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 of 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 - foam). Asbestos, felt or tarpaulin blankets also have fire extinguishing properties.
According to the principle of action, they are divided into cooling (water, carbon tetrachloride), diluting flammable substances or reducing the oxygen content in the combustion zone (water, water vapor, carbon dioxide) and chemically inhibiting the combustion process (ethyl bromide, methyl).
The most widely used fire extinguishing agents are water, carbon dioxide, foams, powders, sand and other substances.
Water is the cheapest and most common means of extinguishing fires. It is used in pure form and with various additives of surfactants.
Water is used to extinguish fires of solid combustible materials, create water curtains and cool objects located near the source of combustion. It cannot be used to extinguish fires in energized electrical installations. When extinguishing with water, oil products and other flammable substances float and continue to burn on the surface, so the effect of extinguishing such substances is sharply reduced. Its negative properties are also, education explosive concentrations when exposed to layers of dust (coal, grass flour, cement dust), the risk of mechanical damage to hot objects, poor wettability of some fibrous and solid substances packed in bales (cotton, flax, 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 fire-extinguishing property, and at the same time cool the surface, and when spraying, better conditions are created for the evaporation of water and, therefore, for cooling and diluting the flammable medium.
Sand and dry earth with their mass stop the access of oxygen to the combustion zone. Not used to charge a fire extinguisher.
Penu used for extinguishing solid flammable substances and materials, flammable liquids with a density of less than 1.0 g/cm3 and insoluble in water. It is a mass of gas bubbles enclosed in thin shells of liquid. Spreading over the surface of the burning liquid, the foam cools and insulates the combustion site, and the released carbon dioxide reduces the concentration of oxygen in the surrounding air. There are two types of foam: chemical and air-mechanical.
Chemical foam is formed as a result of the reaction between an alkali and an 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. Durability of 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 produce, and harmless to people and animals. The fire extinguisher is designed to extinguish fires
various materials, including flammable liquids; It is prohibited to use for extinguishing live electrical installations and alkali metals.
Inert thinners(water vapor, carbon dioxide, nitrogen, argon, flue gases, volatile inhibitors). Extinguishing when diluting the medium with inert diluents is associated with heat losses for heating these diluents, a decrease in oxygen concentration, the rate of the process and the thermal effect of the combustion reaction.
water vapor(technological, spent) are used to extinguish fires in closed, poorly ventilated rooms with a volume of up to 500 m3 and to create steam-air curtains in open technological sites and installations. The fire 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, it is impossible to extinguish alkaline and alkaline earth
metals, some metal hydrides. For most substances, the 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 (paralysis of the respiratory system occurs).
Nitrogen used when extinguishing substances that burn in flames. It does not extinguish substances that can smolder (wood, paper) well, and practically does not extinguish fibrous substances (fabric, cotton wool). The fire extinguishing concentration of nitrogen in the air should be 35% of the volume. Diluting air with nitrogen to an oxygen content of 12-16% by volume is safe for humans.
Halocarbons(freons) are classified as inhibitory agents. The most effective effects are provided by bromine and fluorine derivatives of methane and ethane. Halocarbons are used for extinguishing chemical production workshops, dryers, spray booths, warehouses with flammable liquids, electrical installations under voltage. Not used for extinguishing metals, a number of metal-containing compounds, metal hydrides, materials containing oxygen. They (narcotic, toxic effects) 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, live electrical installations, valuable documents, paintings and other materials damaged by water and foam. The powders are harmless to people, economical, and 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 make it possible to increase the efficiency of extinguishing fires. These include water-halogen-hydrocarbon emulsions, a combined nitrogen-carbon dioxide composition for extinguishing alkali metals indoors, aqueous solutions of bicarbonate of soda, carbon dioxide, potash, ammonium chloride, table salt, Glauber's salt, ammonia-phosphorus salts, copper sulfate, carbon tetrachloride, bromoethyl, nitrogen-halone, carbon dioxide-halone compounds.
A variety of means used to extinguish fires are called fire extinguishing agents. Substances and materials that have certain properties in solid, liquid and gaseous states can be used as fire extinguishing agents.
The most commonly used substances for extinguishing fires include the following substances.
Water has a high heat capacity and is capable of absorbing a significant amount of heat from burning substances and materials. About 2688 J of heat is consumed to heat and convert 1 liter of water into steam.
Water does not wet many substances well (for example, wood and charcoal, cotton, wool, etc.), so the coefficient of its use when extinguishing fire is very low. To increase the wetting ability of water and increase the efficiency of extinguishing, various types of wetting agents are added to it, and are also used in the form of sprayed jets, since in this case its unproductive losses are significantly reduced. Finely sprayed water is also used to extinguish certain flammable and combustible liquids.
However, it is not allowed to use water to extinguish fires in cases where it chemically interacts with a particular substance (for example, quicklime, calcium carbide, alkali metals, etc.). Another disadvantage of water is its electrical conductivity, so it is not allowed to use it to extinguish electrical installations.
Water vapor has a cooling effect on burning substances, and also helps to dilute the concentrations of reacting substances in the combustion zone and isolates it from the surrounding air. Water vapor is used to extinguish fires in various types of apparatus and in small enclosed spaces. The extinguishing effect using water vapor is achieved with a mass flow rate of at least 0.002 kg/s-m3.
Fire extinguishing foams obtained by mixing gas and liquid, resulting in the formation of bubbles containing gas particles. Chemical and air-mechanical foams are used to extinguish fires.
Fire extinguishing properties foam is that, by covering the surface of a burning substance with a layer, it isolates it from the combustion zone, reduces the flow of hot vapors and gases into it and somewhat cools the burning substance.
