An Evaluation of Phase Contrast Microscopes for Asbestos Counting.
NIOSH 1974 Mar:9 pages
An evaluation was made of five phase contract microscopes for asbestos (1332214) counting, to determine whether there was a possibility of gross differences in asbestos fiber count results when the same filter was counted on different microscopes by the same personnel. Five trained persons counted the fibers on five filter wedges using five microscopes. The samples were collected by drawing air through a membrane filter by means of a battery powered vacuum pump. The filter was charged into a transparent homogeneous plastic mount, and the fibers sized and counted by the microscopes which were modified for use with phase contrast techniques. For each of the five counters the counts obtained using a Nikon microscope were 45 percent higher than those obtained using the particular Leitz, Zeiss, Olympus, or Bausch and Lomb microscopes in this study. The results indicated that film thickness was uniform and that clumping of fibers did not occur. Taking the average of the three counters as 100 percent (as they had statistically homogeneous counts), counter A's average was 16 percent lower and counter E's average was 27 percent higher than this average. Not only did significant differences occur depending on the equipment used, but also with different trained operators.
NIOSH-Author; Airborne-particles; Air-quality-monitoring; Laboratory-workers; Asbestos-dust; Mineral-dusts; Task-performance; Laboratory-equipment; Fibrous-dusts;
NTIS Accession No.
Division of Laboratories and Criteria Development, NIOSH, U.S. Department of Health, Education, and Welfare, Cincinnati, Ohio, 9 pages