Hot-Particle Ignition of Typical Fuels in the Wildland-Urban Interface and Subsequent Fire Behaviors

The hot-particle ignition is a common cause of wildland and building fires. This study investigates the ignition of three typical fuels (straw, pine needles, and cotton) in the wildland-urban interface (WUI) by a hot metal particle of different temperatures and void ratios. In the absence of wind, the ignition of cotton is the easiest, where a flame occurs directly without clear smoldering. As the particle becomes hollow, the required minimum particle temperature for igniting cotton becomes smaller, because of a longer contact time between particle and fuel surface. Once ignited, the flaming of cotton is the weakest, with a mass loss of less than 25% because of an intensive charring. The burning of straw and pine needles is intense, with a large flame height and very little residue. Materials with finer and thinner structure like cotton are easy to initiate a flame by a hot particle while hard to sustain smoldering ignition. The hollow-structure or large-porosity materials like straw are prone to smoldering ignition under a weaker spot heating source. The fast-cooling void particles cannot induce a smoldering ignition of all three WUI fuels, because smoldering ignition requires a longer effective heating duration. This study helps understand the ignition propensity of WUI fuels by a hot particle and the subsequent flame-spread and burning process, which supports the fire protection design for WUI communities.