What is the difference between lvzh and zhzh. Combustion and flammable properties of substances

Various in chemical composition solid materials and substances burn differently. Simple ones (soot, charcoal, coke, anthracite), which are chemically pure carbon, heat up or smolder without the formation of sparks, flames and smoke. This is due to the fact that they do not need to be decomposed before entering into a combination with atmospheric oxygen. Such (flameless) combustion is usually slow and is called heterogeneous(or surface) combustion. Combustion of chemically complex solid combustible materials (wood, cotton, rubber, rubber, plastic, etc.) proceeds in two stages: 1) decomposition, the processes of which are not accompanied by flame and light emission; 2) proper combustion, characterized by the presence of a flame or smoldering. Thus, complex substances do not burn themselves, but the products of their decomposition burn. If they burn in the gaseous phase, then such combustion is called homogeneous.

A characteristic feature of the combustion of chemically complex materials and substances is the formation of flame and smoke. The flame is formed by luminous gases, vapors and solids, in which both stages of combustion proceed.

Smoke is a complex mixture of combustion products containing solid particles. Depending on the composition of combustible substances, their complete or incomplete combustion, the smoke has a certain color and smell.

Most plastics and man-made fibers are combustible. They burn with the formation of liquefied resins, emit a significant amount of carbon monoxide, hydrogen chloride, ammonia, hydrocyanic acid and other toxic substances.

combustible liquids more flammable than solid combustible substances, since they ignite more easily, burn more intensely, and form explosive vapor-air mixtures. Combustible liquids do not burn on their own. Their vapors are burning above the surface of the liquid. The amount of vapors and the rate of their formation depend on the composition and temperature of the liquid. Combustion of vapors in air is possible only at certain concentrations, which depend on the temperature of the liquid.

To characterize the degree of fire hazard of combustible liquids, it is customary to use the flash point. The lower the flash point, the more dangerous the liquid in terms of fire. The flash point is determined by a special technique and is used to classify combustible liquids according to their degree of fire hazard.

Combustible liquid (GZh) It is a liquid capable of burning on its own after removal of the ignition source and having a flash point of more than 61 °C. Flammable liquid (flammable liquid) It is a liquid with a flash point up to 61°C. Carbon disulphide has the lowest flash point (-50 ºС), linseed oil has the highest (300 ºС). Acetone has a flash point of minus 18, ethyl alcohol - plus 13?

For flammable liquids, the ignition temperature is usually higher than the flash point by several degrees, and for FL by - 30…35?С.

The autoignition temperature is much higher than the ignition temperature. For example, acetone can spontaneously ignite at a temperature of more than 500 ° C, gasoline - about 300 ° C.

Other important properties (in terms of fire) of combustible liquids include high vapor density (heavier than air); low density of liquids (lighter than water) and the insolubility of most of them in water, which does not allow the use of water for extinguishing; the ability to accumulate static electricity during movement; high heat and combustion rate.

combustible gases (YY) represent a great danger not only because they burn, but also because they are able to form explosive mixtures with air or other gases. Thus, all combustible gases are explosive. However, combustible gas can form explosive mixtures with air only at a certain concentration. The lowest concentration of combustible gas in air at which ignition (explosion) is already possible is called lower concentration flammable limit (LEL). The highest concentration of combustible gas in air at which ignition is still possible is called upper concentration flammable limit (UCL). The concentration region lying inside these boundaries is called ignition area. LEL and VKVV are measured in% of the volume of the combustible mixture. When the concentration of combustible gas is less than the LEL and more than the LEL, the mixture of combustible gas and air does not ignite. Combustible gas is the more dangerous in terms of explosion and fire, the larger the ignition area and the lower the LEL. For example, the area of ​​ignition of ammonia is 16...27%, hydrogen 4...76%, methane 5...16%, acetylene 2.8...93%, carbon monoxide 12.8...75%. Thus, acetylene, which has the largest ignition area and the lowest LEL, has the greatest explosion hazard. Other dangerous properties of combustible gases include the large destructive force of the explosion and the ability to generate static electricity when moving through pipes.

combustible dust are formed during the manufacturing process during the processing of some hard and fibrous materials and pose a significant fire hazard. Solids in a highly crushed and suspended state in a gaseous medium create a dispersed system. When the dispersed medium is air, such a system is called aerosol. The dust that settles from the air is called airgel. Aerosols can form explosive mixtures, while aerogels can smolder and burn.

