Quantifying wind-driven firebrand production from roofing assembly combustion

Abstract

Large outdoor fires present a risk to the built environment. Examples often in the international media reports are wildfires that spread into communities, referred to as wildland-urban interface (WUI) fires. Other examples are large urban fires including those that have occurred after earthquakes. Firebrands are a key mechanism on how rapidly fires spread in urban fires and WUI fires. An experimental protocol has been developed to ignite full-scale roofing assemblies and quantify the degree of firebrand production during the combustion process. As wind is an important factor in firebrand generation, the experiments were conducted under a range of wind speeds at the Building Research Institute's Fire Research Wind Tunnel Facility. A further unique aspect of this work is that the experimental results are compared to firebrand size and mass distributions collected from an actual large-scale urban fire in Japan. Results of these experiments demonstrate that when only oriented strand board is applied as sheathing, a significant number of firebrands collected from roofing assemblies were less than 1 g and 10 cm2. It was also observed that experiments on individual building component firebrand generation provided useful insights into actual urban fire firebrand generation.