Document MG7bYYG40m5kvVG6v0rXnvg0y

/ THE ACTUAL CONTRIBUTION OF GARLOCK ASBESTOS GASKET MATERIALS TO THE OCCUPATIONAL EXPOSURE OF ASBESTOS WORKERS CARL A. MANGOLD, C.I.H. October 1982 Bellevue, Washinotor. PRIVILEGED AND CONFIDENTIAL MATERIAL. NO USE OR PUBLICATION MAY BE MADE OF THIS MATERIAL WITHOUT THE PRIOR WRITTEN AFFROVAL OF THE AUTHOR. EXHIBIT NO.-i abstract Hard-pressed or encapsulated asbestos gasket materials manufactured by Carlock release only small amounts of fibers during handling, processing or removal in industrial operations. A recent Department of the Navy study confirmed that the total occupational exposures related to gasket materials are at the minimum risk levels compared to current Federal standards. This study, commissioned by Carlock Inc, shows that work area contamination - i.e. , ambient pollution from other sources in industrial areas,^.asbestos-laden clothing, and general atmospheric pollution - far exceeds any contributions from such casket materials and makes emission from gaskets insignificant by comparison. - When these nongasket sources of contamination are minimized the actual occupational exposure of the gasket materials is in the range of the levels of exposure expected in downtown city streets on dry summer days experienced by the public. The breathing zone concentrations of asbestos fibers from Garicck, Styles 7021, 900/7735 and 605 gasket materials prepared as they were in the 1940-1970's are near the lower limit of detection. .Xo_the_extent_thev _are_measure.ab.le. the. val ue r_ average. 1/lCOth of the current allowable exposure of two X;.h.-. ..per..cubic centime_te.r._.gr.eat.er..than...five-micrpmeters .in 1 ength..^s_ce_t.ermined_by_ph.2s^_c.ontr.est microscopy and_based_on _ar. eicht-hour time-weighed ave rage . work . day. The actual contribution of the Carlock asbestos gasket materials described and evaluated in work environments constitute a negligible exposure and risk to workers. The occupational exposures, are often lower than contamination levels of industrial work areas where asbestos is processed, the exposure to the general population living near these industrial areas, or in downtown city streets on dry summer days. - or DISCLAIMER The author is solely responsible for the contents and conclusion in this report which may not'necessarily reflect the official opinion of contributors, the U.S. Department of Navy, or U.S. Department of Labor. acknowledgements and contributors 1. J. D. Wendlick, Corporate Industrial Hygenist, The Weyerhaeuser Company, Tacoma, Washington. 2. Zidell Corporation, Tacoma, Washington. 3. Northwest Health Services, Richland, Washington. 4. Devine Diving & Salvage, Portland, Oregon. 5. Dorothy Gockel, Researcher, Department of. Community Medicine, University of Washington, Seattle, Washington. 6. Mine Safety & Appliance Company, Seattle, Washington. (ii ) TABLE OF CONTENTS ': Page abstract ....................................................................................................................... (^ ) Disclaimer .............................................................................. .................................. (* ) Acknowledgements ............................. '.............................................................. (ii) I. History .................................................................................................... 1 11 . Background ............................................................................................ 5 " III. Introduction ....................................................................................... 6 IV. Methods of Investigation ................................................. 17 V. Findings ................................................................................................. 19 A. Exposure to City Dwellers ....................................... 19 . 5. Effects of Asbestos Contaminated Clothing ............................................................................. 24 C. Workplace Contamination Levels of Airborne AsbestosFibers'....................................... 29 - D. Casket Processing ............................................................. 34 E. Flange Gasket Operations ......................................... 39 VI. Conclusions .......................................................................................... 41 VII. References ............................................................................................. 44 12 5 53 (iii )  * r . I.. . history Asbesto_s_i s_ one _of our _most_ plentiful, .useful, and cheap industrial minerals. Consequently, because of.its high.-thermal stability and resistance to corrosion it appears in more than 3,000 manufactured^ goods_in_the .United-States. Estimates are that at least 30,000,000 tons have .been used in.construction and manufacturing since the year 1900. This common use of asbestos has led to the exposure of millions of Americans at levels that may have a significant impact on their health. Today, large numbers of Americans are exposed to asbestos both r. industry, as veil as in cur environment. Environmental . exposure occurs in our cities,, near industrial complexes, from soil h: gh .in asbestos content, and even in rural areas affected_ by natural erosion of asbestos containing..rock. Therefore, :cst r.r.srica ns receive at least some regular low-level exposi ire tc asbestos in their lifetimes. However, some experience much higher levels from occupational sources or have had high exposures in past years. The concerns about the role of asbestos in the development of the lung disease, known as asbestosis, began in the United States in the 1930's and progressed slowly as more was learned of the pathogenesis of the disease. Most of the attention was centered on disabled workers with an obvious work-related exposure pattern involving exposure to raw fiber. controls, were followed so Few, if any asbestosis. This continued until the 1960's when signs of asbestos-related cancers began to reshape thinking and action about occupational exposures to asbestos. Today the exposures of workers have been markedly reduced through various means of voluntary controls and legislation that led to the first Federal standards in 1972. In 1964, Marr [1] concluded that asbestos-associated disease was an important problem among insulators working in naval shipyards. However, the methods of assessment weakened the conclusions. Pioneer work was begun at Puget Sound Naval Shipyard (FSNS) in 1965, culminating in a conclusive report by Fence id, Beckett. & Eessmer in 1970 [2, 3). Most of the attention was directed at the products and operations that produced high-level exposures to asbestos workers and associated trades. The.conclusions were_that the threshold limit was still too high at 5 million particl.es_per_cubic._foot... (mppcf) (equivalent to approximately 50 fibers per .cubic centimeter (cc)) and that intermittent peak exposures were far. more important than previously^considered. Both have been corroborated by more recent literature. About 1964, Selikoff |4, 5] and others began reporting the appearance of asbestos specific cancers in work groups with high exposures to asbestos and long work histories. 