Q. Were the radon test canisters left too long?

Q. Hey Mark,
The buyers of a home I have listed hired a company to do a radon test. The test came back a little high (4.9). I’m concerned about the test because they used canisters, and they left them in place from Wednesday through Saturday. Wouldn’t this increase the radon levels in the canisters by leaving them longer than 48 hours?

A. Hey Michelle,
The simple answer to your question is no. The radon levels don’t increase the longer the canister is in place. However the validity of the result in this circumstance is dependent upon the type of measuring device used. Also, in the case of “canister” types of tests, there should be two tests taken simultaneously. If both are above 4.0 or below 4.0, they should be averaged, and the recommendations for mitigation would be based on that result. If one is above or one is below, another protocol should be followed that is beyond the scope of this response.

To properly evaluate the validity of your test, I would need some additional information and documentation. I would need to know how many canisters were used, the exact length of time they were in place, the types of canisters, their placement, and the results of each canister. This is because there are many different types of radon testing devices, and they all have different protocols and sensitivities.

First of all, there are charcoal canister devices which allow the continual absorption and desorption of radon. Open-faced canisters will be biased to the radon concentration of the last 12-24 hours of the exposure period. These types of devices may be sensitive to temperature, humidity and airflow extremes and the sampling periods are limited to a few days. So if the test you are asking about was made with a charcoal canister, then 4 days could possibly be too long for an accurate result.

For alpha track detectors efficiency and sensitivity is relatively low, requiring exposure over long periods. Typically, for at least 90 days and often up to a year. For this reason they are not typically used for a real estate transaction.

Electret Ion Chambers can be used for a minimum of 2 days and for as long as a year. There are two types of electret chambers available. The more sensitive short-term would be more appropriate for a real-estate transaction. These devices are sensitive to background radiation, and excess humidity. It is also problematic that if the readings are made in an environment much colder or much warmer than the environment they were calibrated at, it could affect the results.

The best method for short term testing (especially in the context of a real-estate transaction) is to use a continuous electronic radon monitor (CRM). There are many suitable EPA-approved monitors on the market and most have the capability to detect whether they have been tampered with or un-plugged. Some have the ability to read the radon levels on an hourly basis, as well as the temperature and humidity. CRM’s are very reliable. They also give the technician additional information beyond the radon levels, to help them to property interpret the results and to determine if the proper protocols were maintained during the testing period.

Mark Nahrgang is the owner of Kingdom Inspection Network Group – St. Louis and is a professional NACHI certified building inspector in the St. Louis metro area. Mark performs home inspections as well as commercial inspections throughout St. Louis and St. Charles County.


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