What is radon? Learn about this dangerous gas found in homes

January is National Radon Action Month, and according to the U.S. Environmental Protection Agency (EPA), more than 6 million U.S. homes have indoor concentrations of radon that exceed safe levels (1). Radon causes between 3 and 14 percent of all lung cancer cases worldwide (2). If you smoke, you're 25 times more at risk from radon.

Radon causes between 3 and 14 percent of all lung cancer cases worldwide.


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What is radon?​ 

Radon is a naturally forming, radioactive, colorless, odorless, and tasteless gas. It’s found in almost all soil and is produced by a natural process as uranium breaks down into radium and then into radon gas. Radon in turn breaks down into solid radioactive elements known as “radon progeny” (such as polonium – 218) that attach to airborne particles.

Where is radon found?

Radon enters a building through cracks in the floor or walls of the basement or foundation.

Naturally occurring indoor radon concentrations can vary widely around the world; for example, there are lower concentrations of indoor radon in the Netherlands than there are in nearby southern Belgium and Luxembourg (3). A global estimate of radon risk found it to be most deadly in Armenia, where it’s been linked to 29 to 30 percent of all lung cancer cases and 6 percent of all cancer deaths (4). Research found radon’s reach to be significant in China, Russia, and the United States as well.

Elevated radon levels have been found in every state in the United States.

The U.S. Environmental Protection Agency (EPA) warns that radiation levels should be reduced in nearly one in 15 homes and encourages testing in homes, schools, and businesses (5). Though certain areas of the U.S. have higher potential for elevated indoor radon levels – in particular in the Appalachian Mountains and in the Northern Plains and Rocky Mountain states - elevated radon levels have been found in every state of the United States (6).

Radon health effects

Because they are radioactive, radon and radon progeny emit alpha particles, a high-energy radiation that damages DNA in human cells and causes lung cancer. When radon is inhaled, particles become lodged in the lungs where they continue to emit alpha particles.

Radon exposure is the second leading cause of lung cancer among nonsmokers in the U.S., after secondhand smoke exposure. The National Institutes of Health estimates that between 15,000 and 22,000 annual U.S. lung cancer deaths can be attributed to radon exposure (7). Many of these victims never smoked.

A systematic review and analysis of studies have demonstrated strong evidence linking high indoor radon levels in Europe to an increased risk of both lung cancer and childhood leukemia due to radon inhalation. (8).

How do you remove radon from your home?

Here are a few simple steps you can take to control radon levels in your home, school, or business and help protect everyone:

  • Test for Radon. The first step in managing the risk of radon is to have your home tested. Every home is unique, and a home with dangerous radon levels can be next door to a home with virtually no radon. Any radon level higher than 4 picocuries per liter is considered by health authorities to be unsafe. Testing should always be conducted by a qualified contractor and should include both short-term and long-term testing. State and federal health agencies can recommend a qualified testing company in your area.
  • Mitigate Radon. A qualified radon mitigation contractor will help you determine the most effective radon reduction techniques for your home. These techniques include:
  • Sealing cracks. Since radon enters your home through cracks in the floor and walls of the foundation, sealing cracks and leaks is an important first step. However, sealing cracks will limit but not completely stop the flow of radon into a home.
  • Suction. Pipes inserted into or below the foundation slab are connected to a vent fan that pulls radon from below the house and out into the open air.
  • Depressurization. This generally involves drilling a hole in the basement floor and extending a pipe beneath the slab of the house. The pipe runs up through the home and then vents outward with the help of an inline fan.
  • Ventilation. Installing a heat recovery ventilator increases ventilation by drawing outside air into the house and expelling radon-contaminated air. Air is warmed or cooled as needed, and air filtration can be added to filter the outdoor air coming in.
  • Filtration. Research by the American Association of Radon Scientists and Technologists showed that even standard HEPA filters can reduce radon by as much as 85%. The U.S. EPA does not generally recommend air cleaning to control radon because most filtration systems, even HEPA filters, are incapable of stopping the tiniest particles to which radon progeny adhere. IQAir HyperHEPA filtration, on the other hand, filters particles down to 0.003 microns – the smallest particles that exist.

For whole-house air filtration of potentially radioactive particles of all sizes, IQAir recommends a high-performance air purifier. For specific areas within a home or for homes without centralized heating or cooling systems, the HealthPro Plus and the GC MultiGas systems are recommended.


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If a mitigation specialist recommends overpressure, an IQAir InFlow or OutFlow Kit can be combined with an IQAir room air purifier to draw outdoor air into the indoor environment, creating overpressure in the process.

The Takeaway

While naturally occurring radon is an indoor health risk, testing can help you determine your level of risk. Through proactive testing and mitigation, you can control indoor radon levels and make your building safer.

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