Fundamentals of the choice of fire extinguishing agents. The choice of fire extinguishing agents and fire extinguishing agents

In order to effectively combat the flames during a fire, special substances are needed that will help to localize and neutralize the fire, preventing it from spreading over large areas. These include special fire extinguishing agents, the main tasks of which are:

• exclude air access to the source of ignition;
• stop the supply of combustible liquid and gaseous substances to the combustion area;
• reduce the activity of chemical reactions that support combustion;
• cool the combustion area to temperatures at which spontaneous combustion does not occur;
• dilute gaseous and liquid combustible environment incombustible components.

In order to be able to quickly and effectively extinguish a fire, it is important to choose the right extinguishing agent and ensure its quick delivery to the source of ignition. The choice of compositions for fighting a fire at a particular facility is determined based on their physical and chemical characteristics.

Application area

Fire extinguishing agents are special substances that are used to fill primary fire extinguishing systems, as well as for the use of various fire equipment used to eliminate fires and open flames.

Primary fire extinguishing equipment includes individual funds fire fighting in the form of manual and mobile fire extinguishers, autonomous fire extinguishing systems connected to the fire alarm system.

Depending on the object on which the fire occurred, and on the class of fire, one or another type of substance can be used to effectively fight the fire. To correctly select fire extinguishing agents, the concept of their classification is an important aspect.

Substance classification

To fight fire, means are used that are able to ensure a quick cessation of combustion both on the surface and in volume due to the chemical and physical impact on the object of combustion. All extinguishing agents can be divided into several categories.

• Coolant extinguishing agents. They provide a decrease in the temperature regime in the combustion centers, which eliminates the spontaneous ignition of nearby materials and the subsequent spread of fire. These include water and solid carbon dioxide.

• Insulating. These substances ensure that the supply of oxygen to hot surfaces is interrupted, which prevents the continuation of combustion. These include various non-combustible dry powders, air-mechanical foam, non-combustible solutions.

• Dilution fire extinguishing agents. With their help, the concentration of oxygen in the combustion chambers is reduced, and the combustible agent is diluted with additives that do not support combustion. Such substances include inert gas and carbon dioxide, steam and sprayed water.

• inhibitory. These substances provide a decrease in the activity of the chemical reaction of combustion, as a result of which the flame begins to go out and goes out. Such substances include halogenated hydrocarbons.

Chemical and physical properties of fire extinguishing agents

To understand what substance should be used to extinguish a fire, consider what fire extinguishing agents are and their properties.

Water and aqueous salt solutions

Water is one of the most common substances for extinguishing fires of various classes. wide practical use water is due to the fact that it is cheap, easily supplied to the place of ignition and can be stored for a long time.

High rates of fire extinguishing with water are determined by its high heat capacity, which at T=+20ºС is 1 kcal/l. When water evaporates from one liter of it, more than 1500 liters of supersaturated steam H 2 O can be formed, which subsequently displaces O 2 from the combustion area. In the process of vaporization, about 540 kcal of energy is needed, which can significantly reduce the temperature of the combustion area.

Since water has a high surface tension, its penetrating properties are not always sufficient, especially when pulverized materials are burning. In this case, it is used in conjunction with surfactants (0.50 ... 4%).

Note!

To effectively extinguish forest / steppe fires, various salts are dissolved in water. The most commonly used ammonium sulphate, calcium chloride, caustic salt, etc.

Restrictions:

Important to remember!

Water is not a universal fire extinguishing agent.

From its use should be when extinguishing:

• electrified equipment that is under high voltage;
• alkali and alkaline earth metals, with which water reacts with the subsequent release of combustible hydrogen and a large amount of heat;
• substances that support combustion and without air access.

Fire extinguishing foam

These extinguishing agents and their classification provide for the use of two types of foam - created by a chemical reaction or mechanically using air.

Chemical foam is obtained as a result of a chemical reaction between an alkaline and an acidic medium. The shell of individual bubbles of this type of foam includes a foaming material and an aqueous saline solution. The bubbles themselves are filled with CO 2, which appears as a result of the ongoing chemical reaction.

Air foam is obtained when the air flow is mixed with special foaming agents. The shell of the bubbles of this foam contains only a foaming agent.

Restrictions:

Foam cannot be used to extinguish:

• electrified installations;
• alkaline earth and alkali metals.

carbon dioxide

It is used in solid, in the form of "carbon dioxide snow", or in a gaseous / aerosol state.

The use of "carbon dioxide snow" can significantly reduce the temperature in the fire, and also reduces the concentration of oxygen supplied to the flame. CO 2 in the solid state has a density of 1500 kg / m 3, and up to 500 liters of gas can be obtained from one liter of this substance.

These extinguishing agents in gaseous form are effectively used for extinguishing in volume. Gas fills the entire room, displacing oxygen from the combustion zone.

Aerosol mixtures of carbon dioxide will be useful when there is a high concentration of small combustible particles in the air, which can be deposited with an aerosol.

Restrictions:

Important to remember!

CO 2 in any state is dangerous to humans. Therefore, access to the room where this material was used should be carried out using special protective equipment.

CO 2 cannot be used for extinguishing:

• ethyl alcohol;
• substances and materials that burn and smolder without access to oxygen.

Freons for extinguishing

These agents are high performance formulations containing halocarbons. Freon substances will be effective for quickly extinguishing fires of various classes, including installations under operating voltage. Their effect is based on a decrease in the activity of chemical reactions that support combustion, as well as the possibility of interaction with oxygen. air environment which reduces its concentration.

Limitation:

Freons are toxic and dangerous to humans. With their help, you can not extinguish:

• acidic substances;
• alkali and alkaline earth metals.

Detailed description of fire extinguishing agents

Conclusion

Thanks to a wide range of different extinguishing agents, it is possible to effectively fight fires of various classes and of varying complexity. To quickly neutralize the fire, it is important to choose the right material for extinguishing. The choice should take into account the restrictions on extinguishing certain substances, as well as the fact that some fire extinguishing material is toxic and may be dangerous to people and the environment.

Before proceeding to the classification and designs of fire extinguishers, it is necessary to consider the properties of the most common fire extinguishing agents used for charging into fire extinguishers.

