Fire extinguishing agents and their properties. Characteristics of the main extinguishing agents Fire extinguishing agents and their characteristics
In scientific language, a fire extinguishing agent is a substance that has the necessary properties that make it possible to create conditions for the termination of the combustion process.
In practice, fire extinguishing agents are empirically determined, selected substances in a different aggregate state, used by different ones, through a long-term selection; incl. fire equipment, primary means for the operational fight against beginning fires in buildings, structures, on territories settlements, enterprises, organizations.
These are the well-known portable, mobile fire extinguishers, PCs with sets of hoses, barrels; with installed on them, without which today it is difficult to imagine the interior of office, administrative, business buildings; shopping and entertainment, sports, exhibition centers.
Classification of extinguishing agents
The classes of fire extinguishing substances according to the physical characteristics of the impact on the fire site, the process of its localization with subsequent elimination, according to the main principle of stopping the combustion reaction, are divided into the following main groups and include:
- - water, aqueous solutions of salts, with the addition of wetting agents - surfactants, as well as carbon dioxide in a solid state of aggregation - in the form of snow.
- ... Air-mechanical foam of various expansion rates - from low to high degree; powder formulations; dry non-combustible substances: sand, earth, crushed stone, small pebbles, waste from boiler houses, metallurgical industries - slags, fluxes; as well as sheet, covering materials, such as bedspreads, which are successfully used to fight small foci of an incipient fire.
- - inert gases: argon, nitrogen; water vapor, mist from water mist, mixtures of gases with water, and flue gases.
- Fire extinguishing agents chemical inhibition of the combustion reaction... In scientific terminology, they are also called combustion inhibitors. These are freons; halogenated hydrocarbons, compositions based on them; aerosol fire extinguishing compositions; sprayable aqueous bromoethyl solutions; powder formulations.
By physical characteristics
- Fire extinguishing liquids.
- Powder formulations.
- Gases, gas extinguishing compositions.
Fire extinguishing agents can also be divided into classes where possible. electricity, which is important, must be taken into account in the design, installation and application as primary funds fight against starting fires, and when starting manual, automatic:
- Conducting electric current - water and its solutions of salts of various acids, water vapor, fog, suspension, incl. formed by water fire extinguishing installations, as well as all types of air-mechanical foam.
- All gas and powder compositions used both in portable, mobile fire extinguishers and in, are not electrically conductive.
It is also important to know that not all fire extinguishing substances waiting in the wings before use are useful to a person, some may well harm him in one way or another, they are classified according to toxicity to the body as a whole, danger to the respiratory system:
- Low-toxic - carbon dioxide.
- Toxic - freons, halogenated hydrocarbons.
- Hazardous to breath without individual funds protection - powder, aerosol suspensions, gases formed in the airspace of premises protected by gas, powder, aerosol systems, fire extinguishing installations,
This is often forgotten by manufacturers and suppliers of such equipment, offering them as an equivalent and cheaper alternative to traditional and, most importantly, safe for people in protected areas, water and.
Requirements for extinguishing agents
They can be formulated in order of priority:
- Efficiency of application, the ability to use on various types of fire loads.
- Low, preferably low cost.
- Availability, availability, the ability to quickly replenish stocks. So, if water acts as a fire extinguishing agent, then the ideal option is the presence of an external network fire-fighting water supply for extinguishing the territory, buildings of cities, settlements; internal fire water supply for work from a PC inside buildings. The worst, but acceptable option would be the presence, or for the possibility of installing fire-fighting vehicles, connection.
- Safety for the health of people, both inside buildings and structures protected by automatic fire extinguishing installations, and directly using them in the course of extinguishing from fire equipment, by manual means fire fighting.
Alas, as a rule, the safety of people is not a priority compared to the ability to quickly extinguish a fire with one or another fire extinguishing agent. Therefore, designers, developers of equipment, creating, constructing, forced supply of clean air, try to compensate for this in various ways; informing about the danger, providing the opportunity for people to quickly leave buildings, structures, using smoke-free.
In general, fire extinguishing agents are subject to the following regulatory requirements in the field of PB:
- must ensure the elimination of the focus by a surface, volumetric method or combined methods of their supply, taking into account the characteristics of fire extinguishing agents, and in accordance with the tactics of extinguishing the fire.
- must be used to extinguish fires with those materials, interaction with which does not lead to the danger of explosion or new sources of ignition.
- must fully preserve their physical and chemical properties necessary for extinguishing a fire during storage, within the specified timeframe, and during transportation / delivery.
- must not have a dangerous effect on human health and environment exceeding the accepted MPC.
Lecture on the topic
Water and its various solutions remain the main means of localization and elimination of fires that occur both on the territory of settlements and outside the city limits. It is the most accessible, inexpensive, easily transported substance supplied to the places of fire, harmless to people; well stored, most importantly, very effective in extinguishing most combustible, combustible substances, materials of both natural and artificial / synthetic origin - from wood to plastics, plastics.
In those cases when water, due to its physical and chemical properties, cannot cope with extinguishing organic substances, for example, during the combustion of most commercial oil products; then the effective extinguishing agent is foam generated from aqueous solutions of the foaming agent, both by hand and stationary devices.
If for some reason the combustion of substances is difficult or impossible to eliminate with water or foam, then powder, gas or aerosol fire extinguishing compositions are used that effectively cope with this task.
