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.

To tally violations at other Massey sites, The Associated Press checked inspection records for all of the company's approximately 70 underground coal mines in the U.S. from April 5 through Thursday. Mines operated by other companies also were inspected during the same period.

Stricklin said the MSHA hasn't been disproportionately targeting Massey since the blast, nor has it increased the pace of inspections. He did say inspectors have responded to hazard complaints at two Massey mines.

"We're just going about our regular business," Stricklin said. "I didn't give any instructions to go and look at Massey mines."

Still, Stricklin sharply criticized the company for violations found in the last 10 days.

The violations include conveyor belt problems at Massey's Aracoma Alma No. 1 mine in West Virginia, where a belt fire killed two men in 2006.

"I'm very disappointed," Stricklin said. "You would think that personnel associated with Massey would be really more careful."

The company's Solid Energy No. 1 mine in Kentucky was cited for allowing coal dust to pile up on three occasions since the explosion.

"That's very troubling," Stricklin said. "Pitiful."

Mines are required to keep methane well below explosive levels with sophisticated ventilation systems and control coal dust by keeping it from piling up and covering it with noncombustible material.

Stricklin has told district managers to look more closely at all mine ventilation systems and the buildup of methane, and to move rock dusting surveys to the front end of the quarterly inspection.

Stricklin said he was embarrassed the industry wasn't able to prevent the Upper Big Branch tragedy.

"An explosion of this magnitude basically sends us back 40 years. All explosions are preventable," he said.

Massey is facing its first wrongful death lawsuit over the blast, filed by Marlene Griffith in Raleigh County Circuit Court. The lawsuit also targets Performance Coal, the Massey subsidiary that operated the underground mine.