NASHVILLE (AP) — The Tennessee Department of Environment and Conservation is offering free radon test kits through next Monday.

Radon is a naturally occurring gas that can seep into homes through cracks and openings in the foundation. In concentrated levels, it can threaten human health. Federal statistics show it as the No. 1 cause of lung cancer among non-smokers in the United States.

The kits are available at www.tn.gov/environment/ea/radon . A limit number are available at local county offices of the Division of Ground Water Protection.

The best time to use the kits is in cold weather, usually from October to March.