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Officials describe immense power of San Bruno explosion

September 11, 2010 |  8:38 am

San Bruno explosion aftermath

Officials described the immense power of the gas pipeline explosion that leveled homes and killed four people in San Bruno, Calif.

The crater left by Thursday evening's explosion in a Bay Area suburb measures 50 feet by 40 feet, San Bruno Fire Chief Dennis Haag said. It's unclear how deep the crater is.

Christopher Hart, vice chairman of the National Transportation Safety Board, said he had inspected a length of the transmission pipeline that ruptured Thursday. 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.

The blast injured dozens of other and ignited fires that destroyed 37 homes in the hilly neighborhood of San Bruno.

The National Transportation Safety Board, which is leading the investigation, and the pipeline owner, Pacific Gas & Electric, said they were looking into reports that residents smelled gas in the days before Thursday's explosion.

Among the dead were a 44-year-old employee of a state agency that oversees the gas industry and her teenage daughter, officials said. Eight people remained hospitalized Friday, including some with severe burns. There were still some badly charred homes to be searched, but fire officials said they had no reports of people still missing.

The blast left a gaping crater in the street above a 30-inch gas transmission line, the sort officials say is used to transport massive volumes of gas to residential and business distribution grids.

The wind-whipped inferno, reaching 1,000 feet high at one point, rapidly spread from house to house as smaller gas lines in the area burst open, officials said. Workers were unable to shut off the fuel supply for at least an hour.

When the smoke cleared Friday, investigators began picking their way past torched homes and burned-out vehicles toward a huge piece of the massive steel pipeline jutting out of the blackened ground. At an evening news conference, the NTSB's Hart said the force of the blast had thrown a large section of pipe out of the ground, an indication of the explosion's power. "It's an amazing scene of destruction," he said.

A final report on the cause of the disaster will not be completed until late next year at the earliest, Hart said. Among the possibilities investigators will probably focus on is possible corrosion of the pipe, which has been a factor in pipeline failures, including the 2000 explosion of a 30-inch New Mexico pipe that killed a dozen people, experts said. NTSB officials said the San Bruno line was installed in 1956.

On Friday, San Bruno police said they were treating the blast site as a possible crime scene until foul play is ruled out.

PG&E officials vowed to cooperate with the federal investigation, but did not say whether the company's pipeline caused the 6:30 p.m. explosion.

"It does everyone a disservice to point fingers before any investigation of the facts has even begun," said PG&E spokesman Andrew Souvall.

-- John Hoeffel in San Bruno

Photo: Scene of the destruction in San Bruno, Calif. Credit: Don Bartletti / Los Angeles Times

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