Health hazard evaluation report: HETA -99-0177-2828, Boeing Commercial Airplane Group, Oak Ridge, Tennessee.
On April 14, 1999, the National Institute for Occupational Safety and Health (NIOSH) received a request for a health hazard evaluation (HHE) from three persons employed at the Boeing Commercial Airplane Group parts manufacturing plant in Oak Ridge, Tennessee. The requesters listed several health effects, including respiratory conditions and skin, kidney, bladder, and prostate problems that they believed were related to exposure to the synthetic metal-working fluid (MWF) used in the machine shop. NIOSH investigators made three site visits to the Boeing facility to evaluate MWF exposures and employees' health concerns. The exposure assessment included measurements of MWF aerosol and triethanolamine (TEA) exposures, real-time measurements of aerosol exposures, and a microbial characterization of MWF. Because four machinists had been newly diagnosed with asthma in 1998, medical evaluations focused on respiratory effects. The medical evaluation included questionnaires, lung function surveys, and serial peak flow testing on participants determined to have bronchial hyperresponsiveness during the pulmonary function testing. MWF exposures were measured on 55 workers, representing both machinists and a comparison group of assembly workers. With one exception, all personal exposure values were below the NIOSH Recommended Exposure Limit (REL) of 0.4 milligrams per cubic meter (mg/m3). The geometric mean (GM) exposures for 42 samples collected on machinists was 0.07 mg/m3 (geometric standard deviation [GSD], 2.1 mg/m3). Mass concentrations were significantly lower for workers in the comparison area, 0.02 mg/m3 (GSD, 2.7 mg/m3). All TEA exposures were well below the 5 mg/m3 American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV). Peak exposures were attributable to activities involving workers placing their head inside the machine. These activities include the insertion of a part to be machined, adjustments to the part placement, and the removal of the part. Activities which generated aerosols, such as the use of the pressurized air gun to clean parts, the application of MWF to the machine during cleaning, or the grinding and polishing of finished parts, also resulted in higher concentrations. Bacterial activity in the fluid ranged from very low to moderate. A clear disparity, in count and species present, was evident between MWF samples collected in the central system and MWF samples collected from stand-alone machines. All samples collected in the central system contained only Gram-positive bacteria, and counts were below 10 colony forming units per milliliter (CFU/mL). In contrast, Gram-negative bacteria were identified in the stand alone reservoirs at concentrations of up to 4.7 x 105 CFU/mL. Questionnaire and lung function surveys were offered to all 204 employees working in the machining areas and all 141 of those working in the assembly area. A total of 284 workers (82%) completed the questionnaire. Of the 284 participants in the questionnaire survey, 101 were asked to participate in pulmonary function testing (PFT) because their questionnaire responses indicated work-related respiratory symptoms; 66 participated. Nine of these sixty-six employees were determined to have bronchial hyperresponsiveness (BHR); seven of one hundred and eighty-eight were exposed to MWF (3.7% ), and two of ninety-two were unexposed (2.2%). These nine performed 7 to 10 days of serial peak flow measurements. One of the nine (a machinist) had a work-related pattern of peak flow variability, three (all machinists) did not provide sufficient data, three (one machinist and two assembly workers) had a pattern not related to work, and two (machinists) had peak expiratory flow (PEF) changes with no discernable pattern. Controlling for effects of age and current number of cigarettes smoked, the workers exposed to MWF had almost three times the rate of asthma symptoms (defined by questionnaire), six times the rate of work-related asthma symptoms (defined by questionnaire), and more than five times the rate of one or more work-related respiratory symptoms (as defined by questionnaire) as unexposed workers. Based on our findings of increased symptoms among exposed individuals, a health hazard exists for employees working in the machine shop at Boeing. Although MWF exposures were below the NIOSH REL of 0.4 mg/m3, workers in the machine shop reported more respiratory symptoms than assembly shop workers. Exposure to a synthetic MWF appeared to be related to the occurrence of asthma symptoms. Based on the measurements and observations made during the evaluation, NIOSH investigators offer several recommendations for the control of MWF exposures, and management of workers' health. These include reducing exposures to MWF by using engineering and/or controls, and personal protective equipment. Recommendations also address a medical monitoring program.