【文章內(nèi)容簡介】 the fuel surface in a storage tank, and although there has been an understanding that there would be some loss in efficiency under these conditions, no quantitative information is available .The work described in this paper was undertaken in an attempt to provide such quantitative information . LABORATORY TESTS A smallscale laboratory test having a fire area of ft2 was set up in which foam produced in a laboratory foam generator3 was applied as a straight stream onto burning 90 octane gasoline. The size of the orifice was adjusted with changes in application rate to give a constant stream velocity of m/sec ,which is similar to that obtained with conventional equipment. Foam was applied at a series of rates, and critical application rates were determined by plotting the time required for extinguishment against the rate of application of foam liquid (Figure i). It was found that the critical application rates were greatly affected by changes in the temperature of the fuel, and to examine this, tests were performed in which pre burn times of up to 15 min were allowed, The temperature profile in the fuel at different preburn times is shown in Figure 2. The tests were made using 4 per cent solutions of two mercially available hydrolyzed protein foams and a recently developed fluoroprotein foam (. 70). Table 1 gives the foam properties obtained . In Figure 3, the critical application rates for the three foams are plotted against fire preburn times, and several observations are evident . ? The critical application rate for all three foams increased as the preburn time increased. ? Even with short preburn times, the critical application rates for foams A and B, applied as a straight stream to the fuel surface,were appreciably higher than the results obtained from gentle application to the fuel surface. ? The fluoroprotein foam, . 70, appeared to have a performance superior to the hydrolyzed protein foams. Preburn times Because of the small size of vessel used,the fuel temperature gradient obtained with the laboratory fires was not thought to relate cIosely to the temperatures obtained with fires in larger tanks. It was decided to measure the subsurface temperature profile on larger outdoor fires before carrying out tests with foam. A report by Burgoyne and Katan4gives useful information on the subsurface temperatures obtained with fires in a 22in. diameter tank containing low grade gasoline . Their results showed that a layer of hot fuel or a hot zone was formed under the burning surface with a temperature of about 90 176。 C (194 176。 F). Distillation tests showed that this temperature would give a 19 per cent distillation of the fuel rate at which the depth of the hot zone increased was between 24 and 36 in./hr , and a sharp temperature gradient existed between the hot zone and the cool fuel beneath . TABLE 1. Properties o/the Foams Used in the Fire Tests Critical shear 25 per cent drainage stress time Type of foam Expansion (dynes/cm2) (min) Hydrolyzed protein A 8 250 35 Hydrolyzed protein B 8 370 25 Fluoroprotein foam . 70 8 250 24 O Hydrolizod protein A [3 Hydrolized protein B A Fluoroprotein foom FP70 Tests with regular grade 90 octane gasoline were irst made using a 22in. diameter tank. Asbestos insulation was used to reduce heat transfer from the flames to the fuel via the sidewalls, and a constant head device allowed the addition of fuel to the base of the tank with minimum disturbance so that constant ullage could be maintained during burning. Fires of 30min duration were used, and fuel temperatures were measured at 1in. interva