The radiative heat transfer is often the main thermal impact of a wildfire on people fighting the fire or on structures. Thus, the estimation of the radiation coming from the fire font and hitting a target is of primary importance for forest and urban managers. A new flame model based on the solid flame assumption is developed by considering a finite fire front width. The realistic description of finite fire front widths allows proposing a new criterion for the estimation of the radiative impact of the fire, which is based on the ratio fire front width/ flame length, opposed to the classical approach of considering only the flame length. The new model needs to be solved numerically so an analytical approximation is proposed to obtain a simple and useful formulation of the acceptable safety distance. A sensivity analysis is conducted on the different physical and geometrical parameters used to define the flame front. This analysis shows that the flame temperature is the most sensitive parameter. The results of the analytical model are compared with the numerical solution of the flame model and previous approaches based only on flame length. The results show that the analytical model is a good approximation of the numerical approach and displays realistic estimations of the acceptable safety distance for different fire front characteristics.

This paper proposes a comparison between two simplified flame models. The first flame model uses the radiant surface approach with a new analytical expression for the heat flux. The second one is derived from the Radiative Transfer Equation. The fire front has been considered as a line characterized by some geometric and physical parameters. Two assumptions are used to model the flame either a radiant plane or a volumetric flame. The flame parameters have been identified from experiments using video records and applying an inverse method. These two models were tested against fires carried out in a fire tunnel and found to perform very well considering the complicate nature of the flame geometry and flame characteristics. The need to determine the heat flux from a large scale fire has lead to make a number of assumptions. By means of the proposed modeling, this study tries to determine the extent to which the range of assumptions made disqualifies some simplified flame models from use.