ethylene oxide, polymerization can begin at room temperature especially when the starting compounds are contaminated with substances that accelerate polymerization. Ethylene oxide can also isomerize to acetaldehyde exothermically:
CH2CH2O - CH3HC = O + 113.46 kJ/mol
Condensation reactions are widely used in the production of paints, varnishes and resins and, due to the exothermic nature of the process and the presence of volatile components, sometimes lead to explosions
To find out general conditions, favorable for the occurrence of combustion and its transition to an explosion, consider the graph (Figure 1) of the dependence of the temperature developed in a combustible system on time in the presence of volumetric heat release with it due to a chemical reaction and heat loss.
If we imagine temperature T1 on the graph as the critical point at which combustion occurs in the system, it becomes obvious that under conditions where heat loss exceeds heat gain, such combustion cannot occur. This process begins only when equality is reached between the rates of heat release and heat loss (at the point of tangency of the corresponding curves) and can then accelerate with increasing temperature and. thereby, the pressure before the explosion.
Thus, in the presence of conditions favorable to thermal insulation, the occurrence of an exothermic reaction in a combustible system can lead not only to combustion, but also to an explosion.
The resulting uncontrolled reactions that favor an explosion are due to the fact that the rate of heat transfer, for example, in vessels is a linear function of the temperature difference between the reaction mass and the coolant, while the rate of the exothermic reaction and, thereby, the heat flow from it grows according to a power law with an increase in the initial concentrations of the reagents and increases rapidly with increasing temperature as a result of the exponential dependence of the rate of a chemical reaction on temperature (Arrhenius's law). These patterns determine the lowest combustion rates of the mixture and the temperature at the lower concentration limit of ignition. As the concentration of fuel and oxidizer approaches stoichiometric levels, the combustion rate and temperature increase to maximum levels.
Gas concentration of stoichiometric composition - the concentration of a flammable gas in a mixture with an oxidizing medium, which ensures complete chemical reaction fuel and oxidizer mixture.
3. Features of a physical explosion
Physical explosions are usually associated with explosions of vessels from vapor pressure and grooves. Moreover, the main reason for their formation is not a chemical reaction, but a physical process caused by the release internal energy compressed or liquefied gas. The strength of such explosions depends on internal pressure, and destruction is caused by a shock wave from expanding gas or fragments of a ruptured vessel. A physical explosion can occur if, for example, a portable gas cylinder under pressure falls and a pressure-reducing valve breaks. The pressure of liquefied gas rarely exceeds 40 bar (the critical pressure of most conventional liquefied gases).
Physical explosions also include the phenomenon of so-called physical detonation. This phenomenon occurs when hot and cold liquids are mixed, when the temperature of one of them is significantly higher than the boiling point of the other (for example, pouring molten metal into water). In the resulting vapor-liquid mixture, evaporation can occur explosively due to the developing processes of fine phlegmatization of melt droplets, rapid heat removal from them and overheating of the cold liquid with its strong vaporization.
Physical detonation is accompanied by the appearance of a shock wave with excess pressure in the liquid phase, reaching in some cases more than a thousand atmospheres. Many liquids are stored or used in conditions where their vapor pressure significantly exceeds atmospheric pressure. Such liquids include: liquefied flammable gases (for example, propane, butane) liquefied refrigerants ammonia or freon, stored at room temperature, methane, which must be stored at a reduced temperature, superheated water in steam boilers. If a container with superheated liquid is damaged, steam leaks into the surrounding space and rapid partial evaporation of the liquid occurs. If the steam flows out and expands quickly enough, blast waves are generated in the environment. The causes of explosions of vessels containing gases and vapors under pressure are:
Violation of the integrity of the housing due to the breakdown of any component, damage or corrosion due to improper operation;
Overheating of the vessel due to disturbances in electrical heating or the operating mode of the combustion device (in this case, the pressure inside the vessel increases, and the strength of the body decreases to a state in which damage occurs);
Explosion of a vessel when the permissible pressure is exceeded.
