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International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire

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:

International Journal of Wildland Fire 32(11) 1576-1599
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)



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.


We aimed to quantify firebrand flux on houses for three Fire Danger Indices (FDIs).


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.


Adusumilli S, Hudson T, Gardner N, Blunck DL (2021) Quantifying production of hot firebrands using a fire-resistant fabric. International Journal of Wildland Fire 30(2), 154-159.
| Crossref | Google Scholar |

Alberta Government (2013) ‘FireSmart Guide book for community protection: A Guidebook for Wildland/Urban interface communities.’ (Alberta Government: Canada)

Albini FA (1979) Spot fire distance from burning trees: a predictive model. USDA General Technical Report INT-56. (USDA Forest Service: Utah, USA)

Aston A (1985) Heat storage in a young eucalypt forest. Agricultural and Forest Meteorology 35(1–4), 281-297.
| Crossref | Google Scholar |

Australia Bureau of Meteorology (2006) ‘Average 9 am and 3 pm relative humidity. Commonwealth of Australia 2023.’ (Bureau of Meteorology) Available at [verified 16 September 2023]

Australia Bureau of Meteorology (2022) ‘Australia in March 2022. Areal average temperatures.’ (Bureau of Meteorology Australia) Available at [verified 16 September 2023]

Australian Government (2020) Your Home. Australia’s Guide to Environmentally Sustainable Homes. Available at [verified 16 September 2023]

Bahrani B (2020) Characterization of firebrands generated from selected vegetative fuels in wildland fires. PhD thesis, The University of North Carolina, Charlotte, USA.

Blanchi R, Leonard JE, Leicester RH (2006) Lessons learnt from post-bushfire surveys at the urban interface in Australia. Forest Ecology and Management 234(1), S139.
| Crossref | Google Scholar |

Bovio G, Camia A, Marzano PD (2001) ‘Prevenzione antincendi boschivi in zona di interfaccia urbano foresta.’ (Universitadi Torino–Regione Piemonte) [In Italian]

Byram GM (1959) Combustion of forest fuels. In ‘Firest fire: control and use’. pp. 61–89. (McGraw-Hill) Available at:

California Standard (2016) Califonia Fire Code. Ch. 49: Requirements for wildland–urban interface fire areas. Available at [verified 16 September 2023]

Cruz M, Sullivan A, Leonard R, Malkin S, Matthews S, Gould J, McCaw W, Alexander M (2014) ‘Fire behaviour knowledge in Australia.’ (Bushfire Cooperative Research Centre)

Cruz M, Gould J, Alexander M, Sullivan A, McCaw W, Matthews S (2015) ‘A guide to rate of fire spread models for Australian vegetation.’ (CSIRO Land and Water Flagship Canberra ACT and AFAC Melbourne: Vic., Australia)

CSGNetwork (2022) ‘Drought Factor Calculator.’ (Palm Springs, CA) Available at [verified 16 September 2023]

Department of Building and Housing (2012) ‘Extract from the New Zealand Building Code: Clauses C1–C6 Protection from Fire, Clause A3 Building Importance Levels.’ (New Zealand Government) Available at [verified on 16 September 2023]

Edel S (2002) ‘Colorado wildland–urban interface hazard assessment methodology.’ (Colorado State Forest Service)

Ellis PF (2000) The aerodynamic and combustion characteristics of eucalypt bark: a firebrand study. PhD thesis, The Australian National University, Canberra, Australia. doi:10.25911/5d7a2814c478d

Francaise R (2017) Code forestier. (Legifrance) Available at [verified 16 September 2023] [In French] 

Gould JS, McCaw W, Cheney N, Ellis PF, Knight I, Sullivan AL (2008) ‘Project Vesta: fire in dry eucalypt forest: fuel structure, fuel dynamics and fire behaviour.’ (CSIRO Publishing)

Haider A, Levenspiel O (1989) Drag coefficient and terminal velocity of spherical and non-spherical particles. Powder technology 58(1), 63-70.
| Crossref | Google Scholar |

