The Effect of Aspect Ratio on Fiber Counts: A Preliminary Study (1978)

This 1978 preliminary report described a round-robin study of whether changing the rules for which particles are counted as fibres would make asbestos fibre counts by the NIOSH method agree better between laboratories. Twelve laboratories (government, research and industry) counted two membrane filter samples from each of six plants: one asbestos-cement, one brake lining, two ore treating mills and two textile. Practically all fibres were chrysotile. Counters used length-to-width (aspect) ratios of 3:1, 5:1 and 10:1 and minimum lengths of 5 or 10 micrometres. The coefficient of variation was 0.38 for 5:1 with 5 micrometres, 0.41 for 3:1 with 5 micrometres, 0.54 for 10:1 with 5 micrometres, and 0.49 for 3:1 with 10 micrometres. At one laboratory, electron microscope and optical counts of fibres longer than 5 micrometres were strongly correlated (correlation coefficient 0.978, which the authors called highly significant). No such relationship was found for shorter fibres. Counters found aspect ratio much harder to judge than length. The authors suggested that a 5:1 ratio and a 5 micrometre minimum gave better precision. They called the work preliminary to a larger, statistically designed study.

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From J-M's medical library

This copy comes from the Johns-Manville medical library. It is a copy from J-M's medical library.