Measurements · Radiation & Light
Radon
Also known as radon gas, radon test
Radon gas activity concentration. Radon is a radioactive indoor-air carcinogen.
What it is
What is radon?
Radon is a naturally occurring radioactive gas produced by the decay of uranium in rock and soil. It is colorless, odorless, and tasteless, so it cannot be detected without instruments. Radon seeps out of the ground and enters buildings through foundation cracks, sumps, service penetrations, and cavities, where it can accumulate to concentrations far above outdoor levels, especially in basements and ground-floor rooms, and in well-sealed, energy-efficient buildings with limited air exchange.
Because the source is geological, radon risk varies widely by location, and two neighboring buildings can differ significantly depending on construction and ventilation.
Health and operational effects
Radon is the second leading cause of lung cancer after smoking, and the leading cause among people who have never smoked. The risk comes not from the gas itself but from its radioactive decay products, which lodge in the lungs and irradiate tissue over years of exposure. There is no safe threshold; risk accumulates with concentration and time. Because the harm is long-term and invisible, radon is a classic case where continuous or long-term measurement is the only way to know a building is safe.
For property owners, schools, and employers, radon increasingly carries legal disclosure obligations and features in healthy-building programs. Mitigation is well understood, but only measurement shows when it is needed.
Limits
Radon Limit Values
The published values, by averaging period; each links to the standard that sets it.
A01, occupied spaces at or below grade
EPA action level
WHO reference level
Radon is reported in becquerels per cubic meter (Bq/m³) or picocuries per liter (pCi/L); 1 pCi/L ≈ 37 Bq/m³. Action and reference levels, such as the US EPA action level of 4 pCi/L and the WHO reference level of 100 Bq/m³, are the concentrations at which mitigation is recommended, not safety thresholds. Because radon varies so much over time, compare a long-term average against the action level rather than reacting to a single reading, and remember that levels below the action level still carry some risk.
How it is measured
How Radon Is Measured
Continuous radon monitors typically use a pulse ionization chamber or a silicon photodiode that counts the alpha particles emitted as radon decays to give a running concentration. Short-term test kits (charcoal canisters, alpha-track detectors) provide a snapshot over days to months but no real-time picture. Because radon fluctuates strongly with weather, season, ventilation, and occupancy, a continuous monitor gives a far more reliable assessment than a single short test. This matters most when a one-off kit reads borderline.
An instrument on Thiamis1
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing radon sensors
Measure in the lowest occupied level of a building (basements and ground floors), since radon is heaviest near its point of entry. Place the monitor away from drafts, exterior doors, and windows that would dilute the reading, at a height representative of occupancy. Because levels swing with weather and season, a measurement period of weeks to months, or permanent monitoring, gives a truer average than a short test.
Every device and option that measures Radon 1
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
 Durridge · RAD7 | Specialty Air Analyzers | Thiamis |
Where it is monitored
Solutions That Monitor Radon
Each one links to the solution page showing what that industry measures it for.
Indoor Air Quality
Often addedOffices, schools, homes, and public buildings
Article Library
Reading on Radon
WELL Building Standard Air Quality: CO2 & PM2.5 Limits 2026
WELL v2 air quality limits: PM2.5 at 15 µg/m³, formaldehyde at 50 µg/m³, CO2 at 900 ppm for ventilation monitoring, plus the monitoring WELL verifies.
Related
More in Radiation & Light
Questions
Radon FAQ
Why is radon dangerous if I can't smell or see it?
Radon's danger is precisely that it is undetectable without instruments and acts over years. Its radioactive decay products lodge in the lungs and cause cellular damage that, with long exposure, leads to lung cancer. It is the second leading cause after smoking. The only way to know your exposure is to measure.
What radon level requires action?
The US EPA sets an action level of 4 pCi/L (about 148 Bq/m³) and the WHO a reference level of 100 Bq/m³, above which mitigation is recommended. These are practical intervention points, not safe thresholds: risk continues below them, so lower is better.
Is a short radon test enough?
A short test gives a snapshot but radon swings widely with weather, season, and ventilation, so a borderline short-test result is unreliable. A continuous monitor or a long-term (weeks-to-months) measurement gives a far more trustworthy average for deciding whether to mitigate.
How can I monitor radon continuously?
Pair a Thiamis gateway with a continuous radon monitor to track concentration over time in basements and ground-floor spaces. Use the configurator to combine radon with PM2.5, CO₂, and VOC for a full indoor-air and healthy-building panel.
Monitor Radon on the Record
Schedule a callConfigure Radon Monitoring All parameters
A 30-minute call: you tell us about your application, then we demo the solution for it.