Asbestos exposure during routine brake lining manufacture

Our plain-English summary of Asbestos exposure during routine brake lining manufacture, by H. Kakooei, M. Sameti, A.A. Kakooei (Industrial Health, 2007).

The study

• Authors: H. Kakooei, M. Sameti, A.A. Kakooei
• Journal: Industrial Health
• Published: 2007;45(6):787-92
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Occupational exposure to asbestos fiber and total dust of workers of a major brake lining manufacture plant in a developing country were examined and compared with those in developed countries. Time weighted average of total dust and asbestos fiber concentration in the potential sources of exposure were monitored. All personal air sampling were collected on membrane filters and analyzed by phase contrast optical microscopy (PCM) for comparison with the occupational safety and health administration (OSHA) permissible exposure limit (PEL) of 0.1 f/cc, 8-h time--weighted average. This study demonstrates that routine mixing, polishing and beveling process in the brake lining production can result in elevated levels of airborne asbestos. Greater releases of airborne asbestos were observed during mixing process and mixer machine. The results also showed that the employees working in the process had the exposure to total dust concentrations ranging from 2.08 to 16.32 mg/m(3) that is higher than OSHA, recommendation. According to OSHA definition of fibers, it has been indicated that from 3,000 counted particles, 90% of particles are in the form of non-fiber and reaming have fiber-shaped. The particle analyze gives the geometric mean diameter as 6.02 mum, and also indicated that the arithmetic mean of the number distribution for the particle population was 8.4 mum. Approximately 60.4% of the counted fibers were lower than 10 mum in length, from which only 8% consists of fibers (>5 mum in length). In conclusion, the analysis showed a presence in the air of only chrysotile asbestos and an absence of other types of asbestos. During an 8-h shift, the average asbestos fiber exposure (0.78 f/cc) were 7.8 time in excess of OSHA PEL. Additional studies in occupational exposure to asbestos are needed.

In plain English

This study measured airborne asbestos and total dust at one Iranian plant making brake linings and brake pads. In June and July 2002, the authors took 75 personal asbestos samples, counted by phase contrast microscopy, and area samples of total dust. The plant used chrysotile, and the airborne asbestos was reported as predominantly chrysotile. Every individual asbestos sample, each lasting 30 to 60 minutes, exceeded 0.1 fibers per cc, which is OSHA's 8-hour average limit. The authors stated that 8-hour averages calculated from these levels would also exceed it. The average across processes was 0.78 f/cc, which the authors described as 7.8 times that limit. The highest process average, 1.85 f/cc, was at the old mixer. Total dust averaged 9.6 mg/m3 (range 2.08 to 16.32). It was highest at beveling and lowest at milling, and 25% of dust samples exceeded OSHA's 15 mg/m3 value for total (nuisance) dust. The authors concluded that exposures were generally higher than in similar operations in developed countries. They noted that the plant was not randomly chosen, the samples were few, and sampling was done in summer with the windows open.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Workplace air-sampling (exposure measurement) study at a single plant, using personal and area samples
• Who was studied: Workers and work stations at one friction-material (brake lining and brake pad) manufacturing plant in Iran, sampled in June and July 2002. There were 75 personal breathing-zone asbestos samples. Total dust was sampled at fixed operator work stations (the tables list 45 samples). The number of workers is not given.
• Exposure: Chrysotile asbestos and total dust in dry-process brake lining manufacture. Jobs included mixing, loading, milling, pressing, drilling, grinding, cutting, polishing and beveling. Crocidolite and amosite were not used. Asbestos fibers were counted by phase contrast microscopy on personal samples lasting 30 to 60 minutes, and total dust was measured by weighing filters.
• Main results:
  • All individual personal asbestos fiber measurements, across all processes, exceeded the 0.1 f/cc value of the OSHA permissible exposure limit.
  • The OSHA limit used for comparison is an 8-hour time-weighted average, while personal asbestos samples lasted 30 to 60 minutes. The authors stated that 8-hour averages calculated from the measured levels would exceed the limit.
  • The average personal asbestos fiber concentration across the processes was 0.78 f/cc, which the authors described as 7.8 times the OSHA limit.
  • The old mixer had the highest mean asbestos fiber concentration of any process: 1.85 f/cc (SD 0.07) from 10 samples, with a reported range of 1.84 to 1.91 f/cc. The text calls 1.85 the highest individual concentration.
  • Total dust across processes and operations averaged 9.6 mg/m3, with a range of 2.08 to 16.32 mg/m3.
  • Total dust was highest for bevel process work (16.32 plus or minus 0.5 mg/m3) and lowest for milling process work (2.08 plus or minus 0.16 mg/m3).
  • At operators' work stations, 25% of total dust samples exceeded the 15 mg/m3 value that OSHA recommends for total (nuisance) dust. 50% exceeded the ACGIH value of 10 mg/m3.
  • Of 3,000 counted particles, 90% were non-fibers and 10% were fiber-shaped under the OSHA definition.
  • The count mode and geometric mean diameter of the counted particles were 1.5 µm and 6.02 µm.
  • The airborne asbestos structures were predominantly chrysotile.
• The authors' conclusion: The authors concluded that exposure to total dust and airborne asbestos in this brake lining plant in a developing country was generally higher than in similar operations in developed countries. They attributed this in part to imported machinery assembled without adequate engineering controls.
• Limitations the authors state:
  • The factory was not selected randomly, and the number of samples was small.
  • Sampling was done in summer with the side windows fully open. The authors state that airborne particulate levels were much higher in winter, when the windows are kept closed; earlier in the article this is attributed to what workers claimed.
  • The dust collector (bag house) may have been turned on during sampling, which would increase air exchange.
  • Phase contrast microscopy cannot see fibers thinner than 0.25 µm, so the authors say the results should be read with the limits of the light microscope in mind.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Brake Lining, Occupational Exposure, Air Sampling, OSHA, Permissible Exposure Limit (PEL), Chrysotile.

Related studies

• Environmental and occupational health hazards associated with the presence of asbestos in brake linings and pads (1900 to present): a "state-of-the-art" review — D.J. Paustenbach, B.L. Finley, et al. (2004)
• Environmental and occupational health hazards associated with the presence of asbestos in brake linings and pads (1900 to present): A "state-of-the-art" review — S.S. Paskal (2004)
• Asbestos exposure during brake lining maintenance and repair — A.N. Rohl, A.M. Langer, et al. (1976)
• Asbestos fibres in the lungs of an American mechanic who drilled, riveted, and ground brake linings: a case report and discussion — M.M. Finkelstein (2015)
• Evaluation of exposure to the airborne asbestos in an asbestos cement sheet manufacturing industry in Iran — D. Panahi, H. Kakooei, et al. (2011)
• Experimental studies on the effects of heated chrysotile asbestos and automobile brake lining dust injected into the body cavities of mice — J.M. Davis, S.W. Coniam (1973)

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