1256C 2 Since that time, wide attention has been given to the diseases of asbestos by physicians, scientists, and researchers md driven by Federal Regulation that lead to the lowering of allowable occupational exposure levels and the marked increase in claims based on previous high-level exposures. In 1978, Dr. Irving Selikoff of the Mount Sinai Hospital and a team of medical scientists conducted a study on the Disability Compensation for Asbestos-Associated Diseases in the United States [6]. The study was completed in 1982 and clearly defines the latent_ef fects..of exposure.and probable cc_se-response relationship based on time and intensity of expcsur_e. However, J. E. Craghead, et al. [7], M. R. Becklake, v.'. J. IE], Nicholson, et al. [9], raise reasonable cuestions about the validity ofjthe probable dose-response relationship because of th.e_I.aj:e_ ncy,,.faetcrs and the ill-defined respenses to low-:evej_ exposure. Nicholson |9| observes that the lone lapse time from exposure to ..the or.s_et of asbestosis. .or. asbestos-rehted cancers,, crej.t e s_ si gni f i cant difficulties in . attempting to establish a dose-response relationship. The disease i no i dense ..today. i s frjem decades past when few measuremier.ts of asbestos concentrations were_made, exposures were high, and controls were few. Churg 110] described the relatively high level of_ a_sbestos fibers in the lungs of city dwellers not occupationally exposed- This suggests a typical sigmoid, or "s" shaped form found in dose-response 1256C 3 ' re 1ationship s _ wh e r e...a lover no-Jfect 1 eye 1 is..reached, rather ' " ` than the -direct dose-response curve vhich takes the form of -a , straight -line. There is a linearity of effect with increasing amounts of asbestos inhaled for.related asbestos induced cancers. There are differences in the slopes of the dose-response curves.and. some literature implies that a linear, or direct response exi sts . at..any. leyel_of..exposure,. In reality, these are extrapolations.^rom epidemiological data on_deaths_which resulted from unknown,., or ..previous high level exposures to. asbestos. _Fiber exposures of long ago are of more importance ir. determining the risk of cancer than more recent exposures.16 ] They do not relate to very low concentration exposure patterns, therefore extrapolations that approach the idea ir. the singlemhit mathematical model is extreme, and without solid proof to ascertain the actual occupational exposure from, individual products. The discovery that elevated levels of exposure to asbestos fibers may lead to related cancer, and the trends in Tort claims requires a knowledge of the exposure potential of each product. Obvious attention is now given to lower levels of exposure than ever before. As technology and preventive work practices lower occupational exposure, the contributions of each asbetsos product becomes important. When high-level exposure occurred during uncontrolled work situations or even at allowable 1256G 4 exposures of 5 mppcf (SO f ib_exs/g-CjL_under the_prior recommended TLV, contributions from encapsulated gaskets were fractional and negligible. In short, the extremely low level contribution from such gaskets is obscured by the high background levels from other asbestos sources, or their residual contamination. II. BACKGROUND The earlier works of Marr |1) and others 111] used methods and instruments which are now unsuitable for the assessment of asbestos exposure based on the current Federal occupational standard of two fibers per.._cubic centimeter greater than five r:crc-sters in diameter as collected on a membrane filter and counted by phase contrast microscopy at 400X. When the asbestos dust levels were elevated, little attention was given to- background contamination and the sampling and counting errors because c their negligible effects. As the allowable exposure levels were reduced over the years, effects of background centen.ination have become important factors in asses ament of exposures that are in the range of these sources of contamination. The current Federal standard ^requires evaluation that is approaching the lower limits of detection by phase contrast _micros_cqpy..within acceptable, stati sti c al_ limits. In fact, R. D. Zumwalde and J. M. Dement [12).observe^ that 0.1 fibers/cc greater than five micrometers in diameter is 1256G 5 the lower.limit of. detection that, maybe _us.ed _wi th_any -- reliability. These_assumptions are based on the__countiiu3 3 limitations by phase contrast microscopy_and the known_r.andom _ sampling errors. Reported values .below 0.1.fibers/cc become suspect unless rigorous procedures are followed to avoid._large errors and the effects of contamination. Therefore, it is ' useful to reevaluate previously reported exposures to asbestos casket materials 115), to validate them and to judge the effect cf these factors. ' '. Kenneth A. Busch, et al. |13 ], further describes the limitations of the method and the potential for large co-ef: 1:ier.fs cf variation when low levels of asbestos are a z. e j * c. ^ Earlier determinations cf the low level of fibers released from encapsulated gasket materials must be re%'ised to still lower values because prior measurements did net accurately take accouno cf contamination in the work area, and other bias such as the limitations of the counting method, or arbitrary samp line considerations. 111. INTRODUCTION . Because naval shipyards were large-volume users of asbestos products, the occupational exposures in the 1940's, 1950's and 1960's were often elevated |1, 2, 3, 6]. Most of the eva luation, 1256 6 engineering, change or work practices, and personal protective measures .were directed toward these obvious sources of exposure. Each of the asbestos products were used in a unique way ranging from blankets of asbestos used for thermal insulation that caused high exposures to the negligible exposures caused by gasket materials. Products like gaskets contributed a comparatively small, almost unmeasureable, proportion to .the overall occupational exposure. Therefore, little attention was given to these low-level sources of exposure because the high volume, high-exposure level sources needed primary attention. In 1945, the American Conference of Governmental Industrial Kyrerists (ACGIH) adopted a Threshold Limit Valve (TLV) for particulate in air based on 5 million particles per cubic foot (rcprf) for an 8 hour time-weighted average workday, which remained in effect until 1969, when it was reduced to 2 mppcf. The analytical procedure required that air samples were drawn through midget impingers containing distilled water at a rate cf .1 cubic foot per minute. An aliquot of the solution was transferred to a microscope counting