Federal State Budgetary Educational Institution of Higher Professional Education
RUSSIAN ACADEMY
NATIONAL ECONOMY AND PUBLIC SERVICE
under the PRESIDENT OF THE RUSSIAN FEDERATION
CHELYABINSK BRANCH
Department of Economics and Management
Fire extinguishing agents and their properties.
Purpose, device and principle of operation of foam fire extinguishers
Dindiberina Yulia Olegovna
4th year students, groups Mo-41-11
Supervisor:
Rudakova T.I. Ph.D., Assoc.
Chelyabinsk
Introduction
Chapter 1
Fire concept
Water as fire extinguisher
Foam
Fire extinguishing powders
Halons
Handy fire extinguishers
Chapter 2. Foam fire extinguishers
Appointment of foam fire extinguishers
The device and principle of operation of foam fire extinguishers
Conclusion
Bibliographic list
Introduction
IN this moment There are many different fire extinguishing media, with different characteristics and applications. In this regard, I believe that every firefighter should know the classification of these substances and their scope. This is due to the fact that the speed and efficiency of extinguishing a fire or fire, as well as the life and health of personnel participating in emergency response, will directly depend on the correct choice of a fire extinguishing agent. It is also important to know how to properly combine the supply of a particular fire extinguishing agent and its quantity necessary to achieve maximum effect.
The relevance of the problem of the topic under consideration lies in the fact that fires are one of the most common and dangerous disasters on the planet. Every year, tens of thousands of people die and are injured in fires, and billions of dollars worth of valuables are burned.
Every day we receive information from the media about fires from all continents. Huge tracts of forests and settlements are burning out in Asia, Europe, America, America and Africa. Therefore, the problem of fighting fires is a global problem.
It is safe to say that now in Russia there are 10 times more fires than 100 years ago. There are about 300,000 of them every year. The relative level of losses in Russia is the highest among the highly developed countries of the world. It exceeds the comparable losses of Japan - 3.5 times, Great Britain - 4.5 times, USA - 3 times.
On the territory of Russia, on average, about 600 fires occur daily, in which 55 people die; about 200 buildings are destroyed. 70% of all fires occur in cities.
The purpose of this work is to analyze the currently existing fire extinguishing agents, their characteristics and methods of application in the course of extinguishing fires that have arisen at various objects and under certain conditions characteristic of a particular fire.
To achieve the goal, it is necessary to solve a number of tasks:
Give the concept of what a fire is, a fire extinguishing agent;
Describe fire extinguishing agents;
Specify methods of using fire extinguishing agents.
Chapter 1
Fire concept
What is a fire as a social phenomenon? These are uncontrolled burnings that cause material damage, harm to the life and health of citizens, the interests of society and the state.
Typically, fires occur at fire hazardous facilities (FBOs). EET should include such facilities that contain flammable or combustible substances or liquids. Flammable substances or liquids include substances or liquids having an ignition temperature below 48°C; to fuel - over 45 ° C.
Fires are classified according to the following criteria: by the place of occurrence, by cause of occurrence, by type of fire, by intensity of burning, etc.
Statistics gives us the following picture of the distribution of fires:
as a result of economic activity of aborigines - 64.8%;
the work of loggers, expeditions, and other organizations causes 8.8% of fires;
agricultural burns - 7.3%;
lightning - 16%;
arson and unidentified causes - 3.1%.
Fire extinguishing is the process of the impact of forces and means, as well as the use of methods and techniques for extinguishing a fire.
When extinguishing a fire, the following extinguishing agents are usually used:
Fluids: water spray; foam.
Gases: carbon dioxide; halons 12B1, 13B1.
Fire extinguishing powders: ammonium phosphate; bicarbonate of soda; potassium bicarbonate; potassium chloride.
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 Regulation defines the classes of fires:
|
Fire class |
Characteristics of burning materials and substances |
Fire extinguishing compositions |
||
|
Combustion of solid combustible materials other than metals (wood, coal, paper) |
Water and other means |
|||
|
Combustion of liquids and consumable materials |
Water spray, foam, powders |
|||
|
Burning gases |
Gas compositions, powders, cooling water |
Combustion of metals and their alloys (Na, Mg, Al) |
Powders when they are quietly fed to a burning surface |
|
|
Burning equipment under voltage |
Powders, carbon dioxide, freon, AOC |
Table 1. Classification of fires and methods of extinguishing them
Water is mainly a coolant. It absorbs heat and cools burning materials more effectively than any other commonly used fire extinguishing agent. Water is most effective for absorbing heat at temperatures up to 100°C. At a temperature of 100°C, the vault continues to absorb heat, turning into steam, and removes the absorbed heat from the burning material. This quickly lowers its temperature to below its ignition temperature, causing the fire to stop.
Water has an important secondary effect: turning into steam, it expands 1700 times. The resulting large cloud of steam surrounds the fire, displacing the air, which contains the oxygen necessary to support the combustion process. Thus, in addition to the cooling ability, water has the effect of volumetric quenching.
Water is a widely used fire extinguishing agent, this is due to the following advantages of water:
cheapness and availability;
relatively high specific heat capacity;
chemical inertness to most substances and materials.
Foam is an accumulation of bubbles that contributes to the suppression of a fire, mainly due to the surface extinguishing effect. Bubbles are created when water is mixed with a foaming agent. Foam is lighter than the lightest flammable oil product, so when applied to a burning oil product, it remains on its surface.
Fire-extinguishing foam effect. Foam is used to create a layer on the surface of flammable liquids, including petroleum products. The foam layer prevents flammable vapors from escaping the surface, and oxygen from penetrating to the combustible substance. The water contained in the foam solution also has a cooling effect, which allows the foam to be successfully used to extinguish class A fires.
An ideal foam should flow freely enough and quickly cover the surface, bonding firmly to it to create and maintain a vapor barrier, and retain the amount of water needed to provide a durable layer for an extended period of time. With a rapid loss of water, the foam dries out and breaks down under the influence of the high temperature generated during a fire. The foam must be light enough to float on flammable liquids, yet heavy enough not to be blown away by the wind.
Foam quality is usually determined by:
destruction time of 25% of its volume,
relative expansion
ability to withstand heat (resistance to flashback).
These qualities are affected by the chemical composition of the foaming agent, the temperature and pressure of the water, and the efficiency of the foaming device.
Foam that quickly loses water is practically a liquid. It freely flows around obstacles and spreads rapidly.
