Ignition dynamics of moist fuel beds under combined firebrand pile and radiative heat exposure

Background Firebrands are a major cause of ignition and fire spread in wildland and wildland–urban interface (WUI) fires. Aim This study aims to understand the ignition dynamics of moist forest fuel beds exposed to a combination of firebrand piles and external radiant heat. Method Laboratory experiments were conducted using pine needle and eucalyptus fuel beds subjected to various firebrand pile masses (0.5 to 1.0 g) and wind speeds (1 to 4 m/s). Fuel bed characteristics (fuel type, bulk density and moisture content (MC)) were examined. External radiant heat on ignition behaviour was evaluated. Key results External radiation enhanced ignition by reducing ignition delay time, increasing ignition probability and accelerating the rate of fuel consumption. At wind speed of 3 m/s and 0.5 g firebrand pile mass, external radiation reduced the average ignition delay time by a factor of approximately 3.7 for pine needle and 2.75 for eucalyptus fuel beds. Conclusions Fuel type, wind speed, MC and radiant heat all significantly influence ignition behaviour of wildland fuel beds. Pine needle exhibited greater susceptibility to ignition, while eucalyptus showed higher resistance. Implications These findings highlight the importance of firebrand piles and radiant heat interactions in examining wildfire ignition risk and improving prevention strategies in wildland and WUI areas.