The impact of transfer efficiency on worker exposure during spray painting

Compressed air spray guns are commonly used for paint application in industry. Paint mists generated from a spray gun contain large amounts of toxic chemicals. Research has found that high risks of respiratory, systemic, and possible carcinogenic effects are related to long-term paint exposure. A spray gun with high transfer efficiency is considered a control intervention that minimizes spray-painter exposure. However, no scientific methodology has been established to evaluate the association between transfer efficiency and worker exposure. This research expands upon an existing exposure model for spray-painting tasks by characterizing and modeling the paint transfer process. The transfer efficiency model was first validated in the laboratory. The results showed that the predicted transfer efficiency agreed with the measured values within the model uncertainty limits.; The transfer efficiency model was then extended to account for solvent volatilization. A mass balance was performed to predict the transfer efficiency bounds, and the average of the bounds was used to estimate the transfer efficiency based on total mass of paint sprayed. The original model was also converted to predict transfer efficiency based on the mass of solids. This prediction was within the 95% confidence interval of the measured transfer efficiency.; The final phase of this research was the field application of the transfer efficiency - exposure model. The model was tested with both non-volatile oil and volatile paints. When spraying with non-volatile oil, six of the nine workers' transfer efficiencies agreed with the model predictions; six of the nine workers' exposure levels agreed with the predictions. Twenty paint samples were collected from three workers during their routine spray painting tasks. The model predicted task exposure within a factor of three of the model predictions; it predicted worker average exposure within the 95% confidence interval; and it predicted overall group mean exposure within one standard error. This work provides essential information about the impact of process parameters and work practices on the transfer efficiency of spray guns and worker exposure. The modeling concept here could be applied to other industrial operations, as well as other routes of exposure.