The National Transportation Safety Board Wednesday released preliminary findings in its investigation into the rupture of a PG&E gas pipeline that exploded in San Bruno on Sept. 9, killing eight people and destroying dozens of homes.
The NTSB report stated that PG&E was working on a power supply system at its Milpitas terminal that caused a malfunction of a valve system regulating pressure in the pipeline that ruptured just minutes later.
“The electronic signal to the regulating valve for Line 132 was lost,” the report said of the portion of pipeline beneath the Glenview neighborhood, which caused the valve to move from “partially open to the full open position.”
The 30-inch natural gas pipeline that PG&E installed in 1956 had a maximum operating pressure of 375 pounds per square inch gauge, according to the NTSB, and a maximum allowable pressure of 400 psig.
The malfunction of the valve regulation system caused pressure in the San Bruno pipeline to increase to 390 psig just minutes before the rupture occurred at 6:11 p.m.
The explosion that followed the rupture launched a 27-foot, 8-inch portion of pipeline 100 feet into the air and sparked a massive natural gas-fed fireball above the residential neighborhood.
PG&E crews were dispatched to manually shut the “upstream” supply valve at 6:45 p.m., according to the report, and the valve was successfully closed at about 7:40 p.m.
Rep. Jackie Speier, whose district includes San Bruno, reacted to the NTSB report in a statement Wednesday afternoon.
“PG&E did not dispatch crews until 6:45 p.m., 33 minutes after 100-foot-high flames in Glenview were clearly visible from (U.S. Highway) 101, more than 10 miles away,” Speier said. “Why?”
Speier also reacted to NTSB findings that the ruptured section of pipe was determined to be made up of one main section and four smaller pieces that were welded together.
“Four girth welds in the 28-foot section of pipe that ruptured are damning evidence, especially when one of the breaks occurred at a weld,” Speier said.
PG&E President Chris Johns issued a statement welcoming the preliminary NTSB findings.
“Although a final report and a conclusive set of findings are likely to be many months down the road, this initial release of information is an essential first step,” Johns said.
The NTSB is continuing its laboratory analysis on the pipe at a facility in Ashburn, Va.
Speier plans to schedule a briefing meeting later this month with PG&E officials and mayors of 27 cities in San Mateo County.
She also plans to hold a public town hall meeting in San Bruno on Oct. 29 to “hear from PG&E if it will relocate the pipeline away from Glenview, as I have requested, as 88 households have requested.”
“The process is far from over,” Speier said.
Chris Cooney, Bay City News