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Suolong Fire Digital Science Museum-"Foam Fire Extinguishing Technology" (V)
Release time:
2021-11-18
The scope of application of foam fire extinguishing agent and the choice of the industry have a point of view, normal temperature and pressure can be liquid can use air foam fire, in many manuals can be liquid fire extinguishing methods are basically foam as an option. However, according to years of research and testing by the Tianjin Fire Research Institute of the Ministry of Public Security, it has been revealed that not all flammable liquids can be extinguished with air foam. 01 ordinary low expansion foam scope of application ordinary low expansion foam is generally used for hydrocarbon liquid fire. However, foam cannot be used for high-temperature combustible liquid storage tanks with storage temperature greater than 100 ℃. If foam is used, it will not only help to extinguish the fire, but may be as stated in Chapter 2.
Application Scope and Selection of Foam Extinguishing Agent
There is a view in the industry that air foam can be used to extinguish fires in liquids under normal temperature and pressure, and foam is basically used as an option in many manuals. However, according to years of research and testing by the Tianjin Fire Research Institute of the Ministry of Public Security, it has been revealed that not all flammable liquids can be extinguished with air foam.
01
Application scope of ordinary low-expansion foam
Ordinary low expansion foam is generally used for hydrocarbon liquid fire. However, for high-temperature flammable liquid storage tanks with a storage temperature greater than 100°C, foam cannot be used to extinguish fires. If used, it will not only help extinguish fires, but may lead to greater disasters as described in Chapter 2. Regarding the fire extinguishing test of oil temperature, only the spray extinguishing test under foam liquid of crude oil storage tank with storage temperature of about 50 ℃ carried out by Tianjin Fire Research Institute of the Ministry of Public Security in conjunction with relevant units is currently mastered. Therefore, the Code for Design of Foam Extinguishing System GB50151 that the oil temperature specified for spray under foam liquid of oil storage tank is 50 ℃, and the temperature exceeding this temperature should be determined by test.
Low boiling point flammable liquid storage tanks with boiling point lower than 45 ℃ and volume ratio of C5 and below components greater than 30% can use air foam to control fire, but cannot extinguish fire. For motor gasoline storage tanks without wall cooling, it may not be possible to completely extinguish the fire with air foam. For the above-mentioned low boiling point combustible liquid storage tank, the Tianjin Fire Research Institute of the Ministry of Public Security and Hangzhou New Era Fire Technology Co., Ltd. have developed a heptafluoropropane foam fire extinguishing technology, and the technology has fulfilled the market access procedures used.
Due to the strong permeability of the aqueous film foam extinguishing agent, it has higher fire extinguishing efficiency than pure water for A fire, so it is also suitable for extinguishing wood, fabric, paper and other A fires.
02
Anti-dissolving foam scope of application
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At present, anti-dissolving foam is also a low-expansion foam. According to the national standard "Foam Extinguishing Agent" GB 15308-2006, anti-dissolving foam (anti-alcohol foam) is now tested for 120# solvent gasoline on a standard plate with an area of 4.52 m2 (diameter 2.4m), and then tested for acetone on a standard plate with a diameter of 1.73 m2 (diameter 1.48m). Both tests are qualified. From the perspective of anti-soluble foam formulation, the anti-burning performance of the foam is enhanced by the addition of anti-alcohol polymer compounds such as xanthan gum. Therefore, anti-soluble foam is not only suitable for water-soluble flammable liquids, but also suitable for hydrocarbon liquids.
As mentioned above, anti-soluble foam is not suitable for all flammable liquids. In addition to the above-mentioned flammable liquids, anti-soluble air foam cannot extinguish the fire of low-boiling water-soluble liquids such as propylene oxide, ethyl ether, diethylamine, etc., and even cannot control the fire.
03
High-multiplier, medium-multiplier foam scope of application
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The scope of application of high-multiplier and medium-multiplier foam is more accurate in combination with its fire extinguishing system, and the chapter on the design of high-multiplier and medium-multiplier foam system is more accurate. Generally speaking, it is suitable for the control of solid fire, hydrocarbon liquid fire, coal mine fire and liquefied natural gas leakage.
04
Selection of Foam Extinguishing Agent
After many years of fire extinguishing tests, the fire extinguishing efficiency of aqueous film forming foam extinguishing agents of 1A and 1C is good and should be the main option. However, from the perspective of environmental protection, fluorine protein foam cannot be eliminated. In terms of the type of mixing ratio, the efficacy of the 3% type and the 6% type also showed no difference. No matter from the convenience of use, especially in the petrochemical industry, serious fire fighting, or from the reduction of production, certification, logistics costs, and even from the convenience of supervision departments, the fewer varieties and specifications, the more convenient. Therefore, for the low-expansion foam system of hydrocarbon liquid, 3% aqueous film forming and fluorine protein foam liquid should be selected.
For water-soluble anti-film foam, the viscosity of the 3% type is twice that of the 6% type. However, in January 2016, the 2015 Ministry of Public Security's special project "Research on Foam Extinguishing Mechanism and Technology of Water-soluble Combustible Liquid Storage Tank" showed that under the condition of foam liquid at 5 ℃, the rated mixing ratio can be achieved by using the bladder pressure proportional mixing device and the balanced proportional mixing device, but the foam liquid pump suction head in the balanced proportional mixing device is required to be larger, and there is no technical problem. 3% type low viscosity fluorine soluble protein foam is more without any obstacles. To sum up, 3% type anti-dissolving water film forming foam liquid or 3% type low viscosity anti-dissolving fluorine protein foam should be selected.
Regarding high-multiple, medium-multiple foam liquid, ordinary type, seawater-resistant type, temperature-resistant and smoke-resistant type, there is no technical problem in selecting 3% foam liquid.
Some designs or owners put forward special requirements for the flow point of foam liquid according to their own subjective judgment. It should be emphasized that the general flow point of foam liquid produced according to normal process is -10 ℃ ~-7.5 ℃. If it is required to be above -5 ℃, normal production is usually not possible; below -10 ℃, more ethylene glycol needs to be added, which affects the stability and fire extinguishing performance of the foam. The national standard "Foam Extinguishing Agent" GB 15308-2006 stipulates that the foam liquid needs to be frozen and thawed for fire extinguishing test, and a freezing during transportation will not cause the foam liquid to fail. The storage temperature is generally 0 ℃ ~ 40 ℃. For high and cold areas, the foam liquid should be stored in a room with heating.
