Radon is a chemical element with an assigned symbol of Rn and the atomic number 86. It is a radioactive, colorless, odorless, tasteless gas, occurring naturally as an indirect decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days. Radon is one of the

Radon is one of the densest substances that will remain a gas under normal conditions. It is also the only gas that contains radioactive isotopes and is considered a health hazard.

Radon gas is generated in rock and soil and creeps up through cracks or spaces between particles. Outdoor concentrations of radon are typically safe at about 0.4 picocuries per liter (pCi/l) of air. When radon gas seeps into poorly ventilated buildings through foundation cracks or openings, it can rapidly accumulate leading to unhealthy indoor air quality and serious health risks.


Radon gas is heavier than air, so it accumulates in low areas such as basements and crawl spaces. It can also be found in some spring waters and hot springs.

Radon is an invisible gas and is thus easily inhaled. Studies have shown a link between breathing high concentrations of radon and incidence of lung cancer.

According to the EPA, radon is the second leading cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States. About 2,900 of these deaths occur among people who have never smoked. While radon is the second most frequent cause of lung cancer, it is the number one cause among non-smokers.