January is National Radon Action Month. If you’re unsure whether your home has a high level of radon, it's time to find out if your house is among the estimated 1 in 15 with a dangerous level of the cancer-causing radioactive gas, which is estimated to claim 21,000 lives a year in this country.

"We know that radon-related deaths can be prevented," says EPA Mid-Atlantic Regional Administrator Donald S. Welsh. "No one has to live in a home with high radon levels because virtually any home with a radon problem can be fixed. Our hope is that once people understand this health risk, they will test their homes for radon and fix any problems they find."

There is no national requirement to test for radon, and the gas is found in every state, though the potential for high levels is greater in some locations (the EPA radon zone map is shown) particularly in the Northeast and Midwest. Check with your state radon office to learn about state-specific regulations and to find certified radon-testing and radon-mitigation companies.

What Is Radon?
You can't smell or see radon. It's an odorless, colorless gas that is the second-leading cause of lung cancer in the U.S. A study published in 2005 in the journal Epidemiology concluded your chance of getting lung cancer increases by 11 percent to 21 percent at average radon concentrations of about 3.0 picocuries per liter (pCi/L) of air over an exposure period of 5 to 30 years. The EPA recommends radon mitigation at 4.0 pCi/L. And if you're a smoker, the presence of radon in your home will considerably increase your chance of getting lung cancer.

The presence of radon doesn't mean your home was built over an atomic-waste dump. Its origins are natural—from the breakdown of uranium found in almost all soil. The gas finds its way into a home through such paths as cracks and other holes in the foundation.

Home Testing
While you might have had your home tested for radon when you purchased it, research indicates as many as 80 percent of American homes still need to be tested, according to the EPA and the Surgeon General's Office. Consumers Union, the nonprofit publisher of Consumer Reports, recommends not waiting for a home sale to check for the gas. If a test already has been completed, it is not necessary to repeat the test, unless you've fundamentally changed your home in a way that could allow more radon to enter the structure. Those changes include adding new windows and doors, modifying your heating or cooling system, adding or changing exhaust systems or any other element that could change the pressure and ventilation characteristics of the house, and building an addition.

Home test kits that measure the level of radon typically cost less than $20. In many locations, you can get discounted kits through your state or county health department or environmental-affairs department. The New York State Department of Health, for example, offers residents a kit for $6.75 and will provide a free kit within a year to any resident who has already had work done by a mitigation contractor and wants to verify that the radon level is low.

Short-term testing takes 2 to 7 days; long-term testing runs for 90 days, giving a more accurate picture of the year-round level. About all you have to do is place a sampling container in the lowest occupied level of your home, typically the basement. Seal the container immediately after the specified test period and send it to the laboratory marked on the package.

After the test is processed, sometimes in just a few days, you’ll receive a report by mail or e-mail or through a Web site that will show the measure of gas detected. You should perform a short-term or long-term follow-up test if the reading is more than 4.0 picocuries per liter (pCi/L). (Sometimes the test results show "Working Levels," or WL. The threshold of 4.0 pCi/L corresponds to 0.016 WL.)

If the radon level is high, you can hire a certified radon-remediation contractor. Find one through your state radon office or through these private organizations: the National Environmental Health Association and the National Radon Safety Board. Expect to pay about $800 to $2,500, with an average bill about $1,200.

Contractors will reduce the level of gas in your home by:
• Installing a suction system to draw the gas out of and away from the home
• Changing the ventilation and pressurization in the basement
• Sealing foundation cracks and openings

If you live in an area with a cold climate, it's best to test during the winter months, when windows are closed, limiting air exchange. The low pressure created by a chimney or other ventilation device can draw soil gases into the home near the foundation.

Essential information: To learn about other indoor-air-quality issues, read our report Indoor Air Quality: How Clean is the Air in Your Home? And watch this public-service announcement from the EPA.