Asbestos Exposures of Mechanics Performing Clutch Service on Motor Vehicles

Abstract

A study was conducted to assess historical asbestos exposures of mechanics performing clutch service on motor vehicles. For most of the 20th century, friction components used in brakes and manual transmission clutches contained approximately 25–60% chrysotile asbestos. Since the late 1960s, asbestos exposure assessment studies conducted on mechanics performing brake service have frequently reported levels below the current OSHA permissible exposure limit (PEL) of 0.1 fiber/cc (flcc). Although there is a robust asbestos exposure data set for mechanics performing brake service, there are almost no data for mechanics removing and replacing clutches in manual transmission vehicles. Personal and area airborne asbestos samples were collected during the removal of asbestos-containing clutches from 15 manual transmissions obtained from salvage facilities by an experienced mechanic. Clutch plates and debris were analyzed for asbestos using EPA and ISO published analytical methods. More than 100 personal and area air samples were collected and analyzed for asbestos fibers using NIOSH methods 7400 and 7402. A separate study involved a telephone survey of 16 automotive mechanics who began work prior to 1975. The mechanics were asked about the duration, frequency, and methods used to perform clutch service. Wear debris in the bell housing surrounding clutches had an average of 0.1% chrysotile asbestos by weight, a value consistent with similar reports of brake debris. Asbestos air sampling data collected averaged 0.047 flcc. Mechanics participating in the telephone survey indicated that clutch service was performed infrequently, the entire clutch assembly was normally replaced, and there was no need to otherwise handle the asbestos-containing clutch plates. These mechanics also confirmed that wet methods were most frequently used to clean debris from the bell housing. Combining the asbestos exposure that occurred when mechanics performed clutch service, along with the duration and frequency of this task, the incremental contribution of this task to mechanics' 8-hr time-weighted average (TWA) asbestos exposures was 0.0016 flcc. Using the range of data inputs that were obtained, the authors calculated a range of TWA exposures of 3.75 × 10⁻⁵ flcc to 0.03 flcc. The mean value of 0.0016 flcc is below background levels of asbestos that have been reported in garages during this time and below the current OSHA PEL of 0.1 flcc.

Keywords:

• asbestos
• automobile
• clutch
• exposure assessment

ACKNOWLEDGMENT

Financial support for this project was provided by the Borg Warner Corporation. Borg Warner is currently engaged in litigation involving asbestos-containing friction products manufactured for vehicle clutches.

Notes

^AEPA PLM method EPA/600-R-93/116 was used to analyze the clutch plate; ISO SEM method 14966 was used to analyze the asbestos content of the debris; and NIOSH PCM method 7400 and TEM method 7402 were used to analyze air sampling results.

^BOne clutch plate had no detectable amount of asbestos and was excluded from these analyses.

^CFive of 12 samples had levels <0.01%. A value equal to one-half the limit of detection was used in calculating the mean value.

^DThese values were obtained from 11 vehicles (no personal air sampling was performed on 4 vehicles, including one that had no asbestos in the clutch plate). Four of the 46 samples were nondetected and these ranged from <0.030 to <0.041 flcc. For values that were below the limit of detection, one-half of this value was used in calculating the mean value.

^EThese values were obtained from 14 vehicles (data was not used from the one vehicle that did not have asbestos in the clutch plate). Eleven of the 58 samples were nondetected and ranged from <0.004 to <0.019 flcc. For values that were below the limit of detection, one-half of this value was used in calculating the mean value.

^AData exclude one mechanic who did not perform brake service and one mechanic who estimated that the ratio of brake to clutch jobs was 216:1.