The warning letters give the mines 90 days to improve or face receiving the actual pattern of violation orders. Upper Big Branch had received a warning letter two years earlier, in 2007, but improved its record and avoided a formal enforcement order.

If a warning letter had been issued following the 2009 review, Massey would still have avoided a formal order because the company cut its serious safety violations by 65 percent during the next 90 days, Wagner said.

"Even if the pattern of violation had been discovered, the Upper Big Branch Mine would not have been placed on a pattern of violations," Wagner said during a phone interview Tuesday afternoon.

For several years, mine safety advocates have argued against the use of the warning letters -- which are not required by federal law or formal regulations -- saying MSHA should not give operators so many chances to avoid mine closures.

On Monday evening, Kentucky mine safety lawyer Tony Oppegard and Wes Addington of the Appalachian Citizens Law Center wrote a letter that urged MSHA chief Joe Main to revoke the agency's current policies.

"Indeed, the extensive and flagrant violation history of the Upper Big Branch mine makes clear that that mine should have been "placed on a pattern" long before the recent disaster," Oppegard and Addington said.

"Had MSHA used this enforcement tool as Congress intended, the mine would have received the stricter scrutiny that might have prevented the disaster."

On Tuesday, Rep. Nick Rahall, D-W.Va., joined House Labor Committee Chairman George Miller, D-Calif., in seeking a Labor Department Inspector General review of MSHA's use of its "pattern of violations" order authority and of the computer glitch cited in the Upper Big Branch case.

In a statement, Rahall, Miller and House Workforce Protections Subcommittee Chairwoman Lynn Woolsey called the MSHA announcement of the computer problem "deeply disturbing."

"In light of this disclosure, we will be asking the Labor Department's Inspector General to examine issues surrounding this disclosure," the statement said. "The miners who died so tragically at the Upper Big Branch Mine, their families, and all the men and women who go to work in our mines each day deserve nothing less."

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

CHARLESTON, W.Va. -- Federal regulators revealed Tuesday that they believe a faulty computer program led them not to send Massey Energy a "pattern of violations" warning letter late last year for the company's Upper Big Branch Mine, where 29 workers died in a massive underground explosion last week.

U.S. Mine Safety and Health Administration officials said the computer system, in use since 2007, missed eight "unwarrantable failure" enforcement orders, any one of which would have placed Upper Big Branch in line for the MSHA warning letter.

Greg Wagner, deputy assistant labor secretary for MSHA, said the Raleigh County operation was the only one of the more than 2,000 coal mines nationwide impacted by the "computer programming error." Wagner conceded "it's a low probability" that the programming error would have affected only the one coal mine that blew up a few months later.

In the wake of the Upper Big Branch deaths -- the worst U.S. coal mining disaster in 40 years -- national media and safety advocates have questioned why MSHA did not shut down the mine, given indications of growing safety problems there.

Under federal law, MSHA generally does not have broad authority to simply close a troubled coal mine unless it seeks a federal court injunction to stop anything its inspectors believe "constitutes a continuing hazard to the health and safety of miners."

But on its own authority and without going to court, MSHA can issue what the law calls "withdrawal orders" that force all miners to be removed from areas until significant hazards are eliminated.

Citing a mine for a pattern of violations, though, kicks the operation into a much tougher enforcement bracket. Each time an additional serious citation is issued, that part of the mine is closed. Mines can have the pattern of violations designation lifted only if they go an entire quarterly inspection without a serious violation.

Last week, MSHA officials said that during a September 2009 review, Upper Big Branch met nine of 10 agency "screening criteria" for the warning letter.

But, they said, the operation did not have on its record a final order citing the company for "unwarrantable failure" to comply with safety rules. Upper Big Branch had received 16 such orders during the two-year period examined by MSHA, but appeals of all of them were pending, agency officials said.

Wagner said, though, that the computer error "did not have an impact on this tragedy."

Under internal MSHA policy, mines that meet the agency's pattern of violations screening guidelines receive warning letters, rather than actual pattern of violations orders.

The warning letters give the mines 90 days to improve or face receiving the actual pattern of violation orders. Upper Big Branch had received a warning letter two years earlier, in 2007, but improved its record and avoided a formal enforcement order.

If a warning letter had been issued following the 2009 review, Massey would still have avoided a formal order because the company cut its serious safety violations by 65 percent during the next 90 days, Wagner said.

"Even if the pattern of violation had been discovered, the Upper Big Branch Mine would not have been placed on a pattern of violations," Wagner said during a phone interview Tuesday afternoon.

For several years, mine safety advocates have argued against the use of the warning letters -- which are not required by federal law or formal regulations -- saying MSHA should not give operators so many chances to avoid mine closures.

On Monday evening, Kentucky mine safety lawyer Tony Oppegard and Wes Addington of the Appalachian Citizens Law Center wrote a letter that urged MSHA chief Joe Main to revoke the agency's current policies.

"Indeed, the extensive and flagrant violation history of the Upper Big Branch mine makes clear that that mine should have been "placed on a pattern" long before the recent disaster," Oppegard and Addington said.

"Had MSHA used this enforcement tool as Congress intended, the mine would have received the stricter scrutiny that might have prevented the disaster."

On Tuesday, Rep. Nick Rahall, D-W.Va., joined House Labor Committee Chairman George Miller, D-Calif., in seeking a Labor Department Inspector General review of MSHA's use of its "pattern of violations" order authority and of the computer glitch cited in the Upper Big Branch case.

In a statement, Rahall, Miller and House Workforce Protections Subcommittee Chairwoman Lynn Woolsey called the MSHA announcement of the computer problem "deeply disturbing."

"In light of this disclosure, we will be asking the Labor Department's Inspector General to examine issues surrounding this disclosure," the statement said. "The miners who died so tragically at the Upper Big Branch Mine, their families, and all the men and women who go to work in our mines each day deserve nothing less."

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