Health hazard evaluation report: HETA-2002-0155-2886, DaimlerChrysler Transmission Plant, Kokomo, Indiana.
In February and March 2002, the National Institute for Occupational Safety and Health (NIOSH) received requests from employees of the Indiana Transmission Plant (ITP) in Kokomo, Indiana, the International Union of United Automobile, Aerospace, and Agricultural Implement Workers of America (UAW), and DaimlerChrysler corporate management to conduct a health hazard evaluation (HHE). The request concerned respiratory problems and hypersensitivity pneumonitis (HP) thought to be associated with occupational exposures to metalworking fluids (MWFs) at ITP. The request specifically asked for assistance in assessing peak exposures to MWF aerosol and in laboratory testing to determine whether mycobacteria isolated from bulk samples of MWF at ITP might be the causative agent in the observed illnesses. In response to the HHE request, NIOSH investigators performed multiple site visits in April-July 2002. The plant primarily uses metalworking machines which are enclosed and exhausted to the outdoors. Review of industrial hygiene information revealed that all but one of the company's recent measurements (including area samples [using a direct-reading instrument] and personal breathing zone samples) of MWF aerosol were below the current NIOSH recommended exposure limit for MWF aerosol (total particulate mass) of 0.5 milligrams per cubic meter (mg/m3). Fifty-five percent (28 of 51) of the direct-reading measurements were below 0.2 mg/m3. Analysis of bulk samples from the central MWF systems revealed contamination of several systems with Mycobacteria immunogenum. Several parts washers in machining departments were also contaminated with fungi of the genus Fusarium. Subsequent to several workers being diagnosed with HP, ITP took actions related to: 1) maintenance and monitoring of MWF; 2) cleaning and re-charging of machines and central systems, and 3) modification of work practices related to entry into enclosed machines (including a new standard operating procedure requiring MWF to be shut off within machine enclosures during work tasks inside the enclosures). Based on our review of industrial hygiene records, the engineering controls in place at ITP appeared to be effectively maintaining the workers' ambient exposure to MWF aerosol to concentrations substantially less than the NIOSH REL. The actions taken by ITP in response to workers' illnesses directly addressed the potential for workers to be exposed to greater concentrations of MWF aerosol for short periods of time due to job tasks which entail entering the machine tool enclosures. To evaluate the potential for such peak exposures to occur even after the change in operating procedures regarding MWF flow in the machines, the NIOSH industrial hygiene evaluation involved use of video exposure monitoring (VEM, a real-time aerosol monitor along with digital video). Unfortunately, technical difficulties in performing this sampling prohibited us from collecting any interpretable data. Had these data been interpretable, they are likely to have differed from the MWF aerosol concentrations to which workers may have been exposed prior to the institution of the new procedures (during the time the workers were diagnosed with HP). For that reason, a return site visit to perform the VEM at ITP was not conducted. The medical evaluation included medical record review, questionnaire administration, and analysis of the blood of 56 workers for factors related to cell-mediated and humoral immunity. The goal of the questionnaire was to identify symptomatic and asymptomatic groups of employees to take part in an immunologic evaluation which would help us determine if workers were sensitive to M. immunogenum. Using three distinct assay systems, we evaluated the secretion of three different cytokines, including interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and interleukin 8 (IL-8). A total of 19 medical records were reviewed for the HHE, and seven persons met the definition of HP. Among the seven were 2 operators, 2 job setters, 2 toolmakers, and one janitor. Among these seven workers, symptoms began between June 2001 and January 2002. After providing informed consent, 58 workers were scheduled for participation in our medical evaluation, including six of the seven workers with HP. An index measure of IL-8 was statistically significantly greater among those exposed to MWF compared to the unexposed. There were no statistically significant differences in the concentrations of IFN-gamma (both absolute secretion and index values) between the groups using these assays. Antibody levels against both M. immunogenum and Fusarium antigens were greater among persons with HP compared to those without HP. Antibody levels against M. immunogenum were greater among persons exposed to MWF compared to those unexposed. The results of our testing for antibodies against M. immunogenum were consistent with antibody testing (in other settings) against causative antigens in the evaluation of other types of HP. However, based on antibody testing alone, we cannot determine which antigen(s) are involved in the pathogenesis of HP observed among workers at ITP. Seven employees working in the machining areas of ITP met our case definition for HP. A number of interventions were made by ITP in response to these illnesses. We cannot determine which intervention(s) were effective in reducing or eliminating the exposure(s) related to HP, however, the successful return of some affected workers to machining areas suggests that the causative exposure(s) have been substantially reduced in those areas. The engineering controls in place at ITP appeared to be effectively maintaining the workers' ambient exposure to MWF aerosol to concentrations substantially less than the NIOSH-recommended exposure limit. Our evaluation suggests that changes in work practices, implemented by ITP during the course of this HHE, would likely reduce short-term exposures to MWF aerosol and minimize potential health effects related to exposure to MWF. Recommendations are provided to assist in minimizing safety and health issues related to occupational exposures to MWF at ITP.