Burning rates of individual firebrands on shredded paper beds

Every year, homes and buildings are destroyed by wildland fires. In most situations, the structures are ignited by firebrands landing on a combustible surface within or in the direct vicinity of the structure. The mass burning rate, which is directly proportional to the energy produced through combustion, provides an indication of the ignition hazard posed by firebrands to nearby materials or structures. In this study, the combined burning rates of firebrands and fuel beds were measured under different air flow conditions. Two types of firebrands (birch and cedar) were used, and the fuel bed was made of shredded printer paper. The bulk fuel bed density and the fuel moisture content were varied in the experiments. An infrared (IR) camera was used to measure initial firebrand temperatures immediately after deposition on the fuel bed and to record the surface temperatures of the fuel bed. The IR measurement was used to calculate the reacting area within the fuel bed throughout the experiments. It was found that the air flow condition had the greatest effect on the combined mass burning rate and the reacting area growth rate within the fuel bed. The initial temperature was also correlated with the air flow condition. The birch firebrands tended to exhibit higher mass loss rates and higher reacting area growth rates than the cedar cases. The initial cedar firebrand temperatures were higher than those of the birch firebrands. There was no clear trend in the burning rate, reacting area growth, or initial firebrand temperature with the bulk fuel bed density and fuel moisture content under the experimental conditions used in this study.