At correct use, foam is an effective fire extinguishing agent. However, there are certain limitations in its application.
Since the foam is an aqueous solution, it conducts electricity, so it should not be applied to live electrical equipment.
Foam, like water, cannot be used to extinguish combustible metals.
Many types of foam should not be used with fire extinguishing powders. The exception to this rule is "light water", which can be used with extinguishing powder.
Foam is not suitable for extinguishing fires associated with the combustion of gases and cryogenic liquids. But high-expansion foam is used in extinguishing spreading cryogenic liquids to quickly heat vapors and reduce the dangers associated with such spreading.
If the foam is applied to burning liquids whose temperature exceeds 100°C (for example, asphalt), the water contained in the foam can cause them to swell, splatter and boil.
The stock of foaming agent should be enough to cover the entire surface of the burning material with foam. In addition, it should be sufficient to replace the foam that burns out and fill the gaps that form on its surface.
Despite existing limitations in use, foam is very effective in fighting class A and B fires.
Foam is a very effective fire extinguishing agent, which, in addition, has a cooling effect.
The foam creates a vapor barrier that prevents flammable vapors from escaping to the outside. The surface of the tank can be covered with foam to protect it from a fire in an adjacent tank.
Foam can be used to extinguish class A fires due to the presence of water in it. "Light water" is especially effective.
Foam is an effective fire extinguishing agent for covering spreading oil products. If the oil leaks out, one should try to close the valve and thus interrupt the flow. If this is not possible, the flow should be blocked with foam, which should be applied to the area of the fire to extinguish it and then to create a protective layer covering the seeping liquid.
Foam is the most effective extinguishing agent for extinguishing fires in large containers with flammable liquids.
To obtain foam, fresh or outboard, hard or soft input can be used.
Foam is not prone to rapid destruction, with proper supply, it extinguishes the fire gradually.
The foam stays in place, covers the burning surface and absorbs the heat contained in those materials that could cause a re-ignition.
Foam provides economical water consumption and does not overload ship's fire pumps.
Foam concentrates are lightweight, foam extinguishing systems do not require much space.
Fire extinguishing powders
Fire extinguishing agents in powder form are divided into fire extinguishing powders. general purpose and special-purpose fire-extinguishing powders, which are used only for extinguishing combustible metal fires.
There are currently five types of general purpose fire extinguishing powders in use. Similar to other fire extinguishing media, fire extinguishing powders can be used in stationary systems and in portable as well as stationary fire extinguishers.
Bicarbonate of soda. It is one of the main fire extinguishing powders. It is widely used due to the fact that it is the most economical of all existing ones. It is especially effective in 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, one should always be aware of the possibility of flame backflow onto the surface of the burning oil.
potassium bicarbonate. This extinguishing powder was originally developed for use in "light water" dual systems, but is now generally used on its own. It has been found to be very effective in extinguishing liquid fuel fires. The use of potassium bicarbonate makes it possible to successfully prevent backfire. This powder is more expensive than sodium bicarbonate.
potassium chloride. It is a fire extinguishing powder that is compatible with protein-based foam. Its fire extinguishing properties are approximately equivalent to those of potassium bicarbonate, the only drawback is that after its use for extinguishing fires, corrosion may occur.
A mixture of urea and potassium bicarbonate. This powder, developed in England and consisting of urea and potassium bicarbonate, is the most effective of all fire extinguishing powders tested. However, it has not found wide application due to its high cost.
ammonium phosphate. This powder is versatile because it can be successfully used to extinguish fires of classes A, B and C. Ammonium salts break the chain reaction of fiery combustion. Phosphate is converted by an increase in temperature caused by a fire into metaphosphoric acid, a vitreous fusible substance. The acid coats hard surfaces with a flame retardant layer, so this fire extinguishing agent can be used to extinguish fires associated with the burning of conventional combustible materials such as wood and paper, as well as fires of flammable oil products, gases and electrical equipment. But as for fires, the sources of which are located at a considerable depth, this powder only allows you to take the fire under control, but does not provide complete extinguishment.
For the final elimination of such a fire, extinguishing with water is required. In general, you should always remember the advisability of having a rolled-out fire hose on hand, which can be used as an additional tool when using a powder fire extinguisher.
Limitations in the use of fire extinguishing powders
Release a large number 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 will not extinguish fires associated with the combustion of materials containing oxygen.
Extinguishing powder can leave an insulating layer on electronic or telephone equipment, affecting the operation of this equipment.
When extinguishing combustible metals such as magnesium, potassium, sodium and their alloys, general purpose powder does not have a fire extinguishing effect, and in some cases can cause a violent chemical reaction.
In places where there is moisture, fire extinguishing powder may cause corrosion or deformation of the surface on which it is deposited.
Safety
Fire extinguishing powders are considered non-toxic, but if inhaled they can cause respiratory irritation. Therefore, as in the case of carbon dioxide extinguishing, in rooms that can be filled with fire extinguishing powder, it is necessary to provide preliminary signals. In addition, if the personnel taking part in extinguishing a fire need to enter the room where the powder was supplied before the end of the ventilation, they must use breathing apparatus and signal cables.
The use of fire extinguishing powders is very effective for extinguishing gas fires. Flammable gases must be extinguished when the source of gas is blocked.
Halons
Halons are made up of a hydrocarbon and one or more halogens: fluorine, chlorine, bromine, and iodine. In Russia, two halons are used: bromotrifluoromethane (known as freon 13B1) and bromchlorodifluoromethane (freon 12B1).
Halons 13B1 and 12B1 are supplied to the combustion zone in the form of gas. Most experts believe that halons interrupt the chain reaction. But it is not known for sure whether they slow down the chain reaction, interrupt its course, or cause some other reaction.
Halon 13B1 is stored and transported in a liquid state under pressure. When released into the protected room, it evaporates, turning into a colorless, odorless gas, and is fed into the combustion zone under the same pressure under which it is stored. Halon 13B1 does not conduct electricity.
Halon 12B1 is also colorless, but has a slight sweet smell. This halon is stored and transported in a liquid state and maintained under nitrogen gas pressure, which is necessary to ensure that it is properly supplied to the fire zone, since the vapor pressure of halon 12B1 is too low for this. It does not conduct electricity.
Application of halons
The fire-extinguishing properties of Halons 12B1 and 13B1 allow them to be used to extinguish various fires, including:
fires of electrical equipment;
fires in rooms in which burning of flammable oils and greases is possible;
class A fires involving solid combustibles, however, if the fire is located deep below, water spraying may be required to extinguish the fire;
To extinguish fires associated with the burning of electronic computers and control stations, it is recommended to use halon 13B1. Halon 12B1 should not be used in these cases.