cell in the laboratory and the particles counted by light field microscopy at 100X power. Ayer at. al. (14) conducted comparative sampling in asbestos plants in 1965 using the impinger/light field microscopy technique and the current membrane filter/phase contrast microscopy method. They concluded that 50 asbestos 1256G 7 fibers/cc. greater than five micrometers in diameter by the membrane filter method was comparable to 5 mppcf by the '.mpinger/light field microscopy technique. This comparison is important to show the comparatively high allowable leyel__of occupational exposure to asbestos fibers in air during 1946 through 1969 when the 5 mppcf TLV was applied. Accordingly, standard shipbuilding and repair practices such as magnesia block cutting ana_ installation, or asbestos_ cement mixing created equivalent fiber.counts.ranging from.167 to 475_fibers/cc on an eight-hour time-weighted average basis / -/ Because of these high contamination levels from all other srurces. Mangold, Beckett & Eessner justifiably ignored the casket contribution in their studies culminating in the 1970 F3NS report [3]. It was not until 1978, that the Department cf Navy | 13], as part of a continuing evaluation program set about evaluating asbestos exposures to workers from storing, handling, and processing asbestos gaskets of all kinds. The Fuget Sound Naval Shipyard (PSNS) was selected as the lead shipyard in the evaluation which produced the 1976 report. This evaluation is important because there exist few such publications that identify and estimate the occupational exposure to asbestos gasket materials. The report concludes that even the simplest of general housekeeping controls or work practices are sufficient to maintain occupational exposure 1256C 8 below the current Federal standard for an eight-hour TWA exposure of two fibers/cc, greater than five micrometers in diameter or the proposed N10SH standard of 0.5 fibers/cc, greater than.five micrometers in diameter. In fact, many of he__e_xpesures were found to be less than 0.1 fiber/cc at which level medical examinations are no longer required [16], according to a current interpretation of the Federal Standard, for Asbestos. * It is reasonable to conclude that the same types of qasket materials used in the same manner from 1940-1970 would produce the same negligible contribution to the overall occupational ex;:sure. Secondly, the contribution from encapsulated gaskets was much below generally accepted allowable exposures. For examrle, the recommended threshold limit value (TLV) was 12 mere; (12C fibers cc) until 1946 when it was reduced to 5 ir.ppcf (about 52 fibers cc) until 1969, when it was further reduced to t: two m.ppcf (about 12 fibers/cc). In 1972, a still more stringent Federal standard of five fibers/cc, greater than 5 mm. in diameter cn an eight-hour time-weighted average was adopted, ar.t thi s too was later reduced to two fibers/cc in 1976. Thus encapsulated gaskets, found to emit less than .01 fibers/cc, _arj_.at_lev.els. more .than 200 times below the current Federal /' standard and thousands of times less than earlier accepted standards. Page 10 depicts a graph illustrating the manyears of allowable exposure to asbestos fibers from 1946 to 1982. 12560 Q U lMAMILAJlii OF ALLUUAULli 'OJUlUt a 10 Sourest 1. iRaJhan a , Q.H. Dra E n g ln o u rln g Aapocta o f *bor Sciancs P u h lla h o ra , 19?0 ''o Lluat C o n tro l However, the .techniques and methodology used in the PSNS gasket report may provide misleading information that would cause higher levels of asbestos exposure in the breathing zone of workers to be reported than actually exists in a work day from processing asbestos gasket materials. The 1978 PSNS report [15] does achieve the intended purpose to determine the exposure to any and all asbestos in the breathing zo.ne of workers but does not determine the actual contribution from the gaskets "alone. Samples were collected in sene work areas under uncontrolled conditions and later in the same work area under controls without regard to potential.pripr, contamination. While exposures were reduced by cleanup, the contamination from past operations would be present in the air and.-cr red: sbursed from previous activities. Tiny fibers of asbestos remain airborne indefinitely under such conditions of turbulence [17, 18, 19, 20, 21, 22).. Because the airborne c one er.tr ati ons reported in the FSNS gasket report [15] are extremely low, often .01 fibers/cc or less, the potential for contamination is certain and would be expected to substantially skew reported values upward. The__s_ample periods in the FSNS report range from six minutes to 132 minutes which is another factor whi ch _l_imi ts the precision of the method. Also, the limitations in the counting techniques |12, 26, 27, 28, 29] indicates that at least ten fibers/100 microscope fields within an effective microscope counting area of .005 mm2 must be 1256G 11 viewed to remain within the very large co-efficient of variation of 0.41 at that concentration |25). Additionally,1 single samples collected for short sample times and using an arbitrary lower cutoff of .01 fibers counted introduced unequa and vide systematic error by the report's own statements |15] on page 3. Furthermore, membrane filters like the Killipore AA, .8u pore sire have a background of 0.1 fibers pe .microscope Forton recticle field or ten fibers/100 fields |29]. Therefore, larger air volumes must be collected to be able to measure the airborne contribution with any certainty when airborne asbestos levels are in the ranges reported. The report assumes 0.01 fibers counted as a lower limit for low . values regarrless cf actual existence of the fibers, thereby iutroc_c:im.g the systematic error. The sample periods were limited to actual exposure time curing the sample period and may not reflect a complete unit operation or am. eicht-hour time-weighted exposure, and mere likely reflect intermittent peak, exposures. The report concludes that exposures do not exceed the current Federal standard'of two iibers/cc, cn an eicht-hour Tv.'.