The most recent accident was in Allentown, Pa., on Feb. 9, but the board had to leave that one to the state authorities, because the accidents have come faster than its four pipeline specialists can investigate them. That explosion killed five people.
It is also looking into accidents in Florida, Illinois, Michigan and Texas. The board has not identified a common thread, but the chairwoman, Deborah A. P. Hersman, said last week that one obvious fact is that the average age of pipelines is rising rapidly.
“Fifty percent of the pipeline infrastructure is at least 30 years old, around the country,” Ms. Hersman said. “The fact that a pipeline is aging is not necessarily a problem, but you need to be sure you’re doing the due diligence.” That was true no matter the age of the pipe, she said.
The pipe in San Bruno, south of San Francisco, was laid around 1956. Age may be a factor, but so may errors made when the pipe was laid. Records kept by the utility, Pacific Gas & Electric, showed that the pipe had no seam; it was extruded in a pipe shape, rather than formed from a flat plate bent into a circle. But the pipe dug out of the ground shows a seam with possible welding problems.
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