Dr. Donald Rasmussen, physician in charge of the Black Lung Laboratory at the Appalachian Regional Hospital in Beckley, W.Va., in June 1974.

Mark McCowan, 47, was diagnosed with black lung seven years ago. The disease has since progressed to the worst stage.

Mark McCowan of Pounding Mill, Va., ran a longwall mining machine that cut through large swaths of coal quickly, generating huge dust clouds. "By the time I was 40 years old, I had mined more coal than most miners mine in a lifetime," he said.

A coal miner blows into a tube to measure his lung function in a test known as spirometry at Dr. Donald Rasmussen's clinic.

A coal miner performs a lung function test in a mobile clinic run by the National Institute for Occupational Safety and Health (NIOSH) in Norton, Va. After decades of decline, black lung is back. Its resurgence is concentrated in central Appalachia, and younger miners are increasingly getting the most severe, fastest-progressing form of the disease. Federal regulators are assembling a team of lawyers and other experts to consider how to bolster coal mine dust enforcement given systemic weaknesses revealed by the Center for Public Integrity and NPR.

A coal miner receives a chest X-ray at the NIOSH mobile clinic.