The September 9, 2010, explosion and fire in San Bruno killed eight people, injured dozens more and destroyed or damaged more than 100 homes.
The NTSB posted online its 140-page report and a 20-minute video, pulling together information gathered in a yearlong investigation of the Sept. 9, 2010, explosion and fire in San Bruno, Calif. Escaping gas fed a pillar of flame 300 feet tall for more than 90 minutes before workers were able to manually close valves that cut off gas to the ruptured pipeline.
The board unanimously agreed at a meeting last month that the accident was caused by what NTSB chairman Deborah Hersman called "a litany of failures" by PG&E, one of the nation's largest gas companies, as well as weak oversight by regulators. She called the explosion the nation's most significant pipeline accident in the last decade, not only in terms of its destructiveness, but also for the significant safety lapses it revealed.
The report finds events that led up to the accident began more than 50 years ago with the installation of substandard pipe with inferior welds. PG&E didn't discover the problem because it failed to conduct proper pressure tests or visual inspections of the pipeline. Key records relating to the pipeline's origin are missing. Other records incorrectly describe the section pipe that ruptured as being seamless rather than welded, which led the gas company to place a maximum gas pressure limit on the line that was too high for the pipe to withstand.
As a result of the accident, the board has issued 39 safety recommendations to PG&E, gas pipeline operators, and federal and state regulators. But a safety advocate who has followed the case said it's not clear whether Congress and federal regulators will embrace some of the more significant recommendations.
The Associated Press contributed to this report.