EPA recommends that you fix your home if the radon level is 4 pCi/L or more. Because there is no known safe level of exposure to radon, EPA also recommends that you consider fixing your home if the radon level is between 2pCi/L and 4 pCi/L. EPA's estimate of 21,000 lung cancer deaths per year due to radon is based on the average radon concentration in American homes, which is about 1.3 pCi/L. The average concentration of radon in outdoor air is 0.4 pCi/L, or 1/10 of EPA's 4 pCi/L action level.