Fire Safety Science Digital Archive

A fairly extensive programme of laboratory experiments on the surface application of foam to petrol fires bas been carried out. For a criterion of performance of a foam the time of control of the fire to which it was applied was used. This has been defined as the time taken to reduce the total radiation from the fire to one third of its value at the commencement of foam application. The critical rate of application of foam, i.e. the minimum rate at which the fire is likely to be controlled, has been determined for a number of foam compounds. The possibility of scale effects has been investigated and an examination has been made of the influence of expansion factor, critical shearing stress and type of foam compound upon the relationship between the control time and the rate of application. The results of the experiments contained in this report suggest that, when foam is applied at a rate higher than the critical rate, its ability to combat a petrol fire is a function of its water content and of its ability to flow over the petrol surface. The loss of foam due to destruction by the heat radiated from fire appears to be of little importance with most compounds. The fact that there is little to be gained by applying foam to a fire unless the critical rate of application can be exceeded is emphasized. It is thought that the accepted rate of application of 1 gal. per sq. ft. per min. is unnecessarily high for good protein compounds.