Document xzgdGaVqR5d6vgK8yDJ3G52b1

- 3V. /7 -/7~ STOOI1557 v ASBESTOS - All Ferns wV'-<' C 5 mppc (2 mppcf, time-weighted average) \^ or 12 fibers /1 > 5 (* in length Asbestos Is e generic tern thee applies to e number of nleerel silicates. Incombustible in air and separable into filaments. The most widely used in industry is chrysotlle, a magnesium silicate from serpentine. Other types include amoalte (an iron magnesium silicate) crocldolite (a sodium iron sill* cate), tremollte (a calcium magnesium silicate) and anthophyllita (also an Iron magnesium silicate). That exposure to asbestos is associated with development of a poten tially disabling pneumoconiosis in man has been amply demonstrated by indus trial experience (1,2,3,!*, 5,6, 7, 8, 9). A threshold limit of 5 mppcf was recommended by Dreessen et al. (6), in 1938 after studying 5^1 employees in k asbestos textile plants where massive exposures to chrysotlle occurred. Only 3 doubtful cases of pneumoconiosis were found at the time of the study in these exposed to dust concentrations under 5 mppcf, whereas numerous well- marked cases were found above 5 mppcf. Counts were from implnger-collected samples in ethyl alcohol and distilled water. Both fibrous and nonfibrous particles were counted, but the latter greatly predominated. Although chemical analyses of collected samples of air-borne dust corresponded to those of settled dust, it is believed that dust counts of particulates by lmplnger can be expected to give only an indirect measure of the risk cf asbestos is because lmplnger sampling collects all particulates, including asbestos. A conference on the biologic effects of asbestos (10) in I965. called attention to the very real probability that the 5 mppcf limit reeonmended by Dreessen is inadequate to give complete working-life-time protection against all forms of asbestos. Medical data on which the limit had been based were DOW 06840 /\ S T00I1558 .'.sbestos - coned. -2 - Inadequate; more than half of the asbestos workers studied were under 30 years of age and thus provided an insufficient exposure tlaa for asbestosis to develop. Of the 10$ workers exposed to < $ mppcf, 62 had worked < $ years; 101. < 10 years; only 4 had > 10 years exposure. Seven of 36 workers exposed to $ - 9.9 nppcf for 5 - 9.9 years had asbestosis; 3 of 50 workers exposed to 10 - 19.9 mppcf for < 5 years had asbestosis (6). Moreover, it was a "point* in time" study; aany of the ill were missing and the dead uncounted, hence not considered in the over-all evaluation of the limit. The asbestos conference (10) further called attention to the rising worldwide race cf Increase in lung cancer among asbestos workers, particularly bronchial cancers, and also noted with alarm a widespread Incidence of pleural and diffuse mesotheliomas, tumors heretofore overlooked and only recently (1959) associated with exposure to asbestos. The epidemiology of the early cases was especially revealing in pointing out the scope of asbestos exposures; many of the mesothelioma cases had no industrial association, but were "neighborhood" cases or cases traced to users of asbestos. Exposures to asbestos extend far beyond those of miners and millers of asbestos or textile weavers, and include carpenters (sawing asbestos board). Insulators and pipe loggers, dockers hand ling asbestos cargo, brake-lining workers, rubber compounders and several others. The Cosaittee on Hygienic Standards of the British Occupational Hygiene Society from an evaluation of medical evidence from Great Britain and data from the U. S. Public Health Service Study (6) has recommended the following criteria for limiting exposure to chrvsotile asbestos assuming a l risk of contracting asbestos disease during a 50-year working exposure (11). DOW 06841 STOOI1559 A*bescos, coacd 3 Ouse Category Flbsrs N Negligible Lov Medium High <0.5 0.5 - 2.0 >2 - 10 > 10 a) Averaged during a 