Document e78R4ZDV7DX0qn8OVbV34x60y

k l&-r7375 Evaluation of Asbestos Exposures in the Working Environment c 'S ;. .. . - >. T?- he extensive use of asbestos in industrial and con-yi I . susner products and the related occurrence of occu- ri pational diseases, especially asbestosis and neoplasms, associated with excessive exposure to the airborne as bestos fibers- have stimulated much research over the / past decade in many countries on exposure to asbestos as related to health, establishment of standards, and monitoring of the environment. The procedures used in --. .* the various countries for enumerating and characterizing . exposures .to respirable. asbestos fibers differ considerjablyvmalUng-it extremely difficult, or impossible, to . - -cejmpSre'and interchange seemingly similar date between countries. The impact of-the worldwide research on asbestos wrould be much greater if uniform procedures were used to collect, enumerate, and characterize expo- -;v- suresro respirable.asbestos fibers. This would permit the data from different countries to be interrelated and ia- - eluded in a collective data bank, thus increasing the scope, reliability, and usefulness of the data. The Sub-Committee on Asbestosis of the Permanent Commission and International Association on Occupa tional Health recommends the following procedures for collecting, enumerating, and characterizing respirable as bestos fibers in the working environment: A. Fiber Exposure Evaluation Procedures 1. Collection of Airborne Sample The membrane filter technique should be used for collecting airborne asbestos fibers. The respirable frac tion should be used in making measurements for relating levels of exposure to health effects and for determining compliance of standards. Specific proceduies recommended for collecting membrane filter airborne samples of asbestos fibers in cluding equipment, sampling rate and type of filter have been developed for the Asbestosis Research Council, , England, and the National Institute for Occupational Safety and Hearth. United States. These procedures ate ' described in "The Measurement of Airborne Asbestos Dust by the Membrane Filter Method"1 and "The Method Used by the U.S. Public Health Sendee for Enu meration of Asbestos on- Membrane Filters."2 Each of the methods described gives comparable lesults. 2. Sanipli'ig Location' The purpose for which the sample is to be used will determine not only the type of sample to be ob- tained but also the location where it should be taken. Airborne samples collected ar the breathing zone of the workers should be used in obtaining exposure data for application in studies on health effects and in evalu- - ations for compliance of standards. These samples may be taken with personal samplers located on the workers2 - or by an operator holding the sampling equipment near the breathing zone of the workers. Stationary (fixed y site) airborne samples may be collected for obtaining data to assure that dust control equipment and proce dures at specific operations are functioning properly and efficiently. . 3. Sampling Time .......... ... In collecting a sample of airborne asbestos dust, the length of time needed for collecting the sample wiU depend.on the sampling rate of the instrument, the rela tive concentration of dust in the air, and the purpose for which the sample is collected. A relatively short sam- . pline time but frequent sample taking should be utilized in determining maximal levels of exposure and their intermittency. In contrast, longer time samples should be taken for determining weighted exposures. Most sam pling regimens, both for obtaining exposure data for cor relation with health effects and for compliance with standards, will require both short- and long-term sam pling times. In some instances, the regulations will specify both the sampling instruments and the sampling times to be used.3 Both the sampling time and number of sampiies taken at any given operation should be so related as to give reliable data to fulfill the purpose for which the samples were taken. I. Fiber Enumeration Although the specific eliologic agents responsible for the health effects from excessive exposure to asbes tos dust are not known, the accepted best index of expo sure is the quantity of respirable fibers in the worker's bieathing zone. It would be impossible to count all of the respirable fibers, smee many of these are sub-micron in size and would icquire the use of the electron micro scope for quantitation. The latter would be too time consuming and costly to use as a routine counting proce dure. Consequently, at present it is feasible to count and use as an index of the ovcrall.spcctruin of exposure oijly the respirable fibers that can be detected using specific optical microscopic equipment and'pioccdures.. 28' INDUSTRIAL-MEDICINE. VOL. <11, NO. 1, JANUARY 1972 411596 0027 For differential purposes and based on past usage, a fiber is arbitrarily defined as a particulate in which the ratio of the length to the diameter is equal to or greater than 3 to 1. Fiber counts should be expressed in number of fibers per cubic centimeter (or milliliters) greater than 5.0 microns (or micrometers) in length. Fibers greater than 5.0 microns in diameter should be excluded since they are predominantly non-respirable. Asbestos fibers should be counted using phase contrast microscopy at around 400-500 x magnification. The treatment of the membrane filter on which the asbestos fibers are de posited and the microscopic counting technique involved are described in "The Measurement of Airborne Asbes tos Dust by the Membrane Filter Method"1 and "The Method Used by the U.S. Public Health Service for Enu meration of Asbestos Membrane Filters."2 Each of the procedures gives comparable data. In addition, for research purposes, limited measure ments of the respirable fibers on the membrane filter samples should be made by means of both optical and electron microscopy to establish the ratio of fibers under 5.0 microns in length to fibers greater than 5.0 microns in length, as well as their respective distribution based on diameter. These measurements are needed since the bio logic importance of sub-micron asbestos fibers is largely unknown and the fibers equal to or greater than 5.0 microns in length may not always be a valid index of exposure expressing the relation and