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Safe vs. Action Levels

Official Limits on Radon levels


The Radon Act 51 passed by the US Congress set the natural outdoor level which averages 0.4 pCi/L as the target radon level for homes which unfortunately most homes (two thirds) exceed.

The Environment Protection Agency was given the task of developing practical guidelines. Considering the high cost of mitigation methods available to homeowners in 1980s (averaging $1,200 but up to $2,500), EPA issued its recommendations:

  • 4 pCi/L … the “action” limit (fix your home)
  • 2 pCi/L … the “consider action” limit (consider fixing your home)

EPA did not want to force homeowners to install costly radon mitigation systems, leaving the decision up to each homeowner. But at the same time, EPA has made it clear that the 4 pCi/L action limit is not a “safe” level and warned the public:

Any radon exposure has some risk of causing lung cancer. The lower the radon level in your home, the lower your family’s risk of lung cancer.


Action limit is not a safety limit!


“Action limit” does not imply safety. It is merely the result of a macroeconomic cost/benefit analysis for the US population at large. Shockingly, the cancer risk from radon at the “action” limit is about 1,000-times higher than the safety limits allowed for suspected carcinogens and toxins in food or drinking water.

The societal cost of mitigating all homes to a 4 pCi/L level was estimated at $44 billion but that would rise to $101 billion if the action level was set at 2 pCi/L. Most radon-attributed deaths (70%) are caused by radon levels lower than 4 pCi/L (BEIR VI, 1998). Setting the limit at 4 pCi/L benefits (but does not necessarily save) only 30% of the 21,000 people that die each year of radon-attributed lung cancer, while a lower limit of 2 pCi/L would benefit 50%. The high “action limit” reduces the number of lives saved.

And, the societal cost of lung cancer deaths caused by radon is relatively low because it kills so quickly, often within months. Its 5-year survival rate is only 10–14 percent and thus, it costs only several billion dollars per year. Spending money, for example, on an anti-smoking campaign saves more lives, even though it is unfair to non-smokers and children who may be exposed to radon gas. (Radon causes 26% of lung cancer deaths among non-smokers.)

The “action” limit is based on the average cost of a radon mitigation system in 1980s – $1,200. If the cost of radon mitigation was only $600, the action limit recommended to homeowners would have been set at 2 pCi/L.


How safe is the 4 pCi/L radon “action limit”?


People spend most of their time at home – on average 70%, but more in case of women and particularly, children. Although the 4 pCi/L level has become a benchmark for real estate transactions, it still carries considerable risks – equivalent to getting a chest x-ray or smoking 10 cigarettes each day. (EPA)

When relaxing at home, we breathe in radon. It is soluble in blood and circulates through the body and all organs. Some tends to accumulate in fatty issues. Then, almost all is harmlessly exhaled by our lungs or skin until equilibrium is established between the ambient and internal radon concentrations.

But radon decay products, radioactive solid particles, much smaller than household dust, float in the air and get trapped in our lungs, trachea, and bronchi. At 4 pCi/L each liter of air contains 70,000 radon atoms. But less than 1% of the inhaled atoms get trapped and we thus accumulate in our airways about 600,000 radioactive particles every hour. When they shoot out alpha particles, they damage the DNA of epithelial cells, causing mutations and lung cancer.

The risk to the average person of dying of radon-caused lung cancer due to a lifetime exposure to 4 pCi/L radon level at home is 2.3 percent. If there are five people in your family, the chances that someone becomes a victim of radon is over 10 percent.

The most substantial epidemiological study ever on the link between residential radon and lung cancer was published the University of Iowa in 2000. This 5-year study proves that radon even at the low levels found in homes causes lung cancer and that the risk is proportional to the radon level.

The study shows that the exposure of adult women to radon over 15 years at the EPA “action” level of 4 pCi/L increases the lung cancer risk by 50 percent.


What is a safe and acceptable level of radon gas?

This is actually two separate questions. The first is: “What is a safe level of radon gas?” The second is: “What is an acceptable level of radon gas?”

What is a safe level of radon gas?

This is the simpler of the two questions. A safe level of radon gas is no radon gas. Radon gas is a carcinogen which causes lung cancer. The US EPA has put it plainly, stating, “Any radon exposure has some risk of causing lung cancer. The lower the radon level in your home, the lower your family’s risk of lung cancer.” The average person receives a higher dose of radiation from the radon levels in their home than from their combined exposure to all other radiation sources, natural or man-made. Radon gas is a

naturally-occurring byproduct of the radioactive decay of Uranium in the soil. Depending on your geographic location, the radon levels of the air you breathe outside of your home may be as high as 0.75 pCi/L. The national average of outside radon levels is 0.4 pCi/L and it is estimated by the National Academy of Sciences that outdoor radon levels cause approximately 800 of the 21,000 radon induced lung cancer deaths in the US each year. Your risk of lung cancer increases substantially with exposure to higher radon levels.

What is an acceptable level of radon gas?

Radon Act 51 passed by Congress set the natural outdoor level of radon gas (0.4 pCi/L) as the target radon level for indoor radon levels. Unfortunately two-thirds of all homes exceed this level. The US EPA was tasked with setting practical guidelines and recommendations for the nation. To this end, the US EPA has set an action level of 4 pCi/L. At or above this level of radon, the EPA recommends you take corrective measures to reduce your exposure to radon gas. This does not imply that a level below 4.0 pCi/L is considered acceptable, as stated in the BEIR VI study. It is estimated that a reduction of radon levels to below 2 pCi/L nationwide would likely reduce the yearly lung cancer deaths attributed to radon by 50%. However, even with an action level of 2.0 pCi/L, the cancer risk presented by radon gas is still hundreds of times greater than the risks allowed for carcinogens in our food and water.


While no level of radon gas is completely safe, as with most things in life we must balance the benefits and costs to find our own “acceptable” levels. We walk outside and work in the sun, exposing ourselves to ultraviolet radiation and increasing our risk of developing skin cancer. We drive in automobiles almost every day even though greater than 1 in 86 deaths is a result of automobile accidents. People smoke, eat poorly, and engage in dangerous behaviors on a daily basis. To some degree, radon gas is another daily risk that we all must take. However, you choose what you eat, whether or not you smoke, and how and when you drive. You have no choice but to breathe the air in your home. A simple and inexpensive radon test can give you the information you need to make an informed decision about what level of radon gas exposure is acceptable to you.