MS-QA_06-2019 rev5

ANSI/AARST MS-QA 2019 12 Radon Measurement Systems Quality Assurance Continuous Radon Monitors (CRM) 4 CONTINUOUS RADON MONITORS (CRM) QC All the requirements described in Section 3 apply to CRMs, and field operations for using CRM devices require QC procedures that include: 1. Instrument Checks 2. Comparison Checks , and 3. Calibrations Records of within-limit QC check results at frequencies described in this standard are required to defend the data validity. 4.1 CRM Instrument Checks Standard operating procedures are to include checks of instrument functionality at the beginning of each test conducted. Informative advisory —The instrument checks, that include review of instrument warning indicators, should comply with manufacturer instructions and user procedures. For example, some CRM designs include automatic generators of electronic pulses resulting in a signal that would be produced by radon decay products in the detection chamber. These generators can serve as both instrument checks and as a QC measure. 4.2 CRM Comparison Check Requirements Note— Comparison checks are collocated , simultaneous measurements conducted for at least 48 hours to verify and document the continued stable and in-control operation of a CRM by comparing a result to another radon measurement device not necessarily of the same method category. The purpose of both a comparison check and a duplicate are to verify and document that there have been no increases in the measurement system imprecision since the last passing QC check or calibration . 4.2.1 CRM Comparison Checks—Frequency and Procedure Comparison checks are to be made with approximately every tenth measurement (i.e., 10%), so that the checks are distributed across the range of conditions, operators and usage patterns experienced by the radon measurement provider. CRMs used in a comparison check are to be operated in the manner that they are typically deployed in the normal course of business. The results of comparison checks shall be recorded and analyzed so that the QP better understands the expected imprecision during routine, stable operations (e.g., “ in-control ” conditions). Informative advisory —It is recommended that routine procedures for beginning chain of custody of CRMs when they are received, either new or from recalibration, include a comparison check with another CRM. This practice can identify malfunctions or damage during shipping and handling. 4.2.2 CRM Comparison Check—Statistic The test statistic for a comparison check and a duplicate is the RPD, which represents imprecision as a percentile of the best estimate of the known concentration. Note that the RPD is always positive, as the smaller measurement result is subtracted from the greater measurement result. The average of the two devices is used in the denominator because neither comparison checks, nor duplicates can assume that either result is more reliable. Informative advisory —If repeated checks are made with the same CRMs, it is important to document whether one CRM is producing results that are consistently greater than or less than the comparison CRM, as that indicates potential bias error and warrants investigation.