[Optical and electron microscopic methods for counting respirable fibers of asbestos: considerations on relative...

The paper reports experience of the use of optical and electronic microscope methods for assessment of the concentration of airborne asbestos fibres and their respective identification. The results described are derived from the extensive experience of three Italian university institutes, which have used optical methods of observation for over 35 years (phase contrast technique, at times associated with the use of polarized light) and have examined altogether about 11,000 samples of airborne dust and fibres. After considering in more detail certain values of asbestos fibre concentrations in various environments, measured parallely with optical and electronic microscope, and assessing their basic comparability, attention is drawn to a number of ambiguities and contradictions contained in Law D.M. 6/9/1994, which tends to discourage the use of the optical microscope (especially using the phase contrast technique), without however taking into consideration the improved cost/benefit ratio in the assessment of respirable asbestos fibres present in working and living environments. On this topic, attention is drawn to the fact that the limits for occupational exposure to asbestos, proposed and/or adopted in the international scientific literature, are based on the numerical count of fibres with the optical microscope using the phase contrast technique (MOCF).