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Fire pours through a manhole in San Francisco. The underground blast left thousands without power. (NOAH BERGER/SAN FRANCISCO CHRONICLE VIA ASSOCIATED PRESS FILE 2009)

PG&E's natural gas lines aren't the only worry lurking underground. State regulators are concerned about the scores of incidents in recent years in which the utility's subterranean electrical gear has belched smoke, spewed flames and in some cases exploded with such force that 100-pound manhole covers were sent flying.

Research by this newspaper turned up at least 78 such mishaps in the Bay Area since 2005, the most recent of which occurred Wednesday, when residents near Delmas and Park avenues in San Jose heard a blast, and about 1,000 PG&E customers lost power for about an hour.

While many of the accidents were minor, explosions were reported in 31 cases, with manhole covers dislodged in at least 14. Two people were injured, including Lisa Nash, of Redwood City. She was burned over half her body, and her right elbow was shattered by a manhole cover that was hurled 30 feet when an underground electrical vault erupted beside her as she strolled toward her San Francisco office in 2005.

"I remember opening my eyes, seeing a cloud of black smoke and thinking to myself, 'Thank God I can still see,' " said the 52-year-old Nash, who spent more than two months being treated at St. Francis Memorial Hospital's burn unit, which she praises for saving her life. Nash, who received a $20 million settlement after suing PG&E, said she can't recall the actual explosion and added, "I hope I never do."

Although fires and occasional manhole blasts have plagued PG&E's aging underground electrical gear for decades, the California Public Utilities Commission recently has decided to examine the problems in depth, according to its executive director, Paul Clanon. He said the inquiry is part of a broad look at dangers posed by various industries the commission regulates after the Sept. 9 explosion of a PG&E natural gas pipe in San Bruno, which claimed eight lives and destroyed 38 homes.

"As a result of San Bruno, we've done some soul-searching internally and looking at how we approach all of our safety programs," Clanon said. Given the potential for injury from underground electrical equipment, he added, "it's obviously something that needs attention."

PG&E packs a wide array of its gear into underground compartments -- which range from spaces barely big enough for one person to much-larger cubicles called vaults -- and it's unclear if any single factor other than the equipment's age is causing it to fail so frequently.

No one in the Bay Area has been killed when these chambers erupt, but the events often knock out power to the surrounding area and can be terrifying.

In August, residents around East Capitol Expressway and Silver Creek Road in San Jose reported hearing an explosion and feeling the ground shake from an underground electrical compartment that caught fire. In September 2009, another San Jose incident in the 1900 block of Loch Ness Way spit four-foot flames amid clouds of black smoke and knocked out power to 300 homes. And in September 2005, an underground electrical blast in Berkeley heaved a manhole cover onto a Mercedes, whose driver was injured by an air bag that inflated after the impact.

But the vast majority of the incidents -- and some of the most spectacular -- have occurred in San Francisco, which has the greatest concentration of PG&E's underground electrical devices, according to company officials. Of the 78 incidents the newspaper counted since 2005, 62 were in San Francisco, making its streets at times as seemingly precarious as a minefield.

  • On March 28 of this year, Union Square shoppers were startled when an underground power cable failed, triggering a blast that sent a manhole cover flying on Grant Avenue.

  • On June 24, 2008, an underground explosion near California and Drumm streets blew fragments off two manhole covers, frightening office workers and shaking buildings.

  • On Dec. 18, 2005, a failed electrical switch caused an explosion near Jackson and Locust streets with such force a fire department report said it split a cast-iron manhole cover in half and pushed up a concrete slab.

    The repeated accidents have left some San Francisco officials deeply frustrated.

    After the Aug. 19, 2005, explosion that burned Nash, then-mayor Gavin Newsom warned, "enough is enough, excuses be damned "... If this happens again, PG&E is in real trouble." After another detonation in 2007 reportedly shot flames 6 feet high, the utility formally apologized to Newsom. Yet more accidents occurred, including one the morning after the San Bruno gas-line eruption, prompting Newsom to declare, "I can't accept another."

    Since then, San Francisco has had at least two more mishaps. But Mark Johnson, PG&E's vice president of electric transmission and engineering, insisted his company has been working hard to minimize the incidents. He noted that PG&E spent about $200 million from 2007 to 2009 to upgrade its aged subsurface gear in San Francisco and is installing 350 specially designed manhole covers that won't fly off in a blast.

    "Safety to our employees and the public is our highest priority," he said. "So any time you have a failure, we're concerned about it."

    Underground electrical fires and explosions sometimes result from equipment that short-circuits or when oil leaks from transformers and switches, according to a study by corporate giant Siemens. Another cause is combustible gas that is released by deteriorating electrical cables or filters into the vault from nearby natural gas and sewer lines.

    San Francisco Fire Department spokeswoman Lt. Mindy Talmadge praised PG&E for training firefighters to deal with the accidents and for giving her department special equipment to extinguish electrical fires. She added that the number of such incidents seems to be dropping off. Yet the department's data failed to include 17 incidents the newspaper turned up from news stories, including several reports that indicated that her department had responded.

    The statistics kept by PG&E and the Public Utilities Commission are similarly inconsistent.

    While the newspaper counted 78 Bay Area underground mishaps since 2005, PG&E said before Wednesday's incident that it knew of just 35 throughout its entire service territory, which covers 70,000 square miles from Eureka to Bakersfield. The California Public Utilities Commission -- which only tracks the worst accidents -- said it is aware of 11 PG&E incidents during that period, six for Southern California Edison and none for San Diego Gas & Electric.

    Nationwide statistics also are inconsistent, according to George Gela of the Electric Power Research Institute, who has studied the subject. But while his organization notes in a brochure that "the energy released in a major manhole explosion is equivalent to several sticks of dynamite," Gela said, "your chances of injury in a car are much greater."

    Even so, Nash, who is CEO of Blue Planet Network, which promotes safe drinking water worldwide, said PG&E needs to do more "proactive maintenance" to make sure no one else experiences what she has endured.

    Although she has recovered from the accident, to this day, she said, "I walk around every manhole cover I see."

    Contact Steve Johnson at sjohnson@mercurynews.com or 408-920-5043.