Main said the numbers show the new system is working: In 2010, 53 mines were identified during the screening process, and 17 received letters they could be labeled pattern violators. Last year, only 20 mines met the screening criteria, and only four received such notices.
That shows the new rules "will not affect most of the mines in this country," Main said. "And those who have problems have opportunities to fix those problems."
The National Mining Association, however, said the rule means some operators will "unjustifiably" be put on a pattern of violations list, "the agency's most severe enforcement tool, with little or no protection."
Operators and the public have been able to view violation data online since April 2011, and Main said it is up to the companies to check for any potential problems.
There is nothing in the Mine Act, Main said, that requires MSHA to warn the operators. But those who see they have a problem developing can submit an improvement plan to MSHA, which can consider that as a mitigating circumstance in its review.
The rule is the third regulation MSHA has issued to try to prevent coal dust explosions like the one at Upper Big Branch.
In June 2011, it passed new standards for rock dusting, or the application of pulverized limestone to render coal dust inert. Last year, it passed rules related to problems at Upper Big Branch, including ventilation, methane, roof control and accumulation of combustible materials.
U.S. Rep. George Miller of California, the senior Democrat on the House Education and the Workforce Committee, praised the Labor Department for closing loopholes that he said some mine operators have "exploited to the detriment of workers' lives and limbs."
But both Miller and Sen. Jay Rockefeller, D-W.Va., called on Congress to do more and vowed to reintroduce the Robert C. Byrd Mine and Workplace Safety and Health Act this year.
The legislation was first introduced in 2010, a month after the death of its namesake, the late Democratic senator from West Virginia. It was reintroduced in 2011 and revised by Rockefeller in 2012 but has languished in the Republican-controlled House.
Among other things, the bill would strengthen whistleblower protections for miners who report safety concerns, increase MSHA's oversight and accountability, and give the agency tougher enforcement tools.