MS-QA_06-2019 rev5

ANSI/AARST MS-QA 2019 24 Radon Measurement Systems Quality Assurance Laboratories—All Methods Laboratories who assemble detectors are responsible for testing the homogeneity of the batch using standard sampling techniques, tracking which detectors were constructed from which batch , and setting limits on the ranges of the characteristics that affect their use as detectors (e.g., background and response to radon exposure) so that the requirements in this standard are met. 7.5 Calibration To operate within the requirements of this standard, a radon measurement analysis laboratory shall develop and document operating procedures and calibration relationships specific to the laboratory, analysis equipment, and detector material and configuration. 7.5.1 Calibration Chamber The calibration system chamber must meet the requirements of a standard test atmosphere for radon, as defined in this standard. 7.5.2 Exposures The requirements of Section 3.4 Measurement System Calibrations and Evaluations apply to all methods, including those detector characteristics that require calibration exposures to include exposures of sets of devices to different environmental conditions. If the device configuration is affected by temperature and relative humidity, as are charcoal adsorption methods, calibration exposures are to expose at least five, and preferably more, devices at a time in an exposure calibration chamber to combinations of three parameters. These include separate exposures to environments of: a) three different relative humidity ranges, including an RH less than 30%, an RH between 40% and 60%, and an RH greater than 60%; b) two different temperatures, including one greater than 70° F; and c) at least three different durations/integrated concentrations. (Note—These combinations result in a total of up to 18 separate exposure sets of at least five devices in each set.) Full calibration is to include using the resulting corrected count rates in nonlinear regression analyses to generate interpolated functions (curves), which best represent the relationship between counts and the radon concentration to which the device was exposed. Informative advisory —The use of tabular-only calibration factor “lookup” values is discouraged, because computer algorithms can be used to arrive at interpolated correction factors specific to, for example, the duration and change the specific CAD mass. 7.6 Initial and Ongoing Warning and Control Limits for Laboratory Assessments of Bias and Imprecision Note—Laboratories assess components of error in their operations using various QC checks as part of their routine operations. For example, conducting a second analysis of the same device assesses imprecision due to the analysis system only. Other checks assess imprecision of the entire laboratory system, such as with lab duplicates exposed to a concentration greater than the MDC. Other checks assess bias, such as a laboratory control sample that is used to verify and document that no drift has occurred in the analysis system electronics, or a laboratory control matrix spike device is introduced in the beginning of the lab custody to assess total error in laboratory operations. Informative advisory —QA managers must be vigilant and imaginative in assessing these results as well as inserting QC checks into other operations as investigative tools.