Methods for extinguishing gzh and lvzh. What liquids are lvzh and gzh What liquids burn

By burning is called a chemical reaction of oxidation of a substance, accompanied by the release of a large amount of heat and usually a bright glow (flame). The combustion process is possible in the presence of three factors: a combustible substance, an oxidizer and a source of ignition (impulse). Oxidizing agents can be oxygen, chlorine, fluorine, bromine, iodine, nitrogen oxides.

Burning can result from flash, ignition, ignition, spontaneous combustion, self-ignition or explosion of a combustible substance.

Flash is a rapid combustion of a combustible mixture, not accompanied by the formation of compressed gases when an ignition source is introduced into it. In this case, the amount of heat that is formed during the short-term process of the outbreak turns out to be insufficient for the continuation of combustion.

Combustion - the phenomenon of occurrence of combustion under the influence of an ignition source. Ignition sources can be flame, radiant energy, spark, hot surface, etc.

Ignition Is a fire accompanied by the appearance of a flame. In contrast to a flash, the amount of ignition heat transferred to the combustible from the ignition source is sufficient to continue combustion, i.e. for the timely formation of vapors and gases above the surface of a substance capable of burning.

In this case, the entire remaining mass of the combustible substance remains relatively cold.

Spontaneous combustion– the phenomenon of a sharp increase in the rate of oxidation of a substance, leading to the occurrence of combustion in the absence of an ignition source. Oxidation takes place due to the adsorption of oxygen in the air and constant heating of the substance due to the heat of the chemical oxidation reaction. Cleaning materials impregnated with industrial oil, peat, coal, etc. can ignite spontaneously.

Self-ignition- This is spontaneous combustion, accompanied by the appearance of a flame.

Explosion (explosive combustion) Is the combustion of a substance, accompanied by an extremely rapid release of a large amount of energy, which causes heating of combustion products to high temperatures and a sharp increase in pressure.

By fire called uncontrolled combustion outside a special hearth.

Inhibition- intensive slowing down of the rate of chemical reactions of oxidation in the flame.

All combustible substances can be in liquid, gaseous and solid state.

Flammable liquids. The main parameters of the flammable properties of a liquid are the flash point, ignition and autoignition points, as well as the concentration and temperature limits of ignition of a mixture of liquid vapors with air.

Flash point is one of the main features that determine the fire hazard of liquids.

Liquids, depending on the flash point of vapors, are divided into two classes:

1.Flammable liquids (FL) with a flash point not exceeding 61 * C (in a closed crucible) or 66 * C (in an open crucible). Such liquids are, for example, gasoline, acetone, etc .;

2.flammable liquids (FL) with a flash point above 61 * C (in a closed crucible), for example, oil, fuel oil, etc.

Ignition temperature is called the temperature of a combustible substance at which it emits combustible gases and vapors at such a rate that after they are ignited from the ignition source, stable combustion occurs.

Autoignition temperature is of great importance for assessing the explosion hazard of processes proceeding under pressure in closed vessels. It characterizes the possibility of the beginning of a fiery combustion of a substance when it comes into contact with atmospheric oxygen.

The most dangerous are liquids with a self-ignition temperature of less than 15 * C

A mixture of combustible substances with an oxidizer is capable of burning only with a certain amount of fuel in it. Lower (upper) concentration flammable limit the minimum (maximum) possible spread of the flame through the mixture at any distance from the ignition source is called.

Ignition temperature limits- these are the temperatures of the combustible substance at which its saturated vapors form in a particular oxidizing environment concentrations equal to the lower and upper concentration limits of ignition, respectively.

Combustible gases. The main parameters of the explosiveness of combustible gases are the lower and upper concentration limits of ignition, characterized by the volume fraction of combustible gases in the mixture (%). The interval between the lower and upper concentration limits is called the area of ​​ignition. Only in this area is the mixture capable of being ignited by an ignition source, followed by flame propagation. For example, the lower and upper limits of ignition in a mixture with air are (in%): for ammonia - 15 and 288, for hydrogen - 4 and 75, for methane - 5 and 15. At concentrations less than the lower limit, the mixture is poor in combustible and released during a flash not enough heat to ignite other particles. At concentrations above the upper limit, the mixture is too rich in flammable and ignition does not occur due to the lack of oxidizing agent.

