BECKLEY, W.Va. (AP) — Federal investigators are looking into allegations that Massey Energy Co. illegally warned workers when safety inspectors arrived at its operations, the head of the federal Mine Safety and Health Administration said Monday.

Relatives and colleagues of 29 West Virginia miners killed in the nation's worst coal industry disaster in 40 years made the allegations Monday before the U.S. House Education and Labor Committee, where they described the Upper Big Branch mine as a disaster waiting to happen.

Massey used codes to warn workers when regulators showed up, said Gary Quarles, whose son Gary Wayne Quarles died in the explosion.

"When an MSHA inspector comes onto a Massey mine property, the code words go out, 'we've got a man on the property,'" Quarles testified. "Those words are radioed from the guard gates and relayed to all working operations in the mine."

After that, workers are expected to do everything possible to quickly correct problems or divert the inspectors' attention from any issues, Quarles said.

The witnesses also described illegal ventilation changes, methane gas fireballs and thick accumulations of combustible coal dust.

The congressional committee is investigating the April 5 explosion. Committee members said they are considering hiring more inspectors, removing loopholes that companies exploit to avoid being labeled persistent violators, and stronger protections for whistleblowers.

Warning of an impending inspection is a civil violation of federal mining regulations, MSHA chief Joe Main told The Associated Press after the hearing. Whether it's a crime as well is under consideration and may be looked into by other federal agencies.

The secretary of labor, MSHA's parent agency, sued two companies and three officials earlier this month for allegedly tipping off workers that inspectors had arrived. The agency says the warnings are a misdemeanor crime, punishable by up to six months in prison and a $1,000 fine.

"What some companies may be doing is trying to hide outlaw and illegal activities," Main said.

Miner Adam Morgan once told of being ordered to apply rock dust quickly because an inspector was heading underground, said his father, Steve Morgan.

And miner Stanley "Goose" Stewart, who was about 300 feet inside Upper Big Branch when the explosion occurred, said methane gas and dust clouded the mine. He's been unable to work since the blast.

"You couldn't see your hand in front of your face," he said.

Adam Morgan routinely asked about ventilation problems and, despite being a trainee, fixed some on his own, said Steve Morgan, himself a veteran underground coal miner.

"He said just about every shift he worked he had to do some kind of ventilation repairs and some, like I said, he had to do on his own," Steve Morgan said. When Adam Morgan complained, a Massey supervisor told him to consider a different line of work.

Massey repeated that it's continuing to cooperate with investigators and reiterated claims by Chief Executive Don Blankenship that it does not put profits ahead of safety.

"Our focus remains on providing for the families affected by this tragic accident and cooperating with state and federal agencies to determine its cause," the company said.

Leo Long said his grandson Ronald Lee Maynor worked in dangerous conditions out of fear of losing his job.

"If they found a violation, the boss would tell 'em, 'Get back to work.' If they don't go back to work, they'd be fired," Long said.

Clay Mullins dismissed Blankenship's assertion that Massey puts safety first as he related a final conversation with his brother Rex Mullins the day before he died.

"I talked to him Easter Sunday before this happened and the only thing that he said to me was all that was thought about there was running coal," Mullins said. Performance Coal executives only wanted "to run, run, run, no matter what the conditions were."