Preliminary study on extinguishing shielded fire with water mist

Abstract

Fires in commercial and industrial areas, such as large warehouses containing goods on shelves, are inevitably shielded by nearby objects that act as obstacles, making such fires difficult to extinguish. Water mists, as an alternative to the halon fire-extinguishing agent, are capable of bypassing obstacles owing to the small size of the water particles. Therefore, by varying the distance between a plate obstacle and the nozzlefire source, half-scale experiments were performed under different working pressures to determine the critical condition of shielded sand-burner fire extinguishment. The flame temperature and radiant heat flux were measured using thermocouples and a radiometer. The interaction between a water mist spray and a shielded fire was visualized via laser light sheet illumination. The fire-extinguishing capability was analyzed based on the plate obstacle block ratio and the plume–spray thrust ratio. The results indicate that an empirical linear correlation can be adopted to predict the critical plume–spray thrust ratio required for fire extinguishment under different block ratios. In addition, Fire Dynamics Simulator was used to simulate the spray–plume interaction under the shielding conditions employed. The experimental and numerical results show a similar suppression tendency in cases with a low block ratio and fire size. This preliminary study may provide some raw data on shielded fire suppression with a water mist, in addition to serving as a reference for the optimal design of water mist systems.