National Transportation Safety Board investigators questioned Pacific Gas and Electric Company employees at a hearing Tuesday about a company memo that said installing the valves would have "little or no effect on increasing human safety or protecting properties."
Chih-hung Lee, author of the memo, said he considered only industry studies, not government studies, in reaching his conclusions.
After a Sept. 9 explosion in a San Francisco suburb, gas continued to feed a pillar of fire for an hour and a half before workers could manually shutoff the flow. Eight people were killed and dozens of homes destroyed.
