| Insufficient characterization and development of methods for estimating exposure to airborne contaminants often increases uncertainties and decreases accuracy and precision of personal exposure estimates. The investigation of fundamental physical factors that influence exposure estimates can minimize errors and enhance understanding of the impact of those factors on exposure assessment and control. Here four physical factors, temperature, worker's location, air inlet type, and worker's activity, were investigated in a steady-state experimental room (volume = 19.2m3). A tracer gas (99.5% propylene), continuously injected at a constant rate through the top of a 1-m high pedestal, was monitored automatically at 144 sampling points with a photoionization detector. Three constant dilution air flowrates, 5.50 m3/min, 3.27 m3/min and 0.88 m3/min, were employed. The north wall was heated or cooled to represent a building's external wall. A heated mannequin was used to investigate the impact of a stationary worker's presence. Also, the concentration outside the facepiece of an air-supplied respirator was measured for a person at various locations and orientations, and for various activities.;Because simulated summer and winter conditions generated greatly different dispersion patterns at breathing zone level, occupational hygiene professionals should not assume that monitoring data from a single season is representative of the entire year. The worker presence influenced the contaminant dispersion pattern only in the occupied portion of the room, and breathing zone concentrations depended strongly on the worker's location. The ceiling diffuser inlet was more efficient than the wall jet because only a small volume immediately above the source had high tracer concentrations, and the rest of the room was virtually well mixed. The experimental results clearly demonstrated the importance of basing exposure estimates on personal sampling rather than area sampling whenever possible because of the impact of worker orientation and movement on the breathing zone concentrations.;The findings from this investigation indicate that incorporating the effect of physical factors in exposure assessment promises improved accuracy and better understanding of uncertainties. |
