For example, Main told the families the longwall shearer "was totally out of compliance," according to several people who attended the family meeting. But Main repeatedly declined to characterize for reporters what the evidence uncovered so far said about how well Massey protected its workers.

"Once we conclude our full investigation, we'll be laying out the facts as we find them," Main said.

Still, the picture painted by MSHA officials Wednesday directly contradicted in many ways the theory that Massey Energy has tried to promote: That a huge, uncontrollable burst of methane -- with no coal dust involved -- caused a horrific explosion that overwhelmed any safety systems Massey could have had.

Massey officials have tentatively scheduled their own meeting with the miners' families for Friday at a Charleston hotel. Shortly before retiring, former Massey CEO Don Blankenship had promised the company would release more information to back up its theory.

"Our findings are different than MSHA's working theory, as we understand it," said Massey general counsel Shane Harvey. "We do not currently believe that there were issues with the bits or the sprays on the shearer that contributed to the explosion.

"We likewise do not believe that coal dust played a meaningful role in the explosion," Harvey said. "We currently believe that the mine was well rock dusted and that the mine exploded due to an infusion of high levels of a natural gas."

But MSHA released some evidence Wednesday that the agency said directly contradicted Massey's theory.

For instance, MSHA investigators said that they found no evidence of a major explosion on the "tailgate" end of the longwall face area. That's the part of the mine where Massey has pointed to a large floor crack it believes allow a huge influx of methane into the mine.

MSHA investigators believe the lack of such evidence supports their view that a smaller ignition of a smaller volume of methane occurred on the longwall tailgate, and then expanded through the mine, following a trail of coal dust.

Previously, the agency had publicly said that roughly 80 percent of the 1,800 samples taken showed inadequate "rock-dusting" to control explosive coal dust. Massey disputes the agency's testing procedures and the results.

MSHA investigators believe miners working in the longwall section on April 5 received some sort of warning -- either a spiked methane detector or, more likely, the actual ignition -- and shut down the shearer's power and water supply in an effort to stop any machinery that might make cause and explosion.

At least two of the workers appear to have tried to exit the area, making it 400 to 500 feet from the shearer to the middle of the longwall face in less than 90 seconds before the larger blast erupted, investigators said.

Stricklin said that MSHA is now investigating a report from a family member who says he was in the mine office at about 3 p.m., just minutes before the explosion, when the longwall section workers called to report such a problem. Massey has not produced any records of such a call, Stricklin said.

MSHA officials declined to answer specific questions about what sorts of ventilation changes Massey may have made at the mine, but said it is looking into whether such changes were made over the Easter weekend just before the explosion.

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

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CHARLESTON, W.Va. -- Mining bits on the longwall machine were worn out, exposing steel shafts that could easily spark when they hit a piece of rock embedded in the coal seam. Key water sprays were missing or inoperable, leaving miners without an important protection against methane ignitions.

Mine operators ignored repeated warnings from their own workers to spread more crushed stone, or rock dust, to prevent coal dust that had built up along miles of underground tunnels from providing fuel for an explosion.

Federal investigators on Wednesday outlined these allegations as the likely factors that combined to produce the huge explosion that killed 29 miners in April 5 at Massey Energy's Upper Big Branch Mine.

U.S. Mine Safety and Health Administration officials provided the most detailed media briefing to date on their investigation into the worst U.S. coal-mining disaster in nearly 40 years.

MSHA released a lengthy slide presentation outlining the agency's major evidence. They made public video of tests the agency said clearly showed major problems with the water spray system on the cutting tool, or shearer, on the Raleigh County mine's longwall mining machine.

"The investigation is still ongoing, and we have a large number of pieces of evidence to evaluate to provide a more clear picture of what happened," said Joe Main, assistant labor secretary for MSHA. "But you can see from some of the evidence that there are some problems here we clearly should be looking at."

MSHA coal administrator Kevin Stricklin and Labor Department Solicitor Patricia Smith joined Main for a media briefing held the morning after government officials provided families of the fallen Upper Big Branch miners their first in-person briefing in four months.

