CHARLESTON, W.Va. (AP) -- Federal investigators say a small methane gas ignition fueled by excessive coal dust that piled up at Massey Energy Co.'s Upper Big Branch mine caused the April 5 explosion that killed 29 miners.
The Mine Safety and Health Administration revealed the findings Wednesday.
MSHA says Massey also was running the mine's main cutting machine with missing water sprayers, which help control dust and douse small methane ignitions before they turn into explosions.
MSHA official Kevin Stricklin says there's no evidence supporting Massey's theory that a massive burst of gas from a floor crack that overwhelmed safeguards.
MSHA's final report is due in two to three months. Federal prosecutors continue a separate criminal investigation.
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