Physical Scaling of Water Mist Suppression of Pool Fires in Enclosures

Abstract

A series of fire suppression experiments was conducted in two geometrically similar enclosures of 1-to-3 ratio to evaluate whether the Froude-modeling-based scaling methodology could reasonably reproduce the pool fire development under water mist application in different scales. The parameters considered in the evaluation were: enclosure size, door opening size, water mist spray condition, fire size, fire location and fire-shielding condition. The two enclosures measured 1.22x1.22x1.22 m and 3.66x3.66x3.66 m. Two door opening sizes were tested for each enclosure: 0.30x0.61 m high and 0.61x0.61 m for the Scale-1 enclosure, and 0.91x1.83 m high and 1.83x1.83 m for the Scale-3 enclosure. Two heptane fire sizes were selected for each enclosure. The quasi-steady heat release rates of the two pool fires for the Scale-1 enclosure were 25 and 57 kW, and the corresponding heat release rates were 380 and 860 kW for the two pool fires used in the Scale-3 experiments. Besides matching the quasi-steady heat release rates according to the scaling requirement, the fire developments under free-burn were also carefully scaled. Two water mist nozzles were used to produce the water mist sprays in the Scale-1 and Scale-3 enclosures; these two nozzles were operated at the designated pressures of 13.8 bar and 41.4 bar, respectively. In each enclosure, nine ceiling-mounted nozzles were arranged in a 3 x 3 pattern with equal nozzle-to-nozzle and nozzle-to-wall spacing. The experiments showed that the fire development in terms of heat release rate could be reasonably reproduced during free-burn and water mist application in the Scale-1 and Scale-3 enclosures, so was the oxygen concentration inside the enclosure.