Domestic and foreign scientists and engineers were engaged in burning processes. The founder of the modern thermal combustion model is V.A. Michelson. The author of the theory of branched chain reactions, which is the basis of the provisions on the mechanism of combustion - N.N. Semenov. Kinetics (speed) chemical combustion reactions studied - V.N. Kondratiev, N.M. Emanuel, Zeldovich, Frank-Kamenetsky, leadership, Belyaev, Andreev, Leipunsky.

Consider Concepts, terms and definitions in the theory of burning and explosion, the conditions for the occurrence and development of combustion processes, the basics of thermal and chain mechanisms of ignition and combustion.

Under the alignment, they understand the rapid physico-chemical oxidative and reduction process with heat release capable of self-proliferation and often accompanied by the glow and formation of the flame. Classic examples of combustion - the reaction of oxidation of organic substances or carbon oxygen by air: combustion of stone coal, oil, firewood, etc.

The combustion process is complex and consists of many interconnected individual processes, both physical and chemical.

The combustion physics is reduced to the processes of heat and transfer and transfer in the reaction zone.

The combustion chemistry is to flow as in reactions consisting of a number of elementary acts and connected to the transition of electrons from one atoms in the substance to others - from the reducing agent to the oxidizer.

Oxidative and recovery reactions burning may be intermolecular and intramolecular :

- Intermolecular reactions proceed with a change in the degree of oxidation of atoms in different molecules;

– intramolecular The combustion reactions flow with a change in the degree of oxidation of atoms in the same molecule (usually the reaction of thermal decomposition of substances).

Combustion - relatively fast process, therefore, there is not all o-in the reaction. Slow reactions (low-temperature oxidation, biochemical) and too fast (explosive transformation) are not included in the concept of burning.

The combustion determine the reaction, the flow time of which is usually measured by seconds or shares of seconds.

The combustion is accompanied by heat release, therefore exothermic reactions lead to the combustion. The combustion is a self-sustaining process due to energy, so the combustion causes those exothermic reactions, the total heat of which is sufficient for self-proliferation. In practice, combustion reactions are used, the heat of which is sufficient to obtain a useful effect. Reactions going with the cost of heat from outside do not relate to burning.

The concept of burning includes a wide variety of chemical reactions between the elements and their compounds and the reaction of the decay of the compounds.

The combustion occurs not only due to the formation of oxides, but also fluorides, chlorides, nitrides; In addition - borides, carbides, silicides of a number of metals. Heat release and combustion can occur when sulphides and phosphides of some elements are formed.

Energy, released during combustion as a result of the flow of chemical reactions, spent on maintaining the burning process , and part of it scattered into the surrounding space . Stationary (sustainable) burning occurs when equality of heat transfer and heat To prepare for the burning of the next servings of the substance.

IN the process of burning required 2 stages :

- creation of molecular contact between reagents and

- The interaction of molecules to form reaction products. The rate of transformation of the source products into the final depends from the speeds of reagents and on the speed of the chemical reaction.

IN limit case combustion characteristics can be determined only by the speed of chemical interaction - kinetic constants and factors ( kinetic combustion regime ), or only the speed of mixing - diffusion ( diffusion combustion mode ).

The substances involved in burning can be in a gaseous, liquid and solid state, are mixed with each other or not mixed.

If the system does not have the surface of the section between reagents, then such a system is called homogenic If there are surface surfaces - heterogeneous.

The combustion is often accompanied by the glow of combustion products and the formation of the flame. The flame is a gaseous medium comprising dispersed condensed products in which physico-chemical transformations of reagents occurs.

For gaseous systems, the entire process of burning flows into the flame. When combining condensed systems, part of the physicochemical transformations (heating, melting, evaporation, initial decomposition and reagent interaction can occur outside the flame. Flame-free burning is known when the process proceeds only in the condensed system with almost no gas formation and dispersion (combustion of mixture of metals with non-metals).

The flame is characterized by visible radiation, but transparent flames are also known. The most high-temperature fraction of the flame is called the main reaction zone, the front of the flame.

After initiating the combustion process, it extends throughout the volume. In contrast to the explosion, the combustion process spreads at a speed not exceeding the speed of sound.

If the reagents before the start of burning were not mixed, then burning and flames are called diffusion because The mixing of fuel with an oxidizer is achieved by diffusion. A simple example is the flame of the candle, here is the oxidizing agent (oxygen) and fuel - organic matter of the phytil (flax, cotton).