Explosions of gas containers followed by combustion in the atmosphere basically contain the same reasons that are described above and are characteristic of physical explosions. The main difference is the formation in this case of a fireball, the size of which depends on the amount of gaseous fuel released into the atmosphere. This amount depends, in turn, on the physical state in which the gas is located in the container. When the fuel is kept in a gaseous state, its quantity will be much less than if stored in the same container in liquid form. The parameters of an explosion that determine its consequences are mainly determined by the nature of the energy distribution in the explosion area and its distribution as the blast wave spreads from the source of the explosion.
4. Energy potential
The explosion has great destructive power. The most important characteristic explosion is the total energy of matter. This indicator is called the energy potential of explosion hazard; it is included in all parameters characterizing the scale and consequences of an explosion.
In the event of an emergency depressurization of the device, its complete opening (destruction) occurs;
The area of liquid spillage is determined based on constructive solutions buildings or outdoor installation sites;
Evaporation time is assumed to be no more than 1 hour:
E= EII1+ EII2+ EII1+ EII2+ EII3+ EII4,
explosion firefighter room danger
where EI1 is the sum of the energies of adiabatic expansion and combustion of the vapor-gas phase (PGPC directly located in the block, kJ;
EI2 is the combustion energy of the GPF supplied to the depressurized area from adjacent objects (blocks), kJ;
EII1 is the combustion energy of GTHF generated due to the energy of the superheated liquid fluid of the block under consideration and received from adjacent objects kJ;
EII2 is the energy of combustion of PHF formed from the liquid phase (LP) due to the heat of exothermic reactions that do not stop during depressurization, kJ;
EII3 is the combustion energy of PHF. formed from liquid fluid due to heat influx from external coolants, kJ;
EII4 is the energy of combustion of PHF generated from liquid fluid spilled on a solid surface (floor, pallet, soil, etc.) due to heat transfer from environment(from a solid surface and air, to liquid along its surface), kJ.
Based on the values of the general energy potentials of explosion hazard, the values of the reduced mass and relative energy potential that characterize the explosion hazard of technological units are determined.
The reduced mass is the total mass of flammable vapors (gases) of an explosive vapor-gas cloud, reduced to a single specific combustion energy equal to 46000 kJ/kg:
Relative energy potential of explosion hazard Qв of a technological unit, which characterizes the total combustion energy and can be found by calculation using the formula:
where E is the total energy potential of the explosion hazard of the technological unit.
Based on the values of the relative energy potentials Ov to the reduced mass of the vapor-gas medium m, the technological blocks are categorized. The explosion hazard category indicators for process units are given in Table 1.
Table No.
| Explosion category | Ov | m |
| I | >37 | >5000 |
| II | 27 − 37 | 2000−5000 |
| III | <27 | <2000 |
5. TNT equivalent. Excessive pressure in the shock wave front
To assess the level of impact of accidental and intentional disruptions, the TNT equivalent assessment method is widely used. According to this method, the degree of destruction is characterized by a TNT equivalent, where the mass of TNT that is required to cause a given level of destruction is determined. The TNT equivalent of an explosion of a vapor-gas environment Wτ(kg) is determined according to the conditions of the adequacy of the nature and degree of resolution in explosions of vapor-gas clouds, as well as solid and liquid chemically unstable compounds, calculated using the formulas:
1 For vapor-gas media
q/ − specific heat of combustion of the vapor-gas medium, kJ kg,
qT is the specific explosion energy of TNT kJ/kg.
2 For solid and liquid chemically unstable compounds
where Wk is the mass of solid and liquid chemically unstable compounds; qk is the specific explosion energy of solid and liquid chemically unstable compounds. In production, when a gas-air, steam-air mixture or dust explodes, a shock wave is formed. The degree of resolution of building structures, equipment, machinery and communications, as well as damage to people, depends on the excess pressure in the shock wave front ΔRF (the difference between the maximum pressure in the shock wave front and normal atmospheric pressure ahead of this front).
Calculations for assessing the effect of flammable chemical gases and liquids come down to determining the excess pressure in the shock wave front (ΔRF) during the explosion of a gas-air mixture at a certain distance from the container in which a certain amount of the explosive mixture is stored.
6. Calculation to determine excess explosion pressure
Calculation of excess explosion pressure for flammable gases, flammable vapors and combustible liquids is carried out according to the methodology set out in NPB 105-03 “Determination of categories of premises, buildings and outdoor installations for explosion and fire hazards”.
Assignment: determine the excess pressure of a hydrogen sulfide explosion in a room.