The following fire extinguishing agents are used as charges in fire extinguishers:
. Water and aqueous solutions chemical substances;
. Foam;
. Powder formulations;
. Aerosol formulations;
. Gas compositions;

Water extinguishing agents:

Water is the most common means of extinguishing fires, due to its availability, low cost, significant heat capacity and high latent heat of vaporization. However, water has a fairly high freezing point, low thermal conductivity, and a high coefficient of surface tension (which prevents it from spreading quickly over the surface of burning solid materials, penetrating deep and wetting them). In this regard, water is more often used in the form of solutions with various additives that give it special properties: reduce the freezing point, or reduce the surface tension coefficient, increasing its wetting ability, or increase its viscosity.

Extinguishing flammable liquids with a compact jet of water leads to its inefficient use. This is explained by the fact that water has a low coefficient of thermal conductivity, therefore, passing through the torch, it almost does not have time to heat up and absorb heat; in the form of large drops, it flies further or falls down. This can lead to an increase in the fire area as a result of splashing the burning liquid or spreading it over the surface of the water.

The most fire-extinguishing ability has a fine spray water jet - with a droplet diameter of less than 150 microns, which, evaporating intensively, take a significant amount of heat from the fire and reduce the oxygen content of the air (turning into steam, water increases in volume by about 1700 times). Water mist does not spray the burning liquid. And besides, it combines the advantages of both liquid and gas extinguishing agents. Obtaining a fine spray is achieved by using special nozzles, heating water above its boiling point and then ejecting superheated water to the fire, or creating a gas-saturated CO2 solution in water using special sprayers. However, a finely dispersed jet of water, as a result of a decrease in the diameter of the droplets and their entrainment by ascending gas flows, has insufficient penetrating power, which makes it difficult to extinguish (since one has to get close to the fire). So, when extinguishing solid materials stacked in a pile, the jet does not penetrate into it and does not suppress combustion. The solution to this problem was the use of a pulsed ejection of water with a high rate of its supply to the combustion source.

Foam:

Another effective and no less common fire extinguishing agent than water is foam. It is often used to extinguish fires, as it can have both an insulating and a cooling effect at the same time. The cooling effect of the foam makes it possible in many cases to exclude the re-ignition of a combustible substance after the destruction of the foam layer.
Foam is a dispersed system of the gas-liquid type, in which each gas bubble (for fire extinguishers it is air) is enclosed in a shell of a thin film and they are connected to each other by these films into a single frame.
However, not all foams can be used to extinguish fires. It is useless, for example, to extinguish a burning liquid with soapy foam, since it is instantly destroyed in the fire. Foams used for these purposes must have high structural and mechanical strength, so that during the time necessary for its accumulation and fire extinguishing, it will remain on the surface of a combustible liquid. Therefore, in addition to surfactants, which actually participate in the creation of foam, a stabilizer is necessarily introduced into the foaming agent formulation.
In addition to foam, air emulsion is also used to extinguish fires. It, unlike foam, is a system consisting of individual air bubbles, and connected by a single frame and freely distributed in the liquid. Such an emulsion is formed when the sprayed liquid charge of the fire extinguisher hits the surface of the burning substance.
In domestic practice, aqueous solutions of foaming agents "in pure form" are practically not used as a charge in air-foam fire extinguishers. Since foam concentrates cannot be stored in the form of working solutions for a long time, special salts are added to them, which increase the stability of working solutions and the fire-extinguishing ability of the foam obtained from them (especially for extinguishing solids).
The main component for producing fire-extinguishing foam are aqueous solutions of foaming agents.
According to the chemical composition, foam concentrates are divided into hydrocarbon (PO-3NP, PO-6NP, PO-6TS, PO-6TsT, TEAS, MORPEN, etc.) and fluorine-containing (PO-6TF, PO-6A3F, Merkulovsky, Film-forming " and etc.)
According to their purpose, foam concentrates are divided into foam concentrates general purpose(PO-3NP, PO-6TS) and special purpose (PO-6NP, MORPEN, Polyarny, fluorine-containing), which are used in special conditions or to extinguish a specific group of combustible substances.
The foam is characterized by a number of parameters, one of which is the multiplicity value - the ratio of the volume of the foam to the volume of the solution from which it was obtained, i.e. to the volume of its liquid phase. Chemical foam has an expansion not higher than 5. Air-mechanical foam can be of low expansion (from 4 to 20), medium (from 21 to 200) and high expansion (over 200). To obtain high expansion foam, special foam generators are required, often with a fan that provides forced air supply with the required flow rate. Therefore, high expansion foam generators are not used in fire extinguishers.

Powder formulations:

Another fire extinguishing agent that is gaining popularity due to its versatility is powder formulations, which are finely dispersed mineral salts that are treated with special additives to make them flow and reduce the ability to wetting and absorbing water. The greatest effect of powder extinguishing is achieved when its particles have a size of the order of 5-15 microns, however, such a powder is difficult to apply to the combustion center. Therefore, the powder is usually made polydisperse, i.e. consisting of large (size from 50 to 100 microns) and small particles. When powder is supplied from a barrel or fire extinguisher, the flow of large particles captures and delivers small particles to the combustion source. To obtain powder compositions, ammonium salts of phosphoric acid, carbonates, bicarbonates, alkali metal chlorides and other compounds are used.
Depending on the purpose, powder formulations are divided into general-purpose powders that can extinguish fires of solid carbon-containing and liquid combustible substances, combustible gases and electrical equipment under voltage up to 1000 V, and powders special purpose, which are used to extinguish metals, organometallic compounds, metal hydrides (class D fires) or other substances with unique properties. Extinguishing fires with general-purpose powders is carried out by creating a fire-extinguishing concentration in the volume above the burning surface, with special-purpose powders - by backfilling and isolating the fuel surface from air oxygen.