If the reagents are pre-stirred (homogeneous mixture), the combustion process is called homogeneous burning . Heterogeneous burning It occurs on the surface of the phase section. One of the reactors is in the condensed phase, another (oxygen) is different in the gas phase. Examples of heterogeneous burning - coal burning, non-volatile metals.

In a combustion technique, the condition of complete preliminary mixing of reagents is not always carried out and transient combustion modes are possible.

Depending on the nature of the flow of the gas flow forming the flame, the laminar and turbulent flames are distinguished. In the laminar flame the laminar flow, layered. Mass transfer and transfer processes are carried out by molecular diffusion and convection.

Combustion- A complex physico-chemical, quickly leaking process, which is accompanied by the release of a significant amount of heat and a bright glow.

The combustion occurs as a result of oxidation of a substance capable of burning (fuel), oxidizer (air oxygen, chlorine).

Types of fire:flash, ignition, self-ignition, self-burning.

The burning is a complex of interrelated chemical and physical processes.

The combustion property is the ability of the focus of the flame to move throughout the combustible mixture by transferring heat from the burning zone in the fresh mixture.

Ignition sources are sparks, flames, rolled items, friction, blow.

To occur, the combustion process is characterized by the presence of critical conditions (according to the composition of the mixture, pressure, temperature, geometric size of the system) of the emergence and distribution of the flame.

Three typical stages are characteristic of combustion: the occurrence, the propagation of B repayment of the flame.

Depending on the state of the fuel and oxidant, three types of burning distinguish:

Homogeneous combustion of gases in the gaseous oxidizing agent medium;

Heterogeneous combustion of liquid b solid combustible substances in the oxidizer gaseous medium;

Burning explosives.

The oxidizer is air oxygen. Oxidifiers can be fluorine, bromine, sulfur, which, when heated, decompose with oxygen release.

Flash- Fast combustion of a mixture of gas with air, which may occur from contact with a mixture with a flame, spark, without transition to burning. On the outbreak, the burning stops, as only a couple have to burn.

Ignition- This is a process in which the substance is heated to the boiling point and burns while the volatile hydrocarbons are released.

Self-ignion- The process when the substance is heated from the foreign source of heat, constantly moving to self-heating.

Spontaneous combustion- The process of self-heating and subsequent ignition of the substance without the impact of an open source of ignition. The lower the temperature at which the process of self-burning occurs, the substance is more dangerous. The process of self-burning may begin at a temperature of 10-20 OS.

Self-turning substances are divided into three groups: self-turning from the effects of air (vegetable oils), causing combustion when exposed to water (calcium carbide), self-coating when interacting with other substances (at intercutants).

Fire and explosive gases are characterized by the following indicators: concentration of flame propagation, minimal ignition energy, combustion temperature and flame distribution speed.

The burning is two species: full and incomplete.

Full burningit occurs with the excess amount of oxygen and is accompanied by the formation of water vapor and carbon dioxide.

Incomplete burningit is very dangerous, as it happens with a lack of oxygen, while the toxic carbon oxide is formed.

Two combustion modes:the first mode in which a combustible substance forms a homogeneous mixture with air to the start of burning, the second mode in which the fuel and oxidizer is originally separated, and the burning flows in the area of \u200b\u200bmixing them (diffusion burning).

The heat flux that comes from the burning area to solid fuel depends on the energy that is released during the combustion process and on the heat exchange conditions between the combustion zone and the solid fuel surface. Under these conditions, the mode and the combustion rate may depend on the physical state of the combustible substance, its distribution in space and environmental characteristics.

Depending on the rate of propagation of the flame, combustion can occur in the form of flagazing combustion, explosion and detonation.

Explosion- The process of rapid allocation of a large amount of energy. As a result of the explosion, the explosive mixture is converted into highly heated high pressure gas, which with great power affects the environment and causes the formation of an explosive wave.

The destruction caused by the explosion is due to the action of an explosive wave. As the explosion is removed from the site, the mechanical effect of the explosive wave is weakening.

The rate of spread of the flame during the explosion reaches hundreds of meters per second. When the flame is accelerated, the compression of the unburned gas is enhanced by the compression of the unburned gas in the form of consecutive shock waves, which are connected to one powerful shock wave of highly compressed and preheated gas. As a result, a stable reaction propagation mode occurs. The type of combustion spreading at a speed exceeding the speed of the sound is called detonation. It is characterized by a sharp pressure jump in the explosion site, which has a great destructive action.

Liquids and solids form flammable mixtures with increasing them to a temperature at which gaseous products are formed in sufficient quantity. Explosive are mixes of dust with air. Valid dust can be in suspension and settle on walls, equipment.

