A review of radiant heat flux models used in bushfire applications

Abstract

The need to determine the radiant heat flux (RHF) from bushfires for fire behaviour prediction, firefighter safety, or building protection planning purposes has lead to the development and implementation of a number of RHF models, most of which are based on the Stefan-Boltzmann equation of radiative heat transfer. However, because of the complex nature of bushfire flames, a number of assumptions are made in order to make the implementation of the radiative heat transfer equation practical for wildland fire applications. The main assumptions are: bushfire flame characteristics (geometry, temperature), flame radiative qualities (emission type, emissivity), and the view of the flame at the receiving element. The common assumption of a uniform emissivity of unity and an isothermal rectangular emitting surface produces a generic RHF model described here as an 'opaque box'. Because of the broad assumptions inherent in the opaque box model, it predicts the RHF of bushfires poorly. A comparison is made between the generic opaque box RHF model and the measurements of radiant heat flux emitted by a stationary propane-fuelled artificial bushfire flame front. Knowledge about the geometry and an understanding of the flame characteristics of a bushfire front are needed before generic RHF models will adequately describe the RHF emitted from bushfire flames.