Among the fire extinguishing agents acceptable for use in extinguishing various substances, first of all, water and aqueous solutions with wetting agents and salts of various acids dissolved in it should be isolated; foam obtained from aqueous solutions different types fire-fighting foaming agents.
It is possible to effectively localize and eliminate both incipient foci and developing fires of the following substances and materials:
- Combustion of solids.
- Fires of flammable liquids, incl. petroleum products, including such as tar, asphalt, paraffin.
- Natural and synthetic rubber.
(the table in high resolution is available by clicking the download button after the article)
When extinguishing fires, such substances as water, its vapors, as well as other liquids, gases, powders of some substances that have the most effective fire extinguishing effect, are widely used.
Extinguishing agent- is a substance with physicochemical properties, allowing you to create conditions for the cessation of combustion. Fire extinguishing agents can be in solid, liquid or gaseous state (GOST 12.1.033).
When choosing a fire extinguishing agent, it is necessary to take into account its compatibility with the burning material, i.e. exclude the possibility of an explosion, the release of poisonous, corrosive and other substances in the fire zone.
The most common extinguishing agent is water.
As stated above, water is the cheapest and most widespread means of extinguishing fires. It has a high heat capacity, a heat of vaporization of 2258 J / g, an increased thermal stability (over 1700 ° C), a significant increase in volume during vaporization (1 kg of water forms over 1700 liters of steam upon evaporation).
Water also has three fire extinguishing properties: it cools the burning zone or burning substances, dilutes the reactants in the burning zone and isolates the combustible substances from the burning zone.
Water is used to extinguish solid combustible materials, create water curtains and cool objects (technological installations, apparatus, structures, buildings, etc.) located near combustion centers.
Water is not used to extinguish installations and equipment under voltage due to its high electrical conductivity.
When extinguishing water-insoluble light oil products and other combustible substances with a density less than the Density of water, they float and continue to burn on its surface. Moreover, the area of the burning surface increases, which can significantly complicate the conditions for extinguishing a fire.
The water supply to the combustion center can be in the form:
· Continuous (compact) jet from fire monitors with nozzles with a diameter of 28: -50 mm or from manual fire nozzles with nozzles with a diameter of 13-25 mm;
· Sprayed jet with a diameter of water droplets over 100 microns;
· A fine spray with a water droplet diameter of up to 100 microns, obtained from stationary or portable sprayers;
· Solutions containing 0.2-2.0% of the mass of wetting agents to reduce surface tension;
· A water-bromoethyl emulsion containing 90% of the mass of water and 10% of ethyl bromide.
Water in the form of compact and atomized jets is used to extinguish solid substances and materials of organic origin, flammable liquids, such as dark oil products.
Compact jets knocks down flames while cooling surfaces. They are used mainly when water is supplied over a long distance or to impart an impact force to it, when fires are extinguished at a considerable height or with a large fire center that does not allow to come close to the combustion center, as well as if it is necessary to cool buildings and structures adjacent to a burning object. , metal structures, tanks, etc.
Depending on the pressure and flow rate of water, the radius of action of the compact part of the jet varies from 6 to 30 m and more. The advantages of compact jets include range, maneuverability, and the ability to bring down flames.
The disadvantages of using compact jets are the low efficiency of cooling the reactants, which is due to the short duration of contact with the combustion zone and the electrical conductivity of the water flow; the possibility of the formation of mixtures of explosive concentrations when a jet of water comes into contact with combustible dust; danger of mechanical damage, for example, instrumentation, equipment, as well as injury to people.
In many cases, a spray jet is more effective in extinguishing a fire due to the best conditions for the evaporation of water, hence for increased cooling and dilution. combustible environment.
Spray spray is achieved by passing it through the nozzle. Such jets have a more developed surface, therefore, at the same water flow rate, they remove much more heat from the combustion zone per unit time than compact ones.
Sprayed jets are recommended to be used when extinguishing small fires, when it is possible to come close to the fire site, to cool structures, substances and materials located in the zone of intense heat exposure, to protect firefighters and fire fighting equipment.
Water in the form of atomized and finely atomized jets is used to extinguish flammable and flammable liquids immiscible with water.
When flaming liquids hit the surface, water droplets evaporate and vapor bubbles form a non-flammable emulsion with the liquid. Because the emulsion is lighter than the liquid, it covers its surface, isolating the fuel from the combustion zone. Small droplets of water lower the temperature of the flame, cool the burning liquid, slowly sinking into it; reduce the concentration of flammable vapors due to evaporation above the surface of the liquid. Small droplets of water do not splash or splash burning liquids. Finely atomized water forms an aerodynamic system - a fog, in which it is little or practically non-conductive, therefore, it can be used in case of fires in electrical installations.
For extinguishing fires of flammable liquids (diesel fuel, kerosene, transformer oil, lubricating oils, etc.), water is mainly sprayed in the form of drip jets with an optimal droplet size of 0.3 to 0.8 mm, depending on the pressure of the jet. The best effect of extinguishing flammable liquids (with a low ignition temperature) is achieved by finely sprayed and foggy water jets.
To increase the penetrating power of water, it is necessary to reduce its surface tension. For this purpose, surfactants (surfactants) are introduced into the water. The addition of surfactants (wetting agents) reduces water consumption by a factor of 2.0-2.5 and significantly reduces the time to extinguish a fire. For example, the introduction into water from 0.5 to 2.0% of a wetting agent increases the effect of extinguishing fires of poorly wetted substances and materials almost twofold. To obtain water-chemical solutions, sulfonates, sulfonols, wetting agents and foaming agents are used.