When burning, poisonous gases are distinguished: Sinyl Acid, phosgene and others, and the oxygen content in the air drops. That is why it is dangerous not only and not even so much fire as smoke and nothing from him. It is necessary to take into account the possible reactions of the human body with increasing concentration of combustion products:

carbon monoxide: 0.01% - weak headaches; 0.05% - dizziness; 0.1% - fainting; 0.2% - coma, fast death; 0.5% - instant death;

carbon dioxide: up to 0.5% - does not affect; from 0.5 to 7% - the increase in cardiac rhythm, the beginning of the paralysis of the respiratory centers; Over 10% - palsy of the respiratory centers and death.

Requirements for safe operation of household gas devices (and gas plates in particular)

Norms of equipping premises with manual fire extinguishers

Table1

	2	Fire class	Foam and aqueous fire extinguishers with a capacity of 10 liters	Powder fire extinguishers with a capacity, l / mass of fire extinguishing agent, kg			Cladon fire extinguishers Capacity 2 (3) l	Carbon dioxide fire extinguishers with a capacity, l / mass of fire extinguishing agent, kg
									5 (8)/3(5)
A, B, B (combustible gases and liquids)
Public buildings

Notes:

1. To extinguish fires of various classes, powder fire extinguishers must have appropriate charges: for class A - ABC (E) powder; For classes in, C and E - Sun (E) or ABC (E), for class D - D.

2. For powder fire extinguishers and carbon dioxide fire extinguishers, double marking is given: the old marking for the capacity of the housing, l / new marking by weight of the fire extinguishing composition, kg. When equipping premises with powder and carbon dioxide fire extinguishers, fire extinguishers are allowed both with old and new marking.

3. The "+ +" sign indicates fire extinguishers, "+" facilities - fire extinguishers, the use of which is allowed in the absence of recommended and with the appropriate substantiation; The sign "-" - fire extinguishers that are not allowed to equip these objects.

4. In closed rooms, no more than 50 m 3 3 to extinguish fires instead of portable fire extinguishers or in addition, fire extinguishers of self-screening powder can be used.

Norms of equipping premises by mobile fire extinguishers

table 2

	Limit protected area, m 2	Fire class	Air-foam fire extinguishers with a capacity of 100 liters	Combined fire extinguishers with a capacity (foam, powder) 100 liters	Powder fire extinguishers with a capacity of 100 liters	Carbon dioxide fire extinguishers with a capacity, l
A, B, B (combustible gases and liquids)
In (except combustible gases and liquids), g

Notes:

1. To extinguish the foci of fires of various classes, powder and combined fire extinguishers must have appropriate charges: for class A - ABC (E) powder; for class B, C and E - Sun (E) or ABC (E); For class D - D.

2. The values \u200b\u200bof the characters "+ +", "+" and "-" are shown in Note 2 to Table 1.

Simplifying under the alignment understands the rapid exothermic process of oxidation of substances by oxygen with the release of a significant amount of heat and light radiation.

The combustion is a complex physicochemical process of interaction between a fuel and an oxidant, as well as the decomposition of some substances characterized by self-esteem transformation with the release of a large amount of heat and radiation of light. Usually, oxygen with a concentration of 21 participates as an oxidizing agent in this process. about. %. For the occurrence and development of the combustion process, a fuel, an oxidizing agent and a ignition source, initiating a certain chemical reaction rate between the flammable and the oxidizing agent, are necessary.

The combustion, as a rule, occurs in the gas phase, therefore combustible substances that are in condensed state (liquid and solid substances), for the occurrence and maintenance of combustion should be subject to gasification (evaporation, decomposition). The combustion is distinguished by the variety of species and features caused by the processes of heat and mass transfer, gas-dynamic factors, kinetics of chemical reactions and other factors, as well as feedback between external conditions and nature of the development of the process.

2.4.2.1. Classification of burning processes.

The burning can be homogenic and heterogeneous Depending on the aggregate state of combustible substances and the oxidizing agent.

Homogeneous burning flows in the case when the reacting components of the combustible mixture have the same aggregate state. Homogenic burning can be kinetic and diffusion Depending on the conditions for mixing the combustible components and on the ratio of the rates of chemical reactions and mixing formation. This or that combustion regime is implemented, for example, in a fire, depending on which the stages of the combustion process is limiting: the speed of mixing or the rate of chemical reactions.

