NY Times: Methane, a Common Danger of Coal Mines

[Omaha Steve]

http://www.nytimes.com/2010/04/07/science/07methane.html

By MATTHEW L. WALD Published: April 6, 2010

Coal mines will always have methane, often in explosive concentrations, geologists and engineers say. The only question is how diligently miners and mining companies will work to avoid explosions.

Though there is no definitive proof yet that it was a methane explosion that killed 25 miners in West Virginia on Monday, miners have said the gas has been a constant problem there, leading to several evacuations in recent months and a history of violations.

The gas, like coal, is a molecule made of hydrogen and carbon, and it is produced from the same raw material as coal, ancient piles of biological material, by the same processes. Much of the natural gas sold in the United States is drawn from coal seams.

In undisturbed coal deposits, the methane is loosely attached to the coal molecules when the deposit is under pressure; when the area is opened up by miners, the pressure is reduced and the methane bubbles out.

“Methane is ubiquitous on the coal mines,” said Neville A.H. Holt, a chemical engineer and researcher at the Electric Power Research Institute, in Palo Alto, Calif.

Often, the deeper the mine, the more pressure is released in mining and the more methane is freed. The Upper Big Branch mine, where the explosion occurred on Monday, is more than 1,000 feet deep.

Methane has no smell. It is the main ingredient of natural gas, but the smell that consumers associate with natural gas is actually a chemical added by the gas company to make leaks obvious. Humans cannot sense methane itself, although at times it is present with another gas, hydrogen sulfide, that has an evident stink. But because the methane is often pure, miners long ago began carrying canaries to work with them, knowing that when the birds showed signs of distress it was time to get out.

FULL story at link.