The National Transportation Safety Board's interim report on the Sept. 9 natural-gas pipeline rupture and explosion that killed eight people in San Bruno, Calif., focuses on defective pipe welds as a cause of the blast.
Owner Pacific Gas & Electric’s records indicate the pipeline was seamless, but NTSB's report, released on Dec. 14, says a portion near the rupture was seam-welded. The report rules out external corrosion and damage caused by a third party as reasons for the explosion.