Experimental Investigation of Factors Affecting Individual Firebrand Heat Transfer

Firebrand ignition is a significant contributor to the spread of wildfires into communities. This study investigates effects of flow velocity, firebrand wood type and size, and substrate material on the peak heat flux and total heat transfer from individual disc-shaped firebrands. Firebrand heat transfer to a surface is measured with a thin skin calorimeter embedded in the substrate. Peak heat fluxes were between 25 kW/m2 and 85 kW/m2 and were higher for the smaller radius firebrands. The total heating to the substrate also tended to be higher for the smaller radius firebrands and for the substrate with higher conductivity, density and specific heat. Notably, flow velocity had almost no impact on peak heat flux, and higher velocities increased the total heating only for some firebrand wood types. Two correlations were determined to predict peak heat flux and total heating based on experimental parameters, which included the measured firebrand temperature. These correlations confirmed the importance of substrate properties on firebrand heat transfer.