There are some restrictions on the use of halons. They are unsuitable for extinguishing substances containing oxygen, combustible metals and hydrides.
Safety
Inhalation of Halons 13B1 and 12B1 may cause dizziness and incoordination. These gases can impair visibility in the area of their application. Above 500°C, both halon gases decompose. Generally, vapors below this temperature are not considered very toxic, but decomposed gases can be very dangerous, depending on their concentration, temperature and quantity.
Halon 12B1 is not recommended for filling confined spaces. If halon 13B1 is used to fill rooms that may contain people, a warning signal must be provided, upon hearing which it is necessary to leave the room immediately. When using a Halon 13B1 fire extinguisher, all persons not directly involved in working with the fire extinguisher should immediately leave the fire area. After using a fire extinguisher, the person working with it should leave as quickly as possible. The room must not be entered until it has been thoroughly ventilated. If you need to stay in or enter the room where the 13B1 halon was administered, you should use a breathing apparatus and a signal cable
Handy fire extinguishers
Sand, sawdust, steam
Sand used to extinguish a fire is not as effective as modern fire extinguishing agents.
Sand makes it possible to eliminate oil fires, creating the effect of volumetric extinguishing and covering the surface of the burning substance. However, if the burning oil is about 25 mm thick and there is not enough sand available to the firefighters to cover all the burning oil, the sand will settle under the surface of the oil and the fire will not be extinguished. When properly applied, sand can be used as a barrier to spreading oil or to cover it.
Sand should be fed to the fire with a shovel or shovel. Its already insignificant effectiveness can be further reduced by inept presentation. After the fire is extinguished, the problem of cleaning up the sand arises. In addition to these shortcomings, it is worth mentioning the abrasive properties of sand when it gets into mechanisms and other equipment.
It is difficult to put out with sand a fire associated with the burning of combustible metals, since at the very high temperature that accompanies such fires, the sand releases oxygen. The presence of water in the sand will intensify the fire or cause a steam explosion. Sand can only be used as a barrier to the spreading molten metal, and special purpose powder should be used to extinguish such a fire.
Sometimes sawdust soaked in soda is used to extinguish small fires. Like sand, they are fed to the fire with a shovel from a short distance. The disadvantages of sawdust as a fire extinguishing medium are the same as those of sand. A more effective substitute for sawdust is a fire extinguisher suitable for class B fires, for the same reasons given for sand.
Steam is a bulk fire extinguishing medium that prevents air from reaching the fire and reduces the oxygen concentration in the air around the fire. As long as the steam fills the volume, re-ignition will not occur. But it has a number of disadvantages, especially in comparison with other fire extinguishing media.
Steam has a weak heat-absorbing capacity, as a result of which its cooling effect is very small. In addition, when the supply is stopped, steam begins to condense. Its volume is significantly reduced, and combustible vapors and air immediately begin to flow to the fire, displacing the steam. At this point, if the fire has not been completely extinguished, a re-ignition is likely. The temperature of the vapor itself is high enough to ignite many liquid fuels. Finally, steam is a danger to people, as the heat it contains can cause severe burns.
Chapter 2. Foam fire extinguishers
Appointment of foam fire extinguishers
Foam fire extinguishers are designed to extinguish fires and fires of solid substances and materials, flammable liquids and combustible liquids, except for alkali metals and substances that burn without air, as well as electrical installations under voltage.
According to the type of extinguishing agent, foam fire extinguishers are classified:
chemical foam (OHP);
air-foam (ORP);
The industry produces three types of hand-held chemical foam fire extinguishers: OHP-10, OP-M, OP-9MM. Chemical foam fire extinguishers are designed to extinguish fires with chemical foam, which is formed as a result of the interaction of the alkaline and acid parts of the charges.
It is strictly forbidden to use a fire extinguisher to extinguish fires in electrical installations under voltage, as well as alkali metals. The fire extinguisher is recommended to be used at stationary facilities of the national economy at an ambient temperature of +5 to +45 °C. fire extinguisher foam extinguishing
Air-foam fire extinguishers are designed to extinguish fires of various substances and materials, except for alkali metals and substances burning without air access, as well as electrical installations under voltage. As a rule, a 6% aqueous solution of foaming agent PO-1 is used as a charge.
The device and principle of operation of foam fire extinguishers
To activate a chemical foam fire extinguisher, lift the handle that opens the acid glass valve and tip the fire extinguisher upside down. The acid part of the charge flowing out of the glass mixes with the alkaline part of the charge poured into the fire extinguisher body, and a reaction occurs between them with the formation of carbon dioxide, which fills the foam bubbles.
Carbon dioxide creates a pressure of 1.4 MPa (14 kg / cm2) inside the housing, which pushes the foam out of the fire extinguisher in the form of a jet. Due to the fact that in the cases of chemical foam fire extinguishers a relatively high pressure, before work, it is necessary to clean the spray with a pin suspended from the fire extinguisher handle.
The OP-M chemical thick-foam marine fire extinguisher is designed to extinguish fires on ships, in port facilities and in warehouses. Chemical foam fire extinguisher OP-9MM is designed to extinguish fires and fires of all combustible materials, as well as electrical installations under voltage.
Rice. 1. Scheme of chemical foam fire extinguisher OHP-10: 1 - fire extinguisher body; 2 - acid glass; 3 - safety membrane; 4 - spray; 5 - fire extinguisher cover; 6 - stock; 7 - handle; 3 and 9 - rubber gaskets; 10 - spring; 11 - neck; 12 - top of the fire extinguisher; 13 - rubber valve; 14 - side handle; 15 - bottom.
Fig.2. Air-foam fire extinguisher OVP-10: I - steel case; 2 - carrying handle; 3 - cartridge for pushing gas; 4 - air-foam nozzle with a spray; 5 - trigger mechanism; 6 - cover of the fire extinguisher body; 7 - siphon tube nozzle.
There are two types of air-foam fire extinguishers (Fig. 2, 3): manual (OVP-5 and OVP-10) and stationary (OVPU-250 and OVP-100). To activate the fire extinguisher, press the trigger lever. In this case, the seal breaks, and the shield pierces the cylinder membrane. Carbon dioxide leaving the can through the nipple creates pressure in the fire extinguisher body, under the action of which the solution flows through the siphon tube through the sprayer into the nozzle. In the nozzle, the solution is mixed with air and an air-mechanical foam is formed.
