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NTSB official describes blown gas pipeline, course of the investigation in San Bruno explosion and fire

September 10, 2010 | 11:23 pm

At a news conference late Friday in a San Bruno shopping center, Christopher Hart, vice chairman of the National Transportation Safety Board, said he had inspected a length of the transmission pipeline that ruptured Thursday, resulting in the explosion and fire that killed four people and injured more than 50 others.

The piece of pipeline had exploded and was flung onto a road, Hart said.

“A large portion of the pipe was actually blown out of the ground, and it is resting on the street some distance from the hole from which it was blown,” he said. “It is really quite amazing to see this huge piece of pipeline blown the distance it was blown.”

He said he could not say how large the section was or how far it was propelled.

Hart described the pipeline as 30-inch diameter carbon steel with a .375-inch wall thickness. He said it was installed in 1956.

He declined to comment on the average lifespan of such a pipe. “I think that depends considerably with the conditions of operation. I’m not sure there is a specific number that you could call the average.”

Hart said investigators would look into the protocol for replacing a pipeline that old.

He said investigators want to interview witnesses who claimed to smell gas in the weeks before the explosion, but would not speculate on what those reports meant. He said that high-pressure lines are not required to have odor added to help detect leaks and said the probe would determine whether it was.

In addition to the NTSB, Hart said the investigation also will include PG&E, the federal Pipeline and Hazardous Materials Safety Administration and the California Public Utilities Commission.

“We are not here to determine liability or blame,” he said. “We are here to determine the cause of the accident.”

Ravindra Chhatre, the lead investigator, is an expert in metallurgy who has been at the NTSB for a dozen years and has worked for PG&E for about 20 years. Investigators will look at the operation of the pipeline and the qualifications and training of the employees who ran it. 

-- John Hoeffel in San Bruno