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Assessment of evaporative losses during sampling of metalworking fluid mist.
Proceedings of the Health Effects of Mineral Oil Mist and Metalworking Fluids Symposium, October 2-4, 2002, Cincinnati, Ohio. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, 2002 Oct; :1
Sampling onto membrane and fiber filters is the method used commonly to assess concentrations of metalworking fluid (MWF) mist in workplaces for regulatory purposes and for exposure assessment in epidemiological studies. Airborne MWF mist droplets can evaporate significantly. If the droplets evaporate further after being sampled onto a filter, mist concentrations may be underestimated. The purpose of this research was to use numerical modeling and laboratory experiments to determine the importance of evaporative losses during MWF mist sampling. To predict evaporative sampling losses numerically, two linked models were required. The first model tracked the evaporation of airborne droplets before sampling; the second model predicted evaporation of the collected droplets from the filter after sampling. Modeling was conducted for fluids of different composition, at different airborne concentrations, with different air turnover rates, and with different mixing conditions. For the laboratory experiments, a chamber was constructed for assessment of mist concentrations in controlled and repeatable conditions. Samples were taken with glass fiber and PTFE filters for comparison to samples taken with an electrostatic sampler, which sampled droplets with minimal evaporation. Parameters such as fluid type, generation rate, ventilation rate, and mixing level were varied during tests to evaluate the importance of each factor. The modeling output and experimental data indicated that fluid type was the most important factor in determining if sample loss due to evaporation occurred. Relatively volatile straight oils exhibited significantly greater evaporation than lower volatility straight oils. Soluble oils and synthetic fluids exhibited low levels of sample loss because the aqueous portions of these fluids evaporated quickly from the airborne droplets, leaving only low volatility compounds in the mist when it was sampled. The results also indicated that concentration was an important factor in determining the percentage of a sample that volatilized into passing air. The modeling suggested that 100% of volatile oil droplets at 0.4 mg/m3 could evaporate if the air was not mixed well in the area in which sampling occurred. At higher concentrations, the losses were predicted to be lower. With more complete mixing, the models also predicted less sample loss. The laboratory experiments indicated that sample losses were inconsequential if droplets were not highly volatile and if ventilation rates were low. These findings demonstrated that evaporative losses were minimized whenever the droplets had sufficient time to equilibrate with the vapor in the surrounding air. Evaporative losses are a concern if the oil phase of the mist being sampled is on the volatile end of the range of oils used as MWFs. When samples are taken close to the source of the mist, evaporative losses may be more pronounced because the sampled mist will have less time to come to equilibrium with surrounding vapor. If mist concentration levels are low, losses will be greater on a percentage basis than in situations in which concentrations are high. Personal samples may be influenced by evaporative losses more than area samples because a worker may move between areas of high and low mist concentrations, giving mist sampled in high concentration regions opportunity to evaporate when the worker is in a low concentration area.
Exposure-assessment; Exposure-levels; Exposure-methods; Filters; Metal-fumes; Metallic-compounds; Metal-refining; Metalworking; Metalworking-fluids; Occupational-exposure; Occupational-hazards; Oils; Oil-vapors; Particle-aerodynamics; Particle-counters; Particulates; Particulate-sampling-methods; Safety-measures; Safety-research Vapors; Vapor-volume; Ventilation-equipment; Ventilation-systems; Work-areas; Work-environment; Work-operations; Work-performance; Workplace-studies; Work-practices
Proceedings of the Health Effects of Mineral Oil Mist and Metalworking Fluids Symposium, October 2-4, 2002, Cincinnati, Ohio
University of Minnesota Twin Cities
Page last reviewed: April 9, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division