Fire Safety Science Digital Archive

A series of tests have been carried out on the effect of water sprays on a kerosine fire burning in a vessel 30 cm diameter. The sprays were produced by a battery of impinging jets which enabled a study to be made of the effect of drop size and rate of flow of spray at pressures between 5 and 85 lb/in2, while maintaining in each test a fairly even spatial pattern of spray about the fire area. It was found that at a given pressure there was a drop size which was most efficient in reducing the rate of burning of the fire, and at this drop size the rate of flow required to extinguish the fire was also at a minimum. At drop sizes greater than this efficient drop size there was much splashing; at smaller drop sizes a large fraction of the water spray applied to the fire did not penetrate through the flames and the kerosine, and the drops which reached the kerosine caused much sputtering. The most efficient drop size decreased with increase in pressure. The efficiency of the spray in extinguishing the fire increased with increase in pressure. This was shown by a reduction in the minimum rate of flow required to extinguish the fire and also by a reduction in the time which was required for extinction with a given rate of flow. A reason for this result was that an increase in pressure brought about an increase in the velocity of air entrained by the spray. This helped to push the flames away and allowed the presentation of fine drops with a high capacity for heat transfer to those parts of the flame near the uprising vapour, and to the burning liquid. At low pressures (10 and 30 lb/in2), the fire was extinguished mainly by the kerosine being cooled to the fire point. It was estimated that the sprays which extinguished the fire in this way removed heat from the flames at a rate less than 0.2 - 0.3 cal/cm3 of flame(s). At a higher pressure (85 lb/in2) the extinctions took place without cooling the liquid to the fire point and there was evidence to indicate that the flame itself was extinguished. It was estimated in most of these extinctions that the sprays removed heat from the flame at a rate greater than 0.2 - 0.3 cal/(cm3 of flame)(s). There was no evidence that the formation of an oil in water emulsion played any part in the extinction process. The practical implications of the results are discussed.