It’s a question worth billions of dollars: How did California’s most destructive wildfire start?

One year after the Tubbs fire burst from a spark and became a wind-driven inferno, thousands of people who lost homes as well as relatives of the 22 people killed are still waiting to learn what caused the wildfire that upended their lives.

Cal Fire has concluded PG&E power lines and equipment sparked 16 of the 18 fires that broke out Oct. 8 and 9 across Northern California. Investigators handed reports for 11 of those fires — including the Atlas fire that killed six people in Napa County — to local prosecutors, who will review evidence asserting the utility company hadn’t followed safety laws and was criminally negligent.

But the agency has not yet revealed the results of its investigation into the Tubbs fire, which burned 36,807 acres from Calistoga west over the Mayacamas Mountains, destroying entire Santa Rosa neighborhoods and causing nearly $8 billion in insured losses in Sonoma County.

The only other pending fire investigation from October 2017 is for the 10,000-acre Cascade fire in Yuba County, and that report is expected to be announced within the next week, according to Cal Fire spokesman Scott McLean.

Investigation began immediately

The high-stakes investigation into the Tubbs fire has no timeline, McLean said.

Its conclusions have major consequences for PG&E, which is already anticipating up to $17 billion in potential liabilities from the 2017 fires. The investigation will impact hundreds of people who are suing the San Francisco-based utility in anticipation that its power equipment led to the initial spark.

“There is a lot riding on those fires,” said veteran fire investigator Dan White, a Redding-based division chief in Cal Fire’s fire prevention and law enforcement division. “They were extremely devastating. People lost their homes and lost their lives. Sometimes with fires like that, it takes longer.”

When the first firefighters raced toward the wind-whipped fires that broke out a year ago across the North Bay, an army of state fire investigators also fanned out, identifying early on the suspected origins of the blazes.

Working parallel to fire crews, inspectors recorded clues from the way the fires burned and the scorched evidence was left behind — the first phase of what became monthslong examinations into the deadliest and most destructive siege of wildfire ever in California.

Power equipment suspected

The Tubbs fire ignited about 9:45 p.m. Oct. 8 at rural residential property on Bennett Lane north of Calistoga in the northern end of Napa Valley. It quickly spread west, raging in hot and dry conditions, driven by fierce winds.

Cal Fire investigators seized as evidence damaged power equipment from a property near the fire’s origin, according to state regulators. For weeks after the Tubbs fire started, private security guards and yellow crime scene tape barred entry to two Bennett Lane driveways leading up to the side of a wooded hill overlooking vineyards.

PG&E has asserted it may have been a private power line “owned, installed and maintained by a third party,” and not the utility’s equipment that started the Tubbs fire, according to court documents filed by lawyers representing the utility giant against a mounting number of civil lawsuits alleging the company was negligent in its care of the power grid.

In response to questions about the Tubbs fire investigation, PG&E spokeswoman Deanna Contreras issued a statement that the utility is “focused on doing everything possible to help further reduce the wildfire risk” by boosting safety measures. That includes its new protocol for de-energizing the power grid when the risk of fire is high and opening a 24/7 wildfire operations center to anticipate and respond quickly to fires.

Contreras said the company is “further cutting back vegetation and expanding safety clearance around power lines in neighborhoods and communities that face the greatest wildfire risk.” PG&E will “do everything we can to address this growing risk and help keep our customers and communities safe,” she said.Geisha Williams, chief executive officer for PG&E — California’s largest utility, providing gas and electric service to 16 customers people across 70,000 square miles — has said climate change is fueling the hot and dry conditions making way for mega-fires.

But John Fiske, an attorney representing Sonoma, Napa and Mendocino counties in their litigation against PG&E, said private investigators hired by his firm long ago concluded the North Bay fires were started by PG&E equipment.

Fiske said investigations completed by Cal Fire show a clear pattern of failures on the part of the company: Not keeping power lines clear of trees and other vegetation and not implementing fire-prevention measures for high-wind conditions, such as deactivating devices known as reclosers that send bursts of electricity when power is lost in an attempt to restart service.

Fiske said he would be surprised if Cal Fire finds another cause of the fire, and that his firm’s experts would scrutinize the state’s findings.

Exacting work with no end in sight

The only natural cause of a wildfire is lightning. The vast majority of fires start with human factors, such as the 2015 Valley fire in Lake County that ignited with a spark from faulty hot tub wiring, according to the state. The Valley fire investigation took nearly a year.

Most Cal Fire investigations are conducted by about 90 specially trained fire prevention personnel with both fire expertise and peace officer authority, according to McLean. Of those, 26 were assigned to investigate the October 2017 North Bay fires.

McLean couldn’t provide a cost estimate for these investigations because it is wrapped into the overall cost of the fire response. The state spent $384.8 million to battle and recover from wildfires statewide in 2017, according to the 2018-2019 budget report.

Fire investigations all start the same way: Examine fire behavior, burn scars and ash marks; interview witnesses; review 911 calls; record and collect evidence that might point to an ignition source. From there, investigators might consult with arborists, forest specialists, metallurgists and other experts to further analyze what story the evidence tells about the fire’s start.

The more complex a blaze, the longer it takes to analyze all factors contributing to its cause, said White, who oversees a group of lead investigators.

And the fires keep coming, forcing inspectors to juggle new and existing cases.
California nearly exhausted its current annual wildfire budget in July and August alone. On July 23, the Carr fire in Shasta County ignited with a spark from a flat tire, burning nearly 230,000 acres, destroying 1,079 homes and killing eight people, including three workers engaged in the fire response. Four days later, the largest wildfire in California history — the Ranch fire — started near Potter Valley and scorched 410,203 acres in Mendocino, Lake, Colusa and Glenn counties. Its cause remains under investigation.“We want to make sure everything is accurate,” White said. “It’s not easy to wait. A lot of people’s lives were turned upside down and we want to make sure that when the report comes out people are as satisfied as they could possibly be.”

You can reach Staff Writer Julie Johnson at 707-521-5220 or On Twitter @jjpressdem.