Firebrands generated from structures in built environment

• Wooden structures were burned in outdoor settings under low outdoor winds (1-2 m/s). • Total firebrand yield (count) from a single structure was quantified for the first time. • Specific firebrand yield (count/kg) was determined for structures for the first time. • Effects of scale, and construction material (e.g., siding and roofing) were evaluated. • Firebrand generation behavior of structures was compared with that of vegetation. Understanding how the characteristics of a structure (e.g., size and materials) influence firebrand production is critical for fire prevention and mitigation in communities. Here, we quantify sensitivities of firebrand generation to structure scale and materials. Twenty-three structures were burned under low outdoor-winds (mean ∼1.0–2.0 m/s). Firebrand number density (count/m²) measured on a gridded field was mapped using interpolation-extrapolation, and integrated to estimate total firebrand yield. Burned mass of structures and burn duration were measured. Three scales (height ∼1.0–3.6 m), three siding-materials, and two roofing-materials were evaluated – total firebrand yields ranged from ∼2,000 to ∼24,000 and burned-mass specific yields (total yield/burned mass) ranged from ∼50 to ∼135 firebrands/kg. Increasing structure scale increased total yield and fuel-load specific yield (firebrand/kg/m 2 ), whereas mass-specific yield (firebrand/kg) showed no clear dependence on scale. In contrast, more combustible materials (e.g., cedar siding) increased the total yield and specific yields (mass and fuel-load based) – further tests are needed to reduce uncertainty. This work provides a dataset of specific firebrand production terms. It is anticipated that these terms can be used to estimate firebrand generation from burning structures, at least for the size and materials evaluated here, if the mass consumed can be determined. These values and the associated uncertainty help to bound potentials for firebrand generation.