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Feb 6, 2019

PG&E Contains Gas Leak That Caused San Francisco Explosion

By David R Baker and Will Wade

A gas main fire burns out of control in San Francisco on Feb. 6, 2019.
A gas main fire burns out of control in San Francisco on Feb. 6, 2019.
Photographer: David Paul Morris/Bloomberg
Photographer: David Paul Morris/Bloomberg
PG&E Corp. has contained a natural gas leak from a pipe that exploded on Wednesday along a major thoroughfare in San Francisco, engulfing in flames a stretch known for its bars and restaurants.
The blaze, which had spread to at least five buildings as of Wednesday afternoon, triggered an evacuation order for people within a block of the site on Geary Boulevard -- a major artery that leads into downtown San Francisco. Eight workers near the explosion were accounted for and no injuries were reported, San Francisco Fire Chief Joanne Hayes-White told reporters.
Workers may have struck the distribution pipeline while installing fiber-optic equipment beneath the street, she said. Helicopter footage of the fire scene showed a blackened backhoe near the source of the flames. The flames burned for about two and a half hours before the fire department reported that the flow of gas had been shut off.
About 300 PG&E customers were without gas service Wednesday evening, company spokeswoman Melissa Subbotin said. Roughly 2,500 customers lost electricity service, because the flames damaged an overhead power line.
PG&E’s stock plunged as much as 6.3 percent as yet another accident threatened to plague California’s largest utility. Just a week ago, the company declared bankruptcy after being saddled with as much as $30 billion in liabilities from deadly wildfires that its equipment may have ignited in 2017 and 2018. And the utility is still dealing with the consequences of the 2010 San Bruno gas pipeline explosion that killed eight people and leveled 38 homes.
Hayes-White described the explosion and ensuing fire as extensive but noted that it’s “not as extensive” as the San Bruno blast.
The National Transportation Safety Board didn’t immediately say whether the agency is sending a team to the incident. The U.S. Transportation Department’s Pipeline and Hazardous Materials Safety Administration, which regulates pipeline safety, is gathering information on the blast to determine whether it will dispatch investigators, according to a statement.
“PHMSA recognizes the seriousness of this incident and appreciates the work of the San Francisco Fire Department and all first responders,” the agency said.
In the first six years after the San Bruno explosion, PG&E installed more than 230 automatic or remote-controlled valves on its natural gas transmission network, so workers wouldn’t need to manually shut off the flow of gas in an emergency. The company also replaced all the remaining cast-iron pipes in its system with modern plastic and steel pipes.
But the gas line involved in Wednesday’s fire was part of PG&E’s distribution network, a complex web of pipes smaller than the transmission line that exploded beneath San Bruno.
Distribution lines rarely have automatic or remote-controlled valves, said pipeline safety expert Richard Kuprewicz.
Shutting off the flow of gas on a distribution network can be complex, Kuprewicz said. Gas can be flowing from multiple directions, forcing the utility to switch off multiple valves. If some of the lines are small enough, workers can physically crimp them closed.
PG&E would need to take care, Kuprewicz said, not to knock out service to more people than necessary. “You’ve got to know which valves to close to shut off this street and not take out the next street,” said Kuprewicz, president of Accufacts Inc. in Redmond, WA.
PG&E representative Subbotin said the company had to switch off six valves and squeeze shut one four-inch plastic line to stop the gas. She said people had asked why the company couldn’t simply shut down the nearest transmission line with an automatic valve to stop the fire faster.
“Had gas been turned off at the transmission line, that would have shut off nearly the entire city of San Francisco,” Subbotin said.
— With assistance by Alan Levin, and Ryan Beene

Source: Bloomberg

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