What’s Causing California’s Annual Wildfires

(Bloomberg) -- For the second year in a row, wildfires in California have killed dozens of people, forced thousands from their homes and caused billions of dollars in property damage. And once again, investigators are eying power lines owned by the state’s largest utilities as a possible cause. The biggest utility, PG&E Corp., lost about a third of its market value in the days after the blazes broke out this year. Wildfires have become such a threat to utilities that they have begun switching off lines when high winds kick up, hoping to prevent sparks.

1. Did power lines cause the current fires?

Very possibly. The Camp Fire, which has burned 125,000 acres and killed at least 42 people in the Sierra Nevada foothills northeast of San Francisco, was reported minutes after a nearby PG&E transmission line went out in high winds, and the company said it found a damaged transmission tower close to where the fire began. The day before, PG&E emailed a nearby resident, saying workers needed access to her property because lines were sparking, according to the Associated Press. In the case of the Woolsey Fire near Los Angeles, utility owner Edison International said a power outage occurred near its suspected starting point, raising the prospect that an electrical spark may have been the cause.

2. How unusual are forest fires caused by power lines?

Not unusual in California, where investigators have pointed to PG&E equipment as the probable cause of 17 fires in 2017.

3. How do power lines start fires?

Most power distribution lines -- the ones leading to neighborhoods or individual homes -- rest on wooden poles. Strong winds can snap poles or tear down lines, and a live wire falls into dry grass, setting it ablaze. Strong winds also can cause parallel lines on the same pole to sway close enough to each other that electrons jump from one line to another, causing sparks that fall into grass. Trees toppled by winds, or limbs ripped from trees, can strike a power line. Some lines are equipped with devices that automatically try to restart power lines when the flow of electricity is interrupted, like in a blackout. But it can be catastrophic if lines snap and the devices, called reclosers, shoot electricity into dry grass. And transformers atop poles can emit showers of sparks when power on a line surges.

4. What can utilities do?

They are responsible for trimming trees near lines. California recently adopted the nation’s toughest standards in that regard, and a state law enacted in September requires utilities to file annual wildfire-prevention plans. In response, Edison asked regulators for permission to charge customers $582 million to replace almost 600 miles (1,000 kilometers) of overhead power lines with insulated wires, add weather stations and install high-definition cameras. PG&E plans to spend $6 billion on its own wildfire-prevention efforts. And both utilities have begun proactively cutting power when fire risk peaks.

5. Why haven’t these steps worked?

Most of the measures are too new to have had their full effect. California adopted the stricter tree-trimming standards in late 2017. The utilities’ wildfire-prevention plans are largely on the drawing board. And while PG&E warned customers it might cut power in the days before the fire north of San Francisco began, it opted not to do so in the end. Meantime, California is increasingly becoming a tinder box, as scant rainfall and hot, dry winds have left millions of acres bone dry.

6. Who’s liable when power lines cause fires?

California utilities can be held liable for wildfires started by their equipment -- even if the companies properly trimmed trees and did everything according to code. PG&E, Edison and others pushed this year to reform that system, based on a legal doctrine called inverse condemnation, but lawmakers couldn’t agree how. Instead, they passed a law to help utilities cover costs from the highly destructive 2017 wildfires, including by selling bonds backed by customer bills. But it didn’t specifically address how to handle the costs of any fires in 2018. So utilities may need to turn to lawmakers for another fix. Meantime, lawsuits stemming from the current fires are already in the works.