Monday, November 12, 2018

Power Lines and the WUI

Photo from: LA Times
As fires continue to rage throughout California, investigations into the twelve fires that occurred earlier this year, and burned 245,000 acres, have been concluded. Investigators with Cal Fire have determined that these fires were caused by Pacific Gas & Electric Company power lines. High winds in the area caused trees and branches to fall onto the lines, and in at least one case a power pole failed and collapsed. PG&E currently has a vegetation control program in place with a budget of $400 million per year.

NFPA 1, Fire Code provides clear guidance on how to prevent fires from electrical lines. Chapter 17, Wildland Urban Interface outlines the following  requirements for vegetation clearance around electrical transmission and distribution lines, conductors, and their appurtenances.

  • 10 feet clearance is required around all poles or towers
  • At the time of trimming, the following minimum clearances should be provided based on the line voltage:

  • As the growth returns, it is permitted to grow to within the clearances shown in the table below. Once this minimum distance is reached vegetation must be trimmed back to the required minimum clearance.
                             
  • The AHJ has authority to adjust clearance requirements based on local needs or conditions, and vegetation type