Water cannot be used to extinguish a number of organic liquids that float and continue to burn on the surface of the water.
When water gets on bitumen, fats, oil, sodium peroxide, petrolatum, on the contrary, combustion intensifies as a result of the release, splashing, boiling of these materials.
Water contains various natural salts, which leads to an increase in its corrosivity and electrical conductivity. These properties are enhanced by various additives introduced to increase the extinguishing efficiency: antifreezes and foaming agents.
Fire extinguishing foams... Foam is a system in which the dispersed phase is always gas. Gas bubbles are enclosed in thin shells - films of liquid. Gas bubbles can form inside a liquid as a result of chemical processes or mechanical mixing of a gas (air) with a liquid. The smaller the size of the gas bubbles and the surface tension of the liquid film, the more stable the foam.
At a low density (0.1-0.2 g / cm 3), the foam spreads over the surface of the burning liquid, cooling and isolating it from the flame. In this case, the flow of combustible vapors into the combustion zone stops and the flame goes out.
To extinguish fires, a stable foam is used, which can be obtained by introducing small amounts (3.0-4.0%) of a foaming agent into the water, which can reduce the surface tension of the water film.
Foaming agents- these are substances that are in a colloidal state and can be sorbed in the surface layer of the solution at the liquid-gas interface. These substances include natural foaming agents, licorice root extract, saponin, albumin, etc.
Currently, synthetic hydrocarbon and fluorine-containing foaming agents are most often used, such as "Film-forming Barrier", Barrier-612, TEAS, PO-6 OST, etc.
The fire-extinguishing properties of foam are determined by its stability, expansion rate, biodegradability and wetting ability.
Stability of nena is its ability to preserve its original properties.
Multiplicity of nena- the ratio of the volume of the foam to the volume of the solution from which it is formed. Foams with higher expansion are less resistant.
The quality of the foam is largely determined by its dispersion. The higher the dispersion, the greater the resistance of the foam and the higher its fire extinguishing efficiency.
Depending on the magnitude of the expansion ratio, the foam stability is subdivided into low expansion (<20), среднекратную (20-200) и высокократную (>200).
Neny's fire extinguishing efficiency characterized by the intensity of its supply and specific consumption.
Two types of resistant fire-extinguishing foams are widely used: air-mechanical and chemical. They are used to extinguish solids, flammable liquids with a density less than 1 and do not dissolve in water. Chemical foam is generally more durable than mechanical foam.
Air mechanical foam is a mechanical mixture of air, water and a surfactant (foaming agent). It contains about 99% air, 1% water and 0.04% foaming agent.
The durability of air-mechanical foam is less than that of chemical foam, and the durability decreases with increasing foam expansion. To obtain air-mechanical foam, it is necessary to introduce the foaming agent into the water in the suction line of the pump or in the pressure line. Usually, a foaming agent of the PO-1 type is used, consisting of a kerosene contact, wood glue and ethyl alcohol.
To obtain air-mechanical foam, special devices are used, the so-called foam chambers.
Foam cameras installed near the upper edge of the tank for uniform distribution of foam over the surface of the burning liquid.
A stationary foam camera for extinguishing the fire of tank 1 is connected to a fire pump (Fig. 2). The foam concentrate solution enters the foam chamber 2 through hose lines 6, laid from the fire truck 5, which is located on the road near the embankment 3 and takes water from the fire hydrant 4. The foam concentrate from the fire truck tank is introduced into the water stream by a dispenser located in the dispenser compartment of the car. The water solution of the foaming agent supplied in this way turns in the foam chambers into air-mechanical foam, which spreads over the surface and extinguishes the combustion center, isolating the liquid from the flame.
The standard intensity of medium expansion foam supply depends on the properties of flammable liquids and ranges from 0.05-0.30 dm3 / (m2s).
Special dosing devices with heads for producing foam are used in sprinkler and deluge automatic fire extinguishing installations.
On the surface of burning liquids, foam forms a stable film that does not collapse under the influence of a flame for 30 minutes, a time that is quite sufficient to extinguish combustible liquids and flammable liquids in tanks of any diameter.
Air-mechanical foam is completely harmless to people, does not corrode metals, is almost non-conductive and very economical. It is also used to extinguish solid burning substances (wood, etc.). Wooden structures covered with air-mechanical foam for a long time (up to 40 minutes) resist the effects of radiant energy and do not ignite. Under the same conditions, unprotected structures ignite after 15 minutes.
Foam installations are widely used at enterprises for the storage and processing of flammable liquids with a flash point of vapors above 28 ° C and solid combustible materials and products.
Chemical foam formed by the interaction of sodium carbonate or bicarbonate or other salts with an acid in the presence of a foaming agent. Such foam is obtained from foam powder and water in foam generators, which are special ejector portable devices.
Foam powder consists of dry sodium bicarbonate salts, stabilizers, licorice extract or other foaming agent. When interacting with water, salts dissolve, react to form carbon dioxide. The release of a large amount of carbon dioxide results in a stable foam.
When spreading chemical foam, a very stable layer 7-10 cm thick is formed, which is little destroyed by flame. Chemical foam does not interact with oil products and forms a dense cover that does not allow liquid vapors to pass through.
Stability of chemical foam more than 1 hour. recent times there has been a tendency to reduce the use of chemical foam, which is associated with its relatively high cost and the complexity of organizing fire extinguishing.
