Of coal mines and methane


Yesterday, an explosion in the Upper Big Branch Mine in Montcoal, West Virginia, killed 25 miners. Four others are still missing. It's the largest mining disaster the U.S. has seen in decades. The explosion was massive. "Rails used to move heavy equipment inside the mine were left 'twisted like pretzels' by the force and heat of the blast," according to the Washington Post.

Right now, nobody knows what caused the blast, but one likely candidate is a build-up of methane—natural gas—in the mine. I called Christopher Bise, Ph.D., chair of West Virginia University's Mining Engineering department, to find out how methane gets into the mines, why the weather matters for mine safety and how one of the best ways to protect miners from methane can actually improve the mine's bottom line.

Maggie Koerth-Baker: How does methane get into the mines to begin with?
Christopher Bise: Methane is natural gas—colorless, odorless and tasteless. It just flows through sedimentary strata around coal seams and other rock strata. It's just naturally there and it's highly explosive, if the concentration is between 5% and 15%. The most violent explosions happen around 9% methane concentration. In underground coal mines, they try to control it by pumping in vast quantities of air to keep the concentration below 1%.

MKB: Why is it only dangerous in that narrow range?
CB: You need the right mix of methane and oxygen. Just like any other kind of explosion, you need fuel, oxygen and something to ignite it. The methane is the fuel. If you get too much fuel, you don't have the right ingredients for an explosion.

MKB: What about the ignition source? Where does that come from? I'm sure they're pretty careful about open flames down there.
CB: Oh, yes, they're very careful about open flames. But let's say the mining machinery was ripping away at the coal seam and one of the bits happened to strike a rock and make a spark, like a boy scout starting a fire. Sparks occur. That's why all the machinery has detectors on it. If the methane concentration gets above 1.5%, the detectors are supposed to automatically de-energize the equipment. But that's not foolproof. You could get a rush of methane that happens too fast.

MKB: Are there characteristics that make a methane explosion more likely?
CB: Weather can actually play a role. If the atmospheric pressure is lower, more methane comes out of the rock. The depth of the mine also makes a difference. If a coal seam is 1000 ft. down, it's very hard to have the methane travel and be exposed to atmosphere and move out. If a coal seam is close to the surface and outcrops, that's where methane can escape into atmosphere.

MKB: Is there any reliable way to remove methane from coal mines, or is it a fact of life that you can mitigate, but not really control?
CB: Some companies are using a successful approach called coal seam degasification. In advance of opening a mine, they drill the coal seem and drain off the methane. That way they're getting rid of the natural gas and then they turn around and they're selling it. They're producing an energy product rather than wasting it, and they're making the mine safer. Consol Energy is one of the largest coal mining companies, and they also have a gas division and they make a lot of money selling gas drawn off from their gassy coal mines.

For more information on yesterday's disaster, check out this live-chat interview with Jeff Goodell, author of Big Coal: The Dirty Secret Behind America's Energy Future. He's got a lot of insight into the politics side of mine safety.

Vintage postcard image of coal miners comes from the Flickr stream of j3net.