Gas pipeline blast probe looks for link with sewer line work

It’s been a week since that natural gas pipeline ruptured in the San Francisco suburb of San Bruno. Four people died in the blast and fire; thirty-seven homes were destroyed. Investigators are taking a look at sewer repairs close to the site of the blast.

A couple years ago, San Bruno city workers replaced part of a sewer line in the Glenview neighborhood. That job happened near the section of the natural gas pipeline that ruptured last week.

San Bruno city work crews replaced a six-inch diameter pipe with a 10-inch one. They used a “pipe-bursting” method that pulls a high-pressure tool through the old pipe and cracks it apart; the tool also drags the new pipe through the bigger hole.

Fred Nesbitt used to live in San Bruno’s Glenview neighborhood.

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"There was a whole lot of pumping going on because these pulses are built up in this machine and they go 'Boom! Boom! Boom!' all day long, and it lasted about a week and a half to two weeks."

Nesbitt says he thinks all that pumping two years ago contributed to the rupture of the natural gas pipeline last week — but that’s just his guess.

At a community forum this week, Christopher Hart with the National Transportation Safety Board told residents they’d look at whether the sewer line “pipe bursting” weakened the gas line — and led to the explosion. But he said investigators will also look whether the gas line was corroded — or failed from fatigue.

"We don’t know whether this fracture resulted from fatigue — where, because of the pressurization changes in the pipe, that caused the pipe to expand and contract and expand and contract repeatedly. Just like you take a coat hanger and bend it back and forth until it eventually breaks." Hart said.

The gas line was installed in the 1950s, when San Bruno’s population was much smaller. Investigators will look at whether Pacific Gas & Electric properly monitored and maintained the pipe.

Fred Nesbitt says he wishes someone had told him about that natural gas line when he was living in Glenview.

The house where he used to live was 200 feet from the section that ruptured; the fireball destroyed it.

Nesbitt wasn’t there because he’d lost the house to foreclosure three weeks earlier. He calls himself the luckiest man in San Bruno.