CHARLESTON, W.Va. — Airtight chambers could save trapped miners and should be installed in the nation's 731 underground coal mines, federal researchers have concluded.

Researchers at the National Institute for Occupational Safety and Health researchers also have found the current approach — building barricades from fire-resistant or plastic sheets — won't keep trapped miners alive, according to a report sent to Congress this past week.

The report suggests reversing more than a century of practice in the U.S. coal industry and decades of inaction by the federal Mine Safety and Health Administration. Congress gave federal regulators the authority to require refuge chambers in the Coal Mine Health and Safety Act of 1969, but MSHA has never exercised that power.

If shelters are required it would be another in a long string of mine safety changes adopted after 12 men died of carbon monoxide poisoning following the January 2006 explosion at the Sago Mine in West Virginia.

Aiming to improve protection for the nation's 43,000 underground coal miners, Congress ordered the study in the Mine Improvement and New Emergency Response Act, or MINER Act, in 2006. The sweeping safety law was approved after Sago and two other high-profile fatal accidents in 2006. Those other accidents killed seven miners.

In Utah, nine people died in two cave-ins at the Crandall Canyon mine in August.

Airtight chambers "have the potential for saving the lives of mine workers if they are part of a comprehensive escape and rescue plan," NIOSH wrote in its report obtained by The Associated Press.

"These alternatives are practical, survivable, useful," said Jeff Kohler, NIOSH's associate director for Mine Safety and Health Research. "Eighteen months ago, when Congress was crafting and writing the MINER Act, in Congress' mind, there were serious questions."

Currently, the federal Mine Safety and Health Administration requires coal mines to provide 96 hours of breathable air for trapped miners and allows operators to rely on barricades, which has been the approach since the start of the 20th century.

Only West Virginia, the nation's largest underground coal producer, and Illinois, require refuge chambers, though some mining companies, among them Sago owner International Coal Group, are placing the devices in all their mines.

Congress has required MSHA to propose regulations for refuge chambers by June 15. Final regulations are due by Dec. 31.

"We're in the process of evaluating this report," MSHA spokesman Matthew Faraci said Thursday.

The report says questions remain about refuge chambers, including whether they should be moveable or constructed as part of a mine, how they should be designed and what they should do.

National Mining Association spokesman Luke Popovich praised NIOSH for recommending that mine operators be allowed to choose between mobile refuges and hardened ones. The industry has almost 750 mobile rescue chambers on order, at about $100,000 a piece, he said.

NIOSH estimates portable refuge chambers will cost the industry far more. The report says an $80,000 shelter would cost another $261,000 to $354,000 for training, maintenance and moving over a 10-year life span.

The United Mine Workers also praised NIOSH.

"We agree with the NIOSH findings that these things need to be deployed in underground mines. We've always said that," spokesman Phil Smith said. "It's disappointing that it's taken 30 some years since the first time that this was mentioned."