Fire extinguishing foams are used to extinguish flammable and combustible liquids, as well as most solid combustible substances. Foam is supplied to the source of the fire using special devices - foam fire extinguishers, foam nozzles or foam generators. Recently, medium and high expansion foam has become widespread in the Soviet Union, which is successfully used to extinguish fires in industrial and residential buildings, on ships, etc.
Carbon dioxide(obsolete names: “carbon dioxide”, “carbon dioxide”), nitrogen and combustion products of liquid and solid fuels widely used as fire extinguishing agents.
The fire extinguishing properties of carbon dioxide (as well as other inert gases) lie in the fact that it to some extent isolates the burning surface from air access, cools it and dilutes the concentration of reacting substances entering the combustion zone.
The rapid evaporation of liquid carbon dioxide is accompanied by the formation of snow (this property of CO 2 is used in special fire extinguishers). The fire extinguishing concentration of carbon dioxide when extinguishing fires in closed spaces is 30% (by volume). Since this gas has toxic properties, when extinguishing a fire, you should immediately leave the room when it is filled with carbon dioxide. Carbon dioxide does not conduct electricity, therefore it is used to eliminate combustion in electrical installations. Carbon dioxide cannot be used to extinguish burning magnesium, sodium, aluminum, potassium and electrons, since it decomposes with the release of oxygen and thereby intensifies combustion. These metals can be extinguished with special fire extinguishing powders or liquid nitrogen.
Along with carbon dioxide and nitrogen, halogenated hydrocarbons are currently widely used to extinguish fires, which include liquid compositions of type 3.5, BF-1, BF-2, BM and freon 114B2. Their fire extinguishing effect is based on chemical inhibition of the combustion reaction when vapors of these compounds are introduced into the fire zone.
In cases where the use of the above means is ineffective or unacceptable, special powder formulations. In the USSR, the powder composition GISB (based on sodium bicarbonate) is used to extinguish oil products, alcohols, and protect transformers. Powder powders are used to extinguish molten alkali metals. with PS type stakes.
Fire extinguishing agents and their properties
In accordance with the conditions necessary for the occurrence and spread of combustion, its termination can be achieved by the following methods:
Termination of access to the combustion zone of an oxidizer (air oxygen) or flammable substance, as well as a reduction in their intake to values at which combustion is impossible;
By cooling the combustion zone below the auto-ignition temperature or by lowering the temperature of the burning substance below the ignition temperature;
Diluting flammable substances with non-flammable ones;
Intensive inhibition of the rate of chemical reactions in the flame, mechanical separation of the flame by a strong jet of gas or water.
The methods and techniques used to stop combustion during fires are based on these fundamental methods.
The main fire extinguishing agents: water, chemical and air-mechanical foams, aqueous solutions of salts, inert and non-flammable gases, water vapor, halogen-hydrocarbon fire extinguishing compounds and dry fire extinguishing powders, compressed air.
Water can be used alone or mixed with various chemicals. In comparison with other means, water has such advantages as wide availability and low cost, high heat capacity, which ensures heat removal from hard to reach places, high transportability, chemical neutrality and non-toxicity. Disadvantages of water include freezing at a temperature of 0° C, which can result in rupture of fire hoses and breakdown of the pump; inapplicability for extinguishing burning liquid substances (flammable liquids and gases) with a density less than one (gasoline, kerosene, acetone, alcohols, oils, ether, etc.). Being lighter than water, they float to the surface, continue to burn and, spreading, increase the combustion area. Do not extinguish live electrical networks and electrical installations with water, since the stream of water is a conductor and can cause electric shock.
Chemical foam is produced by the interaction of alkaline and acid solutions in the presence of foaming agents. This produces gas (carbon dioxide).
Gas bubbles are enveloped by water and a foaming agent, resulting in a stable foam that can remain on the surface of the liquid for a long time.
Air-mechanical foam is a mixture of air (~90%), water (~9.7%) and foaming agent (~0.3%). The characteristic of foam is the expansion ratio - the ratio of the volume of the resulting foam to the volume of the starting substances (the usual expansion ratio of foam is up to 20). Recently, in the practice of extinguishing fires, high-expansion foam (expansion over 200) has been used, which is much more voluminous and lasts longer. It is obtained in high-expansion foam generators, where air is not sucked in, but is pumped under some pressure.
Water vapor is used to extinguish fires in rooms with a volume of up to 500 m 3 and small fires in open areas and installations. Steam moistens burning objects and reduces oxygen concentration. The fire extinguishing concentration of water in the air is approximately 35% by volume.
Inert and non-flammable gases (nitrogen, argon, helium, carbon dioxide) reduce the concentration of oxygen in the combustion area and inhibit the intensity of combustion. Inert gases are usually used in relatively small spaces. Fire extinguishing concentration of inert gases during extinguishing in indoors is 31-36% of the volume of the room.
Aqueous solutions of salts are among the liquid fire extinguishing agents. Solutions of sodium bicarbonate, calcium chlorides, etc. are used. Salts, falling out of an aqueous solution, form insulating films on the surface of the burning substance, removing heat.
The fire extinguishing effect of halohydrocarbon fire extinguishing compounds is based on chemical inhibition of the combustion reaction. Compositions used: 3.5; 4ND; 7; SRC; BF; etc. (the numbers 3.5 and 7 mean that these compounds are 3.5 and 7 times more effective than carbon dioxide).
Fire extinguishing powders are finely ground mineral salts with various additives that prevent them from caking and clumping. They have good fire extinguishing ability.
