Vegetation Clearance Distances to Prevent Wildland Fire Caused Damage to Telecommunication and Power Transmission Infrastructure

Towers and poles supporting power transmission and telecommunication lines have collapsed due to heating from wildland fires. Such occurrences have led to interruptions in power or communication in large municipal areas with associated social and political implications as well as increased immediate danger to humans. Unfortunately, no studies address the question of what is the appropriate clearance needed to prevent damage to the conductors and support towers by wildland fires. This study presents preliminary findings from two independent studies focused on this question. Findings suggest that steel towers provide the greatest resistance to fire damage; however, when failure occurs it is catastrophic, wood poles and towers do not fail catastrophically and thus may provide longer term resistance to failure. Minimum clearance for steel towers in surface and crown fires is 1 to 21 m. The minimum clearances for wood poles exposed to surface fires of low to moderate intensity are on the order of 1 to 33 m. For crown fires in tall brush and tree canopies, wood poles and towers require clearances of 20 to 33 m. The susceptibility of wood poles to ignition and sustained burning is dependent on the age and condition of the wood surface: aged poles that present fissures for ember accumulation have the greatest risk. Clearance around telecommunication towers is dependent on the exposure of cables, guy wires, and other materials near the ground. Analysis and conclusions from this study should be characterized as preliminary.