What Radon Level Is Dangerous? EPA Limits Explained

How Radon Is Measured

Radon is measured in picocuries per liter of air (pCi/L). Your home test kit or radon professional will report a number like 2.1, 4.3, or 8.7 pCi/L.

The outdoor air average in the United States is about 0.4 pCi/L. Inside homes, the national average is 1.3 pCi/L.

EPA Action Levels

The Environmental Protection Agency (EPA) sets the benchmark most homeowners and real estate professionals rely on:

| Radon Level | EPA Guidance |

|---|---|

| Below 2 pCi/L | Generally acceptable; difficult to reduce further |

| 2–4 pCi/L | Consider mitigation; fix if possible |

| 4 pCi/L or higher | Mitigate — EPA action level |

| 8 pCi/L or higher | Elevated risk; act promptly |

| 20 pCi/L or higher | Very high; treat as a priority |

The EPA action level is 4 pCi/L. If your test comes back at or above this number, the EPA recommends fixing your home. Approximately 1 in 15 U.S. homes exceeds this level.

Is 4 pCi/L the "Safe" Level?

Not exactly. The EPA acknowledges that there is no completely "safe" level of radon — any radon exposure carries some risk. The 4 pCi/L action level is a practical threshold based on what mitigation systems can reliably achieve, not a declaration that 3.9 pCi/L is harmless.

The EPA also recommends *considering* mitigation even between 2 and 4 pCi/L, especially if you spend a lot of time in your basement or have children at home.

How Long Does Exposure Matter?

Radon risk is cumulative — it builds up over years of breathing elevated concentrations. A short visit to a high-radon building poses little risk. Living in one for decades without mitigation raises your lifetime lung cancer risk significantly.

For context, the EPA estimates that radon at 4 pCi/L causes about 7 deaths per 1,000 people — comparable to the risk of dying in a car accident. At 20 pCi/L, that risk rises to roughly 36 per 1,000.

What to Do If Your Level Is High

1. Get a confirmatory test. Short-term tests (2–7 days) are quick but less precise. A long-term test (90+ days) gives a more accurate annual average.
2. Hire a certified mitigator. The EPA recommends using a contractor certified through NRPP or NRSB. These professionals are trained and tested on safe, effective installation.
3. Install a mitigation system. The most common solution is sub-slab depressurization — a pipe and fan system that draws radon from under the foundation and vents it outside. Most systems cost $800–$2,500 and can reduce radon by up to 99%.
4. Test again after mitigation. A post-mitigation test confirms the system is working.

Find a Certified Radon Mitigator Near You

RadonBase lists NRPP- and NRSB-certified radon mitigators across the United States. All professionals in our directory hold active certifications.

Search the directory →

*Sources: U.S. EPA, "A Citizen's Guide to Radon." NRPP/NRSB certification standards.*