Dry, clean and sifted sand extinguishes fire almost as well as water vapor and inert gases. When sand is thrown onto a burning object, heat is absorbed and the surface is isolated from air oxygen.
Blankets (asbestos sheets, tarpaulin, felt) are used to extinguish small burning surfaces and burning clothing on a person (the burning substance is isolated from access to air oxygen). Mechanical means(tarpaulin, felt, sand, earth) are used where flammable substances have not yet had time to heat up, that is, at the beginning of ignition.
In practice, wetting agents are also used. The main physical property of wetting solutions is to improve the wettability of flammable substances (for example, rubber, coal dust, fibrous materials, peat). Wetting agents include soap, synthetic solvents, amyl sulfates, alkyl sulfonates and other substances.
When choosing extinguishing agents, one should proceed from the possibility of obtaining the best fire extinguishing effect when minimum costs. The most important parameters fires that determine fire extinguishing conditions are:
Physico- Chemical properties flammable material, on which the choice of fire extinguishing agent depends;
Fire load, which means the mass of all flammable and flame retardant materials located in the object in question, related to the floor area of the room or the surface occupied by materials in the open air;
Fire load burnout rate;
Gas exchange between the fire source and the environment and the external atmosphere;
Heat exchange between fire sources and surrounding materials and structures;
The size and shape of the fire source and the room in which the fire occurred;
Weather conditions.
The physicochemical properties of the flammable material determine the choice of fire extinguishing agent. To extinguish a fire, do not use substances that react violently with flammable or oxidizing agents. For example, you cannot use water to extinguish materials that interact with it, form flammable gases or emit heat (alkali metals and some other flammable materials).
Particular difficulties are caused by extinguishing fires of smoldering materials due to the difficulty of penetration of fire extinguishing agents into the pores of such materials. Classification of fires depending on physical and chemical properties flammable materials and the possibility of extinguishing them with various fire extinguishing agents and compositions is given in the table
Fire classes
Fire load, which includes flammable materials structural elements buildings, and the rate of its burnout determine the main characteristics of the fire, as well as the temperature regime and duration of the fire, hazardous factors (HFP) affecting people.
The fire load is differentiated depending on its distribution over the area into distributed and concentrated and is characterized by mass per unit floor surface (kg/m2). The development of a fire and its parameters largely depend on the type and magnitude of the fire load.
According to the method of fire load distribution, premises are divided into two classes:
Premises of large objects in which the fire load is concentrated and combustion can develop in separate isolated areas without the formation of a common combustion zone;
Premises in which the fire load is dispersed over the entire area in such a way that combustion can occur to form a common combustion zone. Depending on the class of the room, the fire extinguishing method is chosen. A fire can be divided into three zones: combustion, heat and smoke.
The combustion zone occupies part of the space in which combustion directly occurs. It may be limited by the building's boundary structures, walls technological equipment. Combustion in a fire has a diffusion turbulent character.
Unlike gases and liquids, combustion of solid materials can occur horizontally, obliquely and vertical surfaces. The speed of flame propagation strongly depends on the angle of inclination and direction of combustion propagation. The speed of propagation vertically downwards is two times lower than on a horizontal surface, and 8-10 times higher when the flame propagates vertically upwards.
The heat affected zone is the part of the space adjacent to the combustion zone in which heat exchange occurs between the combustion zone and surrounding structures, materials and space.
Fire extinguishing methods are classified according to the type of fire extinguishing substances (compositions) used, the method of their application (supply), the environment, purpose, etc. All fire extinguishing methods are primarily divided into surface extinguishing, which consists of supplying fire extinguishing agents directly to the source of combustion, and volumetric extinguishing, which consists of creating an environment in the area of the fire that does not support combustion.
Surface fire suppression, also called area fire suppression, can be used for almost all types of fires. For this type of extinguishing, fire extinguishing compounds are used that can be supplied to the fire at a distance (liquid, foam, powder).
Volumetric extinguishing can be used in a limited volume; it is based on the creation of a fire extinguishing medium throughout the entire volume of the protected object. Thus, surface extinguishing in the state described above is applicable to fires in class I premises, volumetric extinguishing -0 to fires in class II premises. Sometimes the volumetric extinguishing method is used for fire protection local area in large volumes (for example, fire hazardous areas in large rooms). But this provides for increased consumption of fire extinguishing agents. For volumetric extinguishing, fire extinguishing agents are used that can be distributed in the atmosphere of the protected volume and create a fire extinguishing concentration in each of its elements. As such, gas and powder compositions are used. The volumetric extinguishing method seems to be the most progressive, since it provides not only a quick and reliable cessation of combustion at any point in the protected volume, legs and phlegmatization of this volume, that is, prevention of the formation of an explosive atmosphere. In addition, this method is the most cost-effective because it is easy to automate, it is fast and has other advantages.
Fire equipment, depending on the method of fire extinguishing, is divided into primary means - fire extinguishers (portable and portable) and fire hydrants located in buildings, mobile - various fire trucks, as well as stationary - special installations with a supply of fire extinguishing agents, activated automatically or manually, fire monitors trunks and others. Surface extinguishing is carried out by all types of fire equipment, but mainly primary and mobile ones; volumetric extinguishing - only with stationary installations.
The extinction temperature is significantly higher than the auto-ignition temperature; therefore, to stop combustion, it is sufficient to lower the temperature of the reaction zone below the extinction temperature, increasing the intensity of heat removal or reducing the rate of heat release. So, if you change the concentration of oxygen in the air by adding a non-flammable gas to it, then the rate of heat release per unit surface area of the reaction zone will decrease and the combustion temperature will decrease. At a certain concentration of non-flammable gas, the combustion temperature will drop below the extinction temperature and combustion will stop ( Fig.1.) .