Fire extinguishing powders, depending on which classes of fire they can extinguish, are divided as follows:
. ABCE type powders, the main active component of which is phosphorus-ammonium salts (Pirant-A, Vekson-AVS, ISTO-1, Phoenix, etc.). They are designed to extinguish solid, liquid, gaseous combustible substances and electrical equipment under voltage.
. Powders of the VSE type, the main component of which can be sodium or potassium bicarbonate, potassium sulfate, potassium chloride, an alloy of urea with carbonic acid salts, etc. (PSB-3M, Vekson-VSE, PKhK, etc.). These powders are designed to extinguish liquid, gaseous combustible substances and electrical equipment under voltage (it is useless to extinguish class A fires with these powders).
. Type D powders (special purpose powders), the main component of which is potassium chloride, graphite, etc. (PHC, Vekson-D, etc.); used to extinguish metals, metal-containing compounds.
Powders are environmentally inert and can be used to extinguish almost any class of fires of combustible substances in a wide temperature range (from -50 to +50).
Like other fire extinguishing agents, powders have a number of significant drawbacks. So they do not have a cooling effect, therefore, after extinguishing, there may be cases of ignition of an already extinguished substance. They pollute the extinguishing object. As a result of the formation of a powder cloud, visibility is reduced (especially in a small volume). In addition, the powder cloud has irritating effects on the respiratory and vision organs. Since powders are finely dispersed systems (the bulk of powder particles are less than 100 microns in size), powder particles tend to agglomerate (lump formation) and caking, and the substances that are included in their formulation - to absorb water and its vapors (including from the air).

Aerosol formulations:

Recently, aerosol fire extinguishing compositions have been increasingly used. As a source for their production, special aerosol-forming solid fuel or pyrotechnic compositions capable of burning without air access are used. Aerosol fire extinguishing compositions are formed directly at the moment of extinguishing during the combustion of such compositions. During the combustion of the aerosol-forming composition, a fire-extinguishing aerosol is released, 35-60% consisting of solid particles of salts and oxides of alkali metals 1-5 microns in size, non-combustible gases and vapors (N2, CO2, H2O, etc.). The high fire-extinguishing efficiency (but only with the volumetric method of extinguishing) of aerosol compositions is due to the rather long time of the aerosol cloud remaining above the combustion source and maintaining the initial fire-extinguishing concentration, as well as high penetrating ability. According to this parameter, aerosol compositions approach gas fire extinguishing agents. At the time of application of aerosol extinguishing agents, the oxygen of the air in the atmosphere of a closed volume is also burned out, it is diluted with inert combustion products of the charge, and the oxidation chain reaction in the flame is inhibited by highly dispersed active solid particles. Aerosol formulations do not cake; solid fine particles with a developed surface are highly active, as they are formed directly at the time of application; aerosol generators do not require laborious maintenance, etc. However, for all their positive qualities, aerosol compositions have many of the disadvantages inherent in fire extinguishing powders. In addition, the devices develop high temperatures during their use, and in some designs there is an open flame, so they themselves can be a source of ignition (for example, with a false alarm). Designers have to use special devices in order to remove an open flame and reduce the temperature of the resulting aerosol.

Gas compositions:

The most "clean" fire extinguishing agents are gas compositions. Gas fire extinguishers use carbon dioxide and freon as charges.

Carbon dioxide (carbon dioxide) at a temperature of 20 0C and a pressure of 760 mm Hg. It is a colorless gas with a sour taste and a slight odor, 1.5 times heavier than air. Being an inert gas, carbon dioxide does not support combustion; when it is introduced into the region of fiery combustion in an amount of about 30% vol. and lowering the oxygen content to 12-15% vol. the flame goes out, and when the oxygen concentration in the air drops to 8% vol. the processes of smoldering also stop. When liquid carbon dioxide (which is in this form in a fire extinguisher) passes into gas, its volume increases by 400-500 times, and this process proceeds with a large absorption of heat. Carbon dioxide is used either in the gaseous state or in the form of snow. It does not pollute and has almost no effect on the extinguishing object itself; has good dielectric properties, sufficiently high penetrating power; does not change its properties during storage.
The greatest effect is achieved when extinguishing carbon dioxide fires in confined spaces.

Of the shortcomings that this fire extinguishing agent has, the following should be noted: cooling of the metal parts of the fire extinguisher to a temperature of the order of minus 60 0C; accumulation on the plastic socket of significant charges of static electricity (up to several thousand volts); decrease in the use of oxygen in the atmosphere of the room, etc.

In conclusion, it should be noted that only fire extinguishing agents that have a sanitary and epidemiological conclusion and a certificate can be used for charging into fire extinguishers. fire safety Russia. For fire extinguishers supplied from abroad in a charged form, a fire safety certificate for a fire extinguishing agent is not required, only a sanitary and epidemiological conclusion is required.

federal state budgetary educational institution higher professional education

RUSSIAN ACADEMY

NATIONAL ECONOMY AND PUBLIC SERVICE

under the PRESIDENT OF THE RUSSIAN FEDERATION

CHELYABINSK BRANCH

Department of Economics and Management

Fire extinguishing agents and their properties.

Purpose, device and principle of operation of foam fire extinguishers

Dindiberina Yulia Olegovna

4th year students, groups Mo-41-11

Supervisor:

Rudakova T.I. Ph.D., Assoc.

Chelyabinsk

Introduction

Chapter 1

Fire concept

Water as fire extinguisher

Foam

Fire extinguishing powders

Halons

Handy fire extinguishers

Chapter 2. Foam fire extinguishers

Appointment of foam fire extinguishers

The device and principle of operation of foam fire extinguishers

Conclusion

Bibliographic list

Introduction

AT this moment There are many different fire extinguishing media, with different characteristics and applications. In this regard, I believe that every firefighter should know the classification of these substances and their scope. This is due to the fact that the speed and efficiency of extinguishing a fire or fire, as well as the life and health of personnel participating in emergency response, will directly depend on the correct choice of a fire extinguishing agent. It is also important to know how to properly combine the supply of a particular fire extinguishing agent and its quantity necessary to achieve maximum effect.

The relevance of the problem of the topic under consideration lies in the fact that fires are one of the most common and dangerous disasters on the planet. Every year, tens of thousands of people die and are injured in fires, and billions of dollars worth of valuables are burned.

Every day we receive information from the media about fires from all continents. Huge tracts of forest and settlements burn out in Asia, Europe, America, America and Africa. Therefore, the problem of fighting fires is a global problem.

It is safe to say that now in Russia there are 10 times more fires than 100 years ago. There are about 300,000 of them every year. The relative level of losses in Russia is the highest among the highly developed countries of the world. It exceeds the comparable losses of Japan - 3.5 times, Great Britain - 4.5 times, USA - 3 times.

On the territory of Russia, on average, about 600 fires occur daily, in which 55 people die; about 200 buildings are destroyed. 70% of all fires occur in cities.

