Mine safety experts have said the explosion was almost certainly caused by a buildup of methane that was somehow ignited, and then made far worse by accumulations of coal dust underground.
Upper Big Branch had been repeatedly cited for violating its mine ventilation plan and for allowing explosive coal dust to accumulate.
During a Jan. 9 inspection that focused on the misdirected air flow, the unnamed MSHA inspector pulled workers on the affected part of the mine aside and asked them about the problem.
"[The workers] informed me that they questioned management about this condition and they were told it was fine, not to worry about it," the MSHA inspector said.
The workers told the inspector they had questioned Performance Coal President Chris Blanchard and company Vice President Jamie Ferguson about the ventilation issue.
Moore, the mine foreman, told the inspector the problem had existed since he took over that job three weeks earlier.
The violation was fixed later that day, but MSHA inspectors cited the company for "unwarrantable failure" to follow safety rules and fined the company $70,000, according to agency records.
"Mr. Moore engaged in aggravated conduct constituting more than ordinary negligence in that he was aware of the condition" for three weeks without making sure it was fixed, the MSHA citation said.
Massey has defended its safety record and company CEO Don Blankenship has said "any suspicion that the mine was improperly operated or illegally operated or anything like that would be unfounded."
In a prepared statement, Massey has also said, "We do not condone any violation of MSHA regulations, and we strive to be in compliance with all regulations at all times."
But during one inspection in early January, mine official Gary May complained that MSHA "comes in here expecting the worst and not giving them the benefit of the doubt," according to the inspector's notes.
"I explained to him that I would be writing what I saw," the inspector added.
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.