Respirable silica, a material present in cement construction products, including roof tiles, has been a known occupational health hazard for more than a century. However, because symptoms associated with respirable silica often mimic other diseases, silicosis, the disease caused by respirable silica, often is misdiagnosed. The National Institute for Occupational Safety and Health (NIOSH) has undertaken studies to determine how to protect roofing workers from suffering deadly diseases related to respirable silica. The first large-scale incident related to respirable silica in the U.S. was the Hawk's Nest Tunnel disaster in 1920-30. In 1920, a Union Carbide subsidiary won a contract to build a hydroelectric project in the mountains of West Virginia. Workers primarily were poor locals and newly arrived African Americans from the South. Wearing no protective gear, 476 men digging a tunnel though a mountain died from acute silicosis. The mountain later was found to contain rock that was 99.7 percent silica. Outcry about the deaths led to a Congressional hearing regarding the incident in 1935 during which it was stated such blatant abuse of workers was "hardly conceivable in a democratic government in the present century." The hearings resulted in legislation to compensate the sickened workers and protect future ones. Newspapers interviewed many families who stated they had lost all their male members who worked in the tunnel to acute silicosis.