All substances flammable and ignitable , are divided into 8 groups:

1 - Explosives - nitroglycerin, tetryl, TNT, ammonites. dynamite; 2– Explosive substances - dinitrochlor, benzene, nitric acid esters, ammonium nitrate;

3 - Substances capable of forming explosive mixtures with organic products, - potassium perchlorate, sodium, potassium and barium peroxides, potassium nitrate, barium, calcium, sodium;

4 - Compressed and liquefied gases:

a) flammable and explosive gases - hydrogen, methane, propane, ammonia, hydrogen sulfide;

b) inert and incombustible gases - argon, helium, neon, carbon dioxide, sulfur dioxide;

c) gases supporting combustion - compressed and liquid oxygen and air.

5 - Substances that ignite spontaneously on contact with air or water,- metallic potassium, sodium and calcium, calcium carbide, phosphorous calcium and sodium, zinc dust, aluminum powder, pyrophoric messalic powders and compounds.

6 - Flammable and combustible substances:

a) liquids - gasoline, benzene, carbon disulfide, acetone, xylene, turpentine, kerosene, toluene, organic oils, amyl acetate, ethyl and methyl alcohols;

b) solids - red phosphorus, naphthalene;

7 - Substances liable to cause inflammation, - bromine, nitric, sulfuric and chlorosulfonic acids, potassium permanganate.

8 - Flammable substances- cotton, sulfur, soot.

The occurrence of fires in buildings and structures, the characteristics of the spread of fire depend on what materials these buildings and structures are made of, what their dimensions are.

The ability of building materials and structures to ignite, burn or smolder under the influence of fire or high temperature is called flammability.

By the degree of flammability building materials and structures are divided into three groups:

non-combustible- under the influence of an ignition source (fire, high temperature), they do not ignite, do not smolder and do not char (for example, concrete, reinforced concrete, brick, etc.;)

hardly combustible- under the influence of an ignition source, they are difficult to ignite, smolder or char and continue to burn or smolder only in the presence of an ignition source. After removing the source of fire, combustion and smoldering cease. Non-combustible include gypsum and concrete products with organic fillers, wood impregnated with fire-resistant compounds, etc .;

combustible- ignites under the influence of a source of ignition and continues to burn or smolder after its removal. Combustible are timber, bitumen, roofing felt, and many plastic materials.

The flammability of building structures is determined, as a rule, by the flammability of materials. However, in some cases, the flammability of structures is less than the flammability of its constituent materials.

The ability of structures to resist the effects of fire over time while maintaining their operational properties is called fire resistance.

Fire resistance of structures is characterized by the fire resistance limit, which is the time after which the structure loses its load-bearing or enclosing capacity in case of fire.

Fire resistance buildings are divided into 5 degrees, while the fire resistance limit decreases with increasing degree. For example, in buildings of 1 and 2 degrees of fire resistance, all structures (walls, ceilings, coatings, partitions) are made of non-combustible materials with fire resistance limits from 0.25 to 4 hours.

In buildings of the 3rd degree, the walls are made of non-combustible materials, ceilings and partitions are made of non-combustible materials, and the combined coatings are made of combustible materials. Buildings of 4 degrees of fire resistance have walls and ceilings made of non-combustible materials, and combined coatings and partitions are made of combustible materials. In buildings of the 5th degree, all structures are made of combustible materials.

Assessment of fire, explosive and explosion hazard of production.

The conditions contributing to the emergence and development of a fire in industrial premises and determining its possible scale and consequences depend on what substances are used, processed or stored in a given building or structure, as well as on the features of its design and planning solution.

In accordance with building codes and regulations industrial buildings and warehouses for explosive, explosion and fire hazard are divided into 6 categories: A, B, C, D, D, E.

Category A- explosive production associated with the use of flammable gases, the lower explosive limit of which is 10% or less than the volume of air; liquids with a flash point of vapors up to 28 * C inclusive, provided that these gases and liquids can form explosive mixtures in a volume exceeding 5% of the volume of the room; substances that can explode and burn when interacting with water, atmospheric oxygen or with each other.

Category A includes industries associated with the use of metallic sodium and potassium, acetone, carbon disulfide, ethers and alcohols (methyl and ethyl, etc.), as well as painting shops, areas with the presence of liquefied gases. By rail. transport - these are points and depots for washing and degassing tanks from flammable liquids (flammable liquids), which include gasoline, benzene, crude oil, etc., warehouses for dangerous goods, paint shops, in which nitro paints, varnishes and solvents are used from flammable liquids with a vapor flash point of 28 * C and below, etc.