Fig.1. Dependence of heat release and heat removal on temperature.
1
- heat release curve: 1"
,1""
,1"""
– heat release curves when its rate decreases; 2
– direct heat removal; ABOUT– beginning of oxidation: P– point corresponding to the extinction temperature; G– point corresponding to the combustion temperature; Tp– extinction temperature; Tg– combustion temperature.
Due to the decrease in oxygen concentration in the air, the curve decreases 1 . If when burning thermal equilibrium established at a point G(intersection of the heat sink straight line 2 and heat release curve 1 ), then with a decrease in the rate of heat release and a decrease in the curve 1 this point will shift to the left and the combustion temperature will decrease. At a certain heat release rate, the direct heat removal 2 in area high temperatures will only touch the heat release curve 1 at the point P. With a further decrease in the heat release rate, the heat removal straight line will be located above the heat release rate curve, and the combustion process will move into the oxidation region (point O). Therefore, the combustion temperature Tp is critical, i.e. extinction temperature. Thus it is possible to reduce the combustion temperature and stop combustion by either increasing the heat removal rate or decreasing the heat release rate.
This can be achieved:
Fig.2. Combustion termination circuit
Each method of stopping combustion can be performed using various techniques or a combination of them. For example, creating an insulating layer on the burning surface of a flammable liquid can be achieved by feeding foam through a layer of fuel, using foam lifters, overhead jets, etc. .
Fig.3. Classification of combustion termination methods.
| Substance, material | Danger level |
|---|---|
| Lead azide | Explodes when humidity increases to 30% |
| Aluminum, magnesium, zinc, zinc dust | When burned, water is decomposed into oxygen and hydrogen. |
| Bitumen | The supply of compact jets of water leads to emission and increased combustion |
| Hydrides of alkali and alkaline earth metals | |
| Sodium hydrosulfite | Spontaneously ignites and explodes when exposed to water |
| Mercury fulminate | Explodes when struck by a compact water jet |
| Silicon iron (ferrosilicon) | Hydrogen phosphide is released, which ignites spontaneously in air. |
| Potassium, calcium, sodium, rubidium, cesium metal | Reacts with water, releasing hydrogen, possible explosion |
| Calcium and sodium (phosphorous) | Reacts with water to release hydrogen phosphide, which is self-igniting in air. |
| Potassium and sodium (peroxides) | If water gets in, an explosive release with increased combustion is possible. |
| Aluminum, barium and calcium carbides | Decomposes, releasing flammable gases, possible explosion |
| Alkali metal carbides | Explode on contact with water |
| Magnesium and its alloys | When burned, water breaks down into hydrogen and oxygen. |
| Metaphos | Reacts with water to form an explosive substance |
| Sodium sulfide and hydrosulfate | It gets very hot (over 400 °C), can cause ignition of flammable substances, as well as burns upon contact with the skin, accompanied by difficult-to-heal ulcers |
Federal state budget educational institution higher professional education
RUSSIAN ACADEMY
NATIONAL ECONOMY AND CIVIL SERVICE
under the PRESIDENT OF THE RUSSIAN FEDERATION
CHELYABINSK BRANCH
Department of Economics and Management
Fire extinguishing agents and their properties.
Purpose, design and principle of operation of foam fire extinguishers
Dindiberina Yulia Olegovna
4th year students, group Mo-41-11
Supervisor:
Rudakova T.I. Ph.D., Associate Professor
Chelyabinsk
Introduction
Chapter 1. Fire extinguishing agents
Fire concept
Water as a fire extinguishing agent
Foam
Fire extinguishing powders
Halons
Handy fire extinguishing agents
Chapter 2. Foam fire extinguishers
Purpose of foam fire extinguishers
Design and principle of operation of foam fire extinguishers
Conclusion
Bibliography
Introduction
At the moment, there are many different fire extinguishing agents, with different characteristics and methods of application. In this regard, I believe that every firefighter should know the classification of these substances and their scope of application. This is due to the fact that the speed and efficiency of extinguishing a fire or ignition, as well as the life and health of personnel taking part in emergency response, will directly depend on the correct choice of fire extinguishing agent. It is very important to know how to correctly combine the supply of a particular fire extinguishing agent and its quantity required to achieve maximum effect.
The relevance of the problem 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 are killed or 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, in Europe, in America, in America and in Africa. And therefore the problem of fighting fires is a global problem.
It’s safe to say that there are 10 times more fires in Russia now than 100 years ago. About 300 thousand occur annually. The relative level of losses in Russia is the highest among the highly developed countries of the world. It exceeds comparable loss figures for Japan - 3.5 times, Great Britain - 4.5 times, and the USA - 3 times.
In Russia, on average, about 600 fires occur every day, 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 use when extinguishing fires that have arisen at various sites and under certain conditions characteristic of a particular fire.
To achieve the goal, it is necessary to solve a number of problems:
Give the concept of what a fire is, a fire extinguishing agent;
Describe fire extinguishing agents;
Indicate methods of using fire extinguishing agents.
Chapter 1. Fire extinguishing agents
Fire concept
What is a fire as a social phenomenon? These are uncontrolled fires that cause material damage, harm to the life and health of citizens, and the interests of society and the state.
Fires usually occur at fire hazardous facilities (FOO). POI should include such objects that contain flammable or combustible substances or liquids. Flammable substances or liquids include substances or liquids having a flash point below 48°C; for flammable materials - over 45°C.
Fires are classified according to the following criteria: by place of origin, by reason of occurrence, by type of fire, by burning intensity, etc.
