Consideration of measurement error when using commercial indoor radon determinations for selecting radon action levels

An examination of year-long, in-home radon measurement in Colorado from commercial companies applying typical methods indicates that considerable variation in precision exsts. This variation can have a substantial impact on any mitigation decisions, either voluntary or mandated by law, especially regarding property sale or exchange. Both long-term exposure (nuclear track greater than 90 days), and short-term (charcoal adsorption 4–7 days) exposure methods were used. In addition, periods of continuous monitoring with a highly calibrated alpha-scintillometer took place for accuracy calibration. The results of duplicate commercial analysis show that typical results are no better than ±25 percent with occasional outliers (up to 5 percent of all analyses) well beyond that limit. Differential seasonal measurements (winter/summer) by short-term methods provide equivalent information to single long-term measurements. Action levels in the U.S. for possible mitigation decisions should be selected so that they consider the measurement variability; specifically, they should reflect a concentration range similar to that adopted by the European Community.