Radon Information & Resources

Radon is a colorless, odorless, tasteless, radioactive gas produced during the natural decay of uranium (an element that occurs in small amounts in rock and soil).  Radon is present in low levels in the outside air we breathe daily.  It is responsible for over 2/3rds of the natural background radiation exposure that humans receive [1].

Where does radon come from?

Through the process of radioactive decay, the uranium naturally present in soil will turn into radon which is a gas [2]. This gas is mobile and is able to navigate through the soil up into the atmosphere.  While this gas is mostly harmless when it is diluted by the outside air, it can also migrate up through soil into buildings where it can become trapped.

Why is radon hazardous?

The process of radioactive decay releases excess energy in the form of waves and particles as elements transform from one to another [5].  This energy can be deposited into tissue causing biological damage.  Radon gas is an inert noble gas which freely enters and exits the lungs with each breath.  However, it will further decay to other elements, progeny or daughters, which are more likely to deposit or “stick” in the lungs where they remain to emit this excess energy.

Is radon a problem around here?

The uranium which leads to radon is present in nearly all soil in varying amounts.  Dane County as a whole has been designated Zone 1 by the EPA.  This zone is characterized as having the highest potential for average indoor radon levels to be in excess of 4.0 pCi/L [4] (where the typical concentration of radon in outdoor air is 0.4 pCi/L [3]).  The Wisconsin Radon Information Centers collect radon testing data and have found that 1 in 10 homes in Wisconsin have high radon.  Additionally, 46% of Wisconsin zip codes report that at least 50% of test results are over the 4.0 pCi/L.

What are the regulations for radon?

Presently there are no regulations at a federal level which govern the acceptable level of radon for indoor environments.  Instead, there exists a disparate set of rules and regulations from state to state.  Within the state of Wisconsin, the only regulations around radon are licensing rules for family childcare centers which require periodic testing of certain spaces used by children and mitigation when results exceed the specified acceptance criteria.

This is an accordion element with a series of buttons that open and close related content panels.

Isn’t the limit 4.0 pCi/L?

The often-referenced value of 4.0 pCi/L is defined as the EPA Action Limit for mitigation (reduction) of radon in residential buildings.  This value seeks to protect the general public which includes the most vulnerable members of our population including young children and the elderly.  Workplace action limits are set to protect healthy working adults and as such are higher than the EPA Action Limit.  There are several other values which are often cited including 100 pCi/L, 25 pCi/L, 30 pCi/L, 7.5 pCi/L, and 8.1 pCi/L.

100 pCi/L – The Occupational Health and Safety Act of 1970 specifies that no employer shall allow for an employee to be exposed to airborne radioactive material in excess limits set forth by 10 CFR Part 20 Appendix B Table 1.  However, it should be noted that the enforceable regulations is the original version of the referenced federal regulation which is the 1969 version of 10 CFR Part 20 Appendix B Table 1 which lists the Maximum Permissible Concentration of Radon-222 as 1E-7 μCi/L, or 100 pCi/L.

25 pCi/L – This number is often referenced as it is 25% of the 100 pCi/L value above.  OSHA defines an airborne radioactive area as one in which material exists in concentrations exceed 25% of the 10 CFR Part 20 Appendix B Table 1 values (again noted that this is the 1969 version).

30 pCi/L – This is the current valued listed in 10 CFR Part 20 Appendix B Table 1 as of March 25, 2021.  This is not the value intended as reference by OSHA.

7.5 pCi/L – This is 25% of the current value from 10 CFR Part 20 Appendix B Table 1, but consistent with OSHA interpretation it is not the correct value for the airborne radioactive area limit for Radon-222.

8.1 pCi/L – This is the value of 300 Bq/m3 after the unit conversion. This value was set forth by the International Commission on Radiation Protection (ICRP) as the upper limit of a range of reference values from 100 Bq/m3 to 300 Bq/m3 (2.7 pCi/L to 8.1 pCi/L).  Their recommendation was that authorities should set national reference levels as low as is reasonably achievable within that range.

As true for any carcinogen, a safe level of radon exposure cannot be identified because damage to a single cell could cause a cancer.  The above listed guidelines were all developed to reduce risk of developing cancer from a lifetime of radon exposure.

What does UW-Madison do?

It is acknowledged that the elimination of all radiation exposure from radon within buildings is not possible [6]. UW-Madison seeks to reduce the exposure to members of our campus community through a combination of testing and mitigation.  The University will use the reference values set forth by the International Commission on Radiation Protection as an initial starting point for control and risk reduction.


This is an accordion element with a series of buttons that open and close related content panels.


  1. National Council on Radiation Protection (NCRP) Report No. 160. Ionizing Radiation Exposure of the Population of the United States. March 3, 2009. (Figure 3.19)
  2. Reynolds, C., Nuclear Forensic Search Project. Decay Chain. Accessed December 28, 2022.
  3. A Citizen’s Guide to Radon – The Guide to Protecting Yourself and Your Family from Radon. EPA 402/K-12/002. 2016. Accessed December 29, 2022.
  4. EPA Map of Radon Zones. Accessed December 29, 2022.
  5. Keith S., Et. al. Toxicological Profile for Radon. Agency for Toxic Substances and Disease Registry (US); Atlanta, GA, USA: 2012.
  6. American Cancer Society. Prevention and early detection: radon. 2006. Atlanta GA. Accessed December 28, 2022