Statistics give us the following picture of the distribution of fire occurrences:
as a result of the economic activities of the aborigines - 64.8%;
the work of loggers, expeditions and other organizations causes 8.8% of fires;
agricultural fires - 7.3%;
lightning - 16%;
arson and unknown causes - 3.1%.
Fire fighting is the process of influencing forces and means, as well as the use of methods and techniques to extinguish a fire.
When extinguishing a fire, the following fire extinguishing agents are usually used:
Liquids: sprayed water; foam.
Gases: carbon dioxide; Halons 12B1, 13B1.
Fire extinguishing powders: ammonium phosphate; bicarbonate of soda; potassium bicarbonate; potassium chloride.
IN Russian Federation Since May 1, 2009, the main classification has been established by the “Technical Regulations on Fire Safety Requirements.” Article 8 of the Regulations defines the classes of fires:
|
Fire class |
Characteristics of burning materials and substances |
Fire extinguishing compounds |
||
|
Combustion of solid combustible materials, except metals (wood, coal, paper) |
Water and other means |
|||
|
Combustion of liquids and melting materials |
Sprayed water, foam, powders |
|||
|
Combustion of gases |
Gas compositions, powders, water for cooling |
Combustion of metals and their alloys (Na, Mg, Al) |
Powders when calmly supplied to a burning surface |
|
|
Burning of live equipment |
Powders, carbon dioxide, freons, AOC |
Table 1. Classification of fires and methods of extinguishing them
Water is primarily a cooling agent. It absorbs heat and cools burning materials more effectively than any other commonly used fire extinguishing agent. Water is most effective at absorbing heat at temperatures up to 100°C. At a temperature of 100°C, the vapor continues to absorb heat, turning into steam, and removes the absorbed heat from the burning material. This quickly reduces its temperature to below its ignition temperature, causing the fire to stop.
Water has an important secondary effect: when it turns into steam, it expands 1,700 times. The resulting large cloud of steam surrounds the fire, displacing the air that contains the oxygen necessary to support the combustion process. Thus, in addition to its cooling ability, water has a volumetric quenching effect.
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 a collection of bubbles that contributes to extinguishing a fire, mainly due to the surface extinguishing effect. Bubbles occur when water and foaming agent are mixed. Foam is lighter than the lightest flammable petroleum product, so when applied to a burning petroleum product, it remains on its surface.
Fire extinguishing effect of foam. Foam is used to create a layer on the surface of flammable liquids, including petroleum products. The foam layer prevents flammable vapors from leaving the surface and oxygen from penetrating the flammable 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.
The ideal foam should flow freely enough to cover the surface quickly, bond firmly to create and maintain a vapor barrier, and retain the amount of water necessary to provide a durable layer over time. With rapid loss of water, the foam dries out and collapses under the influence of high temperatures generated during a fire. The foam must be light enough to float on the surface of flammable liquids, yet heavy enough to not 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 influenced 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 flows freely around obstacles and spreads quickly.
At correct use, foam is an effective fire extinguishing agent. However, there are certain limitations in its use.
Because foam is an aqueous solution, it conducts electricity and should not be applied to live electrical equipment.
Foam, like water, cannot be used to extinguish flammable metals.
Many types of foam cannot be used with fire extinguishing powders. The exception to this rule is "light water", which can be used with fire extinguishing powder.
Foam is not suitable for extinguishing fires involving the combustion of gases and cryogenic liquids. But high-expansion foam is used when extinguishing spreading cryogenic liquids to quickly heat the vapors and reduce the dangers associated with such spreading.
If foam is applied to burning liquids whose temperature exceeds 100°C (for example, asphalt), then the water contained in the foam can cause them to swell, splash and boil.
The supply of foaming agent should be sufficient to cover the entire surface of the burning material with foam. In addition, it should be enough to replace the foam that burns out and fill the gaps that form on its surface.
Despite the current limitations in use, the foam is very effective in fighting class A and B fires.
Foam is a very effective fire extinguishing agent, which also has a cooling effect.
The foam creates a vapor barrier that prevents flammable vapors from escaping. The surface of the tank may be covered with foam to protect it from a fire in an adjacent tank.
The 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 petroleum products. If oil product leaks, you should try to close the valve and thus interrupt the flow. If this cannot be done, the flow must be blocked with foam, which should be applied to the fire area to extinguish it and then to create a protective layer to cover the leaking liquid.
Foam is the most effective fire extinguishing agent for extinguishing fires in large containers with flammable liquids.
To obtain foam, fresh or outboard, hard or soft injection can be used.
Foam is not prone to rapid destruction; when applied correctly, it extinguishes the fire gradually.
The foam is held in place, covers the burning surface and absorbs the heat contained in those materials that could cause a re-ignition.
Foam ensures economical water consumption and does not overload ship fire pumps.
Foam concentrates are lightweight and foam extinguishing systems do not require much space.
Fire extinguishing powders
Fire extinguishing agents in powder form are divided into general purpose fire extinguishing powders and special purpose fire extinguishing powders, which are used only for extinguishing flammable metal fires.
There are currently five types of general purpose fire extinguishing powders in use. Like other fire extinguishing media, fire extinguishing powders can be used in fixed systems and in portable as well as stationary fire extinguishers.
Bicarbonate of soda. This 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 extinguishing fires of animal fats and vegetable oils, because it causes chemical changes in these substances, turning them into non-flammable soap. When using sodium bicarbonate, you should always be aware of the possibility of flame flashing back onto the surface of the burning oil.
