Experimental and numerical study of pool fire suppression using water mist

Abstract

Experiments in a real-scale room were done on water mist application to a pool fire. A fire produced with fuel oil in a 35cm cylindrical pool was used, with a heat release rate reaching 75kW in stationary conditions. Water application was studied with a nominal flow rate equal to 25l/min provided by a set of four nozzles, injecting droplets with mean Sauter diameter equal to 112μm. Observations of fire suppression in these conditions showed two behaviors, which were analyzed and detailed with the help of numerical simulations conducted with FDS.v5. On one hand, a fast suppression (about 10s required) was observed when water mist was applied to a developed fire. In this case, droplets were injected into a hot environment and thus evaporated strongly, generating a significant vapor concentration and resulting in a fast gas cooling and in an inerting effect. On the other hand, when the mist was applied early, fire growth was controlled, but its suppression required a longer application (about 1min) and only occurred after a significant cooling of the flame and the liquid pool. These two mechanisms were detailed numerically through mass and energy balances for both the gas and the liquid phases and could help to derive suppression model improvements.