A fire extinguisher cannot be used to extinguish substances that burn without air (cotton, pyroxylin, etc.), burning metals (alkaline sodium, etc. and light magnesium, etc.). It is forbidden to use for extinguishing electrical installations that are energized. The fire extinguisher is used at ambient temperature from +3 to +50 C.
Rice. 3. Stationary air-foam fire extinguisher OVPU-250: 1 - steel body on supports; 2 - starting cylinder; 3 - foam generator; 4 - reel with hose; 5 - safety valve; 6 - branch pipe for filling the foaming agent solution; 7 - siphon tube of the foam generator; 8 - drain pipe; 9 - foam solution control tube.
Conclusion
The purpose of this abstract was to analyze the currently existing fire extinguishing agents, their characteristics and methods of application in the course of extinguishing fires that have arisen at various objects and under certain conditions characteristic of a particular fire. And in the course of the work it was revealed that the main fire extinguishing agents are: water, powders, foams, gallons, sand, sawdust, steam. Each of the listed substances has its own advantages and disadvantages in the use of fire extinguishing, it largely depends on the types of fires, the classification of which was also given in the work.
Bibliographic list
GOST 28130-89 Fire fighting equipment. Fire extinguishers. Fire extinguishing and fire alarm installations.
Mironov S.K., Latuk V.N. Primary fire extinguishers. Bustard, 2008
Terebnev V.V. Handbook of the head of fire fighting. Capabilities of fire departments. Moscow. "Fire Engineering" 2004
Tutorial. Life safety. YAZRI air defense. 2002.
Yudakhin A.V. Toolkit. Questions of the organization of the UAV in the process of daily activities in parts of the Air Force. 2001.
It involves the use of a wide range of substances, thanks to which the fight against fire is realized. Traditionally, the main substance of this kind is considered to be water. Indeed, this is the most popular filling of fire fighting installations, but this method is far from being effective in all cases. Therefore, other types of fire extinguishing agents are introduced into the working arsenal of fire services, under the properties of which are developed and serving technical means. This is how all new powder components, liquid compositions and aerosols, gas and other variants of substances appear, which make it possible to successfully fight the flame.
Classifications of fire extinguishing agents
The basic principle of separation of fire extinguishing agents is based on the nature of the impact on the fire. The most common way of such influence is the cooling of the combustion zone. In the process of extinguishing, materials that are active from the point of view of a ceasefire are supplied. At the same time, fire service employees should, if possible, mix structural elements and disassemble burning materials, allowing the affected surfaces to cool more efficiently. The following principle is based on the dilution of the reacting elements. In this case, fire extinguishing agents are easily evaporating or decomposing coatings that contribute to a ceasefire. Insulating materials are also common, which affect the activity in the combustion zone by creating special barriers, jumpers, etc.
There is another classification of fire extinguishing materials, which is based on the physical state of the substance. In particular, liquid, gaseous, bulk, solid, as well as fabric fillers of fire installations are isolated. It should be noted that the belonging of fillers to different groups in accordance with this classification is in no way associated with the separation system mentioned above. That is, the classification of fire extinguishing agents according to the principle of impact on the fire zone can allow two or more materials with different physical and chemical properties to be included in one of the categories.
Coolants
Theoretically, combustion can be stopped if heat release is removed at high speed. This principle can be implemented through the use of refrigerants, which, through cooling, regulate the heat removal process and minimize the activity of the combustion source. The classic representative of the group of cooling materials is water - a fire extinguishing agent that has a high heat capacity, availability and chemical inertness.
Like all universal materials, this fluid has drawbacks. First of all, water is characterized by increased electrical conductivity, which in itself imposes serious restrictions on its use. The situation is aggravated when the liquid is mixed with other additives that increase the ability to conduct current. But this is not all the shortcomings. Water also has weak adhesion properties to burning materials, which is why, in fact, special additives are added to it. As a result, other fire extinguishing agents are obtained, which are various mixtures and solutions - as a rule, on a salt basis.
insulating substances
The most common material in this group is foam. The insulating effect contributes to effective flame suppression with minimal losses and risk in terms of toxic safety. The structure of the foam is formed from liquid bubbles that have a gas filling. Often such substances have a double effect - insulating and cooling. At the same time, not all foam fire extinguishing agents can be used in extinguishing fires. For example, a soap solution diluted at home will not give any effect, since the structure of the emulsion will be instantly destroyed in a fire. Therefore, special solutions are used that have a relatively strong bubble structure that can withstand thermal and mechanical stress. In order to strengthen the foamy substance, special stabilizers are added to the solution compositions. The use of air emulsions is also combined with a foaming agent.
Powders intended for extinguishing fires should also be included in the category of insulating materials. Although such substances are universal and have a multifactorial suppressive effect on fire, the ability to isolate fire sources still comes to the fore. For such purposes, for example, fire extinguishing powder based on alkali metals, carbonate, bicarbonate, ammonium salts and other compounds is used. Also, such substances are used purposefully in extinguishing electrical equipment.
Substances of dilution
This is an extensive group of substances that are mainly focused on use in special conditions firefighting. To stop a fire in this way, materials are used that can either dilute combustible vapors with gases to a non-combustible concentration, or minimize the oxygen content in the air to a level where combustion is no longer supported. In this case, various approaches to the supply of materials can be used - for example, into the general fire zone, into the air, or purposefully into the combustion object.
According to the practice of application, the most popular agent of this type is carbon dioxide, which provides the most effective cessation of combustion in a fire. Fire extinguishing agents in the form of nitrogen and water vapor are also useful depending on the conditions of use. For example, water vapor is mainly used in indoor and outdoor hard-to-reach places Oh. During the processing of the object, water vapor fills the entire room, diluting and displacing air masses from it. In this way, the active substance prevents combustion without having a harmful effect on people in the room. In addition, a double effect of extinguishing the flame with steam is sometimes provided. First, there is the cloud itself, which replaces the air. Secondly, the droplets formed from the steam evaporate and absorb heat from the fire source.
Chemically active substances
This is a category of substances that have an inhibitory effect on the combustion process. The extinguishing principle is based on the chemical action of the agent on the fire zone. When the fire extinguishing agent comes into contact with the target object, it interacts with the active centers of the oxidizing reaction, resulting in non-combustible or low-active compounds that stop the combustion reaction.
