Understanding radon

Definition

Radon is a naturally occurring radioactive gas. It has no smell, no color and no taste. It forms in the ground from the natural radioactive decay of uranium found in rocks and soils. Because it cannot be seen, smelled or tasted, your senses cannot detect it: only a measurement can tell you whether it is present in a building — and at what concentration. (WHO) (Health Canada)

How it enters buildings

Radon seeps into buildings from the ground: through cracks in concrete floor slabs, through the joints between the slab and the walls, around service pipes, and through drains and sumps. Because it comes from the ground, its concentration is typically highest in basements and in floors in direct contact with the soil, and decreases on upper floors. (WHO)

Why concentrations vary so much

Radon concentration varies enormously from one building to the next — two neighbouring houses can have very different levels — and it also varies inside a single building, with local geology, how airtight the construction is, ventilation, the season and even the time of day. This is why long-term measurements are the most reliable: they average out these variations instead of freezing a single instant. (WHO)

Radon in Québec

In Québec as elsewhere in Canada, radon is present in the ground at concentrations that depend on the geology. Every region of Canada has homes with elevated radon: no area is “safe by default”, and the only way to know the concentration in a given building is to measure it. (Take Action on Radon) Québec’s own geological context — rock formations and their associated radon potential — is documented by the Institut national de santé publique du Québec. (INSPQ)

The Bq/m³ unit

Bq/m³ = becquerels per cubic meter. It is the unit used to measure radon concentration in air: the higher the number, the higher the concentration. One becquerel (Bq) corresponds to one radioactive decay per second — a concentration of 1 Bq/m³ therefore means that, on average, one radioactive decay occurs every second in each cubic meter of air. On the map, the reading grid follows the tiers already published in the legend: under 100 Bq/m³ (low), 100 to 200 Bq/m³ (worth monitoring), above 200 Bq/m³ (elevated). (WHO)

Lung cancer

Radon is an important cause of lung cancer. Among people who have never smoked, it is the leading cause of the disease. The risk comes from prolonged exposure, built up over years: the gas is inhaled without being noticed and no symptom announces its presence — only a measurement can reveal it. (EPA) (Take Action on Radon) (WHO)

The order of magnitude in Canada

In Canada, radon is responsible for more than 3,000 lung cancer deaths every year. (Take Action on Radon) That is an order of magnitude rather than an exact count, but it gives the scale: radon exposure in homes is one of the most significant known causes of lung cancer in the country — and it can be measured, then corrected.

The dose-response relationship

The higher the long-term average concentration, the higher the risk: the relative risk of lung cancer increases by about 16% per 100 Bq/m³ of long-term average concentration. The relationship is assumed to be linear — every reduction in indoor concentration translates into a reduction in risk. (WHO)

The share of lung cancers attributable to radon

From one country to another, an estimated 3% to 14% of all lung cancers are attributable to radon. (WHO) That is a significant share, for a risk that can be measured and reduced.

Smoking and synergy

Radon and tobacco compound each other: at equal radon exposure, smokers are about 25 times more at risk of lung cancer than non-smokers. (WHO) The two levers of prevention remain distinct and complementary — not smoking, and knowing your indoor concentration by measuring it.

Other health effects

To date, no other health effect — no other cancer and no other disease — has been established for radon exposure in the home. (WHO) Prevention therefore focuses on lung cancer, and on it alone.

The thresholds that apply in Canada

The map’s reading grid is the one already published in the legend: under 100 Bq/m³, acceptable; from 100 to 200 Bq/m³, worth monitoring; above 200 Bq/m³, Health Canada recommends mitigation. That 200 Bq/m³ guideline is the one that applies in Canada. (Health Canada) (WHO)

As international context only: WHO recommends that national programs aim for a reference level of 100 Bq/m³ where achievable, never exceeding 300 Bq/m³. That reference is international guidance designed to steer national programs — it does not replace the Canadian guideline applied on this site. (WHO)

To find out where you stand, the “Measuring radon in your home” page explains the recognized protocol.

The Health Canada protocol

For a reliable result, Health Canada recommends a long-term measurement: 91 days or more — ideally 3 to 12 months — preferably during the heating season. It is the only approach that averages out seasonal variations: a concentration measured over a few days reflects that moment’s weather, not the air you breathe through the year. (Health Canada) (WHO)

The limits of short-term tests

Radon concentration varies from hour to hour and from day to day — ventilation, weather, how the house is lived in. A test shorter than 91 days therefore gives a snapshot, not an average. That is why, on the map, short-term tests are labeled “indicative” and excluded from sector averages: they inform, but they do not feed the statistics. (WHO)

Where to place the detector

As a general rule, the detector goes in the lowest room you actually use regularly — often the basement, if it is genuinely lived in — at breathing height, away from drafts, windows, exterior walls and ventilation equipment. Health Canada’s guide details placement for your house’s configuration: also follow the instructions that come with your detector. (Health Canada)

The three families of detectors

Three families of devices coexist on the market. They do not answer the same need — and only one of them matches the protocol.

The passive long-term detector (alpha-track) — roughly $30 to $60. You expose it for 91 days or more, then mail it back to a laboratory for analysis. It is the recommended default choice: it is what Health Canada’s protocol requires, and it is the most affordable category.

The continuous electronic monitor — roughly $150 to $250. It displays the concentration in real time and tracks its variations day after day. Useful as a complement: post-mitigation follow-up, curiosity, spotting variations. But never as a substitute for the long-term measurement — for a result that counts, the 91-day-or-more measurement is the one that matters. (C-NRPP)

The detector with C-NRPP-accredited laboratory analysis — the full-service option: the device, the accredited analysis and the report all come from the same accredited Canadian service. The “Where to get a detector” selection below includes one (the Quebec Lung Association dosimeter, analysis included); other “detector + analysis” services are ordered directly from the providers listed by C-NRPP. (C-NRPP)

After the measurement

The result is read with the map’s grid: under 100 Bq/m³, acceptable; from 100 to 200 Bq/m³, worth monitoring — re-measure or consider a long-term test; above 200 Bq/m³, Health Canada recommends mitigation, and the “Reducing radon” page explains the options.

And whatever the value, your measurement matters to the map: the more measurements there are, the more sectors stand out. Add my measurement to the map.