2007 年 45 巻 6 号 p. 787-792
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/m³ 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 μm, and also indicated that the arithmetic mean of the number distribution for the particle population was 8.4 μm. Approximately 60.4% of the counted fibers were lower than 10 μm in length, from which only 8% consists of fibers (>5 μm 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.