In terms of fire hazard, dusts are many times superior to the product from which they are obtained, since dust has a large specific surface area. The finer the dust particles, the more developed its surface and the more dangerous the dust in terms of ignition and explosion, since the chemical reaction between the gas and the solid, as a rule, proceeds on the surface of the latter and the reaction rate increases as the surface increases. For example, 1 kg of coal dust can burn in a fraction of a second. Aluminum, magnesium, zinc in a monolithic state are usually not capable of burning, but in the form of dust they are capable of exploding in the air. Aluminum powder can ignite spontaneously in the airgel state.

The presence of a large surface area of ​​the dust determines its high adsorption capacity. In addition, dust has the ability to acquire charges of static electricity in the process of its movement, due to friction and impacts of particles against one another. When transporting dust through pipelines, the charge accumulated by it can increase and depends on the substance, concentration, particle size, speed of movement, humidity of the environment and other factors. The presence of electrostatic charges can lead to the formation of sparks, ignition of dust-air mixtures.

However, the flammable and explosive properties of dust are determined mainly by its self-ignition temperature and the lower concentration explosive limit.

Depending on the state, any dust has two self-ignition temperatures: for airgel and for aerosol. Auto ignition temperature airgel is much lower than aerosol, because. the high concentration of the combustible substance in the airgel favors the accumulation of heat, and the presence of a distance between the dust particles in the aerosol increases the heat loss in the oxidation process during self-ignition. The autoignition temperature also depends on the degree of fineness of the substance.

Lower explosive limit(ELL) is the smallest amount of dust (g/m3) in the air at which an explosion occurs in the presence of an ignition source. All dusts are divided into two groups. To group BUT include explosive dusts with LEL up to 65 g/m3. AT group B includes flammable dusts with LEL higher than 65 g/m3.

In production areas, dust concentrations are usually well below the lower explosive limits. The upper explosive limits of dust are so high that they are practically unattainable. So, the concentration of the upper limit of the explosion of sugar dust is 13500, and peat - 2200 g/m3.

The ignited fine dust in the aerosol state can burn at the rate of combustion of the gas-air mixture. In this case, the pressure may increase due to the formation of gaseous combustion products, the volume of which in most cases exceeds the volume of the mixture, and due to their heating to a high temperature, which also causes an increase in their volume. The ability of dust to explode and the magnitude of pressure during an explosion largely depend on the temperature of the ignition source, the humidity of dust and air, the ash content, the dispersion of dust, the composition of the air and the temperature of the dust-air mixture. The higher the temperature of the ignition source, the lower the dust concentration can explode. Increasing the moisture content of air and dust reduces the intensity of the explosion.

The flammable properties of gases, liquids and solids can be judged by combustibility coefficient To, which is determined by the formula (if the substance has a chemical formula or it can be derived from the elemental composition)

K = 4C + 1H + 4S - 2O - 2CI - 3F - 5 Br,

where C, H, S, O, Cl, F, Br are the number of atoms, respectively, of carbon, hydrogen, sulfur, oxygen, chlorine, fluorine and bromine in the chemical formula of the substance.

With K? 0 the substance is non-combustible, at K > 0 it is combustible. For example, the combustibility coefficient of a substance having the formula C5HO4 will be equal to: K \u003d 4 5 + 1 1-2 4 \u003d 13.

Using the flammability coefficient, it is possible to determine quite accurately the lower concentration limits of ignition of combustible gases of a number of hydrocarbons by the formula NKPV = 44 / K.

