Abstract
Number concentrations of airborne asbestos fibers in work space and in the atmosphere are usually measured by visual counting with PCM (Phase Contrast Microscope). Since counting process of the PCM Method requires skill and much labor, the counts obtained by this method significantly vary from facility to facility and therefore the reliability is limited. In this paper, cross-check of the counting values among seven counting facilities was performed to obtain the basic information for the improvement of reliability of counting value. Seven counting facilities, one a university laboratory which is developing AFACS (Asbestos Fibers Automatic Counting System), one local self-governing body, one foundation and four private companies were involved in this study. The aim of this cross-check is to elucidate the variation in the judgement of individual asbestos fibers among the counting facilities. The results are; (1) The ratio of the maximum counts to the minimum was about 5. (2) The maximum value of the coefficients of concurrence between two arbitrary counting facilities was 50.2%. Even if their counting values were similar, the counted asbestos fibers were different from facility to facility. (3) Visual counting facilities had a tendency to overestimate fiber diameter, which resulted in underestimation of counting value. (4) Counting value with the AFACS was the medium of those measured by six visual counting facilities.
