Estimation of required monitoring time for obtaining validation data in enclosed spaces.
Methods for estimating airborne contaminant concentrations at specific locations within enclosed spaces, such as mathematical models and computational fluid dynamics (CFD), often are validated against directly measured concentrations. However, concentration variation with time introduces uncertainty into the measured concentration. Failure to determine monitoring time requirements can lead to errors in quantifying representative concentrations, which are likely to be attributed to errors in the method being validated. In the current study, to obtain the representative concentrations at multiple locations with a direct reading instrument, we used the standard deviation ratio (SDR) method to determine the required minimum monitoring time within a specified precision limit. To demonstrate the use of the SDR approach in constructing precision confidence intervals, tracer gas concentrations at nine sampling locations in an experimental room were measured to obtain population parameters. Three flow rates of 0.9, 3.3 and 5.5 m(3) min(-1) were employed and contaminant concentrations were measured using a photoionization analyser. Monitoring time requirements varied substantially with location within the room and were strongly dependent upon the flow rate of air through the room. The proposed method would be very useful for industrial hygienists and indoor air researchers who sometimes need to obtain several hundred measured concentrations for validation purposes or to perform tests under repeatable conditions in enclosed spaces. This study also showed that the proposed method can be used to devise efficient indoor monitoring strategies.
Lee
Eun Gyung
EG
Exposure Assessment Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA. dtq5@cdc.gov
Feigley
Charles E
CE
Hussey
James R
JR
Slaven
James E
JE
D000393:Air Pollutants / Q000032:analysis*; D002151:Calorimetry; D004784:Environmental Monitoring / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
D000393:Air Pollutants