Firefighters had just arrived to investigate the smell of gas when they heard the explosion that shattered windows and sent a garage door flying into the middle of the street.
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The blast triggered the hurried evacuations of about 100 residents, as police went door to door inside apartment buildings. Some left in their pajamas.
VIDEO: Sky7 over natural gas explosion in SF
RAW VIDEO: Gas leak triggers explosion in San Francisco
"They're not even letting us go in to grab our wallets or keys or anything," said Kee Hanumanthagowda, who said she planned to head to a friend's house to shower before going to work.
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Hanumanthagowda said this is the second gas leak in the neighborhood in just a few weeks. The first was in her building, which is across the street from this latest incident.
No one was injured in the explosion, but firefighters say the house where it happened is still not habitable.
"We have been in contact with the building owner. He does have about 8 tenants that will now be getting services from the American Red Cross," said Francis Zamora, a spokesperson for San Francisco's Department of Emergency Management.
While PG&E has hired an outside firm to investigate the cause of the explosion, firefighters offered one theory.
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"I would expect that gas was filling up that garage, and it hit a pilot light, and that's what caused the explosion. There's no other real reason for that," said San Francisco Fire Department Division Chief Rex Hale.
PG&E crews with shovels and heavy machinery scrambled to dig two large holes in the pavement on either side of the explosion, to cap off the gas line from both ends. It took them just over three hours before they gave firefighters the all-clear.
"This was a tedious task that included turning off two valves at an off-site location, as well as digging these two holes behind me, in order for crews to safely access the pipe and stop the flow of gas," said PG&E spokesperson Andrea Menniti, who addressed reporters at the scene as evacuees were returning home.
Menniti said at the height of the incident, 470 customers were without gas. Service has now been restored to most of them, but she said gas will remain off for 120 customers until the investigation is complete.