09/17/2010 02:02 pm ET Updated May 25, 2011

Officials Find Signs of Excessive Coal Dust in Mine That Exploded

Federal investigators searching for the cause of the April 5 Upper Big Branch Mine disaster have collected evidence suggesting that the mine owner, Massey Energy, failed to adequately control coal dust.

During a Friday morning press conference, the federal Mine Safety and Health Administration said it has collected 1,803 rock dust samples from the mine, and so far 79 percent of the rock dust samples are not in compliance.

"It's fair to say coal dust played a role, but we have to evaluate the coking process," said Kevin Stricklin, who heads MSHA's coal division.

MSHA started taking rock dust samples every 500 feet beginning at the mantrip where some of the miners were found, and then decreased the space of the rock dust samples to every 100 feet. Then, as MSHA got to the working section, the investigators took samples at every cross cut.

When asked about the reliability of the samples, Stricklin said they are reliable because "the explosion would have used up some of the combustible content in the rock dust samples," so the samples may actually show less explosive content after the explosion than before the explosion.

MSHA said 90% of the investigation is complete. MSHA has collected 260 pieces of evidence, 183 documents, 3,000 underground photos with up to 20 teams underground doing their work.

The agency has also been able to pinpoint the exact time of the explosion at 3:02 p.m. and forty seconds.

MSHA said it still cannot find one methane detector from the longwall face. It has found five detectors from headgate 22, two from the headgate of the longwall, one from the longwall face, three on the mantrip where some of the miners bodies had been found.

The agency said it still has to clear water from headgate 22.

MSHA said it is considering questioning Massey Energy CEO Don Blankenship, but only if questioning can help in the investigation, and that it is planning a public hearing.