Agency officials told families that a report would be issued within 60 to 90 days. They said witness interviews are finished, except for some people who will be asked to return for more questioning and for 18 people who invoked their Fifth Amendment rights and refused to testimony.

MSHA officials also defended their agency when asked how conditions at Upper Big Branch could have deteriorated to the point that multiple safety systems aimed at preventing just such a disaster were in such bad shape that they failed to protect Massey's workers.

Stricklin noted that MSHA inspectors had written hundreds of violations and issued more serious mine closure orders at Upper Big Branch than at any other mine in the months prior to the explosion.

"Based on the numbers I've seen, I think my folks were enforcing the law here," Stricklin said.

The media briefing also was held just days after MSHA confirmed it had agreed to a request from federal prosecutors to delay any public hearings or the release of witness interview transcripts to avoid jeopardizing U.S. Attorney Booth Goodwin's ongoing criminal investigation of the disaster.

Smith, the agency's top lawyer, said she didn't ask Goodwin for examples of how releasing witness testimony of discussing the disaster in a public hearing would hamper his criminal probe. So far, no charges have been filed against anyone in connection with the explosion.

During Wednesday's briefing, MSHA provided the media and the public with essentially the same information released Tuesday night during a closed-door meeting with the disaster victims' families. But agency officials were more cautious in their media comments.

For example, Main told the families the longwall shearer "was totally out of compliance," according to several people who attended the family meeting. But Main repeatedly declined to characterize for reporters what the evidence uncovered so far said about how well Massey protected its workers.

"Once we conclude our full investigation, we'll be laying out the facts as we find them," Main said.

Still, the picture painted by MSHA officials Wednesday directly contradicted in many ways the theory that Massey Energy has tried to promote: That a huge, uncontrollable burst of methane -- with no coal dust involved -- caused a horrific explosion that overwhelmed any safety systems Massey could have had.

Massey officials have tentatively scheduled their own meeting with the miners' families for Friday at a Charleston hotel. Shortly before retiring, former Massey CEO Don Blankenship had promised the company would release more information to back up its theory.

"Our findings are different than MSHA's working theory, as we understand it," said Massey general counsel Shane Harvey. "We do not currently believe that there were issues with the bits or the sprays on the shearer that contributed to the explosion.

"We likewise do not believe that coal dust played a meaningful role in the explosion," Harvey said. "We currently believe that the mine was well rock dusted and that the mine exploded due to an infusion of high levels of a natural gas."

But MSHA released some evidence Wednesday that the agency said directly contradicted Massey's theory.

For instance, MSHA investigators said that they found no evidence of a major explosion on the "tailgate" end of the longwall face area. That's the part of the mine where Massey has pointed to a large floor crack it believes allow a huge influx of methane into the mine.

MSHA investigators believe the lack of such evidence supports their view that a smaller ignition of a smaller volume of methane occurred on the longwall tailgate, and then expanded through the mine, following a trail of coal dust.

Previously, the agency had publicly said that roughly 80 percent of the 1,800 samples taken showed inadequate "rock-dusting" to control explosive coal dust. Massey disputes the agency's testing procedures and the results.

MSHA investigators believe miners working in the longwall section on April 5 received some sort of warning -- either a spiked methane detector or, more likely, the actual ignition -- and shut down the shearer's power and water supply in an effort to stop any machinery that might make cause and explosion.

At least two of the workers appear to have tried to exit the area, making it 400 to 500 feet from the shearer to the middle of the longwall face in less than 90 seconds before the larger blast erupted, investigators said.

Stricklin said that MSHA is now investigating a report from a family member who says he was in the mine office at about 3 p.m., just minutes before the explosion, when the longwall section workers called to report such a problem. Massey has not produced any records of such a call, Stricklin said.

MSHA officials declined to answer specific questions about what sorts of ventilation changes Massey may have made at the mine, but said it is looking into whether such changes were made over the Easter weekend just before the explosion.

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