What is the control limit for RPD calculations if both radon results are above 4 pCi/L?

The control limit for Relative Percent Difference (RPD) calculations is an important factor in ensuring the accuracy and reliability of radon test results. When both radon results exceed 4 pCi/L, the threshold for acceptable variability is set at 36%. This percentage is established based on statistical analysis and is designed to indicate whether the differences between duplicate radon measurements are within acceptable limits given the potential variance in testing conditions and laboratory methods.

In practical terms, if the RPD falls below this threshold of 36%, it suggests that the two measurements are sufficiently close to each other, reflecting consistency and reliability in the testing process. As a result, a control limit of 36% provides a benchmark for quality assurance in radon measurements, especially when higher levels of radon are present, where precision becomes critical for assessments and mitigation decisions.