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Investigators issued a report Tuesday eliminating possible causes of the deadly gas line explosion.
The NTSB found there was no evidence of corrosion, external damages or pre-existing leaks in the portion of a natural gas pipeline that exploded three months ago, killing eight people and destroying 35 homes.
The report said in part, "no physical evidence suggests that a pre-existing leak occurred in the ruptured pipe pieces." The NTSB says it knows what happened, but not why. Officials said the explosion happened after pipeline No. 132, which runs from Milpitas north, "experienced a sudden gas pressure surge."
Rep. Jackie Speier and San Bruno Mayor Jim Ruane made that announcement at a news conference.
The report came with a few things that clearly concerned Speier. For one, it found the 30-inch pipe did have welding seams, which was in contrast to previous claims by PG&E that it was seamless.
"They didn't know what they had under the ground in this location," Speier said. "It troubles me greatly and I think this is one of the issues we have to address swiftly."
And the news Tuesday from the NTSB did not answer the big question: What caused the pipe to explode?
The Los Angeles Times notes that the report found the section in question only had welding on the outside of the pipe. The NTSB was checking into the standard practice for 1956, the year the pipeline in question was installed. The significance of the find was not clear.
A final NTSB report that may or may not have that answer is not expected to be released until next fall.
Experts have said from the beginning that any uncertainties over what caused that section of pipe to burst leaves them concerned about other section of pipe that lie underneath much of Northern California.