[Firefighting knowledge] Application of gas fire extinguishing technology in firefighting

Abstract: The importance of fire protection for, introduced the common market, several gas extinguishing technology is, by comparing the performance of several technical gas fire, analysis, combined with the practical application of the project, proposed clean gas fire extinguishing technology will be the future of Fire mainstream point of view, to promote gas extinguishing technology applications.

Keywords : gas extinguishing system , extinguishing medium , clean gas fire extinguishing agent

With the rapid development of the national economy , the use of buildings has become increasingly complex . Fire hazards have increased year by year , posing a great threat to people’s personal and property safety and social and public safety. According to Ministry of Public Security Fire Department statistics show that in 2007 China fires a total of 159,000 since (not including forests, grasslands, military, underground mine fire), which caused electrical fires up to a total of 45,703, accounting for the total number of 28 .8% . At present , there are a variety of industrial and civil firefighting technology measures , such as fire hydrant systems, automatic sprinkler systems, foam fire extinguishing systems, and gas fire extinguishing systems. The traditional fire fighting mainly rely on water as the extinguishing medium, although it has good fire performance, and prepare to take cheap, but can not fully meet the needs of building fire, which provided a broad space for the development of gas fire extinguishing agent.

1 Performance comparison of various gas fire extinguishing systems

The gas extinguishing system is a fire extinguishing system using liquefied gas or non-liquefied gas as a fire extinguishing medium . It mainly relies on the physical or chemical action of the extinguishing medium to extinguish the fire . The physical effects include asphyxiation, isolation and cooling . The chemical reaction is to suppress the combustion through chemical reactions. . Gas fire extinguishing system can be used for electrical fires, fires a solid surface, liquid fire extinguishing can be cut and a front gas fire gas source [1], in particular in an electrical fire, the fire extinguishing efficiency of the gas is much higher than other techniques extinguishing technology. Currently, for the user to select the type of gas extinguishing systems on the market many common gas fire extinguishing system carbon dioxide, fluorine-containing gas, an inert gas, and aerosols (Long EMC) gas fire extinguishing system, the extinguishing agent for various gases different characteristics, it is necessary for the works, environmental protection and fire performance of various gas extinguishing systems were analyzed to provide a theoretical basis for practical application.

1.1 Carbon dioxide

Carbon dioxide is a gas fire extinguishing agent after the first use of an alkyl halide, colorless state at normal temperature, odorless, non-corrosive and non-conductive, the density is 1.5 times that of air, it is easy to store and transport. Carbon dioxide gas fire extinguishing system is mainly composed of fire extinguishing agent storage bottle, bottle valve, check valve, manifold, safety device, selection valve, pressure reducing device, pipe network and nozzle, and the system is divided into high pressure ( storage pressure 5. 17 MPa ) and low pressure ( storage pressure 2.07 MPa) two. System at high pressure or low temperature liquefied carbon dioxide into the fire space, while reducing the oxygen content within the protected area to prevent burning (when the volume percent oxygen in the air less than 12%, will not continue burning), while the gas Liquefaction absorbs ambient heat and cools the fire scene. At present , carbon dioxide gas fire extinguishing agent is the only gas fire extinguishing system that can be applied locally , and is particularly suitable for protecting specialized equipment in high spaces or open spaces.

Since the amount of fire extinguishing agent during a minimum of 34%, far greater than the acceptable range of the human body (the carbon dioxide concentration exceeds 20%, people will suffocate), together with the extinguishing medium in the protected object while cooling, because the temperature The rapid decline has caused a certain impact on precision equipment . Therefore, the carbon dioxide gas fire extinguishing system should not be used in places where there are personnel activities and store valuable equipment . However, liquid carbon dioxide has good permeability and can extinguish the solid depth fire . It is often used in books and archives. , cultural relics and other data warehouses.

Recently, various scientific studies, carbon dioxide and global warming have a certain relationship, and therefore from the viewpoint of environmental protection, the use of carbon dioxide gas extinguishing technology, subject to certain restrictions, and is gradually being replaced by clean gas extinguishing agent.

1.2 fluorine gas

Fluorine-containing gas fire extinguishing system composed mainly trifluoromethane and heptafluoropropane two kinds of fluorine-containing gas total flooding fire extinguishing system with carbon dioxide fire extinguishing system, the extinguishing agent stored in the gaseous state, a liquid state is released, the decomposition products of extinguishing agent at a high temperature burning material consumption The active group in the medium , thus interrupting the combustion chain to achieve the effect of extinguishing the fire , thus acting as a chemical extinguishing agent.

