By Kevin Fagan
The San Francisco Chronicle
SAN FRANCISCO — Putting out a big natural gas fire is a bit like trying to swat down a barn fire with a squirt gun, experts say — it’s just about impossible to do it quickly.
The best way to attack a blaze from a ruptured gas line, such as the one that destroyed a San Bruno neighborhood Thursday night, is to crimp off the fuel source enough to be able to douse it with chemical retardant, fire industry guidelines say. But until then, firefighters are initially stuck trying to contain the damage.
The trouble is that in a street gas line, the pressure of the fuel whooshing through the pipe and the volatility of the gas is too much for firefighters to handle. That’s what appeared to be the case for two hours after Thursday’s explosion, while the flames jumped from home to home.
“In something that big, you can’t put the gas out,” said Albany Fire Chief Marc McGinn, who sent a strike team Thursday evening to help in San Bruno. “If it’s a small line, like from a house, you might cap it. But a house line has maybe half a pound of psi pounds per square inch coming through it — in a street line, it’s more like 200 psi.”
Normal firefighting procedure is to attack a natural gas fire with dry chemical or foam extinguishing agents. Pouring water directly onto the gas is not an effective weapon.
“You have to put a natural gas fire out at the source by shutting off its fuel,” McGinn said. “You might be able to extinguish the flames without doing that, but the gas will still be venting and can catch on fire again when it encounters something that ignites it.”
Natural gas causes an average of about 2,000 home structure fires every year, according to the National Fire Protection Association.
Copyright 2010 San Francisco Chronicle