3-month period b) Greater than 5 ^ In length From cheae criteria, a limit of 100 fibera/ml-yeara vaa proposed, hence a limit of 2 fibers/ml averaged over a 50-year period. In arriving at an asbestos limit based on American experience and considerations applicable to the American industrial scene, the following predominated. Recent evaluation of the health experience in asbestos plants indicated that the 5 mppcf limit was not sufficiently low to protect workers exposed for 30 years, a period rarely exceeded in America. Balzer and Cooper (12) supported this view in a report that asbestosls Is occurring among insulation workers from levels thee were deemed highly unlikely to have exceed ed a time-weighted average of 5 mppcf. A retrospective investigation of the association between lung cancer in asfcestof workers and smoking by Sellkoff et al. (13) revealed that asbestos neoplasias were strongly associated with smokers. In accordance with these findings, the 5 mppcf limit was made a ceil ing value below which all concentrations should fluctuate. This is equiva lent to a time-weighted average value of slightly less than 2 mppcf, as shown by Ayer (1U) from the following determined for asbestos, where of the samples only exceed the 5 mppcf limit: *** 06842 S T 0 0 I1560 4- Asbestos, contd. % Samples Exceeding 5 mppef Average Concentration mppef 1 1.3 2 1.5 10 C*V 25 4.5 Inisouch as tha count by laplnger procedure often consists prinertly of extraneous particulates (textile plants) an alternate fiber-count say be oada by the membrane filter method using phase-contrast illumination at 430 X magnification (15). For the purposes of determining significant asbestos exposure, the membrane*filter method in which only fibers greater than 5 micra (pi) in length are counted, is recommended. On this basis, 6 fibers/milliliter greater than 5 H had been founi to be equivalent to 1 mppef. Hence for a time-weighted average limit by count of asbestos particles of 2 mppef, the corresponding limit based on fibers of specified size is 12 flbers/ml. This limit is intended to reduce to an insignifi cant risk, the occurrence of asbestos disease among those exposed for 30 years to all forms of asbestos. Thera is still asbestos disease;appearing in industry. It is not known to what extent this represents a reservoir effect of past exposures, or if the 5 mppef level is still contributing to the disease incidence. For this reason the 5 mppef is reconaended as a celling value (2 rppcf as a time-weighted average) until a more definite value can be established based on medical findings. DOW 06843 STOOI1561 Atbestoa, coned. 5 RgEREWCESt 1. Merevether, E. R. A.: J. lad. Hyg., J2, 196, 239 (1950). Fnetmoconlosis Abstracts, 1926-1938, Vol. 1 p. 128. 2. Wood, W. B., Gioyne, S. R.: Lanett, Dee. 22, lS0fc, pp. 1388*1363. 3. Fulton, W. B, Dooley, A., Matthew, J. L., Coots, R. Lt Penn. Dept, of Labor and Xnd. Bull. 42 (1933). 4. Lanza, A. J-, McConnell, W. J., Pehnel, J. W.: Pub. Health Rep. JO, 1 (1595)* 5. Donnelly, J.: J. ind. Kyg. & To*. 18, 222,(1936). 6. Dreessen, W. C., DellaValle, J. V., Edvarda, T. T., Miller, J. W., Sayers, R. R.: Pub. Health Bull. No. 2Ul, Washington, D. C. 1938. 7. Lynch, M.: Arch. Ind. Health 11, 185, (1955). 8. Smith, R. W.: Arch. Ind. Health 12, I98 (1955). 9. Cartier, P.j Arch. Ind. Health 11, 204 (1955). 10. Biologic Effecta of Asbestos, H. E. Whipple, ed.. Ana. N. ?. Acad. Sciencea 132. Art. 1, 1965, 765 pp. 11. Report of Committee on Hygier.e Standarda, Brit. Occ. Hlth. Soc. "Hygiene Standarde for Chrysotile Asbestos Dust" December 1967. 12. Balzer, J. L., Cooper, U. C., Ind. I!yg. Nava Report Dec. 1C67. 13. Selikoff, I. V., Haocand, 2. C., Churg, V., J. Am. Med. Assn. 204. 10U (1968). 14. Ayer, H. E.: Memorandum to Committee Member Jan. 1968. 15. Ayer, H. E., Lynch, J. R., Penney, J. H.: Ann. N. Y. Acad. Sciences 132, Art. 1, p. 274 (1965). OOUJ O6844 r I