The product code of trifluoromethane is HFC-23, and it is a colorless, non-conductive gas at room temperature . The density is 2.4 times of the air density , and the destruction coefficient of the gas to the ozone layer is ODP = 0, which is a clean gas extinguishing agent. Due to their high trifluoromethane saturation vapor pressure, low density liquid, no nitrogen pressure to meet the needs of different protective space height, plus the use of an ambient temperature of 20 ℃ ~ 50 ℃, suitable for use in cold regions. At the same time , trifluoromethane does not affect the maximum concentration of heart and lung function NOAEL> 50%, which is much higher than its design concentration (14.9%), so it is suitable for places where people are infested.

Hexafluoropropane is codenamed HFC-227ea or FM200. It is gaseous at room temperature , colorless, odorless, and non-conductive . Its density is 6 times that of air , and it has no damage to the atmospheric ozone layer (ODP=0). It is also a clean gas extinguishing agent. All gas can volatilize at normal temperature and pressure conditions, no residue after the fire, a safe belonging to the fire extinguishing agent. Because the NOAEL of heptafluoropropane is 9%, it is mostly used in communication equipment room and computer room ( fire extinguishing design concentration is 8%) . Since the saturated vapor pressure of the gas is low ( vapor pressure at 20 °C is 0.391 MPa), nitrogen gas pressurization is required , so the protected area is limited.

Since the fluorine-containing gas fire extinguishing agent at a high temperature, the gas generated by the decomposition of hydrogen fluoride (HF) gas bound water, HF and air, hydrofluoric acid is formed having a corrosive effect, not only corrosion metals, leather, paper and glass surfaces, and also Stimulates the human respiratory system and eyes. At the same time , the gas is highly volatile and cannot penetrate the depths of fire objects , making it difficult to extinguish solid-level fires.

1.3 Inert gas

Inert gas fire suppression system is a representative Inergen (INGEREN, inert (Inter) and abbreviations nitrogen (Nitrogen) two English words), which is composed of 52% nitrogen, 40% argon, carbon dioxide consisting of 8% Mixed gas , also known as IG-541 . Because the mixed gas is colorless and odorless , it does not decompose under heat , and the values ​​of ODP, GWP ( greenhouse effect ) and ALT ( survival life in the atmosphere ) are all equal to 0, which is arguably the most clean and environmentally friendly extinguishing medium. The inert gas extinguishing system extinguishes the fire by diluting the concentration of oxygen in the air in the protected area . The extinguishing mechanism is the same as the carbon dioxide gas extinguishing system , and the extinguishing efficiency is lower than that of the fluorine-containing gas extinguishing system. Because the fire extinguishing agent is stored in the gaseous state , the storage space occupied by the storage bottle is large , and the system pressure is high , making the cost of the equipment and the pipe network high . Therefore, the initial investment of the system is higher than other gas fire extinguishing systems.

1.4 Aerosol

The aerosol fire extinguishing system is a solid mixture composed of an oxidant, a reducing agent, a combustion rate control agent and a binder . It is divided into a hot aerosol and a cold aerosol . The application mainly involves hot aerosols. Aerosol enabled self extinguishing combustion of the fuel have some suspended solids, the valve is opened, the compressed gas mixture agent discharge inhibiting combustion in the protected object, and absorbs ambient temperature. Although the resulting product was cooled release, aggregated microparticles can be suspended in the air for a long time, and can bypass the obstacles, has a high fire-extinguishing efficiency, but the injection of smoke and dust reduce visibility of the protected area, thereby affecting passenger evacuation. At the same time , the product has a certain degree of corrosion , causing some damage to the metal equipment and instruments. However, the aerosol gas fire extinguishing system does not need to be provided with a pipe network , which can significantly reduce the initial investment when used to protect a large space area.

2 engineering application of gas fire extinguishing system

In the practical application of the gas fire extinguishing system , first of all , the personal safety of the personnel needs to be placed first . According to the size of the protection space and the frequency of the personnel activities , a reasonable injection time and concentration are set ; secondly , from the perspective of environmental protection Start , minimize pollution and damage to the environment ; Third , we must combine appropriate protection and external environment and other factors , select suitable, high-efficiency systems ; Finally , the above conditions , but also to meet the needs of economic investment. The parameters used in the design of common gas fire extinguishing systems are shown in Table 1 .

Table 1 Parameters used in firefighting design of common gas fire extinguishing systems

3 Conclusion

With the continuous improvement of science and technology, gas extinguishing technology in special places will gradually replace the traditional fire suppression systems, fire extinguishing meet special needs of a variety of important functional areas of the building. At the same time , as people's awareness of environmental protection increases , gas fire extinguishing technology is developing in the direction of cleanliness, safety and environmental protection , and will play an important role in the future of fire fighting.

This article comes from "Shanxi Architecture" Volume 34, Issue 23, and was reorganized and edited by China Rescue Equipment Network.