Radon Levels and Radon Zones

Radon Measurement

We measure the concentration of radon in the air in units of picocuries per litre (pCi/L) or becquerels per cubic meter (Bq/m3). The pCi unit is used in the United States because of federal law requirements. The World Health Organization (WHO) and most other countries measure the levels of radon in becquerels.

  • 1 pCi/L is equal to 37 Bq/m3

The ideal number of radon measurement would be zero but, unfortunately, this level is nonexistent. Radon is a naturally-occurring radioactive gas that is found everywhere.

  • The average global outdoor radon level varies between 0.135-0.405 pCi/L.
  • Acceptable indoor radon levels vary by country. As a rule, the lower the number, the lower the health risks.

The World Health Organization’s general action level is 2.7 pCi/L. Homes or structures measuring higher are advised to take remedial action to lower that number. In the United States, the Environmental Protection Agency (EPA) action level of 4 pCi/L is the standard, a little higher than that of the WHO. EPA estimates that two-thirds of all homes in the US exceed the recommended action level. Reducing levels to sub-4.0 p/Ci would cut yearly cancer deaths from radon in half.

Don’t know the level of radon in your home or workplace? Contact us and request more information on professional radon testing.

Radon Action Levels

EPA Map of Radon Zones

EPA developed the Map of Radon Zones in 1993 to identify areas of the U.S. with the potential for elevated levels of indoor radon. It helps governments and other organizations target risk reduction activities and resources. The Map of Radon Zones does not show if individual homes need to be tested. No matter where you live, test your home for radon.


Click on the picture to see a bigger image

The Map of Radon Zones divides the country in three main zones, depending on the average radon screening levels. It uses data on indoor radon measurements, geology, aerial radioactivity, soil parameters, and foundation types.

  • Highest Risk – Zone 1: Counties with predicted average indoor radon screening levels greater than 4 pCi/L
  • Medium Risk – Zone 2: Counties with predicted average indoor radon screening levels from 2 to 4 pCi/L
  • Little Risk – Zone 3: Counties with predicted average indoor radon screening levels less than 2 pCi/L

EPA recommends fixing your home if the radon level is 4 pCi/L or higher. Consider fixing if the level is between 2 and 4 pCi/L. Regardless of the results, you should re-test the buidling every couple of years because the concentration of radon is not constant. The health risks of radon are often understimated but they are a serious threat to everyone.

Radon in Ohio

Ohio is one of the states with the highest levels of radon in the country. According to the Ohio Department of Health, half of Ohio homes have levels above the EPA’s recommended action level. In some areas, such as Licking County and Knox County, nearly 75% of all homes have elevated levels of radon. In fact, most of Ohio falls under Radon Zone 1, the EPA highest-risk zone.

The reasons for these elevated levels are complex. First, much of Ohio’s geological formations and soil are rich in uranium which decays and turns into radon gas. Second, numerous geological studies of radon occurrence have concluded that permeability of rock, sediment, or soil is a key factor in elevated levels of indoor radon. This means that even rocks or sediments (such as sand and gravel) that have low uranium concentrations but high permeability may yield relatively high radon values. Lastly, some construction types “trap” the radon gas inside of buidlings, making the indoor radon level dangerously high.

However, even if your home is located within an area with elevated radon concentration, this does not automatically mean your property is at danger. Testing is the only way to determine radon levels because each house is different. You cannot predict radon levels based on state, local, and neighborhood radon measurements. Even if your neighbor’s home has acceptable levels of radon, it does not mean your house would show the same results.

Here is some further information about radon in Ohio: