Stripping the appeal from the current system denies operators their due-process rights, the association contends.MSHA has said that until 2007, its pattern of violations screening was "decentralized and lacked a consistent, structured approach." That changed after back-to-back disasters in 2006 at the Sago and Aracoma mines in West Virginia, and at the Darby No. 1 mine in Kentucky. MSHA developed new screening criteria and a scoring system to produce new computer-generated lists. 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.