Radon is about 8 times as dense as air and tends to accumulate in the basements of buildings. It is a colourless and odourless gas.
In areas with a high risk of exposure to radon-222 buildings are built with special safety features.
This can take the form of a plastic liner below the floorboards or even incorporated into the foundations of the building.
Another approach is to install a radon sump, an underground hole filled with porous materials and vented a safe distance away from the building allowing the radon to be carried away by the wind.
Existing buildings may have extractor fans fitted in the basement or electrostatic precipitators to remove radioactive dust.