Experimental Investigation of Fire Spread and Eruption Mechanism in Canyons

Extreme fire behavior can lead to a transition from an initial low-intensity quasi-steady fire spread state to a new state with increased rates of spread (ROS) and burning intensity. Eruptive fire, a typical extreme fire behavior, occurs frequently in canyons. This study systematically conducted a series of experiments under different topographic conditions to explore the combustion dynamics of canyon fires and the mechanism of eruptive fires. The fire head direction in both symmetric and one-sided canyon fires deviated from the line of maximum slope and shifted toward the canyon centerline. The ROS of symmetric canyon fires exhibited dynamic characteristics, with eruptive fire observed at α = 30°, where the ROS increased sharply. In contrast, one-sided canyon fires and two-point-ignited upslope fires spread at approximately a steady rate. Through thermal modelling and analysis of symmetric canyon fires spread, it was found that significant convective heating occurred ahead of the fire front during eruptive fires. The interaction between the two lateral flame fronts and the chimney effect induced by canyon terrain collectively contributed to a significant enhancement of convective heating, which is identified as the key mechanism of eruptive fires in canyons.