Initial conditions
Hydrogen dioxide is constantly present in a 20 m3 apparatus. The device is located on the floor. The total length of pipelines with a diameter of 50 mm, limited by valves (manual) installed on the inlet and outlet sections of the pipelines, is 15 m. The consumption of hydrogen sulfide in the pipelines is 4·10-3 m3/s. The dimensions of the room are 10x10x4 m.
The room has emergency ventilation with an air exchange rate of 8 h-1. Emergency ventilation is provided with backup fans, automatic start-up when the maximum permissible explosive concentration is exceeded, and power supply according to the first reliability category (PUE). Devices for removing air from the room are located in close proximity to the site of a possible accident.
The main building structures of the building are reinforced concrete.
Justification of the design option
According to NPB 105-03, the most unfavorable version of the accident, which involves the largest number of substances that are most dangerous in terms of the consequences of an explosion, should be taken as the design version of the accident.
And as a design option, the option of depressurization of the container with hydrogen sulfide and the release of both the inlet and outlet pipelines of hydrogen sulfide into the volume of the room was adopted.
1) Excessive explosion pressure for individual flammable substances consisting of atoms C, H, O, N, Cl, Br, I, F is determined by the formula
(1)
where is the maximum explosion pressure of a stoichiometric gas-air or steam-air mixture in a closed volume, determined experimentally or from reference data in accordance with the requirements of clause 3 of NPB -105-03. In the absence of data, it is allowed to take equal to 900 kPa;
Initial pressure, kPa (allowed to be equal to 101 kPa);
Mass of flammable gas (GG) or flammable vapors (FLV) and flammable liquids (FL) released into the room as a result of the accident, kg;
The coefficient of participation of fuel in an explosion, which can be calculated based on the nature of the distribution of gases and vapors in the volume of the room according to the application. It is allowed to take the value according to the table. 2 NPB 105-03. I take it equal to 0.5;
Free space volume, ;
The maximum absolute air temperature for the city of Ufa is taken as the design temperature, equal to 39°C (according to SNiP 23-01-99 “Building climatology”).
Below is a calculation of the values required to determine the excess pressure of a hydrogen sulfide explosion in a room.
Density of hydrogen sulfide at design temperature:
where M is the molar mass of hydrogen sulfide, 34.08 kg/kmol;
v0 – molar volume equal to 22.413 m3/kmol;
0.00367− coefficient of thermal expansion, deg -1;
tp – design temperature, 390С (absolute maximum air temperature for the city of Ufa).
The stoichiometric concentration of hydrogen sulfide is calculated using the formula:
;
where β is the stoichiometric coefficient of oxygen in the combustion reaction;
nc, nn, n0, nх, is the number of C, H, O atoms and halogens in a fuel molecule;
For hydrogen sulfide (H2S) nc= 1, nн = 4, n0 = 0, nх = 0, therefore,
Substituting the found value of β, we obtain the value of the stoichiometric concentration of hydrogen sulfide:
The volume of hydrogen sulfide entering the room during a design accident consists of the volume of gas leaving the apparatus and the volume of gas leaving the pipeline before closing the valves and after closing the valves:
where Va is the volume of gas leaving the apparatus, m3;
V1T is the volume of gas released from the pipeline before it was turned off, m3;
V2T is the volume of gas released from the pipeline after it was turned off, m3;
where q is the liquid flow rate, determined in accordance with the technological regulations, m3/s;
T is the duration of gas flow into the volume of the room, determined according to clause 38 of NPB 105-03 s;
where d is the internal diameter of pipelines, m;
Ln is the length of pipelines from the emergency apparatus to the valves, m;
Thus, the volume of hydrogen sulfide entering the premises during the considered accident scenario:
Mass of hydrogen sulfide in the room:
In the case of circulation of flammable gases, flammable or combustible gases, flammable or combustible liquids in the room when determining the value of mass , it is allowed to take into account the operation of emergency ventilation if it is provided with backup fans, automatic start-up when the maximum permissible explosion-proof concentration is exceeded and power supply according to the first reliability category (PUE) ), provided that devices for removing air from the room are located in close proximity to the site of a possible accident.