Kinetic is the combustion of pre-mixed gas or steam-air mixtures (the limiting stage of the process - the rate of chemical reactions), which often has an explosive character (if the mixture is formed in a closed space), because The energy released does not have time to be discharged beyond this space. Kinetic burning can be calm if the combustible mixture is pre-created in a small, unlocked space with a continuous fuel supply in the burning area.

The diffusion combustion mode is implemented when it creates a combustible mixture directly in the combustion zone when the oxidizer enters it at the expense of diffusion processes, for example, heterogeneous burning.

Heterogeneous combustion is carried out at various aggregate states of the combustible substance and the oxidant. In heterogeneous combustion, the intensity of the vapor flow of steam generated from condensed combustible substances (liquid, solids) plays an important role in the reaction zone.

With gas-dynamic positions, combustion may be laminarand turbulent.

The laminar mode of the combustion process is carried out in the case when the components of the combustible mixture enter the reaction zone at small values \u200b\u200bof the Reynolds criterion (0< R E. < 200), т.е. в основном за счёт молекулярной диффузии. Процесс характеризуется малыми скоростями газовыхfuel and oxidizing and layered propagation of the reaction zone (the front of the flame) in space. The combustion rate in this case depends on the rate of formation of a combustible mixture.

The turbulent process mode is implemented when the combustible mixture components go to the reaction zone at large values \u200b\u200bof Reynolds criterion (230< R. E.< 10000). Combustion In this mode, happens with increasing gas speed streamWhen the laminarness of their movement is disturbed. In turbulent combustion mode, the twigscence of gas jets improves the mixing of reacting components, while the surface area increases through which the molecular diffusion occurs, the result of which is an increase in the flame propagation rate in space.

By the speed of flame spread in space, the burning is divided into:

– delagrate(Flame distribution speed m / S.);

– explosive (Flame distribution dozens and hundreds m / S.But no more speed of the propagation of sound in the air (344 m / S.));

– detonation (Flame spread speed is greater than the speed of sound in the air).

Depending on the depth of leakage of chemical reactions, combustion may be full and incomplete.

With full combustion, the reaction proceeds to the end, i.e. Before the formation of substances, unable to interact with each other, with a flammable and oxidizing agent (the initial ratio of the fuel and oxidant is called stoichiometric). As an example, consider the complete burning of methane flowing by reaction

Ch 4 + 2O. 2 = Co. 2 + 2H. 2 O.+ Q.

Where Q. - heat released as a result of the flow of exothermic reaction, J..

With full combustion of hydrocarbons, reaction products are carbon dioxide and water, i.e., non-toxic and non-combustible substances. Complete combustion can be realized both in the stoichiometric ratio of the fuel and oxidant, and during an excess of the oxidant with respect to its stoichiometric content in a combustible mixture.

Incomplete combustion is characterized by the incompleteness of the chemical reaction, i.e. Reaction products in the presence of an oxidant can further interact with it. There is incomplete combustion with insufficient (compared to the stoichiometric) content of the oxidizing agent in the combustible mixture. As a result of incomplete combustion, for example, hydrocarbons, the formation of toxic and combustible components such as Co., H. 2, benzpins, FROM (soot), organic resins, etc., only about 300 chemical compounds and elements.

All other things being equal in complete combustion, higher temperatures are developing than in incomplete.

2.4.2.2. The main mechanisms of combustion processes.

The burning is accompanied by the release of heat and the radiation of light and arises in the conditions of progressive self-confidence of the process associated with the accumulation of heat in the heat system ( thermal burning) or catalyzing active intermediate reaction products ( chain burning).

Thermal combustion is possible at an exothermic reaction, the speed of which is rapidly increasing under the influence of the heat accumulating in the system, leading to an increase in temperature. When the temperature is reached, in which the arrival of heat from the reaction exceeds the thermal losses into the environment, the system self-desepression occurs, ending with the self-ignition of the combustible mixture. Under these conditions, spontaneous development of the reaction was observed, accompanied by heating the products formed to such a temperature at which they begin to radiate light (more than 900 ° S.). The thermal burning includes processes and with the participation of oxygen air, and without it (decomposition of explosives, ozone, acetylene, peroxides (for example, N. 2 ABOUT 2), the interaction of some metals with halogens, sulfur, etc.).

