According to Health Canada, radon is a naturally occuring gas that happens as uranium breaks down in the rocks and soil in our environment. It is colourless, has no smell and no taste.
Outside our buildings, radon is harmless when it disapates in the air. But when it collects inside our buildings, it may be inhaled and accumulate in our lungs. The breakdown that was happening in the soil and rocks continues inside our bodies, with radioactive particles giving off energy as they decay. Our cells are damaged by this energy and may develop cancer due to the damage.
The only way to detect radon is to test it. This is done with a device that will detect radon amounts in a unit called "becquerels" measured per cubic metre of air (Bq/m3) The more becquerels measured and the longer the exposure, the greater the risk of developing health problems. A measurement above 200 Bq/m3 is considered hazardous.
Health Canada points out that radon is likely to enter a building anywhere that there is contact with the ground:
When we're creating and retrofitting buildings for airtightness, we must account for the presence of radon - and good news: it's relatively easy to make this accomodation. The installation of exhaust fans can be done, or in new construction, including a radon evacuation pipe in the foundation construction is possible.
FURTHER INFORMATION FROM HEALTH CANADA: radon-reduction-guide-canadians-hc.pdf 2 MB