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ANALYSIS OF A TYPICAL RELATION USED FOR DESCRIPTION OF DEPENDENCE OF THE EXTINGUISHING TIME OF FLAMMABLE LIQUIDS AND THE SPECIFIC CONSUMPTION OF VARIOUS EXTINGUISHING AGENTS ON THEIR FLOW RATE

Journal: Pozharovzryvobezopastnost/Fire and Explosion Safety (Vol.25, No. 3)

Publication Date:

Authors : ;

Page : 66-76

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Abstract

On the basis of analysis of experimental data on extinguishing of flammable liquids it is offered the model of extinguishing process which includes local interaction of the base of dispersed stream with part of a flame jet and further spreading of extinguishing layer on the burning surface of oil product. The basis of analysis is a dual suppression mechanism of fire extinguishing agents. The dual suppression mechanism is universal and is especially strongly revealed during extinguishing of flammable liquids by dispersed streams of water and freon, by stream of powder and air, by foam giving into the bottom of burning tank with oil product. The dual mechanism is accompanied by fact that the stream of agent carries away atmospheric oxygen that sharply increases volume of flame jet at the initial stage of stream supplying. Taking into account action of inflow of additional air we can reveal the nature of extreme dependence of specific consumption on flow rate of extinguishing agent and existence of its optimal flow rate during fire extinguishing. Material balance of extinguishing process of hydrocarbon flame using method of covering of the burning surface by layer of fire extinguishing agent (FEA) is considered. As a result, it was defined that the thickness of layer in the place where stream falls onto the burning surface depends on flow rate of dispersed stream. Dependence of average thickness of extinguishing layer on flow rate of stream is offered. Based on the results of experiment, conducted on specific model of extinguishing of gasoline flame using water with high dispersion degree, it was described dependence of specific consumption of FEA and extinguishing time on its flow rate. This allowed us to determine the optimal flow rate and the minimal specific consumption of dispersed water. The analysis of formulas, deduced during research, shows that multiplication of extinguishing time by corresponding value of flow rate of dispersed stream allow to obtain the extreme dependence of specific consumption of extinguishing agent on its flow rate. This effect was found in all experiments on fire extinguishing of hydrocarbons by dispersed water, dispersed freon or extinguishing powder. The analysis of extinguishing of gasoline flame by dispersed freon 114B2 and fire extinguishing powder is carried out. Process of extinguishing of a heptane flame by giving of foam onto the burning surface and into the layer of oil product is considered. It is shown that description of extinguishing process of diesel fuel due to giving of air into the bottom of tank reveal the reverse, as compared with dispersed water, situation. In case of application of dispersed water, extinguishing process is realized due to the steam layer which is formed as a result of evaporation of water drops. If extinguishing is realized due to the giving of air, its stream carries away the flow of liquid. As in the previous case, the initial value is a flow rate of air which carries out cold layers of oil product to the upper level. Suppression of flame will occur when the entire burning surface will be covered by hydrocarbon layer which temperature is lower than temperature of ignition.

Last modified: 2018-10-18 17:27:05