Chain burning is possible only with reactions for which the basis of ignition or explosion is a chain process. The latter is accompanied by the formation of unstable intermediate reaction products regenerating active centers (atoms and molecules having free chemical bonds) that accelerate the process. The accumulation of sufficient number of active centers contributes to the transition of the chain process in thermal and increase the temperature of the mixture to the point of its self-ignition. There are such active centers as a result of an increase in the speed of the thermal oscillatory movement of molecules, and increase due to the branching of the chains. At the initial stages of reactions flowing through the chain mechanism, the chemical energy of the reactive substances passes mainly into the formation of new active centers. The process of changing the concentration of active centers is described by the equation:

where n. - the number of active centers in the reaction zone;

τ - time;

w. 0 - the rate of origin of active centers;

φ - Constant, characterizing the difference of ramifications and circuit breaks.

From the standpoint of the molecular-kinetic theory (MKT) of the structure of matter, the chemical combustion reactions occur as a result of the interaction of fuel and oxidant molecules. The forces of molecular interaction between the two components of the combustible mixture are manifested in a very small distance, and with an increase in the latter decreasing sharply. Therefore, the interaction between the fuel and oxidizer molecules is possible only with their full convergence, which can be considered as collision. Consequently, the chemical reaction between the combustible and oxidant must precede the mixing of components and the physical act of the elastic collision of molecules.

The number of collisions of gas molecules per unit volume is easily calculated. For example, for a stoichiometric mixture of hydrogen and oxygen (2 N. 2 + ABOUT 2) at a temperature of 288 TO and atmospheric pressure (~ 101325 PA) Number of collisions for 1 from in 1 cM 3. Reaching 8.3 · 10 28. If all these collisions led to a chemical reaction, the entire mixture would react very quickly. Practice shows that under these conditions, the combustion reaction does not proceed at all, because All these collisions do not lead to chemical interaction.

In order for the chemical reaction to occur, the reacting molecules must be in an excited state. Such an excitation can be chemical when the atoms of molecules have one or two free valences (such molecules are called radicals and are indicated, for example, SN 3 , IS HE , SN 2, etc.) and physical when, as a result of slow heating, the molecule acquire kinetic energy above the critical value.

Molecules with the necessary energy reserve for breaking or weakening existing connections are called active chemical reaction centers.

The difference between the average levels of the energy of the molecules in the active state and are in normal, i.e. an inactive, unexcited state, is called activation energy ( E. but). The higher the numerical value of the activation energy, the harder it is to force this pair of reagents to enter the chemical reaction and vice versa. Therefore, activation energy is as if an indirect indicator of the degree of fire hazard of combustible substances.

It is possible to estimate the amount of activation energy by the formula:

where E. but- activation energy, J.;

k. - Permanent Boltzmanna, equal to 1.38 · 10 -23 J / K.;

T.- absolute temperature, TO.

The nature of the underlying chemical combustion process depends on a number of physical processes:

- movement of reacting substances and reaction products (diffusion processes);

- allocations and propagation of heat (heat transfer processes);

- aero and hydrodynamic conditions providing heat transfer and substance (convection processes).

The need for accounting of these factors significantly complicates the study and theoretical description of combustion processes.

The combustion of solids that do not form when heating the gas (steam) phase is heterogeneous and flows on the surface of the phase section, therefore, along with the factors considered above, the size and nature of the solid phase surface play an extremely important role (this is especially important for aerosols).

2.4.2.3. Impulses of ignition.

For the occurrence of combustion, in addition to the combustible substance and the oxidizing agent, the initial energy impulse is necessary (more often than the allocation of heat), which causes the ignition of a small volume of combustible mixture, after which the combustion spreads throughout the space in which it is distributed.

The impulse of ignition may occur in the flow of physical, chemical and microbiological processes that contribute to the formation of heat. Depending on the nature of these processes, impulses are respectively and divided into Physical, chemical, I. Microbiological.

Since, when exposed to a physical impulse system, heat is allocated, which is not the result of the chemical process, then this pulse is considered as thermal. The effect of the thermal pulse causing the heating system may be:

– contact - heat transfer is carried out by contacting the combustible mixture with its source;

– radiation- heat transfer of the combustible mixture occurs with electromagnetic radiation from the heating source;

– convection - heat transfer of the combustible system is made by substance (air or other gas located in motion);

– hydraulic (dynamic) - the formation of heat due to the rapid decrease in the volume of the gas mixture, accompanied by an increase in pressure of the latter.

The main sources of thermal impulse are:

- Open flame (temperature ~ 1500 ° S.);

- Heated surfaces (Temperature\u003e 900 ° S.);

- Mechanical sparks (Temperature ~ 1200 ° S.)

- Electric sparks (temperature up to 6000 ° S.).

With chemical and microbiological impulses, the accumulation of heat in the system occurs due to the chemical reaction, the physicochemical process (for example, adsorption) and the vital activity of microorganisms for which the fuel substance is food.

