Everybody knows that cigarettes are the leading cause of lung cancer.

If you don’t smoke and you don’t hang out in smoky places, though, it’s easy to avoid exposure to that risk.

Not as many people know that the second-leading cause of lung cancer in the United States is an odorless radioactive gas that often seeps into homes at dangerous concentrations. In Tennessee, an estimated 16 percent of homes contain radon gas at high levels, and in some counties that number is as high as 75 percent, according to the Tennessee Radon Program.

The Environmental Protection Agency has selected January to be National Radon Action Month. As a result, the American Lung Association wants to remind Americans of three steps that they can take to confront the threat of radon.

Those three steps include:

1. Testing for radon in homes

2. Encouraging officials to test for radon in other public and private spaces such as schools

3. Supporting legislation that could mitigate the radon threat, such as changes to building codes that would require radon-resistant construction materials.

Radon is considered to be a Class A carcinogen and causes an estimated 21,000 deaths in the United States each year, according to a document from the Tennessee Radon Program. It is especially important for homeowners to test their homes in Williamson County because it has been designated a Zone 1 radon area by the EPA. This means that homes there are at the highest risk of having elevated radon levels. Most of the counties surrounding Williamson have been marked Zone 1, including Davidson.

Homeowners can buy radon testing kits themselves or hire professionals to conduct the testing. Tennesseans can request a free radon testing kit here, from the Tennessee Radon Program.

The Tennessee Radon Program recommends that, if hiring a professional, homeowners choose one that has been certified by either the National Radon Safety Board or the National Environmental Health Association. A search of the former found only three certified specialists in the entire state of Tennessee, the closest being in Cookeville. The NEHA site, however, turned up a number of certified radon service providers in the state. A list of them can be found here.

The good news is that there are ways to mitigate the problem in indoor spaces. Radon — which is produced in soil when uranium decays — rises and settles in homes through cracks in foundations or other openings. One popular method of radon reduction involves installing a system of fans and venting pipes below the main living area of a house which will redirect radon gas outdoors. Some radon reduction systems can diminish a home’s radon concentrations by up to 99 percent, according to the EPA.

Radon levels are measured in units called picocuries. The EPA states that any home with a concentration higher than 4 picocuries of radon per liters of air should be worked on to lower the radon risk, although there is no truly safe level of radon. Higher exposures for longer periods of time, however, carry the greatest risk.

Geneica Jones, the program manager for the American Lung Association in Tennessee, hopes that people will consider investigating the issue of radon in their homes this month.

“Too many people do not know that they may have this dangerous threat in their homes,” Jones said in a news release. “Testing is easy and it’s the only way for people to know how serious the risk of exposure is. Because most of us keep our homes closed up in colder weather, January provides a great time to test for radon. It’s something every home and business owner in Tennessee should do.”

More information about radon from the American Lung Association can be found here. The National Radon Action plan, a joint effort of the American Lung Association, the EPA, the Children’s Environmental Health Network, and other organizations, can be found here. It lays out strategies and goals related to radon reduction in the United States.