Radon in the home
Radon is a radioactive gas produced by the natural decay of uranium in soil and rock. It moves up through the ground and enters buildings through cracks in slabs and foundations, gaps around pipes, sumps and crawl spaces. Because it is invisible and odorless, the only way to know your level is to test. Levels vary widely, even between neighboring houses.
Units
In the United States, radon is measured in picocuries per liter (pCi/L). Most other countries use becquerels per cubic meter (Bq/m³), the number of radioactive decays per second in a cubic meter of air:
1 pCi/L = 37 Bq/m³
Action levels
| Level | Recommendation |
|---|---|
| 4 pCi/L (148 Bq/m³) or more | EPA: fix your home |
| 2 to 4 pCi/L (74 to 148 Bq/m³) | EPA: consider fixing |
| 2.7 pCi/L (100 Bq/m³) | WHO reference level where possible |
| about 0.4 pCi/L | average outdoor level |
The average indoor level in the US is about 1.3 pCi/L. The EPA estimates that nearly 1 in 15 homes has a level of 4 pCi/L or more.
Dose and risk
The calculator estimates the yearly dose with the UNSCEAR approach: concentration × an equilibrium factor of 0.4 × hours at home × 9 nanosieverts per Bq·h/m³. Pooled studies of homes in Europe and North America found that lung cancer risk rises by about 16% for each 100 Bq/m³ of long-term exposure. Smokers face a much higher absolute risk, because radon and tobacco multiply each other’s effects.
Example
A test result of 5 pCi/L equals 185 Bq/m³, above the EPA action level. Spending 16 hours a day at home, the yearly dose is about 3.9 mSv, more than the average yearly dose from all natural radiation in the US, about 3 mSv, and the relative risk of lung cancer is about 30% higher than with no radon.
Testing
- Short-term tests (2 to 90 days) give a quick result; long-term tests (more than 90 days) better reflect the yearly average.
- Test the lowest lived-in level, away from drafts, windows and humidity.
- Retest after renovations, foundation work or a new HVAC system.
Fixing high levels
The most common method is sub-slab depressurization: a pipe and fan draw radon from beneath the slab and vent it above the roof. Sealing cracks and improving ventilation help. Systems usually cost about $800 to $2,500 and can cut levels by up to 99%. Use a certified radon mitigation professional and retest afterward.