Category B- explosive and fire hazardous industries associated with the use of flammable gases, the lower explosive limit of which is more than 10% of the air volume; liquids with a flash point of vapors from 28 to 61 * С inclusive; liquids heated under industrial conditions to a flash point and above; combustible dusts and fibers, the lower explosive limit of which is 65 g / m3 cubic and less to the volume of air, provided that these gases, liquids and dusts can form explosive mixtures in a volume exceeding 5% of the volume of the room. This category includes workshops, sections, departments of carriage, locomotive, motor car depots and workshops of factories with the production of painting works and the use of alcohol varnishes and paints with a flash point of pores from 28 to 61 * C inclusive, warehouses and storerooms of specified varnishes and paints, warehouses diesel fuel, pumping and unloading racks for overflowing this fuel, repair shops for diesel locomotives with flushing fuel tanks, etc.

Category B- fire hazardous industries associated with the use of liquids with a vapor flash point above 61 * C; combustible dusts or fibers, the lower explosive limit of which is more than 65 g / m3 cubic to the volume of air; substances that can only burn when interacting with water, atmospheric oxygen or with each other; solid combustible substances and materials. Examples of production in this category are the lubrication facilities of locomotive and carriage depots and factories, the oil facilities of traction substations, sleepers impregnation and sleepers repair plants, and timber warehouses. container bases, ticket offices, communication houses, libraries, etc.

Category D- production related to the processing of non-combustible substances and materials in a hot, molten or incandescent state, accompanied by the release of radiant heat, sparks and flame; solid. liquid and gaseous substances that are burned or disposed of as fuel. This category of industries includes diesel locomotive depots, hot stamping shops, casting, bandage, carriage, welding sections of various shops, forging shops, etc.

Category D- production related to the processing of non-combustible substances and materials in a cold state. These include workshops for cold metal working, blowing and compressor stations, electric locomotive depots, etc.

Category E- explosive production associated with the use of flammable gases without a liquid phase and explosive dust in such an amount that they can form explosive mixtures in volume. exceeding 5% of the volume of the room, and when, according to the conditions of the technological process, only an explosion is possible (without subsequent combustion); substances that can explode (also without subsequent combustion) when interacting with water, atmospheric oxygen or with each other. Productions of category E are batteries, sections and stations for the production of acetylene, premises for automatic telephone exchanges, stations for signaling and communication, etc.

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According to the "Rules for Electrical Installations", the definition of a combustible liquid sounds rather laconic - it is a liquid that flares up at a temperature of more than 61 ℃, after which it continues to burn independently without external initiation or influence. A flammable liquid according to the PUE is a GJ with a flash point of not more than 61 ℃, and those that have an evaporation pressure of at least 100 kPa at T = 20 ℃ are explosive.

GZh are classified as fire hazardous materials, but they are explosive if heated up to T flash during the technological process.

Such a preliminary categorization of protected objects allows at the design stage, the start of operation to make organizational, technical solutions for selection, installation, suitable for the requirements of regulatory documents, for example, such as types, types, incl. explosion-proof flame detectors, smoke detectors for APS installations, stationary fire extinguishing systems; for the elimination of primary foci of fire in rooms with the presence of flammable liquids, combustible liquids.

Additional information in the table:

A source: Yu.A. Koshmarov Predicting Indoor Fire Hazards: A Tutorial

Flammable liquid fire class

Flammable and combustible liquids due to their parameters during combustion both in closed premises of industrial, warehouse buildings, technological structures, and on open industrial sites; where external installations for the processing of oil, gas condensate, devices for chemical organic synthesis, storage facilities for raw materials, finished products are located in the event of hot spots, the spread of a fire, it is classified as class B.

The symbol of the fire class is applied to containers with flammable and combustible liquids, objects of their storage, which allows you to quickly make the right choice, reducing the time for exploration, localization and elimination of foci of ignition of such substances, their mixtures; to minimize material damage.

Classification of flammable liquids

The flash point of a combustible liquid is one of the main parameters for the classification, assignment of GF to one type or another.

