An empirical firebrand pile heat flux model

Abstract

Firebrand exposure has been identified as a leading cause of structure losses during wildfires. However, only a limited number of studies have attempted to quantify the incident firebrand heat flux to a target substrate surface. In this study, a bench-scale wind tunnel retrofitted with an IR thermal imaging system was used to generate high-resolution temperature data for the back surface of a thin, non-combustible insulation board exposed to a glowing firebrand pile at 0.9–2.7 m s−1 air flow velocities and 0.06 and 0.16 g cm−2 firebrand coverage densities. An inverse heat flux modelling technique utilizing a solid-phase pyrolysis solver, ThermaKin, was employed to determine transient firebrand pile heat flux profiles underneath and directly in front of a glowing firebrand pile. The inverse modelling technique used both the experimental back surface temperature data and the insulation's thermophysical properties. Average incident firebrand pile heat flux values obtained for all testing conditions ranged between 28 and 80 kW m−2. For the first time, an empirical model capturing the firebrand pile incident heat flux dependence on time, air flow velocity and firebrand coverage density was developed.