Hays RL (1975) The thermal conductivity of leaves. Planta 125(3), 281-287.
| Crossref | Google Scholar | PubMed |

Hudson TR, Bray RB, Blunck DL, Page W, Butler B (2020) Effects of fuel morphology on ember generation characteristics at the tree scale. International Journal of Wildland Fire 29(11), 1042-1051.
| Crossref | Google Scholar |

International Botanic Gardens Conservation (2023) GlobalTreeSearch. Available at [verified 16 September 2023]

International Code Council (2022) International Wildland–Urban Interface Code (IWUIC). Availble at [verified 16 September 2023]

Intini P, Ronchi E, Gwynne S, Bénichou N (2020) Guidance on design and construction of the built environment against wildland–urban interface fire hazard: a review. Fire Technology 56(5), 1853-1883.
| Crossref | Google Scholar |

Jarrin N, Benhamadouche S, Laurence D, Prosser R (2006) A synthetic eddy-method for generating inflow conditions for large-eddy simulations. International Journal of Heat and Fluid Flow 27(4), 585-593.
| Crossref | Google Scholar |

Khan N, Sutherland D, Wadhwani R, Moinuddin K (2019) Physics-based simulation of heat load on structures for improving construction standards for bushfire-prone areas. Frontiers in Mechanical Engineering 5, 35.
| Crossref | Google Scholar |

Koo E, Pagni PJ, Weise DR, Woycheese JP (2010) Firebrands and spotting ignition in large-scale fires. International Journal of Wildland Fire 19(7), 818-843.
| Crossref | Google Scholar |

Leonard J (2009) ‘Report to the 2009 Victorian Bushfires Royal Commission. Building performance in bushfires.’ (CSIRO Publishing)

Leonard J, Blanchi R, Bowditch P (2004) Bushfire impact from a house’s perspective. In ‘Earth, Wind and Fire – Bushfire 2004 Conference’. (CSIRO Publishing: Adelaide, Australia)

Manzello SL, Cleary TG, Shields JR, Yang JC (2006) On the ignition of fuel beds by firebrands. Fire and Materials 30(1), 77-87.
| Crossref | Google Scholar |

Manzello SL, Maranghides A, Mell WE (2007) Firebrand generation from burning vegetation. International Journal of Wildland Fire 16(4), 458-462.
| Crossref | Google Scholar |

Manzello SL, Park SH, Suzuki S, Shields JR, Hayashi Y (2011) Experimental investigation of structure vulnerabilities to firebrand showers. Fire Safety Journal 46(8), 568-578.
| Crossref | Google Scholar |

Manzello SL, Suzuki S, Gollner MJ, Fernandez-Pello AC (2020) Role of firebrand combustion in large outdoor fire spread. Progress in Energy and Combustion Science 76, 100801.
| Crossref | Google Scholar | PubMed |

Maranghides A, Mell W (2011) A case study of a community affected by the Witch and Guejito wildland fires. Fire Technology 47(2), 379-420.
| Crossref | Google Scholar |

McDermott R, McGrattan K, Hostikka S (2008). ‘Fire Dynamics Simulator (Version 5) technical reference guide.’ (National Institute of Standards and Technology (NIST) special publication: USA).

McGrattan K, Hostikka S, McDermott R, Floyd J, Weinschenk C, Overholt K (2013). ‘Fire Dynamics Simulator technical reference guide. Vol. 1.’ (NIST special publication: USA)

McGrattan KB, Forney GP, Floyd J, Hostikka S, Prasad K (2005) ‘Fire Dynamics Simulator (Version 5): User’s guide.’ (US Department of Commerce, Technology Administration, NIST: USA)

Menzemer LW (2021) Numerical simulations of brand transport in large outdoor fires. MSc thesis, Ghent University, Ghent, Belgium.

