Evaluation of minimum detectable activity and false alarm rate relationships for the eberline alpha-6 continuous air monitors at the Waste Isolation Pilot Plant

The U.S. Department of Energy rule for Occupational Radiation Protection and the DOE Radiological Control Manual (the RCM) (DOE/EH-0256T, Rev 1, April 1994) require the use of continuous air monitors (CAMs) in normally occupied areas there an individual is likely to be exposed to a concentration of airborne radioactivity exceeding the derived air concentration (DAC) or where there is need to alert potentially exposed individuals to unexpected increases in airborne radioactivity levels. The DAC is the airborne concentration that equals the annual limit on intake divided by the volume of air breathed by an average worker for a working year of 2,000 h (assuming a breathing volume of 2,400 m3). It is equivalent to the airborne concentration to which a worker could be exposed for an entire year (2,000 h) without exceeding the annual limit on intake. The rule and the RCM further require that real-time air monitors have an alarm capability and sufficient sensitivity to alert potentially exposed individuals that immediate action is necessary in order to minimize or terminate inhalation exposures. The RCM also recommends that real-time air monitors should be capable of measuring 1 DAC when averaged over 8 h (8 DAC) under laboratory conditions. This report was prepared jointly with actual data from the CAMs in use at the WIPP by ITRI, WID, and EEG and provides an evaluation of minimum detectable activity (MDA) or concentration and false alarm rate relationships. The methodology used in this report is adapted from Inhalation Toxicology Research Institute Annual Report for 1993-1994, ITRI-144, pp 18-22, December 1994