Abstract
Australian building standard AS 3959 provides mandatory requirements for the construction of buildings in bushfire prone areas in order to improve the resilience of the building to radiant heat, flame contact, burning embers, and a combination of these three bushfire attack forms. The construction requirements are standardised based on the bushfire attack level (BAL). BAL is based on empirical models which account for radiation heat load on structure. The prediction of the heat load on structure is a challenging task due to many influencing factors: weather conditions, moisture content, vegetation types and fuel loads. Moreover, the fire characteristics change dramatically with wind velocity leading to buoyancy or wind dominated fires that have different dominant heat transfer processes driving the propagation of the fire. The AS 3959 standard is developed with respect to a quasi-steady state model for bushfire propagation assuming a long straight line fire. The fundamental assumptions of the standard are not always valid in a bushfire propagation. In this study, physics based large-eddy simulations were conducted to estimate the heat load on a model structure. The simulation results are compared to the AS 3959 model; there is agreement between the model and the simulation, however, due to computational restrictions the simulations were conducted in a much narrower domain. Further simulations were conducted where wind velocity, fuel load, and relative humidity are varied independently and the simulated radiant heat flux upon the structure was found to be significantly greater than predicted by the AS 3959 model. The effect of the mode of fire propagation, either buoyancy-driven or wind dominated fires, is also investigated. For buoyancy dominated fires the radiation heat load on the structure is enhanced compared to the wind dominated fires. Finally, the potential of using physics based simulation to evaluate individual designs is discussed.
Highlights
Bushfire or wildfire is an integral part of the Australia environment and costs millions of dollars every year in terms of losses to the economy
There are at least 6.17 housing units/km2 with vegetation area of more than 50% of terrestrial area, or Abbreviations: Fire danger index (FDI), Fire Danger Index; grassland fire danger index (GFDI), Grass Fire Danger Index; RoS, Rate-of-spread; bushfire attack level (BAL), Bushfire attack level
In this work we conduct simulations to compare the radiation heat load upon a structure, as close as computationally possible, from the fire scenario in AS 3959 predicted by the BAL set out in the standard, to the radiation heat load simulated by a physics based model
Summary
Bushfire or wildfire is an integral part of the Australia environment and costs millions of dollars every year in terms of losses to the economy. Wildfires are classified as mega wildfires if the fire occurs at large spatial scale coupled with strong wind reaching up to 100 km/h, firestorm events and massive ember generation can cause massive evacuation, devastation, and loss of life. These fires are dynamic and difficult to manage (Mell et al, 2010). Some of the recent “mega wildfires” are the 2016 Fort McMurray fire, Canada; the 2017 Californian wildfires, USA; the 2017 Portugal wildfires, Portugal (Ronchi et al, 2017) The effect of these bushfires is not limited to economical damages, the fires cause massive evacuation of communities and present challenges to emergency personnel. City planners and building authorities must plan new developments to be resilient to the risks of bushfires
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