Summary of life safety

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

Combustion requires a combustible substance, an oxidizing agent, and an ignition source to initiate a reaction between the fuel and the oxidizing agent. Combustion is distinguished by a variety of types and features. 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). 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 stream of combustible vapors enters the air). The combustion process is limited by the diffusion of the oxidizer. Combustion characterized by the presence of a phase separation in a 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 over a fresh combustible mixture) and turbulent (mixing of flow layers with an increased burnout rate).

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

For the origin of an endogenous fire, it is necessary to have a substance that can quickly oxidize at low temperatures, as a result of which spontaneous combustion can occur. This property of a substance is called the chemical activity of spontaneous combustion. As a result of oxidation and heat accumulation, self-heating turns into ignition.

Ignition - this is a qualitatively new and different process from self-heating, characterized by high oxidation rates, heat release and light emission. Self-heating and self-ignition originate in 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 risk of spontaneous combustion can be divided into four groups:

* Substances capable of spontaneous combustion upon contact with air at normal temperature (vegetable oils, drying oil, oil paints, primers, brown and hard coals, white phosphorus, aluminum and magnesium powder, soot, etc.);

* substances capable of spontaneous combustion 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 self-ignition (nitro-lacquer films, pyroxylin and nitroglycerin powders, vegetable semi-drying oils and drying oils prepared from them, turpentine etc.);

* substances whose contact with water causes a combustion process (alkali metals, alkali metal carbides, calcium, aluminum carbide, etc.);

* substances that cause spontaneous combustion of combustible substances upon contact with them (nitric, magnesium, hypochlorous, chloride and other acids, their anhydrides and salts; peroxides of sodium, potassium, hydrogen, 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 source of fire, and after the source of fire is removed, burning and smoldering cease.

* combustible materials, which, under the influence of fire or high temperature, ignite or smolder and continue to burn or smolder after the source of fire has been removed.

Some chemicals, combustibles and lubricants in certain concentrations and conditions are capable of not only igniting from heat sources, but also exploding.

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 a 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.

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

For flammable liquids(FL) include liquids that can burn independently after the ignition source is removed and have a flash point not higher than 61 °? in a closed crucible and 66°C in an open crucible.

For flammable liquids(GZH) include liquids that can burn on their own after the ignition source is removed and have a flash point above 61 °? in a closed crucible and 66°C in an open crucible.

Flash point 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) 5 s. The flash point is more dangerous than the flash point, as the vapors and liquid, when ignited, continue to burn after the flame has been removed.

During construction work, especially during 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, and in the conduct of work. From the point of view of fire safety, it is very important to make the right planning decision, offer protection for building structures, and provide for the necessary escape routes.

An explosion is a type of combustion and is characterized by extremely fast processes of physicochemical 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 of explosive substances.

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

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 even more rapid spread of fire. Thus, the speed of flame propagation in an explosive mixture located in a closed pipe is 2000 - 3000 m / s. Combustion of a mixture at this rate is called detonation. The occurrence of detonation is explained by compression, heating and movement of the unburned mixture ahead of the flame front, which leads to an 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 supply of energy and propagate over considerable distances. While moving, 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 f? 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 on the basis of pressure in the front of the shock wave, since in explosions, f is always many times greater than 11 ms

burning called a chemical oxidation reaction 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 oxidizing agent and an ignition source (impulse). Oxidizing agents can be oxygen, chlorine, fluorine, bromine, iodine, nitrogen oxides.

Burning may result from flash, fire, ignition, spontaneous combustion, spontaneous 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, for the continuation of combustion, the amount of heat that is formed during the short-term flash process is insufficient.

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

Ignition It is an ignition accompanied by the appearance of a flame. In contrast to a flash, the amount of ignition heat transferred to the combustible substance 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.

At the same time, the rest of the 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 atmospheric oxygen and the constant heating of the substance due to the heat of the chemical oxidation reaction. Cleaning materials impregnated with technical oil, peat, coal, etc. can ignite spontaneously.

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

Explosion (explosive burning)- this is the combustion of a substance, accompanied by an extremely rapid release of a large amount of energy, causing heating of the combustion products to high temperatures and a sharp increase in pressure.

by fire called uncontrolled combustion outside a special focus.

inhibition– intensive deceleration of the rate of chemical oxidation reactions in the flame.

