Self-extinction of wood plate : effect of fuel thickness and flame spread orientation

Abstract

Flame spread behaviour is a key element in evaluating material fire hazards, and studying the flame spread on wood helps understand the fire safety of timber structures. This work tests the flame spread on wood plates with different thicknesses from 1.0 mm to 30.0 mm under different irradiations and sample orientations. Various flame spread phenomena are observed, including flame spread without fuel burnout, flame spread with fuel burnout, and self-extinction. The wood flame tends to self-extinguish, as the sample thickness increases or the orientation changes from upward to downward. Minimum flame spread rate is found to be ∼0.03 cm/s for the upward flame spread, below which self-extinction occurs. Without irradiation, self-extinction limit for upward flame spread is quantified to be about 7.5 mm. As the irradiation increases, self-extinction becomes more difficult, because of the enhanced heating in both preheating and burning regions. For irradiation larger than 15 kW/m2, the surface flame spread significantly increases due to irradiation-assisted preheating before the fire front. Flame spread gradually transitions from the surface ignition process to the gas-phase flame propagation. This work quantifies the self-extinction limits of wood flame spread as a function of sample thickness, irradiation, and orientation, which helps to improve fire resilience for future timber buildings.