GOST 12.1.044-89 defines it as the lowest temperature of a condensed substance having vapors above the surface that can flare up in the air of a room, or in an open space when a low-calorie source of open flame is brought up; but a stable combustion process does not arise in this case.

And the flash itself is the instantaneous burnout of an air mixture of vapors, gases above the surface of a combustible liquid, which is visually accompanied by a short period of visible glow.

The value of T ℃ obtained as a result of tests, for example, in a closed laboratory vessel, at which the GJ flashes, characterizes its explosion and fire hazard.

Important parameters for combustible liquids, flammable liquids specified in this state standard are also the following parameters:

• Ignition T is the lowest temperature of flammable liquids that emit flammable gases / vapors with such an intensity that when a source of open fire is brought up, they ignite, continuing to burn when it is removed.
• This indicator is important when classifying the flammability groups of substances, materials, hazards of technological processes, equipment in which GF are involved.
• T self-ignition is the minimum temperature of the GF at which self-ignition occurs, which, depending on the prevailing conditions in the protected room, storage facility, body of technological equipment - apparatus, installation, may be accompanied by burning with an open flame and / or explosion.
• The data obtained for each type of combustible liquids capable of self-ignition allows the selection of suitable types of electrical equipment in explosion-proof design, incl. for installations of buildings, structures, structures; for the development of measures for explosion and fire safety.

For information: "PUE" defines an outbreak by rapid burnout of a combustible air mixture without the formation of compressed gas; and the explosion - by instantaneous combustion with the formation of compressed gases, accompanied by the appearance of a large amount of energy.

Also important are the rate and intensity of the evaporation of hot liquids, flammable liquids from a free surface with open reservoirs, containers, and casings of technological units.

GZh fires are also dangerous for the following reasons:

• These are spreading foci of fires, which is associated with the pouring, free spreading of flammable liquids over the areas of premises or the territory of enterprises; if no isolation measures have been taken - dumping of storage tanks, external technological units; the presence of building barriers with walls installed in the openings.
• GZh fires can be both local and volumetric, depending on the type, storage conditions, volume. Since volumetric combustion intensively affects the supporting elements of buildings, structures, it is absolutely necessary.

It should also:

• Install on the air ducts of ventilation systems in rooms where there are combustible liquids to limit the spread of heat through them.
• Conduct for shift, operational / duty personnel, organize those responsible for the fire condition of storage facilities, processing, transportation, transit of flammable liquids, combustible liquids, leading specialists, engineering and technical personnel; conducting regular practical trainings with members of the DPD of enterprises, organizations; toughen the process, carry out strict control over the venue, incl. after graduation.
• Install on chimneys, exhaust pipes of heating, power units, stoves, install on pipelines of the technological chain for the transportation of flammable and combustible liquids through the territory of industrial enterprises.

The list, of course, is far from complete, but all the necessary measures can be easily found in the regulatory and technical base of industrial safety documents.

How to properly store flammable liquids and combustible liquids, probably this question is asked by most people. The answer can be found in the "Technical Regulations on Fire Safety Requirements" dated 22.07.2008 No. 123-FZ ", in Table 14 Categories of warehouses for storing oil and oil products. For more information on storage and distance to objects, see. (SP 110.13330.2011)

Extinguishing class B fires, according to the standards, is carried out as follows:

• Air-mechanical foam obtained from aqueous solutions of a foaming agent. They are especially effective for extinguishing industrial, warehouse buildings.
• Fire extinguishing powder, for which it is used.
• They are used for small in area, volume of premises, compartments, for example, fuel and lubricants supply depots, engine rooms.

The use of sprayed water to extinguish the flame of gasoline and other combustible liquids with a low flash point is difficult, since water droplets cannot cool the heated surface layer below the flash point. The decisive factor in the mechanism of fire extinguishing action of the VMP is the insulating capacity of the foam.

When the liquid burning mirror is covered with foam, the flow of liquid vapors into the combustion zone stops, and combustion stops. In addition, the foam cools the heated layer of liquid by the evolving liquid phase - the compartment. The finer the foam bubbles and the greater the surface tension of the foaming agent solution, the higher the insulating capacity of the foam. Inhomogeneity of the structure, large bubbles reduce the effectiveness of the foam.

