This case involves a fire which was allegedly sparked by a power line that came into contact with a tree, resulting in a wildfire that spread across numerous ranches and homes in Montana. After an investigation, it was determined that the fire started near a site where a municipal crew was trimming tree limbs away from a roadway near power lines. At some point, it was believed that the crew removed a large branch that caused one of the power lines to come loose, sparking a fire on the side of the road that eventually grew into the wildfire. The fire ultimately resulted in millions of dollars worth of property damage.
Question(s) For Expert Witness
- 1. What policies do you recommend utilities companies follow so as to avoid wildfires?
Expert Witness Response E-134215
In my opinion, there are 2 aspects to this: (1) power line failure where broken lines have contact with vegetation on the ground and (2) trees falling over or branches and debris falling on the line, in which case the line could break as in (1). There is also some debate as to whether wildfire risk occurs when conductors are forced together by the weight of branches causing hot pieces to be sprayed on the ground vegetation. This is being debated in the scientific literature as people are unsure whether the pieces would retain enough heat to ignite the surface vegetation. When considering a risk reduction strategy it must be understood that even when risk is as low as humans can make it through adaptation (e.g. 0.0001% chance of an event), the event can still happen due to extreme events such as weather. It seems sensible to suggest the following approaches: 1. Removal of trees to a distance of 2x the height of the highest tree or the height of the power lines (whichever is greater) in a strip on both sides of the power line. 2. In this strip, control vegetation via non flammable objects or controlled burning to limit the ignitability in that zone. Ideally, this zone should have no vegetation or flammable objects. #1 would reduce the risk of falling trees and branches causing failures of the power lines #2 would reduce the risk of broken lines igniting surface vegetation. In each case, although the risks of a future wildfire would be lowered, a wildfire may nevertheless still occur.