CUTTING FLUID HEALTH HAZARDS

It has been estimated that between 700,000 and one million workers are exposed to cutting fluids in the United States [Bennett E.O. "Water based cutting fluids and human health", Tribology international,1983.]. Since cutting fluids are complex in composition, they may be more toxic than their components and may be an irritant or allergenic even if the raw materials are safe [Bienkowski, 1993]. Also, both bacteria and fungi can effectively colonize the cutting fluids and serve as source of microbial toxins [Thorne et al., 1996]. Significant negative effects, in terms of environmental, health, and safety consequences, are associated with use of the cutting fluids. The health effects of exposure to the fluids have been studied for over 50 years, beginning with the concern that cutting fluid oil is a potential etiologic factor for occupational skin cancer [Epidemiological studies indicate that long-term exposure to metalworking fluids can lead to increased incidence of several types of cancer. The international Agency for Research on Cancer has concluded that there is Òsufficient evidenceÓ that mineral oils used in the workplace are carcinogenic.[Peter C. Raynor, Steven Cooper and David Leith, ÒEvaporation of Polydisperse Multicomponent Oil Droplets,Ó American Industrial Hygiene Association, 1996.] Basically, Workers are exposed to metal cutting fluids via three routes [Bennett E.O., and Bennett D.L.]: Skin exposure is the dominant route of exposure, and it is believed that about 80 percent of all occupational diseases are caused by skin contact with fluids [Bennett E.O., and Bennett D.L.]. Cutting fluids are important causes of occupational contact dermatitis, which may involve either irritant or allergic mechanisms [Byers, 1994]. Water mixed fluids generally determine irritant contact dermatitis and allergic contact dermatitis when they are in touch with workers skin. Non-water-miscible fluids usually cause skin disorders such as foliculitis, oil acne, keratoses and carcinomas.

Besides potential skin and eye contact, inhalation is also a way to occupational exposure. Mists are aerosols comprised of liquid particles less than 20m. During machining process (Fig. 1), a considerable amount of heat generated may result cutting fluid arrive a temperature sufficiently higher than the saturation temperature as it impacting the cutting zone. The vapor then is produced at the solid-liquid interface as a result of boiling. Vapor also may be generated at the liquid-air interface when the fluid vapor pressure is less than the saturation pressure, namely as evaporation phenomena. Vapor generated then may condense to form mist. The non-aqueous components of the cutting fluid, such as the biocide additives, then become a fine aerosol that can enter the workroom air. Also, the cutting fluids impact both stationary and rotating elements within the machine tool system which leads to mechanical energy being transmitted to the fluid. Thus, the cutting fluid has higher surface energy and becomes less stable and disintegrates into drops (atomization). Mist also may be generated by the spray from the fluid application. A total daily fluid loss of 5 to 20 percent may occur from the combination of evaporation, atomization, splashing and dragout processes [Iowa waste reduction center, 1996]. Whether formed by atomization or evaporation/condensation, small droplets may be suspended in the air for several hours even several days possibly in the workersÕ breathing zones. These drifting droplets tend to get more evaporate. Inhaled particles (with aerodynamic diameters less than 10 m) deposit in the various regions of the respiratory system by the complex action of the different deposition mechanisms. The particulates below 2.5 m aerodynamic diameter deposit primarily in the alveolar regions which is the most sensitive region of lung. The particulates in size range from 2.5 m to 10m deposit primarily in the air-ways. The potential health effects of exposure to cutting fluid mists have been the subject of epidemiological studies in the automotive industry [Hands et al., 1996]. The mist droplets can cause throat, pancreas, rectum, and prostate cancers, as well as breathing problems and respiratory illnesses [Mackerer, 1989]. One acute effect observed is mild and reversible narrowing of airways during exposure to cutting fluid mist [Kennedy, S.M., et al., ÒAcute Pulmonary Responses Among Automobile Workings Exposed to Aerosols of Machining FluidsÓ, American Journal of Industrial Medicine, Vol. 15, 1989, pp. 627-641.] Several other epidemiological studies have also suggested that exposure to fluid mist may be associated with increased risk of airway irritation, chronic