In this case, the mass of flammable gases or vapors of flammable or combustible liquids, heated to the flash point and above, entering the volume of the room should be divided by the coefficient determined by the formula
where is the air exchange rate created by emergency ventilation, 1/s. This room has ventilation with an air exchange rate of 8 (0.0022s);
The duration of entry of flammable gases and vapors of flammable and combustible liquids into the volume of the room, s, is taken to be 300 s. (clause 7 NPB 105-03)
Mass of hydrogen sulfide present in the room during the considered accident scenario:
Explosion calculation results
| Option No. | Flammable gas |
Value, kPa | ||
| Hydrogen sulfide | 5 | Average damage to buildings | ||
Table. Maximum permissible excess pressure during combustion of gas, steam or dust-air mixtures indoors or in open space
The initial and calculated data are summarized in Table 2.
Table 2 - Initial and calculated data
| No. | Name | Designation | Magnitude |
| 1 | Substance, its name and formula | Hydrogen sulfide | H2S |
| 2 | Molecular mass, kg kmol-1 | M | 34,08 |
| 3 | Liquid density, kg/m3 | ρzh | - |
| 4 | Gas density at design temperature, kg/m3 | ρg | 1,33 |
| 5 | Ambient temperature (air before explosion), 0C | T0 | 39 |
| 6 | Saturated vapor pressure, kPa | Rn | 28,9 |
| 7 | Stoichiometric concentration, % vol. | Cst | 29,24 |
| 8 | Room dimensions − length, m − width, m − height, m |
||
| 9 | Pipe dimensions: − diameter, m −length, m |
||
| 10 | Heptane flow in the pipeline, m3/s | q | 4·10-3 |
| 11 | Valves closing time, s | t | 300 |
| 12 | Emergency ventilation rate, 1/hour | A | 8 |
| 13 | Maximum explosion pressure, kPa | Pmax | 900 |
| 14 | Initial pressure, kPa | P0 | 101 |
| 15 | Leakage and nonadiabatic coefficient | Kn | 3 |
| 16 | Coefficient of fuel participation in explosion | Z | 0,5 |
According to NPB 105-2003, categories of premises for explosion and fire hazards are accepted in accordance with Table 4.
| Room category | Characteristics of substances and materials located (circulating) in the premises |
And the explosion and fire |
Combustible gases, flammable liquids with a flash point of not more than 28 ° C in such quantities that they can form explosive vapor-gas mixtures, upon ignition of which a calculated excess explosion pressure in the room develops, exceeding 5 kPa. Substances and materials capable of exploding and burning when interacting with water, air oxygen or with each other in such quantities that the calculated excess explosion pressure in the room exceeds 5 kPa. |
|
explosion and fire hazardous |
Combustible dusts or fibers, flammable liquids with a flash point of more than 28 ° C, flammable liquids in such quantities that they can form explosive dust-air or steam-air mixtures, the ignition of which develops a calculated excess explosion pressure in the room exceeding 5 kPa. |
| B1-B4 fire hazardous | Flammable and low-flammable liquids, solid flammable and low-flammable substances and materials (including dust and fibers), substances and materials that, when interacting with water, air oxygen or with each other, can only burn, provided that the rooms in which they are in stock or in circulation and do not belong to categories A or B. |
| G | Non-combustible substances and materials in a hot, incandescent or molten state, the processing of which is accompanied by the release of radiant heat, sparks and flames; flammable gases, liquids and solids that are burned or disposed of as fuel. |
| D | Non-flammable substances and materials in a cold state, |
Conclusion: The room belongs to category A, since it is possible for flammable gas (hydrogen sulfide) to escape in such quantities that it can form explosive vapor-gas-air mixtures, upon ignition of which a calculated excess explosion pressure in the room develops, exceeding 5 kPa.
8. Determination of the values of energy indicators of the explosion hazard of a technological unit during an explosion
The explosive energy potential E (kJ) of a block is determined by the total combustion energy of the vapor-gas phase located in the block, taking into account the magnitude of the work of its adiabatic expansion, as well as the magnitude of the energy of complete combustion of the evaporated liquid from the maximum possible area of its spillage, and it is considered:
1) in the event of an emergency depressurization of the device, its complete opening (destruction) occurs;
2) the area of liquid spillage is determined based on the design solutions of buildings or the outdoor installation site;
3) evaporation time is assumed to be no more than 1 hour:
Sum of energies of adiabatic expansion A (kJ) and combustion of PHF located in the block, kJ:
q" =23380 kJ/kg - specific heat of combustion of HHF (hydrogen sulfide);
26.9 - mass of flammable gas
.