When extinguishing fires in tanks with oil products, chemical or air-mechanical foam is fed into the combustion center by stationary foam generators GPS-600, GPS-2000, foam mixers (foam chambers) GPSS-600, GPSS-2000 or mobile foam lifters.
Currently, high expansion foam generators (HPVC) and high-pressure foam generators (HPG) are widely used to produce foam. Chemical foam is formed in the hose line, which transports the aqueous solution of the foam generator powder, as the flow moves to the foam drain.
However, in most cases, chemical foam is successfully replaced by air-mechanical foam.
Inert diluents. In the event of the possibility of an explosion due to the accumulation of flammable gases or vapors in a burning room, it is necessary to create an environment in it that does not support combustion. This is achieved by using inert diluents as fire extinguishing agents, such as water vapor, nitrogen, carbon dioxide, argon, flue gases and some other substances. Inert diluents slow down the reaction rate, since part of the heat of combustion is spent on heating them.
Water vapor- technological and spent - used to create steam-air curtains in open technological installations, as well as to extinguish fires in small rooms and technological equipment(dryers, reactors, columns, etc.). The extinguishing concentration of water vapor in this case is about 35% of the volume.
Nitrogen used mainly for extinguishing substances that burn with a flame. It poorly extinguishes substances that can smolder (wood, paper), and practically does not extinguish fibrous substances (fabric, cotton wool, cotton). The extinguishing concentration of nitrogen in the air is taken to be at least 35% by volume. Dilution of air with nitrogen to an oxygen content of 12-16% by volume is safe for humans. Higher dilution is dangerous.
Carbon dioxide used for volumetric extinguishing of fires in flammable liquids warehouses, accumulator stations, in drying ovens, at stands for testing motors of electrical equipment, etc.
Carbon dioxide is a colorless gas; from one liter of liquid carbon dioxide at 0 ° C, 506 liters of gas are formed. For most substances, its fire-extinguishing concentration is 20-30 "VO volume. However, when using carbon dioxide in fire extinguishing, its toxicity at high concentrations must be taken into account. Inhalation of air containing 10% CO 2 is fatal.
Therefore, in the extinguishing system using carbon dioxide, it is necessary to provide a signaling device to ensure the timely evacuation of people from the premises.
The supply of carbon dioxide for extinguishing can be twofold: through sockets-diffusers or through a perforated pipeline. In the first case, supercooling of the outgoing liquefied carbon dioxide (carbon dioxide) occurs with the formation of solid dioxide in the form of snow, and the quenching effect is achieved by the cooling principle, in the second case - by the dilution method. For the supply of CO 2, fire extinguishers or stationary installations are usually used.
Halogenated hydrocarbons. Halogenated hydrocarbon formulations- fire extinguishers based on hydrocarbons, in which one or more hydrogen atoms are replaced by halogen atoms. They belong to inhibiting or phlegmatizing agents, extinguishing by which occurs as a result of inhibition of chemical reactions.
The most effective action is provided by bromine and fluorine derivatives of methane and ethane. In this case, the reactivity and the tendency to thermal decomposition depend on the halogen replacing hydrogen. These properties increase in the fluorine - chlorine - bromine - iodine series.
Modern trade names for halogenated hydrocarbons freons, previously - freons. Abroad they are called gallons. According to the nomenclature adopted in our country, the freon number is composed as follows: the first digit is the number of carbon atoms minus one, the second is the number of hydrogen atoms plus one, and the third is the number of fluorine atoms. Bromine is characterized by the letter B.) And by the number of atoms, the number of chlorine atoms is determined by the free bonds.
The most widespread for extinguishing fires are halogenated hydrocarbons such as trifluorobromomethane (freon 13B1), difluorochlorobromomethane (freon 12B1), dibromotetrafluoroethane (freon 114V2), dibromodifluoromethane (freon 12V2). Freons 114B2, 12B2 and ethyl bromide are heavy liquids with a smell, the rest of freons under normal conditions are gases. They are poorly soluble in water, but miscible well with many liquid organic substances.
Freons are used for volumetric extinguishing, for surface extinguishing of small fires and to prevent the formation of explosive environment... They are used to protect highly hazardous workshops. chemical production, Dryers, paint booths, warehouses with flammable liquids, etc. Freons are not recommended for extinguishing metals, a number of metal-containing compounds, metal hydrides, as well as materials containing oxygen.
The versatility of their application is explained by a number of specific properties. Freons have good dielectric properties, which makes them suitable for extinguishing fires in electrical equipment under voltage. As a result of the high density, freons in liquid and gaseous states form a stream well, and freon drops easily penetrate the flame. Their low freezing point allows them to be used at subzero temperatures, and their good wettability allows them to extinguish smoldering materials.
However, freons, as a means of extinguishing fires, are not without drawbacks. First of all, almost all of these compounds are harmful to the human body. Moreover, the freons themselves are weak narcotic poisons, and the products of their thermal decomposition are highly toxic. Freons are also characterized by high corrosive activity.
Solid and combined fire extinguishing agents. These substances in the form of powders have a high extinguishing efficiency. They are capable of suppressing the combustion of various, including pyrophoric compounds and substances that cannot be extinguished with water or foam.
The principle of extinguishing with powder formulations is either to isolate the burning materials from the air, or to isolate vapors and gases from the combustion zone. In addition, powder formulations, when entering the combustion center, are capable of inhibiting the flame. Therefore, the fire extinguishing effect of, for example, powders based on alkali metal bicarbonates is much greater than the effect of cooling or dilution with carbon dioxide released during the decomposition of these powders.
