Estimation of required monitoring time for obtaining validation data in enclosed spaces

Abstract

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.

Representativeness of shorter measurement sessions in long-term indoor air monitoring

“…An inadequate choice may result in large uncertainties or even in wrong information, potentially leading to incorrect conclusions. 16 This problem is associated with the temporal variability of indoor T, RH and contaminant concentration. Their variation is caused by the inuence of numerous factors on indoor air.…”

“…Our work contributes to the development of the relevant methodology. 16,21 The objective of this work is to determine whether the long-term monitoring session can be represented by a shorter measurement period. We proposed to apply scaled relative entropy as a measure which may be used to evaluate the representativeness of dataset in indoor air monitoring.…”

A novel physiologic sampling pump capable of rapid response to breathing

“…The 15 second averaging period was long enough to allow a resting wearer several complete breaths.'' Yet, data from Lee et al 5 found that the magnitude of exposure concentration indoors may change an average of 15% within 4 s with a standard deviation (SD) of 20% (n ¼ 284) even when source concentration was held constant. Hart 4 performed rigorous experiments and determined that the pumps she used stabilized to new speeds in about 1 s (page 128).…”

“…Assessing worker exposures to airborne hazards is an essential element of industrial hygiene practice. Personal exposures must be known in order to (1) determine compliance with exposure limits set by various regulatory agencies, (2) specify personal protective equipment to be worn to isolate workers from hazards, (3) tailor the design of control systems for work sites and to measure the effectiveness of these controls, (4) develop databases for epidemiological dose-response studies, and (5) project the risks of contracting diseases from exposures. Collecting samples representative of exposures is the foundation underlying valid assessment.…”

Diffusive and subdiffusive dynamics of indoor microclimate: A time series modeling

“…Actually, it is transient most of the time. Because of these circumstances, valuable knowledge of the environmental parameters should be based on series of measurements performed in the time domain in properly selected locations [5,6].…”