Age of pipes blamed for deadly San Bruno gas explosion
Robots called “smart pigs” can inspect new pipelines, and modern pipelines have automated valves that stop gas flow when sensors detect a pressure drop — but the natural gas pipeline in San Bruno, California, is 54-years old; to shut off the old pipeline after the deadly explosion, workers had to retrieve keys and drive to two secured sites 1.5 to 2 kilometers from the fire, then manually crank valves shut
Last week’s explosion of a 54-year-old, 76-centimeter (30-inch) diameter high-pressure natural gas pipeline in San Bruno, California, raises troubling questions about ageing U.S. infrastructure. The explosion and subsequent fire, fuelled by leaking gas, destroyed many houses and killed at least four people, with more deaths suspected.
According to the San Francisco Chronicle, workers from Pacific Gas and Electric, which operated the line, needed two hours to stop the gas flow.
Jeff Hecht writes that modern pipelines have automated valves that stop gas flow when sensors detect a pressure drop. To shut off the old pipeline, however, workers had to retrieve keys and drive to two secured sites 1.5 to 2 kilometers from the fire, then manually crank valves shut.
The company was meant to replace an older section of the same line in 2007, says the Chronicle, but never got around to it. Robots called “smart pigs” can inspect newer pipelines (“Pipe inspecting robot,” 24 June 2008 HSNW), but PG&E said the pipeline had too many twists and turns to accommodate the robot.
Investigators are now trying to find out what caused the explosion. They are examining the ageing pipeline, which is made of 1-centimeter-thick carbon steel buried 1-meter deep. “As things get older, they corrode,” says Theofanis Theofanous, director of the centre for risk studies and safety at the University of California, Santa Barbara.
The pipeline is near the famous San Andreas fault, but Theofanous says that is pretty much unavoidable in California, and anyway the state is riddled with faults. No seismic activity was reported at the time, except for the explosion itself. The environmental awareness group SkyTruth.org has plotted the explosion as being at the edge of a ravine, and speculates that gradual earth movement may have stressed the pipe.
The Los Angeles Times reports that investigators are also looking at whether work on a nearby sewer two years ago may have played a role in the explosion. Any excavation rearranges soil and can lead to settling that causes problems, even without any obvious damage to the pipeline.
