Towards Developing the Scientific Basis for New Testing Methodologies to Quantify and Compare Firebrand Generation from Building Components

Abstract Firebrands are a dangerous threat, leading to fire spread at distances far away from the original fire location. Testing methodologies are needed to be develop materials so that buildings produce less firebrands during actual fire events. Through dedicated experiments focused on understanding the complex process of firebrand generation from full-scale buildings and building components under wind, a reduced-scale test method capable of comparing firebrand generation from mock-up assemblies has been developed. Here, a new series of full-scale experiments under wind, focused on roof assemblies fitted with cedar roof coverings, was undertaken to determine if the reduced-scale experimental method could indeed predict the full-scale experimental observations. The reduced-scale experimental method correctly predicted that: fire retardant cedar shakes would produce the least number of firebrands, the overall range of firebrand sizes generated from all types of cedar coverings utilized, and that the firebrand coefficient, namely, firebrand density times average thickness of firebrands, $${(\rho }_{fb}\times {\delta }_{ave, fb} ={\alpha }_{fb}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>ρ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>fb</mml:mi> </mml:mrow> </mml:msub> <mml:mo>×</mml:mo> <mml:msub> <mml:mi>δ</mml:mi> <mml:mrow> <mml:mi>a</mml:mi> <mml:mi>v</mml:mi> <mml:mi>e</mml:mi> <mml:mo>,</mml:mo> <mml:mi>f</mml:mi> <mml:mi>b</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msub> <mml:mi>α</mml:mi> <mml:mrow> <mml:mi>fb</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) increased as the wind speed increased for cedar shingles. Cedar shakes resulted in a different trend in firebrand coefficient, which may be expected due to their more non-uniform shape prior to combustion.