Fire extinguishing agents are subdivided according to the dominant principle of stopping combustion for four groups:

• cooling action;
• insulating action;
• diluting action;
• inhibitory action .

The most common extinguishing agents related to specific cessation principles are listed below.

Fire extinguishing agents used to extinguish fires

Water and its properties

The specific heat, equal to 4.19 J / (kg'grad), gives water good cooling properties. In conditions of extinguishing a fire, turning into steam (from 1 liter, 1700 liters of steam are formed), water dilutes the reacting substances. The high heat of vaporization of water (2236 kJ / kg) allows a large amount of heat to be removed in the process of extinguishing a fire. Low thermal conductivity contributes to the creation of reliable thermal insulation on the surface of the burning material. The significant thermal stability of water (it decomposes into oxygen and hydrogen at a temperature of 1700 0 C) promotes extinguishing of most solid materials, and the ability to dissolve some liquids (alcohols, acetone, aldehydes, organic acids) allows them to be diluted to incombustible concentrations. Water dissolves some vapors and gases, absorbs aerosols. It is available for fire extinguishing purposes, is economically feasible, inert with respect to most substances and materials, and has low viscosity and incompressibility. When extinguishing fires, water is used in the form of compact, atomized and atomized jets.

However, water is also characterized by negative properties: electrically conductive, has a high density (not used for extinguishing oil products as the main extinguishing agent), is capable of reacting with some substances and react violently with them, has a low utilization factor in the form of compact jets, a relatively high freezing point (extinguishing in winter is difficult) and high surface tension - 72.8 × 10 3 J / m 2 (which is an indicator of the low wetting ability of water).

Water mist(droplet sizes less than 100 microns) is obtained using special equipment: spray barrels, torque converters operating at high pressure (200 - 300 m). Water jets have a small impact force and flight range, but they irrigate a significant surface, are more favorable to water evaporation, have an increased cooling effect, and dilute the combustible medium well. They allow not to excessively moisten the materials when extinguishing them, contribute to a rapid decrease in temperature, and the deposition of smoke. Water mist is used not only for extinguishing burning solid materials, oil products, but also for protective actions.

Water with a wetting agent.

The addition of wetting agents can significantly reduce the surface tension of water (up to 36.4 × 10 3 J / m 2. In this form, it has a good penetrating ability, due to which the greatest effect is achieved in extinguishing fires, especially when burning fibrous materials, peat, soot. Aqueous solutions of wetting agents can reduce water consumption by 30 ... 50%, as well as the duration of extinguishing a fire.

To obtain VMP, (PO) are used.

The characteristics of the most common foaming agents are given below (Table 1).

Types of used foaming agents and their parameters

table no. 1

Fire extinguishing properties of various types of foaming agents

table 2

Legend: * - weak, ** - average, *** - good, **** - excellent.

Characteristics of the most common foaming agents

Table 3

Fire extinguishing powder compositions (OPS) are versatile and effective means of extinguishing fires at relatively low specific costs.

Powders are used to extinguish fires of most classes, including: A - combustion of solids, both accompanied by smoldering (wood, paper, textiles, coal, etc.) and not accompanied by smoldering (plastic, rubber). B - combustion of liquid substances (gasoline, oil products, alcohols, solvents, etc.). D - combustion of gaseous substances (household gas, ammonia, propane, etc.). E - combustion of materials in electrical installations under voltage. Therefore, powders can be used to extinguish any substances and materials known to date.

Powder for extinguishing fires of classes A, B, C, E is considered universal. Powders intended for extinguishing only fires of classes B, C, E or D are called special.

