Performance-Specifications-for-Instrumentation-Systems

MS-PC 2015: Performance Specifications for Instrumentation Systems Designed to Measure Radon Gas in Air Page 12 of 20 7.2 Minimum Detectable Concentration 7.2.1 Criteria The device shall have an MDC of no greater than 37 Bq/m 3 (1 pCi/L) for the minimum measurement period recommended by the provider and when using the procedures recommended by the provider. This criterion applies to a measurement of at least 2 days in duration. As discussed in Section 6.1, an additional criterion applies to 1-hour measurements made with CRMs. For 1-hour measurements, the MDC shall be no greater than 148 Bq/m 3 (4 pCi/L); and, as previously noted, 1-hour measurements are not used in decisions on the need for mitigation. 7.2.2 Test for Minimum Detectable Concentration The basis for the MDC assessment is the count rate of an appropriate set of blanks, or the background of a representative continuous radon monitor when measuring nitrogen or aged air for a time period sufficient to produce a reliable estimate of device response to an atmosphere free of radon. Device providers should calculate and report MDCs specific to minimum exposure durations and typical processing. For devices that measure counts, the MDC shall be calculated using the LLD CT equation in Section 4, derived specifically for methods that use counting technology. For devices that measure something other than counts, such as a drop in voltage on an electret, the background response and its variability are used in the alternate equation (LLD NCT ). For example, the EPA requires that the MDC for ozone be calculated from the variability (measured by the sample standard deviation) of the ozone analyzer’s response to ozone-free air (40 CFR 53.23). It is incumbent on the provider (or manufacturer) to provide such statistics in at least the level of detail as described in Section 8. 7.3 Proportionality 7.3.1 Criteria The difference between the average IPE of a set of five devices exposed at a non-zero low concentration (or integrated concentration) and the average IPE of a set of five devices exposed at a high concentration (or integrated concentration) shall be in the range of 0 ± 15%. The results of the test performed for the criteria in Section 7.1 m ay be used for the set of devices exposed to a low concentration (or integrated concentration). The requirements for the high concentration (or integrated concentration) are discussed in Subsection 7.3.2. As in Section 7.1, the IPE of each individual measurement shall be in the range of 0 ± 25%, and the COV of each set of measurements shall be no greater than 15%. 7.3.2 Test for Proportionality A set of at least five devices shall be exposed in a STAR u nder the same conditions as described in Section 7.1 for the exposure at a low concentration or integrated concentration. The results from the test in Section 7.1 m ay be used here in lieu of repeating the exposure for this test. For the exposure at a high concentration, a set of at least five devices shall be exposed in a STAR under the same conditions of temperature and relative humidity, as far as possible, used for the exposure at low concentration, but with a radon concentration in the range of 1110 – 2220 Bq/m 3 (30 – 60 pCi/L), or at least three times the low concentration range, whichever is greater. Where an integrated exposure is more appropriate, the exposure to a high integrated exposure shall be to a value of approximately 10% less than the upper range recommended by the provider, taking into account the limitations o f the STAR. The test for proportionality is the difference between the averages of the IPEs from the two exposures in the STAR. As an example, the average of the IPE values from the exposure at a low concentration (or integrated concentration) might be 5%, indicating that the devices exposed to the lower concentrations are biased high