Halogenated hydrocarbons are capable of providing this effect. These are fire-extinguishing agents with an inhibitory effect that inhibit the activity of the combustion process. But it is important to consider that such materials are dangerous with toxic effects. In terms of extinguishing efficiency, this is perhaps the best group of fire extinguishing materials. But, again, undesirable chemical activity significantly limits the scope of such substances. If we talk about specific compounds, then inhibitory substances can be represented by freons and other halogenated compounds based on ethane and methane. Experts call such materials freons, attributing to them special designations indicating chemical composition. In accordance with the labeling, the permissible conditions for the use of substances are also determined.
Mobile and stationary fire extinguishers
By itself, the effectiveness of substances that can theoretically assist in the fight against fire is minimal if there is no established material supply system. For this purpose, mobile and stationary installations are used that introduce or spray the active substance. Mobile vehicles include fire trucks that are operated by security services. However, these are not only ordinary vehicles with personnel. Trains, airplanes and ships performing fire suppression under appropriate conditions can also be included in this category. Stationary fire extinguishing installations, which are designed to release a fire extinguishing agent, are also common. For example, such systems are most often used in enclosed spaces and work with diluting active materials.
Among the main tasks that stationary installations perform, one can note the elimination or, as a minimum goal, the localization of a fire. At the same time, there are many options for the design of such complexes. In particular, a distinction is made between modular and aggregate systems. Also, against the background of extensive automation of security systems, they are moving away from manual control and fire extinguishing installations, complemented by modern electronics and the latest remote control systems.
The use of fire extinguishing agents in fire monitors
Fire monitors for supplying fire extinguishing materials, as a rule, are designed at the stage of construction of the facility in which they will be installed. The fact is that such systems are the most demanding in terms of communication support, so the initial calculation of their location and installation is especially important. Typically, such units are used at production facilities, where containers for fire extinguishing agents of a particular type are also located. These can be, for example, water tanks or cylinders filled with foam or gas. Some modifications, by the way, are not designed specifically for the complete elimination of the flame. Their main tasks are to protect production equipment or communications - for example, by water irrigation.
Installations of this type may differ in the way they are constructed. Far from always, carriage structures have a stationary position. It can be mobile with an addition in the form of software or remote control. Of course, stationary installations are also common, the supply of fire extinguishing agents in which is often carried out through common network engineering and communications. Such a connection allows you not to waste time on organizing a working infrastructure and immediately start the fire extinguishing process.
Automation in fire extinguishing installations
Modern automatic fire fighting installations allow, regardless of human participation, to control the factors indicating the danger of a fire, and to start the extinguishing process in a timely manner. Usually, at the moment when the values set in the program are exceeded, the supply of the active substance begins and at the same time an alarm is triggered. At the same time, there are different approaches to the means of managing such systems. For example, sprinkler models are fully automated, but there are other systems that provide for manual control. Thus, the fire extinguishing agent in the installations can be released both automatically and at the command of the operator through the control panel. But such a control system already depends on the type of installation itself - modular ones focus on greater autonomy, while centralized ones allow the maximum range of management approaches.
It is important to note the safety factors that may not always be taken into account during operation. automatic systems. Equipping with such installations justifies itself only in cases where the elimination of fires with primary tools is impossible. Also, at some production facilities, personnel maintain security systems not around the clock. It is obvious that in such situations one cannot do without an automatic means of fighting fire. Another thing is that in order to minimize risks, one should initially do right choice extinguishing agent, automatic feed which, as a maximum, will entail only planned and pre-calculated damage.
Classification of installations by fire extinguishing agent
For each type of fire extinguishing installation, a specific type of active substance is used. For safety reasons, the use of several materials in one complex is rarely practiced. The most common system is the water extinguishing design. Deluge complexes are especially common, which are used to protect premises with a high risk of fire. Efficiency similar devices due to the fact that they can provide simultaneous irrigation of the entire area of the protected site. They include pumping equipment, control panels, pipelines, water tanks, warning devices, etc.
The second most popular substance used in deluge structures is foam. Such systems are used to protect local areas in industrial premises, prevention of ignition of transformers and electric devices. Sprinkler installations with foam fire extinguishing material are also widely used. By the way, such units have much in common with water installations, with the exception of special approaches to dosing. These are the main fire extinguishing agents used in stationary and mobile means of fighting fires, but there are also specialized gas systems, powder and aerosol. As a rule, fire protection equipment with such fillers is used in special conditions - for example, in places where there are increased requirements for the maintenance of electrical equipment.
Conclusion
With all the variety of substances used in modern fire extinguishing systems, experts still cannot name a universal and most effective way to fight fire. There is a fairly clear segmentation of materials into classes depending on their technical and operational qualities. At the same time, the impact of fire extinguishing agents on people and objects that are in the ignition zone plays an important role. For example, fire suppression systems with chemical fillers could well be the only means of suppressing a fire. As practice shows, it is required minimal amount fire-extinguishing material of this type to fight medium class fires.
But the problem lies in the consequences that the use of chemically hazardous substances entails. For this reason, technologists are mastering new methods of fire extinguishing, including structural ones. An effective fire extinguishing agent can reveal its full potential only if the system for combating ignition sources has been properly organized. And in this regard, it is worth noting the importance of both basic installations that supply material for extinguishing, and control methods - automatic or manual.
Thermophysical explanation of the fire extinguishing process
Elimination of combustion from a physical point of view is the effect on heat generation and heat transfer. With a decrease in heat release or with a decrease in heat transfer, the temperature and rate of the reaction decrease. When fire extinguishing agents are introduced into the combustion zone, the temperature can reach a value at which combustion stops. The minimum combustion temperature, below which the rate of heat removal exceeds the rate of heat release and combustion stops, is called the extinction temperature.The extinction temperature is much higher than the self-ignition temperature, therefore, to stop combustion, it is enough 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-combustible 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-combustible 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"""
– curves of heat release with decreasing its speed; 2
– direct heat sink; ABOUT– start of oxidation: P is the point corresponding to the extinction temperature; G is the point corresponding to the combustion temperature; Tp is the extinction temperature; Tg- combustion temperature.
In connection with a decrease in the concentration of oxygen in the air, the curve decreases 1 . If, during combustion, thermal equilibrium is established at the point G(crossing of direct heat sink 2 and heat release curve 1 ), then with a decrease in the heat release rate and a decrease in the curve 1 this point will shift to the left and the combustion temperature will decrease. At a certain rate of heat release, the direct heat removal 2 in area high temperatures only touches the heat release curve 1 at the point P. With a further decrease in the heat release rate, the heat removal 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 both by increasing the rate of heat removal and by reducing the rate of heat release.