To practically determine the energy of the adiabatic expansion of the PHF, you can use the formula
where b1 - can be taken from the table. 5. With adiabatic index k=1.2 and pressure 0.1 MPa, it is equal to 1.40.
Table 5. The value of coefficient b1 depending on the adiabatic index of the medium and pressure in the process unit
| Index | System pressure, MPa | |||||||||
| adiabats | 0,07-0,5 | 0,5-1,0 | 1,0-5,0 | 5,0-10,0 | 10,0-20,0 | 20,0-30,0 | 30,0-40,0 | 40,0-50,0 | 50,0-75,0 | 75,0-100,0 |
| k = 1.1 | 1,60 | 1,95 | 2,95 | 3,38 | 3,08 | 4,02 | 4,16 | 4,28 | 4,46 | 4,63 |
| k = 1.2 | 1,40 | 1,53 | 2,13 | 2,68 | 2,94 | 3,07 | 3,16 | 3,23 | 3,36 | 3,42 |
| k = 1.3 | 1,21 | 1,42 | 1,97 | 2,18 | 2,36 | 2,44 | 2,50 | 2,54 | 2,62 | 2,65 |
| k = 1.4 | 1,08 | 1,24 | 1,68 | 1,83 | 1,95 | 2,00 | 2,05 | 2,08 | 2,12 | 2,15 |
0 kJ is the combustion energy of PHF supplied to the depressurized area from adjacent objects (blocks), kJ. There are no adjacent blocks, so this component is zero.
0 kJ is the combustion energy of PHF, generated due to the energy of the superheated liquid fluid of the block under consideration and received from adjacent objects during time ti.
0 kJ is the energy of combustion of PHF formed from liquid fluid due to the heat of exothermic reactions that do not stop during depressurization.
0 kJ is the energy of combustion of PHF formed from liquid fluid due to heat influx from external coolants.
0 kJ is the energy of combustion of PHF generated from liquid fluid spilled on a solid surface (floor, pallet, soil, etc.) due to heat transfer from the environment (from the solid surface and air to the liquid along its surface.
The explosive potential of the block is equal to:
E=628923.51 kJ.
Based on the values of the general energy potentials of explosion hazard E, the values of the reduced mass and relative energy potential that characterize the explosion hazard of technological units are determined.
The total mass of flammable vapors (gases) of an explosive vapor-gas cloud t, reduced to a single specific combustion energy equal to 46,000 kJ/kg:
The relative energy potential of explosion hazard Qv of a technological unit is found by calculation using the formula
Based on the values of the relative energy potentials Qв and the reduced mass of the vapor-gas medium m, the technological blocks are categorized. The category indicators are given in table. 5.
Table 4. Indicators of explosion hazard categories of technological units
| Explosion category | Qв | m, kg |
| I | > 37 | > 5000 |
| II | 27 - 37 | 2000 - 5000 |
| III | < 27 | < 2000 |
Conclusion: The room belongs to the III category of explosion hazard, since the total mass of the explosive vapor-gas cloud of hydrogen sulfide reduced to a single specific combustion energy is 16.67 kg, the relative energy potential of the explosion hazard is 5.18.
9. Calculation of the explosive concentration of the gas-air mixture in the room. Determination of the class of premises according to explosion and fire hazard according to the Electrical Electrical Regulations
Let us determine the volume of explosive concentration of hydrogen sulfide in the room:
where t is the mass of the steam-air mixture in the room, kg,
LKPV - lower concentration limit of ignition, g/m3.
The concentration of the steam-air mixture in the room will be:
where VCM is the volume of explosive concentration of hydrogen sulfide in the room, m3, VC6 is the free volume of the room, m3.
The calculation results are presented in Table 6.
Table 6. Results of calculating the concentration of the gas-air mixture
According to the PUE, the premises in question belong to class B-Ia - zones located in premises in which, during normal operation, explosive mixtures of flammable gases (regardless of the lower flammability limit) or flammable liquid vapors with air are not formed, but are possible only as a result of accidents and malfunctions.
