Visual analysis of firebrand generation from a large mass timber compartment fire

Abstract

Firebrands, the solid burning fragments transported by fire and wind, are a key mechanism of wildfire spread. Firebrands are also generated by building fires, but are not typically considered in building fire protection, and can be a more prevalent hazard in mass timber buildings. This paper presents the first study of firebrands generated from a large mass timber compartment fire (CodeRed $\#01$) and ejected from openings. Firebrand location and velocity was studied using particle Streak Velocimetry. Commercial cameras were used as a simple and field-deployable alternative to more complex approaches, whilst also providing a method of approximating the gas flow-field. Over 15600 firebrands were ejected from one opening over 17 min, reaching up to 300 firebrands in one instance. Maximum firebrand velocities of 14 $m{s}^{-1}$ and mean velocities between $2-6m{s}^{-1}$ were observed. Firebrands had greater velocities along the external venting flame centreline, while the peak of firebrand number densities were at the outer region of the external venting flame. Computer vision was trained and validated to rapidly and automatically detect firebrands whilst minimising false negatives and false positives. This paper finds that firebrands can be generated in significant quantities from mass timber building fires, posing a significant hazard to nearby structures.