This can be achieved:
Fig.2. Burnout scheme
Ways to stop burning
Ways to stop burning are presented on fig.3.Each of the ways to stop burning can be performed by various methods or a combination of them. For example, the creation of 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, and the like. .
Fig.3. Classification of ways to stop burning.
Classification of fire extinguishing agents
Based on these methods of stopping combustion, fire extinguishing agents can be classified as follows:Substances and materials to which water and its solutions cannot be supplied
| Substance, material | Degree of danger |
|---|---|
| lead azide | Explodes when humidity increases to 30% |
| Aluminium, magnesium, zinc, zinc dust | When burned, water decomposes into oxygen and hydrogen. |
| Bitumen | The supply of compact jets of water leads to ejection and increased combustion |
| Alkali and alkaline earth metal hydrides | |
| sodium hydrosulfite | Spontaneously ignites and explodes from the action of water |
| Mercury fulminate | Explodes when struck by a compact water jet |
| Silicon iron (ferrosilicon) | Hydrogen phosphorous is released, self-igniting in air |
| Potassium, calcium, sodium, rubidium, cesium metal | Reacts with water to release hydrogen, may explode |
| Calcium and sodium (phosphorous) | React with water to release hydrogen phosphide, which ignites spontaneously in air |
| Potassium and sodium (peroxides) | If water enters, an explosive release with increased combustion is possible |
| Aluminum, barium and calcium carbides | Decomposes, releasing flammable gases, explosion possible |
| Alkali metal carbides | Explode on contact with water |
| Magnesium and its alloys | When burned, water decomposes into hydrogen and oxygen. |
| Metaphos | Reacts with water to form an explosive substance |
| Sodium sulphide and hydrosulphate | Extremely hot (over 400 °C), may cause ignition of combustible substances, as well as burns on contact with the skin, accompanied by difficult-to-heal ulcers |
FIRE EXTINGUISHING AGENTS - substances with physical and chemical properties that allow you to create conditions for the cessation of combustion. To O. in. include water, foams, powders, gases, aerosols. The most widespread O. in. - water. It can be applied in the form of continuous and sprayed (finely sprayed) jets.
Fire extinguishing foam is a colloidal system consisting of gas bubbles surrounded by liquid films. It is formed when foaming agents are added to water. There are foams of low (up to 20), medium (20-200) and high (more than 200) expansion. The most effective foam is obtained from fluorine-containing blowing agents with a film-forming effect. It can be used to extinguish hard materials and all classes of combustible liquids, except chemically interacting with water.
Fire extinguishing powders - finely ground (20-60 microns) mineral salts with various additives that ensure fluidity and prevent caking (lumping). General purpose powders are used to extinguish burning solid materials, flammable liquids, gases and electrical equipment under voltage. Special purpose powders are used to extinguish metals, organometallic compounds. All types of powders quickly suppress combustion, but do not have a cooling effect.
Fire extinguishing gases include inert diluents: carbon dioxide, nitrogen, argon, water vapor, flue gases and volatile inhibitors - some halocarbons (freons). Carbon dioxide is used for volumetric extinguishing of combustible liquids, electrical equipment, etc. Freons, primarily bromine-containing ones, are more effective. The chlorofluorocarbons developed and used to replace bromine-containing freons are inferior to them in terms of fire extinguishing ability.
Very effective O.'s class in. volumetric extinguishing - fire extinguishing aerosols obtained by burning special solid fuel compositions in generators. Consist of solid particles less than 2 microns in size and gases. The greatest prospects are the so-called. cold aerosols. They are more effective than bromine-containing freons and can be used to extinguish solid materials, except for those burning in smoldering mode, and combustible liquids.
30 Fire extinguishers, automatic fire extinguishing installations.
Automatic fire extinguishing installation (AUPT) - a fire extinguishing installation that automatically operates when the controlled fire factor (factors) exceeds threshold values in the protected area. Distinctive feature automatic installations is their performance of the functions of automatic fire alarm. At the same time, all automatic fire extinguishing installations (except sprinkler ones) can be activated manually and automatically. Sprinkler fire extinguishing installations are activated exclusively automatically.
As of 1914, more than 400 automatic fire extinguishing installations were installed in Russia.
Buildings, structures and structures must be equipped with automatic fire extinguishing installations in cases where it is not possible to extinguish a fire with primary fire extinguishing equipment, as well as in cases where service personnel are in protected buildings, structures and structures outside the clock.
Automatic fire extinguishing installations must achieve one or more of the following objectives:
Elimination of a fire in a room (building) before the occurrence of critical values of dangerous fire factors;
Elimination of a fire in a room (building) before the limits of fire resistance of building structures;
Elimination of a fire in a room (building) before causing the maximum allowable damage to the protected property;
Elimination of a fire in a room (building) before the danger of destruction of technological installations.
The type of automatic fire extinguishing installation, the type of fire extinguishing agent and the method of its supply to the fire site are determined depending on the type of combustible material, space-planning decisions of the building, structure, structure and environmental parameters.
In real conditions, fires can occur in places that are hard to reach for the delivery of dispersed and foam fire extinguishing agents supplied by stationary fire extinguishing installations with the formation of numerous "shadow" zones. For these reasons, fixed fire extinguishing installations often provide only fire containment. In addition, a number of installations, according to the principle of operation, are intended only for localizing a fire. These include automatic fire-blocking shutters and doors, water curtains, etc. In connection with the foregoing, the use of automatic fire extinguishing installations implies the mandatory participation in the elimination of a localized fire of operational fire departments or voluntary formations.
Water AUPT
Water AUPT - use water or water with additives as a fire extinguishing agent. They are divided according to the type of sprinklers into sprinkler and deluge.
Water mist fire extinguishing system
Deluge water fire extinguishing installations (DUVP) are used, as a rule, to protect premises with increased fire hazard when the effectiveness of fire extinguishing can be achieved only with simultaneous irrigation of the entire protected area. Deluge installations are also used for irrigating vertical surfaces (fire curtains in theaters, technological apparatuses, oil tanks, etc.) and creating water curtains (protecting openings or around any apparatus).
The composition of the water AUPT includes:
pump units;
Distribution pipelines with sprinklers;
incentive systems;
Control nodes;
Shut-off, shut-off and control and protective fittings (gate valves, valves, check valves);
tanks (reservoirs and hydraulic accumulators);
dispensers;
Compressor;
Annunciators;
Electroautomatic equipment (control and management);
Technical means of fire detection.
