Compliance · US EPA / WHO
Radon Action / Reference Levels
Indoor air: radiological
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It is colorless and odorless, seeps into buildings through foundations and basements, and accumulates indoors where, breathed over years, it becomes a leading cause of lung cancer. Because there is no threshold below which radon is entirely safe, health bodies define action and reference levels: concentrations at which mitigation is recommended, rather than absolute safety limits. The US Environmental Protection Agency (EPA) publishes an action level at which it advises fixing the building, and the World Health Organization (WHO) publishes a lower reference level as a goal for reducing risk.
The standard
What Radon Action and Reference Levels Are
These are practical decision points that tell a building owner when radon warrants action. The EPA and WHO values are given in the limit table on this page.
Limit values
Radon Action Levels Limit Values
Every value US EPA and WHO publish for the parameter below, with its averaging period, as the standard states it.
Who it applies to
Who Uses It
Homeowners, landlords, schools, and employers use radon action levels to decide whether a building needs mitigation, and radon-measurement professionals and mitigation contractors use them as the trigger for remedial work such as sub-slab depressurization. Property transactions frequently prompt testing, and in radon-prone regions building codes, health departments, and real-estate practice all reference the action level. Anyone responsible for a building's indoor air, particularly one with occupied basements or ground-floor rooms, has reason to test against these levels.
Monitoring
How Monitoring Demonstrates Compliance
Radon is assessed by measuring its concentration in indoor air, and because levels vary enormously with weather, season, and ventilation, duration matters. A short-term test over a few days gives a quick screen, but a long-term measurement over months, or a continuous radon monitor logging hour by hour, gives a far more reliable picture of the average exposure to compare against the action and reference levels in the limit table on this page. Continuous monitors reveal how radon builds up overnight and after a building is closed up, which is why testing is done in the lowest occupied level under closed-house conditions. After mitigation, a repeat measurement confirms the level has fallen below the action level.
Recommended
best match-
Thiamis connects 1 instrument
A gateway that connects the third-party instruments you choose to the Aethair Platform.
Also measures 2 more
Relative HumidityAir Temperature -
Who measures each parameter
| Parameter |  Aethair PRO |  Aethair IAQ | External |
|---|---|---|---|
| Radon | — | — | 1 instrument via Thiamis |
Devices
Devices That Cover Radon Action Levels
How much of this standard one Aethair monitor covers, followed by the third-party instruments in the sensor catalog that measure its parameters. Each connects to Environet through a Thiamis gateway, which adds whatever the monitor leaves out.
Covers it on its own
Solutions
Solutions Judged Against Radon Action Levels
Indoor Air Quality
Offices, schools, homes, and public buildings
Questions
Radon Action Levels FAQ
Is there a safe level of radon?
No level of radon is completely without risk, since the health effect accumulates with exposure over time. Action and reference levels are practical points at which mitigation is recommended and risk is meaningfully reduced, not thresholds below which the gas is harmless. Lowering the concentration further always lowers the risk.
Where and when should radon be measured?
Radon is measured in the lowest lived-in level of a building (often a basement or ground floor) under closed-house conditions, because that is where it concentrates. Since levels swing with weather and season, a longer measurement or a continuous monitor gives a more representative average than a brief snapshot.
What is the difference between the EPA action level and the WHO reference level?
The EPA action level is the concentration at which US guidance recommends fixing a building, while the WHO reference level is a lower value proposed internationally as a goal for reducing population risk. Both are given in the limit table on this page; the WHO figure reflects the more conservative target.
How do I monitor radon in a building?
Use a continuous radon monitor placed in the lowest occupied level under closed-house conditions, logging over days to months for a representative average. Use the configurator to add a radon sensor to an indoor air quality station so radon is tracked alongside your other indoor parameters.
Monitor Against Radon Action Levels
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