The purpose of this work is to analyze the currently existing fire extinguishing agents, their characteristics and methods of application in the course of extinguishing fires that have arisen at various objects and under certain conditions characteristic of a particular fire.

To achieve the goal, it is necessary to solve a number of tasks:

Give the concept of what a fire is, a fire extinguishing agent;

Describe fire extinguishing agents;

Specify methods of using fire extinguishing agents.

Chapter 1

Fire concept

What is a fire as a social phenomenon? These are uncontrollable burnings causing material damage harm to the life and health of citizens, the interests of society and the state.

Typically, fires occur at fire hazardous facilities (FBOs). EET should include such facilities that contain flammable or combustible substances or liquids. Flammable substances or liquids include substances or liquids having an ignition temperature below 48°C; to fuel - over 45 ° C.

Fires are classified according to the following criteria: by the place of occurrence, by cause of occurrence, by type of fire, by intensity of combustion, etc.

Statistics gives us the following picture of the distribution of fires:

as a result of economic activity of aborigines - 64.8%;

the work of loggers, expeditions, and other organizations causes 8.8% of fires;

agricultural burns - 7.3%;

lightning - 16%;

arson and unidentified causes - 3.1%.

Fire extinguishing is the process of the impact of forces and means, as well as the use of methods and techniques for extinguishing a fire.

When extinguishing a fire, the following extinguishing agents are usually used:

Fluids: water spray; foam.

Gases: carbon dioxide; halons 12B1, 13B1.

Fire extinguishing powders: ammonium phosphate; bicarbonate of soda; potassium bicarbonate; potassium chloride.

AT Russian Federation since May 1, 2009, the main classification has been established " technical regulations on fire safety requirements. Article 8 of the Regulation defines the classes of fires:

Table 1. Classification of fires and methods of extinguishing them

Water is mainly a coolant. It absorbs heat and cools burning materials more effectively than any other commonly used fire extinguishing agent. Water is most effective for absorbing heat at temperatures up to 100°C. At a temperature of 100°C, the vault continues to absorb heat, turning into steam, and removes the absorbed heat from the burning material. This quickly lowers its temperature to below its ignition temperature, causing the fire to stop.

Water has an important secondary effect: turning into steam, it expands 1700 times. The resulting large cloud of steam surrounds the fire, displacing the air, which contains the oxygen necessary to support the combustion process. Thus, in addition to the cooling ability, water has the effect of volumetric quenching.

Water is a widely used fire extinguishing agent, this is due to the following advantages of water:

cheapness and availability;

relatively high specific heat capacity;

chemical inertness to most substances and materials.

Foam is an accumulation of bubbles that contributes to the suppression of a fire, mainly due to the surface extinguishing effect. Bubbles are created when water is mixed with a foaming agent. Foam is lighter than the lightest flammable oil product, so when applied to a burning oil product, it remains on its surface.

Fire-extinguishing foam effect. Foam is used to create a layer on the surface of flammable liquids, including petroleum products. The foam layer prevents flammable vapors from escaping the surface, and oxygen from penetrating to the combustible substance. The water contained in the foam solution also has a cooling effect, which allows the foam to be successfully used to extinguish class A fires.

An ideal foam should flow freely enough and quickly cover the surface, bonding firmly to it to create and maintain a vapor barrier, and retain the amount of water needed to provide a durable layer for an extended period of time. With a rapid loss of water, the foam dries out and breaks down under the influence of the high temperature generated during a fire. The foam must be light enough to float on flammable liquids, yet heavy enough not to be blown away by the wind.

Foam quality is usually determined by:

destruction time of 25% of its volume,

relative expansion

ability to withstand heat (resistance to flashback).

These qualities are affected by the chemical composition of the foaming agent, the temperature and pressure of the water, and the efficiency of the foaming device.

Foam that quickly loses water is practically a liquid. It freely flows around obstacles and spreads rapidly.

When used correctly, foam is an effective fire extinguishing agent. However, there are certain limitations in its application.

Since the foam is an aqueous solution, it conducts electricity, so it should not be applied to live electrical equipment.

Foam, like water, cannot be used to extinguish combustible metals.

Many types of foam should not be used with fire extinguishing powders. The exception to this rule is "light water", which can be used with extinguishing powder.

Foam is not suitable for extinguishing fires associated with the combustion of gases and cryogenic liquids. But high-expansion foam is used in extinguishing spreading cryogenic liquids to quickly heat vapors and reduce the dangers associated with such spreading.

If the foam is applied to burning liquids whose temperature exceeds 100°C (for example, asphalt), the water contained in the foam can cause them to swell, splatter and boil.

The stock of foaming agent should be enough to cover the entire surface of the burning material with foam. In addition, it should be sufficient to replace the foam that burns out and fill the gaps that form on its surface.

Despite existing limitations in use, foam is very effective in fighting class A and B fires.

Foam is a very effective fire extinguishing agent, which, in addition, has a cooling effect.

The foam creates a vapor barrier that prevents flammable vapors from escaping to the outside. The surface of the tank can be covered with foam to protect it from a fire in an adjacent tank.

Foam can be used to extinguish class A fires due to the presence of water in it. "Light water" is especially effective.

Foam is an effective fire extinguishing agent for covering spreading oil products. If the oil leaks out, one should try to close the valve and thus interrupt the flow. If this is not possible, the flow should be blocked with foam, which should be applied to the area of ​​the fire to extinguish it and then to create a protective layer covering the seeping liquid.

Foam is the most effective extinguishing agent for extinguishing fires in large containers with flammable liquids.

To obtain foam, fresh or outboard, hard or soft input can be used.

Foam is not prone to rapid destruction, with proper supply, it extinguishes the fire gradually.

The foam stays in place, covers the burning surface and absorbs the heat contained in those materials that could cause a re-ignition.

Foam provides economical water consumption and does not overload ship's fire pumps.

Foam concentrates are lightweight, foam extinguishing systems do not require much space.

Fire extinguishing powders

Powder fire extinguishing agents are divided into general purpose fire extinguishing powders and special purpose fire extinguishing powders, which are only used to extinguish combustible metal fires.

There are currently five types of general purpose fire extinguishing powders in use. Similar to other fire extinguishing media, fire extinguishing powders can be used in stationary systems and in portable as well as stationary fire extinguishers.

