ON THE FLIGHT PATHS OF METAL PARTICLES AND EMBERS GENERATED BY POWER-LINES IN HIGH WINDS - A POTENTIAL SOURCE OF WILDLAND FIRES

In dry grasslands, dangerous wildfires are of particular concern durin g hot, dry seasons in regions encountering high winds. It is possible that such winds can cause power cables to come close enough together t o are or collide with trees, and produce metal sparks or burning ember s which can be carried by the wind and land in adjacent areas of dry v egetation. A major issue is whether or not such possibly generated par ticles 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 stu died: (I) hot particles produced by arcing copper power lines; (2) bur ning sparks produced by arcing aluminum power lines; and (3) burning e mbers produced by the collision of high voltage power lines with surro unding 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 siz e. Since copper particles do not emerge burning, they immediately cool down insight, as they are carried away by the wind. Nonetheless, with a slightly larger heat capacity than that of aluminum (and non-regres sing size), a copper particle can bring with it a significant amount o f heat into its area of impact. Although smaller aluminum particles ca n burn out while inflight, larger aluminum particles can land while st ill burning. Burning embers or firebrands burn heterogeneously and are not susceptible to high Re extinction due to flame blow-off: Larger e mbers can land still burning, however, they may carry less heat than t heir metal counterparts. (C) 1998 Elsevier Science Ltd. All rights res erved.