This study evaluated the ability of commercially available air filtering cleaners installed on more than 25 machining centers to control mist emissions and to reduce workers' mist exposure. In a machining center used to produce transmission parts, a mist of synthetic metalworking fluid (MWF) was generated as a result of drilling and tapping holes at rotational speeds of 1000 to 3000 rpm. The MWF was flooded over the parts at 80 psi during most machining operations. To facilitate metal chip removal during some operations, MWF was pumped through the orifices in some tools at a pressure of 800 psi. These machining operations were performed in nearly complete enclosures that were exhausted to air cleaners, whose fans moved approximately 2400 cfm of air.

To evaluate air cleaner performance, the concentration of triethanolamine and total particulate were measured before and after the installation of the air cleaning units. Area concentrations were reduced from a high of 0.48 mg/m3 to 0.04 mg/m3 or less. The total particulate concentrations on the personal samples showed a four-fold decrease from 0.22 mg/m3 to 0.06 mg/m3.

An aerosol photometer (HAM, ppm, Inc., Knoxville, TN) and video monitoring were used to identify peak exposures to machine operators in the course of their work. Peaks occurred when operators entered or partially entered the machining center enclosures. Some sources of increased air contamination were identified by use of an eight-channel optical particle counter (Portable Dust Monitor, Model 1105, Grimm Ainring, Germany); the most significant sources were partially or unenclosed machining centers and inadequately covered flumes returning the MWF to the Hydromation (fluid recirculation and filtration) unit.

A quartz crystal microbalance cascade impactor (model PC2, California Measurements, Sierra Madre, CA), and eight-stage particle fractionating samplers (1 ACFM Ambient Particle Sizing Sampler, Anderson Samplers, Inc., Atlanta, GA) showed that particles larger than 9 ¦Ěm were present in the plant environment. This suggests that besides the machining centers tested, there were other relatively minor sources of particulate such as uncontrolled machining operations.

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