A federal safety panel on Tuesday is expected to reveal the results of a yearlong investigation into a natural gas pipeline explosion near San Francisco that killed eight people, incinerated a suburban neighborhood and prompted a national reevaluation of pipeline safety.
Investigators for the National Transportation Safety Board were to lay out their analysis of what caused the Sept. 9, 2010, rupture of a large Pacific Gas & Electric Co. transmission line buried beneath the community of San Bruno, Calif., and how the accident might have been avoided or its consequences mitigated.
The explosion sent a giant pillar of fire into the air that continued to burn like a massive blowtorch for an hour and a half before PG&E employees were able to shut off the flow of gas. Dozens of people were injured and 55 homes destroyed or damaged.
“This is the worst pipeline accident we’ve had in over a decade,” NTSB Chairman Deborah Hersman told reporters Monday.
The board has made public 14,000 pages of information related to the accident. Information already disclosed has raised questions about whether PG&E’s corporate culture put profits ahead of safety, contributing to the accident.
The NTSB has identified a substandard seam weld that went only halfway through the pipe wall as the rupture point. The pipe, installed in 1956, had other substandard welds as well.
PG&E says it didn’t know of the welds because its records incorrectly listed the pipe as seamless. The utility also has been unable to produce other key records regarding the pipeline.
The pipeline also lacked automatic or remotely controlled shut-off valves. If valves on the line had closed immediately after the initial explosion, the gas-fed fire probably would have gone out in under 10 minutes, according to safety experts.
Coroner’s reports indicate at least five of the eight killed were trying to flee when they died. It is unclear based on information released so far whether the deaths of any of the five could have been avoided if different valves were in place, but experts said it was possible – and that others who were injured and homes that were leveled might have been spared.
Four years before the accident, PG&E officials rejected installing more automatic shut-off valves. A 2006 company memo said installing the valves would have “little or no effect on increasing human safety or protecting properties.”
A month after the San Bruno explosion, PG&E wrote California regulators that replacing or retrofitting the current 300 manual values in the company’s network with automatic or remote valves would cost $100,000 to $1.5 million per valve, depending on the difficulty of the installation.
Last week, federal regulators proposed forcing utilities to step up testing of older transmission lines and install more automatic shut-off valves.
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