Powder compositions are used to extinguish metals and metal structures, organometallic compounds, pyrophoric substances, and gas flames.
Powder compositions have such advantages as high fire extinguishing efficiency; versatility; the possibility of extinguishing fires of electrical equipment under voltage, and their use at subzero temperatures. They are non-toxic, do not have a corrosive effect, they can be used in combination with sprayed water and foam extinguishing agents, do not render equipment and materials unusable.
The disadvantages of their use are caking and clumping. but modern technologies obtaining powder formulations makes it possible to largely avoid these disadvantages.
Currently, powders of the following composition are produced and used in fire extinguishing:
PSB (sodium bicarbonate, 10% talc, 1-2% organosilicon additives AM-1-300);
PS (sodium carbonate, 2.5% metal stearate, 1% graphite);
P-1A (phosphorus-ammonium salts with additives AM1-300);
SI-2 (silica gel brand MSK, ShSK or KSK 50%, freon 114V2 50%);
PF (phosphorus-ammonium salts, 5% talc, 1-2% AM-1-300).
Powders of PSB and PF composition are capable of creating a fire extinguishing cloud and are intended for extinguishing fires of hydrocarbons, wood, electrical equipment.
Powders of the PS type create an insulating layer on the surface of burning materials and are intended for extinguishing metals, organometallic compounds, etc.
Combined formulations- these include water-halide hydrocarbon emulsions, a combined nitrogen-carbon dioxide composition for extinguishing alkali metals in rooms, aqueous solutions of bicarbonate of soda, carbon dioxide, potash, ammonium chloride, sodium chloride, Glauber's salt, ammonium-phosphorus carbonate, copper sulfate, and a sulfate , bromoethyl and other halogen compounds. Combined nitrogen-halon and carbon-dioxide-halon compositions for volumetric extinguishing have also been developed.
Combined powders of the SI type are widely used for quenching organic liquids, pyrophors, metal hydrides, and some organosilicon compounds.
The fire-extinguishing properties of combined aqueous solutions of salts differ from the fire-extinguishing action of water in that salts, falling out of solutions, form insulating films on the surface of the burning substance, on which a certain part of the heat of the fire is spent. Inert extinguishing gases are released during the decomposition of salts.
Fire extinguishing agents are selected in each specific case, taking into account the conditions of the combustion process, fire hazard and physical and chemical properties of substances and materials.
Similar information.
Before moving on to the classification and designs of fire extinguishers, it is necessary to consider the properties of the most common fire extinguishing agents used to charge fire extinguishers.
The following extinguishing agents are used as charges in fire extinguishers:
... Water and aqueous solutions chemical substances;
... Foam;
... Powder formulations;
... Aerosol formulations;
... Gas compositions;
Extinguishing media:
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 sufficiently high freezing point, low thermal conductivity, and a high coefficient of surface tension (which prevents its rapid spreading over the surface of burning solid materials, penetration into the depths and their wetting). In this regard, water is more often used in the form of solutions with various additives that give it special properties: they lower the freezing point, or lower the surface tension coefficient, increasing its wetting ability, or increase its viscosity.
Extinguishing flammable liquids with a compact jet of water leads to its ineffective use. This is explained by the fact that water has a low coefficient of thermal conductivity, therefore, passing through the torch, it has almost no 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 area of the fire as a result of splashing the burning liquid or spreading it over the surface of the water.
The most fire extinguishing ability is possessed by a fine spray water jet - with droplets less than 150 microns in diameter, which evaporate 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 burning liquid. And besides, it combines the advantages of both liquid and gas extinguishing agents. Fine atomization is achieved by using special nozzles, heating water above its boiling point and then ejecting superheated water onto the fire site or creating a gas-saturated solution of CO2 in water using special atomizers. However, a finely dispersed stream of water, as a result of a decrease in the diameter of droplets and their entrainment by ascending gas flows, has insufficient penetrating ability, which complicates extinguishing (since it is necessary to come close to the fire source). So when extinguishing solid materials stacked in a pile, the jet does not penetrate inside it and does not suppress the 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 center.
Foam:
Another effective and no less common than water, fire extinguishing agent is foam. It is often used to extinguish fires because it can have both insulating and cooling effects at the same time. The cooling effect of the foam makes it possible in many cases to exclude the re-ignition of the 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 thin film shell 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, as it instantly collapses in the fire. Foams used for these purposes must have high structural and mechanical strength, so that during the time required for its accumulation and extinguishing a fire, it remains on the surface of a combustible liquid. Therefore, in addition to surfactants, which actually participate in the creation of the foam, a stabilizer is necessarily introduced into the foaming agent formulation.
In addition to foam, an air emulsion is also used to extinguish fires. Unlike foam, it is a system consisting of separate air bubbles, connected by a single frame and freely distributed in the liquid. Such an emulsion is formed when a sprayed liquid charge of a fire extinguisher strikes the surface of a burning substance.
In domestic practice, aqueous solutions of foaming agents "in pure form" are practically not used as a charge for air-foam fire extinguishers. Since foaming agents cannot be stored for a long time in the form of working solutions, 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.
By chemical composition, foaming agents are subdivided into hydrocarbon (PO-3NP, PO-6NP, PO-6TS, PO-6TsT, TEAS, "MORPEN", etc.) and fluorinated (PO-6TF, PO-6A3F, "Merkulovsky", "Film-forming " and etc.)