Potassium bicarbonate. This extinguishing powder was originally developed for use in dual "light water" 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 can successfully prevent backfire. This powder is more expensive than sodium bicarbonate.
Potassium chloride. This 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 corrosion may occur after it is used to extinguish fires.
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 widespread use due to its high cost.
Ammonium phosphate. This powder is universal because it can be successfully used in extinguishing fires of classes A, B and C. Ammonium salts break the chain reaction of flaming combustion. Phosphate transforms with an increase in temperature caused by a fire into metaphosphoric acid, a glassy fusible substance. The acid coats hard surfaces with a fire retardant layer, so this extinguishing agent can be used to extinguish fires involving common combustible materials such as wood and paper, as well as fires involving flammable petroleum 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 bring the fire under control, but does not provide complete extinguishing.
To completely extinguish 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 means when using a powder fire extinguisher.
Restrictions on the use of fire extinguishing powders
Release large quantity fire extinguishing powder may have 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 do not extinguish fires associated with the combustion of materials that contain oxygen.
Fire extinguishing powder may leave an insulating layer on electronic or telephone equipment, affecting the operation of that equipment.
When extinguishing flammable metals such as magnesium, potassium, sodium and their alloys, general purpose powder does not provide a fire extinguishing effect, and in some cases can cause a violent chemical reaction.
In areas 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 may cause respiratory irritation if inhaled. 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 personnel taking part in extinguishing a fire need to enter the room where the powder was supplied before ventilation is completed, they must use breathing apparatus and signal cables.
The use of fire extinguishing powders is very effective for extinguishing gas fires. Flammed gases must be extinguished when the gas source is shut off.
Halons
Halons consist 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 bromochlorodifluoromethane (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 area, it evaporates, turning into a colorless, odorless gas, and is supplied to 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 faint sweetish odor. This halon is stored and transported in a liquid state and maintained under nitrogen gas pressure, which is necessary to ensure proper delivery to the fire zone, since the vapor pressure of 12B1 halon is too low to do so. It does not conduct electricity.
Application of halons
The fire extinguishing properties of halons 12B1 and 13B1 allow them to be used for extinguishing various fires, including:
electrical equipment fires;
fires in premises where flammable oils and greases may burn;
Class A fires involving combustion of solid flammable substances, however, if the fire is located deep below, wetting with water may be necessary 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 not suitable for extinguishing substances containing oxygen, flammable metals and hydrides.
Safety
Inhalation of halons 13B1 and 12B1 may cause dizziness and loss of coordination. These gases can reduce visibility in the area where they are used. At temperatures above 500°C, the gases of both halons 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 in which people may be present, a warning signal must be provided, upon hearing which it is necessary to immediately leave the room. When using a fire extinguisher with halon 13B1, all people not directly involved in working with the fire extinguisher must 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 it is necessary to remain in or enter a room where Halon 13B1 has been supplied, use breathing apparatus and a safety rope.
Handy fire extinguishing agents
Sand, sawdust, steam
Sand used to extinguish fires is not as effective as modern fire extinguishing agents.
Sand makes it possible to extinguish oil fires, creating a volumetric extinguishing effect and covering the surface of the burning substance. However, if the burning oil is approximately 25 mm thick and those fighting the fire do not have enough sand at their disposal to cover all the burning oil, the sand will settle under the surface of the oil and the fire will not be extinguished. At correct use sand can be used as a barrier to the spreading oil or to cover it.
Sand should be applied to the fire using a scoop or shovel. Its already insignificant effectiveness can be further reduced by inept delivery. After the fire is extinguished, the problem of sand removal arises. In addition to these disadvantages, mention should be made of the abrasive properties of sand when it gets into mechanisms and other equipment.
It is difficult to extinguish with sand a fire associated with the combustion of combustible metals, since at the very high temperature that accompanies such fires, sand releases oxygen. The presence of water in sand will intensify the fire or cause a steam explosion. Sand can only be used as a barrier in the path of spreading molten metal, and to extinguish such a fire, a special-purpose powder should be used.
Sometimes sawdust soaked in soda is used to extinguish small fires. Like sand, they are applied 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 the flow of air to the fire and reduces the concentration of oxygen in the air around the fire. As long as steam fills the volume, re-ignition will not occur. But it has a number of disadvantages, especially when compared to other fire extinguishing media.
Steam has a weak heat-absorbing ability, as a result of which its cooling effect is very small. In addition, when the supply is stopped, the steam begins to condense. Its volume is significantly reduced, and flammable vapors and air immediately begin to flow to the fire, displacing the steam. At this point, if the fire has not been completely extinguished, it is likely to re-ignite. The temperature of the steam itself is high enough to ignite many liquid flammable substances. Finally, steam poses a danger to people because the heat it contains can cause severe burns.
Chapter 2. Foam fire extinguishers
Purpose of foam fire extinguishers
Foam fire extinguishers are designed to extinguish fires and fires. solids and materials, flammable liquids and gases, except for alkali metals and substances whose combustion occurs without air access, as well as electrical installations under voltage.
Foam fire extinguishers are classified according to the type of extinguishing agent:
chemical foams (OCF);
air foam (AFP);
The industry produces three types of manual 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 acidic parts of the charges.
It is strictly forbidden to use a fire extinguisher to extinguish fires of electrical installations under voltage, as well as alkali metals. The fire extinguisher is recommended for use on stationary objects National economy at ambient temperatures from +5 to +45 °C. fire fire extinguisher foam extinguishing
Air-foam fire extinguishers are designed to extinguish fires of various substances and materials, except for alkali metals and substances that burn without air access, as well as live electrical installations. As a rule, a 6% aqueous solution of foaming agent PO-1 is used as a charge.
