Wednesday, September 22, 2010
PG&E exceeded its own maximum pressure standard at San Bruno
SAN FRANCISCO, Calif. - Federal investigators have determined that the natural gas in the Pacific Gas & Electric pipeline that exploded in San Bruno was running at a higher pressure than the maximum limit PG&E has told the public it maintained.
At the time of the explosion, the utility's computers showed that the gas was at least 386 pounds per square inch. PG&E spokesman Jeff Smith said on Sept. 16 that the maximum the company operated the line at was 375 psi, a figure that PG&E Vice President Geisha Williams also cited in a news conference on Sept. 13.
Overpressurized lines have been a cause of explosions in other pipeline
On Sept. 17, Smith said PG&E could not discuss the exact pressure in the 30-inch transmission line at the time of the explosion because it is under review by the National Transportation Safety Board.
Smith noted that the pipe had a "maximum allowable operating pressure" of 400 psi.
Pipeline safety experts said the fact that the pressure in the pipe exceeded PG&E's maximum pressure level is not automatically cause for alarm. But they said if the pipe had flaws - such as corrosion or cracked welds - running the pressure close to the limit could be a significant factor in the explosion.