-.. This is misleading since cm.ly the intermittent peak exposures of single or parts of an operation were reported. These intermittent peak, values may be several orders of magnitude higher than the actual eight-hour time-weighted 12Sc3 12 average, 'based on a 40-hour week,_and..adjusted for background .. contamination^ In some cases, _only .single ..samples-were -collected~f or' an operation, .guch single samples _only__serve as. indicators .and are not_relevant ..nor statisti_c.ally._significant. The low-exposure levels reported do not.jconsider p-e_existing contamination, and therefore do.not necessarily rerresent the actual airborne contribution from the_ gasket materials. Section XII of the 1978 PSNS report shows consistently hither reported values for samples collected at Lor.c Beach Naval Shipyard by the Naval Regional Medical Center, Oakland, i..am. reported by FSN5. There is no evaluation or comparison cf t r. i s c a t a . The l?Tc FSKS report is unique because there are only a few sorb reports that evaluate the contribution of various types cf asbestos casket to the occupational exposure according to the state-cf-the-art work practices conducted in large shipyards by highly mobile work forces. Nonetheless, the data shows only a small _ccontribution by gasket materials to the overall c o cupa oiona 1 exposures.which include atmospheric pollution, contamination, redi spe.r si_on of fallen asbestos fibers and dirty clothing, and reflects higher intermittent peak exposures of, unit operations. Although the 1978 PSNS Casket Report is an important work, a redefinition is needed to show the actual 12S6C 13 exposure of gasket products. This would exclude other sources of exposure or make adjustments for them because there is a common thread of error of assurr.ption, _jiamely .that the sampling w_f_ low-level airborne asbestos levels in a highly contaminated _ environment reflects the actual gasket exposure pattern.. The technical objections previously stated introduce large systematic errors from counting assumptions and background contamination that skew the actual airborne exposure levels substantially upward. Therefore, the values are overstated and co net reflect actual eight-hour time-weighted exposure patterns. The accumulated contamination is a function of location, operation, use rate and work practices. The 19~E FSNS report makes arbitrary sampling and r.irrcscope counting decisions that affect the lower limit of detection cf the methodology. For example, a 15 minute sample as a lower limit cf detection of .0= fibers/cc at 1 fiber/lTC microscope fields counted. Valves below .01 fibers counted were assumed tc be .01 fibers found. This was done for cer.veni ence but nonetheless leads to higher values reported than, actually found. Insufficient fibers collected cn the filter caused by short sample periods would introduce large ccurtmg errors using the above assumption. The l-.'IOSH Revised Recommended Asbestos Standard of 1976 130] shows that under the most optimum conditions using a microscope field counting area of .0071 mm2, the lower limits 12360 14 of detection range from .04 fibers/cc, greater than 5 um in length for a 15-minute sample up to .001 fibers/cc, greater than 5 um in length for an eight-hour time-weighted exposure. This is equivalent to the discovery of the adjusted net count of one | 1 ] asbestos fiber, greater than 5 um in length in 100 microscope fields. The gross count is adjusted for fibers already on the membrane filter as stated by the manufacturer | 2?]. There is no basis or current procedure that justifies identification of less than one [1] fiber in 100 fields counted. The NIOSH Revised Recommended_Asbestos Standard of 1 ? ~ 6 | 20 ] shows the procedure, fails due to large errors when less than cr.e |1] fiber/100 fields is considered based cn known s'-- * ' o c f '* c rr: (1) Uneven distribution of fibers on the filter surface; (2) Variance of distribution on any given filter wedge (f ) .Variability m microscopes; (-4 )___ Differences in technique and ability of analyst; (5) Variations between laboratories. Regardless of its limitations, phase-contrast microscopy is the only reasonable technique available for routine asbestos fiber counting and is the only method that relates directly to _the federal standard that sets allowable occupational exposures to airborne asbestos fibers, and the requirements for medical examinations. |24, 25, 26, 28, 30, 31, 32] 12560 15 Since 1964 when the threat of asbestos-related cancers were defined (4.5) and with the increasing knowledge about asbestos <posure, the focus has shifted to the concept of reduction to lower and lover allowable occupational exposures. However, there is some question about the extrapolation of data from . studies conducted at much higher levels of exposure to these lover levels of exposure with the same expected dose-response _ relationship. The technical ability to measure low airborne concentrations of asbestos fibers have been made possible by phase contrast microscopy but the analytical method approaches the limits of accuracy and precision (12) when lower levels of asbestos fibers are measured. Seme products like asbestos casket materials contribute negligibly to the overall occupational exposure of workers. Bur these small contributions are confounded or obscured by high background contamination levels where asbestos products are processed, such as, nearby dusty operations, contaminated clothing, and atmospheric pollution. Consequently, the actual contribution cf casket materials that produce only lew level exposure to the overall occupational exposure of workers becomes important and because few studies have attempted to differentiate the actual exposure from these sources of contamination. 12553 16 The average overall asbestos dust levels in cities and near industrial areas often reach levels in the range of the contribution of certain industrial products like gasket materials_._ Therefore, the need to study and determine' the actual contribution of gasket materials to the potential occupational exposures to asbestos is readily apparent, and to place the previous studies of Mangold (3), and Beckett 115] in perspective.. Eecause of this, a comparative evaluation was developed to measure the actual contribution of Carlock asbestos gasket materials to the occupational exposure of workers in large industrial settings based on the eight-hour time-weichted average. IV. METHODS OF INVEST! C-.VT I ON The lev.- results of some of the gasket operations evaluated in the 197 FSNS report at the .01 to .04 fiber/cc levels suggest that ether sources of airborne asbestos fibers were part cf those reported values, as well as some of the more elevated values cr single samples reported. The sources of sample contamination are: (3) General atmospheric pollution; (2) Kedispevsion of fallen dust in the work area; (3) Sources of asbestos dust from adjacent operations; 12550 17 (4) Contaminated work clothing. (The Bample cassette is attached'to the lapel as a standard practice 132].) (5) Contaminated sampling equipment that introduces fibers into the air where cassettes are opened for processing. The comparative evaluation commissioned by Carlock Inc was intendsd-t o: (1) Sample typical gasket materials under rigorously controlled conditions to exclude contaminated sources, and to collect enough samples to ensure the validity of the findings. (2) Specify Carlock products manufactured in the same manner as in the period 1940-1970. Styles 900/7035, 7021, and 625 were used because they best represent materials used in industrial operations during the period 1940-1970. (5) '.elate the sample data to the Federal standard of two fiber greater than 5 urn in diameter for an eight-hour TWA, and the C.l fiber 'cc level that requires medical surveillance by interpretation of the standard [16, 32]. (4) Preferentially examine hand punching, machine punching, machine shearing, nibbling, and flange gasket preleases t: clear anomalies in the 197S FSNS gasket report ! 