Employees were questioned about a 2006 memo that said installing the valves would have "little or no effect on increasing human safety or protecting properties."
Gas engineer Chih-hung Lee, author of the memo, said he considered only industry studies, not government studies, in reaching his conclusions. Industry studies, he said, found that most of the damage in gas pipeline accidents occurs in the first 30 seconds.
When the pipeline ruptured on Sept. 9 in San Bruno, gas continued to feed a pillar of fire for an hour and a half before workers could manually shut off the flow. Eight people were killed, many more injured and dozens of homes destroyed.
NTSB officials say the PG&E line had bad welds. Investigators also found a flawed seam weld on the line, which they identified as the starting point of the deadly explosion.
Keith Slibasager, PG&E's manager of gas system operations, said it took control room employees about 15 minutes following the explosion to figure out what had happened and would have taken about another 15 minutes to shut off the gas using automatic or remotely controlled valves. That's an hour less than it took in San Bruno.
The Associated Press contributed to this story.