Domestic fire-extinguishing powder compositions (OPS) of general purpose include:

• - PSB-ZM (active base - sodium bicarbonate) for extinguishing fires of classes B, C and electrical installations under voltage;
• - P2-APM (active base - ammophos) for extinguishing fires of classes A, B, C and electrical installations under voltage;
• - fire extinguishing powder PIRANT-A (active base - phosphates and ammonium sulfate) for extinguishing fires of classes A, B, C and electrical installations under voltage;
• - powder "Vekson-AVS" is intended for extinguishing fires of classes A, B, C and electrical installations under voltage;
• - powders "Phoenix AVS-40" and "Phoenix AVS-70" are intended for extinguishing fires of classes A, B, C and electrical installations under voltage;
• - "Phoenix AVS-70", being a powder of increased efficiency, is specially designed for equipping automatic modules of powder fire extinguishing.

An example of a special purpose fire extinguishing system is the PKhK fire extinguishing powder, which is mainly used by Minatomenergo to extinguish fires of classes B, C, D and electrical installations.

In recent years, foreign powders have been certified in Russia, which have a wider range of operating temperatures from + 85 to - 60 ° C. The manufacturer recommends them for extinguishing fires in electrical installations with voltages up to 400 kV.

The elimination of combustion with powder compositions is carried out on the basis of the interaction of the following factors:

• dilution of the combustible medium with gaseous decomposition products of the powder or directly with a powder cloud;
• cooling the combustion zone due to the consumption of heat for heating the powder particles, their partial evaporation and decomposition in the flame
• the effect of fire barriers by analogy with mesh, gravel and similar fire barriers;
• inhibition of chemical reactions causing the development of the combustion process by gaseous products of evaporation and decomposition of powders or heterogeneous termination of chains of chemical combustion reactions on the surface of powders or solid products of their decomposition;
• heterogeneous termination of reaction chains on the surface of powder particles or solid products of its decomposition.

The dominant role in the suppression of combustion by dispersed particles is played by the last of the listed factors.

When extinguishing fires of solid combustible materials, powder particles caught on a solid burning surface melt, forming a strong crust on the material surface, preventing the release of combustible vapors into the combustion zone.

Important parameters affecting the fire extinguishing ability of powders are their large specific surface area, which is 1500-2500 g for a VCE class powder, 2000-5000 g for ABCE powder, and a high flowability.

It is known from the theory and practice of fire extinguishing that effective extinguishing of fires with any extinguishing agent depends on the intensity of the extinguishing agent supply to the combustion zone and vice versa.

It is also known that there is a certain critical rate of supply of any extinguishing agent, below which extinguishing cannot be achieved regardless of the amount of this extinguishing agent. The flow rate of a substance is understood to mean its second flow rate per unit of protected area or volume, and it has a dimension of kg / cm 2 or kg / cm 3.

The high flowability of powder compositions, comparable in some conditions with a pseudo-liquefied state, allows the powders to be well adapted to systems and means with a high rate of supply of the extinguishing composition to the fire zone.

The main disadvantage of OPS is their tendency to caking and clumping. Due to the high dispersion of OPS, they form a significant amount of dust, which necessitates work in special clothing, as well as in respiratory and eye protection equipment.

(carbon dioxide in a snow-like form) is 1.53 times heavier than air, odorless, density 1.97 kg / m 3. At a pressure of about 4 MPa (40 atm.) And a temperature of 0 ° C, the dioxide liquefies, in this form it is stored in cylinders, fire extinguishers, etc. When heated, it turns into a gaseous substance, bypassing the liquid phase, which makes it possible to use it for extinguishing materials , which deteriorate when wetted (from 1 kg of carbon dioxide, 500 liters of gas are formed). The heat of vaporization at - 78.5 ° C is 572.75 J / kg. Non-conductive, does not interact with combustible materials.

Solid carbon dioxide has a wide range of applications. It is not used to extinguish ignited magnesium and its alloys, metallic sodium and potassium, as this decomposes carbon dioxide with the release of atomic oxygen. Solid carbon dioxide is used to extinguish burning electrical installations, engines, in case of fires in archives, museums, exhibitions and other places with special values.

