What Is a "Safe" Radon Level?
The EPA's radon risk model treats risk as continuous and roughly linear, meaning there is no level at which risk drops to exactly zero, only lower or higher. The 4 pCi/L action level is the practical line at which the EPA recommends fixing a home, chosen because it represents a reasonable balance between risk reduction and the cost and feasibility of mitigation, not because everything below it is proven harmless.
Understanding this distinction helps make sense of why two houses on the same street, one at 3.8 pCi/L and one at 4.2 pCi/L, are not meaningfully different in actual risk despite one falling just under the action level and one just over it. The number is a policy threshold, not a cliff edge.
For a homeowner deciding whether to mitigate a result just under 4 pCi/L, the reasonable question is not "am I safe" but whether the modest additional risk reduction is worth the mitigation cost for your specific household's risk tolerance, which is a judgment call the EPA leaves to the homeowner in that range.
Common questions
Does the EPA recommend anything for levels between 2 and 4 pCi/L?
Yes, the EPA specifically notes that levels in the 2 to 4 pCi/L range are still worth considering for mitigation, particularly in a home where people spend a great deal of time, even though 4 pCi/L is the formal action threshold.
Why not just set the action level at zero if there is no fully safe level?
Because mitigation to reach an arbitrarily low target has diminishing returns relative to cost, and 4 pCi/L represents where the EPA judged that tradeoff to make sense as general public guidance, not a claim about biological safety at that exact number.
Have a number you want read?
Tell us the result and your town in York County, or call and read it out. We will tell you what it points to and what a system would involve in a house like yours.
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