Radon exposure is the inhalation of radon, a naturally occurring radioactive gas from soil and rock, and its decay products, which can build up indoors and underground and raise lung cancer risk.
Radon exposure is the inhalation of radon, a colorless, odorless radioactive gas formed by the natural breakdown of uranium in soil and rock, along with the radioactive decay products it produces. These decay products can lodge in the lungs and release radiation that damages lung tissue, raising the risk of lung cancer over time.
Radon seeps out of the ground and can build up in enclosed spaces, especially those in contact with soil or rock. Levels vary widely from one building to the next, even on the same street, so the only way to know the level is to test. Because radon cannot be seen or smelled, exposure can continue for years without anyone noticing.
At work, radon is a concern in basements and ground-floor offices, underground mines, tunnels, caves, utility vaults, water treatment plants that use groundwater, and buildings in areas with high natural radon. Radon is a form of ionizing radiation exposure, and the US Environmental Protection Agency (EPA) estimates that radon is linked to about 21,000 lung cancers a year in the United States.
When radon decays, it forms short-lived radioactive particles that attach to dust and can be inhaled. Once deposited in the airways, they emit alpha radiation that can damage cells. Lung cancer is the main health effect, and the risk rises with both concentration and length of exposure. Smoking greatly increases the combined risk.
In the United States, radon in air is usually measured in picocuries per liter (pCi/L). Many other countries use becquerels per cubic meter (Bq/m3). The EPA notes that the average indoor level in US homes is about 1.3 pCi/L and the average outdoor level about 0.4 pCi/L.
The EPA recommends fixing a building when radon levels are 4 pCi/L or higher, and suggests considering fixes between 2 and 4 pCi/L because there is no known safe level of radon exposure. EPA guidance is aimed mainly at homes and schools, but many employers use 4 pCi/L as a practical trigger for action in occupied workplaces.
OSHA does not have a radon-specific standard, but radon is covered by the ionizing radiation standard, 29 CFR 1910.1096. That standard adopts the limits in the Nuclear Regulatory Commission's 10 CFR Part 20, Appendix B, Table I as they stood in 1971. In an interpretation letter, OSHA explained that this sets an enforceable limit for radon-222 of 100 pCi/L averaged over a 40-hour workweek. OSHA has noted that the NRC later adopted a lower value, but OSHA has not updated its standard. In construction, 29 CFR 1926.53 applies, and OSHA has said radon testing may be expected in enclosed or underground work, or in known high-radon areas, where hazardous levels are likely. Excavation rules (1926.651(g)) and underground construction rules (1926.800) also address hazardous atmospheres.
Underground metal and nonmetal mines are covered by MSHA's radon daughter standards beginning at 30 CFR 57.5037, which require monitoring and limit miners' annual exposure. In Great Britain, the Ionising Radiations Regulations 2017 set a workplace radon reference level of 300 Bq/m3 as an annual average.
A county government moves its records department into the basement of an older courthouse. During a facilities review, the safety coordinator learns the county is in an area with elevated natural radon and arranges long-term testing in the new workspace. Results average 7 pCi/L, well above the EPA action level, with the highest readings on weekend mornings when the ventilation system is off.
The county hires a certified mitigation contractor, who installs a sub-slab depressurization system and seals floor cracks and utility penetrations. Follow-up testing shows levels below 2 pCi/L. The safety coordinator shares the results with the records staff, adds the basement to a retesting schedule, and asks facilities to review other below-grade spaces in county buildings.
The EPA says there is no known safe level of radon exposure. It recommends fixing buildings at or above 4 pCi/L and considering action between 2 and 4 pCi/L.
Yes, through the ionizing radiation standard, 29 CFR 1910.1096, which OSHA has interpreted as setting a limit of 100 pCi/L averaged over a 40-hour week. Many employers aim for much lower levels using EPA guidance.
Underground mines, tunnels, basements, caves, utility vaults and buildings in high-radon areas are most likely to have elevated levels, especially where ventilation is limited.
The most common approach is sub-slab depressurization, which draws radon from beneath the building and vents it outside, combined with sealing entry points and improving ventilation.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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