Answer to Question #13424 Submitted to "Ask the Experts"

My question concerns residential basement radon levels and exercising. My home is about five years old. At the time it was built I had the builder convert the "included" passive radon mitigation system to an active system that exhausts through the roof. At the time the system was converted, short-term radon levels in the basement were in the range of 185 Becquerels per cubic meter (Bq m^-3). With the active system, the long-term average is around 37 Bq m^-3, but my monitor has the ability to show weekly and daily averages. Sometimes the daily average can be in excess of 93 Bq m^-3. I know that readings can vary greatly over time and that in most cases the long-term exposure level is what is important. However, in my case I have a treadmill in my basement, which I use on days where the weather outside is uncooperative. Before exercising, I always check the daily reading, and will consider not running on the treadmill if the level is significantly "elevated" at the time. I do have two windows in the basement that I open while exercising, but I don't know how quickly this actually dissipates the radon level as my monitor's daily value is an average of hourly values. It seems as though the short-term value is useful in my case, as I think I would want to avoid gulping many liters of "hot" air in a short period of time while the levels are elevated. Am I being too cautious?

The occasional elevated daily average radon measurement in the basement where you exercise is not a cause for concern. The physical and mental benefits of regular exercise, particularly during these difficult times, far outweigh any incremental radon exposure you might incur from exercising in your basement during periods when the daily average radon concentration is higher than long-term average. As you rightly noted, your risk depends on your cumulative exposure to the radioactive decay products of radon gas. Time spent in an area of your basement during periods when radon levels may be a bit above the annual average would not appreciably affect your cumulative exposure even though your breathing rate would be increased during that relatively short fraction of your day. The fact that you ventilate the area would, to a degree, mitigate the potential exposure to the radioactive decay products of radon, particulates that actually cause the radiation exposure to your lungs. The long-term average radon concentration in your home appears to be in line with typical values, particularly in homes that have been mitigated, even though the daily as well as seasonal averages may vary significantly. Your decision to install a fan to convert your passive mitigation system to an active one is commendable and well worth the extra cost. Based on the information you provided, your long-term average and even your elevated daily average radon concentrations are below the US Environmental Protection Agency guideline of 4 pCi L^-1 (150 Bq m^-3).¹ Enjoy your exercise sessions without concern for the risks from radon. Such activity is important to your physical and mental well-being.

Jan Johnson, PhD, CHP Emeritus

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¹The radon concentration units are given here in pCi L^-1 (called traditional units) because that is the unit used by the US Environmental Protection Agency. However, the Health Physics Society has adopted the SI (International System) of units and these are given in parentheses.