Radon is a naturally occurring radioactive gas produced by the decay of uranium in rock and soil. It is colorless, odorless, and tasteless — completely undetectable by human senses. The only way to know your radon level is to measure it. Radon is measured in picocuries per liter of air (pCi/L).

When radon gas is inhaled, it decays into radioactive particles that can become lodged in lung tissue. As those particles continue to decay, they release bursts of ionizing radiation that damage lung cells and can initiate cancerous mutations. Radon is the leading cause of lung cancer among non-smokers and the second-leading cause overall — responsible for more than 20,000 deaths per year in the United States, according to the EPA. Children may face elevated risk due to faster respiration rates and more rapidly dividing cells.

Radon rises through soil and rock and enters homes primarily through openings in the foundation. Common entry points include: cracks in concrete slab floors; cold joints where the floor meets the foundation wall; plumbing and pipe penetrations; exposed soil in crawlspaces; open cores in concrete block walls; and drainage systems. Because indoor air pressure is typically lower than the pressure in surrounding soil, homes effectively act as a vacuum — drawing radon-laden soil gas inward through any available opening.

There is no level of radon exposure that carries zero risk. The EPA's action level of 4.0 pCi/L was chosen not because it is safe, but because it is consistently achievable through mitigation. At 4.0 pCi/L, radon exposure is roughly equivalent to smoking 8 cigarettes per day. At 2.0 pCi/L, it's equivalent to approximately 100 chest X-rays per year. The EPA recommends considering mitigation at levels between 2.0 and 4.0 pCi/L, and strongly recommends action above 4.0 pCi/L.

Montana ranks sixth nationally for indoor radon concentrations, with an average indoor level of approximately 7.4 pCi/L — nearly double the EPA action level. The state's elevated risk is driven by its geology: uranium-bearing rock formations including granite and shale underlie much of the region. Combined with mountainous terrain, high soil permeability, and tight home construction in cold months, Montana's conditions are among the most favorable in the country for radon accumulation.

Radon levels in a home are not static — they vary by season, weather, and home operating conditions. Levels tend to be highest in winter due to the 'stack effect': as warm indoor air rises and escapes through the upper levels of a home, lower-pressure zones develop at the foundation, drawing in more soil gas. Other factors that can spike radon levels include: strong winds; heavy rainfall (which pressurizes soil); frozen ground (which limits surface dispersion); combustion appliances; whole-house fans; and improperly balanced air exchangers.