On the flight paths of metal particles and embers generated by power lines in high winds--a potential source of wildland fires

Abstract In dry grasslands, dangerous wildfires are of particular concern during hot, dry seasons in regions encountering high winds. It is possible that such winds can cause power cables to come close enough together to arc or collide with trees, and produce metal sparks or burning embers which can be carried by the wind and land in adjacent areas of dry vegetation. A major issue is whether or not such possibly generated particles can initiate a brush or grass fire. In this work, a predictive, numerical model is used to calculate trajectories, combustion rates, and lifetimes of metal particles and burning embers of different sizes for various wind conditions and terrain. Three distinct cases are studied: (1) hot particles produced by arcing copper power lines; (2) burning sparks produced by arcing aluminum power lines; and (3) burning embers produced by the collision of high voltage power lines with surrounding trees. The results show that for the same wind conditions, the distances reached by firebrands are the greatest, followed by aluminum and copper. Large aluminum sparks (e.g. 1·5 mm diameter) that do not burn up in flight travel farther than copper particles of the same size. Since copper particles do not emerge burning, they immediately cool down in flight, as they are carried away by the wind. Nonetheless, with a slightly larger heat capacity than that of aluminum (and non-regressing size), a copper particle can bring with it a significant amount of heat into its area of impact. Although smaller aluminum particles can burn out while in flight, larger aluminum particles can land while still burning. Burning embers or firebrands burn heterogeneously and are not susceptible to high Re extinction due to flame blow-off. Larger embers can land still burning; however, they may carry less heat than their metal counterparts.