Bicarbonate of soda. It is one of the main fire extinguishing powders. It is widely used due to the fact that it is the most economical of all existing ones. It is especially effective in fighting fires of animal fats and vegetable oils, as it causes chemical changes in these substances, turning them into non-flammable soap. When using sodium bicarbonate, one should always be aware of the possibility of flame backflow onto the surface of the burning oil.

potassium bicarbonate. This extinguishing powder was originally developed for use in "light water" dual systems, but is now generally used on its own. It has been found to be very effective in extinguishing liquid fuel fires. The use of potassium bicarbonate makes it possible to successfully prevent backfire. This powder is more expensive than sodium bicarbonate.

potassium chloride. It is a fire extinguishing powder that is compatible with protein-based foam. Its fire extinguishing properties are approximately equivalent to those of potassium bicarbonate, the only drawback is that after its use for extinguishing fires, corrosion may occur.

A mixture of urea and potassium bicarbonate. This powder, developed in England and consisting of urea and potassium bicarbonate, is the most effective of all fire extinguishing powders tested. However, it has not found wide application due to its high cost.

ammonium phosphate. This powder is versatile because it can be successfully used to extinguish fires of classes A, B and C. Ammonium salts break the chain reaction of fiery combustion. Phosphate is converted by an increase in temperature caused by a fire into metaphosphoric acid, a vitreous fusible substance. The acid coats hard surfaces with a flame retardant layer, so this fire extinguishing agent can be used to extinguish fires associated with the burning of conventional combustible materials such as wood and paper, as well as fires of flammable oil products, gases and electrical equipment. But as for fires, the sources of which are located at a considerable depth, this powder only allows you to take the fire under control, but does not provide complete extinguishment.

For the final elimination of such a fire, extinguishing with water is required. In general, you should always remember the advisability of having a rolled-out fire hose on hand, which can be used as an additional tool when using a powder fire extinguisher.

Limitations in the use of fire extinguishing powders

The release of a large amount of fire extinguishing powder can cause bad influence on people nearby. The resulting opaque cloud can significantly reduce visibility and make breathing difficult.

Like other fire extinguishing media that do not contain water, fire extinguishing powders will not extinguish fires associated with the combustion of materials containing oxygen.

Extinguishing powder can leave an insulating layer on electronic or telephone equipment, affecting the operation of this equipment.

When extinguishing combustible metals such as magnesium, potassium, sodium and their alloys, general purpose powder does not have a fire extinguishing effect, and in some cases can cause a violent chemical reaction.

In places where there is moisture, fire extinguishing powder may cause corrosion or deformation of the surface on which it is deposited.

Safety

Fire extinguishing powders are considered non-toxic, but if inhaled they can cause respiratory irritation. Therefore, as in the case of carbon dioxide extinguishing, in rooms that can be filled with fire extinguishing powder, it is necessary to provide preliminary signals. In addition, if the personnel taking part in extinguishing a fire need to enter the room where the powder was supplied before the end of the ventilation, they must use breathing apparatus and signal cables.

The use of fire extinguishing powders is very effective for extinguishing gas fires. Flammable gases must be extinguished when the source of gas is blocked.

Halons

Halons are made up of a hydrocarbon and one or more halogens: fluorine, chlorine, bromine, and iodine. In Russia, two halons are used: bromotrifluoromethane (known as freon 13B1) and bromchlorodifluoromethane (freon 12B1).

Halons 13B1 and 12B1 are supplied to the combustion zone in the form of gas. Most experts believe that halons interrupt the chain reaction. But it is not known for sure whether they slow down the chain reaction, interrupt its course, or cause some other reaction.

Halon 13B1 is stored and transported in a liquid state under pressure. When released into the protected room, it evaporates, turning into a colorless, odorless gas, and is fed into the combustion zone under the same pressure under which it is stored. Halon 13B1 does not conduct electricity.

Halon 12B1 is also colorless, but has a slight sweet smell. This halon is stored and transported in a liquid state and maintained under nitrogen gas pressure, which is necessary to ensure that it is properly supplied to the fire zone, since the vapor pressure of halon 12B1 is too low for this. It does not conduct electricity.

Application of halons

The fire-extinguishing properties of Halons 12B1 and 13B1 allow them to be used to extinguish various fires, including:

fires of electrical equipment;

fires in rooms in which burning of flammable oils and greases is possible;

class A fires involving solid combustibles, however, if the fire is located deep below, water spraying may be required to extinguish the fire;

To extinguish fires associated with the burning of electronic computers and control stations, it is recommended to use halon 13B1. Halon 12B1 should not be used in these cases.

There are some restrictions on the use of halons. They are unsuitable for extinguishing substances containing oxygen, combustible metals and hydrides.

Safety

Inhalation of Halons 13B1 and 12B1 may cause dizziness and incoordination. These gases can impair visibility in the area of ​​their application. Above 500°C, both halon gases decompose. Generally, vapors below this temperature are not considered very toxic, but decomposed gases can be very dangerous, depending on their concentration, temperature and quantity.

Halon 12B1 is not recommended for filling confined spaces. If halon 13B1 is used to fill rooms that may contain people, a warning signal must be provided, upon hearing which it is necessary to leave the room immediately. When using a Halon 13B1 fire extinguisher, all persons not directly involved in working with the fire extinguisher should immediately leave the fire area. After using a fire extinguisher, the person working with it should leave as quickly as possible. The room must not be entered until it has been thoroughly ventilated. If you need to stay in or enter the room where the 13B1 halon was administered, you should use a breathing apparatus and a signal cable

Handy fire extinguishers

Sand, sawdust, steam

Sand used to extinguish a fire is not as effective as modern fire extinguishing agents.

Sand makes it possible to eliminate oil fires, creating the effect of volumetric extinguishing and covering the surface of the burning substance. However, if the burning oil is about 25 mm thick and there is not enough sand available to the firefighters to cover all the burning oil, the sand will settle under the surface of the oil and the fire will not be extinguished. When properly applied, sand can be used as a barrier to spreading oil or to cover it.

Sand should be fed to the fire with a shovel or shovel. Its already insignificant effectiveness can be further reduced by inept presentation. After the fire is extinguished, the problem of cleaning up the sand arises. In addition to these shortcomings, it is worth mentioning the abrasive properties of sand when it gets into mechanisms and other equipment.