Moinuddin KAM, Sutherland D, Mell W (2018) Simulation study of grass fire using a physics-based model: striving towards numerical rigour and the effect of grass height on the rate of spread. International Journal of Wildland Fire 27(12), 800-814.
| Crossref | Google Scholar |

New Zealand Government (2017) ‘Fire and Emergency New Zealand Act 2017.’ (New Zealand) Available at

Nguyen D, Kaye NB (2021) Experimental investigation of rooftop hotspots during wildfire ember storms. Fire Safety Journal 125, 103445.
| Crossref | Google Scholar |

Noble IR, Gill AM, Bary GAV (1980) McArthur’s fire‐danger meters expressed as equations. Austral Ecology 5(2), 201-203.
| Crossref | Google Scholar |

Quarles SL, Standohar-Alfano C, Hedayati F, Gorham DJ (2023) Factors influencing ember accumulation near a building. International Journal of Wildland Fire 32(3), 380-387.
| Crossref | Google Scholar |

Storey MA, Price OF, Bradstock RA, Sharples JJ (2020) Analysis of variation in distance, number, and distribution of spotting in southeast Australian wildfires. Fire 3(2), 10.
| Crossref | Google Scholar |

Suzuki S, Manzello SL (2020) Role of accumulation for ignition of fuel beds by firebrands. Applications in Energy Combustion Science 1–4, 100002.
| Crossref | Google Scholar |

Suzuki S, Manzello SLJS (2021) Ignition vulnerabilities of combustibles around houses to firebrand showers: further comparison of experiments. Sustainability 13(4), 2136.
| Crossref | Google Scholar | PubMed |

Tarifa CS, del Notario PP, Moreno FG (1965) On the flight paths and lifetimes of burning particles of wood. Symposium (International) on Combustion 10, 1021-1037.
| Crossref | Google Scholar |

Thomas JC, Mueller EV, Santamaria S, Gallagher M, El Houssami M, Filkov A, Clark K, Skowronski N, Hadden RM, Mell W, Simeoni A (2017) Investigation of firebrand generation from an experimental fire: development of a reliable data collection methodology. Fire Safety Journal 91, 864-871.
| Crossref | Google Scholar |

Wadhwani R (2019) Physics-based simulation of short-range spotting in wildfires. PhD thesis, Victoria University, Melbourne, Vic., Australia.

Wadhwani R, Sutherland D, Moinuddin K (2019) Simulated transport of short-range embers in an idealised bushfire. In ‘Proceedings for the 6th International Fire Behavior and Fuels Conference’. (Sydney, Australia) (International Association of Wildland Fire: Missoula, Montana, USA)

Wadhwani R, Sutherland D, Ooi A, Moinuddin K (2022) Firebrand transport from a novel firebrand generator: numerical simulation of laboratory experiments. International Journal of Wildland Fire 31(6), 634-648.
| Crossref | Google Scholar |

Weir I (2018) ‘AS 3959: 2018: Construction of buildings in bushfire-prone areas. (Standards Australia: Sydney, Australia)

Whittaker J, Blanchi R, Haynes K, Leonard J, Opie K (2017) Experiences of sheltering during the Black Saturday bushfires: implications for policy and research. International Journal of Disaster Risk Reduction 23, 119-127.
| Crossref | Google Scholar |

Wickramasinghe A, Khan N, Moinuddin K (2022) Determining firebrand generation rate using physics-based modelling from experimental studies through inverse analysis. Fire 5(1), 6.
| Crossref | Google Scholar |

World Agroforestry (2023) Global Tree Knowledge Platform. Available at [verified 16 September 2023]

Wotton BM, Gould JS, McCaw WL, Cheney NP, Taylor SW (2012) Flame temperature and residence time of fires in dry eucalypt forest. International Journal of Wildland Fire 21(3), 270-281.
| Crossref | Google Scholar |

Woycheese J, Pagni P (1999) Combustion models for wooden brands. In ‘Proceeding of 3rd International Conference on Fire Research and Engineering’. p. 53. (Society of Fire Protection Engineers: Washington, USA)