Seattle, Washington – A dangerous gas could already be building inside homes across western Washington as cool, damp spring nights keep windows closed, allowing radon—known as the “invisible killer”—to accumulate indoors within hours. The risk increases quickly when airflow is limited during overnight temperature drops and persistent coastal moisture.
According to the U.S. Environmental Protection Agency, radon is a radioactive gas that forms naturally in soil and can enter homes through foundation cracks, basements, and crawl spaces. Washington is generally considered a low- to moderate-risk state, but elevated levels have been detected in parts of King, Pierce, and Spokane counties, where some homes exceed the EPA action level of 4 picocuries per liter.
In Seattle and surrounding communities including Tacoma, Bellevue, and Everett, homes with basements and crawl spaces are especially vulnerable during early spring. Residents often keep homes sealed overnight to manage cooler air and moisture, which can trap radon indoors. The Washington State Department of Health reports radon is the second leading cause of lung cancer in the United States, linked to about 21,000 deaths annually.
Radon exposure produces no immediate symptoms, making testing critical. Short-term test kits can return results within 48 to 96 hours, and mitigation systems can reduce indoor levels by up to 99 percent when properly installed.
Residents are urged to test homes now as conditions through April continue to support indoor buildup. Additional advisories may be issued as risks persist into early summer across the region.