25 J . (5) ^Collect samples in city streets to show the common exposure to the population of city dwellers and establish the levels for comparison to the occupational exposure 12 56G IE contributions of gasket materials on an eight-hour time-weighted basis. (6) Collect samples in the work areas to establish that the airborne contamination levels of asbestos before gasket materials are processed. Otherwise, data would reflect both sources without distinction. (7) Determine the contribution of contaminated clothing during sampling of low-level exposures such as gasket handling and processing. jContaminated .clothing is known to contribute to the overall daily exposure of asbestos workers [19, 20, 34, 35). (E_i__ Use sampling techniques, laboratory procedures for sample mounting, and fiber counting by phase-contrast microscopy |25, 26, 27, 26, 32, 35] that relate findings to the Federal Asbestos Standard. (?) Compare street and work area exposure data to actual or adjusted casket exposure data to show relevant contributions from each source. V. FINDINGS A. Exposure to Citv Dwellers. ' Tables 1 and 11 show the concentrations of airborne asbestos fibers collected at the breathing zone level during July and August 1982, in Portland, Oregon, and Seattle. 1256G 19 Washington. The same sampling equipment and counting procedures were used to evaluate the street data in order to make dii-ect comparisons to occupational exposures in Tables IV, V and VI. Each sample was collected over an eight-hour period during the work day. Table III shows substantially higher levels of airborne asbestos fibers at the public street level adjacent to Puget Sound Naval ..Shipyard, Bremerton, Washington. The samples were collected during dry days in August 1982, at a location in the city up-and-cown-wind from the shipyard and near the boundary cf JS.'.'S within the city. The data shews surprisingly high levels on certain days, and substantially elevated airborne levels near the industrial area cf ?S.\`S several blocks from the shop that processes asbestos products. The findings are corroborated by data reported by C. S. LeJ-'.nne ir. 1?SI [22] in the City cf Seattle, for ambient asbestos.levels. . Hrake lining, construction, industrial processes, and demolition are the most probable sources of these airborne cc n o_e r.trati o u s of asbestos fibers. However, redi sper si on plays an _ir.portan^_part.in.continuing levels of airborne asbestos found at the street level. 12560 20 'TABLE I Sample 4f 1. 3d Street 2. 3d Street 3. 3d Street 4. 3d Street 5. 4th Street 6. 4th Street 7. 5th Street S. 5th Street 9. 5th Street 10. 5th Street 10-day average Downtown Portland, Oreaon Asbestos Fibers/Cubic Centi meter, greater than 5 um in Diameter Based on an B-hour TWA -005 .008 .010 .010 .009 .020 .005 ' .008 .010 .008 .009 = .01 1256G 21 TABLE II Downtown Seattle, Washington Sample $ Asbestos Fibers/Cubic Centi meter, greater than 5 urn in . Diameter Based on an B-hour TWA 1. 1st Ave. 2 . 1st Ave. 3 . 1st Ave. A *5 . 2d Ave. . 5 . 2d Ave. 6. 2d Ave. 7 . 3d Ave. . A.laska Way c Alaska Way 10. Post Street .050 (downwind from building construction) .005 .010 .050 (building demolition in vicinity) .050 .050 .010 .004 .005 .009 10-day average .024* = .02 ID *tJ this period of cry weather, one large buildir. Serene Avs:v.:s was in demolition and others cn First Avenu under refurbishment. G. S. Lemcine |22] found an average airborne asbestos count of .00-1 f/cc for downtown commercial areas and up tc .004 f/cc for highways, which makes these findings even mere profound. 12 560 22 TABLE III Downtown Bremerton, Washington, Downwind from Puget Sound Naval Shipyard (August 1982) San.ole " Asbestos Fibers/Cubic Cen timeter, greater than 5 um in Diameter Based on 1. Eurvell Street - North 2. Burwell Street - North 3 . Eurwe11 Street - North 4. Burwe 11 Street - Center ~ 5. Eurwe11 Street - Center 6. Eurwe11 Street - Center 7 . Eurwe11 Street - South 6. Eurwe11 Street - South o _ Eu rve 11 Street - South 10. Pacific Avenue 10-day average .002 .020 .015 .020 .050 .025 .015 .010 .002 .016* : .02 "Dr v ca y s ar.pling includes err. issions from. the industrial C * 1 C ^ C * r- the PSNS shipyard. redispersion of asbestos era , and ci ty sources, such as brakelining, construction or -.cl; t.: c n . 12 56C The 1981 findings of LeMoine |22] and this data show that the general population has common exposure to asbestos even in western cities like Portland, Oregon, and Seattle, Washington, with good weather clearance and relatively low astmospheric inversion factors. The data in Tables I, II and III also show that the levels may be elevated during summer or dry days and because most downtown construction occurs then. The levels of exposure are significant because they are in- the same range.of. exposure level as produced by..;gasket materials shown in Table VI. Recent reviews of asbestos fibers in the lungs of the General population show a substantial exposure by measured retention. The review by .Churg and Warnock [10] conclude that city duel ie_rs_ receive a sigm fi cant exposure from the general envi rcnme.nte.i __cc:yt ami nation . . This will contribute to the overall exposure of workers engaged in industrial operations, especially these handling asbestos products. It is obvious that any evaluation of the contribution of a single product to the occupational exposure of workers must consider these elevated exposures.from other sources so as not tc obscure the true lever values and produce misleading information. E . ^Effects c: Asbestos-contaminated Clothing . Current methods of sampling require that occupational exposures of workers be determined by personal samplers attached to the body operating at two liters per minute and 1256C- 24 drawing air at the, breathing zone through a 0.6 micron pore size, 37 millimeter diameter, AA-type membrane, open-faced filter held in a cassette (15, 19, 23, 32]. There i s_no-_specif ied te chnique for pi a cemen t_of__the _ cassette containing the filter, other than common sense. Generally, technicians attach the cassette and hose by a clip snapped on the lapel of the street clothes or outer protective clothing of asbestos workers. _During movement the cassette rests against the clothing in a downward_posit.ion. The clothing forms one edge of a baffle causing some measure of uneven distribution of capture on the filter, thus affecting the variation in fiber counts from different wedges taken from that filter [25], Clothing, highly contaminated with asbestos fibers, may lead tc results up to two fibers/cc, greater than 5 urn in diameter based on an eight-hour TW.