NTSB Report: Pressure Surge Just Before San Bruno Blast
SAN BRUNO (CBS/AP) – A Pacific Gas & Electric Co. natural gas terminal experienced a power glitch that caused a surge in pressure shortly before a pipeline burst in San Bruno last month, causing a blaze that killed eight people and destroyed dozens of homes, according to a preliminary report released on Wednesday afternoon.
The electrical power drop in the pipeline control system came during maintenance work at a terminal in Milpitas, which is nearly 40 miles from the San Bruno blast site, National Transportation Safety Board investigators found.
"The loss of the electrical signal resulted in the regulating valve moving from partially open to the full open position as designed," their report said.
As a result, the NTSB said pressure increased by 15 pounds-per-square-inch, putting the pipeline above its specified maximum operating pressure, just 11 minutes before the pipeline blast.
The NTSB report did not mention whether any pipe corrosion had occurred, although the agency said scientific tests on pipe sections were continuing. In general, the thickness of the pipe walls was described by investigators as "fairly uniform."
NTSB officials said a more detailed report would be released in the coming months after the pipe tests are completed.
The pipeline rupture on Sept. 9 released 47.6 million cubic feet of natural gas and fires from the escaping gas destroyed a total of 37 houses, according to the NTSB.
PG&E President Chris Johns said the utility welcomed the initial NTSB findings and added that the company was engaged in its own review of critical infrastructure to try and prevent a reoccurance of any San Bruno-type tragedies.
"Since the accident, we've re-inspected the three major pipelines that serve the San Francisco Peninsula. We are in the process of conducting aerial inspections and ground leak surveys of our entire gas transmission system," Johns said.
