A fire at a Pacific Gas & Electric substation in SoMa knocked out power to as many as 130,000 customers starting Saturday, leaving thousands in the dark heading into the holiday season and a week of intense storms. Here’s what we know about the outage and state of restoration.

The fire began shortly before 1:10 p.m. Saturday at PG&E’s Mission substation at Eighth and Mission streets, initially affecting 40,000 customers. As firefighters worked to suppress the blaze, crews de-energized additional portions of the electric system for safety, causing outages to peak at approximately 130,000 customers.

The fire damaged critical equipment, including a circuit breaker — a safety switch designed to de-energize the system when problems are detected. Firefighters faced unusual complexities suppressing the fire in the multilevel building, including ventilating carbon monoxide before crews could safely enter.

Firefighters made the building safe for PG&E crews to enter by 6:15 p.m. Saturday. Restoration efforts began immediately. Nearly 32,000 customers were reconnected by 8:45 p.m. Saturday, and about 100,000 — roughly 75% of those affected — were up by 9:30 p.m.

By noon Sunday, 90% of affected customers had power restored. PG&E initially projected full restoration by 2 p.m. Monday; however, a spokesperson said the utility was extending restoration times (opens in new tab) for the remaining 4,400 customers without power. No time frame has been announced.

PG&E says it doesn’t know. COO Sumeet Singh said Monday that the extensive equipment damage makes it difficult to determine a root cause. The utility has hired Exponent, a Bay Area-based engineering firm, to conduct an independent investigation.

“We will determine what occurred to ensure it never happens again,” Singh said at a press conference outside the damaged substation.

PG&E completed preventative maintenance at the Mission substation in October and conducted its most recent bimonthly inspection Dec. 5. Singh said neither inspection identified any problems.

Many customers were irate as they were repeatedly given estimated restoration times that came and went. Singh acknowledged the failure and said PG&E’s estimation systems typically perform well, with more than 91% accuracy systemwide.

“It obviously did not work effectively in the circumstance over this weekend,” Singh said. “We are committed to understanding exactly what happened, why it happened, and owning the fixes.”

Residents have observed a large presence of workers at a substation at 24th Avenue and Balboa Street since Sunday, but the utility has not shared details on what is being done there.

Six hulking diesel generators, which one worker said cost $600,000 to operate daily, were parked outside the substation Monday afternoon. The generators are needed to feed power to the grid while both substations are not fully operational. Crews said they are expected to run for at least two to three days.

Two workers said the substation is undamaged and still online, but its output is diminished because it is fed power by the much larger substation at Eighth and Mission.

However, another said one of the substation’s transformers blew out after a power surge following the fire, and the generators are needed to compensate while workers “update the system” of the west-side substation.

PG&E plans to offer an expedited claims process for affected customers to seek compensation for losses, including spoiled food, lost business revenue, and hotel costs. Singh said details will be available soon on the utility’s website and through customer service.

He declined to specify compensation limits or provide immediate financial relief, saying customers would need to file claims that PG&E would process quickly. The utility opened a community resource center in the Richmond and partnered with 211 to provide hotel accommodations and food vouchers for vulnerable customers.

Singh said PG&E has identified no vulnerabilities at other substations and has made significant upgrades systemwide. Two strong storms forecast for Tuesday and Wednesday (opens in new tab) could bring 4 to 10 inches of rain to Northern California; he said more than 5,500 PG&E workers and contractors are positioned to respond.

The outage occurred 22 years to the day (opens in new tab) after a mass blackout at the same substation in 2003, raising questions about aging infrastructure that Singh did not directly address.