Denver, Colorado – A dangerous gas could already be building inside homes across the Rocky Mountain region as cool spring nights keep windows closed, allowing radon—known as the “invisible killer”—to accumulate indoors within hours. The risk can increase rapidly overnight as sharp temperature swings lead residents to seal homes against lingering cold.
According to the U.S. Environmental Protection Agency, radon is a radioactive gas that forms naturally in soil and seeps into homes through foundation cracks, basements, and crawl spaces. The Rockies region—including Colorado, Wyoming, Montana, Idaho, and Utah—contains some of the highest radon levels in the country, with many areas regularly exceeding the EPA action level of 4 picocuries per liter.
Across cities like Denver, Salt Lake City, Boise, Billings, and Cheyenne, homes with basements are especially vulnerable this time of year. The region’s geology, including uranium-rich rock and porous soils, allows radon to move more easily into structures, especially when homes are sealed overnight.
Health officials warn radon is the second leading cause of lung cancer in the United States, linked to about 21,000 deaths annually. The gas produces no smell or immediate symptoms, making testing the only reliable way to detect it.
Residents across the Rockies are urged to test homes now as conditions through April continue to trap indoor air. Free and low-cost test kits are widely available, and mitigation systems can significantly reduce indoor levels before risks increase into early summer.
