West Virginia ? Federal inspectors have found more than 60 serious safety violations at Massey Energy operations since the explosion that killed 29 miners, adding to fallout from the disaster that includes a wrongful death lawsuit by one of the men’s widows.

Inspectors visited more than 30 underground Massey coal mines in West Virginia, Kentucky and Virginia after the April 5 blast, according to records from the Mine Safety and Health Administration. The agency has tentatively blamed preventable accumulations of explosive methane gas and coal dust for the worst U.S. coal mining disaster since 1970.

The miner’s widow accuses the company of a history of safety violations that amount to negligence in the first wrongful death lawsuit over the explosion, which she filed Thursday.

Investigators were reviewing records from the site of the blast and waiting for dangerous gases to be ventilated before going underground at the Upper Big Branch mine. It will probably be another week until investigators can safely go in, MSHA Administrator Kevin Stricklin said.