Modelling wildfire firebrand accumulation in front of walls perpendicular to the wind

Abstract

Windblown embers, known as firebrands, are generated in large numbers during wildfires and can ignite buildings kilometers away from their origin. Firebrands are often the leading cause of building ignition in the wildland-urban interface. Firebrands can either ignite buildings directly by landing on or inside the structure, or indirectly by igniting adjacent vegetation. Studies have investigated firebrand generation from various fuels, wind-driven transport, and ignition mechanisms on different materials and building features. Less research has been conducted on how firebrands deposit and accumulate around buildings; this knowledge is critical in designing buildings safer to firebrand ignition. Here, we address this less understood part of firebrand processes: landing and accumulation. A computation fluid dynamic Fire Dynamics Simulator (FDS) model simulating published experimental data by Suzuki and Manzello measuring firebrand accumulation region in front of a vertical wall under firebrand exposure created with the NIST Dragon and varying wind speeds (4 m/s - 10 m/s) (Suzuki and Manzello, 2017). The simulated accumulation areas in front of the wall are compared to the experimental observations. The height, width, and thickness of the wall and wind speeds are varied, and the accumulation patterns and sizes are studied to learn the critical design parameters affecting firebrand accumulation. Here we present the set up and vision for this project, and preliminary results from the simulations. FDS measurements do not yet agree with experimental results; authors are working on improving the model planning its potential for investigations once validated.