A natural gas pipeline operated by Pacific Gas and Electric exploded in 2010 in San Bruno, Calif., killing eight people and damaging 38 homes.
The National Transportation Safety Board said PG&E didn't know what kind of pipe was beneath San Bruno. A defective weld seam on the pipeline was blamed for the explosion.
PG&E said it completed several of the 12 safety recommendations outlined by the NTSB in response to the 2010 disaster.
"We still have work to do to achieve our ambitious goal but the change that is under way is real and measurable," Nick Stavropoulos, executive vice president of PG&E's gas operations, said in a statement.
PG&E said it completed pressure validation requirements, work procedures for natural gas systems and public awareness measures.
The company said it "will continue making progress" on other NTSB measures, including recommendations that it improves its management program to ensure pipeline safety.
PG&E admitted negligence in the explosion, though its attorneys said mistakes made decades ago charted the disastrous course.
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