Radon enters a building from the soil beneath the foundation, accumulating indoors, especially in the winter months when buildings are predominantly enclosed and ventilation/aeration habits are low. Cracks and crevices in building materials or leaks around pipes will be the main pathways for radon into a building. Radon accumulation inside buildings is dependent on both natural conditions (geogenic radon, physico-chemical properties of the soil, seasonal freezing and thawing activities) and anthropogenic factors, such as the construction, design, use and current condition of a building, which can allow radon to migrate from the soil via various open pathways into living spaces. The indoor radon concentration is subject to seasonal variability, weather conditions such as temperature differences between outdoor and indoor air that may generate pressure differences.
Although it is a natural gas, found in low concentrations outdoors (between 5 and 15 Bqm-3), radon becomes a life-threatening anthropogenic pollutant when trapped inside buildings.
The International Agency for Research on Cancer classifies radon as a lung carcinogen. The greatest exposure to radon for both adults and children comes from being indoors: in homes, offices, schools, etc. From a health perspective