The United States Environmental Protection Agency (EPA) recommends for homes to be fixed once radon levels reach 4 pCi/L. Being that this is only a recommendation by the EPA, this should not be considered as a "Safe Level" of radon exposure. Radon is a Class A carcinogen that can cause lung cancer over a lifetime of exposure. Because everyone's body responds differently to radon exposure, in reality there is no such thing as a "Safe Level" of radon exposure.