Design and principle of operation of foam fire extinguishers
To activate a chemical foam fire extinguisher, lift up the handle that opens the valve of the acid glass and tip the fire extinguisher down with its head. The acidic part of the charge flowing out of the glass mixes with the alkaline part poured into the body of the fire extinguisher, 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 the housings of chemical foam fire extinguishers create relatively high pressure, before work, it is necessary to clean the spray with a pin suspended from the handle of the fire extinguisher.
The chemical thick foam marine fire extinguisher OP-M is intended for extinguishing fires on ships, in port facilities and in warehouses. The OP-9MM chemical foam fire extinguisher is designed to extinguish fires of all flammable materials, as well as live electrical installations.
Rice. 1. Diagram of the chemical foam fire extinguisher OHP-10: 1 - fire extinguisher body; 2 - acid glass; 3 - safety membrane; 4 - spray; 5 - fire extinguisher cover; 6 - rod; 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 body; 2 - carrying handle; 3 - cartridge for propellant gas; 4 - air-foam nozzle with spray; 5 - trigger mechanism; 6 - fire extinguisher housing cover; 7 - siphon tube nozzle.
There are two types of air-foam fire extinguishers (Fig. 2, 3): manual (OVP-5 and OVP-10) and stationary (OVP-250 and OVP-100). To activate the fire extinguisher, you must press the trigger lever. In this case, the seal breaks and the shield pierces the membrane of the cylinder. The carbon dioxide coming out of the can through the nipple creates pressure in the fire extinguisher body, under the influence 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.
The fire extinguisher cannot be used to extinguish substances that burn without access to air (cotton, pyroxylin, etc.), burning metals (alkali sodium, etc. and light magnesium, etc.). Do not use to extinguish live electrical installations. The fire extinguisher is used at ambient temperatures from +3 to +50 C.
Rice. 3. Stationary air-foam fire extinguisher OVPU-250: 1 - steel body on supports; 2 - launch tank; 3 - foam generator; 4 - hose reel; 5 - safety valve; 6 - pipe for filling the foam solution; 7 - siphon tube of the foam generator; 8 - drain pipe; 9 - tube for monitoring the foam concentrate solution.
Conclusion
The purpose of this essay was to analyze the currently existing fire extinguishing agents, their characteristics and methods of use in extinguishing fires that occurred at various sites and under certain conditions characteristic of a particular fire. And during 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 when used when extinguishing fires; this largely depends on the types of fires, the classification of which was also given in the work.
Bibliography
GOST 28130-89 Fire equipment. Fire extinguishers. Fire extinguishing and fire alarm installations.
Mironov S.K., Latuk V.N. Primary fire extinguishing agents. Bustard, 2008
Terebnev V.V. Firefighting Manager's Handbook. Capabilities of fire departments. Moscow. "Fire engineering" 2004
Tutorial. Life safety. AIR DEFENSE. 2002.
Yudakhin A.V. Toolkit. Issues of organizing UAVs in the process of daily activities in Air Force units. 2001.
LABORATORY AND PRACTICAL WORK
Work 1. Selection of fire extinguishing agents and
fire extinguishing means
Goal of the work: Familiarize yourself with fire extinguishing compounds and choose the means for a specific situation.
Quick and effective fire extinguishing can be achieved if the correct extinguishing agent is selected and its timely supply to the combustion source is carried out. The choice of fire extinguishing agents and fire extinguishing agents is made based on their classification and characteristics.
Fire extinguishing agents are classified:
According to the method of stopping combustion:
cooling the combustion center: water, solid carbon dioxide.
diluting (reducing the percentage of oxygen in the combustion zone): carbon dioxide and other inert gases, water vapor.
insulating action (isolating the burning surface from air oxygen): air-mechanical foam, powders, sand, solutions.
inhibitory (inhibiting the chemical reaction of combustion): compositions with halogenated hydrocarbons - freons, powder aerosol compositions - AOS.
By electrical conductivity:
electrically conductive: water, solutions, water vapor, foam.
non-electrically conductive: gases, powder compositions.
By toxicity:
non-toxic: water, foam, powder compounds, sand.
low toxic: carbon dioxide
toxic: freons, halogenated compounds No. 3, 5, 7, etc.
Water and solutions. Water is the main means of extinguishing fires. It is cheap, accessible, easily supplied to the burning site, preserves well for a long time, has no toxic properties, and is effective in extinguishing most combustible materials.
The high fire extinguishing ability of water is determined by its significant heat capacity. At normal atmospheric pressure and temperature 20° C, the heat capacity of water is 1 kcal/kg. From 1 l. 1750 liters of water are generated. dry saturated steam. This consumes 539 kcal. thermal energy. The released steam displaces oxygen from the combustion zone.
However, water has a high surface tension, so the penetrating ability of water is not always sufficient. There are a number of materials known (dust, cotton, etc.) into the pores of which water is not able to penetrate and stop smoldering. In such cases, to reduce surface tension and increase penetrating ability, a certain amount (from 0.5 to 4% by weight) of surfactant wetting agents is added to the water. The most common wetting agents are: foaming agent PO-1, PO-5.
The use of wetting agents, all other things being equal, reduces water consumption by 2-2.5 times and reduces extinguishing time by 20-30%. The disadvantage of wetting agents is their aggressiveness.
To extinguish fires, water is used in the form of continuous and finely sprayed 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 environment into the combustion zone. Oxygen that has penetrated 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 flame separation and, to a lesser extent than sprayed water, for cooling 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, salts of calcium chloride, caustic soda, Glauber's salt, ammonium sulfate, etc. are added to water, which increase the heat capacity of water and, after evaporation, form a film of salts on the surface treated with the solution. This film prevents sparks and embers from re-igniting an extinguished fireplace.
