CHARACTERIZING FIREBRAND EXPOSURE DURING WILDLAND-URBAN INTERFACE FIRES

摘要

This study examines the size distribution and other characteristics of firebrand exposure during the2007 Angora Fire, a severe Wildland-Urban Interface (WUI) fire in California. Of the 401 houses thatreceived direct interface fire exposure 61% were destroyed and 30% did not burn at all. The ignition ofbuildings by wind-blown embers, known as firebrands, and the starting of “spot fires” in unburned vegetationahead of wildfires has been observed for centuries and studied extensively for decades. Empiricallyquantifying the exposure severity or describing how many firebrands of what size and over what duration anddistance cause ignition problems of concern has not yet been possible. However, a seemingly rare opportunityto gather empirical firebrand data from an actual interface fire evolved in the days immediately following theAngora Fire. Firebrand size distributions are reported and compared to firebrand size distributions fromexperimental firebrand generation in both recent laboratory building ignition studies conducted by NationalInstitute of Standards and Technology (NIST) and from historical firebrand field studies. Such data is neededto form the basis of effective and appropriate interface fire hazard mitigation measures as well as modeling firespread. Comparisons are made to current wildfire protection building construction regulations and teststandards. The most salient result of this study is documentation of the consistently small size of firebrandsand the close correlation of these results with the sizes of experimentally generated firebrands.