Deep in the earth's crust, the toxic substance rises in the air as miners drill into massive layers of rock. As they work the controls of the big machines, dust from the ancient sandstone fills the caverns and slips into the nose and mouth, down the throat and into the chest. A stealth intruder, the tiny particles invade the pink membranes of the lungs, posing incalculable harm to workers who are prone to developing the most dreaded disease of their time: black lung. To fight the devastating illness, the U.S. Mine Safety and Health Administration launched a campaign more than a decade ago to crack down on coal operators who expose workers to dangerous levels of coal dust, and to force mine owners to reduce the threats. "End Black Lung — act now!" was the slogan unveiled by the agency at a news conference in West Virginia in 2009. But the agency entrusted with protecting the lives of workers has repeatedly allowed operators to violate the very regulations put in place to stem the l...