Nitrogen N 2 . It is non-flammable and does not support the combustion of most organic substances. The density under normal conditions is 1.25 kg / m 3, in the liquid phase (at a temperature of - 196 ° C) - 808 kg / m 3. Stored and transported in cylinders in a compressed state. Used in stationary installations. They are used to extinguish sodium, potassium, beryllium, calcium and other metals that burn in an atmosphere of carbon dioxide, as well as fires in technological devices and electrical installations. Estimated fire extinguishing concentration - 40% by volume.

Nitrogen cannot be used to extinguish magnesium, aluminum, lithium, zirconium and some other metals that can form nitrides, have properties and are sensitive to impact. An inert gas is used to extinguish them. argon .

Table 2 shows the fire extinguishing agents allowed for use in extinguishing fires of various substances and materials.

Fire extinguishing agents permissible for use in extinguishing fires of various substances and materials

table 2

It involves the use of a wide range of substances, thanks to which the fight against fire is realized. Traditionally, water is considered the main substance of this kind. Indeed, this is the most popular filling of fire-fighting installations, but not in all cases this method turns out to be effective. Therefore, other types of fire extinguishing agents are introduced into the working arsenal of fire services, for the properties of which the technical means are developed and serviced. This is how new powder components, liquid compositions and aerosols, gaseous and other variants of substances appear that make it possible to successfully fight the flame.

Fire extinguishing agent classifications

The basic principle of the separation of fire extinguishing substances is based on the nature of the effect on the fire. The most common way to do this is to cool the combustion zone. During the extinguishing process, ceasefire-active materials are supplied. At the same time, fire service personnel should, if possible, mix structural elements and disassemble burning materials, allowing more efficient cooling of the affected surfaces. The next principle is based on the dilution of the reacting elements. In this case, fire extinguishing agents are highly volatile or degradable coatings that contribute to a ceasefire. Insulating materials are also common, which affect activity in the combustion zone by creating special barriers, bridges, etc.

There is another classification of fire extinguishing materials, which is based on the physical state of the substance. In particular, they emit liquid, gaseous, free-flowing, solid, as well as tissue fillers for fire installations. It should be noted that the belonging of fillers to different groups in accordance with this classification is in no way associated with the above-mentioned separation system. That is, the classification of fire extinguishing substances according to the principle of impact on the fire zone may allow two or more materials with different physicochemical properties to fall into one of the categories.

Coolants

In theory, combustion can be stopped if heat is removed at high speed. This principle can be realized through the use of refrigerants, which, by means of cooling, regulate the heat removal process and minimize the activity of the combustion source. The classic representative of the group of cooling materials is water - a fire extinguishing agent that has a high heat capacity, availability and chemical inertness.

As with all versatile materials, this fluid has drawbacks. First of all, water is characterized by increased electrical conductivity, which in itself imposes serious restrictions on its use. The situation is aggravated when the liquid is mixed with other additives that increase the ability to conduct current. But these are not all the disadvantages. Water also has a weakly expressed ability to adhere to burning materials, which is why, in fact, special additives are introduced into it. As a result, other fire extinguishing agents are obtained, which are various mixtures and solutions - as a rule, on a salt basis.

Insulating substances

The most common material in this group is foam. The insulating effect promotes effective flame suppression with minimal loss and toxicity risk. The structure of the foam is formed from liquid bubbles, which are filled with gas. Often these substances have a double effect - insulating and cooling. At the same time, not all foam extinguishing agents can be used to extinguish fires. For example, a soap solution diluted at home will not give any effect, since the structure of the emulsion will instantly be destroyed in the fire. Therefore, special solutions are used that have a relatively strong bubble structure that can withstand thermal and mechanical stress. In order to strengthen the foam, special stabilizers are added to the compositions of the solutions. Also, the use of air emulsions is combined with a foaming agent.

Powders intended for extinguishing fires should also be included in the category of insulating materials. Although such substances are universal and have a multifactorial suppressive effect on fire, the ability to isolate sources of fire still comes to the fore. For such purposes, for example, a fire extinguishing powder based on alkali metals, carbonate, bicarbonate, ammonium salts and other compounds is used. Also, similar substances are used purposefully in extinguishing electrical equipment.