bronchitis, asthma and even laryngeal cancer [Benndy, E., and D. Bennett, ÒOccupational airway Diseases in the Metal-working Industry,' The Occupational Safety and Health AdministrationÕs (OSHA) standard for airborne particulate (largely due to fluid mist) is 5 mg/cubic meter, and the United Auto Workers (UAW) has proposed a reduction in the standard to 0.5 mg/cubic meter. Reducing aerial pollution Different cutting fluids exhibit the different tendency to produce smoke or mists. The oil mist level in a plant ranged from 4.2 to 15.6 mg/m3 but fell to between 0.47 to 1.68 mg/m3 when a different cutting fluid was substituted in the system [Welter, E.S., ÒManufacturing Exposure to Coolant-Lubricants,Ó J. Occupied. Med., 20, pp 535-538,1978.]. Anti misting compounds, such as a polymethaacrylate polymer, polyisobutylene and poly-n-butane in concentrations of 0.2% as well as poly (1, 2-butene oxide) have been suggested for be formulated into cutting fluids [Bennett, E.O., and D.L. Bennett, 1987] [Wayen state univer.] But, consideration must be given to the effects of these chemicals upon humans. The most effective way to control mist exposure is to use mist collector to prevent mist from entering plant air [Leith, D.,P.C. Raynor, M. G. Boundy and S. J. Cooper, ÒPerformance of Industrial Equipment to Collect Coolant Mist,Ó AIHA Journal No. 57, Dec. 1996.] Many collectors use several stages of filters in series to enhance the efficient. Other collectors use centrifugal cells or electrostatic precipitators as intermediate stages. Any collector using a 95% Dioctyl Phthalate (DOP) or High-Efficiency Particulate Air (HEPA) filter as a final collection stage has been tested as high efficiency when new; however, its effencicy will decrease with the time and finally lost its performance. Moreover, the oil droplets may experience partial or complete evaporation as they travel to collector [Raynor, P.C., S.Cooper and D. Leith, ÒEvaporation of Polydisperse Multicomponent Oil Droplets,Ó AIHA Journal (57) Dec. 1996]. The generated organic vapors may return to the room and affect work health, and may recondense on the cool surface causing safety and maintenance problems. Tribology International, Vol. 18, No.3, 1985,pp. 169-176] [Eisen, E.A., P.E. Tolbert, M. F. Hallock, R. R. Monson, et al., Mortality studies of machining fluid exposure in the automobile industry: iii. A case-control study of larynx cancer,Ó Am. J. Ind. Med. 26:185-202 (1994).] [Marano described the other negative effects of fluid mist: poor air quality, housekeeping safety issues, fire propagation upon introduction of a spark, and environmental concerns if oil on the roof is carried down storm drains [Marano, 1995]. The Occupational Safety and Health AdministrationÕs (OSHA) standard for airborne particulate (largely due to fluid mist) is 5 mg/cubic meter, and the United Auto Workers (UAW) has proposed a reduction in the standard to 0.5 mg/cubic meter. Reducing aerial pollution Different cutting fluids exhibit the different tendency to produce smoke or mists. The oil mist level in a plant ranged from 4.2 to 15.6 mg/m3 but fell to between 0.47 to 1.68 mg/m3 when a different cutting fluid was substituted in the system [Welter, E.S., ÒManufacturing Exposure to Coolant-Lubricants,Ó J. Occupied. Med., 20, pp 535-538,1978.]. Anti misting compounds, such as a polymethaacrylate polymer, polyisobutylene and poly-n-butane in concentrations of 0.2% as well as poly (1, 2-butene oxide) have been suggested for be formulated into cutting fluids [Bennett, E.O., and D.L. Bennett, 1987] [Wayen state univer.] But, consideration must be given to the effects of these chemicals upon humans. The most effective way to control mist exposure is to use mist collector to prevent mist from entering plant air [Leith, D.,P.C. Raynor, M. G. Boundy and S. J. Cooper, ÒPerformance of Industrial Equipment to Collect Coolant Mist,Ó AIHA Journal No. 57, Dec. 1996.] Many collectors use several stages of filters in series to enhance the efficient. Other collectors use centrifugal cells or electrostatic precipitators as intermediate stages. Any collector using a 95% Dioctyl Phthalate (DOP) or High-Efficiency Particulate Air (HEPA) filter as a final collection stage has been tested as high efficiency when new; however, its effencicy will decrease with the time and finally lost its performance. Moreover, the oil droplets may experience partial or complete evaporation as they travel to collector [Raynor, P.C., S.Cooper and D. Leith, ÒEvaporation of Polydisperse Multicomponent Oil Droplets,Ó AIHA Journal (57) Dec. 1996]. The generated organic vapors may return to the room and affect work health, and may recondense on the cool surface causing safety and maintenance problems.