Physics-based modelling for mapping firebrand flux and heat load on structures in the wildland–urban interface

Abstract

Background This study investigates firebrand and heat flux exposures of structures in the wildland–urban interface (WUI). Australian Building Standard AS3959 defines Bushfire Attack Levels (BALs) based on radiant heat flux exposure of properties at the WUI. Despite the fact that firebrands are one of the main causes of house losses in the WUI, firebrand attack levels on houses are still not quantified owing to inherent difficulties. Aims We aimed to quantify firebrand flux on houses for three Fire Danger Indices (FDIs). Methods Three wildfires with varying fireline intensities were modelled to mimic wildfire exposure at FDIs of 100, 80 and 50. The current model was improved by adding the effects of fuel moisture content (FMC), vegetation and wind speed to estimate firebrand generation rates in different vegetation species for various fire severities, and these rates were used to simulate firebrand attack on structures. The firebrand and radiative heat fluxes on the structures were calculated to develop correlations to quantify firebrand attack. Key results A logarithmic relationship between firebrand flux and radiative heat flux was found. Conclusions and implications The findings are beneficial in quantifying firebrand flux on houses for different vegetation fires to improve building construction requirements and mitigate the vulnerability of structures at the WUI.