Predicting the ignition of crown fuels above a spreading surface fire. Part I: model idealization

Abstract

A model was developed to predict the ignition of forest crown fuels above a surface fire based on heat transfer theory. The crown fuel ignition model (hereafter referred to as CFIM) is based on first principles, integrating: (i) the characteristics of the energy source as defined by surface fire flame front properties; (ii) buoyant plume dynamics; (iii) heat sink as described by the crown fuel particle characteristics; and (iv) energy transfer (gain and losses) to the crown fuels. Fuel particle temperature increase is determined through an energy balance relating heat absorption to fuel particle temperature. The final model output is the temperature of the crown fuel particles, which upon reaching ignition temperature are assumed to ignite. CFIM predicts the ignition of crown fuels but does not determine the onset of crown fire spread per se. The coupling of the CFIM with models determining the rate of propagation of crown fires allows for the prediction of the potential for sustained crowning. CFIM has the potential to be implemented in fire management decision support systems.

Effect of Wildfire-Induced Thermal Bubble on Radio Communication

“…Visible flaming edges are at lower temperature of about 600 K [11] than at the combustion zone, which can be up to 1300 • C [5]. This produces temperature gradients between the edges and fire center.…”

Synthesis of knowledge of extreme fire behavior: volume I for fire managers

“…An example of such an approach is the semiphysically based crown fuel ignition model (CFIM) developed by Cruz et al (2006b) (Albini 1996, Butler et al 2004). Measurements of flame radiometric properties and temperatures allowed for the parameterizing of the heat transfer components in Albini's (1996) crown fire rate of spread model.…”

Evaluation of the FCCS crown fire potential equations in Aleppo pine (Pinus halepensis Mill.) stands in Greece

“…This model is intended to objectively assess, on a relative scale, the probability of experiencing torching or active crown fire spread in any FCCS fuelbed. Currently applied crown fire models, [2,7,[13][14][15][16][17], are largely empirically based and appropriate only when applied to the range of stand structures and fire behaviours observed. While these models are very useful under certain circumstances, they do not provide the broad conceptual framework or applicability necessary to compare the crown fire potential within families of dissimilar fuelbeds.…”

“…The body of literature advancing the science of crown fires, [7][8][9][10][11][12][13][14][15][16][17], shows that the potential for crown fire initiation and spread does not depend on any single element of the fuel complex, fire weather environment, or topography, but rather from combinations of interrelated variables, including: surface fire intensity, canopy closure, crown density, the presence of ladder fuels, height to base of the combustible crown, crown foliar moisture content, and wind speed. The FCCS crown fire potentials are based on an updated semi-empirical model that describes crown fire initiation and propagation in vegetative canopies based on the work by Van Wagner [2] and Rothermel [3], but updated with additional physical concepts for modelling crown fire behaviour derived from the reformulated Rothermel [4] surface fire equations proposed by Sandberg et al [5].…”