Fire Investigation 10
Fire Investigation 10 : (3) The New Science of Post-Flashover Burning: If there is an irregular burn pattern on the carpet in that area, even in the absence of a positive laboratory report, the investigator may conclude that the fire was intentionally set using a flammable liquid. Many investigators have made errors using this kind of "negative corpus" determination. Finding the correct origin the key to a correct fire cause determination, and is the most difficult part of the investigation of a fully involved compartment fire. In 2007, ATF agents refined and repeated the Las Vegas experiment, this time in Oklahoma City. They set up three burn cells, with identical fuel and identical ventilation, but different points of origin. The cells were allowed to burn for 30 seconds beyond flashover, 70 seconds beyond flashover, and 3 minutes beyond flashover. To put these times in context, the best fire departments in big cities might have a three-minute response time. If they are not called until someone sees the fire venting out a window (a sign of flashover) the chances of them extinguishing the fire with less than three minutes of post-flashover burning are practically zero. The results of the Oklahoma City experiment validated the data from Las Vegas obtained two years earlier. Further, it became clear that the longer the fire was allowed to burn after flashover, the less likely the fire investigators were to correctly identify the quadrant of origin. The results of the Oklahoma City experiment - of 3 burn cell tests conducted to measure fire investigators' ability to determine the correct quadrant of origin - are as follows: Time: 30 sec, # responses: 70, # correct: 59, % correct: 84; Time: 70 sec, # responses: 64, # correct: 44, % correct: 69; Time: 3 min, # responses: 53, # correct: 13, % correct: 25
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