Exposure models for contaminant control decisions involving ventilation.

This paper discusses two complementary techniques for modeling human exposures to airborne contaminants with a focus on control decisions involving ventilation. Particular attention is given to: (I) the use of empirical-conceptual models with dimensional analysis and (2) computational fluid dynamic simulations. Both techniques provide valuable information. An empirical -conceptual model is formulated with dimensional analysis for a spray painting operation. Parameter estimates are obtained from wind tunnel studies to develop specific equations for worker exposure as a function of nozzle air pressure, mass overspray generation rate, paint viscosity, booth air velocity, worker orientation to the air flow and object, and worker size. Field data confirm the model and illustrate its utility. Eight workers were sampled for a total 55 spraying tasks involving conventional air atomization applications conducted in spray booths. The model predictions provided a nearly unbiased estimator with 71 % of the measured exposures within a factor of 3 of the predictions, and 40% within the measurement uncertainty of the methods employed. Transport processes related to the interaction of the spray-gun, the worker position, and the spray-booth air flows are examined with the computational fluid dynamic simulations and corroborated with flow visualizations. Steady state solutions of the Navier-Stokes equations employing k-e turbulence models and particle tracking are presented. The simulations confirm the flows observed experimentally and identify the recirculation zones responsible for exposure. The model is used to speculate on optimization of control decisions as well as the limits of control achievable subject to real-world constraints .