Pacific Gas and Electric Co. (PG&E) said late Wednesday the ongoing investigation by the National Transportation Safety Board (NTSB) has still not "gotten to the bottom" of the explosion and fire that killed eight people and destroyed 37 homes. The San Francisco-based combination utility pledged to continue to support the investigation.
NTSB's initial assessment lays out the possibility that a glitch at a PG&E terminal in the southern end of San Francisco Bay could have sent a surge of pressure that compromised a section of one of three major 30-inch diameter transmission pipelines that run through the peninsula area south of San Francisco.
"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," said PG&E utility President Chris Johns. "We welcome and appreciate the painstaking efforts of the NTSB experts to conduct a thorough and comprehensive investigation to determine the root cause of this terrible accident."
The American Gas Association (AGA) echoed PG&E's reaction, noting that "important facts" have now been brought out in the preliminary report but "additional testing still needs to be done." The Washington, DC-based trade group for the distribution side of the gas industry said it was "eager" to learn the root cause of the incident.
According to the NTSB's preliminary report, the blast released 47.6 MMcf of gas (see Daily GPI, Oct. 14). The ruptured pipeline was fractured length-wise and at welds that held the pipe sections together, but the report did not mention corrosion. The thickness of the pipe's walls was described in the report as "fairly uniform."
Line 132 that runs from the Milpitas terminal up the peninsula from south to north, was running at a maximum operating pressure of 375 pounds per square inch (psi) on Sept. 9, the day of the blast, the report stated. The maximum allowable operating pressure was 400 psi.
In another sliver of information emerging from the now more than-month-old investigation, PG&E may appear more culpable, and in its response to the NTSB report the private sector utility again "pledged" to customers and government officials to "operate our infrastructure safely and securely," adding that the company intends "to take any and all appropriate steps to ensure we're meeting this fundamental commitment."
Separately, Northwest Natural Gas Co. director for gas supply Randy Friedman told an industry meeting in Los Angeles Wednesday that he thinks the San Bruno tragedy could have a major impact on capital spending in the industry on pipeline maintenance and safety programs."I think the San Bruno explosion will have incredible impacts on the industry in terms of cost and assuring the integrity of our pipelines. That's going to be on the radar, and there could be legislation that impacts costs and operations."
PG&E reiterated that it has re-inspected the three major transmission pipelines that serve the San Francisco Peninsula, and it is in the process of conducting aerial inspections and ground leak surveys of its entire gas transmission system. Although under fire for allegedly holding back information, the utility again said it will "take steps" to share more information about the gas pipeline system with public officials, emergency personnel and customers.
"We continue to extend our support and our sympathies to the San Bruno community and the residential affected by this tragedy," Johns said.
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