Published: Sep 17, 2010 4:02 PM EDT
Updated: Sep 17, 2010 1:02 PM EDT

CHARLESTON, W.Va. (AP) - A federal official says tests show more than 1,400 samples collected inside West Virginia's Upper Big Branch mine contained excessive amounts of highly explosive coal dust when an explosion killed 29 miners and injured two.

The Mine Safety and Health Administration's Kevin Stricklin revealed the results during a conference call with reporters Friday.

Stricklin says 79 percent of 1,803 samples taken from the Raleigh County mine contained too little inert material. Moreover, he says the samples would have contained more coal before the April 5 explosion burned away a portion of the dust.

Massey Energy, the mine's Virginia-based owner, had no immediate comment.

The explosion was the deadliest at a U.S. coal mine since 1970.