CHARLESTON, W.Va. -- West Virginia and federal investigators have discovered more problems with a water-spray system in the longwall unit of Massey Energy's Upper Big Branch Mine, a finding that could be a key piece of evidence about the April 2010 explosion that killed 29 miners.

More missing and malfunctioning water sprays were confirmed during testing of the longwall machine's cutting tool in late December, although officials have not released an exact count of the problems that were found.

Massey officials confirmed that at least six sprays were missing from the cutting tool, called a shearer, but said it's not clear if they were destroyed by or were missing before the deadly explosion.

State and independent investigators said they are looking closely at the water-spray system as part of their investigation of the worst U.S. coal mining disaster in more than 40 years.

"It gives us something to research and try to find out why they were not functioning the way they were supposed to be," said C.A. Phillips, acting director of the West Virginia Office of Miners Health, Safety and Training. "They're there for a reason."

Water sprays on the longwall machine help hold down dust that can cause black lung disease and can contribute to explosions. They also help control sparks or flames that can occur when the mining machine cuts into coal and surrounding rock.

"Obviously, the question of whether these preventative tools were in place at the time of the explosion is a matter of great concern to us," said Davitt McAteer, who was appointed by former Gov. Joe Manchin to perform an independent inquiry of the disaster. "It is a matter we're spending a lot of time exploring."

Along with state, federal an independent civil investigations, the April 5 explosion also is the subject of a criminal inquiry by federal prosecutors, special MSHA investigators and the FBI. Investigators believe the blast involved the ignition of methane gas and was made far worse by a buildup of highly explosive coal dust underground.

In mid-November, the Gazette reported that investigators had found at least four water sprays missing from the longwall shearer itself. At the time, MSHA and Massey were in the midst of an argument over when and how investigators would test the water-spray system.

More missing and malfunctioning water sprays were confirmed during testing of the longwall machine's cutting tool in late December, although officials have not released an exact count of the problems that were found.

Massey officials confirmed that at least six sprays were missing from the cutting tool, called a shearer, but said it's not clear if they were destroyed by or were missing before the deadly explosion.

State and independent investigators said they are looking closely at the water-spray system as part of their investigation of the worst U.S. coal mining disaster in more than 40 years.

"It gives us something to research and try to find out why they were not functioning the way they were supposed to be," said C.A. Phillips, acting director of the West Virginia Office of Miners Health, Safety and Training. "They're there for a reason."

Water sprays on the longwall machine help hold down dust that can cause black lung disease and can contribute to explosions. They also help control sparks or flames that can occur when the mining machine cuts into coal and surrounding rock.

"Obviously, the question of whether these preventative tools were in place at the time of the explosion is a matter of great concern to us," said Davitt McAteer, who was appointed by former Gov. Joe Manchin to perform an independent inquiry of the disaster. "It is a matter we're spending a lot of time exploring."

Along with state, federal an independent civil investigations, the April 5 explosion also is the subject of a criminal inquiry by federal prosecutors, special MSHA investigators and the FBI. Investigators believe the blast involved the ignition of methane gas and was made far worse by a buildup of highly explosive coal dust underground.

In mid-November, the Gazette reported that investigators had found at least four water sprays missing from the longwall shearer itself. At the time, MSHA and Massey were in the midst of an argument over when and how investigators would test the water-spray system.

During tests last month, investigators found more missing sprays on the shearer and also determined that some sprays on other parts of the longwall unit were not functioning properly, officials confirmed this week.

Shane Harvey, Massey's general counsel, said the company could confirm that six out of 109 sprays were missing, but that those figures were only for the longwall shearer itself.

"The sprays are used for suppressing respirable dust and we have not been able to tell whether they were missing before the explosion or are missing as a result of the explosion," Harvey said in an e-mail.

"I'm not aware of any evidence that anyone in mine management or on the crew was aware of the sprays being missing," Harvey said. "I will say that this was an experienced crew and I speculate that they would not have operated if missing sprays were causing trouble with dust."

When asked last month about the water-spray testing, MSHA officials said that they did not have a firm count on how many were missing and, once they did, would not make that information public until it was first shared with the families of the miners killed in the explosion.

On Thursday, MSHA spokeswoman Amy Louviere would not confirm any information about the outcome of the water-spray testing until agency officials schedule a meeting to provide that information to the families.

"That has always been our policy," Louviere said.

Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.