An investigation into the cause of deadly fires sweeping across California wine country includes scrutiny of the Pacific Gas and Electric Co.’s power lines and transformers and whether they sparked any of the blazes, according to fire officials.

The speed with which 17 blazes moved through Napa, Sonoma and other Northern California counties took residents and even firefighters by surprise Sunday night into Monday morning, as people evacuated suddenly in the early hours. By Friday, at least 31 people had been killed, more than 100 had been treated for fire-related injuries, and more than 3,500 homes and businesses had been destroyed.

The California Department of Forestry and Fire Protection, or Cal Fire, said its investigators were looking for links between the fires and the utility's power lines and transformers as they fanned out across the region. An examination of Cal Fire and Sonoma County records by NBC Bay Area revealed that one of the first emergency calls at 9:22 p.m. reported a vegetation fire in the hard hit city of Santa Rosa. Less than a minute later, dispatchers noted an "electrical investigation" and at 9:24 p.m., they sent out alerts of a transformer explosion.

Scott L. Stephens, a professor in the College of Natural Resources at the University of California, Berkeley, said that all of the fires seemed to ignite between midnight and 2 a.m. Monday, when 50-mph winds were the strongest. Branches or trees could have fallen on the lines or the lines themselves failed, he said.

Arson is also being considered, he said.

The Mercury News found that Sonoma County dispatchers sent fire crews to at least 10 locations for sparking wires, exploding electrical transformers, fallen power lines and other electrical problems in Sunday night’s high winds. The Bay Area News Group, of which it is part, reviewed emergency calls over a 90-minute period starting at 9:22 p.m. Sunday.

The San Francisco-based PG&E acknowledged problems with its electric lines but told the news group in a statement that questions about maintenance were “highly speculative.”

“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,” a spokesman, Matt Naumann, said. “In some cases, we have found instances of wires down, broken poles and impacted infrastructure. Where those have occurred, we have reported them to the CPUC and CalFire.”



In April, PG&E was fined $8.3 million for failing to maintain a power line that sparked a massive fire in Northern California in 2015, The Associated Press reported. The California Public Utilities Commission levied the fine for poor tree maintenance by the utility and its contractors and for its failure to report that one of its power lines might have started the Butte Fire in September 2015. An investigation by Cal Fire found that the fire was ignited by a gray pine tree that slumped onto a line.

J. Keith Gilless, the dean of the College of Natural Resources, said that Sunday’s weather — high winds, high temperatures and low relative humidity — was conducive for bad fires.

“And of course it became far worse than just bad; it became catastrophic,” he said.

The high winds threw lots of embers in front of the large fires, creating many smaller ones, Gilless said. The vegetation of brush, grass and trees added to the hazard, unlike a redwood forest, which is moister and protected from the winds.

“We’ve had this phenomenon a couple of times recently and not far from there,” he said.

The Jerusalem and Valley fires in Lake County in Northern California in 2015 surprised firefighters with how quickly they spread, he said.

Gilless said that the 50-mph gusts meant that firefighters were focused on keeping people safe rather than suppressing the fires, and they continue to struggle to contain the firestorm amid strong winds. The National Weather Service has issued a red flag warning, signalling critical conditions, for the North Bay mountains and East Bay hills that is in effect through Thursday afternoon.

The worst fires in Northern California typically strike in October. Twenty-five years ago, the October 1991 Tunnel fire in the Oakland hills left 25 dead.