A memorial at the entrance to Massey Energy's Upper Big Branch coal mine represents the 29 coal miners who were killed in an explosion in 2010. Jeff Gentner/AP hide caption

itoggle caption Jeff Gentner/AP

Mine helmets and painted crosses at the entrance to Massey Energy's Upper Big Branch coal mine, as a memorial to the 29 miners killed there. Jeff Gentner/AP hide caption

itoggle caption Jeff Gentner/AP

Coal miner Lee Hipshire in 1976, shortly after emerging from a mine in Logan County, W.Va., at the end of his shift. A few years later, Lee took early retirement because of pneumoconiosis, or black lung disease. He died at 57. Courtesy of Earl Dotter hide caption

itoggle caption Courtesy of Earl Dotter

Coal miners are tested for black lung. Recently, the deadly disease has been discovered in younger miners and at more advanced stages. David Deal for NPR hide caption

itoggle caption David Deal for NPR

Coal miner Lee Hipshire in 1976, shortly after emerging from a mine in Logan County, W.Va. at the end of his shift. At age 36, he had worked 26 years underground. A few years later, Lee took early retirement because of pneumoconiosis, or black lung disease. He died at 57. Courtesy of Earl Dotter hide caption

itoggle caption Courtesy of Earl Dotter

Coal miners are tested for black lung at a clinic in West Virginia. David Deal for NPR hide caption

itoggle caption David Deal for NPR