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

combustible liquids. The main parameters of the combustible properties of a liquid are the flash, ignition and self-ignition temperatures, as well as the concentration and temperature limits of ignition of a mixture of liquid vapor 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 (flammable liquids) 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. combustible liquids (LL) with a flash point above 61 * C (in a closed crucible), for example, oil, fuel oil, etc.

Flash point called the temperature of a combustible substance at which it releases combustible gases and vapors at such a rate that, after igniting them from an ignition source, stable combustion occurs.

Auto ignition temperature is of great importance for assessing the explosiveness of processes occurring under pressure in closed vessels. It characterizes the possibility of starting 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 oxidizing agent is capable of burning only at a certain content of fuel in it. Lower (upper) concentration flammability limit called the minimum (maximum) possible flame propagation through the mixture at any distance from the ignition source.

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

combustible gases. The main parameters of the explosiveness of combustible gases are the lower and upper concentration ignition limits, characterized by the volume fraction of combustible gases in the mixture (%). The gap between the lower and upper concentration limits is called the ignition area. Only in this area is the mixture capable of being ignited by an ignition source with subsequent 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 below the lower limit, the mixture is poor in combustible and released during a flash there is not enough heat to ignite other particles. At concentrations above the upper limit, the mixture is too rich in fuel and ignition does not occur due to a lack of oxidizing agent.

All substances flammable and combustible are divided into 8 groups:

1 - Explosives - nitroglycerin, tetryl, trotyl, ammonites. dynamite; 2- Explosives - dinitrochlor, benzene, nitric acid esters, ammonium nitrate;

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

4 - Compressed and liquefied gases:

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

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

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

5 - Substances that ignite spontaneously on contact with air or water,- metallic potassium, sodium and calcium, calcium carbide, calcium and sodium phosphorous, 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 capable of causing ignition, - bromine, nitric, sulfuric and chlorosulfonic acids, potassium permanganate.

8 - Flammable substances- cotton, sulfur, soot.

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

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

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

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

slow-burning- under the influence of an ignition source, it is difficult to ignite, smolder or char and continue to burn or smolder only in the presence of an ignition source. After the source of fire is removed, combustion and smoldering cease. Slow-burning products include gypsum and concrete products with organic fillers, wood impregnated with fire-resistant compounds, etc.;

combustible- under the influence of an ignition source ignites and continues to burn or smolder after its removal. Combustible are timber, bitumen, roofing material, 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.

The 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.

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

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

Assessment of fire, explosion and explosion hazard of production.

The conditions that contribute to the emergence and development of a fire in industrial premises and determine 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, explosive and fire hazard are divided into 6 categories: A, B, C, D, D, E.

Category A- explosive industries associated with the use of combustible gases, the lower explosive limit of which is 10% or less of the volume of air; liquids with a flash point of vapors up to 28*С inclusive, provided that these gases and liquids can form explosive mixtures in a volume exceeding 5% of the volume of the room; substances capable of exploding and burning 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 paint shops, areas with the presence of liquefied gases. On the railway 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 that use nitro-paints, varnishes and solvents 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 combustible gases, the lower explosive limit of which is more than 10% of the air volume; liquids with vapor flash point from 28 to 61 *C inclusive; liquids heated under production conditions to a flash point and above; combustible dusts and fibers, the lower explosive limit of which is 65 g / m3 or less relative 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 wagon, locomotive, multi-unit 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 pantries of the indicated varnishes and paints, warehouses diesel fuel, pumping and drain racks for the overflow of this fuel, diesel locomotive repair shops with fuel tank washing, 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/m cubic to air volume; 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 wagon depots and factories, the oil facilities of traction substations, sleeper impregnation and sleeper repair plants, timber warehouses. container bases, ticket offices, communication houses, libraries, etc.

