statistics collected by the u.s. department of labor and analyzed by the u.s. centers for disease control and prevention show a correlation between drilling activity and the number of occupational injuries related to drilling and motor vehicle accidents, explosions, falls, and fires. extraction workers are also at risk for developing pulmonary diseases, including lung cancer and silicosis (the latter because of exposure to silica dust generated from rock drilling and the handling of sand). the u.s. national institute for occupational safety and health (niosh) identified exposure to airborne silica as a health hazard to workers conducting some hydraulic fracturing operations. niosh and osha issued a joint hazard alert on this topic in june 2012.