Document LoJbpdnN2xrG50OZ2ZDyNVgjb

The Interrelationships of Selected Asbestos Exposure Indices JEREMIAH R. LYNCH, HOWARD E. AYER, and DOUGLAS L. JOHNSON* Bureau of Occupational Safety and Health, Public Health Service, Department of Health Education, and Welfare, 1014 Broadway, Cincinnati, Ohio 45202 ` @ Based on the assumption that the biological effect of asbestos is related to the concentration of respirable fibers, an index was developed which yields the con centration in numbers of asbestos fibers visible under 430 X phase-contrast illumina tion. Data are presented relating this index to overall dustiness as measured by impinger counts and to absolute fiber concentration and distribution as measured by electron microscopy. The relation between count estimates and gravimetric measures of total dust and chrysotile asbestos deduced from magnesium analyses are given for gross and respirable samples. These relations are developed for use in operations in the manufacture of asbestos textile, friction, cement, and insulation products. The most convenient, practical, and direct index of asbestos fiber exposure proved to be the concentration of fibers longer than 5 microns counted on membrane filters at 430 X phase-contrast illumination. Introduction A T THE NEW YORK ACADEMY OF SCIENCES Conference on the Biologi cal Effects of Asbestos in 1965, Gilson1 noted the proliferation of dust sampling methods and appealed for international comparability of dust measurement data to be related to bio logical data. He also observed that, as dust levels are lowered, it becoines more important to use the index that is biologically most ap propriate. At the present time the goal of internation al comparability has been partly achieved by the adoption of the concentration in numbers of fibers longer than 5 microns counted on membrane filter samples at 430 X magnifica tion with phase-contrast (PC) illumination as the standard method in both Britain and ,the United States.2'3 However, information that would permit evaluation of the biological ap *U.S. Department of Health, Education, and Welfare, Public Health Service, Region IX Federal Office Building, 50 Fulton Street, San Francisco, California 94102. propriateness of this index is still noifi plete. It is rarely possible to make an ah) measurement of that characteristic of ai borne dust which is directly responsible! biological effect. To be practical, me,; ment for the purpose of assessing hazare evaluating control must not only be co ient and relevant but also permit theigj statistically adequate sampling strategi|| evaluate indices obtained from varyip posure situations, an examination of tHej sistency of their relation to other and aj measures was undertaken. The large number of methods whichi be used to measure exposure to airborj| containing fibers results from what rnjgj called the "degrees of freedom" of tn cloud. In measuring the concentratip^fi gas in air, there is only one attribute measured, and one accurate method giff same result as another. With granulcm however, the attribute could be eithb|f ber or weight, and with fibrous dust;|| gives another degree of freedom; furthej 598 SCF-FA-6470