Radon gas is colorless and odorless. It is classified as a noble gas, or an inert gas, because its atoms do not combine readily with other atoms. Radon gas may become a health hazard in certain buildings. The main sources of radon in buildings are the soil and rocks beneath basements. Minor sources include water that comes from wells and building materials such as granite and gypsum that come from the ground.
Some areas have a high concentration in the ground.
The gas seeps from soil and rocks into water and air. Radon may enter a basement through cracks or other openings. If the building is in a high-radon area, the gas may build up inside to an unhealthy level. Radon atoms decay by giving off a form of radiation called an alpha particle. When a radon atom decays, it becomes an atom of the radioactive element polonium.