Glossary · Health & indoor air

Radon action level (4 pCi/L)

Also called: action level · EPA action level

EPA's radon action level: fix your home if testing shows 4 pCi/L or more, and consider fixing it between 2 and 4 pCi/L.

What it means

EPA recommends fixing your home if radon is 4 pCi/L or more, and considering a fix between 2 and 4 pCi/L, because no level is risk-free. Canada's guideline is higher, 200 Bq/m³ (about 5.4 pCi/L), so the same result can mean fix it now in the US and keep watching in Canada.

Why it matters in an audit

Your test result is compared with these levels to decide whether a radon mitigation system is needed and how soon.

Typical numbers

Reference values with their sources. Your auditor’s report gives the figure for your own house.

What	Value	Source
Canada (Health Canada, page modified 2025-09-24)	200 Bq/m³ annual average in the normal occupancy area; act within 1 year, sooner the higher the level	canada.ca ↗
US (EPA)	Fix at 4 pCi/L or more; consider fixing between 2 and 4 pCi/L	epa.gov ↗
Same result, two answers	150 Bq/m³ (about 4 pCi/L) is above EPA's action level but below Health Canada's guideline	Arithmetic (1 pCi/L = 37 Bq/m³)

Sources

Related terms

Radon A natural radioactive gas from uranium in soil and rock that can build up in homes; long-term exposure raises the risk of lung cancer.
Radon units: Bq/m³ and pCi/L The US measures radon in picocuries per liter (pCi/L) and Canada in becquerels per cubic meter (Bq/m³); 1 pCi/L equals 37 Bq/m³.
Radon test (long-term vs short-term) Measuring radon with a detector left in the home; long-term tests, over 90 days, give the most reliable yearly average.
Radon mitigation (sub-slab depressurization) Fixing high radon, usually with a pipe through the basement floor and a fan that pulls soil gas from under the slab and vents it outside.
EPA radon zone EPA's 1993 county map of radon potential, from Zone 1 (highest) to Zone 3 (lowest); EPA says not to use it to decide whether to test.

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