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Model development for the design of better mist filters.

NIOSH 2003 Jan; :1-19
More than one million workers are exposed to metalworking fluid mists in the United States. Epidemiological studies indicate that exposure to these mists is related to respiratory ailments such a chronic cough, bronchitis, and hypersensitivity pneumonitis and skin disorders such as dermatitis. Some research has suggested that exposure to metalworking fluid mists may be related to certain types of cancer, particularly those in the gastrointestinal tract. In workplaces, mist droplets are collected by local exhaust ventilation and the captured air is often passed through mist collectors containing filters before the cleaned air is recirculated to the workplace. Thus, the filters should be able to maintain flow through the system and collect as many droplets as possible. Prior research has shown that pressure drop increases and efficiency decreases for mist filters as they are used. The objective of this research was to determine if altering the kind of fibers used in a filter and the dimensions of a filter could be tools to make mist filters more effective than they are now. The influence of fiber material on filter performance was evaluated by making test filters by hand from either glass fibers or polyaramid fibers. The filters were exposed to mist from bis(2ethylhexyl) sebacate or a straight oil metalworking fluid until they reached a steady operating state. Pressure drop was monitored using a manometer while efficiency was measured using impactors. Results showed that the filters made from polyaramid fibers, which allowed liquid to spread and drain more easily, exhibited smaller increases in pressure drop at steady state than filters made from glass fibers. However, the reduction in efficiency was the same as liquid accumulated within filters made from both kinds of fibers. The influence of filter height and thickness was measured by installing hand-made test filters in a new apparatus constructed for this project. Pressure drop was measured with a manometer while filtration efficiency was evaluated using a real-time particle sizing and counting instrument as the filter collected droplets from when it was clean until it achieved a steady operating condition. The data indicated that thinner filters accumulated more liquid per unit volume than thicker filters, particularly when the fiber diameter was small. Pressure drop increases were influenced only slightly by the thickness of the filter. Filter height did not affect filter performance at all. Filtration efficiency in these tests increased with time, unlike most of the prior studies. This increase may have occurred because of the high incoming mist concentrations used to accelerate the filter loading in these tests. This study suggests that using alternative fibers with high surface energy may improve the performance of mist filters. In addition, more research may be warranted to develop equations to optimize the thickness and other properties of mist filters in order to achieve the best combination of efficiency and pressure drop.
Models; Metal-workers; Metalworking; Metalworking-fluids; Metalworking-industry; Occupational-exposure; Engineering-controls; Epidemiology; Exhaust-ventilation; Filtration; Filters; Aerosols; Control-technology; Engineering-controls
Publication Date
Document Type
Final Grant Report
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Fiscal Year
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NIOSH Division
Priority Area
Research Tools and Approaches: Control Technology and Personal Protective Equipment
Source Name
National Institute for Occupational Safety and Health
Performing Organization
University of Minnesota, Minneapolis, Minnesota