This week, NPR’s Howard Berkes released an investigation into federal records that show more than 2,000 coal miners are now suffering from the most severe form of black lung disease, Progressive Massive Fibrosis, or PMF.

Berkes found that despite clear warnings two decades ago, the mining industry and government regulators did little to stop exposure to a form of rock dust that’s linked to the disease.

Jeff Young of the Ohio Valley ReSource spoke with Berkes about the investigation, which will be his last in a nearly 40 year career at NPR. Listen to the interview below.