Today the five-member National Transportation Safety Board cited a California utility operator’s lax approach to pipeline safety and the inadequate oversight of two government agencies in the probable cause of the most devastating pipeline accident in a decade.

“Our investigation revealed that for years, PG&E exploited weaknesses in a lax system of oversight,” said NTSB Chairman Deborah A.P. Hersman. “We also identified regulators that placed a blind trust in the companies that they were charged with overseeing to the detriment of public safety.”

The nearly year-long NTSB investigation revealed that PG&E did not know what kind of pipe it had installed beneath the city of San Bruno in 1956. PG&E records initially provided to NTSB investigators indicated that the ruptured section of pipe was a 30″ seamless pipe when in fact, at the time, no manufacturer produced seamless pipe.

Investigators also determined that the ruptured section of pipe was a collection of short pipe pieces, commonly known as “pups,” joined together with welds. Further metallurgic assessment by NTSB investigators determined that some of the pipe sections did not meet minimum material specifications and that the welds were poorly constructed.

The defective welds would have been visibly detectable at the time of the installation, but, because of PG&E’s inadequate quality control during the construction project and its failure to maintain accurate records, the poorly welded section of pipe went undetected for over 50 years. Failure of one of the improperly welded seams caused the Sept. 9, 2010, rupture during an increase in pressure resulting from repair work being performed at a terminal upstream of the rupture site.

At about 6:11 p.m. (PDT) on September 9, 2010, a 30-inch diameter segment of a natural gas transmission pipeline, owned and operated by PG&E, ruptured in a residential neighborhood in San Bruno, California. The force of the rupture ejected a 3000-pound 28-foot-long section of pipe about 100 feet from where it had been buried four feet underground. The released natural gas ignited into a towering fire that destroyed 38 homes and damaged 70. As a result, eight people were killed, dozens were injured, and many more were evacuated from the area and displaced from their homes.

The Board determined that the accident was clearly preventable stating that PG&E’s inadequate pipeline integrity management program failed to identify, detect, and remove the substandard pipe segments before they ruptured.

“This tragedy began years ago with PG&E’s 1956 installation of a woefully inadequate pipe,” said Chairman Hersman. “It was compounded by a litany of failures – including poor recordkeeping, inadequate inspection programs, and an integrity management program without integrity.”

In its examination of the history of oversight of PG&E, the NTSB found that two key regulatory decisions (one by CPUC in 1961 and one by PHMSA in 1970), which “grandfathered”, or exempted, older pipelines from the testing protocols required of newly constructed ones, allowed the flawed pipe to escape detection.

The Safety Board found that CPUC, did not effectively evaluate or assess the safety of PG&E’s integrity management program. On the federal side, the NTSB said that PHMSA’s grandfathering of pre-1970 pipe contributed to the accident.

“For government to do its job – safeguard the public – it cannot trust alone, it must verify through effective oversight,” said Hersman. “As we saw in San Bruno, when the approach to safety is lax, the consequences can be deadly.”

At the meeting today, the NTSB made a total of 29 safety recommendations to PG&E, CPUC, PHMSA, the American Gas Association, the American Petroleum Institute, the Gas Technology Institute, the Interstate Natural Gas Association of America, the International Association of Fire Chiefs, the International Association of Firefighters, and the National Volunteer Fire Council.

During the course of the investigation, the NTSB issued 10 safety recommendations (six of them classified as urgent) to PG&E, PHMSA and CPUC to address issues in record-keeping, information sharing, pipeline testing, and emergency preparedness and notification procedures.

A synopsis of the NTSB report, including the probable cause, conclusions, and a complete list of all the safety recommendations, is available. The NTSB’s full report will be available on the website in several weeks.