A report recently published by NIOSH details the agency’s evaluation of employee exposures to radon gas at a national park. The U.S. National Park Service requested NIOSH’s assistance to examine potentially elevated radon concentrations within an underground tourist cavern and its connected buildings. Staff from NIOSH’s Health Hazard Evaluation Program visited the park four times during different seasons to assess exposures to radon and radon decay products within the park’s main cavern, attached visitor’s center, a cave that had periodic guided tours, and other administrative buildings. Investigators also evaluated ventilation within the visitor’s center.  NIOSH personnel found that radon gas was entering the visitor’s center by way of the elevator shaft connected to the main cavern and noted that radon concentrations in the center were greater than concentrations found outdoors and in other park buildings nearby. NIOSH ultimately recommended that the park use engineering and administrative controls to decrease workers’ exposures to radon. The agency also noted seasonal differences in radon concentrations and urged the park to schedule non-time-sensitive cavern work during wintertime, when concentrations are lower. “In the higher radon concentrations months (i.e., summer months), employees should be limited to no more than 225 hours per quarter [in the main cavern],” NIOSH’s report states.  Further details are available in NIOSH’s report (PDF).