EPA action level: 4 pCi/L (picocuries per liter) - Average U.S. indoor radon level: approximately 1.3 pCi/L - Average outdoor level: approximately 0.4 pCi/L - At 4 pCi/L: approximately 7 lung cancer deaths per 1,000 people over a lifetime (EPA estimate) - At 20 pCi/L: approximately 36 lung cancer de