MAH_2019

MAH 2019 Companion Guidance Section B Radon Test Devices and QC Terminology 4 MAH Companion Guidance Section B DESCRIPTIONS OF TEST DEVICES Passive Device Measurement Systems As used in this standard, “Passive devices” are measurement systems that collect a time-weighted average and do not provide hourly readings. - Charcoal adsorption detectors (CAD) CAD detectors employ activated charcoal that adsorbs radon from the surrounding air. Exposure durations are typically limited to 2-7 days. After exposure, detectors must be sent to the laboratory without delay. Detectors are configured for either Gamma-ray Spectroscopy or Liquid Scintillation Spectroscopy analysis. - Alpha-track detectors (ATD) ATD detectors utilize a piece of plastic inside a container. Alpha particles emitted from radon strike the plastic detector and create damaged “tracks” that are visible with a microscope. The track density is determined by the laboratory to achieve an average radon concentration for the time period the detector is exposed. - Electret ion chamber detectors (EIC) EIC detectors use a chamber made of, or lined with, an electrically conductive material with an electrically charged electret as the detecting mechanism. The decay of radon discharges voltage from the electret. The radon concentration is calculated by comparing the electret voltage measured before and after exposure. - Electronic integrating devices (EID) An EID is an electronic measuring device similar to a continuous monitor but is not recording a retrievable time series of 1 hour measurements. EID devices are categorized as passive devices because such devices do not provide the additional measurement data points needed for making mitigation decisions. Continuous Radon Monitors (CRM) A CRM is an electronic device that is automatically recording a retrievable time series of numeric measurements of radon concentration averaged over time intervals of 1 hour or less. These additional data points can help to judge whether or not there was an unusual occurrence during the test that might invalidate the overall measurement. TERMINOLOGY ASSOCIATED QUALITY CONTROL (QC) Advisory —See ANSI/AARST MS-QA, “Radon Measurement Systems Quality Assurance” for more information. Duplicate or Comparison Check Measurements Duplicates or comparison check measurements are pairs of detectors or monitors deployed in the same location, side-by-side for the same measurement period. The purpose is to evaluate and track imprecision or agreement between detectors or monitors across time. Using calculations for relative percent difference (RPD): - In an environment with a radon concentration ≥ 4 pCi/L, the goal for agreement is an RDP ≤ 14%. The warning limit is an RPD ≥ 28% and the control limit is an RPD ≥ 36%. - Between 2 and 4 pCi/L, the goal for agreement is an RDP of ≤ 25%. The warning limit is an RPD ≥ 50% and the control limit is an RPD ≥ 67%. Calibration Calibration means to adjust or determine or both, the response of an instrument or device relative to a series of conventionally true values. Ongoing calibration is part of all quality assurance efforts. Blank Measurements Blanks are CAD, ATD or EIC devices deployed to verify and document the absence of effects on the measurement resulting from sources other than the air being tested. Since blanks are not exposed (i.e., not left open to permit radon to enter the detector), their measurement value should be below the lower limit of detection. Spiked Measurements Spikes are CAD, ATD or EIC detectors that have been exposed in an approved reference chamber to a known concentration of radon (i.e. “spiked” with radon). Using spiked measurements helps to validate the accuracy of a laboratory analysis and/or detectors supplied by a laboratory.