Elimination of hotbeds of flammable liquids, combustible liquids is also carried out for especially important objects of protection; as well as for premises with different types of fire loads, which are difficult or impossible to extinguish with a single fire extinguishing agent.

Table of the rate of supply of a 6% solution when extinguishing flammable liquids with air-mechanical foam based on the PO-1 foam concentrate

According to . V.P. Ivannikov, P.P. Klus,

Notes:

An asterisk indicates that extinguishing with low expansion foam of oil and oil products with a flash point below 280 C is allowed in tanks up to 1000 m 3, excluding low levels (more than 2 m from the upper edge of the tank side).

When extinguishing petroleum products using the PO-1D foaming agent, the intensity of the foaming solution increases by 1.5 times.

Class B fires are combustion of liquid substances that can be soluble in water (alcohols, acetone, glycerin) and insoluble (gasoline, oil, fuel oil).

Just like solids, flammable liquids give off vapors when they burn. The vaporization process differs only in speed - for liquids it happens much faster.

The hazard level of flammable liquids depends on the flash point - the lowest temperature of a condensed substance at which vapors above it can flare up under the influence of an ignition source, but combustion does not occur after its elimination. Also, the degree of danger of flammable liquids is influenced by the flash point, flammability range, evaporation rate, reactivity under the influence of heat, density and diffusion rate of vapors.

Flammable liquids are considered to be liquids with a flash point of up to 61 ° C (gasoline, kerosene), combustible - with a flash point above 61 ° C (acids, vegetable and lubricating oils).

Class B fires

A class B fire can result from the combustion of the following materials:

• paints and varnishes;
• flammable and flammable liquids;
• liquefied solids (paraffins, stearins).

1. Varnishes, paints, enamels. Water-based fluids are less hazardous than oil-based fluids. The flash point of the oils contained in paints, varnishes and enamels is quite high (about 200 ° C), but the flammable solvents contained in them flare up much earlier - at a temperature of 32 ° C.

Paints burn well, producing a lot of thick black smoke and toxic gases. When paints or varnishes ignite, the containers in which they are located often explode.

It is impossible to extinguish paints, varnishes and enamels with water due to the low flash point. Water can only be used to cool the surrounding objects or extinguish dry paint.

The burning of paints and varnishes is suppressed with foam, in some cases - carbon dioxide or dry powder fire extinguishers.

1. Flammable and flammable liquids. Their combustion is accompanied by the release of non-standard combustion products characteristic of just such liquids.

Alcohols burn with a blue transparent fire with a small amount of smoke.

Combustion of liquid hydrocarbons is characterized by an orange flame and the formation of thick, dark smoke.

Esters and terpenes burn accompanied by boiling on their surface.

In the process of burning petroleum products, oils and fats, a poisonous irritating gas, acrolein, is released.

Extinguishing flammable and combustible liquids is not easy, and each fire has its own characteristics and sequence of suppression. First, you need to shut off the ingress of liquid into the fire.

The surrounding objects and containers with burning liquids should be cooled with water. There are several ways to extinguish a class B fire:

• a foam or powder fire extinguisher or a sprayed stream of water can cope with a small fire;
• in the case of a large spread of flammable liquid, it is better to use dry powder fire extinguishers in conjunction with fire hoses to supply foam;
• if the liquid burns on the surface of the water, then first you need to limit its spreading, and then cover the flame with foam or a powerful water jet;
• when extinguishing equipment operating on liquid fuel, spray water or foam must be used.

Paraffins and other similar refined products. Putting them out with water is strictly prohibited and dangerous. Small fires can be suppressed with carbon dioxide fire extinguishers. Large fires - with foam.

Combustion of liquids.

All flammable liquids are capable of evaporating, and their combustion occurs only in the vapor phase located above the surface of the liquid. The amount of vapor depends on the composition and temperature of the liquid. Combustion of vapors in air is possible only at a certain concentration.

The lowest temperature of a liquid at which the concentration of its vapors in a mixture with air ensures the ignition of the mixture from an open ignition source without subsequent stable combustion is called the flash point. At the flash point, stable combustion does not occur, since at this temperature the concentration of the mixture of liquid vapors with air is not stable, which is necessary for such combustion. The amount of heat released during the flash is not enough to continue burning, and the substance is not yet sufficiently heated. In order to ignite a liquid, you need not a short-term, but a long-term ignition source, the temperature of which would be higher than the autoignition temperature of a mixture of vapors of this liquid with air.

