Thursday night's firestorm in San Bruno brings to mind everyone's need to know how to shut off gas supplies to their own residence.
Officials from the National Transportation Safety Bureau investigating the natural-gas pipeline accidents in San Bruno are working today to trace the origin of the early-evening explosion when a 30-inch PG&E gas pipe ruptured and escaping gas found an ignition source.
A quick glance at a federally issued map of natural-gas transmission lines shows a web of pipelines enmeshing the Bay Area, running underneath cities and suburbs alike.
If your own neighborhood is located over or near one of these underground highways for compressed gas through your own neighborhood, "there's nothing you can do about that," except to leave the area at once and call 911 if you smell gas, said Napa Fire Captain Scott Sedgley.
Even if you live far from a major transmission line, virtually every home has a gas line of its own. Though far smaller — about five-eighths of an inch — residential gas lines can also leak and explode.
"Everybody should know how to turn off their own gas service," Sedgley said. "In case of an earthquake, you should have a wrench and the knowledge to turn off your gas service if you smell gas."
For instructions on turning off residential gas service and other safety tips, PG&E has a page at http://www.pge.com/about/edusafety/. Click on the Gas and Electric safety ink on the left hand rail for more details about how to locate your main gas shutoff valves.
Sedgley, a 25-year firefighting veteran who's seen his share of gas leaks and explosions — though nothing near the magnitude of the San Bruno disaster — said large high pressure natural gas lines were placed in many areas long before homes were built nearby.
"You're not going to put a high pressure gas line in a neighborhood that's already established. It is the same thing with electric transmission," Sedgley continued. "Those lines used to be out and away, but in our quest for new land we start to build up closer to those transmission lines, both electric and gas."
Sedgley also said gas-fed fires can often burn for hours as firefighters often need to let the fire burn itself out.
"It's safer to let it burn," Sedgley said. "The best thing to do is to let it burn until you find the ignition source. Otherwise, you've got all this gas floating around looking for a new source."
Natural gas can only ignite under certain conditions, Sedgley continued: It's explosive when the gas-to-oxygen ratio is from 5 to 15 percent.
"Generally, natural gas is lighter than air, so when it leaks it goes up and floats away and everything is cool; but if it finds an ignition source, you've got a problem," he said.