By purpose, foam concentrates are divided into general-purpose foam concentrates (PO-3NP, PO-6TS) and intended purpose(PO-6NP, "MORPEN", "Polar", fluorinated), which are used in special conditions or for extinguishing 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 foam volume to the volume of the solution from which it was obtained, i.e. to the volume of its liquid phase. Chemical foam has a multiplicity of no more than 5. Air-mechanical foam can be of low expansion (from 4 to 20), medium (from 21 to 200) and high expansion (more than 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 extinguishing agent that is increasingly used due to its versatility is powder formulations, which are finely dispersed mineral salts that are treated with special additives to make them fluid and reduce their ability to wet and absorb water. The greatest effect of quenching with a powder is achieved when its particles have a size of about 5-15 microns; however, such a powder is difficult to supply to the combustion center. Therefore, the powder is usually made polydisperse, i.e. consisting of large (from 50 to 100 microns) and small particles. When powder is fed from a barrel or a fire extinguisher, a stream of large particles captures and delivers small particles to the combustion site. To obtain powder compositions, ammonium salts of phosphoric acid, carbonates, bicarbonates, alkali metal chlorides and other compounds are used.
Depending on the purpose, powder compositions 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 used to extinguish metals, organometallic compounds, metal hydrides (class D fires) or other substances with unique properties. Fire extinguishing with general-purpose powders is carried out by creating a fire-extinguishing concentration in the volume above the burning surface, special-purpose powders - by filling and isolating the fuel surface from air oxygen.
Fire extinguishing powders, depending on what classes of fire they can extinguish, are subdivided as follows:
... Powders of ABCE type, the main active component of which is phosphorus-ammonium salts (Pirant-A, Vekson-ABC, 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 may 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 intended for extinguishing liquid, gaseous combustible substances and electrical equipment under voltage (it is useless to extinguish class A fires with these powders).
... D-type powders (special-purpose powders), the main component of which is potassium chloride, graphite, etc. (PHK, Vekson-D, etc.); used for extinguishing metals, metal-containing compounds.
Powders are environmentally inert and can be used to extinguish almost any class of combustible fires in a wide temperature range (from -50 to +50).
Like other fire extinguishing agents, powders have a number of significant disadvantages... So they do not have a cooling effect, therefore, after extinguishing, cases of ignition of an already extinguished substance are possible. They contaminate the target. As a result of the formation of a powder cloud, visibility is reduced (especially in a small room). In addition, the cloud of powder is irritating to the respiratory and visual organs. Since powders are finely dispersed systems (the bulk of powder particles have a size less than 100 microns), powder particles are prone to agglomeration (lump formation) and caking, and substances that are part of their formulation tend to absorb water and its vapors (including out of thin air).
Aerosol formulations:
In recent years, 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 time 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 alkali metal oxides 1-5 microns in size, non-combustible gases and vapors (N2, CO2, H2O, etc.). High fire extinguishing efficiency (but only with a volumetric method of extinguishing) aerosol compositions is due to a sufficiently long time of preservation of the aerosol cloud over the combustion center and maintaining the initial fire extinguishing concentration, as well as high penetrating ability. According to this parameter, aerosol compositions are close to gaseous means of extinguishing a fire. At the time of application of aerosol extinguishing agents, oxygen in the air is also burned out in an atmosphere of a closed volume, it is diluted with inert combustion products of the charge, and the chain reaction of oxidation in a flame is inhibited by highly dispersed active solid particles. Aerosol formulations do not cake; solid fine particles with a developed surface are highly active, since they are formed immediately at the time of application; aerosol generators do not require labor-intensive maintenance, etc. However, for all their positive qualities, aerosol formulations have many of the disadvantages inherent in fire extinguishing powders. In addition, high temperatures develop in devices during their use, and in some structures there is an open flame, so they themselves can be a source of ignition (for example, in case of a false alarm). Designers have to use special devices in order to remove open flames and reduce the temperature of the resulting aerosol.
Gas compositions:
The most "clean" extinguishing agents are gas compositions. Carbon dioxide and freon are used as charges in gas fire extinguishers.
Carbon dioxide (carbon dioxide) at a temperature of 20 ° C and a pressure of 760 mm Hg. is a colorless gas with a sourish taste and faint odor, 1.5 times heavier than air. As an inert gas, carbon dioxide does not support combustion; when it is introduced into the area of flame combustion in an amount of the order of 30% vol. and lowering the oxygen content to 12-15% vol. the flame goes out, and when the oxygen concentration in the air decreases to 8% vol. the processes of decay also cease. When liquid carbon dioxide (which is in this form in the fire extinguisher) passes into gas, its volume increases by 400-500 times, and this process is accompanied by a large absorption of heat. Carbon dioxide is used either in a gaseous state or in the form of snow. It does not pollute and has almost no effect on the extinguishing object itself; possesses 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.
Among the disadvantages that this fire extinguishing agent possesses, the following should be noted: cooling the metal parts of the fire extinguisher to a temperature of the order of minus 60 0С; accumulation of significant charges of static electricity (up to several thousand volts) on the plastic bell; a decrease in the oxygen content in the atmosphere of the room during its application, etc.
In conclusion, it should be noted that only fire extinguishing substances with 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.
Substances that reduce the rate of combustion or completely stop it when introduced into the combustion zone are called fire extinguishing agents. According to their state of aggregation, they are divided into liquid (water, ethyl bromide), solid or powdery (dry sand, earth, bicarbonate soda), gaseous
(inert gases, nitrogen, carbon dioxide, water vapor) and mixed (gaseous with solid - a mixture of carbon dioxide or air with powdery substances, gaseous with liquid - foams). Asbestos, felt or tarpaulin covers also have fire-extinguishing properties.
