Understand the different fire extinguishing agents and the use of
Fire extinguishing agent is a substance that can effectively destroy the combustion conditions and stop burning. Modern use of fire extinguishing agents in addition to water has developed to a variety of types, including foam, halogenated alkane, carbon dioxide, dry powder, etc.. However, fire extinguishing agent is still only the fire fighting “ammunition”, only in conjunction with the appropriate fire fighting equipment and equipment, in order to give full play to its fire fighting effectiveness; especially important is that fire extinguishing agents have different properties, must be used correctly to different fire fighting, in order to quickly extinguish the fire. Therefore, to do a good job in enterprise fire safety, it is necessary to understand and be familiar with the physical and chemical properties of various fire extinguishing agents and the principle of fire extinguishing, the scope of application, etc. in detail, the right remedy for the highest efficiency of fire extinguishing. The following will be described separately for the enterprise commonly used several fire extinguishing agents.
Water is a non-combustible liquid, is a natural fire extinguishing agent, it is the most widely used in fire extinguishing, is the best extinguishing agent, can put out most of the fire. But water is not a universal extinguishing agent, some substances on fire can not be extinguished with water, but will occur when new dangers. Including electrical appliances, frying pans, calcium carbide, gasoline, acids and some active metals on fire, bear in mind that water can not be used to extinguish.
Can be miscible with water, and through chemical reaction or mechanical methods to produce fire extinguishing foam extinguishing agent, called foam extinguishing agent. Foam extinguishing agent has the characteristics of high fire extinguishing strength, high speed, low water loss, easy to resume work, low product cost, non-toxic, non-corrosive. For low temperature or normal boiling point of water-soluble and non-water-soluble combustible liquid fires, closed electrically powered equipment fires and control of liquefied petroleum gas, liquefied natural gas flow of the fire are also very effective. Such as fighting fires in automobile depots, automobile repair rooms, combustible liquid engine rooms, oil plants and depots, cavernous oil depots, boiler rooms of fuel oil pump rooms, aircraft depots, aircraft repair depots, ship cabins, tanker cabins, basements, underground buildings, coal mine pits and other limited space fires are particularly suitable; also suitable for fighting oil pool fires and dispersed liquid fires caused by combustible liquid leaks; due to the small relative density of high-frequency foam, the It is also suitable for fighting oil pool fires and dispersed liquid fires caused by combustible liquid leaks.
It is important to note that the high multiplier foam can not be used to put out oil tank fires. Because when the oil tank is on fire, the hot gas above the tank is very strong, and the specific gravity of the foam is very small, so it cannot cover the oil surface. High multiplier foam extinguishing agent is also not suitable for fighting water-soluble combustible liquid fires, but a small amount of indoor storage of water-soluble combustible liquid fires, can also be used to extinguish the full-filled method. Foam can conduct electricity, in fighting electrical equipment fires, the power must be cut off.
Dry powder, also known as chemical powder fire extinguishing agent, it is an easy to flow micro-fine solid powder. Generally with the help of a special fire extinguisher or fire extinguishing equipment in the gas pressure will be dry powder from the container spray, in the form of powder mist fire. At present, the main dry powder extinguishing agent used are ordinary dry powder extinguishing agent and multi-purpose dry powder extinguishing agent two. Ordinary dry powder extinguishing agent is mainly all-siliconized sodium bicarbonate dry powder, its price is cheaper, is the production and the largest amount of a class of dry powder extinguishing agent. This type of extinguishing agent is suitable for extinguishing B class fires and C class fires, also known as BC class dry powder. Multi-purpose dry powder extinguishing agent is mainly ammonium phosphate dry powder, with anti-combustion properties, not only for fighting liquid, gas fires, but also for fighting general solid material fires (Class A fire), so also known as ABC class dry powder.
