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

Amila Wickramasinghe; Nazmul Khan; Alexander Filkov; Khalid Moinuddin

doi:10.1071/WF22119

RESEARCH ARTICLE (Open Access)

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

Amila Wickramasinghe

^A , Nazmul Khan

^A , Alexander Filkov

^B and Khalid Moinuddin ^A ^*

+ Author Affiliations

- Author Affiliations

^A Institute for Sustainable Industries and Liveable Cities, Victoria University, Melbourne, Vic. 3030, Australia.

^B School of Agriculture, Food and Ecosystem Sciences, Faculty of Science, University of Melbourne, Vic. 3363, Australia.

^* Correspondence to: Khalid.Moinuddin@vu.edu.au

International Journal of Wildland Fire 32(11) 1576-1599 https://doi.org/10.1071/WF22119

Submitted: 30 June 2022 Accepted: 21 September 2023 Published: 13 October 2023

© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of IAWF. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

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.

Keywords: Australian Standard AS3959, bushfire attack level, firebrands, firebrand flux, physics-based modelling, radiative heat flux, radiant heat, wildland fire.

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