Engineering the chronic exposure of animals to laboratory produced automobile exhaust.
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A doorless assembly system (the Nagamachi System) was first implemented at Nissan Motor's Zama Plant and has since spread throughout Japan and the rest of the world. With this system all doors are taken off a car body in the first process of a car assembly line and assembled in a separate door assembly line. This system aims to obtain an ergonomic profit from the reduction of a worker's workload. The implementation of the system results in such a reduction in workload, as well as an increase in work efficiency, and higher productivity.
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This study was undertaken to determine the impact of exposure to metal removal fluids (MRFs) on the respiratory health of exposed workers. The outcome measure selected was the rate of hospital admissions for nonmalignant respiratory disease episodes as determined from healthcare insurance claims data. A cohort of MRF-exposed employees was assembled from 11 manufacturing facilities where MRFs were extensively used in the manufacture of automotive engines, transmissions, and other machined parts. The MRF-exposed cohort included 20,434 employees of such facilities who worked at any time from 1993 through 1997. A non-MRF-exposed cohort was assembled from other employees of the same company during the same time period, but working in warehouse operations and other manufacturing facilities that did not use MRFs or any known respiratory sensitizing agents. The non-exposed cohort included 8681 employees. The crude hospital admission rate for the MRF-exposed cohort was 44 percent higher than that of the non-exposed cohort over the 5-year study period (6.67 vs. 4.62 per 1000 person years at risk, p < 0.05). With age adjustment, the MRF population's rate was still 35 percent higher, and still statistically significant. A nested case-control study was also conducted to determine whether the risk of hospital admission increased with the level of MRF exposure in the population working in MRF plants. The industrial hygiene reconstruction found the levels of exposures of both cases and controls to be very low, with the vast majority of study subjects (more than 90%) having exposures of less than 0.5 mg/m(3). The case-control study did not find any association between increased levels of MRF exposure and risk of hospitalization. The study did document an elevated risk of hospitalization among a sizable population employed in manufacturing operations where MRFs are used.
Per vehicle crash involvement rates were compared for otherwise identical vehicle models with and without electronic stability control (ESC) systems. ESC was found to affect single-vehicle crashes to a greater extent than multiple-vehicle crashes, and crashes with fatal injuries to a greater extent than less severe crashes. Based on all police-reported crashes in 7 states over 2 years, ESC reduced single-vehicle crash involvement risk by approximately 41 percent (95 percent confidence limits 3348) and single-vehicle injury crash involvement risk by 41 percent (2752). This translates to an estimated 7 percent reduction in overall crash involvement risk (310) and a 9 percent reduction in overall injury crash involvement risk (314). Based on all fatal crashes in the United States over 3 years, ESC was found to have reduced single-vehicle fatal crash involvement risk by 56 percent (3968). This translates to an estimated 34 percent reduction in overall fatal crash involvement risk (2145).
The current metal-working fluid exposures at three locations that manufacture automotive parts were assessed in conjunction with epidemiological studies of the mortality and respiratory morbidity experiences of workers at these plants. A rationale is presented for selecting and characterizing epidemiologic exposure groups in this environment. More than 475 full-shift personal aerosol samples were taken using a two-stage personal cascade impactor with median size cut-offs of 9.8 microns and 3.5 microns, plus a backup filter. For a sample of 403 workers exposed to aerosols of machining or grinding fluids, the mean total exposure was 706 micrograms/m3 (standard error (SE) = 21 micrograms/m3). Among 72 assemblers unexposed to machining fluids, the mean total exposure was 187 +/- 10 (SE) micrograms/m3. An analysis of variance model identified factors significantly associated with exposure level and permitted estimates of exposure for workers in the unsampled machine type/metal-working fluid groups. Comparison of the results obtained from personal impactor samples with predictions from an aerosol-deposition model for the human respiratory tract showed high correlation. However, the amount collected on the impactor stage underestimates extrathoracic deposition and overestimates tracheobronchial and alveolar deposition, as calculated by the deposition model. When both the impactor concentration and the deposition-model concentration were used to estimate cumulative thoracic concentrations for the worklives of a subset of auto workers, there was no significant difference in the rank order of the subjects' cumulative concentration. However, the cumulative impactor concentration values were significantly higher than the cumulative deposition-model concentration values for the subjects.
Inhalation exposure to manganese (Mn) was measured for a group of garage mechanics and a control group of nonautomotive workers. The airborne Mn exposure of 35 garage mechanics suspected of being relatively highly exposed to Mn from MMT was measured at the workplace over one-week period. It also was measured for 30 nonautomotive workers at the University of Montreal. The environmental exposure also was measured for the two groups, as was the exposure to three other metals, aluminum (Al), iron (Fe), and zinc (Zn). At work the mechanics were exposed to Mn concentrations varying from 0.010 to 6.673 micrograms m-3 with a mean of 0.45 microgram m-5, while the control group was exposed to concentrations varying from 0.011 to 1.862 microgram m-3 with a mean of 0.04 microgram m-3. The mean environmental exposure for the two groups was similar to the Mn concentrations gathered in Montreal in 1992. Workplace concentrations of Al, Fe, and Zn also were higher for the garage mechanics. The results suggest that less than 10% of the Mn exposure of the garage mechanics was due to MMT. The levels of the metals measured were below the established limits for industrial and even environmental exposure.
Personal monitoring of extremely low frequency magnetic fields was conducted at a large automatic transmission plant for a case-control study of primary brain cancer. Current workers were selected to represent the jobs most commonly held by study subjects. Several exposure indices, corresponding to different plausible biological mechanisms, were computed for each of 81 workers who wore the monitoring instrument for one-half shift. Average exposures covered a range from 0.16 to 46 mG; median exposure was 1.3 mG. Nonparametric correlations were estimated to learn whether all of these indices rise and fall together. Results were mixed, in that indices sensitive to high values showed correlations above 0.7, but other correlations were between 0.4 and 0.6. Different indices may thus identify different groups as "highly" exposed. The authors also tested whether indices based on the fraction of time spent above hypothesized thresholds were accurately predicted by a lognormal model. For 47% of the workers, the observed indices significantly exceeded those predicted by such a model, suggesting that lognormality is not a good model for distributions of individuals' short-term exposures.