Machinery's Handbook, 31st Edition
EXPOSURE TO METALWORKING FLUIDS 1255 captures the contaminants and conveys them to a point where they can either be discharged or removed from the airstream. Exhaust hoods are classified by their position relative to the process as canopy, side draft, down draft or enclosure. ANSI Technical Report B11 TR 2-1997 contains guidelines for exhaust ventilation of machining and grinding operations. Enclosures are the only type of exhaust hood recommended by the ANSI committee. They consist of physical barriers between the process and the worker’s environment. Enclosures can be further classified by the extent of the enclosure: close capture (enclosure of the point of operation, total enclosure (enclosure of the entire machine), or tunnel enclosure (continuous enclosure over several machines). If no fresh make up air is introduced into the plant, air will enter the building through open doors and windows, potentially causing cross-contamination of all process areas. Ideally, all air exhausted from the building should be replaced by tempered air from an uncontaminated location. By providing a slight excess of make up air in relatively clean areas and slight deficit of make up air in dirty areas, cross-contamination can be reduced. In addition, this air can be channeled directly to operator work areas, providing the cleanest possible work environment. Ideally, this fresh air should be supplied in the form of a low-velocity air shower (<100 ft/min or <30 m/min) to prevent interference with the exhaust hoods) directly above the worker. Protective Clothing and Equipment: Engineering controls are used to reduce worker exposure to MWFs. But in the event of airborne exposures that exceed the NIOSH REL or dermal contact with the MWFs, the added protection of chemical protective clothing (CPC) and respirators should be provided. Maintenance staff may also need CPC because their work requires contact with MWFs during certain operations. All workers should be trained in the proper use and care of CPC. After any item of CPC has been in routine use, it should be examined to ensure that its effectiveness has not been compromised. Selection of the appropriate respirator depends on the operation, chemical components, and airborne concentrations in the worker’s breathing zone. Table 2 lists the NIOSH- recommended respiratory protection for workers exposed to MWF aerosol. Table 2. Respiratory Protection for Workers Exposed to MWFAerosols * Concentration of MWF aerosol (mg/m 3 ) Minimum respiratory protection a #0.5 mg/m 3 (1 REL) b No respiratory protection required for healthy workers c #5.0 mg/m 3 (10 REL) Any air-purifying, half-mask respirator #12.5 mg/m 3 (25 REL) Any powered, air-purifying respirator equipped with a hood or helmet and a HEPA filter f a Respirators with higher assigned protection factors (APFs) may be substituted for those with lower APFs [NIOSH 1987a]. b APF times the NIOSH REL for total particulate mass. The APF [NIOSH 1987b] is the minimum anticipated level of protection provided by each type of respirator. c See text for recommendations regarding workers with asthma and for other workers affected by MWF aerosols. d A respirator that should be discarded after the end of the manufacturer’s recommended period of use or after a noticeable increase in breathing resistance or when physical damage, hygiene considerations, or other warning indicators render the respirator unsuitable for further use. e An APF of 10 is assigned to disposable particulate respirators if they have been properly fitted. f High-efficiency particulate air filter. When organic vapors are a potential hazard during metalworking operations, a combination particulate and organic vapor filter is necessary. * Only NIOSH/MSHA-approved or NIOSH-approved (effective date July 10, 1995) respiratory equipment should be used. including a disposable respirator d,e equipped with any P- or R-series particulate filter (P95, P99, P100, R95, R99, or R100) number
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