-. when no other source of asbestos is present. These values were detected in earlier studies by the author and studied by J. Wer.dlick, Corporation Industrial Hynenist, Weyerhaeuser Company, in a cooperative exchange |1, 33]. _ Devices were developed to hold the filter ay from the clothing and reduce the contribution of fibers a the surface of the clothing which showed upward skewing of dat dependen_t_on the degree of clothing contamination. Not only can this procedure give positively skewed results when evaluating the actual contribution of a sinale product. 1236G 25 but asbestos contaminated clothing is a serious source of occupational exposure to asbestos workers. Table IV shows the various levels of asbestos fibers collected on the open-faced filter placed on the lapel of contaminated work clothes and pointed downward as required [32]. Contaminated cloth coverall work clothes were collected from various industrial operations where asbestos was in use. The clothing was placed on the workmen in clean environments during an eight-hour period in which no asbestos material was handled in order to determine the actual exposure from the ashesrcs contaminated clothing. 1256C 26 TABLE IV Contribution of Asbestos-Contaminated Personal Protective Clothing to the Occupational Exposure______________________ . ' Descriction of Clothing Concentration of Asbestos fibers/cc, greater than 5 um in Diameter Based on an 8-hour TWA, Col lected on an Open-faced . 8m\u-' pore-sized 37 mm diametertype AA millipore filter!*1] Heavily contaminated coveralls used curing rip-out of pipe insulation S-Hr. TWA 1.0 1.8 1.5 Average f/cc 1.4 Nediun contaminated coveralls worn three cays before change " .2 .5 .8 .5 Lightly contaminated coveralls worm, three cays before change ' . .1 .2 .05 .1 Coveralls worn during gasket handling and ether small asbestos parts .05 .05 .03 .05 Nr'. cover a 1 in centrolled 002 C03 003 .0031*21 urvarc s/.ew c lcthi.no . - contributions from, air pollution, and positive g c: results by baffling effects from contaminated c.zz rc-arhes ths iewer ii counting methodology. tmospheric pollution in the city and t of detection of the sampling and 1255G & 27 These..values show that improper placement of the cassette and heavily contaminated coveralls can; 1. Provide a substantia^ contribution to the_overa11 exposure of asbestos workers from__failure_ to regularily change clothing contaminated ..with asbestos----- 2. Result in values that..do .not..ref lect the__true breathing zone __ exposure level.. The baffling effect of the edge cf the coveralls to the open-faced cassette is known to cause uneven collection of fibers on the filter, and to collect more fibers on the filter because of the proximity to the surface contamination in the coveralls [30]. 3. Cause the collection of large amounts of asbestos fibers that may obscure the lower actual airborne concentrations released from, encapsulated, or pressed asbestos gasket materials. This affected early sampling results where standards did net require the regular changing of asbestos-contaminated clothing. The Department cf the Navy, a leader in asbestos control development in the 1960's and 1970's, did not seriously require protective clothing control until about 1969-1972, as introduced in the works of Karr |1] and of Mangold, Beckett, and Eessmer [2, 3) and later by directive. Such practices did cause gross contamination of street and_ protective clothing.. adding a significant contribution to the total exposure. Workmen wearing highly contaminated clothing therefore carried 1256G 2e a significant source of exposure wherever they went during the work day.' C. Workplace Contamination Levels of Airborne Asbestos Fibers. , The earlier works of Mangold, Eeckett, and Bessmer [2, 3, 36] ignored consideration of gasket materials as a contribution to the potential occupational exposure to asbestos workers and associated trades. The asbestos control program was directed at known high'level and uncontrolled sources of airborne asbestos fibers related to known work practices. The 1978 FSNS report conducted by Liukonen, Still and Beckett [15] was aimed at the total occupational exposure of workers t: airborne asbestos fiber concentrations while conductin' unit operations related to the use of asbestos casket materials. The report relates the unit operation peak exposure and states that the values are not comparable to the current Federal standard of 2f'CC greater than 5 urn in diameter cm. a time-weighted basis because cf the short sample duration. However, such comparisons are made later in the report. Thereicre. the values are much higher than expected when nonexposure periods during the workday are included in the eight (8) hour time-weighted average and contamination factors are considered. Secondly, the intermittent peak exposure values necessarily reflect any concentration of airborne asbestos fibers in the breathing rone of the worker because the 1978 FSNS report did 12 5 6G 29 not consider contributions from other sources of airborne asbestos fibers such as contamination. ' The PSNS report does not reflect the level of airborne contamination before the samples were collected or makes any adjustment in the data. Therefore, the'values reported reflect the airborne fibers released by gasket handling and processing including all other sources of production, redispersion, or atmospheric pollution present at the time. This consideration is important because some of the values reported in the 197B FS.N'S report (15) are near the lower limit of detection of the sampling method and are in the range of known work area contamination levels. In order to determine the low-level cor.triruticn of the Garlock encapsulated gasket materials, air samples were collected in work areas used for asbestos, but when no casket processing was in progress. Samples were then collected in the same work area when.the asbestos products were processed. The difference in results are shown in Tables V and Tacle V shows the effects of ventilation, air turbulence, movement cf materials and the motion of employees in a work area contaminated with asbestos fibers. The data represents the eight-hour time-weighted average exposure due to contamination or nearby sources. The background contamination levels cf asbestos are substantial as expected from accumulation of fibers redispersed to, or contained in the 1256G 30 ambient air. Such high levels of contamination obscure the small contribution caused by gasket processing as shown in Table VI. 12S6T- 31 TABLE V CONTAMINATION LEVELS .Airborne asbestos concentrations in work areas from atmospheric contamination, redispersion of fallen fibers, or nearby sources. No gasket operations conducted. Location S Sample Fibers/cc greater than 5 urn in diameter. Eight-Hour TWA STORAGE OF GASKET MATERIAL 1 .01 2 .02 3 .01 4 .02 5 JD4 5-day average .02 5-day average ha::: cref.ated keckanica : 2 j r> 5-day average . 02 .02 .05 .05 .02 .04 .Cl . C2 .02 . C2 . C2 .02 12 550 32 MACHI.NE PUNCH AREA >: . <? 1 2 3 4 5 5-day average KANO SHARI NO TAELE AREA 1 2 3 4 ' 5 5-day average MACHINE SHEAR INC AREA. 1 2 2 4 5 5-day average NI EE LEA MACHINE WORK AREA 1 2 2 4 5 5 - d a y a v e r a :: e .08 .02 .10 .20 ^05 .09 .01 .02 .02 .08 _^02 f ' .03 .03 .03 .10 .07 .05 . .07 .03 .03 .10 .20 10 . 