It is difficult to put out with sand a fire associated with the burning of combustible metals, since at the very high temperature that accompanies such fires, the sand releases oxygen. The presence of water in the sand will intensify the fire or cause a steam explosion. Sand can only be used as a barrier to the spreading molten metal, and special purpose powder should be used to extinguish such a fire.

Sometimes sawdust soaked in soda is used to extinguish small fires. Like sand, they are fed to the fire with a shovel from a short distance. The disadvantages of sawdust as a fire extinguishing medium are the same as those of sand. A more effective substitute for sawdust is a fire extinguisher suitable for class B fires, for the same reasons given for sand.

Steam is a bulk fire extinguishing medium that prevents air from entering the fire and reduces the oxygen concentration in the air around the fire. As long as the steam fills the volume, re-ignition will not occur. But it has a number of disadvantages, especially in comparison with other fire extinguishing media.

Steam has a weak heat-absorbing capacity, as a result of which its cooling effect is very small. In addition, when the supply is stopped, steam begins to condense. Its volume is significantly reduced, and combustible vapors and air immediately begin to flow to the fire, displacing the steam. At this point, if the fire has not been completely extinguished, a re-ignition is likely. The temperature of the vapor itself is high enough to ignite many liquid fuels. Finally, steam is a danger to people, as the heat it contains can cause severe burns.

Chapter 2. Foam fire extinguishers

Appointment of foam fire extinguishers

Foam fire extinguishers are designed to extinguish fires and fires of solid substances and materials, flammable liquids and combustible liquids, except for alkali metals and substances that burn without air, as well as electrical installations under voltage.

According to the type of extinguishing agent, foam fire extinguishers are classified:

chemical foam (OHP);

air-foam (ORP);

The industry produces three types of hand-held chemical foam fire extinguishers: OHP-10, OP-M, OP-9MM. Chemical foam fire extinguishers are designed to extinguish fires with chemical foam, which is formed as a result of the interaction of the alkaline and acid parts of the charges.

It is strictly forbidden to use a fire extinguisher to extinguish fires in electrical installations under voltage, as well as alkali metals. The fire extinguisher is recommended to be used at stationary facilities of the national economy at an ambient temperature of +5 to +45 °C. fire extinguisher foam extinguishing

Air-foam fire extinguishers are designed to extinguish fires of various substances and materials, except for alkali metals and substances burning without air access, as well as electrical installations under voltage. As a rule, a 6% aqueous solution of foaming agent PO-1 is used as a charge.

The device and principle of operation of foam fire extinguishers

To activate a chemical foam fire extinguisher, lift the handle that opens the acid glass valve and tip the fire extinguisher upside down. The acid part of the charge flowing out of the glass mixes with the alkaline part of the charge poured into the fire extinguisher body, and a reaction occurs between them with the formation of carbon dioxide, which fills the foam bubbles.

Carbon dioxide creates a pressure of 1.4 MPa (14 kg / cm2) inside the housing, which pushes the foam out of the fire extinguisher in the form of a jet. Due to the fact that relatively high pressure is created in the bodies of chemical foam fire extinguishers, it is necessary to clean the spray with a pin suspended from the fire extinguisher handle before use.

The OP-M chemical thick-foam marine fire extinguisher is designed to extinguish fires on ships, in port facilities and in warehouses. Chemical foam fire extinguisher OP-9MM is designed to extinguish fires and fires of all combustible materials, as well as electrical installations under voltage.

Rice. 1. Scheme of chemical foam fire extinguisher OHP-10: 1 - fire extinguisher body; 2 - acid glass; 3 - safety membrane; 4 - spray; 5 - fire extinguisher cover; 6 - stock; 7 - handle; 3 and 9 - rubber gaskets; 10 - spring; 11 - neck; 12 - top of the fire extinguisher; 13 - rubber valve; 14 - side handle; 15 - bottom.

Fig.2. Air-foam fire extinguisher OVP-10: I - steel case; 2 - carrying handle; 3 - cartridge for pushing gas; 4 - air-foam nozzle with a spray; 5 - trigger mechanism; 6 - cover of the fire extinguisher body; 7 - siphon tube nozzle.

There are two types of air-foam fire extinguishers (Fig. 2, 3): manual (OVP-5 and OVP-10) and stationary (OVPU-250 and OVP-100). To activate the fire extinguisher, press the trigger lever. In this case, the seal breaks, and the shield pierces the cylinder membrane. Carbon dioxide leaving the can through the nipple creates pressure in the fire extinguisher body, under the action of which the solution flows through the siphon tube through the sprayer into the nozzle. In the nozzle, the solution is mixed with air and an air-mechanical foam is formed.

A fire extinguisher cannot be used to extinguish substances that burn without air (cotton, pyroxylin, etc.), burning metals (alkaline sodium, etc. and light magnesium, etc.). It is forbidden to use for extinguishing electrical installations that are energized. The fire extinguisher is used at ambient temperature from +3 to +50 C.

Rice. 3. Stationary air-foam fire extinguisher OVPU-250: 1 - steel body on supports; 2 - starting cylinder; 3 - foam generator; 4 - reel with hose; 5 - safety valve; 6 - branch pipe for filling the foaming agent solution; 7 - siphon tube of the foam generator; 8 - drain pipe; 9 - foam solution control tube.

Conclusion

The purpose of this abstract was to analyze the currently existing fire extinguishing agents, their characteristics and methods of application in the course of extinguishing fires that have arisen at various objects and under certain conditions characteristic of a particular fire. And in the course of the work it was revealed that the main fire extinguishing agents are: water, powders, foams, gallons, sand, sawdust, steam. Each of the listed substances has its own advantages and disadvantages in the use of fire extinguishing, it largely depends on the types of fires, the classification of which was also given in the work.

Bibliographic list

GOST 28130-89 Fire fighting equipment. Fire extinguishers. Fire extinguishing and fire alarm installations.

Mironov S.K., Latuk V.N. Primary fire extinguishers. Bustard, 2008

Terebnev V.V. Handbook of the head of fire fighting. Capabilities of fire departments. Moscow. "Fire Engineering" 2004

Tutorial. Life safety. YAZRI air defense. 2002.

Yudakhin A.V. Toolkit. Questions of the organization of the UAV in the process of daily activities in parts of the Air Force. 2001.

