CHARLESTON, W.Va. — More than 1,400 samples collected inside West Virginia's Upper Big Branch mine show excessive amounts of coal dust were present before an explosion killed 29 miners in April, a federal official said today.

A majority of the samples came from areas affected by the explosion.

"It's going to be fair to say that coal dust played a role," said Kevin Stricklin of the Mine Safety and Health Administration. "We just aren't in a position to say how big of a role."

The findings bolster MSHA's preliminary findings issued 10 days after the explosion that a mix of methane and coal dust were responsible for the blast. Federal law requires coal mines to coat coal dust with pulverized stone or other inert material to prevent and contain explosions.

The explosion was the deadliest at a U.S. coal mine since 1970 and is now the subject of civil and criminal investigations.

Mine owner Massey Energy criticized MSHA for releasing the test results.

"This is not the first time MSHA has attempted to use unproven or faulty coal dust claims in their investigation efforts," the Richmond, Va.-based company said in a statement.

MSHA contends samples taken after an explosion contain less coal dust than they would have before a blast. "The explosion has had the opportunity to eat up or use up, burn up some of the combustible materials," Stricklin said.

By The Associated Press