The Health Canada guideline: 200 Bq/m³
Health Canada's action guideline is 200 becquerels per cubic metre (Bq/m³). A becquerel is one radioactive decay per second — so 200 Bq/m³ means 200 radon atoms are decaying in every cubic metre of your home's air each second. At or above this level, Health Canada recommends reducing radon.
It's important to understand this is an action guideline, not a hard safety threshold. There is no radon level that is completely free of risk. The guideline is set at a level where the health benefit of reducing radon clearly outweighs the cost — but lower is always better, and the World Health Organization suggests considering action even below 200 Bq/m³.
What each range means
Below 200 Bq/m³: No action needed. Your home is within the guideline. You can re-test every few years or after major renovations to confirm.
200–600 Bq/m³: Mitigation is recommended within 2 years. Your long-term lung cancer risk is elevated. The sooner you reduce it, the lower your cumulative exposure.
Above 600 Bq/m³: Mitigation is recommended within 1 year. This is a high level and warrants prompt action to protect your family's health.
Why 'lower is always better' is the real rule
Radon risk is cumulative — it's about your total lifetime exposure. A person living in a home at 150 Bq/m³ for 30 years has a higher lifetime risk than someone at 250 Bq/m³ for 5 years. This is why even results below 200 Bq/m³ are worth paying attention to, and why reducing from 400 to 50 is a bigger health win than the guideline alone suggests.
If your result is just under 200, consider re-testing to confirm, and think about whether mitigation makes sense for your household — especially if anyone smokes, has lung disease, or spends a lot of time in the basement.
Smoking and radon: a dangerous combination
Radon is the second leading cause of lung cancer after smoking, and the combination is multiplicative, not just additive. A smoker exposed to high radon has a far higher lung cancer risk than the sum of each risk alone. If anyone in your home smokes, radon reduction is even more urgent — bringing radon down meaningfully lowers that combined risk.