By the end of 2012, the national fire department had equipped more than 1,360 compressed air Class A foam vehicles. Compressed air A-type foam elimination vehicles are installed in a large number of units, which greatly enhances the fire control capability of building fires and the fire fighting and rescue capabilities of high-rise buildings. Since the introduction of compressed air type A foam fire trucks is not long, the actual combat factors affecting the fire extinguishing efficiency in China are not very deep, which affects its application in actual combat to a certain extent. Therefore, it is necessary to carry out the factors affecting the actual combat. Analysis. IS07203 fire extinguishing agent foam concentrate and GB15308-2006 foam fire extinguishing agent>) The main characteristics of foam fire extinguishing agent are: freezing point, anti-freezing, melting, sediment (volume fraction), specific fluidity, pH value, surface tension, Diffusion coefficient, corrosion rate, foaming multiple, (5%) liquid deposition time (min), anti-burning time, fire extinguishing time. Among these main performance indicators, the fire-extinguishing performance characteristics of Class A foam fire extinguishing agents are mainly reflected in the expansion ratio and the liquid discharge time. This paper explores the actual combat factors affecting the fire-extinguishing performance of compressed air Class A foam fire engines through a large number of compressed air Class A foam fire extinguishing agent supply tests for firefighting forces.
2 Influence of liquid supply pressure on fire extinguishing efficiency From the working principle of compressed air type A foam fire extinguishing system, the working pressure of Class A foam fire extinguishing system consists of air and water. At present, the fire pump pump pressure gauge configured on the Class A foam fire truck only shows the pressure of the water supply part, and the pressure of the gas phase part needs to be tested by special equipment. The SZX5130GXFAP24 type A foam fire truck produced by Shanghai Aurora Fire Equipment Co., Ltd., because the pressure of water is affected by the voltage regulation system, the supply pressure of the pump is higher, and the liquid phase is always stable. 8MPa or so. The performance curve of the Class A foam fire truck and the performance curve of the air compressor provided by the US company, the water supply pressure of the fire pump and the air flow provided by the air compressor are all related to the speed. The lower the water supply pressure of the fire truck pump, the lower the speed; the lower the speed, the smaller the air flow provided by the air compressor. According to this, the air compressor performance of the fttl line can be rotated by 1 rpm. Divided into a performance chart of a fire truck air compressor for compressed air foam, when the supply pressure does not reach the specified pressure value, the air flow supplied by the system is smaller than the rated value, and the ratio of air to liquid phase will be less than 7:1. That is, the foaming effect is not ideal.
When the supply pressure exceeds the specified pressure value, the air flow supplied by the system is larger than the rated value, and the ratio of air to liquid phase will be greater than 7:1. If the system is excessively foamed, the fire extinguishing ability will also decrease.
3 Influence of liquid supply distance (height) on fire-extinguishing efficiency In March 2010, the compressed air A-type foam test was conducted at Taiping Financial Building in Pudong New Area. The test data is shown in Table 1.
Table 1 Vertical liquid supply fire extinguishing efficiency test data table No. Set mixing ratio Pump pressure (MPa) Liquid supply height (m) Foam multiple precipitation time May 2011, different distances for compression in Xinjiangwan City, Yangpu District Air class A foam test, test data shown in Table 2.
Table 2 Horizontal liquid supply fire extinguishing efficiency test data table No. Set mixing ratio Pump pressure (MPa) Supply distance (m) Foaming multiple water precipitation schedule 1, Table 2 shows that the foaming ratio of compressed air foaming agent The liquid distance (height) increases and the mixing ratio of the foam liquid to water increases. When the expansion ratio exceeds a certain value, the fire-extinguishing performance of the compressed foam fire extinguishing agent is mainly reflected in the heat insulation protection, and its cooling and extinguishing ability will be lost.
4 Effect of foam mixture ratio on fire extinguishing efficiency The data in Table 1 shows that the foaming multiple of compressed air foam fire extinguishing agent increases with the increase of foaming liquid mixing ratio when the liquid supply distance and the liquid supply pressure are the same. In general, a foam mixture of 0.3% mixing ratio, a foaming ratio of about 6 times, a foam mixture of 0.5% mixing ratio, a foaming ratio of about 9 times, a foam mixture of 0.8% mixing ratio, The expansion ratio is 10 times or more. There are also materials showing that. 1%.3% mixed ratio foaming liquid, mainly used for wetting and infiltration; 0.3% 0.5% mixed ratio foaming liquid, mainly used for fighting building fires; 0.5% 0.7% mixed ratio foaming liquid, mainly used for overhaul Building; 0.7% 1.0% mixed ratio foam, mainly used to prevent heat radiation. This is also consistent with the classification of NFPA by the foaming multiple of class A foam. Therefore, it is recommended that the type A foam fire extinguishing agent used for fire extinguishing should not be >0.5%, and in general, 0.3% is suitable; the type A foam fire extinguishing agent used for heat insulation protection and its mixing ratio Should not <0.5. The impact of the number of shots on the fire-extinguishing efficiency The number of shots of the Class A foam fire extinguishing agent has a great influence on the fire-extinguishing performance of the foam fire extinguishing agent, which is mainly reflected in the stability of the foam - that is, 25% Liquid time. In the process of researching the number of shots on the fire extinguishing performance of the foam fire extinguishing agent, the test data obtained are shown in Table 3.
Table 3 different number of fire extinguishing performance test data serial number set mixing ratio pump pressure (MPa) liquid supply distance (m) number of shots (support) foaming multiple water splitting time water gun range data shows, with the increase in the number of shots The 25% liquid separation time of the foam fire extinguishing agent is significantly reduced, and at the same time, the range of the water gun is also significantly reduced.
The less the 25% liquid separation time, the more unstable the foam is, and it is more easily destroyed by baking and burning. Therefore, it is recommended that when using Class A foam fire extinguishing, the number of shots of the same liquid supply line should not exceed two.
6 Conclusions Through the study of different types of pressure, different liquid supply distance, different foam mixture ratio and different number of shots, the following conclusions can be drawn: (1) Fire truck empty The supply pressure of the press has a great influence on the performance of the compressed air foam. The water supply pressure of the fire pump has little effect on the performance of the compressed air foam. The pressure specified in the instruction manual should be strictly controlled to carry out the liquid discharge operation. Under normal circumstances, when using conventional outlet compressed air foam, the supply pressure should be controlled at 8 to 10 kgf. When using compressed outlet air to release compressed air foam, the supply pressure should be controlled at 12 to 15 kgf, : l for fire extinguishing Class A foam fire extinguishing agent, the mixing ratio should not be >0.5%, in general, 0.3% is suitable; for class A foam fire extinguishing agent used for heat insulation protection, the mixing ratio should not be <0.8%. When a type A foam is used for fire extinguishing, the number of shots of the same liquid supply line should not exceed two.
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