A model to estimate a worker's exposure to spray paint mists

Although local exhaust ventilation reduces exposure to airborne contaminants, current design methodology is limited because the relationship between exposure and ventilation is seldom known for a specific industrial operation. This research addressed this deficiency by introducing the notion of an empirical-conceptual model. These models relate exposure to ventilation through various process parameters responsible for the generation and transport of contaminants. To illustrate the modeling technique, an empirical-conceptual model of a spray painting task was developed. A conceptual model described three processes that determine the exposure: droplet formation, droplet transfer, and droplet transport. Each process was examined and important factors which characterize the processes identified. These factors were then grouped into four dimensionless variables using dimensional analysis. A laboratory set-up used a mannequin, flat plate and spray nozzle in a wind tunnel to find the functional relationship among these variables. The model indicates worker orientation to the freestream has a significant influence on breathing zone concentrations. The magnitude of the dimensionless quantity consisting of nozzle pressure, worker height, liquid viscosity, and freestream velocity determined in which orientation the concentration was higher.;The influence of process parameters on the breathing zone droplet size distributions was then investigated. Droplets were collected on treated polycarbonate membrane filters and sized with a light microscope. The results indicate worker orientation strongly influences the breathing zone size distributions, with larger sizes resulting when the worker stands so the freestream flows to the worker's side than to the back. This difference is attributed to overspray transport mechanisms that depend on the interaction of the spray gun air jet with the freestream.;The empirical model was then evaluated in the field. Eight workers in a paint shop were sampled over five weeks. Forty percent of the measured task exposures are within the estimated experimental error of the model prediction and 71% are within a factor of three of the prediction. Four of the eight worker mean exposures are within one standard error of the model prediction. These results indicate the prospect for empirical-conceptual models to predict exposure and to aid in the design and economic optimization of engineering controls.