Dilution substances

This is a wide group of substances that are mainly focused on use in special fire extinguishing conditions. For a ceasefire in this way, materials are used that are capable of either diluting flammable vapors with gases to a state of incombustible concentration, or minimizing the oxygen content in the air to a level where combustion ceases to be sustained. In this case, various approaches to the supply of materials can be applied - for example, into the general area of ​​the fire, into the air, or purposefully into the object of combustion.

In practice, the most popular of this type is carbon dioxide, which provides the most effective stopping of combustion in a fire. Extinguishing agents in the form of nitrogen and water vapor are also found to be useful depending on the conditions of use. For example, water vapor is used mainly in closed rooms and hard-to-reach places. During the processing of the object, water vapor fills the entire room, diluting and displacing air masses from it. Thus, the active substance prevents combustion without harmful effects on people in the room. In addition, there is sometimes a double effect of extinguishing the flame with steam. First, the cloud itself acts, replacing the air. Second, droplets from the steam evaporate and absorb heat from the fire source.

Chemically active substances

This is a category of substances that have an inhibitory effect on the combustion process. The extinguishing principle is based on the chemical effect of the agent on the fire zone. When a fire extinguishing agent comes into contact with the target object, it interacts with the active centers of the oxidizing reaction, as a result of which non-flammable or low-active compounds remain, which stop the combustion reaction.

Halogenated hydrocarbons are capable of providing this effect. These are extinguishing agents with an inhibitory effect that inhibit the activity of the combustion process. But it is important to take into account that such materials are dangerous with toxic effects. In terms of extinguishing efficiency, this is perhaps the best group of fire extinguishing materials. But, again, unwanted chemical activity significantly limits the scope of such substances. If we talk about specific compounds, then inhibiting substances can be represented by freons and other halogenated compounds based on ethane and methane. Experts call such materials freons, assigning them special designations indicating their chemical composition. In accordance with the labeling, the permissible conditions for the use of substances are also determined.

Mobile and stationary fire extinguishing equipment

By themselves, the effectiveness of substances that theoretically can help in the fight against fire is minimal if there is no well-established material supply system. For this purpose, mobile and stationary installations are used that carry out the introduction or spraying of the active substance. Fire trucks operated by security services can be classified as mobile vehicles. However, these are not only ordinary vehicles with personnel. This category could include trains, airplanes and ships carrying out fire suppression under appropriate conditions. Stationary fire extinguishing installations are also widespread, which are designed to release a fire extinguishing agent. For example, such systems are most often used in closed rooms and work with diluting active materials.

Among the main tasks performed by stationary installations, it is possible to note the elimination or, as a minimum goal, the localization of a fire. At the same time, there are many options for the design of such complexes. In particular, a distinction is made between modular and modular systems. Also, against the background of widespread automation of security systems, they are moving away from manual control and fire extinguishing installations, complemented by modern electronics and the latest remote control systems.

The use of fire extinguishing agents in monitors

Carriage means for supplying fire extinguishing materials, as a rule, are designed at the stage of construction of the facility in which they will be installed. The fact is that such systems are the most demanding in terms of communication support, so the initial calculation of their location and installation is especially important. Typically, such units are used at production facilities, where tanks for specific types of fire extinguishing agents are also located. These can be, for example, tanks with water or cylinders with foam or gas filler. Some modifications, by the way, are not intended specifically for the complete elimination of the flame. Their main tasks are reduced to the protection of production equipment or communications - for example, by means of water irrigation.

This type of setting may differ in the way it is set up. The carriage constructions do not always have a stationary position. It can be mobile with the addition of software or remote control. Of course, stationary installations are also widespread, the supply of extinguishing agents in which is often carried out through common engineering networks and communications. Such a connection allows you not to waste time organizing a working infrastructure and instantly start the fire extinguishing process.