Category G- productions associated with the processing of non-combustible substances and materials in a hot, molten or incandescent state, accompanied by the release of radiant heat, sparks and flames; solid. liquid and gaseous substances that are burned or disposed of as fuel. This category of industries includes diesel locomotive depots, hot stamping workshops, casting, bandage, bogie, welding sections of various workshops, forging workshops, etc.

Category D– industries associated with the processing of non-combustible substances and materials in a cold state. This includes workshops for cold metal processing, blower and compressor stations, electric locomotive depots, etc.

Category E- explosive industries associated with the use of combustible 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 capable of exploding (also without subsequent combustion) when interacting with water, atmospheric oxygen or with each other. Category E industries are accumulators, sections and stations for the production of acetylene, premises for automatic telephone exchanges, signaling and communication posts, etc.

A fire in a tank starts, in most cases, with an explosion of the vapor-air mixture located under its roof. As a result of the explosion, the roof of the tank is completely torn off or partially destroyed and the liquid is ignited on the entire free surface. The strength of the explosion, as a rule, is greater in those tanks where there is a large gas space filled with a mixture of oil vapor with air (low liquid level). Depending on the strength of the explosion in a vertical metal tank, the following situation can be observed: --- - - the roof is completely torn off, it is thrown to the side at a distance of 20-30 m; the liquid burns over the entire area of ​​the tank.

The roof rises somewhat, opens fully or partially, then plunges into the burning liquid.

The roof is deformed and forms small gaps in the places of attachment to the tank wall, as well as in the welds of the roof itself.

The situation on fire as a result of depressurization of the roof of the tank.

In case of fire in reinforced concrete buried (underground) tanks from

explosion, the destruction of the roof occurs, in which large holes are formed, then, during the fire, the coating may collapse.

Collapse of the roof of a reinforced concrete buried (underground) reservoir.

In cylindrical horizontal tanks, during an explosion, one of the end walls most often ruptures, which often leads to the failure of the tank from the foundation, its overturning and spillage of liquid.

Consequences of an explosion in a horizontal cylindrical tank.

When burning petroleum products over the entire area of ​​the tank mirror, the height of the luminous part of the flame is 1.5-2 of the diameter of the tank and is more than 40 m. In windy conditions, the flame tilts at an angle to the horizon, sometimes touching the ground surface, and has approximately the same dimensions.

The released thermal energy is transferred to the walls of the reservoir,

the top layer of the oil product into the environment and causes heating of adjacent tanks and communications. As a result of this, it is possible: the formation of explosive concentrations in neighboring tanks, which can lead to an explosion and its ignition; flare combustion of vapors of oil products at breathing valves or leaks in the roof of neighboring tanks; heating of communications, their deformation, leakage and burning of liquid from them

12. Stationary fire extinguishing systems with air-mechanical foam. In warehouses of oil and oil products, it is necessary to provide for fire extinguishing with air-mechanical foam of medium and low expansion. Installations are provided: stationary automatic fire extinguishing, stationary non-automatic fire extinguishing and mobile. Buildings and premises of the SNS to be equipped with stationary automatic fire extinguishing installations are shown in the table.

A stationary automatic fire extinguishing installation consists of a pumping station, tanks for water, a foam concentrate or its solution, foam generators installed on tanks and in buildings, pipelines for supplying a foam concentrate solution (solution pipelines) to foam generators and automation equipment.

A stationary non-automatic fire extinguishing installation consists of the same elements as a stationary automatic one, with the exception of permanently installed foam generators and automation equipment; on the mortar pipelines, fire hydrants or risers with connecting heads are provided for connecting fire hoses and foam generators for a fire.

13. AUTOMATION OF FIRE EXTINGUISHING SYSTEMS WITH AIR-MECHANICAL FOAM

The composition of the automatic fire extinguishing system a fire pumping station is included, the automation of which should provide: automatic start-up of a working pump;

automatic start of the reserve pump in case of failure of the working pump within the set time;

automatic switching on of shut-off valves with electric drive; automatic switching of control circuits from a working to a backup power supply with electrical energy (in the event of a power failure at the working input);

automatic start-up of the working dosing pump;

automatic start-up of the standby dosing pump in case of failure of the working pump within the set time;

formation of a command impulse for automatic shutdown of ventilation of technological equipment;

formation of a command impulse for automatic shutdown of energy receivers of the 3rd and 2nd category.

