Once again, the dry winds that sweep across California each Autumn are stoking fears that utility power lines will topple and spark wildfires. After two years of devastating blazes, the state’s biggest utility, PG&E Corp., is preemptively cutting power across the northern end of the state in a fire-prevention effort that could eventually leave more than 2.7 million people in the dark. It’s the biggest intentional blackout to date by the San Francisco-based company, which filed for bankruptcy in January facing an estimated $30 billion in liabilities from fires in 2017 and 2018.

1. Who will be affected?

The Bay Area shutoffs will affect major cities including Oakland, San Jose and Berkeley, which warned residents to prepare for six days without power. San Francisco, which is less prone to wildfires because of its cooler climate and minimal open spaces, will be unaffected. Meanwhile, Edison International’s Southern California Edison utility said it was weighing cutting power to 106,000 homes and businesses, most of them in the mountains east of Los Angeles.

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2. Did power lines cause previous fires?

Authorities say yes. In May, state investigators concluded that the 2018 Camp Fire, which killed 86 people, was sparked by PG&E power lines as dry winds raked the region. It was the deadliest blaze in California history, destroying the town of Paradise. PG&E shares tumbled 85% in the months after the blaze. Earlier this year, investigators found power lines owned by Edison International’s Southern California Edison utility ignited the Thomas Fire in late 2017. It consumed almost 300,000 acres north of Los Angeles, killing two people.

3. Does that happen a lot?

It does in California, where investigators have pointed to PG&E equipment as the probable cause of 17 fires in 2017. And the risk is likely to grow: As the region’s climate warms and dries, the massive blackouts could become a new, annual ordeal. “We have a grid that was built to manage a set of circumstances that don’t exist anymore,” said Michael Wara, director of the Climate and Energy Policy Program at Stanford University. “We are having to adapt to new circumstances brought about by climate change.”

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4. 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 when a live wire falls into dry grass it can set it ablaze. Such 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, as in a blackout. But the result can be catastrophic if lines snap and the devices, called reclosers, shoot electricity into dry grass. Transformers atop poles can emit showers of sparks when power on a line surges.

5. What can utilities do?

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Aside from cutting power during wind storms, utilities are responsible for trimming trees near lines. California has adopted the nation’s toughest standards in that regard, and a state law requires utilities to file annual wildfire-prevention plans. Edison asked regulators last year 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.

6. 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 deadly 2018 Camp Fire began, it opted not to do so in the end.

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7. Who pays 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.

To contact the reporters on this story: David R. Baker in San Francisco at dbaker116@bloomberg.net;Christopher Martin in New York at cmartin11@bloomberg.net;Mark Chediak in San Francisco at mchediak@bloomberg.net

To contact the editors responsible for this story: Joe Ryan at jryan173@bloomberg.net, Pratish Narayanan

©2019 Bloomberg L.P.

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