Automation in fire extinguishing installations

Modern automatic fire-fighting installations allow, regardless of human participation, to control the factors indicating the danger of a fire, and to start the extinguishing process in a timely manner. Usually, when the values ​​set in the program are exceeded, the active substance is supplied and an alarm is triggered at the same time. At the same time, there are different approaches to the means of control of such systems. For example, sprinkler models are fully automated, but there are other systems that provide for manual control. So, the fire extinguishing agent in the installations can be released both in automatic mode and at the command of the operator through the control panel. But such a control system already depends on the type of the installation itself - modular ones are oriented towards greater autonomy, while centralized ones allow the maximum range of approaches to management.

It is also important to note safety factors that cannot always be taken into account when operating automatic systems. Equipping with such installations justifies itself only in those cases when the elimination of fires with primary instrumentation is impossible. Also, at some production facilities, personnel do not service security systems around the clock. Obviously, in such situations, one cannot do without an automatic means of fighting fire. Another thing is that in order to minimize risks, one should initially make the right choice of a fire extinguishing agent, the automatic supply of which, as a maximum, will entail only planned and preliminary calculated damage.

Classification of installations by extinguishing agent

For each type of fire extinguishing installation, a specific type of active substance is used. For safety reasons, the use of several materials in one complex is rarely practiced. The most common system is the water-based fire suppression system. Deluge complexes are especially common, which are used to protect premises with a high risk of fire. The effectiveness of such devices is due to the fact that they can provide simultaneous irrigation of the entire area of ​​the protected site. Includes pumping equipment, control panels, pipelines, water tanks, warning devices, etc.

The second most popular substance used in deluge construction is foam. Such systems are used to protect local areas in industrial premises, to prevent the ignition of transformers and electrical devices. Sprinkler installations with foam fire extinguishing material are also widely used. By the way, such units have much in common with water installations, with the exception of special approaches to dosing. These are the main extinguishing agents used in stationary and mobile means of combating fire sources, but there are also specialized gas systems, powder and aerosol. As a rule, fire protection equipment with such fillers is used in special conditions - for example, in places where increased requirements are imposed on the maintenance of electrical equipment.

Conclusion

With all the variety of substances used in modern fire extinguishing systems, experts still cannot name a universal and most effective way to fight fire. There is a fairly clear segmentation of materials into classes depending on their technical and operational qualities. At the same time, an important role is played by the effect of fire extinguishing substances on a person and objects that are in the ignition zone. For example, chemical-filled fire extinguishing systems could well be the only means of suppressing fire. As practice shows, a minimum amount of this type of extinguishing material is required to fight middle-class fires.

But the problem lies in the consequences that the use of chemically hazardous substances entails. For this reason, technologists are mastering new methods of fire extinguishing, including structural ones. An efficiently working substance for extinguishing a fire can reveal its full potential only in that single case, if the system for combating ignition centers has been properly organized. And in this regard, it is worth noting the importance of both the basic installations that feed the extinguishing material, and the control methods - automatic or manual.

LABORATORY AND PRACTICAL WORKS

Job 1. Selection of extinguishing agents and

fire extinguishing equipment

Purpose of work: Familiarize yourself with extinguishing agents and select the means for a specific situation.

Basic concepts

Fast and effective extinguishing of a fire can be achieved if the extinguishing agent is correctly selected and its timely supply to the combustion center is carried out. The choice of fire extinguishing agents, fire extinguishing means is made on the basis of their classification and characteristics.

EXTINGUISHING SUBSTANCES

Classification of extinguishing agents

Fire extinguishing agents are classified:

By way of stopping combustion:

cooling source of combustion: water, solid carbon dioxide.

diluting (reducing the percentage of oxygen in the combustion site): carbon dioxide and other inert gases, water vapor.

insulating action (insulating the burning surface from atmospheric oxygen): air-mechanical foam, powders, sand, solutions.

inhibiting (inhibiting the chemical reaction of combustion): compositions with halogenated hydrocarbons - freons, powder aerosol compositions - AOC.

