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A sample of commercially available, charcoal adsorption type, short-term radon detectors was blind tested under controlled laboratory conditions in order to obtain a “snapshot” of the accuracy and precision of the detectors. The results of the controlled exposures were then compared to a previous field study of the same type of commercially available radon detectors. Radon detectors, purchased from seven different commercial vendors, were exposed to a reference 222Rn gas concentration at the U.S. Environmental Protection Agency’s (EPA) Radon Chamber located at the Radiation and Indoor Environments National Laboratory in Las Vegas, Nevada. EPA Test 1 was performed under a controlled simulated field exposure paralleling, to the extent possible, the previous actual field exposure conditions. A second controlled exposure, EPA Test 2, was performed under a relatively steady state of 222Rn gas concentration, at the same temperature, but a more moderate relative humidity. In the previous field setting evaluation of detectors, five out of six companies tested did not pass the accuracy guideline (all individual relative errors ≤25%) established during the EPA’s former Radon Measurement Proficiency Program (EPA-RMPP). As compared to the field test, the detectors in this study generally exhibited better accuracy and precision. Not surprisingly, it appeared temporal fluctuations in radon concentrations and increased humidity had a negative influence on the accuracy and precision of detectors for some companies. The inability of three out of seven companies to meet former EPA-RMPP guidelines for accuracy, even under ideal exposure conditions (constant temperature, humidity, and radon concentration), highlights the importance of blind testing commercially available radon detectors. Furthermore, the consistent over-reporting or under-reporting trends in the overall results for all three tests suggest a potentially widespread systematic bias for the individual companies that merits further investigation. It is unknown if this one-time “snapshot” represents the overall reliability of commercially available charcoal-based radon detectors. Nonetheless, the findings suggest the need for improved vigilance to assure that the public can rely on commercially available radon detectors to make an informed decision whether or not to perform additional testing or to mitigate.

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