Foam AUPT
Foam fire extinguishing installations are mainly used to extinguish flammable liquids and combustible liquids in tanks, combustible substances and oil products located both inside and outside buildings. Foam APT deluge installations are used to protect local areas of buildings, electrical appliances, transformers. Sprinkler and deluge water and foam fire extinguishing installations have a fairly close purpose and design. A feature of APT foam installations is the presence of a reservoir with a foaming agent and dosing devices for separate storage of fire extinguishing agent components.
The following dosing devices are used:
Dosing pumps that supply the foam concentrate to the pipeline;
Automatic dispensers with a Venturi pipe and a diaphragm-plunger regulator (with an increase in water flow, the pressure drop in the Venturi pipe increases, the regulator provides an additional amount of foam concentrate);
Foam mixers of ejector type;
Dosing tanks using the differential pressure created by the Venturi pipe.
Other distinguishing feature foam fire extinguishing installations - the use of foam sprinklers or generators. There are a number of disadvantages inherent in all water and foam fire extinguishing systems: dependence on water supply sources; the difficulty of extinguishing premises with electrical installations; complexity Maintenance; large, and often irreparable, damage to the protected building.
Gas AUPT
Gas AUPT - a set of technical stationary technical fire extinguishing equipment for extinguishing fires due to the automatic release of a gas fire extinguishing agent (composition). According to the design, they can be of two types: centralized and modular. Liquefied and compressed gases are used as fire extinguishing agents.
Liquefied:
Freon23;
Freon125;
Freon218;
Freon227ea;
Freon318C;
Six-phosphoric sulfur;
carbon dioxide
Inergen.
The composition of the gas AUPT includes:
Distribution pipelines with nozzles;
incentive systems;
Batteries;
Sections type-setting;
Incentive-starting sections;
Air distributors;
Distribution devices;
Cylinder receiver;
Charging station;
Annunciators;
Electroautomatics (control and management), technical means of fire detection.
Powder AUPT
Powder AUPT use fire extinguishing powder. They are used for localization and elimination of fires of classes A, B, C and electrical equipment (electrical installations under voltage). Installations can be used to localize or extinguish a fire in a protected area, local extinguishing of a part of an area or volume, extinguishing the entire protected volume. When using impulse modules powder fire extinguishing the breakdown voltage parameter may not be taken into account.
Installations do not provide a complete cessation of combustion and should not be used to extinguish fires:
Combustible materials prone to spontaneous combustion and smoldering inside the volume of the substance ( sawdust, cotton, grass flour, paper, etc.);
Chemical substances and their mixtures, pyrophoric and polymeric materials prone to smoldering and burning without air access.
The letter of the Director of the Department for Prevention of Emergency Situations M. I. Faleev dated September 13, 2006 contains recommendations on the non-use of powder fire extinguishing systems in a room with a mass presence of people (more than 50 people).
Aerosol AUPT
For the first time, the use of aerosol means for extinguishing fires was described in 1819 by Shumlyansky, who used black powder, clay and water for these purposes. In 1846, Kuhn proposed boxes filled with a mixture of saltpeter, sulfur and coal (smoky powder), which he recommended to throw into a burning room and tightly close the door. Soon the use of aerosols was discontinued due to their low efficiency, especially in leaky rooms.
Volumetric aerosol fire extinguishing installations do not provide a complete cessation of combustion (fire suppression) and should not be used to extinguish:
Fibrous, loose, porous and other combustible materials prone to spontaneous combustion and (or) smoldering inside the layer (volume) of the substance (sawdust, cotton, grass flour, etc.);
Chemical substances and their mixtures, polymeric materials prone to smoldering and burning without air access;
Metal hydrides and pyrophoric substances;
Metal powders (magnesium, titanium, zirconium, etc.).
It is forbidden to use the settings:
In rooms that cannot be left by people before the start of the generators;
Premises with a large number of people (50 people or more);
In the premises of buildings and structures of III and below the degree of fire resistance according to SNiP 21-01-97 installations using fire-extinguishing aerosol generators having a temperature of more than 400 ° C outside the zone 150 mm from the outer surface of the generator.
Robotic fire extinguishing installations
A robotic fire extinguishing installation is a stationary automatic means, which is mounted on a fixed base, consists of a fire nozzle with several degrees of mobility and equipped with a drive system, as well as a program control device and is designed to extinguish and localize a fire or cool process equipment and building structures.
A variety of means used to extinguish fires are called fire extinguishers. Substances and materials having certain properties in the solid, liquid and gaseous state can be used as fire extinguishing agents.
The following substances are most commonly used for extinguishing fires.
Water has a high heat capacity and is able to absorb a significant amount of heat from burning substances and materials. About 2688 J of heat is spent on heating and turning 1 liter of water into steam.
Water poorly wets many substances (for example, wood and charcoal, cotton, wool, etc.), so the coefficient of its use in extinguishing a fire is very low. To increase the wetting ability of water and increase the efficiency of extinguishing, various kinds of wetting agents are added to it, and they are also used in the form of sprayed jets, since in this case its unproductive losses are significantly reduced. mist water also used to extinguish some flammable and combustible liquids.
However, it is not allowed to use water to extinguish fires in cases where it chemically interacts with one or another substance (for example, with 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 the burning substances, and also helps to dilute the concentrations of reactants in the combustion zone and isolates it from the surrounding air. Water vapor is used to extinguish fires and fires in various types of apparatus and in enclosed spaces of small volume. The effect of extinguishing with the help of water vapor is achieved at a mass flow rate of at least 0.002 kg/s-m 3 .
Fire extinguishing foam obtained by mixing a gas and a liquid, resulting in the formation of bubbles, inside which gas particles are enclosed. To extinguish fires, chemical and air-mechanical foams are used.
The fire-extinguishing properties of the foam consist in the fact that, by covering the surface of the 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 fire site using special devices - foam fire extinguishers, foam barrels or foam generators. Behind Lately in the Soviet Union, medium and high expansion foam was widely used, 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 extinguishers.
The fire-extinguishing properties of carbon dioxide (as well as other inert gases) lie in the fact that to some extent it isolates the burning surface from air access, cools it and dilutes the concentration of reactants 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 enclosed 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, so 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 enhances 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 the type 3.5, BF-1, BF-2, BM and freon 114V2. Their fire extinguishing effect is based on the chemical inhibition of the combustion reaction when the 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, for extinguishing oil products, alcohols, protecting transformers, the powder composition GISB (based on sodium bicarbonate) is used. To extinguish molten alkali metals, powder co stavy type PS.
