Metalworking Fluids exposure to MWF aerosol at 1 mg/m 3 (thoracic fraction). This may be an underestimate of effect, as only current workers were included in the study; workers who may have left these three plants as a result of their asthma would not have been included in the study.
Basing an analysis on the same population reported on previously by Greaves et al. , Eisen et al.  used a cohort approach and proportional hazards model to evaluate the association of post-hire asthma to MWF aerosol exposures. Among 1,788 active workers (including assembly workers) in the analysis, 29 reported asthma initially diagnosed after hire. Based on MWF exposures during the 2-year period preceding diagnosis (to correlate with likely time of asthma onset), incidence rate ratios (RRs) were calculated. With adjustment for age and period of hire (before or after 1970), RRs were as follows: 2.0 (95% CI=0.9-4.6) for straight MWF; 0.5 (95% CI=0.2-1.1) for soluble MWF; and 3.2 (95% CI=1.2-8.3) for synthetic MWF. Aerosol exposures for the six asthmatics who worked with synthetic MWFs during the 2 years before diagnosis averaged 0.6 mg/m 3 (inhalable fraction); the range was 0.36 to 0.91 mg/m 3 , and the median was 0.58 mg/m 3 . Kriebel et al.  found that the association was stronger for asthma with onset following employment than for asthma predating employment as a machinist. Aerosol exposure measurements were made using samplers with a seven-hole cassette inlet face selected to approximate collection efficiencies of the American Conference of Governmental Industrial Hygienists/International Standards Organization (ACGIH/ISO) size-selective criteria for inhalable mass . At the time of the questionnaire survey, machinists at this facility who worked with straight oil MWF had a mean aerosol exposure of 0.24 mg/m 3 (inhalable fraction), and those who worked with soluble oil MWF had a mean exposure of 0.22 mg/m 3 (inhalable fraction).
Robins et al.  provided relevant data from a study of machinists exposed to aerosols of soluble MWF and relatively unexposed assembly workers at an automotive transmission manufacturing plant. Among workers who reported not having pre-existing asthma, current asthma was reported and/or a clinically significant cross-shift FEV 1 decrement (of at least 12%) was experienced by 11 of 83 machinists compared with 3 of 44 assembly workers (calculated unadjusted OR=2.1; 95% CI=0.5-12.3).

# RESPIRATORY PROTECTION REQUIRED IN THIS AREA

# CHAPTER 9: Recommendations for an Occupational Safety and Health Program
Good housekeeping includes keeping the floors, equipment, and general work environ-ment clean. Wastes (including floor wash water) should not be dumped or swept into MWF sumps or coolant return trenches.

# Labeling and Posting
Workers should be trained to be aware of labeling practices in accordance with the OSHA hazard communication standards [29 CFR 1910.1200and 29 CFR 1926. Warning labels and signs should be posted on or near hazardous metalworking processes. Depending on the process and MWF exposure concentration, warning signs should state the need to wear protective clothing or an appropriate respirator for exposure to MWF aerosol concentrations exceeding the REL. If respiratory protection is required, the following statement should be posted:
All labels and warning signs should be printed in both English and the predominant language of workers who do not read English. Workers unable to read the labels and signs should be informed verbally about the hazards and instructions printed on the labels and signs.

# Engineering Controls

# Isolation
Skin and inhalation exposures to MWF and MWF aerosol can be minimized by using mechanical parts handling equipment and machine enclosures to isolate the workers. Simple splash-guarding may suffice for low-production machines, but complete enclosure (with ventilation) is required for high-production machines. Plant layouts should be such that transfer machines are isolated from other operations. Workers should be provided with isolation booths or fresh air showers.
Machine enclosures are an effective method of reducing worker exposures. Johnston and White  have described the features that are important in designing effective enclosures. ANSI B11  contains detailed enclosure and mist control designs as well as considerations for installation and use. Hands  examined exposure data collected at an automobile parts manufacturing plant to determine the effect of enclosures on MWF aerosol exposures. This study suggests that enclosures (particularly manufacturer's enclosures that are original equipment) effectively reduce MWF exposures. Retrofitting enclosure structures may also reduce exposures.