A study of the probability distribution of pool fire extinguishing times using water mist

•Two kinds of extinguishing situation of pool fire by water mist were observed.•In one, the flames had not yet been suppressed when the fire was extinguished via a blowoff process.•The primary mechanism for fire extinguishment is flame cooling in the first situation.•In the other one, the flame was first suppressed and then gradually reduced in size.•The primary mechanism for fire extinguishment is fuel surface cooling in the second. Water mist, a replacement for Halon gaseous agents in fire fighting, has been studied for decades. However, the fire-extinguishing reliability of water mist is debated. For example, there are significant differences in extinguishing times between tests conducted under the same conditions, and water mists have difficulty extinguishing small fires. To date, no study of the probability distribution of extinguishing times has been reported. In this study a statistical analysis of the extinguishing time distribution of pool fires extinguished using water mist is presented. The fire sources were circular/square stainless steel pans with gasoline, diesel, ethanol or daqing RP-3 as fuel. Two types of extinguishing scenarios were observed. In one situation, the fire was extinguished via a blow off process, when the flames had not yet been suppressed. Flame cooling is the primary fire extinguishing mechanism; the mass loss rate and combustion heat of the fuel are two key factors. In the other situation, the fire was initially suppressed and subsequently extinguished after a long suppression stage. Surface cooling is the primary fire extinguishing mechanism; the flash point of the fuel is the key factor.