Buses sat idle, Web sites crashed and commercial fire alarms went on the fritz when a massive power outage darkened a huge swath of downtown Tuesday.
The blackout, which Pacific Gas and Electric Co. spokesman Brian Swanson said affected 30,000 to 50,000 customers in San Francisco and the northern Peninsula, registered as a flicker for some, but others experienced extended outages lasting as long as two hours.
At about 1:30 p.m., transmission breakers in the Martin Substation in Daly City opened, cutting off the flow of electricity, Swanson said.
An hour later, a transformer exploded in its vault under a Mission Street sidewalk, Swanson said. However, the explosion did not result in more customers losing power, Swanson said, and the relationship between the Daly City failure and the transformer explosion was unclear. Passers-by reported seeing smoke and flames shoot out of a sidewalk vent leading to the vault.
“We were walking by and we heard this loud boom, and the flames came up about this high,” said actress Jessica Knox, gesturing to her waist. Knox was part of a crew shooting a commercial nearby. No one was hurt in the explosion.
The loss of power also triggered numerous fire alarms downtown. Fire Department Lt. Mindy Talmadge said firefighters responded to 35 calls in the first 30 minutes after the explosion. Fourteen of those calls were automatic building alarms triggered by the outage.
The loss of power temporarily affected AT&T Park, where the Giants played a night game a few hours later, and also temporarily disabled Web hosting services.
Five bus lines — the 14-Mission, 30-Stockton, 41-Union, 45-Union/Stockton and 49-Van Ness — were without overhead power for about 25 to 30 minutes. The Municipal Transportation Agency backfilled power to the lines, agency spokeswoman Maggie Lynch said. BART reported no service interruptions.
Swanson was quick to distance Tuesday’s vault explosion from the one in 2005 that sent a manhole flying, injuring a woman. He said that incident led to regular inspections of transformers, and that Tuesday’s blast was “completely unrelated” to that issue.
“What happened in 2005, that transformer failure was caused by water content in the oil chamber of the transformer, so subsequent to our investigationinto that outage, when we inspect transformers, we sample the oil to measure the water content,” Swanson said. He said that transformer, located under the sidewalk near 560 Mission St., was inspected on May 20, 2006.
Transformers are used in electrical distribution to reduce voltage coming through large transmission lines to smaller, residential and commercial lines. He said crews would replace it Tuesday.
A brief history of power failures
Major power outages caused by infrastructure failures, vandalism, human error and unknown causes in the last five years.
» July 24, 2007: Between 30,000 and 50,000 customers in downtown San Francisco left without power.
» Oct. 24, 2006: Three-hour outage caused by a PG&E worker touching a live wire, affecting 7,000 people in the Sunset, Haight-Ashbury and Twin Peaks neighborhoods.
» Sept. 6, 2006: Outage leaves 30,000 customers in Glen Park, Mission Terrace and Sunset neighborhoods in the dark.
» Dec. 31, 2005: About 280,000 customers throughout The City and the Bay Area are left without power after a massive storm slams the Bay Area.
» Dec. 17, 2004: Outage caused by an equipment failure affects 13,500 customers in the Marina and Russian Hill neighborhoods.
» Dec. 20, 2003: About 120,000 customers left without power for hours after a fire in a PG&E Mission district substation. Vandalism in the same substation left 126,000 people without power in 1997.
» Nov. 2, 2003: Three-hour power outage caused by an equipment failure, affecting 31,700 customers near the San Francisco-Daly City border.
» June 20, 2003:Power outage leaves 14,400 customers in The City in the dark for a few hours.
» Jan. 23, 2003: Outage caused by circuit problems at the Potrero Hill substation, affecting 45,000 people in Potrero Hill, Twin Peaks, Noe Valley and the Mission district.
» June 22, 2002: Outage leaves 28,700 customers without power in San Francisco’s Visitacion Valley, Bernal Heights and Excelsior districts.
Examiner Staff Writer Alexandria Rocha contributed to this report.
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