Quantifying wind‐driven firebrand production from roofing assembly combustion

Summary 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.