"This hampers the ability of investigators to identify key evidentiary facts that can point to the exact cause of the UBB accident," Harvey said.
Twenty-nine miners were killed, and another nearly so, when the Massey-owned Upper Big Branch mine exploded in April. Investigators have yet to determine the cause of the blast, but experts suspect methane gas and accumulated coal dust contributed.
Massey, which has long had a reputation for putting coal production above worker safety, had racked up dozens of safety violations related to ventilation and coal dust at the UBB mine in the months prior to the accident. Massey has blamed MSHA for forcing the company to alter its vent system, filing a lawsuit against the agency last month.