CHARLESTON, W.Va. -- Teams exploring Massey Energy's Upper Big Branch Mine have found a crack and other damage to the mine floor, evidence that could turn into important clues about what caused the April 5 explosion that killed 29 miners and injured two others, government and company officials said Tuesday.

Massey issued a news release saying a crack had been discovered near the longwall section of the mine and described the crack as among the "potential sources" of methane gas that could have fueled the explosion.

In its prepared statement, Massey linked the crack to incidents in 2003 and 2004 in which methane burst through the floor of the Raleigh County mine, in one instance inundating Upper Big Branch with the explosive gas.

Ron Wooten, director of the state Office of Miners Health, Safety and Training, said his agency was aware of reports that the mine floor had buckled in some places on the "longwall tailgate," a separate set of mine tunnels near the longwall area.

"I had heard that there was some bottom hooving, but I am not aware of any cracks," Wooten said.

Joe Main, assistant labor secretary for the U.S. Mine Safety and Health Administration, refused to answer questions about what floor conditions have been discovered in the mine.

But Main issued a prepared statement that downplayed the importance of any information about the 2003 and 2004 "methane outbursts" at the Upper Big Branch Mine.

"While the air quality in the sections of the mine being worked six years ago may provide some insight, the team's primary focus is on the circumstances occurring in the minutes, hours and months leading up to the explosion," Main said in the prepared statement.

Teams of state and federal officials, along with Massey representatives, have been exploring the Upper Big Branch Mine over the past two weeks. They are checking to ensure the mine is safe, so investigators can enter to begin gathering physical evidence for the probe of the worst U.S. coal-mining disaster in 40 years.

Investigators believe the deadly blast involved an ignition of methane gas, and was probably made far worse by the buildup of highly explosive coal dust. State and federal agencies are conducting closed-door interviews as part of a civil investigation, and a federal criminal investigation is also underway.

Over the past two weeks, investigators have focused on the 2003 and 2004 "methane outbursts" documented in a pair of MSHA reports.

CHARLESTON, W.Va. -- Teams exploring Massey Energy's Upper Big Branch Mine have found a crack and other damage to the mine floor, evidence that could turn into important clues about what caused the April 5 explosion that killed 29 miners and injured two others, government and company officials said Tuesday.

Massey issued a news release saying a crack had been discovered near the longwall section of the mine and described the crack as among the "potential sources" of methane gas that could have fueled the explosion.

In its prepared statement, Massey linked the crack to incidents in 2003 and 2004 in which methane burst through the floor of the Raleigh County mine, in one instance inundating Upper Big Branch with the explosive gas.

Ron Wooten, director of the state Office of Miners Health, Safety and Training, said his agency was aware of reports that the mine floor had buckled in some places on the "longwall tailgate," a separate set of mine tunnels near the longwall area.

"I had heard that there was some bottom hooving, but I am not aware of any cracks," Wooten said.

Joe Main, assistant labor secretary for the U.S. Mine Safety and Health Administration, refused to answer questions about what floor conditions have been discovered in the mine.

But Main issued a prepared statement that downplayed the importance of any information about the 2003 and 2004 "methane outbursts" at the Upper Big Branch Mine.

"While the air quality in the sections of the mine being worked six years ago may provide some insight, the team's primary focus is on the circumstances occurring in the minutes, hours and months leading up to the explosion," Main said in the prepared statement.

Teams of state and federal officials, along with Massey representatives, have been exploring the Upper Big Branch Mine over the past two weeks. They are checking to ensure the mine is safe, so investigators can enter to begin gathering physical evidence for the probe of the worst U.S. coal-mining disaster in 40 years.

Investigators believe the deadly blast involved an ignition of methane gas, and was probably made far worse by the buildup of highly explosive coal dust. State and federal agencies are conducting closed-door interviews as part of a civil investigation, and a federal criminal investigation is also underway.

Over the past two weeks, investigators have focused on the 2003 and 2004 "methane outbursts" documented in a pair of MSHA reports.

Federal regulators concluded at the time that a reservoir of natural gas below the Upper Big Branch Mine might easily be released into the active mining operation. They recommended a series of steps to try to prevent such incidents, or at least to control them, hopefully preventing an explosion or fire.

It is not clear what, if any, of those recommendations Massey followed or what actions MSHA took to force the company's hand. The 2003 and 2004 incidents occurred during the mining of previous sections of the mine with Massey's longwall machine, but investigators are concerned the same natural gas reservoir issues could be linked to the April 5 explosion.

Last week, MSHA removed one agency staffer from a team reviewing MSHA actions at Upper Big Branch because he was the agency's acting district manager in Southern West Virginia when the earlier incidents were investigated.

In its statement Tuesday, Massey alleged that the crack and the previous incidents back up its contention that MSHA wrongly ordered ventilation changes the company said reduced fresh-air flow to the longwall section of Upper Big Branch.

MSHA's recommendations following the 2003 and 2004 incidents had included increasing airflow to that part of the mine.

But the MSHA reports also recommended drilling boreholes into the mine to release methane trapped below the floor -- a strategy that Massey CEO Don Blankenship had rejected as inappropriate for Upper Big Branch.

Longtime mine safety advocate Davitt McAteer, who is conducting an independent probe of the disaster for Gov. Joe Manchin, said investigators will need to measure the crack and damaged floor and take samples to see if the explosion might have occurred in the area.

McAteer said teams already underground were not able to do that because they are not part of the investigation staff, and were instead supposed to be focused on checking the mine for fires and dangerous gases.

"There are lots of facts and they all need to be investigated, and they all will be investigated," McAteer said.

McAteer criticized Massey for selectively releasing information, noting that the company didn't issue a news release when MSHA made public information that showed three weeks before the disaster, Massey had not properly rock-dusted Upper Big Branch to control the buildup of explosive coal dust.

"Selective release of information doesn't help," McAteer said. "It has to be taken with a grain of salt until there is an independent review of it."

Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.