In accordance with GOST 12.1.004-76, a combustible liquid (GF) is understood as a liquid that can burn independently after removing the ignition source and has a flash point above + 61 ° C (in a closed crucible) or + 66 ° C (in an open crucible).

A highly flammable liquid (FL) is a liquid that can burn independently after removing the ignition source and has a flash point not higher than + 61 ° C (in a closed crucible) or + 66 ° C (in an open crucible).

Flash point is the lowest temperature at which a liquid becomes especially dangerous in terms of fire, therefore, its value is taken as the basis for classifying flammable liquids according to their degree of fire hazard. The fire and explosion hazard of liquids can also be characterized by the temperature limits of ignition of its vapors.

The temperature of the liquid at which the concentration of saturated vapors in the air in a closed volume is capable of igniting when exposed to an ignition source is called the lower temperature limit of ignition. The temperature of the liquid at which the concentration of saturated vapors in the air in a closed volume can still ignite when exposed to an ignition source is called the upper temperature limit of ignition.

The temperature limits of ignition of some liquids are given in table. 29.

Table 29 The temperature limits of ignition of some liquids: acetone, gasoline A-76, benzene, tractor kerosene, ethyl alcohol.

The temperature limits indicate in which temperature range the liquid vapors will form combustible mixtures with air.

Combustion is a complex physical and chemical process of interaction of a combustible substance and an oxidizer, characterized by a self-accelerating chemical excess and accompanied by the release of a large amount of heat and radiant energy.

For the occurrence and development of the combustion process, a combustible substance, an oxidizing agent and an ignition source are required, which initiates the reaction between the fuel and the oxidizing agent. Combustion is distinguished by a variety of types and characteristics. Depending on the state of aggregation of combustible substances, combustion can be homogeneous and heterogeneous. With homogeneous combustion, the components of the combustible mixture are in the same state of aggregation (more often in gaseous form). Moreover, if the reacting components are mixed, then the combustion of the premixed mixture occurs, which is sometimes called kinetic (since the combustion rate in this case depends only on the kinetics of chemical transformations). If the gaseous components are not mixed, then diffuse combustion occurs (for example, when a flow of combustible vapors enters the air). The combustion process is limited by the diffusion of the oxidant. Combustion characterized by the presence of phase separation in the combustible system (for example, combustion of liquid and solid materials) is heterogeneous. Combustion is also differentiated by the speed of flame propagation, and depending on this factor, it can be deflagration (within a few m / s), explosive (tens and hundreds of m / s) and detonation (thousands of m / s). In addition, combustion can be laminar (layer-by-layer propagation of the flame front along the fresh combustible mixture) and turbulent (mixing of the flow layers with an increased burnout rate).

As a rule, fires are characterized by heterogeneous diffuse combustion, and the rate of combustion depends on the diffusion of atmospheric oxygen in the environment. The emergence and development of fires significantly depends on the degree of fire hazard of substances. One of the criteria for the fire hazard of solid, liquid and gaseous substances is the autoignition temperature, i.e. the ability of a substance to ignite spontaneously.

For the initiation of an endogenous fire, the presence of a substance capable of rapidly oxidizing at low temperatures is necessary, as a result of which spontaneous combustion can occur. This property of the substance is called chemical activity to spontaneous combustion. As a result of oxidation and heat accumulation, self-heating turns into ignition.

Ignition is a qualitatively new process different from self-heating, characterized by high oxidation rates, heat release and light emission. Self-heating and self-ignition are generated by separate small nests, and therefore, it is very difficult to detect it.

Spontaneous combustion occurs due to the accumulation of heat inside the substance and does not depend on the influence of an external heat source.

All substances, according to their danger in relation to spontaneous combustion, can be divided into four groups:

* Substances that can spontaneously ignite upon contact with air at normal temperatures (vegetable oils, drying oil, oil paints, primers, brown and black coals, white phosphorus, aluminum and magnesium powder, soot, etc.);

* substances that can ignite spontaneously at elevated ambient temperatures (50 ° C and above) and as a result of external heating to temperatures close to the temperatures of their ignition and spontaneous ignition (films of nitro-lacquers, pyroxylin and nitroglycerin powders, vegetable semi-drying oils and drying oils made from them, turpentine etc.);

* substances, the contact of which with water causes the combustion process (alkali metals, carbides of alkali metals, calcium carbide, aluminum, etc.);

* substances that cause spontaneous combustion of combustible substances in contact with them (nitric, magnesium, hypochlorous, chloride and other acids, their anhydrides and salts; sodium, potassium, hydrogen peroxides, etc.; gases - oxidizing agents - oxygen, chlorine, etc.).

