It's too late for Ronald Martin of Dema, Kentucky. "I'm in last stage of black lung," he wrote in shaky script, "please help the miners so they won't suffer like I suffer. I can't breathe but a little." Mr. Martin sent his note to the Labor Department's Mine Safety and Health Administration (MSHA) to comment on the agency's proposed rule to reduce workers' exposure to respirable coal mine dust---the dust that damaged his lungs so severely. Other coal miners also sent their comments to MSHA, urging the agency to put a more protective regulation in place as soon as possible to prevent…