Radon is a radioactive gas produced by the natural disintegration of uranium (radium) present in the earth’s crust (soil, rock layers, water).

It is colorless, odorless and tasteless, so it cannot be detected by the senses. In the open air, it dissolves in the atmosphere and is therefore not of concern to your health. But when it enters a closed environment, it can accumulate in high concentrations. And because radon is heavier than air, it tends to concentrate in the lower, less ventilated parts of a building, especially in the basement during winter.

The radon concentration is expressed in becquerels per cubic meter of air (Bq/m³).

How does radon get into homes?

The atmospheric pressure inside a home is generally lower than that in the soil surrounding the foundation. This pressure difference creates a suction of radon and other fumes present in the ground into the house.

Radon can travel through the pores of the soil on which homes are built. It can enter a house through any gap in contact with the ground, such as

• dirt floors (crawl spaces);
• cracks in the walls and floor slab;
• leaky joints in service or drain pipes (water, sewer, electricity, natural gas, fuel oil, etc.);
• basement drains and other plumbing ducts.

It is possible that well water could contain radon which will be released into the air in the house when this water is brewed for showers, laundry, etc. But the concentration is usually not high enough to constitute a risk to health.

Where can you find radon?

Outdoors, average concentrations are about 15 becquerels per cubic meter (Bq/m³). Indoors, they may show more pronounced variations from house to house, even between similar constructions and located close to each other. The average radon concentration in Quebec basements is estimated around 35 Bq/m³. However, some houses may have rates of hundreds or even a few thousand Bq/m3.

When is it too much?

In Canada, there are no standards governing the allowable radon level in homes. But according to a directive adopted in 2007 by Health Canada, mitigation measures - or mitigation - must be put in place if the annual average concentration, in the normally occupied areas of a house, exceeds 200 Bq/m³. Up to 600 Bq, it is recommended to correct it within two years, but if the concentration exceeds 600 Bq, action should be taken quickly, ideally within 12 months.

In addition, in 2009, the World Health Organization (WHO) recommended that allowable radon concentrations be set at no more than 100 Bq/m³.

The dangers of radon

After smoking, radon is the second leading cause of lung cancer, far behind smoking, but it is the leading cause among non-smokers. It is believed to be associated with around 16% of lung cancer deaths.

Moreover, according to Dr. Jean-Claude Dessau, president of the sectorial committee on radon at the Quebec Ministry of Health and Social Services, lung cancer remains the only known risk associated with prolonged exposure to radon.

“Once released into indoor air, radon breaks down into microscopic fragments that attach to the dust we inhale,” he explains. In the lungs, these fragments continue to disintegrate, emitting alpha-type particles which produce ionizing radiation. The more cells in the bronchi are bombarded with these radioactive alpha particles, the greater the risk that they will deteriorate and turn into malignant cells. (Touring, fall 2009)

The Tobacco Factor

The most disastrous radon-tobacco cocktail. According to the National Institute of Public Health of Quebec, approximately 90% of lung cancer deaths attributable to radon occur in smokers. Health Canada data shows that a non-smoker exposed to high levels of radon for a lifetime has a 5% risk of developing lung cancer, compared to a 33% risk for a smoker.

Subjects at risk

We can really talk about an increased risk of lung cancer for a person, especially if he is a smoker, who is exposed to high concentrations of radon, and this, for more than four hours a day in an enclosed space (a basement for example).

It will therefore be necessary to pay attention to the habitat ions whose basement has, for example, a homeworker’s office, a family room used daily, or a bedroom occupied every night.

The ground floor of dwellings without a basement, especially where there is no crawl space, is also susceptible to high concentrations. Keep in mind, however, that radon is heavier than air and therefore always sits fairly close to the ground. In other words, the higher you climb the floors of a building, the less likely you are to be exposed to radon.

Furthermore, there is no need to panic: between exposure to radon and the onset of the disease, it is estimated that many years will pass.