On Aug. 30, the National Transportation Safety Board issued its final report on the fatal pipeline explosion in San Bruno, CA, that occurred on Sept. 9, 2010. The report named Pacific Gas & Electric’s “lax approach to pipeline safety” and the failure of overseeing bodies to check that approach as the main factors in a preventable accident.
While some tried to pin the accident’s cause on a sewer pipe bursting project from more than 18 months earlier, the NTSB apparently found no connection and pipe bursting was excluded as a contributing factor in their report.
The 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-inch 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. Failure of one of the improperly welded seams caused the rupture during an increase in pressure resulting from repair work being performed at a terminal upstream of the rupture site.