Regimes of Fire Spread Across an AFFF-Covered Liquid Pool .

摘要

We have examined the fire suppression performance of AFFF against three fuels that cover a wide range of flash point temperatures. For qualification testing of aqueous film-forming foams under the U.S. Military Specification MIL-F-24385, the fuel used for the test is gasoline, which typically has a flash point of approximately -40oC. In a recent series of tests we compared JP-5 jet fuel (minimum flash point 60oC) with biodiesel (flash point >130oC) under a slightly modified protocol based on the MIL-F-24385 testing. A significant observation is that the mode of flame advancement across a foam blanket differs between the fuels with different flash point ranges. For gasoline, which has a flash point below ambient temperature, transient or steady flames appear at a substantial distance from the reignition source. For the higher flash point fuels, by contrast, the foam has a well-defined lateral boundary which gradually erodes due to heat from the fire, and the burning region is confined to the uncovered fuel surface. For JP-5 (flash point <100oC), essentially the entire fuel surfaces which is uncovered by foam is involved with fire. For biodiesel, which has a flash point significantly above the boiling point of water, there is a lateral standoff distance of several inches from the foam boundary to the limit of the fire. These observations indicate that for low flash point fuels, the ability of the foam to act as a vapor barrier to the fuel is a critical factor in burn back, but for high flash point fuels, the progression rate is governed by the heat capacity and resistance to thermal radiation of the foam.