significance of the spectral distribution of the respirable fibers present. For hazard evaluation and compliance of standards as well as research purposes, it is recommended that the ratio of respirable asbestos fibers to total respirable par ticulates be determined. This is especially important in instances where the other respirable particulates may be biologically reactive per se or additive to the effects of the asbestos and where fiber counts may be relatively low so that the standard for other respirable materials present may become the most relevant factor. B. Chemical Characteiization of Fibers 1. Type of Fibers Different types of asbestos fibers may evoke dif ferent biological responses depending on their chemical and physical characteristics. The type of asbestos present in the respirable fibers, e.g., chrysotile, amosite, crocidolite, etc., should be identified and this information given as a part of the exposure data. This identification may be relatively easy if the source and nature of the parent bulk asbestos is known. In some instances, how ever, a natural mineral such as talc may contain a mix ture of fibers. Also, the source and nature of the asbes tos represented in the respirable sample may be un known. In such instances, polarizing microscopy. X-ray diffraction, electron microscopy, electron microprohe. electron diffraction, and other special techniques may be needed to identify the ratine of the fibers. 2. Metals Asbestos fillers sometimes have .associated wuii them a mmib'er of, metals which may be tiio'ogu. dly active. Those metals may .atisc out of the mi.-enr-my involved m file formation o! the ttbeisoi bom the aimsi vc action of the fibers on the alloy metals m which they are processed. The quantity of the specific metals present in a respirable sample may differ markedly from that of bulk or settled dust samples. For research pur poses, representative airborne samples of respirable as bestos dust collected at strategic operations should be analyzed for biologically active metals, e.g.. nickel, chro mium, cobalt, manganese, iron, etc. Sufficiently sensitive methods should be used to express concentrations accu rately within the lower range of micrograms per cubic meter of air. 3. Free Silica Some types of asbestos fibers may contain appre ciable amounts of free silica. At times, silica may be added in the preparation of an asbestos product such as in shingles, sidings, and pipes. In evaluating the exposure of the asbestos worker, measurements should be made of free silica concentrations at strategic operations where it may be presenfTn "fTfe air in amounts approaching the standard4 for exposure to silica. 4. Organic Contaminants Respirable asbestos dust samples may contain varying amounts of polycyclic aromatic hydrocarbons, depending on the nature and source of the asbestos fiber, the processing and packaging involved, and the absorption of organic compounds from the ambient air on to the fibers. For research purposes, concentrations of cyclohexane extractable materials should be deter mined in airborne samples of respirable asbestos dust collected on glass fiber filters in various working environ ments. High volume samplers should be used where possible to estimate the amounts of common polycyclic aromatic hydrocarbons in the samples. C. Physical Characterization of Fibers Under the microscope, respirable asbestos fibers may at times show physical appearances that are different from those usually observed, e.g., curling of fibers, ex cessive spreading within the fiber bundle, etc. For re search purposes, these patterns, along with their fre quency of occurrence, should be noted and reported. D. Alternative Exposure Evaluation Procedures 1. Counting and Enumeration Many countries have had long years of experience in using specific procedures, such as the konitneter. bright field projection microscopy, etc., for collecting and counting asbestos dust in determining exposure levels ami have developed extensive knowledge by corre lating the data with health effects. It is important that such knowledge not be lost and that an accurate bridge of relation be established between these data and similar data obtained with the use of the uniform procedures recon-mended hy the Sub-Committee oil Asbes'osis. Thus, it is strongly recommended that countries not using the recommended uiufomi procedures .`c-.tiitcly he urged to use these procedures concurrently with then' usual collecting and counting procedures so that com- parati-.c data can ho made available. 2. Other Ptocedmes .- -. Other procedures being selectively u;vu to me.isuto a'--.! characteti/e the respu.ible dust a-sociated'"-. bestos exposure-, utiii/e. dfi.-ct ard indue.; ic.-dr-j due: counters, mass measurements, surface area nivrsuie- MDC'STRIAL MEDICINE. VOL. ^ I, NO. 1. JANUARY 1072 411596 0028 ments. and I he like. The application of these methods of counting and chaiactcri'.ation should he encouraged ami may give new knowledge on the biological response to fibers. It is urged, however, that concurrent data also be obtained with the procedures recommended by the SubCommit lee on Asbcstosis. Sub-Committee on Asbcstosis: Work Gioup on Airborne Measurements Lewis J. Cral/ey, Chairman, U.S.A. Howard E. Ayer, Vice-Chairman, U.S.A. Dr. Claude Amoudru, France Dr. Graham W. Gibbs, Canada Dr. Stephen Holmes, United Kingdom Prof. Enca OcceUa, Italy Dr. Rudolph S.J. duToit, Rep. ofS. Africa REFERENCES 1 Technical Note 1. The Measurement of Airborne Asbestos Dust by ihc Membrane Filter Method. Asbcstosis Research Council. P.O. Box 40. Rochdale. Lancashire. England. 2. Tire Method I'sed by the L.S. Public Health Service for enu meration of Asbestos Dud on Membrane Filters, by G.H. Edwards and J.R. Lynch, li.S. Department of Health. Educa tion, and Welfare, Public Health Service. 1014 Broadway, Cincinnati. Ohio 45202. 3. Technical Note 2. Dust Sampling Procedures to' L's: with the Asbestos Regulations 1969. The Asbcstosis Research Council, P.O. Box 40. Rochdale, Lancashire. England. 4. American Conference of Governmental Industrial Hygienists. Tlte Threshold limit Values of Airborne Contaminants and Intended Changes (1970). Reprint rtouests: Industrial Medicine and Surgery, P.O. Boa 7151, Fort Lauderdale, Fie. 33304. 01972 M.P.I., Inc. 30 INDl'STRIAL MEDICINE, VOL. 41, NO. 1. JANUARY 1972 411596 0029