Assessment of the plume theory predictions of crown scorch or crown fire initiation using transport models

Abstract

The aim of our work is to numerically study crown scorch and crown fire ignition as the effects of a fire line spreading through surface fuel under a tree canopy. The objective was to assess the usual assumptions made when one uses the Van Wagner criteria, based on plume theory, to estimate crown scorch or crown fire ignition. The Van Wagner criteria are indeed simple predictive models for crown scorch height or crown fire initiation occurrence. For this purpose the FIRESTAR 2D and FIRETEC wildfire simulators are used. We simulated the fire line by a heat source at ground level and mainly investigated the temperature field. As a first step, we tested the sensitivity of the simulations to different simulation parameters of the wildfire models. As a second step, we ran computations of thermal plumes with no-wind and with no-canopy, for the first comparison to the plume theory. The influence of crown existence on the temperature field above the heat source, as well as on crown scorch and fire ignition conditions, was then investigated. As a third step, the effect of a wind to the plume was shown for the no-canopy and canopy cases. © 2009 WIT Press.