Radon is a naturally-occurring, invisible, odorless gas that is usually harmlessly dispersed in outdoor air. However, when the gas is trapped in buildings it can be harmful to human health and has been found to cause lung cancer in humans.

Radon is going undetected in homes across the country. It causes no immediate health symptoms, but long-term exposure can be deadly. The invisible gas is the number one cause of lung cancer among non-smokers and the second leading cause of lung cancer overall after smoking. It is responsible for about 21,000 lung cancer deaths every year.

The danger of radon exposure in dwellings was discovered in 1984 with the case of Stanley Watras, an employee at the Limerick nuclear power plant in Pennsylvania. Watras set off the radiation alarms on his way into work for two weeks straight while authorities searched for the source of the contamination. They were shocked to find that the source was astonishingly high levels of radon in his house's basement and it was not related to the nuclear plant.

The risks associated with living in his house were estimated to be equivalent to smoking 135 packs of cigarettes every day. Following this event, which was highly publicized, national radon safety standards were set, and radon detection and ventilation became a standard homeowner concern.

The U.S. Environmental Protection Agency estimates that as many as one in 15 homes across the U.S. has elevated radon levels. Radon test kits are commercially available. The kit includes a collector that the user hangs in the lowest livable floor of the house for 2 to 7 days. The user then sends the collector to a laboratory for analysis.

Indoor radon can be mitigated by sealing basement foundations, water drainage, or by sub-slab de-pressurization. In severe cases, mitigation can use air pipes and fans to exhaust sub-slab air to the outside. Indoor ventilation systems are more effective, but exterior ventilation can be cost-effective in some cases. Modern construction that conserves energy by making homes air tight exacerbates the risks of radon exposure if radon is present in the home. Older homes with more porous construction are more likely to vent radon naturally.