2.4.2.4. The rate of combustion reactions.

The speed of the combustion process in general is determined by the equation:

where but , B. - concentration of reacting components;

τ - time,

where m, N. - Concentration of combustion products.

Increasing the combustion rate is accompanied by an increase in the amount of heat entering the system per unit of time, and, as a result, the increase in the combustion temperature.

2.4.2.5. Combustion temperature.

When combustion, not all selected heat is spent on an increase in the temperature of the reaction mixture, since it is consumed as losses for:

- chemical and physical unsenha, taken into account by the non-delivery ratio ( β );

- Electromagnetic flame radiation, depending on the temperature of the emitting body, its aggregate state and chemical nature. This dependence is determined by the refrigerant black coefficient ( ε ) and the wavelength of electromagnetic radiation;

- Conductive-convective losses.

Based on this, the combustion processes distinguish 3 main types of temperatures:

- calorimetric;

- theoretical (calculated);

- actual.

The calorimetric temperature is achieved in the case when all the heat released during the combustion process is spent on the heating of combustion products, for example, when burning benzene - 2533 TO, gasoline - 2315 TO, hydrogen - 2503 TO, Natural Gas - 2293 TO.

Theoretical (calculated) temperature is determined taking into account the heat loss on the dissociation of combustion products. Significant dissociation of combustion products of hydrocarbon combustible substances begins at temperatures\u003e 2000 TO. Such high temperatures in the fires under production conditions are practically not found, therefore, the loss of dissociation heat in these cases is usually not taken into account.

The actual combustion temperature is determined taking into account the losses of heat into the environment and almost for all combustible substances is ~ 1300 - 1700 TO.

Combustion - complex-chemical process

Combustion - These are intense chemical oxidative reactions that are accompanied by heat release and glow. The combustion occurs in the presence of a fuel, oxidizing agent and source of ignition. As oxidants, oxygen, nitric acid, sodium peroxide, bertolet salt, perchlorates, nitrogenation, etc. can be performed as oxidizing in combustion; many organic compounds, sulfur, hydrogen sulfide, cchedan, t. d.

Combustion - complex physico-chemical process of transformation of starting materials in combustion products duringaccompanied by intense release. Chemical energy, stored in the components of the initial mixture, may also be allocated asand light. The luminous zone is called the front of the flame or simply .

played a key role in the development of human civilization.opened people the possibility of cooking and heating dwellings, and subsequently - developmentand creating new, more advanced tools and technologies.

The burning still remains the main source of energy in the world and will remain as in the nearest foreseeable perspective. In 2010, approximately 90% of the entire energy produced by humanity on Earth was mined with incinerationor , and forecasts , this share will not fall below 80% to 2040 while increasing energy consumption by 56% in the period from 2010 to 2040 . These are connected with thismodern civilization like exhaustion, environment I..

Features of burning, distinguishing it from other types, - this is bigand big , leading to a strong dependence of the reaction rate on temperature. The combustion reactions, as a rule, are followed by an extensive chain mechanism with progressive self-confidence due to heat released in the reaction. As a result, the combustible mixture, capable of stored at room temperature for a long time, can ignore orwhen the critical ignition temperature is reached ( ) or when initiating an external energy source (forced ignition, or ignition).

If the products formed during the combustion of the initial mixture in a small amount in a short period of time make a significant mechanical work and lead to shock and thermal effects on the surrounding objects, this phenomenon is called an explosion. Burning and explosion processes make up the basis for creating, , and various types of conventional weapons.

More than 90% of the entire energy used by humanity today is produced during the combustion process. The beginning of scientific research on the theory of combustion was made by the Russian scientist Michelson V.A.

Combustion - A complex physico-chemical process of transformation of the initial combustible substances and materials into combustion products, accompanied by intensive heat release, smoke and light radiation of the flame torch.

To occur in such a physicochemical reaction underlying any fire, it is necessary to have three required components: a combustible medium, a ignition source and an oxidizing agent.

Fuel environment - Wednesday capable of self-burn after removing the ignition source.

Ignition source - This is a thermal source with sufficient temperature, energy and duration of action for igniting.

Split combustion kinetic and diffusion.

Kinetic burning It is the combustion of pre-mixed combustible gases and oxidizing agent.

Diffusion burning - This is a combustion at which the oxidizer enters the combustion zone from the outside. Diffusion burning, in turn, is laminar (calm) and turbulent (uneven) in time and in space.

Depending on the aggregate state of the initial combustible substance distinguish homogenic, heterogeneous burning and combustion of condensed systems.

