The goal of the NIOSH Pittsburgh Research Laboratory's Firefighting and Prevention Program is to reduce the number of fires and fire-related injuries in the mining industry. Under this effort, water mist is being evaluated for suppressing underground mine fires, such as those in diesel fuel storage areas. In this study, a series of large-scale fire tests was conducted to investigate the effects of ventilation and preburn time on water mist extinguishing of three diesel fuel pool fires with heat release rates of 230 kW, 1 MW, and 3 MW. The experiments were done in a simulated underground coal mine diesel fuel storage area under three ventilation conditions: no ventilation, natural ventilation, and forced ventilation and with two preburn times for the no ventilation condition--30 sec and 1 min. Without ventilation, the 230-kW fire was the most difficult to extinguish; with natural ventilation, the 1-MW fire took the longest time to extinguish; and with forced ventilation, the 3-MW fire was the most challenging. With the 30-sec preburn time, the extinguishing time was nearly the same for the 230-kW fire as for the 1-min preburn time, whereas it increased for both 1-MW and 3-MW fires, with the 1-MW fire being the most difficult to extinguish. The extinguishing mechanisms, including fuel surface cooling, flame cooling, and oxygen depletion and displacement, are discussed. The critical water flow rate is estimated for the fires extinguished by the surface cooling mechanism.
NIOSH Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236