According to the principle of action, they are divided into cooling (water, carbon tetrachloride), diluting combustible substances or reducing the oxygen content in the combustion zone (water, steam, carbon dioxide) and chemically inhibiting the combustion process (ethyl bromide, methyl).
Most widely used to extinguish a fire are water, carbon dioxide, foams, powders, sand and other substances.
Water is the cheapest and most widespread means of extinguishing fires. It is used neat and with various surfactant additives.
Water is used to extinguish fires of solid combustible materials, create water curtains and cool objects located near the combustion center. It cannot be used to extinguish fires on electrical installations under voltage. When extinguishing with water, oil products and other combustible substances float up and continue to burn on the surface, therefore the extinguishing effect of such substances is sharply reduced. Its negative properties are also the formation of explosive concentrations when exposed to layers of dust (coal, grass flour, cement dust), the danger of mechanical damage to hot objects, poor wettability of some fibrous and solid substances packed in bales (cotton, linen, wool).
Water is supplied to the combustion center in the form of continuous or sprayed jets. Continuous powerful jets knock down the flame, which determines its mechanical extinguishing property, and at the same time cool the surface, and when spraying, the best conditions are created for the evaporation of water and, therefore, for cooling and diluting the combustible medium.
Sand and dry earth with its mass stops the access of oxygen to the combustion zone. Do not use to charge a fire extinguisher.
Foam used to extinguish solid combustible substances and materials, flammable liquids with a density of less than 1.0 g / cm3 and do not dissolve in water. It is a mass of gas bubbles enclosed in thin liquid shells. Spreading over the surface of the burning liquid, the foam cools and insulates the combustion site, and the emitted carbon dioxide reduces the oxygen concentration in the surrounding air. There are two types of foam: chemical and air-mechanical.
Chemical foam formed as a result of the reaction between alkali and acid in the presence of a foaming agent (licorice extract, saponin, foaming agents PO-6, PO-1). It consists of 80% by volume carbon dioxide, 19.6% water and 0.4% foaming agent. Chemical foam is electrically conductive and has aggressive properties, which must be taken into account when it comes into contact with human skin. The durability of the foam (from the moment of its
formation until complete destruction) more than 1 hour.
Air mechanical foam obtained by mixing water, air and foaming agents. It consists of 90% air, 9.7% water and 0.3% foaming agent. Compared to chemical foam, it is less stable (about 40 minutes), but more economical, easy and quick to obtain, and harmless to humans and animals. The fire extinguisher is designed to extinguish fires
various materials, including flammable liquids; it is prohibited to use for extinguishing electrical installations under voltage and alkali metals.
Inert diluents(water vapor, carbon dioxide, nitrogen, argon, flue gases, volatile inhibitors). Quenching when diluting the medium with inert diluents is associated with heat losses due to heating of these diluents, a decrease in the oxygen concentration, the rate of the process, and the heat effect of the combustion reaction.
Water vapor(technological, spent) is used to extinguish fires in closed, poorly ventilated rooms with a volume of up to 500 m3 and create steam-air curtains at open technological sites and installations. The extinguishing concentration of water vapor in the air during extinguishing should be about 35% by volume.
Carbon dioxide used to extinguish fires in drying ovens, flammable liquids, live electrical equipment, expensive equipment and valuables that can be damaged by water and foam (computer rooms, valuable documents, art galleries). However, you cannot extinguish alkaline and alkaline earth
metals, some metal hydrides. For most substances, its fire-extinguishing concentration should be 20-30% of the volume. The content of 10% CO2 in the air is dangerous, and at 20% it is fatal to humans (respiratory paralysis occurs).
Nitrogen used for extinguishing substances burning with a flame. It poorly extinguishes substances that can smolder (wood, paper), and practically does not extinguish fibrous substances (fabric, cotton wool, cotton). The extinguishing concentration of nitrogen in the air must be 35% by volume. Dilution of air with nitrogen to an oxygen content of 12-16% by volume is safe for humans.
Halocarbons(freons) are inhibitory agents. The most effective action is provided by bromine and fluorine derivatives of methane and ethane. Halogenated hydrocarbons are used for extinguishing chemical production shops, dryers, painting chambers, warehouses with flammable liquids, electrical installations under voltage. They are not used for extinguishing metals, a number of metal-containing compounds, metal hydrides, materials containing oxygen in their composition. They (narcotic, toxic effect) are harmful to humans and have a corrosive effect.
Fire extinguishing powders are finely ground mineral salts. They have an inhibitory effect, isolate burning materials from the air or isolate vapors and gases from the combustion zone. Designed for extinguishing alkali metals, organometallic compounds, phosphorus, flammable liquids and other substances that react with water, electrical installations under voltage, valuable documents, paintings and other materials damaged by water and foam. Powders are harmless to people, economical, do not freeze at low temperatures. They produce powders of the composition PSB, PF (extinguish hydrocarbons, wood, electrical equipment), PS (extinguish metals, organometallic compounds), etc.
Combined formulations combine the properties of various fire extinguishing agents and improve the efficiency of extinguishing fires. These include water-halide hydrocarbon emulsions, a combined nitrogen-carbon dioxide composition for extinguishing alkali metals in rooms, aqueous solutions of bicarbonate of soda, carbon dioxide, potash, ammonium chloride, sodium chloride, Glauber's salt, ammonium-phosphoric acid, copper tetrachloride, tetrachloride nitrogen-freon, carbon-dioxide-freon compounds.