By electrical conductivity:

electrically conductive: water, solutions, steam, foam.

non-conductive: gases, powder formulations.

Toxicity:

non-toxic: water, foam, powder formulations, sand.

low toxic: carbon dioxide

toxic: freons, halogenated compounds No. 3, 5, 7, etc.

Characteristics of some fire extinguishing agents

Water and solutions. Water is the main means of extinguishing fires. It is cheap, affordable, easily supplied to the place of combustion, it is well preserved for a long time, does not possess toxic properties, and is effective in extinguishing most combustible materials.

The high fire extinguishing ability of water is due to its significant heat capacity. At normal atmospheric pressure and a temperature of 20 ° C, the heat capacity of water is 1 kcal / kg. From 1 p. water is formed 1750 liters. dry saturated steam. This consumes 539 kcal. thermal energy. The released steam displaces oxygen from the combustion zone.

However, water has a high surface tension force, so the penetrating power of water is not always sufficient. A number of materials are known (dust, cotton, etc.), into the pores of which water is unable to penetrate and stop smoldering. In such cases, a certain amount (from 0.5 to 4% by weight) of surfactants-wetting agents is added to the water to reduce the surface tension and increase the penetrating power. The following wetting agents are most common: foaming agent PO-1, PO-5.

The use of wetting agents, all other things being equal, reduces the water consumption by 2-2.5 times and reduces the extinguishing time by 20-30%. The disadvantage of wetting agents is their aggressiveness.

To extinguish fires, water is used in the form of continuous and finely atomized jets. Sprayed water can be successfully used to extinguish oil products. In this case, an important condition for the success of extinguishing is the creation of a sufficiently dense curtain of small drops over the burning surface. This curtain limits the flow of oxygen from the environment to the combustion zone. Oxygen that has penetrated through the curtain into the combustion zone is diluted with steam generated as a result of the evaporation of water droplets. As a result, conditions are created under which combustion is impossible.

Water in the form of continuous streams is used for mechanical separation of the flame and, to a lesser extent than sprayed water, for cooling the surrounding structures. The disadvantage of a continuous jet is a low coefficient of use of the heat capacity of water due to the short time of its contact with the combustion zone.

Various salt solutions are used to extinguish forest and steppe fires. To obtain a solution, calcium chloride salts, caustic soda, Glauber's salt, ammonium sulfate, etc. are added to the water, which increase the heat capacity of water and, after its evaporation, form a film of salts on the surface treated with the solution. This film prevents sparks and embers from re-igniting the extinguished hearth.

However, water is not a universal remedy. With many substances, for example, with alkali and alkaline earth metals, it enters into a chemical reaction with the release of hydrogen, accompanied by a significant release of heat. Some compounds, for example, sodium hydrosulfite, decompose when interacting with water. Therefore, in such cases, as well as when extinguishing electrical installations, water cannot be recommended as a fire extinguishing agent.

Foam are an effective fire extinguishing agent. Fire-extinguishing foams are divided into chemical and air-mechanical... Chemical foam is produced by a neutralization chemical reaction between acid and alkali. The bubble shell of this foam consists of a mixture of aqueous solutions of salts and foaming agents. The bubbles themselves are filled with carbon dioxide, the product of a chemical reaction.

Air-mechanical foam is obtained as a result of mechanical mixing of the foaming solution with air. The shell of air-mechanical foam bubbles consists of an aqueous solution of foaming agents such as PO-1, PO-5.

The resulting fire extinguishing foam is characterized by:

resistance (the ability of the foam to resist destruction for a certain time: the higher the resistance of the foam, the more efficient the extinguishing process);

multiplicity of foam (the ratio of the volume of foam to the volume of the initial products :);

Distinguish: low expansion foams with a frequency of up to 12, medium multiples from 12 to 100 and high expansion K100 (the most effective).

viscosity (the ability of the foam to spread over the surface);

dispersion (bubble size).

