Factors Affecting Worker Exposures to Metal-Working Fluids During Automotive Component Manufacturing

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Abstract
A two-stage personal impactor was used to collect fullshift exposure measurements of metal-working fluid exposures from workers in three automotive component manufacturing facilities. The 403 workers exposed to metal-working fluid in machining and grinding operations had an average total particulate exposure of 706 μg/m3 (standard error = 21 μg/m3). For a subset of 309 workers, information on factors that might influence the exposure level was also collected. This information included the metal-working fluid type, the machine type, the presence of local exhaust, the degree of machine enclosure, the age of the machine, the distance of the worker from the machine, and the indoor and outdoor temperature and humidity. Statistical analysis was used to investigate which factors contribute most significantly to the variability in exposures to large (> 9.8 μm aerodynamic diameter) and small (<3.5 μm) particles. For large particles, the factors of greatest importance in a stepwise analysis of covariance (ANCOVA) model were the machine type, the metal-working fluid type, indoor humidity, and outdoor temperature. For the small particles, the facility/plant, machine type, metal-working fluid type, indoor humidity, and degree of enclosure were the most important factors. When the ANCOVA model was used to further investigate the impact of altering these factors on the exposure level, it was determined that the greatest aerosol concentrations were produced by the high speed operations using a metal-working fluid with a high solute/oil content. Substantial control of exposures could be achieved by altering the machining process, changing the type of metal-working fluid, enclosing the machine, and/or installing local exhaust. Exposures could also be reduced by increasing the fresh air and decreasing the recirculation of the general ventilation of the plants.