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SUMMARYAn experimental apparatus has been built to investigate the ignition of fuel beds as a result of impact with burning firebrands. The apparatus allowed the ignition and deposition of both single and multiple firebrands onto the target fuel bed. The moisture content of the fuel beds used was varied, and the fuels considered were pine needle beds, shredded paper beds and crevices constructed of cedar shingles. Firebrands were simulated by machining wood (Pinus ponderosa) into small disks of uniform geometry and the size of the disks was varied. Firebrand simulation was necessary because it is difficult to capture and characterize firebrands from an actual burning object. The firebrand ignition apparatus was installed into the fire emulator/detector evaluator to investigate the influence of an air flow on the ignition propensity of fuel beds. The results of this study are presented and compared with relevant studies in the literature.

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Firebrands or embers are produced as trees and structures burn in wildland–urban interface (WUI) fires. It is believed that firebrand showers created in WUI fires may ignite vegetation and mulch located near homes and structures. This, in turn, may lead to ignition of homes and structures due to burning vegetation and mulch. Understanding the ignition events that are due to firebrands is important to mitigate fire spread in communities. To assess the ignition propensity of such materials, simulated firebrands of uniform geometry, but in two different sizes, were allowed to impinge on fuel beds of shredded hardwood mulch, pine straw mulch, and cut grass. The moisture content of these materials was varied. Firebrands were suspended and ignited within the test cell of the Fire Emulator/Detector Evaluator (FE/DE) apparatus. The FE/DE was used to investigate the influence of an air flow on the ignition propensity of a fuel bed. Ignition regime maps were generated for each material tested as a function of impacting firebrand size, number of deposited firebrands, air flow, and material moisture content.

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