To increase the stability of the foam, surfactants are used (bone or wood glue), and for storage at low temperatures - ethanol (C 2 H 3 OH) or ethylene glycol.

Foams are used to extinguish fires of class A, B, C. Do not use to extinguish alkali and alkaline earth metals and electrical equipment under voltage.

Carbon dioxide. Carbon dioxide supplied to the fire site can be in a solid state (carbon dioxide snow), gaseous and aerosol. The effect of CO 2 on the combustion center is based on the dilution of oxygen in the combustion zone.

Carbon dioxide snow can be obtained under the condition of rapid evaporation of liquid carbon dioxide. The resulting snow-like carbon dioxide has a density of 1.5 g / cm 3 at - 80? C. Snow-like carbon dioxide lowers the temperature and reduces the oxygen content in the combustion zone. From 1 p. solid acid forms 500 liters. gas.

In the gaseous state, carbon dioxide is used for volumetric extinguishing inside premises, filling the entire volume and displacing oxygen from it. Aerosol carbon dioxide (in the form of the smallest crystalline particles) gives the greatest effect in rooms where the air may contain the smallest combustible particles (cotton, dust, etc.) In this case, carbon dioxide not only extinguishes, but also promotes the rapid deposition of suspended particles. To stop burning in the room, it is necessary to create a 30% concentration of carbon dioxide vapor.

When using carbon dioxide, it must be remembered that it is dangerous to people. Therefore, it is possible to enter the room after filling it with carbon dioxide only in oxygen insulating gas masks.

Carbon dioxide is not electrically conductive and evaporates without leaving any traces. Carbon dioxide is used to extinguish electrical equipment, internal combustion engines, extinguish fires in storages of valuable materials, in archives, libraries, etc. Carbon dioxide cannot be used as a fire extinguishing agent when burning ethyl alcohol, because carbon dioxide dissolves in it, as well as during the combustion of substances that can burn without access to air (termite, celluloid, etc.). In addition to CO 2, other inert gases are also used as fire extinguishing agents: nitrogen, sulfur hexafluoride.

Freon compounds- these are compositions with halogenated hydrocarbons. They are highly volatile liquids, as a result of which they are classified as gases or aerosols. The main compounds used in extinguishing fires are:

freon 125 (C 2 HF 5);

freon 318 (C 4 Cl 3 F 8).

These compounds are currently the most effective fire extinguishing agents. Their action is based on inhibiting the chemical reaction of combustion and interaction with atmospheric oxygen.

They are used to extinguish fires of classes A, B, C and electrical installations at practically unlimited temperatures.

Advantages:

most effective in comparison with all available formulations;

have a high penetrating power;

used at low temperatures (down to -70єC).

Disadvantages:

toxicity;

the formation of corrosive compounds in the presence of moisture;

ineffective for outdoor use;

do not extinguish alkali and alkaline earth metals and acidic substances.

Powder formulations. Powder fire extinguishing compositions currently in use include:

PSB-3M (~ 90% sodium bicarbanate);

Pirant-A (~ 96% ammonium phosphates and sulfates);

PHC (~ 90% potassium chloride);

AOC - aerosol-forming compounds.

In addition to the main components of fire extinguishing powders, they include anti-caking and hydrophobic additives.

Designed to extinguish burning alkali and alkaline earth metals, and are also widely used to extinguish fires of classes: A, B, C, and E.

Powder fire extinguishing compositions are used to extinguish fires of classes A, B, C and E, electrical installations under voltage.

Ineffective for extinguishing:

smoldering materials and substances burning without oxygen.

The action of the fire extinguishing powders PSB-3M and Pirant-A is based on the isolation of the burning surface from the access of oxygen.

The action of the powder compositions of PCA and AOS is to inhibit the chemical reaction of combustion and reduce the O 2 content in the combustion zone.

Powders of PKhK and AOS are the most promising today. Aerosol fire-extinguishing compositions - AOC are especially effective.

