What Is Radon ?
Radon is a naturally occurring radioactive gas that has been identified as the second leading cause of lung cancer . Radon-222 , with a radioactive half-life of 3.8 days , is the main radon isotope of health concern . It is released during the decay of uranium-238 and subsequently radium-226 , which are found in varying amounts in rock , soil and groundwater . Odorless , invisible and without taste , radon cannot be detected with the human senses . Radon is naturally occurring outdoors , but often is substantially concentrated indoors because homes are not normally built to be radon resistant . The potential for radon exposure varies by geographic area ; however , even buildings constructed in areas considered to have low radon potential can exhibit greatly elevated radon concentrations .
* The purpose of this map is to assist national , state and local organizations in their efforts to target their resources and to implement radon-resistant building codes . The EPA recommends that this map be supplemented with updated state specific radon data available from some state health departments . This map is not intended to be used to determine if a home in a given zone should be tested for radon . Homes with elevated levels of radon have been found in all three zones . All homes should be tested regardless of geographic location . State / local data should be used in determining where to implement codes . High radon concentrations frequently are found even in moderate and enhanced radon zones .
U . S . EPA map of radon zones in the United States and Guam . 2