In the premises of the pumping station, a light and sound alarm should be provided:

on the presence of voltage at the main and backup inputs of power supply and grounding of phases to earth (on call);

on disabling the automatic start of pumps and the dosing pump; about the emergency level in the water reservoir and in the drainage pit.

At the same time, signals are sent to the room fire station or other premises with round-the-clock stay of duty personnel:

about the occurrence of a fire; about starting pumps;

on the start of work of sprinkler and deluge installations, indicating the direction in which water is supplied (foaming agent solution);

about turning off the sound alarm about a fire;

about a malfunction of the installation (disappearance of voltage at the main power supply input);

about the pressure drop in the hydropneumatic tank or in the impulse device;

about the emergency water level in the reservoir and drainage pit;

on the position of the valves;

Continuation 13 AUTOMATION OF FIRE EXTINGUISHING SYSTEMS WITH AIR-MECHANICAL FOAM

about damage to the control lines of the shut-off devices installed on the incentive pipelines of the control units of deluge plants and metering pumps.

Sound signals about a fire differ in tone (howlers, sirens) from sound signals about a malfunction (call).

Auto power on The system is duplicated by remote activation from the control panel of the system control station, as well as from the place of a possible fire.

The principle of operation of the fire column KPA is based on opening and closing the valve of a fire hydrant in order to supply water from the water supply. The KPA column is installed on the fire hydrant in such a way that the square key at the bottom of the column enters the square end end of the hydrant rod. The fire column is screwed onto the hydrant by rotating its body clockwise (the socket wrench does not turn). After that, the hydrant valve opens (with the column valves closed), by turning the socket wrench counterclockwise (the hydrant valve opens fully at 10-14 turns of the socket wrench) and water from the water supply network enters the cavity of the fire column. After the hoses are connected to the branch pipes of the fire column, the valves open and water from the fire column enters the hose line.

14. Fire detectors

Fire detectors are classified according to the activation parameter and the physical principle of detection. The following activation parameters are used for fire detection:

The concentration of smoke particles in the air;

Ambient temperature;

Open flame radiation.

There are five main types of fire detectors:

thermal fire detectors

smoke detectors

flame detectors

manual fire detectors

combined fire detectors

Thermal fire detectors respond to changes in ambient temperature. They are installed in the following cases:

When, in a controlled volume, the structure of the materials used is such that, when burned, it gives off more heat than smoke.

When the spread of smoke is difficult due to either close quarters [e.g. behind false ceilings] or external conditions [low temperature, high humidity, etc.]

When there is a high concentration of any aerosol particles in the air that are not related to combustion processes [for example, soot from working machines in a garage or flour in flour mills]

The simplest maximum thermal fire detectors consist of a soldered contact of two conductors. Typically, the maximum temperature set in them is 75 ° C.

More complex maximum thermal fire detectors are equipped with a temperature-sensitive semiconductor element

In all these cases, it is necessary to use thermal linear fire detectors.

An open flame contains characteristic radiation in both the ultraviolet and infrared parts of the spectrum. Accordingly, there are two types of these devices: ultraviolet and infrared flame detectors.

The infrared flame detector uses an IR sensing element and an optical focusing system to register characteristic

Burning liquids.

All combustible liquids are capable of evaporation, 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 source of ignition 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 liquid vapor mixture 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 heated enough. In order to ignite a liquid, not a short-term, but a long-acting ignition source is needed, the temperature of which would be higher than the auto-ignition temperature of the mixture of vapors of this liquid with air.

In accordance with GOST 12.1.004-76, a combustible liquid (FL) is understood as a liquid capable of burning independently after the ignition source is removed and having a flash point above +61 ° C (in a closed crucible) or + 66 ° C (in an open crucible).

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

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

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

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

Temperature limits show in what temperature range liquid vapors will form combustible mixtures with air.