For homogenic burning Oxidizer and fuel are located in the same aggregate state. This type includes combustion of gas mixtures (natural gas, hydrogen, propane, etc. with oxidizing agent - usually oxygen).

For heterogeneous burning Source (for example, a solid or liquid fuel and gas oxidizer) are located in different aggregate states. Solids converted into dust (coal, textile, vegetable, metallic), with air mixing with air form fire-free mixtures.

Combustion condensed systemsrelated to the transition of a substance from a condensed state to gas.

Depending on the speed of the spread of the flame, combustion may be delable - at a speed of several m / s, explosive - speed of about tens and hundreds m / s and detonation - Hundreds and thousands of m / s.

For delable Or the normal propagation of burning is characteristic of heat transfer from the layer to the layer. As a result, the front of the flame moves towards the combustible mixture.

Explosivethe burning is the combustion process with rapid energy release and the formation of overpressure (more than 5 kPa).

For detonation Burning (detonation) The spread of the flame occurs at a speed close to the sound speed or exceeding it.

Detonation There is a process of chemical transformation of the oxidizer system - a reducing agent, which is a totality of a shock wave propagating at a constant speed, and following the front of the chemical transformation zone of the source substances. The chemical energy released in the detonation wave feeds the shock wave without giving it to fond.

The speed of the detonation wave is the characteristic of each specific system. For heterogeneous systems, a low-speed detonation is characterized by the specifics of the gas reaction - a solid. When detonating gas mixtures of the flame propagation rate are (1-3) ∙ 10 3 m / s and more, and the pressure at the front of the shock wave (1-5) MPa and more.

The combustion is characterized by dangerous factors called dangerous fire factors.

Under firemanit is understood as uncontrolled burning, causing material damage, harm of the life and health of citizens, the interests of society and the state.

TO dangerous fire factors (According to GOST 12.1.004-91) include:

Flame and sparks;

Increased ambient temperature;

Reduced oxygen concentration;

Toxic burning products

Thermal decomposition.

Flame - This is the visible part of the space (fiery zone), within which the oxidation, smoke formation and heat generation processes flow, and toxic gaseous products are generated and the oxygen is absorbed from the surrounding space.

The flame in a quantitative relation is mainly characterized by the following values:

Burning area ( F. 0 , m 2), - burnout speed ( Ψ , kg / s), - heat output ( Q. mountains , W) - optical smoke ( Ψd., NEPER ∙ M 2 ∙ kg -1).

Features of burning in a fire, in contrast to other types of burning, are: a tendency to spontaneous spread of fire; A relatively low degree of completeness of combustion and intensive separation of smoke containing full and incomplete oxidation products.

Three zones are formed on fires:

- George Zonei am a part of the space in which the preparation of substances to burning (heating, evaporation, decomposition) and the combustion itself.

- Heat exposure area - A part of the space adjacent to the burning zone in which the thermal impact leads to a noticeable change in the state of materials and structures, and where people are not possible without special thermal protection.

- Zone smoke- Part of the space adjacent to the combustion zone and located both in the heat-exposure zone and outside it and filled with smoke gases in concentrations, threatening life and health of people.

The combustion can be carried out in two modes: self-ignition and distribution Front fame.

Flame spread - the process of propagation of burning on the surface of the substance and materials due to thermal conductivity, heat radiation (radiation) and convection.

Evaluating dynamics of fire development Several of its main phases can be distinguished:

- 1 phase (up to 10 minutes) - the initial stage, including the transition to fire in the fire for about 1-3 minutes and the growth of the combustion zone for 5-6 minutes. At the same time, it takes place mainly linear spread of fire along combustible substances and materials, which is accompanied by plenty of smoke.

- 2 phase - The stage of the volume development of a fire, which occupies 30-40 minutes, is characterized by a rapid combustion process with a transition to volumetric burning. The process of spreading the flame is remotely due to the transfer of combustion energy to other materials. Maximum values \u200b\u200breaches a temperature (up to 800-900 o C) and burnout rates.

The stabilization of the fire at maximum values \u200b\u200boccurs on 20-25 minutes and continues for another 20-30 minutes, while burning the bulk of combustible materials.

- 3 phase- Fire attenuation phases, i.e. Traveling in the form of slow raid. After that, the fire stops.

According to ISO No. 3941-77, fires are divided into the following classes:

- class A. - fires of solids, mainly organic origin, the burning of which is accompanied by a decrease (wood, textiles, paper);

- class B.- fires of combustible fluids or melting solids;

- class S. - Fires gases;

- class D. - fires of metals and their alloys;

- e. class - Fires associated with the burning of electrical installations.

