Invisible danger: radon gas threatens 25% of U.S. homes living in high-risk areas

Research undertaken by Harvard T.H. Chan School of Public Health have discovered that more than 25% of the population in the United States may be living in areas regularly exposed to a level of radon gas concentration associated with developing cancer.

What is radon gas?

Radon gas, odorless and invisible, is radioactive and comes from natural radioactive decay processes in underground uranium. After the uranium decays, it generates radon gas, which can rise and work its way into buildings.

According to the U.S. Environmental Protection Agency (EPA), 148 Bq/ m3 (bq stands for becquerel) is the level at which radon gas can cause a serious cancer threat. Where that number is exceeded in living spaces, the EPA recommends installing a radon mitigation system.

Measuring radon concentrations has historically proved difficult, although there has been a huge improvement in the last few decades.

A study on data from 2001 to 2021 discovered that average radon concentration across the United States was estimated at 53.3 Bq/m3, and established five radon zones based on the averages in different areas (Zone 1 having the lowest, below 37m3, and Zone 5 the highest, above 148 Bq/m3).

Which parts of the United States are most exposed to radon gas?

Zone 5, whose average is above the danger level stated by the EPA, includes most of South Dakota, North Dakota, Nebraska, parts of Iowa, eastern Pennsylvania and central Ohio.

However, the numbers are dynamic, depending on the time of year. For instance, most of Zone 4 (some areas of Colorado, large areas from Canada down to Wisconsin, parts of Illinois, Iowa and Ohio) moves into Zone 5 in the winter.

There are also specific areas in Zones 1, 2 or 3 that are exposed to higher levels of radon concentration than the average in their surroundings. Surprisingly, the study found the majority of at-risk homes were in otherwise low-risk areas.

All in all, it is believed 83.8 million people in the United States, which represents 26.8% of the population, live in areas where their homes can be exposed to more than 148/Bq/m3 of radon concentration.

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