Radon, The 'Silent Killer'

This illustration issued by the EPA breaks the United States into three risk zones. Zone 1 (Red) has a predicted average indoor radon screening level about 4 pCi/L, Zone 2 (orange) has a predicted average indoor radon screening level from 2 to 4 pCi/L, and Zone 3 (yellow) has a predicted average indoor radon screening level less than 2 pCi/L. Elevated levels can be found in buidlings across all zones, and the EPA encourages testing no matter where you fall on the map. (Environmental Protection Agency)