Fire extinguishing agents and their properties
In accordance with the conditions necessary for the initiation and propagation of combustion, its cessation can be achieved by the following methods:
Termination of access to the combustion zone of an oxidizer (air oxygen) or a combustible substance, as well as a decrease in their supply to values at which combustion is impossible;
Cooling the combustion zone below the auto-ignition temperature or lowering the temperature of the burning substance below the ignition temperature;
Dilution of combustible substances with non-combustible ones;
Intensive deceleration of the rate of chemical reactions in the flame, mechanical separation of the flame by a strong jet of gas or water.
These fundamental methods are the basis for the methods and techniques used to stop burning during fires.
Main extinguishing agents: water, chemical and air-mechanical foams, aqueous solutions of salts, inert and non-combustible gases, water vapor, halo-hydrocarbon fire extinguishing compositions 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. The disadvantages of water include freezing at a temperature of 0 ° C, which can result in a rupture of fire hoses and a breakdown of the pump; inapplicability for extinguishing burning liquid substances (LZHV and GZH) 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 burning area. Do not use water to extinguish electrical networks and electrical installations that are energized, as a jet of water is a conductor and can cause electric shock.
Chemical foam is obtained by the interaction of alkaline and acidic solutions in the presence of foaming agents. This produces a gas (carbon dioxide).
Gas bubbles are enveloped in water with 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 a foaming agent (~0.3%). The characteristic of the foam is the expansion - the ratio of the volume of the obtained foam to the volume of the initial substances (the usual expansion of the 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 up to 500 m 3 and small fires in open areas and installations. The steam moistens the burning objects and reduces the oxygen concentration. The extinguishing concentration of water in the air is approximately 35% by volume.
Inert and non-combustible gases (nitrogen, argon, helium, carbon dioxide) lower the oxygen concentration in the combustion chamber and slow down the intensity of combustion. Inert gases are usually used in relatively small spaces. The extinguishing concentration of inert gases when extinguishing in a closed room is 31-36% of the volume of the room.
Aqueous solutions of salts are among the liquid 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 that take away heat.
The fire-extinguishing effect of halocarbon fire-extinguishing compositions is based on the chemical inhibition of the combustion reaction. Compositions are used: 3.5; 4ND; 7; SZhB; BF; and others (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 a fire in much the same way as water vapor and inert gases. When throwing sand on a burning object, heat is absorbed and the surface is isolated from atmospheric oxygen.
Bedspreads (asbestos sheets, tarpaulins, felt mats) are used to extinguish small burning surfaces and burning clothes on a person (the burning substance is isolated from the access of atmospheric oxygen). Mechanical means(tarpaulin, felt, sand, earth) are used where combustible substances have not yet had time to heat up, that is, at the beginning of ignition.
Wetting agents are also used in practice. Main physical property wetting solutions is to improve the wettability of combustible 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 minimal cost. The most important parameters of fires that determine the conditions for fire extinguishing are:
Physico-chemical properties of combustible material, on which the choice of fire extinguishing agent depends;
Fire load, which refers to the mass of all combustible and slow-burning materials located in the object under consideration, referred to the floor area of the room or the surface occupied by materials on outdoors;
Fire load burnout rate;
Gas exchange of the fire seat with environment and with the external atmosphere;
Heat exchange between fires and surrounding materials and structures;
The size and shape of the fire and the room in which the fire occurred;
Weather conditions.
The physico-chemical properties of the combustible material determine the choice of fire extinguishing agent. To extinguish a fire, do not use substances that react violently with a combustible or oxidizing agent. For example, water should not be used to extinguish materials that interact with it, form combustible gases or generate heat (alkali metals and some other combustible materials).
Extinguishing fires of smoldering materials causes particular difficulties due to the difficulty of penetration of fire extinguishing agents into the pores of such materials. The classification of fires depending on the physical and chemical properties of combustible 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 combustible structural elements buildings, and the rate of its burnout determine the main characteristics of the fire, as well as temperature regime and the duration of the fire, hazard factors (HFR) 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 / m 2). The development of a fire and its parameters are highly dependent on the type and magnitude of the fire load.
According to the method of distribution of the fire load, the premises are divided into two classes:
Premises of large facilities 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 with the formation of a common combustion zone. Depending on the class of the room, a fire extinguishing method is chosen. The fire can be divided into three zones: combustion, heat exposure and smoke.
The combustion zone occupies a part of the space in which combustion occurs directly. It can be limited by the bounding structures of the building, the walls of technological equipment. Combustion in a fire has a diffusive turbulent character.
Unlike gases and liquids, combustion of solid materials can occur on horizontal, inclined, and vertical surfaces. The speed of flame propagation is highly dependent on the angle of inclination and the direction of combustion propagation. The rate 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 a part of the space adjacent to the combustion zone, in which heat exchange occurs between the combustion zone and the 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), environment, purpose, etc. All fire extinguishing methods are primarily divided into surface extinguishing, which consists in supplying fire extinguishing agents directly to the combustion source, and volumetric extinguishing, which consists in creating an environment that does not support combustion in the fire area.
Surface extinguishing, also called area fire suppression, can be applied to almost all types of fires. For this type of extinguishing, fire extinguishing compositions are used that can be supplied to the fire at a distance (liquid, foam, powders).
Volumetric extinguishing can be used to a limited extent, it is based on the creation of a fire extinguishing medium in the entire volume of the protected object. Thus, surface extinguishing in the state described above is applicable to fires in class I premises, volumetric -0 to fires in class II premises. Sometimes the method of volumetric quenching is used for fire protection local area in large volumes (for example, fire hazardous areas in large rooms). But at the same time, an increased consumption of fire extinguishing agents is provided. For volumetric extinguishing, fire extinguishing agents are used, which 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 method of volumetric extinguishing seems to be the most progressive, since it provides not only a quick and reliable cessation of combustion at any point of the protected volume, legs and phlegmatization of this volume, that is, the prevention of the formation of an explosive environment. 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 transportable) and fire hydrants located in buildings, mobile - various fire trucks, as well as stationary - special installations with a supply of fire extinguishing agents, actuated automatically or manually, fire monitors and others. Surface extinguishing is carried out by all types of fire equipment, but mainly primary and mobile; volumetric quenching - only by stationary installations.