11 EDI LEE HEAD CASKET INSTALLATION AREA 1 2 3 3-day average BOILER HEADER REMOVAL 1. 2 3 3-day average D N 3-day average .02 .03 ^03 .03 . .06 .04 ^05 .05 .03 .02 .02 .02 GASKET FREVICTSLY REMOVED 1. 2 2 3-cay average .03 .03 J03 .03 D. GarlcckAsbestosCasket Processing. _ Breathing rone samples of workers processing Garlock gasket materials were collected under the following conditions: 1. Methods specified by N10SH and OSHA that relate to the Federal Standard, 29 C.F.R. 1910.1001, Asbestos, were used |23, 30, 32]. 1256C 34 2. Samples were.collected in the breathing tone of the workers using a wire device to hold the filter cassette lvay from the clothing. , 3. Workers wore clean outer clothing or plastic-imprecnated coveralls during each day of the test period. 4. This study, commissioned by Carlock, specified 'asbestos gasket materials which were used because they were prepared in the same manner as products used in the period 1940-1?"0. TABLE VI OARLOCK ASBESTOS CASKET PROCESSING rn . 2 : : 4 - Aver are Total Exposure to all sources of asbestos during Gasket Op e r a t i c n s . G :* 1 c c V'. Materials Background Ccrtam.i nation Leve1s (Table V) Subtraction Actual Cor.tribu of Gasket Ope tion to the 0 cupational E>: sure, 5 fibre greater than in Length, or. 6-Hr. TWA ui in .05 . os .06 .05 .05 .04 .02 35 HAND OPERATED MECHANICAL PUNCH 1 2 3 4 5 Average MACHINE PUNCHING .-.verane I- 1 KG Average .05 .01 .02 .02 .02 02 - .02 Negligible .05 . 18 .09 . 09 .14 . 05 . C5 . 03 .04 .c; 03 . 05 . 07 .15 . 10 . 10 . 09 07 02 01 02 12 3-5 * < (/) i<-- r-i m ^r-i rs ro u i MACHINE NJEBLINC 5 Average T INSTALLATION :i Surface) 1 2 3 Average .20 .08 .15 .19 . 10 .14 - .11 .01 .04 .05 .03 - .03 Negligible 3 r. V 6 1' S o 5 _ _____ 3 ~ r a zj e . 10 . 05 12 . 04 . C3 J_C_2 04 - .05 ' - .02 .03 .07 .02 12SS3 37 (J M M FLANGE GASKET REMOVAL ANO SCRAPING WITH KNIFE Average .08 .03 .05 .05 - .03 .02 12 560 36 E. fFla...n..a* e' Casketi o*perations. > Other laboratory testing of..Carlock asbestos gasket materials, styles 7021 and 900 show a low contribution to _ exposure for gasket preparation, installation and disassembly ranging from none detected for die cutting to .06 fibers/cc for hammer cutting. In order to validate the findings, three large flanges were 'cut from dismantled ships' piping and cleaned. Carlock asbestos gasket material style 7021 was hand punched in a location where ambient levels were at the lower limit of detection, or about .002 fibers/cc. Nine gaskets were hand punched ever a two-hour period to provide a typical operation work pattern. 7he_ breathing tone concentrations of airborne arrester fibers etc not exceed .01 fibers/cc, greater than 5 urn ;r diameter.. This reflects an actual exposure devoid of backgrrurd cor.taminaticn. _Thi s i s. a -.two-hour intermittent peak extcsure that falls in the same range as contaminated shop work areas, or downtown streets on dry summer days. C re c-f the nine gaskets was placed on each of the three flanges, belted and torqued to about 60 pounds, which gives a flange face pressure cf about 3,000 pounds. The three flanges took two hours tc assemble. _The breathing tone concentration of asbestos fiber; did not exceed .02 fibers/cc, greater than 5- um m diameter, and reflects a two hour intermittent peak exposure that is in the same range as contaminated work areas 2 2 56 0- 30 or downtoyn streets on dry summer days^.__ An eight-hour time-weighted average of this actual contribution by the gasket materials would be expected to be even lower. The three flanges were then heated to 200F in a furnace for 48 hours, cooled and disassembled. The asbestos materials were cleaned from the surfaces by scraping. The disassembly took two hours. The breathing rone exposure to airborne asbestos fibers during the disassembly did not exceed .02 fibers cc, greater than 5 urn in diameter. This is an intermittent peak exposure likely to be less on a eight-hour time-vs;ghted average. This gasket cutting, assembly and disassembly of three tyriral large flanges, as used cm ships piping, did not produce am. overall rreathirg core exposure exceeding .02 fibers/cc, greater than 5 um in diameter. The hard pressed surface ar.d ercag sul at: ;r cf the asbestos fibers'or. the C-arlock, style 72C1 asbestos casket material release insignificant quantities cf c r c - * . Tr is' va.idaticn of previous evaluations cf Gerlock asbestos gasket materials and Eeckett's |15] findings is lover because extra tare was given to potential sources of contamination, and longer sample times were conducted. . In summary, each of the operations of gasket cutting, installation and removal did not exceed contamination levels in industrial work areas or busy downtown streets on dry summer 12 56C 0 days. The exposures are about i/100 of_t.he_Federal standard of 2 fibers/cc, greater than_5-um in diameter based _on_ an eight-hour time-weighted basis. VI CONCLUSIONS The accumulations of asbestos fibers in the workplace frcm sources other than encapsulated gasket materials plus the presence cf asbestos fibers on work clothing and the asbestos fibers generally present in the atmosphere, obscure the actual lew level contribution of asbestos fibers to the environment free. Oarlock encapsulated gasketing material. Some current e*o: demic 1 coital data suggests there may be a small risk to health, as long as there are airborne asbestos fibers in the er.vi rcr.me:vt_cf _the magnitude of that existing naturally such as that in sc_:_l . water, and natural atmospheric pollution. Nevertheless, an. allowable exposure has been set since 1945, end defined as an index, based on the theory that low-level exposures may be tolerated without incurring undue risk [37], The ' e i ght-hour tim.e-wei ghted average exposure currently allowed by the Federal Standard is 2 fibers/cc, greater than S micrometers in diameter. This report shows that hardpressed or encapsulated Carlock asbestos gasket products release insignificant levels of asbestos fibers into the breathing zone of workers. In fact. 1255C 41  the exposure levels caused by the handling and use of these products are often well below exposures caused by contaminated work areas, asbestos laden clothing, or downtown exposures to the public on dry summer days. Garlock asbestos gasket materials, styles 7021, 900/7735, and asbestos cloth,. style..605, handled .in._the..same.manne.r__as in heavy_i_ndustry, like shipyard operations, averages .1/100 or .less of. .the current Federal standard. The materials reflect exposure in previous years because they were prepared in substantially the same manner as Garlock prepared the materials in the 1940's to 1970's. ' The levels of occupational exposure to asbestos fibers in the breathing zcne from the use cf these asbestos gasket r-rcbutts actually approach the lever limit of detection of the sampling ar.b microscopy methods required by the Federal standard. They are about 5C% cf the values reported in the lv-5 ; T Tepcrt [15] because contamination levels were not factored erte that report to relate to the actual occupational exposure cf these types of casket materials, and because the Fh data reflects intermittent peak exposure, not eicht-hcur time-va : gr.ted averages . Tine 1950 tc 19~C occupational exposure of workers handling asbestos material in industrial settings were elevated, often uncontrolled, and at an allowable level of 5,000,000 particles per cubic foot or about 50 fibers'cc. Other data shows |3] at least ten times that Threshold Limit Value (TLV) for certain industrial operations have been observed. Therefore, pressed and encapsulated asbestos gasket materials contribute_ insignificantly to the ovej~an_exposu.re.