CHARLESTON, W.Va. -- A federal official says a handheld meter found deep inside the Upper Big Branch mine detected explosive levels of methane before a blast killed 29 miners -- the first concrete evidence of dangerous concentrations of gas ahead of the April 5 disaster.
The meter detected 5 percent methane in the Raleigh County mine's atmosphere, Mine Safety and Health Administration official Kevin Stricklin told The Associated Press.
The find could be significant because methane isn't explosive unless it makes up 5 percent to 15 percent of the atmosphere. While a preliminary report issued by MSHA in April blamed methane and coal dust for the explosion, investigators continue to scour the underground mine to find where the blast started and what may have caused it.
Richmond, Va.-based Massey Energy Co., the mine's owner, has said high levels of methane may have poured into the mine and overwhelmed safeguards just before the explosion.
General counsel Shane Harvey said the monitor shows the mine's methane level going from zero to 5 percent in 3 minutes. "That's the reason we believe, one of the reasons, we believe there's a sudden inundation of methane."
Previously, MSHA had said only that methane monitors from the mine hadn't been tampered with before the explosion. Former Massey employees claimed it was routine to electronically "bridge" machine-mounted monitors to prevent them from cutting power if they detected methane approaching dangerous levels.
Investigators found the handheld meter in an area near six bodies recovered near the mine's longwall mining machine, Stricklin said. It was found several weeks ago and has been tested by the agency.
Investigators hoped to search the area again as soon as Thursday for more handheld gas meters. They should have found at least one more meter because miners routinely carry the devices, among other things, Stricklin said.
MSHA suspects the missing devices could be buried under loose rubble.
"We expected to find at least two remotes and we only got one," Stricklin said. "The one detector that we found was the one detector that had seen 5 percent of gas."
The Upper Big Branch explosion near Montcoal was the worst U.S. coal mining disaster in 40 years. Besides the civil investigation, it is the subject of a federal criminal probe directed by the U.S. attorney's office in Charleston.