Blast Effects on Fires

Experiments on extinction of fires by airblast were conducted in the shocktube facility dedicated to blastfire interaction studies. Three series of tests were conducted to gain practical understanding quantitative and mechanistic of blast effect on fires, using 1 liquid-fuel fires of various sizes 2 liquid-fuel fires, of various sizes, with flow-obstructing barriers upstream of the fuel source and 3 wood-crib fire tests. Results affirm the concept of flame displacement as a mechanism of extinguishment for liquid-fuel fires on flat surfaces but suggest its limitation in describing blastfire interactions when flow-perturbing obstacles are present upstream of the fuel bed. Even small barriers are seen to significantly increase the fire resistance to blowout by blast, by providing flame-retentive flow recirculation in their wake and effectively serving as flame-holders. For charring fuels such as wood cribs, after-shock flame displacement is seen to be augmented by sustained, blast-enhanced char involvement. The crib fire history before blast arrival and the extent of char-combustion enhancement depending on blast strength determine whether the crib fire is reestablished by rapid rekindling.