As the investigation continues surrounding the fire at the SoMa PG&E substation last December, which led to around 120,000 customers losing power, a new report found that it was likely caused by damage and moisture buildup from an incident that occurred the previous month.
A new third-party report by the firm Exponent found that the December fire at Pacific Gas & Electric’s Mission Street substation was likely caused by a combination of equipment damage, moisture buildup, and the layout of the facility, as the Chronicle reports.
The firm does not detail what PG&E could’ve done to prevent the fire, as the circumstances are still being investigated.
As SFist reported in December, a fire at PG&E’s substation in San Francisco’s South of Market District led to a third of the city losing power — on the busiest weekend of the holiday season. Power was still out for 20,000 customers the following day, and 11,600 customers were still without power two days later, including much of Civic Center. The Market Street Muni stations were also out of service.
The more than 70-page report says that PG&E crews replaced a damaged circuit breaker after a failed test during the month before the outage, but they left behind an insulating panel that showed burned spots and warping.
According to KGO, the report also found the substation was prone to elevated humidity and moisture, and that water-saturated ventilation filters in the switchgear room were degraded and no longer properly filtering outside air. Exponent noted that the weather conditions leading up to the fire — a rapid warmup following an extended cool period — may have led to condensation buildup inside the facility.
PG&E told the Chronicle it saw no warning signs of an imminent fire risk before the outage. The utility said it has added humidity controls and weatherproofing at all 16 indoor substations following the December fire. It also inspected substations citywide, accelerated maintenance work, replaced some equipment, and expanded monitoring systems intended to catch future issues earlier.
The blackout renewed criticism from San Francisco officials already pushing to separate the city from PG&E’s power infrastructure. In March, city leaders urged the California Public Utilities Commission to take stronger action as its investigation into the outage continued, per the Chronicle.
City Attorney David Chiu said the findings from Exponent show that the utility was aware of damaged equipment at the substation and failed to adequately address it before the fire and outages.
Supervisor Bilal Mahmood, who previously pushed for hearings on the blackout, also said the report pointed to warning signs PG&E failed to act on. Mahmood said a tour of the facility earlier this year raised concerns about moisture exposure and flooding vulnerabilities inside the substation.
“I urge PG&E to immediately weatherproof its substations, closely monitor humidity and water intrusion risks, and take every necessary step to ensure this never happens again if they want to remain a trusted part of San Francisco’s power system,” Mahmood said, per the Chronicle.
The outage also caused financial losses for small businesses across the city. Jetto Seeto, owner of The Mochi Donut Shop in the Sunset, told KGO that the blackout cost his business thousands of dollars in spoiled ingredients and lost sales, and other businesses have reported similar losses to the media.
The SF Board of Supervisors is expected to discuss the report this week.
Previously: Massive Power Outage In San Francisco Leaves 200,000+ In the Dark, Disrupts Muni and BART
Image: PG&E substation at 8th and Mission streets; Google Street View
