Radon tests will typically have its results expressed in terms or picocurie, which reflects the amount of radioactivity of radium in a liter of air.
* The US EPA action level for radon is 4 picocuries per liter of air (pCi/L), at that point radon mitigation is required. 4.0 pCi/L of radon is comparable to smoking 8 cigarettes per day. The potential risk of getting lung cancer from prolonged radon exposure to 4 pCi/L is approximately 7 in 1,000.
* US EPA Citizen’s Guide to Radon, 1986