Dry powder extinguishing agent is usually stored in the fire extinguisher or dry powder fire extinguishing equipment. When the fire is extinguished by the pressure of pressurized gas (carbon dioxide or nitrogen), the dry powder is shot out from the nozzle, forming a stream of foggy powder with pressurized gas and shot at the burning material. When the dry powder comes into contact with the flame, a series of physical and chemical effects occur, and the flame is extinguished. Pay attention to the phenomenon of pipe plugging. Spraying distance should depend on the object of fighting combustion, in principle, to not blow the fuel and powder, so that it adheres to the surface of the equipment is appropriate. To be in the ventilation
dry place for storage, regular inspection by a person.
Halogenated alkane is a general term for a class of organic compounds obtained by replacing part or all of the hydrogen atoms in the alkane molecule by halogen atoms. Some of the lower alkane halogenates have different degrees of fire extinguishing effect, these low-level halogenated alkanes with fire extinguishing effect is collectively known as halogenated alkane fire extinguishing agent. These chemical names are cumbersome to write, the current international code to indicate. The naming principle is: four Arabic numerals are used to indicate the number of atoms of carbon and halogen elements in halogenated alkanes, the order of carbon, fluorine, chlorine, bromine, if the end of the number is zero is omitted. Such as: difluorine a chlorine a bromide methane (cF2ClBr) → 1211; trifluoro a bromide methane (CF3Br) → 1301; difluorodibromomethane (CF2Br2) → 1202; tetrafluorodibromoethane (C2F4Br2) → 2402.
Halogenated extinguishing agents are suitable for fighting fires of valuable items such as oil, electrically charged equipment and precision instruments. The gas produced by this agent is slightly toxic and should be ventilated after fighting fires indoors to ensure the safety of personnel.
Heptafluoropropane is a kind of halogenated alkane, which is a colorless, odorless and non-conductive gas with good fire extinguishing performance. It is a clean agent and does not contain particles or oil-like residues after release, and does not pollute the environment or the precision equipment being protected. It has the same low toxicity as Halon 1301 and can be used in the protected area where people often work. It is suitable to replace the existing 1301 fire extinguishing agent.
(5) Carbon dioxide
Carbon dioxide, commonly known as carbonic acid gas, is an inert gas that has been used as a fire extinguishing agent since long ago. Carbon dioxide can quickly dissipate after the fire, leaving no trace. It is suitable for fighting all kinds of combustible liquids and water, foam, dry powder and other extinguishing agents to extinguish the fire, easily defaced solid material fire. Such as electrical, precision instruments, valuable equipment, books and archives. Can also put out a variety of electrical equipment fires below 600 volts. However, carbon dioxide can not put out sodium potassium, aluminum, lithium and other alkali metals and alkaline earth metals and their hydrides fires; can not put out fires in inert media can supply their own oxygen combustion material (such as nitrate fiber).
Carbon dioxide is irritating to eye mucous membranes, respiratory tract, skin, etc. When the air contains 2% to 4% (volume fraction) of carbon dioxide gas, human respiration will be accelerated; containing 4% to 6% of carbon dioxide gas, there will be severe heartache tinnitus, heartbeat; content in 6% to 10%, people will lose consciousness; containing 20%, will cause death. Therefore, the use of attention should be paid to prevent the danger of asphyxiation on the human body.
(6) Aerosol extinguishing agent
Aerosol extinguishing agent is a kind of liquid or solid as the dispersed phase, gas as a dispersion medium formed by the particle size of less than 5um of the sol system of fire extinguishing media. Its characteristics are: the solid particles are small and have the characteristics of gas, can not be limited by the direction, bypassing obstacles to reach any corner of the protection space, and can have a long residence time in the fire space, so as to achieve full flooding fire; no pressure-resistant containers; fire extinguishing efficiency is higher than dry powder extinguishing agent; for closed space, can also be used in open space, the depletion of the ozone layer indicators for zero. Because the extinguishing agent has the characteristics of not easy to land and can bypass obstacles and other gases, it is also used as a gas extinguishing agent in engineering. According to the formation of different ways, divided into hot aerosol and cold aerosol two categories.
