Experimental study of parameters affecting Firebrand Transport*

Increasing attention within the wildfire community has been on the role of spotfire spread in disastrous fire events through firebrand transport. Spotfires arise when burning firebrands are lofted into the tree canopy crossflow and transported much further downwind of the source fire to start secondary fires. Despite their significant role in rapidly increasing the rates of spread of wildfires, there is a general lack of understanding of what parameters control the transport of these firebrands. In this experimental flume study, we model the interaction of four key physical parameters that can affect firebrand transport. These include the shape of the firebrands (modeled using particles), the nature of the buoyant thermal plumes that loft the firebrands, gaps in the tree canopy, and the strength of the crosswind and ambient canopy turbulence. Our experimental study tracks the characteristics of the particle transport (velocity, spatial dispersion of settling position) through the use of PTV (Particle Tracking Velocimetry). We also simultaneously characterize the shape and position of the buoyant plumes that loft the particles. Results suggest in addition to their role in the initial lofting of the particles, the nature of the buoyant plumes at the time of lofting have a strong influence on where the particles settle. We also find that the ambient turbulence, due to the presence of large-scale rollers at the canopy/crossflow interface, also strongly affects the distribution of the particle settling distances.