Fire extinguishing agents
| Parameter name | Meaning |
| Topic of the article: | Fire extinguishing agents |
| Rubric (thematic category) | Technologies |
Basic principles of stopping combustion
Burning cessation principles. Fire extinguishing agents.
1. Cooling of reactants.
2. Isolation of reactants from the combustion zone.
3. Dilution of reactants to non-combustible or non-combustible concentrations. (reduction of the content of the combustible component)
4. Inhibition of the rate of chemical reactions of combustion (inhibition)
Fire extinguishing agents that are used to extinguish fires, as a rule, have a combined effect on the combustion process.
Water, mechanical and chemical foams, inert gases, steam, powders, freons, aerosols are used as these substances.
Liquid extinguishing agents
For extinguishing fires, water is widely used as a liquid extinguishing agent.
It has a high heat capacity, a significant increase in volume during vaporization (1 liter in - 1700 liters of steam).
For this reason, covering the surface of burning substances, water absorbs a lot of heat, cooling them to a temperature at which combustion stops, and the resulting steam insulates the burning surface from atmospheric oxygen for a while. At the same time, a jet of water (supplied under pressure) mechanically knocks down the flame from burning surfaces.
For the fire-extinguishing properties of water, special substances are used - wetting agents (PVA), which can reduce water consumption by 2 - 2.5 times.
Extinguishing fires with sprayed water also increases its efficiency (sprayed water intensively cools the surface, and the resulting steam prevents oxygen penetration).
In this case, it is extremely important to take into account its following negative properties as a fire extinguishing agent:
1. Do not extinguish a live electrical installation! Water is a conductor of electricity, therefore, before starting to extinguish a burning electrical equipment, it is extremely important to turn off the current.
2. Do not extinguish with water substances that are flammable or react in contact with it with the release of explosive gases (alkali metal carbides).
3. Do not extinguish flammable liquids with a density lower than that of water, because they float to the surface of the water, increasing the area of combustion.
4. It is impossible to extinguish bitumen and fats (they are thrown out and splashed)
Foam extinguishing agents
They are a mixture of gas (carbon dioxide or air) with a liquid (aqueous solutions of salts, acids). For the stability of the foam, PVA is introduced into it.
The fire-extinguishing effect of foam is associated with the formation of a screen above the flammable liquid, which slows down the rate of formation of flammable gases and vapors, and also reduces the oxygen concentration in the combustion zone. The most widespread are two types of foams:
1) Chemical foam (formed as a result of a chemical reaction associated with the release of gas). For this purpose use special powder aluminum sulfate + sodium bicarbonate Al 2 (SO 4) 3 + NaHCO 3 and surfactant.
2) Air-mechanical foam. Formed by mechanical mixing of air, water and surfactants. They are used to extinguish petroleum products and solid combustible substances.
Foams are characterized by multiplicity (foam volume to liquid volume) and the time of its destruction.
Gaseous extinguishing agents
Carbon dioxide CO 2 (carbon dioxide or dioxide), nitrogen, argon and water vapor are used as extinguishing gases.
Posted on ref.rf
Their action is based on the dilution of a combustible vapor-gas medium, ᴛ.ᴇ. reducing the oxygen concentration to values at which the combustion reaction stops.
1) Carbon dioxide is used to extinguish el. Equipment, internal combustion engines, in cases where the use of water can cause damage to equipment and instruments.
It is a colorless and odorless gas, 1.5 times heavier than air. It evaporates quickly, due to which it causes cooling of the combustion zone, and also dilutes combustible gases and oxygen in the combustion zone. Cannot be used when burning K, Na, alkaline earth metals.
2) Nitrogen. Reduces the concentration of oxygen and combustible gases, does not support combustion.
But the first two groups of substances cannot be used for substances capable of smoldering.
3) Water vapor.
Posted on ref.rf
The effect is to dilute oxygen.
4) The extinguishing composition is obtained by burning a solid fuel composition, which can burn without air access. The aerosol formed as a combustion product consists of a gas phase (mainly carbon dioxide) and suspended particles (like fire extinguishing powders, only with even smaller particle sizes, which increases the fire extinguishing ability).
5) Halons (halogenated hydrocarbons) call the inhibition of combustion reactions, tue. They are inhibitors. They are dialectrics and can be used to extinguish electrical equipment. Have low temperature freezing and can be used at low temperatures. At the same time, the toxic effect of freons and their thermal decomposition products on the human body is dangerous.
Solid extinguishing agents
They are used to eliminate the ignition of alkali metals that cannot be extinguished by other extinguishing agents, as well as to extinguish gas flames.
They are powders of various compositions (soda ash, graphite, stearic acid, iron and aluminum stearates).
The fire-extinguishing effect of powders consists essentially in the fact that they decompose in the combustion zone with the formation of carbon dioxide, which dilutes oxygen and prevents oxygen from entering the combustion zone.
Their mechanism of action is to inhibit combustion, ᴛ.ᴇ. in the inhibition of the rate of chemical reactions of combustion.
The choice of the method of extinguishing and the method of supplying the extinguishing agent is determined by the type of burning substance, material or equipment and the conditions of the fire.
Fire extinguishing agents - concept and types. Classification and features of the category "Fire extinguishing agents" 2017, 2018.
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