Jean-Louis Rossi

A 3D PHYSICAL REAL-TIME MODEL OF SURFACE FIRES ACROSS FUEL BEDS

Abstract This work presents a new modelling approach to the elaboration of a simple model of surface fire spread. This model runs faster than real-time and will be integrated in management tools. Until now, models used in such tools have been based on an empirical relationship. These tools may be efficient for conditions that are comparable to those of test-fires but the absence of a physical description makes them inapplicable to other situations. This paper proposes a physical 3D model of surface fire able to predict fire behaviour faster than real-time. This model is tested on experiments carried out across fuel beds under slope and wind conditions.

An analytical model based on radiative heating for the determination of safety distances for wildland fires

In a wildfire, radiative heat transfer is often the main thermal impact on people fighting the fire or on structures. Thus, the estimation of the radiation from the fire front and the heating of a target is of primary importance for forest and urban managers. An analytical formulation of this radiative heat transfer, based on a solid-flame assumption, is used. The realistic description of finite fire-front widths allows the proposal of a new criterion for the estimation of the radiative impact of the fire, which is based on the ratio of the fire-front width to the flame length, which is opposite to the classical approach of considering only the flame length. A numerical solution is necessary to calculate the safety distance for a fixed radiative threshold value, so an analytical approximation is proposed to obtain a simple and useful formulation of this Acceptable Safety Distance. A sensitivity 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.

Simplified Flame Models and Prediction of the Thermal Radiation Emitted by a Flame Front in an Outdoor Fire

The authors proposed a comparison between 2 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, the authors try to determine the extent to which the range of assumptions made disqualifies some simplified flame models from use.

Physical Modeling of Surface Fire Under Nonparallel Wind and Slope Conditions

The physical model we developed in a previous work (J. H. Balbi et al., 2007) predicts fire behavior with a computational time that is faster than real time. However, it has the inconvenient of introducing an empirical law (B. J. McCaffrey, 1979), which provides flame height according to heat release rate. The authors introduce two improvements of this model: the triangular flame hypothesis and a modification taking into account the air cooling on the rear fire front. To test this variant of their simplified model, it was compared with important experimental results (D. X. Viegas, 2004b). The experiments were performed in homogeneous and plane fuel beds made with dead Pinus pinaster needles under high values of wind and slope. In spite of these high values this physical model provides a good approximation of the fire front perimeter.

Discrete event formalism to calculate acceptable safety distance

The aim of this paper is to present a dimensioning tool for fuelbreaks. It focuses on the overall approach and specifically mapping a physical model to a DEVS model, mapping a DEVS model to a DEVS service, and the client that communicates with the server. In order to assist the firefighters, we focus on a Web Service based on different software tools that can be used by firefighters to forecast fuelbreak safety zone sizes. This Web Service uses a simulation framework based on DEVS formalism, a theoretical fire spreading model developed at the University of Corsica and to display the results on a Google Map SDK. The SDK is embedded in a mobile application for touchscreen tablet. The application sends a request to our DEVS Web Service, with its geolocation, and in response receives data sets that allow to draw the safety distance.