-Q^--WOtkers. The actual contribution is in the range of ambient pollution levels of asbestos in industrial areas and often at ambient asbestos fiber levels.. experienced. by city dwellers on.dry..days for which there is no significant impact on their health.. 1256G 43 VII . references 1. W. T. Marr, "Asbestos Exposure During Naval Vessel Overhaul," Am. Ind. Hyg J. , 25:264 (May-June 1964). 2. C. A. Mangold, R. R. Beckett, D. J. Bessmer, "Asbestos Exposure and Fulmonary X-ray Changes to Pipe Coverers and Insulators at Puget Sound Naval Shipyard," PSNS, U.S. Dept, of Navy, Eremerton, WA (Aug. 196S). . 3. C. A. Mangold, R. R. Beckett, D. J. Bessmer, "Asbestos Exposure Control - Puget Sound Naval Shipyard, U.S. Dept, of Navy" (May 1970). ` 4. I. J. Selikoff, J. Churg, E. C. Hammons, "Asbestos Exposure ar.d Neoplasia," JAMA 185:22 (1964). 5. I. J. Selikoff, J. Churg, E. C. Hammons, "Relation Be tween Exoosure to Asbestos and Mesothelioma," N. Eng. J. Med., 272:560-565 (1965). ' 6. Irving J. Selikoff, K.D.: "Disability Compensation fcr Asbestos-Associated Disease in the United States," Env. Sr;., Lab., Kt. Sinai Kosp., City Univ. N.Y. (Report to U.S. Dept. Labor - Contract J-0-M-E-0165. June 19S2).* 7. J. E. Craghead, B. T. Mossman, "The Pathogenesis of Asbestos - Associated Diseases," N. Eng. J. Med., 306 (June 17, 1952 )'. S. I'.. R. Eeck.lak.e, "Exposure to Asbestos and Human D;sease," K. Eng. J. Med., 306 (June 17, 19S2). 9. v:. J. Nicholson, A. M. Hanger, I. J. Selikoff, "Epidemiological Evidence or. Asbestos, Proceedmos of a v.'crkskop on Asbestos Definitions and Measurement Methods" (July 19./), Gaithersburg., M.D. - U.S. Dept, of Commerce Publication E5D6 (Nov. 1978). 1C. A. Churg and M. Warnock, "Asbestos Fibers in the General Population," Amer. Rev. Resp. Disease, Vol. 122 (19SD). ti 11- v;- E- Fleischer, F. J. Viles, R. L. Cade, P. Drinker, "A He a 1 tli Survey at Pipe Covering Operations in Constructing Naval Vessels," J. Ind. Hyg. S Tox; 2B;9 (Jan. 1946). 1256G 44 12. R. Zumvalde, J. M. Dement, "Review and Evaluation of Analytical Methods for Environmental Studies of Fibrous Particulate Exposures," NIOSH Docu. 77*204, N10SH, U.S. Dept, of HEW, Cincinnati, Ohio (May 1977). 13. K. A. Busch, N. A. Lidel, R. W. Horning, R. J. Smith, "Unbiased Estimates of Co-efficients of Variation for Asbestos Countig Determined from John Mansville Data," NIOSH, U.S. Dept, of HEW, Cincinnati, Ohio (Dec. 1977). 14. H. E. Ayer, J. R. Lynch, J. H. Fanney, "A Comparison of Impinger and Membrane Filter Techniques for Evaluating Air Sam.oles in Asbestos Plants," Ann. N.Y. Acad. Sci., Vol. 132, p. 274 (Dec. 31, 1965). 15. L. R. Liukonen, K. R. Still, R. R. Beckett, "Asbestos Exposure from Gasket Opertions," Naval Regional Medical Center, Erer.ierton, WA (May 1978). 16. Occupational Safety and Health Administration, OSHA Ir.str. CFL 2-2.21A - 29 C.F.R. 1910.1001 (j ) (2 ). (3) and (4), "Kir.mum. Airborne Fiber Concentration for Initiating and Continuing Asbestos Medical Examinations" (Feb. 18, 19B1) . 17. Thomas A. Mercer, "Aerosol Technology in Hazard Evaluation," Academic Press, Inc., N.Y., N.Y. (1973). 1c. J. D. V.'endlick, Corporate Industrial Hygienist, "Asbestos Exposure Control," The Weyerhaeuser Company, Tacoma, v;A (1977 ). ` 19. Leslie Freger, et al., "Asbestos-Related Disease," Crur.e and Stratton, N.Y., N.Y. (1978). 20. C. A. Mangold, "A Model Asbestos Control Froaram for U.S. Fublic Health Services Hospital," Seattle, WA (Oct. 1979) 21. L. Michaels and S. S. Chissick, "Asbestos, Properties Applications and Hazards," Vol. 1, John Wiley & Sons, N.Y., N.Y. (197?). 22. Gary Stephen LeHoine, "A Survey of the Asbestos Level in the Ambient Air of Seattle," Master of Science Thesis, School of Public Health, University of Washington, Seattle, WA (May 1981 ) . ' 23. National Institute for Occupational Safety and Health (HIOSH): Manual of Analytica 1 Methods, Asbestos Fibers in Air Vol. 1, ed. 2, Sup. Docs., U.S. Covt. Printing Office, Washington, D.C., p. 239-1 (Apr. 2977). 1256G 45 : 24. G. A. Peters, J- Peters, Source Book _ Asbestos Diseases: Medical, Leaal and Enoineering Aspects, Garland STPN Press, N.Y., N.Y. (1980). 25. N. A. Leidel, S. G. Bayer, R. D. Zumwalde, K. A. Bosch, "USPHS/NIOSH Membrane Filter Method for Evaluating Airborne Asbestos Fibers," PHEW (NIOSH) publication 79-127 (Feb. 1979). 26. NIOSH Pub. 79-139, "Technical Report: Preparation and Characterization of Analytical Reference Minerals NIOSH," U.S. Dept. HEW, Cincinnati, Ohio (Juner 1979). 27. NIOSH Criteria Document - HSM 72-10276, "Occupational Exposure to Asbestos, Criteria for a Recommended Standard, NIOSH, U.S. Dept. HEW, Cincinnati, Ohio (1972). . 26. S. G. Bayer, R. D. Zumwalde, T. A. Brown, "Equipment and Procedures for Mounting Millipower Filters and Counting Asbestos Fibers by Phase Contrast Microscopy," Bureau of Occupational Safety and Health, U.S. Dept, of HEW, Cincinnati, Ohio' (July 1969) . 29. Killipore Corporation, "Information on Average Background Counts of Pre-prepared Type AA Filters, 0.8 Micron Fore Size, 37mm Diamter." 30. NIOSH, Revi sed Reccmm.er.ded Asbestos Standard, PHEW (NICSH) Pub 77-16? (Dec. 1976). 23. S. J. Rcoker, N. P. Vaughan, J. M. LeOuen, "On the Visibility of Fibers by Phase Contrast Microscopy," Amer. Ir.dust. Kyg. J., Vol. 43, No. 7 (July 1962). 22. Occupational Safety and Health Administration, Ir.dustri al Hygiene Field Operations Manual (CPL 2-2.20, Apr. 2, 1979, and changes). 23. C. A. Mangold, "An Asbestos Control Program.- A Typical Employer's Format," Region X, OSHA (Mar. 19S2). 24. C. A. Mangold, "A Model Asbestos Control Frogram for the Metal Scrap and Shipbreaking Industry, An Employer's Format," Seattle, WA (Aug. 1950). 35. J. D. Wendlick, Corporate Industrial Kygenist, "Asbestos Control - An Industrial Experience," The Weyerhaeuser Company, Longview, WA (1977). 1256G 46 36. C. A. Mangold and R. Beckett, "Collection and Counting Airborne Asbestos Fibers - Phase Contrast Microscopy Method," Puget Sound Naval Shipyard, U.S. Dept, of Navy, Procedure III.B.37 (May 4, 1971). 37. G. S. Rajhans, G. M. Bragg, "Engineering Aspects of Asbestos' Control," Ann Arbor Science Pub., Ann Arbor, Mich. (1978) .