10. Determination of destruction zones during an explosion. Classification of damage zones
The radii of destruction zones during an explosion of a gas-air mixture were determined according to the methodology set out in Appendix 2 of PB 09-540-03.
The mass of vapor-gas substances (kg) involved in the explosion is determined by the product
where z is the fraction of the reduced mass of hydrogen sulfide involved in the explosion (for GG it is equal to 0.5),
t – mass of hydrogen sulfide in the room, kg.
TNT equivalent can be used to assess the level of explosion exposure. The TNT equivalent of an explosion of a vapor-gas environment WT (kg) is determined according to the conditions of the adequacy of the nature and degree of destruction during explosions of vapor-gas clouds, as well as solid and liquid chemically unstable compounds.
For vapor-gas environments, the TNT equivalent of an explosion is calculated:
where 0.4 is the fraction of the explosion energy of the vapor-gas medium expended directly on the formation of the shock wave;
0.9 – fraction of the explosion energy of trinitrotoluene (TNT) spent directly on the formation of a shock wave;
q"—specific heat of combustion of the vapor-gas medium, kJ/kg;
qT is the specific explosion energy of TNT, kJ/kg.
The destruction zone is considered to be an area with boundaries defined by radii R, the center of which is the technological unit under consideration or the most likely place of depressurization of the technological system. The boundaries of each zone are characterized by the values of excess pressure along the front of the shock wave AR and, accordingly, by the dimensionless coefficient K. The classification of destruction zones is given in Table 6.
Table 7. Level of possible destruction during explosive transformation of clouds of fuel-air mixtures
| Fracture zone class | ΔР, kPa | TO | Destruction zone | Characteristics of the affected area |
| 1 | ≥100 | 3,8 | full | Destruction and collapse of all elements of buildings and structures, including basements, percentage of human survival; For administrative buildings and management buildings of conventional designs - 30%; For industrial buildings and structures of conventional designs - 0%. |
| 2 | 70 | 5,6 | strong | Destruction of part of the walls and ceilings of the upper floors, formation of cracks in the walls, deformation of the ceilings of the lower floors. Possible limited use of the surviving cellars after clearing the entrances. Human survival rate: For administrative buildings and management buildings of conventional designs - 85%: For industrial buildings and structures of conventional designs - 2% |
| 3 | 28 | 9,6 | average | Destruction of mainly secondary elements (roofs, partitions and door fillings). Floors, as a rule, do not collapse. Some of the premises are suitable for use after clearing the debris and making repairs. The percentage of people's survival: - for administrative buildings and control buildings of conventional design - 94%. |
| 4 | 14 | 28 | weak | Destruction of window and door fillings and partitions. Basements and lower floors are completely preserved and are suitable for temporary use after removing debris and sealing openings. The percentage of people's survival: - for administrative buildings and control buildings of conventional design - 98%; industrial buildings and structures of conventional designs - 90% |
| 5 | ≤2 | 56 | glazing | Destruction of glass fillings. The percentage of surviving people is 100% |
The radius of the destruction zone (m) is generally determined by the expression:
where K is a dimensionless coefficient characterizing the impact of an explosion on an object.
The results of calculating the radii of damage zones during an explosion of a fuel-air mixture in a room are presented in Table 7.
Table 7 - Results of calculating the radii of damage zones
List of sources used
1. Beschastnov M.V. Industrial explosions. Assessment and prevention. - M. Chemistry, 1991.
2. Life safety, Safety of technological processes and production (Occupational safety): Textbook, Manual for universities / P.P. Kukin, V.L. Lapin, N, L. Ponomarev and others, - M.,: Higher. school t 2001,
3. PB 09-540-03 “General explosion safety rules for fire and explosion hazardous chemical, petrochemical and oil refining industries.”
4. GOST 12.1,010-76* Explosion safety
5. NPB 105-03 “Definition of categories of premises and buildings, outdoor installations for explosion and fire hazards.”
6. SNiP 23 -01-99 Construction climatology.
7. Fire and explosion hazard of substances and materials and means of extinguishing them. Ed. A„ N. Baratova and A. Ya. Korolchenko. M., Chemistry, 1990. 8. Rules for the design of electrical installations. Ed. 7th.