(CNN) -- The operators of West Virginia's Upper Big Branch coal mine dodged federal safety rules and hid violations before the April 2010 explosion that killed 29 men, a scathing report on the disaster concluded Tuesday.
The immediate cause of the blast was a methane ignition that set off a massive coal-dust explosion, the U.S. Mine Safety and Health Administration stated in a report issued Tuesday afternoon. But the agency found the "unlawful policies and practices" of Massey Energy and its subsidiary, Performance Coal Company, laid the foundation for the disaster.
"The evidence accumulated during the investigation demonstrates that PCC/Massey promoted and enforced a workplace culture that valued production over safety, including practices calculated to allow it to conduct mining operations in violation of the law," the report states.
"The investigation also revealed multiple examples of systematic, intentional, and aggressive efforts by PCC/Massey to avoid compliance with safety and health standards, and to thwart detection of that non-compliance by federal and state regulators."
The report was issued the same day that the Justice Department announced a record $209 million settlement with the mine's new owners, Alpha Natural Resources, which bought Massey Energy earlier this year. The settlement allows Alpha to avoid prosecution, but leaves open the prospect of criminal charges against individual Massey employees, the Justice Department said.
Under the deal, Alpha will pay $1.5 million to each family that lost relatives in the blast, spend tens of millions to boost safety in its mines and millions more in penalties.
The MSHA report found Massey Energy kept two sets of books to mislead federal inspectors and its own workers about hazards in the mine, and had twice as many accidents as it reported to regulators, the report says. The company failed to conduct adequate inspections, intimidated workers to prevent them from reporting violations, and tipped off crews to surprise inspections, according to the report.
And the company allowed coal dust and loose coal to build up in the Upper Big Branch mine before the explosion, fueling the blast when it occurred.
"If basic safety measures had been in place that prevented any of these three events, there would have been no loss of life at UBB," the report says.
Alpha, which closed its $8.5 billion purchase of Massey Energy in June, said it would study the MSHA report as part of its own review of the mine explosion. The company said it has taken several steps to reinforce safety "and doing what is right" since the takeover.
"From the outset, Alpha has cooperated fully with all regulatory and enforcement agencies and we believe the agreements we've reached represent the best path forward for everyone," company CEO Kevin Crutchfield said in a written statement on the settlement.
The Justice Department said the settlement is the largest of its kind. In addition to payments to families, Alpha will pay nearly $35 million in fines and $48 million to fund mine safety research, and pledged to spend $80 million on safety improvements at the company's underground mines as part of its settlement with the Justice Department.
"For far too long, we've accepted the idea that catastrophic accidents are an inherent risk of being a coal miner," Booth Goodwin, the U.S. attorney in Charleston, said in a written statement. "It's long past time we put that myth to rest. We believe that this agreement does that."
But the head of the United Mine Workers of America, which had long criticized the non-union Massey Energy, said there would be no justice for the dead miners "until someone goes to jail."
"Since the government is stressing that it is not waiving its right to pursue any individuals who worked for Performance Coal or Massey, we remain hopeful that responsibility will be placed where it belongs: on upper level management at Massey who created the safety-last culture at that company," UMWA President Cecil Roberts said. "We firmly believe the evidence is there for such criminal prosecution."
Melvin Smith, a spokesman for Goodwin's office, told CNN that prosecutors will study the MSHA report, but said any comment on the document was premature Tuesday.
The report states that 18 Massey employees invoked their Fifth Amendment rights against self-incrimination during the investigation -- among them former Massey CEO Don Blankenship. Tuesday's report accuses Blankenship, an outspoken critic of federal mining regulations, of pressuring subordinates to get back to work after halting operations due to safety issues.
"An employee testified that upper management threatened to fire crews when they stopped production and that Massey CEO Don Blankenship himself pressured management to immediately resume production," the report states.
Blankenship retired in December 2010, and his attorney did not return phone calls seeking comment Tuesday.
An earlier state investigation found the disaster stemmed from failures in safety systems and could have been prevented. That probe found the mine lacked adequate ventilation; water sprays on equipment were not properly maintained and failed to function as they should have; and the mining company didn't meet federal and state safety standards for the application of rock dust, a crucial tool in keeping highly volatile coal dust from exploding.
Massey Energy disputed that report, released in May, saying the blast likely occurred when natural gas flooded into the mine. Tuesday's MSHA report said investigators considered that explanation, but said it didn't fit the facts.
CNN's Jake Carpenter contributed to this report.