NASHVILLE (AP) — Tennesseans can access free radon testing kits this month, according to the state Department of Environment and Conservation.

One kit will be made available per household to test for the colorless, odorless, naturally-occurring radioactive gas that threatens human health when trapped in homes and other confined spaces. The kits can be requested online or by calling the department at 800-232-1139.

The department says radon is the second-leading cause of lung cancer in the country, and the number one cause among non-smokers.

The gas is produced when uranium breaks down in rocks and soils. It can only be detected in a home through testing.

Gov. Bill Lee declared January as “Radon Detection Month” in a proclamation last month.