Size Characteristics of Machining Fluid Aerosols in an Industrial Metalworking Environment

Abstract

In an industrial metalworking environment, workplace aerosols are produced continuously during normal operations as machining fluids flood the cutting or grinding tools at the machined surfaces. Since aqueous, synthetic fluids and soluble oils have replaced straight oils for the most part, the physical characteristics of the machining fluid aerosols should be determined to facilitate the assessment and control of potential health hazards in an industrial metalworking environment.

The size distributions and mass concentrations of machining fluid aerosols in an automotive transmission manufacturing plant were determined by cascade impactors, real-time aerosol monitors, and a new area respirable impactor. The aerosols sampled at six sampling sites within the plant were found to be polydispersed with large droplets greater than 8 μm in aerodynamic mass median diameter and fine particles in the 0.1–1 μm size range. The large aerosols were formed from the direct spraying of machining fluids or from emissions from centrifuges in the salvage operations, while the fine aerosols were produced from the actual machining operations at high shear forces and elevated temperatures. During the 16-month study period, a characteristic particle size distribution was observed at each sampling site. The airborne mass concentrations of machining fluid aerosols were unaffected by the existing variations in temperature and relative humidity, but the size characteristics depended greatly on the nature of the metalworking operations and the type of machining fluids used. The viable component of the machining fluid aerosols sampled with a six-stage microbial cascade impactor was greater than 2 μm in all sampling sites.