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Determinants of exposure to metalworking fluid in small machine shops Ross, Andrew Spilsbury

Abstract

The objectives of this study were to measure personal airborne concentrations of metalworking fluids (MWF) in small machine shops by three different methods and to conduct a determinants of exposure analysis to evaluate factors that contribute to or minimize exposure to MWF. The three aerosol exposure measures were "total" aerosol, PM10 aerosol and extractable mass concentration. Eighty-eight machinists, employed at fifteen different machine shops, participated in the study. Side by side full shift "total" and thoracic aerosol samples were obtained from all participants and seventy-three machinists were sampled on two occasions with a minimum of eight days between measurements. There was total of 161 person-days of participation. Machinists were observed for their entire shift and information was collected at 15-minute intervals on different tasks they performed. Shop, machine tool and MWF management characteristics were also collected. Statistical modeling of the collected information was used to identify significant predictors of exposure. Extractable mass concentration was analyzed using a provisional American Society for Testing and Materials (ASTM) method for metalworking fluids. The ASTM method was performed on filters from "total" aerosol (open-faced, 37 mm cassettes). Thoracic aerosol was collected using personal PM10 samplers. The mean "total" aerosol exposure was 0.32 mg/m³ and the mean thoracic aerosol exposure was 0.27 mg/m³. The mean extractable mass exposure was 0.07 mg/m3 and the mean fraction of extractable mass to "total" aerosol was 0.31. Multiple linear regression models explained 0.65, 0.63 and 0.50 of the variance for the "total" aerosol, thoracic aerosol and extractable mass models respectively. The models all indicated shop height was associated with lower exposure. Operating an enclosed computer controlled (CNC) machine tool, operating a wet grinder, operating a wet saw and the presence of welding in the shop were variables that were associated with increased exposure in all three models. Other predictor variables of increased or reduced exposure were associated with the individual models. The extractable mass analysis was found to predict variables related to MWF than the aerosol models.

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