The advantages of hot aerosol fire extinguishing agent is high efficiency; fire extinguishing equipment construction is simple, no pressure-resistant containers; fire extinguishing device for modular combination, at room temperature, atmospheric pressure storage, easy maintenance; long storage period (generally more than 5 years), low cost, cost-effective significantly better than other types of fire extinguishing agents are also more environmentally friendly. However, due to the technology itself, hot aerosols in fire extinguishing will appear outside the flame spray phenomenon, when the agent combustion released a lot of heat, so that the outer wall of the container hot so that people can not approach, and fire extinguishing devices containing cooling elements, cooling consumed part of the active material, so that the fire extinguishing efficiency is affected.
Hot aerosol extinguishing agent is a self-reactive substances, in the storage and transportation process there may be physical or chemical changes, to spontaneous combustion or explosion and other dangerous accidents.
Cold aerosol extinguishing agent is a new type of high-efficiency powder extinguishing agent developed for some shortcomings of hot aerosol extinguishing technology. Cold aerosol fire extinguishing agent aerosol diffusion is not directional, regardless of the direction of the jet or the location of the nozzle, in a very short period of time can quickly spread to the protection of the space, in a fully submerged way to extinguish the fire, and can bypass the obstacles in the fire space has a long residence time, high efficiency; toxicity and corrosion is small, no depletion of the ozone layer; overcome the hot aerosol fire extinguishing agent release of high temperature even
Fire extinguishing agent release when the high temperature associated reaction and other disadvantages, and than it has a higher fire extinguishing efficiency.
(The solid particles of cold aerosol extinguishing agent are irritating to human respiration; after the release of aerosol, the visibility in the fire scene is reduced, affecting the escape of personnel in the fire scene is generally not allowed to be used in places with people, must ensure that personnel evacuate the protected area after spraying); as the smaller the particles, the more surface charge, the van der Waals force between its molecules will be greater than its own gravity, so the aerosol particles of superfluous, will lead to inter-particle agglomeration, sintering and other problems, so it also needs to be strictly surface coating treatment, and the superfine coating process of particles is complex, there is a certain degree of difficulty in manufacturing, high cost; unclean, can not be used for precision instruments and other clean places.
(7) Mixed inert gases
Mixed inert gas extinguishing agent is a mixture of three natural inert gases, according to the ratio of nitrogen 52% argon 40%, carbon dioxide 8% completely natural combination of gas, the relative molecular mass of 34.1, slightly heavier than air, belongs to the inert gas extinguishing agent. Mixed gas extinguishing agent is now internationally recognized as a substitute for halogenated extinguishing agent “green environmental protection extinguishing agent, has been widely used in the international.
Mixed gas extinguishing agent fire extinguishing mechanism and carbon dioxide extinguishing agent is basically the same, that is, by reducing the concentration of oxygen in the protection area (from 21% of the normal oxygen content of air to 12.5% below), so that it can not maintain combustion and achieve the purpose of fire extinguishing. Because it is composed of natural gases in the atmosphere, its release only puts these natural gases back into the atmosphere, and has no adverse effect on the environment because the depletion potential of the ozone layer of the atmosphere ODP=0 (no damage to the ozone layer of the atmosphere) and the greenhouse effect value DWG=0 (no greenhouse effect is caused).
Because the mixture of gases in the fire will not occur chemical reaction, will not form a dense fog and affect the view, do not pollute the environment, the fire extinguishing agent is non-toxic, harmless, non-corrosive to humans, has good electrical insulation performance characteristics, is a safe environmentally friendly fire extinguishing agent, so it is suitable for places where people often work.
(8) Sand and rock powder
Sand and rock powder can cover the source of fire, isolate the burning material and air, so that the fire is extinguished, and can be used to extinguish electrical equipment and oil fires.