Characteristics The combustible mixture in the indicators of fire hazing are:

Combustion groups

Concentration limits of flame distribution (ignition),

Flash temperature, ignition and self-ignition temperature.

A combustion group - An indicator that is applicable to the following aggregate states of substances:

- gaza - substances, the absolute pressure of the steam of which at a temperature of 50 ° C equals or more than 300 kPa or the critical temperature of which less than 50 ° C;

- liquids - substances with a melting point (dropping) less than 50 o C;

- solids and materials with a melting point (dropping) more than 50 ° C;

- dust - Dispersed substances and materials with particle size of less than 850 μm.

Spray - The ability of a substance or material to burning. In combustion, they are divided into three groups.

Non-combustible (non-regulations) - Substances and materials that are not capable of burning in air. Non-combustible substances can be fire hazardous, (for example, oxidizing agents, as well as substances that allocate combustible products when interacting in water, air oxygen or each other).

Harmony (epoprietia) - Substances and materials that can focus in the air from the ignition source, but unable to burn independently after removing it.

Gorry(burned) - Substances and materials capable of self-turn, as well as to focus in the air from the ignition source and independently burn after it is removed.

From this group allocate easy flammable substances and materials- capable of flammable from short-term (up to 30 seconds) effects of low-energy ignition source (flame match, spark, smoldering cigarette, etc.).

Concentration limits of ignition - The minimum and maximum concentration (mass or volume fraction of fuel in the mixture with an oxidation medium), expressed in%, g / m 3 or l / m 3, below (above) which the mixture becomes incapable of spreading the flame.

Distinguish the lower and upper concentration limits of flame propagation (respectively NKPRP and VKPRP).

NKPRP (VKPRP)- minimal (maximum) fuel content in the mixture (fuel - oxidative medium), in which the flame propagation is possible on the mixture at any distance from the ignition source. For example, for a mixture of natural gas consisting mainly of methane, the concentration limit of ignition (detonation combustion) is 5-16%, and the explosion explosion is possible at a content of 21 liters of gas in 1 m 3, and the ignition is at 95 liters.

Flash temperature (t. pm) - The minimum temperature of the combustible substance, at which gases and pairs are formed on its surface, capable of flashing in the air from the ignition source, but the speed of their education is still insufficient for sustainable burning.

Depending on the numerical value T. pm liquids relate to flammable (LVZ) and furious (Gzh.). In turn LVZH are divided into three discharge in accordance with GOST 12.1.017-80.

Especially dangerous LVZH - these are combustible fluids with t. pm From -18 about C and lower in closed or from -13 ° C in open space. These include acetone, diethyl ether, isopentane, etc.

Constantly dangerous LVZ. - these are combustible fluids with t. pm From -18 ° C to +23 ° C in closed or from -13 ° C to 27 ° C in open space. These include benzene, toluene, ethyl alcohol, ethyl acetate, etc.

Dangerous at elevated damage - these are combustible fluids with t. pm From 23 ° C to 61 ° C in closed or higher than 27 ° C to 66 ° C in open space. These include turbid, White Spirit, Chlorbenzene, etc.

Flash temperature is used to determine the categories of buildings and external plants for explosion and fire hazards according to the NPB 105-03, as well as when developing measures to ensure fire and explosion safety processes.

Self-ignion temperature - The lowest temperature of the substance at which there is a sharp increase in energy rate.

The concept of " explosion"Used in all processes that can cause a significant increase in the pressure in the environment.

Based on GOST R 22.08-96 explosion- This is the process of energy release in a short period of time associated with an instantaneous physicochemical change in the state of the substance leading to the occurrence of a pressure jump or shock wave, accompanied by the formation of compressed gases or vapors capable of producing work.

The following types of explosions are possible on explosive objects:

- explosive processes - uncontrolled sharp release of energy in a limited space;

- volume explosion - the formation of clouds of fuel-air or other gaseous, dusty mixtures and their rapid explosive transformations;

- physical explosions - explosions of pipelines, vessels under high pressure or superheated liquid.

Emergency explosion - Emergency situation arising from a potentially dangerous object at any time in a limited space spontaneously, by coincidence or as a result of erroneous actions of personnel working on it

The causes of explosions are mainly:

Violation of technological regulations;

External mechanical impacts;

Aging equipment and installations;

Design errors;

Changing the state of the sealed medium;

Errors of the service personnel;

Fault of control and measuring, regulating and safety devices.