updated 5/9/2007 11:38:02 AM ET 2007-05-09T15:38:02

A lightning bolt likely traveled down a pump cable inside a sealed section of the Sago Mine, where it touch off the methane blast blamed for the deaths of 12 miners last year, the federal Mine Safety and Health Administration said Wednesday.

Lightning is one of three “root causes” the agency cites in its long-awaited investigation into the Jan. 2, 2006, explosion.

Lightning had been suspected from the start, but the report for the first time describes its likely conduit into the mine. Previous reports by the state and the mine’s owner, International Coal Group, Inc., mentioned lightning but not its route.

Contributing to the blast, according to a copy of the report obtained by The Associated Press, methane levels inside the sealed section of the mine were not monitored, and seals used to close off that inactive section from the mine’s working area were not strong enough to withstand the blast.

One man survived
The explosion trapped a team of miners deep inside. By the time searchers reached them about 40 hours later, only one man had survived in the carbon monoxide gas.

It was the highest-profile coal mining accident in recent U.S. history and led to sweeping changes in federal and state mine safety laws.

The company idled the mine in March because of high production costs and low coal prices.

Mine Safety and Health Administration chief Richard E. Stickler and lead investigator Richard Gates met Wednesday morning with the victims’ families and the sole survivor, Randal McCloy Jr., at West Virginia Wesleyan College.

MSHA’s report said officials considered other potential causes, but lightning “has been determined to be the most likely ignition source.”

“Although a roof fall cannot be definitely excluded as a potential ignition source, it is a highly unlikely ignition source,” the report said.

Although Sago was a nonunion mine, the United Mine Workers union participated in the state and federal investigations and issued its own report.

The union’s experts believe the spark that ignited the methane gas came from friction between the mine’s deteriorating rock roof and the metal support system used to hold it up.

The UMW had argued that, unlike other coal mine blasts linked to lightning, there was no metal conduit at Sago that could have carried the charge two miles into the mine to the point where the explosion took place.

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