Analytical formulations with experimental validation for determining the incident heat flux from firefronts

Abstract

Any target exposed to a heat source receives a certain amount of heat flux, depending on the distance, view factor, characteristics of the source, and environmental properties. Incident heat flux is mainly characterized by firefront properties, e.g., flame dimensions, and its thermal attributes by fuel properties, topography, and meteorological factors. Predicting the incident heat flux from the firefronts is crucial for fire risk management and analytical and numerical fire modelling. Based on this specification, safe zones can be defined for elements such as unprotected individuals, firefighters, and buildings. Since the contribution of radiation and convection varies with the fire evolution, it is essential to specify them as a function of distance and slope. This study elaborates determination of radiation and convection for firefronts. Sets of laboratory-scale experiments were conducted using fuel beds of straw with a load of 1.5 kg/m² on the slopes of 0°, 20°, and 40° measuring the incident radiative and total heat fluxes. The proposed methodology was validated using available approaches and correlations between the flame length and the acceptable safety distance (ASD) were established. Unlike the existing models, a nonlinear correlation between convection and radiation during the firefront evolution is proposed.