The most important characteristic of solid bulk materials is the degree of their flammability.

All materials, regardless of the field of application, are divided into three groups:

* Fireproof materials, which, under the influence of fire or high temperature, do not ignite, do not smolder or char.

* Flame retardant materials, which, under the influence of fire or high temperature, ignite, smolder or char and continue to burn or smolder in the presence of a fire source, and after removing the fire source, combustion and smoldering cease.

* Combustible materials, which, when exposed to fire or heat, ignite or smolder and continue to burn or smolder after removal of the fire source.

Certain chemicals, fuels and lubricants in certain concentrations and conditions can not only ignite from heat sources, but also explode.

The fire hazard of substances (gaseous, liquid, solid) is determined by a number of indicators, the characteristics and quantity of which depend on the state of aggregation of the given substance.

Fire hazard criteria for solid, liquid and gaseous substances are: flash point, ignition and self-ignition temperature, flame spread index, oxygen index, smoke production coefficient, toxicity index of combustion products, etc.

One of the criteria for the fire hazard of flammable liquids is the flash point.

Flash point of vapor A combustible liquid is the minimum temperature of the liquid at which, under normal pressure, the liquid releases vapor over its free surface in an amount sufficient to form a mixture with the surrounding air that flares up when an open flame is brought to it.

For flammable liquids(Flammable liquids) include liquids that can burn independently after removing the ignition source and have a flash point of no higher than 61 °? in a closed crucible and 66 ° C in an open crucible.

For flammable liquids(ГЖ) include liquids that can burn independently after removing the ignition source and have a flash point above 61 °? in a closed crucible and 66 ° C in an open crucible.

Ignition temperature is called the minimum temperature at which a liquid heated under certain conditions ignites when a flame is brought to it and burns for (at least) 5s. The flash point is more dangerous than the flash point, since the vapors and liquid, if ignited, continue to burn after the flame has been removed.

During construction work, especially in the preparation of mastics, painting work, it is necessary to clearly know the degree of flammability of nearby materials and structures, properly organize control to prevent fires and provide the necessary amount of extinguishing agents.

Depending on the type of combustible material, fires are divided into classes: A, B, C and D (Fig. 4.2.1.).

Fires are accompanied by dangerous and harmful phenomena that must be taken into account in the design and construction of buildings and structures, in the conduct of work. From the point of view of fire safety, it is very important to make the right planning decision, to offer protection of building structures, to provide for the necessary escape routes.

Explosion is a kind of burning and is characterized by extremely fast processes of physical and chemical transformations of combustible substances with the formation of huge amounts of thermal energy, practically without heat dissipation into the environment.

There are two concentration limits for the explosiveness of substances.

The minimum concentration of gas, vapor or dust in a mixture with air that can ignite or explode is calledlower flammable limit (LP).

The highest concentration of gases or vapors in the air, at which ignition or explosion is still possible (further, with an increase in concentration, ignition or explosion is considered impossible)n calledupper flammable limit (VP).

Explosion differs from combustion by an even greater speed of fire propagation. Thus, the speed of flame propagation in an explosive mixture in a closed tube is 2000 - 3000 m / s. Combustion of a mixture at such a rate is called detonation... The appearance of detonation is explained by the compression, heating and movement of the unburned mixture ahead of the flame front, which leads to acceleration of flame propagation and the appearance of a shock wave in the mixture. The air shock waves formed during the explosion of the gas-air mixture have a large reserve of energy and propagate over considerable distances. While driving, they destroy structures and can cause accidents. The assessment of the danger of air shock waves for people and various structures is carried out according to two main parameters - pressure in the front of the shock wave? P and compression f. The compression phase is understood as the time of action of excess pressure in the wave. When φ? 11 ms, a pressure of 0.9-113 Pa is considered safe for people. Calculations of safe distances for people with a potential explosion threat are carried out only by the pressure in the shock front, since in explosions, f is always many times greater than 11 ms.