Bushfire Decision Support Toolbox Radiant Heat Flux Modelling - Case Study Two: Wangary, South Australia

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Building Engineering
Fire Behaviour
Fire Weather
Fuel Management
Hazardous Materials
TitleBushfire Decision Support Toolbox Radiant Heat Flux Modelling - Case Study Two: Wangary, South Australia
Publication TypeReport
Year of Publication2014
AuthorsNewnham, GJ, Blanchi, R, Siggins, AS, Opie, K, Leonard, JE
Date Published1/05/2014
AbstractThis report is a component of a broader research program being conducted within the Bushfire Cooperative Research Centre for the development of a house and community level Bushfire Decision Support Tools. One aim of the project is to extend the understanding of hazard classification under the current Australian Standard for Construction of Building in Bushfire Prone Areas (AS3959). This report details the second of three case studies used to develop spatial modelling of radiant heat flux incident on a house during a fire and to assess the significance of this modelled radiant heat on historic house loss. The case study uses data collected during and after the fire that occurred at Wangary in South Australia in January 2005. The study develops detailed modelling of radiant heat incident on houses using detailed topographic information, while accounting for all types of vegetation present across the landscape. Case Study One (Siggins et al., 2013) used spatially detailed fuels information based on airborne lidar data. This case study extends Case Study One by investigating the feasibility of applying landscape level radiant heat modelling where only coarse fuels information is available. A key finding of this research is that radiant heat flux modelled using coarse fuels information was a significant indicator of house damage in the case of the Wangary fire. Specifically, the total accumulated energy and the duration of exposure to radiant heat flux greater than 12 kW/m2 were significant predictor variables for house damage, where the house was located on a vegetated site (grassland/cropland or forest). This is despite the relatively low levels of radiant heat generated by the grass fuel dominated Wangary fire. While radiant heat is unlikely to have been the primary mechanism for house ignition it has been shown as a strong surrogate for hazard (independent of the attack mechanism) and may be correlated with the likelihood of embers based ignition and flame contact. Although radiant heat was shown to be significant as an indicator of damage to houses on vegetated sites, there was no relationship shown for damage to homes located directly on unvegetated sites, even when vegetation was in relatively close proximity. We hypothesise that houses located in these urban and bare soil areas (as they have been classified in broad scale land cover datasets) may be subject to combustion of other non-vegetation fuels that are not accounted for within this broad scale fuel mapping framework.