CHARLESTON, W.Va. – Tests of methane monitors taken from the scene of the worst U.S. coal mining disaster in decades show the safety devices had not been tampered with before the explosion, the head of West Virginia's mine safety program said Monday.
The monitors were taken from a longwall mining machine near the site of an April 5 explosion at Massey Energy's Upper Big Branch mine. The blast killed 29 miners and injured two.
Methane monitors are designed to shut down mining machines when they encounter explosive levels of gas. State and federal investigators sought the tests following claims by former Massey employees that monitors were routinely electronically "bridged" so machines would keep running.
Officials with Virginia-based Massey have repeatedly denied the allegations.
State Office of Miners' Health Safety and Training chief Ron Wooten said tests conducted over the weekend showed the monitors "had not been tampered with electronically." The tests were conducted at a federal Mine Safety and Health Administration facility.
There were two sensors on the longwall miner and "electronically, everything tested fine," he said.
Shane Harvey, Massey's vice president and general counsel, said the tests verified "these sensors were in working condition and capable of automatically shutting down the longwall in the event that methane readings exceeded safety thresholds."
Wooten said a black box that recorded the longwall's operations showed the machine shutdown 90 seconds before the explosion.
"It could have been because it was the end of the shift. It could have been a problem that they encountered," he said. "I wouldn't read anything in to that."
Wooten said the tests, however, did not disprove allegations that bags were often put over gas monitor sensors to alter their readings. MSHA spokeswoman Amy Louviere said the tampering investigation was continuing.
Massey spokesman Jeff Gillenwater said he was concerned that investigators and safety officials are now floating the bag theory. If MSHA had found any evidence that bags were covering the sensors, it would have noted that and cited Massey, he said.
"There is no evidence that such things have ever occurred," Gillenwater said.
Company officials have discussed the monitors with the victims' families and also shared information about what it says was a sudden surge in methane levels in the mine. Massey has said it believes the methane may have come from a crack in the mine's floor near the site of the explosion.
One methane monitor was reading high, but Wooten said he considered that an anomaly.
"It was the only indication of anything out of the ordinary," he said. "It wasn't that high ... I don't think it's important at all."
Investigators say it may be next year before an official cause of the disaster is known.
Associated Press writers Vicki Smith in Morgantown and Lawrence Messina in Charleston contributed to this report.