Mist control at a machining center, Part 2: Mist control following installation of air cleaners.

At a machining center used to produce transaxle and transmission parts, aerosol instrumentation was used to quantitatively evaluate size-dependent mist generation of a synthetic metalworking fluid (MWF) consisting primarily of water and triethanolamine (TEA). This information was used to select an air cleaner for controlling the mist. During most machining operations, the MWF was flooded over the part. These machining operations were performed in a nearly complete enclosure that was exhausted to an air cleaner consisting of three sections: a fall-out chamber, a trifilter section to capture metal chips and mist, and a 1.13 m3/sec (2400 ft3/min) blower. The partnering company requested that National Institute for Occupational Safety and Health (NIOSH) researchers perform an evaluation of the effectiveness of a commercially available air cleaner. After NIOSH researchers characterized mist generation at the machining centers and found that performance of a test air cleaner appeared to be suitable, the company installed more than 25 air cleaners on different machining centers in this plant and enclosed the corresponding fluid filtration unit. The facility also has implemented a maintenance program for the air cleaners that involves regularly scheduled filter changes; performance is ensured by monitoring static pressure. A NIOSH-conducted air sampling evaluation showed that area TEA concentrations were reduced from a geometric mean of 0.25 to 0.03 mg/m3. Personal total particulate concentrations were reduced from a geometric mean of 0.22 to 0.06 mg/m3. These results show the effectiveness of this combination of enclosure, ventilation, and filtration to greatly reduce the exposure to MWF mist generated in modern machining centers.