MS-QA_06-2019 rev5

ANSI/AARST MS-QA 2019 27 Radon Measurement Systems Quality Assurance Laboratories—All Methods 7.9 Analysis Laboratory—Duplicates or Recounts (Best Practice) Note—The fourth type of laboratory-specific QC measurement that may be tracked and analyzed using control charts with probability-based limits is laboratory duplicates (side-by-side exposures), which assess imprecision in the entire laboratory system and recounts of the same exposed device, which assess imprecision only in the analysis operation. In either case, the results can be tracked using the RPD of the pairs. Informative advisory —If possible, laboratory duplicates should be exposed in an area with a radon concentration large enough to produce adequate counts or signal. If the distribution of RPD values (mean and sample standard deviation) of lab duplicates and recounts is similar to the distribution of RPD from field duplicates , then documentation will provide evidence that laboratory processes do not add significant variability. 7.9.1 MinimumWarning and Control Limits—Duplicates or Recounts Until a laboratory generates at least 20 laboratory duplicates or recounts, the criteria in Table 7.1 can be used as interim default values. Note—As referenced in Section 3.5 , these limits were derived using the chi square function, when precision error is a constant function of the mean. Table 7.1: Temporary Default Criteria for Lab Duplicates/Recounts Average of the two devices Warning Limit RPD Control Limit RPD ≥ 4.0 pCi/L ( ≥ 150 Bq/m 3 ) 28.0% 36.0% < 4.0 and ≥ 2.0 pCi/L (<148 and ≥ 75 Bq/m 3 ) 50.0% 67.0% < 2.0 pCi/L (< 75 Bq/m 3 ) n/a Absolute value of the difference between the devices ≤ 1.0 pCi/L (37 Bq/m 3 ) or both are reported as less than the MDC