Effects of Fuel Composition and Size on Ember Generation Characteristics for Wildland Fire Applications

摘要

Spot fires caused by lofted embers (i.e., firebrands) can be a significant factor in the spread of wildland fires. Embers can be especially dangerous near the wildland-urban interface (WUI) because of the potential for the fire to be transported and deposited near or on structures. Many studies have explored the transport of lofted embers and the subsequent ignition of material on the ground, but information regarding generation rates from different fuels is sparse. Such information is needed as inputs to transport models and to assess risks of ember generation from different fuel sources. This work identifies ember generation characteristics for different fuel species, moisture contents, and sizes. The fuels are white oak and Douglas-fir, with nominal diameters of 2 and 6 mm. The fuel is burned in a high temperature (700°C) vertical wind tunnel with a 5 m/s cross-flow velocity. A visual camera is used to view the combustion of the fuel pieces and the resulting formation of embers. The time required for ember generation is identified from the measurements. Sample diameter is the most influential parameter on ember generation time with small diameter samples producing embers approximately 5x faster than large diameter. Moisture content has the weakest effect.