In the months since the explosion, Massey critics have focused on the large number of violations of mine ventilation rules and coal-dust regulations cited at the Upper Big Branch Mine in the months before the disaster.

But MSHA records also include at least 16 violations of rules that require proper calibration of methane monitors. MSHA inspectors repeatedly found monitors that indicated incorrect concentrations of methane and that were not re-calibrated every 31 days as required, the records show.

At least four of those violations -- including two that were cited in September 2009 -- are being examined by federal prosecutors as part of their ongoing criminal investigation at Upper Big Branch, according to records obtained by the Gazette.

If investigators find poor maintenance of mine air monitors a culprit in the Upper Big Branch disaster, it won't be the first time such violations were found following deaths at a Massey Energy mine.

After two miners were killed in the January 2006 fire at the company's Aracoma Alma No. 1 Mine, MSHA investigators found that the battery in a smoke alarm on the mine longwall section was disconnected.

"The unit was originally shipped from the manufacturer with the battery disconnected," MSHA said in its report on the Aracoma fire. "The instruction manual for this unit indicated the battery was to be connected prior to use.

"It was not determined if the battery had been connected during installation, or if the battery had been disconnected some time after installation," MSHA said.

MSHA also found a variety of other problems with the Aracoma Mine's carbon monoxide monitoring system, including the lack of alarms in the 2 Section -- where the miners who died had worked -- and a lack of training for workers who installed and operated the system.

Inspectors concluded the lack of training and the missing monitor in the 2 Section contributed to delays in efforts to evacuate the mine the evening of the fire. Aracoma Coal Co. pleaded guilty to a criminal safety violation for the lack of proper training.

But in September 2009, MSHA inspectors cited Performance Coal for not training Upper Big Branch workers how the same sort of mine "atmospheric monitoring system" works, records show.

"The lack of AMS training greatly increases the hazard of exposure to fire and/or smoke," the MSHA inspector wrote in that citation. "The operator has engaged in aggravated conduct by installing the AMS system without providing training. This violation is unwarrantable failure to comply with a mandatory standard."

That violation is also being examined as part of the criminal probe, records show.

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

Government teams hope to get some answers next week, when they run more detailed tests on a "black box" that recorded data from the mine's longwall section for the six days prior to the April 5 explosion that killed 29 Massey Energy miners.

Investigators are looking closely at the methane monitoring practices at the mine, in part because miners have told them automatic shut-off systems for mining machines were routinely bypassed at the mine, but also because Upper Big Branch had a history of not properly maintaining its monitors.

During the two years prior to the explosion, U.S. Mine Safety and Health Administration inspectors cited Massey's Performance Coal at least 16 times for not meeting deadlines to recalibrate methane monitors so they would measure the explosive gas correctly.

"To me that's just unconscionable on the operators' part," said Kevin Stricklin, MSHA's coal administrator. "They are not respecting methane gas."

Mine safety experts believe the Upper Big Branch blast involved an ignition of methane that was then made far worse by a buildup of highly explosive coal dust. The explosion was the worst U.S. coal-mining disaster in 40 years.

Widespread media accounts, including reporting by National Public Radio, have cited an incident in February in which a miner said a Massey electrician was ordered to "bridge out" the device that would shut off a continuing mining machine if methane levels increased toward the explosive range of between 5 and 15 percent.

Ron Wooten, director of the state Office of Miners Health, Safety and Training, said his agency has gathered evidence that convinces investigators such allegations should be closely examined as the probe continues. Wooten declined to elaborate.

Early this week, Massey CEO Don Blankenship and other company officials held a closed-door meeting in which they told families of the Upper Big Branch miners that evidence has shown that methane monitors in the mine's longwall section were not disabled at the time of the explosion.

Massey believes the blast occurred near the longwall machine because of a large crack in the floor that could have allowed methane to seep into the mine. Upper Big Branch experienced such "methane outbursts" from the mine floor in 2003 and 2004 without any injuries. Neither Massey nor government investigators have said what steps were taken to prevent such an incident from recurring.

After Massey's family meeting, Wooten and state special investigator Davitt McAteer told the Gazette that Massey was premature in drawing conclusions about the methane monitors and that much more work needed to be done on that part of the probe.

Wooten later explained that, despite Massey's statements, the "black box" data had yet to be examined in any detail and that his investigators had not reached a conclusion one way or the other about possible tampering with methane monitors. Wooten also said that a preliminary review of the data revealed no sudden rush of methane gas prior to the explosion, as had been hinted at by Massey officials.

The review also indicated that someone hit the shut-off button on the longwall machine about 90 seconds prior to the explosion, Wooten said.

It's not clear why the machine was shut off. Investigators are considering the possibility that some condition in the mine prompted workers to hit the button. Or, Wooten said, workers may have simply shut down the longwall machine for the scheduled shift change. Workers who could have answered that question were killed in the explosion, Wooten noted.

In the months since the explosion, Massey critics have focused on the large number of violations of mine ventilation rules and coal-dust regulations cited at the Upper Big Branch Mine in the months before the disaster.

But MSHA records also include at least 16 violations of rules that require proper calibration of methane monitors. MSHA inspectors repeatedly found monitors that indicated incorrect concentrations of methane and that were not re-calibrated every 31 days as required, the records show.

At least four of those violations -- including two that were cited in September 2009 -- are being examined by federal prosecutors as part of their ongoing criminal investigation at Upper Big Branch, according to records obtained by the Gazette.

If investigators find poor maintenance of mine air monitors a culprit in the Upper Big Branch disaster, it won't be the first time such violations were found following deaths at a Massey Energy mine.

After two miners were killed in the January 2006 fire at the company's Aracoma Alma No. 1 Mine, MSHA investigators found that the battery in a smoke alarm on the mine longwall section was disconnected.

"The unit was originally shipped from the manufacturer with the battery disconnected," MSHA said in its report on the Aracoma fire. "The instruction manual for this unit indicated the battery was to be connected prior to use.

"It was not determined if the battery had been connected during installation, or if the battery had been disconnected some time after installation," MSHA said.

MSHA also found a variety of other problems with the Aracoma Mine's carbon monoxide monitoring system, including the lack of alarms in the 2 Section -- where the miners who died had worked -- and a lack of training for workers who installed and operated the system.

Inspectors concluded the lack of training and the missing monitor in the 2 Section contributed to delays in efforts to evacuate the mine the evening of the fire. Aracoma Coal Co. pleaded guilty to a criminal safety violation for the lack of proper training.

But in September 2009, MSHA inspectors cited Performance Coal for not training Upper Big Branch workers how the same sort of mine "atmospheric monitoring system" works, records show.

"The lack of AMS training greatly increases the hazard of exposure to fire and/or smoke," the MSHA inspector wrote in that citation. "The operator has engaged in aggravated conduct by installing the AMS system without providing training. This violation is unwarrantable failure to comply with a mandatory standard."

That violation is also being examined as part of the criminal probe, records show.

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