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Extinguishing of flammable liquids by film forming foaming agents

Journal: Pozharovzryvobezopastnost/Fire and Explosion Safety (Vol.26, No. 8)

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Authors : ;

Page : 45-55

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Abstract

This paper describes the results obtained during systematic experimental research of the oil product flame extinguishing process by injecting foam onto the burning surface and to the tank base. As a rule, the same foam generator, compound, chemical formula and proprietary component ratio are used for fire extinguishing using subsurface foam injection and and by feeding foam onto the burning surface. The only way to estimate the foam generator efficiency objectively is carrying out comprehensive testing during which curves are plotted for superficial and interfacial tension at the interface of water foam generator solutions with a hydrocarbon. Fluorated foam generators of known brands were used in the experiments: Ansulite AFFF, Shtamex AFFF, Light WaterFS 201, CAPSTONE 1183 and Shtorm-F. Hydrocarbon with different flash temperature was used as combustible liquids. As a result of the conducted experiments, a general regularity was discovered. It is the functional relation between the specific flow rate of foam generators and foam delivery rate shown using curves, the specific flow rate being minimum at the optimum delivery rate. The specific foam extinguishing efficiency characteristics have been determined during combustible liquid flame extinguishing. They are expressed as a complex of indices: critical and optimum delivery rate, and the minimum specific flow rate of the foam generator. The experiment results have shown that during oil product flame extinguishing using film-forming foam generator foam the value of the optimum delivery rate and minimum specific flow rate in case of subsurface foam injection was lower than during feeding of the foam onto the burning hydrocarbon surface by 25 to 30 %. Consequently, the extinguishing efficiency of the tested film-forming foam generators appeared to higher in case of the subsurface extinguishing method. The difference of indices of foam extinguishing efficiency in case of a particular feeding method is due to destructive effect of some contributing factors. While foam is only exposed to flame jet heat flow during the subsurface oil product flame extinguishing, in case of feeding from above foam is also destroyed as a result of the contact with burning oil product surface. Based on the obtained data, a model of the process of oil extinguishing by feeding foam to the tank base was developed. This model takes into consideration decrease of the burning surface temperature during mixing of homotermal layer when the foam emerges.

Last modified: 2018-10-17 22:57:21