It involves the use of a wide range of substances, thanks to which the fight against fire is realized. Traditionally, the main substance of this kind is considered to be water. Indeed, this is the most popular filling of fire fighting installations, but this method is far from being effective in all cases. Therefore, other types of fire extinguishing agents are introduced into the working arsenal of fire services, under the properties of which are developed and serving technical means. This is how all new powder components, liquid compositions and aerosols, gas and other variants of substances appear, which make it possible to successfully fight the flame.

Classifications of fire extinguishing agents

The basic principle of separation of fire extinguishing agents is based on the nature of the impact on the fire. The most common way of such influence is the cooling of the combustion zone. In the process of extinguishing, materials that are active from the point of view of a ceasefire are supplied. At the same time, employees fire service should, if possible, mix structural elements and disassemble burning materials, allowing the affected surfaces to cool more efficiently. The following principle is based on the dilution of the reacting elements. AT this case extinguishing agents are easily evaporating or decomposing coatings that help to stop a fire. Insulating materials are also common, which affect the activity in the combustion zone by creating special barriers, jumpers, etc.

There is another classification of fire extinguishing materials, which is based on physical condition substances. In particular, liquid, gaseous, bulk, solid, as well as fabric fillers of fire installations are isolated. It should be noted that the belonging of fillers to different groups in accordance with this classification is in no way associated with the separation system mentioned above. That is, the classification of fire extinguishing agents according to the principle of impact on the fire zone can allow two or more materials with different physical and chemical properties to be included in one of the categories.

Coolants

Theoretically, combustion can be stopped if heat release is removed at high speed. This principle can be implemented through the use of refrigerants, which, through 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.

Like all universal 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 this is not all the shortcomings. Water also has weak adhesion properties to burning materials, which is why, in fact, special additives are added to 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 contributes to effective flame suppression with minimal losses and risk in terms of toxic safety. The structure of the foam is formed from liquid bubbles that have a gas filling. Often such substances have a double effect - insulating and cooling. At the same time, not all foam fire extinguishing agents can be used in extinguishing fires. For example, a soap solution diluted at home will not give any effect, since the structure of the emulsion will be instantly destroyed in a 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 foamy substance, special stabilizers are added to the solution compositions. The use of air emulsions is also 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 fire sources still comes to the fore. For such purposes, for example, fire extinguishing powder based on alkali metals, carbonate, bicarbonate, ammonium salts and other compounds is used. Also, such substances are used purposefully in extinguishing electrical equipment.

Substances of dilution

This is an extensive group of substances that are mainly focused on use in special fire fighting conditions. To stop a fire in this way, materials are used that can either dilute combustible vapors with gases to a non-combustible concentration, or minimize the oxygen content in the air to a level where combustion is no longer supported. In this case, various approaches to the supply of materials can be used - for example, into the general fire zone, into the air, or purposefully into the combustion object.

According to the practice of application, the most popular agent of this type is carbon dioxide, which provides the most effective cessation of combustion in a fire. Fire extinguishing agents in the form of nitrogen and water vapor are also useful depending on the conditions of use. For example, water vapor is used mainly in enclosed spaces and hard-to-reach places. During the processing of the object, water vapor fills the entire room, diluting and displacing air masses from it. In this way, the active substance prevents combustion without having a harmful effect on people in the room. In addition, a double effect of extinguishing the flame with steam is sometimes provided. First, there is the cloud itself, which replaces the air. Secondly, the droplets formed 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 action of the agent on the fire zone. When the fire extinguishing agent comes into contact with the target object, it interacts with the active centers of the oxidizing reaction, resulting in non-combustible or low-active compounds that stop the combustion reaction.

Halogenated hydrocarbons are capable of providing this effect. These are fire-extinguishing agents with an inhibitory effect that inhibit the activity of the combustion process. But it is important to consider 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, undesirable chemical activity significantly limits the scope of such substances. If we talk about specific compounds, then inhibitory substances can be represented by freons and other halogenated compounds based on ethane and methane. Specialists call such materials freons, attributing to them special designations indicating the chemical composition. In accordance with the labeling, the permissible conditions for the use of substances are also determined.

Mobile and stationary fire extinguishers

By itself, the effectiveness of substances that can theoretically assist in the fight against fire is minimal if there is no established material supply system. For this purpose, mobile and stationary installations are used that introduce or spray the active substance. Mobile vehicles include fire trucks that are operated by security services. However, these are not only ordinary vehicles with personnel. This category also includes trains, airplanes and sea ​​vessels performing fire suppression under appropriate conditions. Stationary fire extinguishing installations, which are designed to release a fire extinguishing agent, are also common. For example, such systems are most often used in enclosed spaces and work with diluting active materials.

Among the main tasks that stationary installations perform, one can 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 aggregate systems. Also, against the background of extensive 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 fire monitors

Fire monitors 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. These units are usually used for production facilities, where containers for fire extinguishing agents of a particular type are also located. These can be, for example, water tanks or cylinders filled with foam or gas. Some modifications, by the way, are not designed specifically for the complete elimination of the flame. Their main tasks are to protect production equipment or communications - for example, by water irrigation.

Installations of this type may differ in the way they are constructed. Far from always, carriage structures 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 fire extinguishing agents in which is often carried out through common engineering networks and communications. Such a connection allows you not to waste time on organizing a working infrastructure and immediately start the fire extinguishing process.

Automation in fire extinguishing installations

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

It is important to note the safety factors that may not always be taken into account during operation. automatic systems. Equipping with such installations justifies itself only in cases where the elimination of fires with primary tools is impossible. Also, at some production facilities, personnel maintain security systems not around the clock. It is obvious that in such situations one cannot do without an automatic means of fighting fire. Another thing is that in order to minimize risks, it is necessary to initially make the right choice of fire extinguishing agent, the automatic supply of which, as a maximum, will only cause planned and pre-calculated damage.

Classification of installations by fire 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 extinguishing design. 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 area. Its composition includes pump equipment, control panels, pipelines, water tanks, warning devices, etc.

The second most popular substance used in deluge structures is foam. Such systems are used to protect local areas in industrial premises, prevention of ignition of transformers and electric 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 fire extinguishing agents used in stationary and mobile means of fighting fires, 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 there are increased requirements for the maintenance of electrical equipment.

