The causes of the fires ripping through the Wine Country and beyond had not been determined by Wednesday, but investigators are looking into reports that strong winds knocked down numerous Pacific Gas and Electric Co. power lines between 9:20 p.m. and 10 p.m. on Sunday night, about the time the fires broke out in Napa and Sonoma counties, officials said.
“We are investigating a number of potential causes, including whether reports of power lines falling down and electrical transformers exploding Sunday night may have caused some of the wildfires in the region,” said Janet Upton, deputy director of the California Department of Forestry and Fire Protection, also known as Cal Fire.
PG&E spokeswoman Ari Vanrenen said the utility, which has mobilized nearly 800 repair workers to the North Bay, has found downed power lines and poles broken by what she called a “historic” wind storm. PG&E has reported all of those problems to Cal Fire, she said.
“These destructive winds, along with millions of trees weakened by years of drought and recent renewed vegetation growth from winter storms, all contributed to some trees, branches and debris impacting our electric lines across the North Bay,” Vanrenen said in an email.
It will take time to determine the cause, Cal Fire officials have said. Accidental factors — a campfire blown out of control, a carelessly tossed cigarette — cannot yet be ruled out. Neither can arson.
But contact between electrical lines and tree branches has often caused blackouts, and fires. The massive August 2003 blackout that cut power to 55 million people from Ontario to New Jersey was caused, in part, by high-voltage lines coming into contact with overgrown trees.
Lines tangling with branches can spark, so utilities are required to trim or remove nearby trees and bushes. For the standard electrical line running through most neighborhoods, branches must be kept at least four feet from the wires and ten feet from each power pole.
Conditions were ripe for fires on Sunday night. Dry winds out of the northeast gusted up to 50 mph, and the vegetation that flourished after last year’s drought-ending rains provided ample tinder.
As the winds picked up Sunday, Pacific Gas and Electric Co. sent out warnings on social media, telling customers that strong gusts could topple power poles and knock out electricity. The utility urged customers to report any downed lines to 911 and avoid touching them, since they could still be carrying electricity.
The warning proved prophetic. Several of the blackouts that swept across the North Bay Sunday night and Monday morning were caused by downed lines or damaged equipment on power poles, according to a PG&E website that tracks outages.
As many as 114,000 PG&E customers in the area lost power by mid-day Monday. By Wednesday, PG&E had restored power to more than half of them, with 53,000 customers still lacking electricity.
21stC Thinking | Chas. Malloy 