Identification and Counting of Asbestos and Non-Asbestos Fibers in an Automobile Brake Manufacturing Industry

Abstract

This study was performed to identify and count both asbestos and non-asbestos fibers during brake manufacture in Iran. A total of 56 respiratory air samples of personnel were measured by phase-contrast microscopy (PCM) and scanning electron microscopy (SEM). The fiber type and its chemical composition were also evaluated by SEM and energy-dispersive X-ray analysis (EDX). Monitoring of total fiber levels demonstrated that its ranges are from 0.23 to 1.50 PCM f/ml. The geometric mean and standard deviation of the airborne asbestos and non-asbestos fiber concentrations were 0.22(1.61) and 0.32(1.61) SEM f/ml respectively. The observed asbestos fiber concentrations in many processes were higher than the threshold limit value (TLV) which is proposed by American Conference of Governmental Industrial Hygienists (ACGIH), as equal as 0.1 f/ml. Based on these findings, the geometric means of the non-asbestos concentrations were considerably lower than TLV of the ACGIH which is 1 f/ml. The SEM data exhibited that fibrous particle consists of chrysotile (40%) and rock wool (60%). It can be concluded that more than 50% of airborne fibers inhaled by the workers were rock wool with fibers greater than 1 μm in diameter. For evaluation of airborne fibers, the PCM method was not able to detect the fibers lower than 0.25 micrometer. This study demonstrated that SEM technique methods are essential elements for accurate characterization of mineral dusts, particularly when dealing with large number of samples.