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Federal investigators start examining San Bruno gas explosion

September 11, 2010 |  9:28 pm

Federal accident investigators on Saturday completed their first full day probing the natural-gas explosion that killed at least four people in San Bruno, releasing a series of measurements that underscored the extraordinary power of Thursday’s blast. 

Christopher Hart, the vice chairman of the National Transportation Safety Board, said a 28-foot section of pipe was propelled about 100 feet from a crater that was167 feet long and 26 feet deep. Investigators could not measure the depth, he said, because the bottom was unstable.  

“It was blown quite a distance,” said Hart.  

The NTSB is the lead agency on an investigation that will also include Pacific Gas & Electric Co., which owns and operates the 30-inch-diameter pipeline; the federal Pipeline and Hazardous Materials Safety Administration; and the California Public Utilities Commission.  

Hart said the investigation will consider whether automatic shutoff values should be required on transmission pipelines that run through residential areas. “That is one of the questions that we’ll be looking at,” he said. Hart said the valves on either side of the explosion were manual.

Investigators had found some circumferential welds that indicated the pipe was made from subsections. Hart said that did not necessarily mean the section was repaired. And he said the welds did not mean it was more at risk of rupturing. “It depends on circumstances,” he said.

PG&E did add odor to the gas that traveled through the pipeline, he said. He had said several times that residents reported smelling gas in the days before the explosion. PG&E said earlier Saturday that it had not yet found any record of customer complaints or crews responding. 

The NTSB has set up an e-mail address -- sanbruno@ntsb.gov -- to encourage residents and witnesses to contact the agency, which is expected to take from 14 to 18 months to complete its final report.  

“We’d welcome them to provide further information,” Hart said.

-- John Hoeffel in San Bruno

Photo: Inspectors from the Department of Transportation and the Public Utilities Commission huddle with a PG&E inspector over a portion of the pipeline that exploded and landed in the street about 100 feet away. Credit: Don Bartletti / Los Angeles Times