August 2011, Vol. 66 No. 8
Features
City of San Bruno Disputes Panel’s Report Blaming Pipe Bursting
A California blue ribbon panel’s report blaming a 2008 sewer pipe bursting project for the natural-gas pipeline explosion that killed eight people in San Bruno, CA, was poorly researched, unsubstantiated and ignored more likely explanations, according to city of San Bruno officials.
San Bruno’s comments were in response to the panel’s report submitted to the California Public Utilities Commission in June. City attorneys filed a response with the state in mid-July claiming the report contained “numerous omissions and erroneous conclusions.”
The five-member panel assembled by the California Public Utilities Commission consisted of academics, attorneys and business leaders working with expert consultants, concluded that construction work to replace a sewer pipe was the “most likely” cause of increased stress on a nearby PG&E gas line running beneath a San Bruno neighborhood — stress that weakened the faulty welds in the pipe that 16 months later exploded, killing eight people and destroying 38 homes. Ground shaking from the work “could have played a key role in transforming a ‘stable’ threat to an ‘unstable’ threat, thus triggering the incident.”
Determining the final cause of the accident still rests with the National Transportation Safety Board, whose report is not expected until fall; the panel’s report has no formal authority.
Results recanted
Ironically, one of the panel’s expert consultants recanted his earlier conclusions shortly after the report was submitted, citing newly discovered details of the gas line’s operating history.
Robert Nickell originally determined that vibrations from the June 2008 sewer pipe bursting project had probably weakened the nearby Pacific Gas and Electric Co. gas transmission pipeline and led to its failure more than two years later. He downplayed the possibility that gas-level fluctuations alone over the years had weakened a poorly constructed seam weld enough so that it finally failed on Sept. 9, 2010.
However, Nickell now says that information contained in hundreds of thousands of documents that PG&E released to the state in July has led him to alter his conclusion. Originally, the gas pressure fluctuations were believed to be only in the 350 – 400 psi range. New information supplied by PG&E now reveal that over the life of the pipeline, gas pressure fluctuations widely varied between 125 and 350 psi. The forces exerted on the pipeline would have been especially damaging if the pressure levels changed often, Nickell observed.
San Bruno attorneys added that the panel incorrectly blamed the sewer project without even interviewing the sewer contractors, reviewing the project specifications or talking to San Bruno engineers who signed off on the work.
Instead, the state-chartered panel relied on a gas industry group’s report, the Interstate Natural Gas Association of America (INGAA), that incorrectly described the scope of the sewer project, plus the findings of a consultant who did not know all the facts, the city claims.
In May, INGAA, whom PG&E joined after the San Bruno blast, suggested pipe bursting as the likely cause. However, the industry group dismissed vibrations from the sewer pipe bursting as being a factor in weakening the PG&E line. Instead, it said forces exerted by a winch used to operate the sewer equipment – and a pulley braced against a pit wall near the gas pipe – had pushed against the PG&E line and bent it out of a round.
A Texas pipeline integrity expert and consultant, Royce Don Deaver, challenged that finding. He said he had modeled the actions of the winch and pulley against the wall and that the actual forces had been negligible, amounting to no more than the load of a 250-pound person standing on one foot.
When queried by local media, the blue-ribbon panel did not defend its original finding. Instead, it alluded to failures by both PG&E and regulators to ensure safety.
Testimony omitted
Further, the city of San Bruno claims that if the state panel had interviewed the sewer project’s contractor, D’Arcy and Harty Construction of San Francisco, it would have learned that the company took standard steps to ensure that workers would not damage the PG&E line.
PG&E, which has issued a public apology for the natural gas explosion in San Bruno, said in an initial court filing in early July that it should not have to make payouts to victims who have sued the company because the blast was caused by third-party damage to a “state of the art” pipeline.
The company also indicated it would seek to assign some of the blame for the losses from the explosion to residents themselves.
PG&E quickly back-pedaled within a week of that filing and assured victims of the San Bruno natural gas pipeline explosion that it did not intend to argue in court that they were to blame for losses they suffered in the disaster.
The company amended its earlier filing and said it wanted to be “crystal clear that no one at PG&E would suggest that the plaintiffs or residents of San Bruno impacted by this accident are somehow at fault for the tragedy.” The amended filing says the company “does not blame the plaintiffs and residents who have been affected by this terrible accident.”
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