AOC are solid propellant or pyrotechnic compositions capable of self-combustion without air access with the formation of fire extinguishing combustion products - inert gases, highly dispersed salts and alkali metal oxides. These compounds are low-toxic and environmentally friendly.

Currently used:

fiery AOS;

chilled AOC.

When the devices of aerosol-forming compositions are triggered, the flame compositions have a flame that reaches several meters and the temperature of the combustion products at the outlet is 1200-1500єC. This is their disadvantage.

Cooled aerosol-forming compositions are obtained using special cooling nozzles. This makes it possible to reduce the temperature of AOC during combustion from 600 to 200єC, but the aerosol mixture will contain products of incomplete combustion of AOC, which significantly increases the toxicity of combustion products in comparison with flame AOC.

AOC is used for extinguishing in fire extinguishers, in generators of various types, both in stand-alone mode and in automatic aerosol fire extinguishing installations.

Water.

Liquid extinguishing agents primarily include water and aqueous solutions. Water is most widely used as a fire extinguishing agent due to some of its properties.

Water is versatile, affordable and efficient. The dominant principle of action is the cooling of the reactants. Water is used for extinguishing, except for the following rare cases: water cannot be used to extinguish flammable substances and materials with which water enters into intense chemical interaction with the release of heat and combustible components (some acids and alkalis).

Some flammable liquids (alcohols, aldehydes, etc.) are soluble in water and, when mixed with it, form less flammable or non-flammable liquids.

Water cannot be used to extinguish fires with temperatures above 1800-2000oС, because at such temperatures, water dissociates into hydrogen and oxygen, which intensifies the combustion process. However, most combustible materials burn at lower temperatures. For this reason, it is unacceptable to use water when extinguishing burning magnesium, zinc, aluminum and some other metals and alloys.

Water should not be used to extinguish fires in which the safety of firefighters is not ensured (for example, electrical installations with high voltage).

Water is difficult to use at low temperatures, because it has a high freezing point.

In addition, the negative properties of water are low viscosity and high surface tension, which leads to poor wettability of fibrous substances.

It is difficult to extinguish burning liquids with water that have a lower density than water. In view of this, the water is not very suitable for extinguishing oil products.

When extinguishing fires, water is used in the form of a jet, drops of various degrees of dispersion or steam.

To reduce the lack of water as a fire extinguishing agent, additives are introduced into it, for example, surfactants.

Foam.

Foams are widely used in fire extinguishing practice. Distinguish between chemical and air-mechanical foams.

The difficulty of obtaining chemical foams, their high cost and toxicity limit their application.

Air-mechanical foam is obtained as a result of mechanical mixing of an aqueous solution of a foaming agent with air.

The foam is characterized by dispersion, viscosity, thermal conductivity, electrical conductivity, resistance. The ratio of the volume of the foam to the volume of its liquid phase is called the multiplicity. The most widely used foams are from 70 to 150.

The main fire extinguishing property of foams is their insulating ability.

Powder fire extinguishing compositions.

Of the powder fire extinguishing compositions (POS) in our country, the most widespread are POS based on sodium bicarbonate and ammonium phosphate.

The mechanism for stopping combustion using the POS is varied. The dominant mechanism depends on the type of fuel, combustion mode, type of POS and other reasons.

POS primarily acts by simple physical dilution of reagents. At the same time, when the POS is heated, a significant amount of heat is removed from the reacting substances.

The advantage of POS is their versatility and high fire extinguishing efficiency. But they are prone to moisture during storage, and it is difficult to feed them into the combustion zone.

Carbon dioxide.

For extinguishing some combustible materials, solid carbon dioxide is used, which, when heated, turns into gas, bypassing the liquid phase. They extinguish materials that deteriorate from moisture. The extinguishing mechanism consists in cooling the burning materials and diluting the products of their decomposition with carbon dioxide.

Gases.

Among the gases used to extinguish fires are carbon dioxide, nitrogen, water vapor, less often helium, argon. When using them, the principle of dilution of reactants is most often implemented.