Fire Investigation 09
Fire Investigation 09 : (3) The New Science of Post-Flashover Burning: These patterns may cease to be created once the transition to flashover has occurred. In ventilation-controlled fires, patterns will be generated around doors and windows, as well as around any places where air leakage existed before the fire, or where such ventilation was created as a result of the fire. When flashover occurs, and every exposed combustible surface ignites almost simultaneously, the fire can consume almost all of the oxygen in the room. After that happens, there will be diminished burning where the oxygen is depleted. The fuel at the origin of the fire will not necessarily continue to burn, and much larger patterns not associated with the origin, can be generated. These new patterns can obscure older, plume-generated patterns, or even if the older patterns persist, the new patterns can be confusing. When the 2005 Las Vegas fire was modeled, the oxygen concentration was shown to be very low throughout the room, except in the immediate vicinity of the doorway, and only near the floor. This oxygen concentration suggested the existence of a "floor jet". This inflowing oxygen collided with the wall opposite the doorway and moved upward, mixing with the unburned fuel, and resulted in a heat flux of more than 150 kW/m2. Clearly, the total energy impact (heat flux multiplied by time of exposure, expressed as kJ/m2) on this surface far exceeded the total energy impact on the wall next to the origin. The principal problem with determining the wrong origin is that the ignition source will not be found there. Finding an origin without an accidental ignition source will lead investigators who fail to understand ventilation to conclude that somebody must have placed some fuel at that origin and ignited it with an open flame
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