Analyzing the ignition capabilities of glowing firebrand accumulations

Firebrand spotting is a significant mechanism for structure losses in wildland–urban interface (WUI) fires. In this work, the ability of firebrand accumulations to cause flaming ignition of an engineered wood material, Oriented Strand Board (OSB), under different flow conditions was experimentally studied. The firebrands were emulated by burning wooden dowels of two sizes, 6.35 & 12.7 mm. Firebrands were dropped onto on the fuel to form accumulations, with the coverage densities of 0.06 to 0.16g/cm2 on the fuel surface. The surface temperature of glowing combustion on the firebrands was measured with color ratio pyrometry. The ignition outcome results show a similar hyperbolic relationship between air flow and coverage density for both firebrand sizes although accumulations of small firebrands can cause the ignition faster. A firebrand combustion model was adopted to predict the surface temperature of accumulated firebrands considering re-radiation between nearby firebrands. A correlation between the ignition time and characteristics of accumulations was also established based on a theoretical combustion and heat transfer analysis.