Conclusion

With all the variety of substances used in modern systems firefighting, experts still cannot name the universal and most effective method fire fighting. There is a fairly clear segmentation of materials into classes depending on their technical and operational qualities. At the same time, the impact of fire extinguishing agents on people and objects that are in the ignition zone plays an important role. For example, fire suppression systems with chemical fillers could well be the only means of suppressing a fire. As practice shows, a minimum amount is required fire extinguishing material of this type for fighting medium 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 effective fire extinguishing agent can reveal its full potential only if the system for combating ignition sources has been properly organized. And in this regard, it is worth noting the importance of both basic installations that supply material for extinguishing, and control methods - automatic or manual.

Objective: 1. Acquaintance with fire extinguishing compositions.

2. Study of fire extinguishing means.

3. Selecting the type and determining the amount of primary funds

firefighting.

Theoretical part.

Fast and effective fire extinguishing can be achieved if the extinguishing agent is chosen correctly and its timely supply to the combustion source is equipped. The choice of fire extinguishing agents, fire extinguishing agents is made on the basis of their classification and characteristics.

1. Fire extinguishing agents. Classification of fire extinguishing agents.

Fire extinguishing agents are classified:

According to the method of stopping burning:

Cooling source of combustion: water, solid carbon dioxide.

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

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

Inhibiting (inhibiting the chemical reaction of combustion): compounds with halogenated hydrocarbons (freons).

For electrical conductivity:

Electrically conductive: water, solutions, steam, foam.

Non-conductive: gases, powder formulations.

For toxicity:

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

Low toxicity: carbon dioxide.

Toxic: freons, halogenated compounds No. 3, 5, 7, and others.

Characteristics of some fire extinguishing agents.

Water and solutions. Water is the main means of extinguishing fires. It is cheap, available, easily supplied to the place of combustion, well preserved for a long time, does not have 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 0 C, the heat capacity of water is 1 kcal/kg. From 1 liter of water, 1750 liters of dry saturated steam are produced. At the same time, 539 kcal is expended. thermal energy. The released steam displaces oxygen from the combustion zone.

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

The use of wetting agents, other things being equal, reduces 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 or thinly spread 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 droplets over the burning surface. This curtain limits the flow of oxygen from the environment into the combustion zone. Oxygen penetrating through the curtain into the combustion zone is diluted with steam formed 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 jets is used for mechanical separation of the flame and for cooling the surrounding structures. The disadvantage of a continuous jet is the low coefficient of utilization 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 salt, Glauber's salt, ammonium sulphate and others are added to 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 the extinguished hearth from re-igniting from sparks and coals.

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, such as sodium hydrogen sulfate, 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 effective fire extinguishers. Fire extinguishing foams are divided into chemical and air-mechanical. Chemical foam is obtained as a result of a chemical neutralization reaction between an acid and an alkali. The shell of the bubbles 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 a foaming solution with air. The shell of air-mechanical foam bubbles consists of an aqueous solution of foam concentrates of the PO-1, PO-5 types.

The resulting fire extinguishing foam is characterized by:

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

Multiplicity of foam (the ratio of the volume of foam to the volume of the original product);

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

Dispersion (bubble size).

Surfactants (bone or carpentry glue) are used to increase the stability of the foam, and ethanol (C 2 H 3 OH) or ethylene glycol is used for storage at low temperatures.

Foams are used to extinguish fires of class A, B, C. It cannot be used to extinguish alkali and alkaline earth metals and electrical equipment under voltage.

carbon dioxide. Carbon dioxide supplied to the fire can be in a solid state (carbon dioxide snow), gaseous and aerosol.

Carbon dioxide snow can be obtained by rapidly evaporating liquid carbon dioxide. The resulting snowy carbon dioxide has a density of 1.5 g/cm 3 at -80 0 C. Snowy carbon dioxide lowers the temperature and reduces the oxygen content in the combustion zone. From 1 liter of solid acid, 500 liters of gas are formed.

In the gaseous state, carbon dioxide is used for volumetric extinguishing indoors, filling the entire volume and displacing oxygen from it. Aerosol carbon dioxide (in the form of tiny crystalline particles) gives the greatest effect in rooms where the air can contain the smallest combustible particles (cotton, dust, etc.). In this case, carbon dioxide not only extinguishes, but also contributes to the rapid deposition of particles suspended in the air. To stop combustion 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 poses a danger to people. Therefore, entering the room after filling it with carbon dioxide is possible only in oxygen insulating gas masks.

Carbon dioxide is not electrically conductive and evaporates without leaving any traces behind. Carbon dioxide is used to extinguish electrical equipment, internal combustion engines, to extinguish fires in valuable material storages, 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 formulations- these are compounds with galloid hydrocarbons. They are volatile liquids, so they are referred to as gases or aerosols. The main compositions used in extinguishing fires are:

Freon 125 (C 2 HF 5)

Freon 318 (C 4 Cl 3 F 8)

These compositions are by far the most effective means of extinguishing fires. Their action is based on the inhibition of chemical reactions 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:

The most effective in comparison with all available formulations;

Have a high penetrating ability;

They are used at negative temperatures (up to - 70 0 С).

Flaws:

Toxicity;

Formation of corrosive compounds in the presence of moisture;

Not effective for outdoor use;

• It is impossible to extinguish alkali and alkaline earth metals and acid-containing substances.

Powder formulations. The powder fire extinguishing compositions currently used include:

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

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

PCA (~90% potassium chloride);

AOS - aerosol-forming compositions.

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

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

Ineffective when extinguishing:

Smoldering materials and substances burning without access to oxygen.

The effect of powder compositions of PCC and AOS is to inhibit the chemical reaction of combustion and reduce the oxygen content in the combustion zone.

PHC and AOS powders are the most promising today. Aerosol fire-extinguishing compositions - AOS are especially effective.

AOS is a solid fuel or pyrotechnic composition 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 applied:

Flaming AOS;

Chilled AOS.

Flame compositions, when actuated by devices of aerosol-forming compositions, have a flame reaching several meters and a temperature of combustion products at the outlet of 1200 - 1500 0 C. This is their disadvantage.

Cooled aerosol formulations are obtained using special chilled nozzles. This makes it possible to reduce the temperature of AOC during combustion from 600 0 С to 200 0 С, but at the same time the aerosol mixture will contain products of incomplete combustion of AOC, which significantly increases the toxicity of combustion products compared to flame AOC.

AOS is used for extinguishing in fire extinguishers, in generators of various types, both in autonomous mode and in automatic aerosol fire extinguishing installations.