Evaporative losses from semi-volatile mist samples.
NIOSH 2004 Jul; :1-21
Metalworking fluid mists pose potential respiratory, cancer, and dermatological concerns for machinists and other exposed workers. Thus, measuring mist concentrations accurately for regulatory and health study purposes is important. However, most metalworking fluids are semivolatile. This leads to the possibility that collected mist droplets can evaporate from sampling filters after they have been captured. If this evaporation occurs, mist concentrations will be underestimated. The purpose of this research was to utilize numerical modeling, laboratory experimentation, and field measurements to determine important factors that might influence the extent of evaporative losses of metalworking fluid mist from sampling filters. Numerical models were developed (1) to predict the evaporation of droplets from the point of generation until sampling onto a filter, and then (2) to predict the amount of the sampled mist that evaporated from the filters. Predictions developed from these models were compared to laboratory experiments to validate the models. The laboratory experiments were also used to investigate factors that influence evaporative losses. Field measurements were utilized to understand the extent of evaporative losses in real machining environments. Results of the laboratory experiments indicated that evaporative losses as great as 60% were possible for straight oils. The loss on a percentage basis was greater for more volatile oils and when mist concentrations were low. The degree of mixing within the environment being sampled did not have a significant effect on the amount of evaporative loss from the sampling filters. Straight oils showed greater propensity for evaporative loss than soluble oils and synthetic fluids. Numerical modeling yielded similar predictions as the laboratory experiments. However, the models predicted less evaporation overall than measured in the experiments. Field measurements showed that evaporative losses could be significant in real machining environments. Measurements of mist levels in an automobile engine plant indicated that losses from sampling filters could be as high as 50%. Industrial hygienists could use samplers other than filters to measure mist concentrations. Electrostatic samplers have been shown to have much less evaporative loss than filters. Realtime light scattering instruments can also measure mist concentrations with reasonable accuracy with proper calibration. For situations in which filters are used for sampling, estimating the true metalworking fluid mist concentration by doubling the measured mist concentration would likely give a result that would be greater than or equal to the true mist concentration. This adjustment might be an appropriate conservative estimate of mist concentration that could protect workers from excessive exposure to potentially harmful metalworking fluid droplets.
Models; Computer-models; Analytical-methods; Analytical-models; Analytical-processes; Metalworking-fluids; Sampling-methods; Sampling-equipment; Sample-preparation
Division of Environmental Health Sciences, School of Public Health, University of Minnesota, Minneapolis, MN 55455
Final Grant Report
NTIS Accession No.
Research Tools and Approaches: Exposure Assessment Methods
National Institute for Occupational Safety and Health
University of Minnesota - Twin Cities, Minneapolis, MN