Fire Investigation 08
Fire Investigation 08 : (3) The New Science of Post-Flashover Burning: Certainly, the participants in the Las Vegas tests were not allowed to interview witnesses, nor were they allowed to shovel any of the debris or perform any of the other activities besides visual observation that typically take place at a fire scene. The qualifications of some of the participants were found to be less than stellar, and some people were taking part in the experiment just to familiarize themselves with fire investigative procedures. No matter how many explanations for the low success rate were offered, however, there was no way to increase the number of correct origin determinations beyond three. Reducing the denominator (the total number of "experienced" participants) might raise the percentage of correct answers to 10% or even 20%, but it is important to remember that 25% is the percentage of correct answers that would be expected if all of the participants were blind. In an attempt to understand the data, Carman and his collaborators at ATF re-created the test fires at the ATF Fire Research Laboratory in Ammendale, MD, and modeled the results using computational fluid dynamics (FDS and Smokeview). What came out of these studies was a better, but certainly not complete, understanding of the effects of ventilation in post-flashover fires. Prior to flashover, a fire grows by involving more fuel. Once flashover occurs, all of the fuel that can be involved is involved, and the fire can only grow where it has sufficient ventilation. The fire is said to have made the transition from a "fuel-controlled" fire to a "ventilation-controlled" fire. Fire investigators looking for the origin of a fire are typically looking for places where the fire plume has interacted with two-dimensional surfaces such as walls and ceilings
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