The effects of ventilation and preburn time on water mist extinguishing of diesel fuel pool fires

The goal of the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Research Laboratory Fire Fighting and Prevention Program is to reduce the number of fires and fire-related injuries in the mining industry. As part of this effort, water mist is being evaluated for the suppression of underground mine fires, such as fires 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 230kW, 1, and 3 MW. The experiments were conducted 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 s and 1 min. Without ventilation the 230 kW fire was the most difficult to extinguish; with natural ventilation the 1 AM fire took the longest time to extinguish; and with forced ventilation the 3 AM fire was the most challenging one. With the 30-s preburn time, the extinguishing time was nearly the same for the 230 kW fire as with the 1-min preburn time, while it increased for both 1 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.