Critical heat flux for ignition of dead and live Pinus halepensis needles. Influence of moisture content

Abstract

Wildland fire spread has been shown to exhibit unexpected behaviors depending on the fuel roughness, wind and land topography. Fire outbreak has attracted for a long time both wildland fire scientists and operational. The critical heat flux for ignition is one of the most important parameters used in fire safety. For example, it is used for the fuel breaks estimation at Wildland Urban Interface. The critical heat flux for ignition of dead and live Pinus Halepensis needles (moist and dry) is investigated using a cone calorimeter. It is determined by using a recently developed method based on the phase transition theory where ignition time follows a power-law trend near threshold. Compared to the usual deterministic methods, this method accounts for the probabilistic ignition behavior observed for porous fuels. Within the errors, the determined critical heat flux for ignition seems to be independent of the state of the fuel (live or dead) and of its moisture content. A heat transfer analysis is realized using the steady temperature which is related to the absorbed incident heat flux. From this analysis it is concluded that surface temperature at ignition does not change for fresh or dry live and dead fuels.