However, water is not universal remedy. With many substances, for example, with alkali and alkaline earth metals, it enters into a chemical reaction with the release of hydrogen, accompanied by a significant release of heat. Some compounds, for example, sodium hydrosulfite, decompose when interacting with water. Therefore, in such cases, as well as when extinguishing electrical installations, water cannot be recommended as a fire extinguishing agent.
Foam are effective means fire extinguishing Fire-retardant foams are divided into chemical And air-mechanical. Chemical foam is obtained as a result chemical reaction neutralization between acid and alkali. The bubble shell of this foam consists of a mixture of aqueous solutions of salts and foaming agents. The bubbles themselves are filled with carbon dioxide, a product of a chemical reaction.
Air-mechanical foam is obtained by mechanically mixing a foaming solution with air. The shell of air-mechanical foam bubbles consists of an aqueous solution of foaming agents such as PO-1, PO-5.
The resulting fire extinguishing foam is characterized by:
durability (the ability of foam to resist destruction for a certain time: the higher the durability of the foam, the more effective the extinguishing process);
foam expansion ratio (the ratio of the volume of foam to the volume of the original products:);
There are: low expansion foams with expansion ratio up to 12, medium expansion foam from 12 to 100 and high expansion foam K100 (the most effective).
viscosity (the ability of foam to spread over a surface);
dispersion (bubble size).
To increase the durability of the foam, surface-active substances (bone or wood glue) are used, and for storage at low temperatures - ethanol (C 2 H 3 OH) or ethylene glycol.
Foams are used to extinguish class A, B, C fires. They cannot be used to extinguish alkali and alkaline earth metals and live electrical equipment.
Carbon dioxide. Carbon dioxide supplied to the fire can be in a solid state (carbon dioxide snow), gaseous and aerosol. The effect of CO 2 on the combustion site is based on the dilution of oxygen in the combustion zone.
Carbon dioxide snow can be produced by rapid evaporation of liquid carbon dioxide. The resulting snow-like carbon dioxide has a density of 1.5 g/cm 3 at - 80? C. Snow-like carbon dioxide lowers the temperature and reduces the oxygen content in the combustion zone. From 1 l. 500 liters of solid acid are formed. gas.
In its 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) has the greatest effect in rooms where the air may contain tiny combustible particles (cotton, dust, etc.). In this case, carbon dioxide not only extinguishes, but also contributes to the rapid deposition of those suspended in the air particles. 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, you can enter the room after filling it with carbon dioxide only in oxygen insulating gas masks.
Carbon dioxide is not electrically conductive and evaporates without leaving any traces behind. Carbon dioxide is used when extinguishing electrical equipment, internal combustion engines, when extinguishing fires in storage facilities for valuable materials, in archives, libraries, etc. Carbon dioxide cannot be used as a fire extinguishing agent in fires. ethyl alcohol, because carbon dioxide dissolves in it, as well as during the combustion of substances that can burn without air access (thermite, celluloid, etc.). In addition to CO 2, other inert gases are used as fire extinguishing agents: nitrogen, sulfur hexafluoride.
Freon compounds- these are compositions with halogenated hydrocarbons. They are easily evaporated liquids, as a result of which they are classified 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 compounds are by far the most effective means of extinguishing fires. Their action is based on inhibiting the chemical reaction of combustion and interaction with atmospheric oxygen.
They are used to extinguish fires of classes A, B, C and electrical installations at virtually unlimited temperatures.
Advantages:
most effective compared to all available formulations;
have high penetrating ability;
are used when negative temperatures(up to -70ºC).
Flaws:
toxicity;
formation of corrosive compounds in the presence of moisture;
ineffective for outdoor use;
Do not extinguish alkali and alkaline earth metals and acid-containing substances.
Powder formulations. 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 compounds.
In addition to the main components of fire extinguishing powders, they contain anti-caking and hydrophobic additives.
Designed to extinguish burning alkali and alkaline earth metals, and are also widely used to extinguish fires of classes: A, B, C, and E.
Powder fire extinguishing compounds are used to extinguish fires of classes A, B, C and E, and live electrical installations.
Ineffective when extinguishing:
smoldering materials and substances that burn without oxygen.
The action of fire extinguishing powders PSB-3M and Pirant-A is based on isolating the burning surface from oxygen.
The effect of PCP and AOS powder compositions is to inhibit the chemical combustion reaction and reduce the O 2 content in the combustion zone.
PHC and AOS powders are the most promising today. Aerosol fire extinguishing compounds - AOS - are particularly effective.
AOS are solid fuel or pyrotechnic compositions capable of self-combustion without air access with the formation of fire extinguishing combustion products - inert gases, highly dispersed salts and alkali metal oxides. These compounds are low-toxic and environmentally friendly.
Currently used:
fiery AOC;
chilled AOS.
Flame compositions, when aerosol-forming composition devices are activated, have a flame reaching several meters and a temperature of combustion products at the outlet of 1200-1500ºC. This is their disadvantage.
Cooled aerosol-forming compositions are obtained using special cooling nozzles. This makes it possible to reduce the temperature of the AOC during combustion from 600 to 200ºC, but the aerosol mixture will contain products of incomplete combustion of the AOC, which significantly increases the toxicity of the combustion products compared to flame AOC.
AOS is used for extinguishing in fire extinguishers and generators various types, both in autonomous mode and in automatic aerosol fire extinguishing installations.
