Quantifying Firebrand and Radiative Heat Flux Risk on Structures in Mallee/Mulga-Dominated Wildland–Urban Interface: A Physics-Based Approach

Abstract

Fire spread in the Wildland–Urban Interface (WUI) can occur due to direct flame contact, convection, radiation, firebrand attack, or their combinations. Out of them, firebrand attack significantly contributes to damaging structures. To improve the resistance of buildings in wildfire-prone areas, the Australian Standards AS3959 provides construction requirements introducing Bushfire Attack Levels (BAL) based on quantified radiation heat flux. However, quantifying firebrand attack presents challenges, and the standard does not provide specific recommendations in this regard. This study aims to address this research gap by quantifying firebrand flux on houses according to the BALs in Mallee/Mulga-dominated vegetation using physics-based modelling. The study follows the AS3959 vegetation classifications and fire-weather conditions. The study considers Fire Danger Indices (FDI) of 100, 80, and 50 and identifies the housing components most susceptible to firebrand attack and radiant heat flux. The findings reveal an increasing firebrand flux with higher BAL values across all FDIs, with a greater percentage difference observed between FDIs 50 and 80 compared to FDIs 80 and 100. Furthermore, an exponential relationship is found between radiative heat flux and firebrand flux. This research contributes the development of effective strategies to mitigate the firebrand danger and enhance the resilience of structures to enhance AS3959.