The West Virginia coal mine where 25 people were killed in an underground explosion tentatively blamed on a buildup of methane gas has been cited for serious safety problems several times this year, federal records show — including ventilation issues.

The Upper Big Branch South Mine, operated by Massey Energy Co., has been assessed about $1.8 million in penalties since 2006, of which the company has paid about $365,000.

The most recent complete safety and health inspection listed by federal regulators lists more than 100 citations and orders this year, about a third of which fell into the "significant and substantial" category.

Among the problems Mine Safety and Health Administration inspectors labeled as "significant and substantial" at the Montcoal, W.Va., mine were those relating to escape routes for miners, the mine's ventilation plan and the accumulation of combustible materials such as coal dust.

The "significant and substantial" designation means a violation is "reasonably likely" to result in a serious injury or illness. Although citations are commonplace in mining, only about one-third get that designation.

Phil Smith, spokesman for United Mine Workers of America, said some of the violations at the non-union mine were minor, others serious breaches that could endanger workers.

"Ventilation — which is very important in mining and when a mine liberates as much methane as this one — and maintenance of mine escapeways are two of the most serious" violations, Smith said.

Three workers have died at the mine in the past 12 years. A laborer was crushed to death in 1998 when an improperly welded steel support gave way. Three years later, a continuous mining machine operator died after a roof collapsed. In 2003, an electrician was killed after touching an exposed cable carrying 480 volts used to power shuttle cars.

More than 100,000 citations and orders are issued to mines around the nation every year. There are about 1,400 coal mines in the U.S.

Mine's Injury Rate Exceeds National Pace

The Upper Big Branch South Mine's record for non-fatal injuries was higher than the national rate in 2008 and 2009, with about six injuries per 200,000 hours worked. The national rate was about four injuries per 200,000 hours worked.

Nationwide, mining fatalities reached a record low last year at 35. Of those, 18 were in coal mines, the MSHA said.

Officials said the explosion at the Montcoal, W.Va., mine Monday afternoon may have been caused by a buildup of methane gas in the pit. After the explosion, dangerous levels of methane and carbon monoxide thwarted rescuers' efforts to reach four co-workers trapped about a 1.5 miles below the surface.

On Tuesday afternoon, volunteers used bulldozers to carve out an access road, allowing drilling equipment to be brought to the site. They planned to drill four shafts 1,100 feet into the earth to vent the gases.

Kevin Stricklin, head of the MSHA, said explosions are preventable if the proper precautions are taken.

"It's quite evident that something went very wrong to have this kind of explosion," he said, adding, "We will leave no stone unturned to find out what was going on."

Officials acknowledged that the chance of finding survivors was low, but they said they have not given up hope.

Labor Secretary Hilda Solis pledged to investigate the tragedy. "Miners should never have to sacrifice their lives for their livelihood," she said in a statement.

Safety 'Top Priority'

Massey Energy stressed the importance of safety in its operations.

"Our top priority is the safety of our miners and the well-being of their families. We are working diligently on rescue efforts and continue to partner with all of the appropriate agencies," Massey Energy Chairman and CEO Don Blankenship said in a statement Monday.

But Smith of the United Mine Workers said Massey Energy has had a spotty safety record at some of its other mines.

"We do know that Massey's overall safety record over the past several years creates concerns," he said, adding that criminal charges were filed against one of the company's subsidiaries in connection with the deaths of two miners in 2006. "There's a longer-term issue with safety."

The MSHA fined the company $1.5 million for 25 violations that inspectors said contributed to the deaths of two miners trapped in a fire at a different mine in Logan County, W.Va., in January 2006. The company later settled a lawsuit naming it, several subsidiaries and Blankenship as defendants. Aracoma Coal Co., a Massey subsidiary, later paid $2.5 million in fines after the company pleaded guilty to 10 criminal charges in the fire.

Based in Richmond, Va., Massey Energy has 2.2 billion tons of coal reserves in southern West Virginia, eastern Kentucky, southwest Virginia and Tennessee, according to the company's Web site. Massey said it posted a excellent safety record that was stronger than the industry average last year.

With reporting from NPR's Deborah Tedford and Robert Benincasa

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