Document Rj6KZoRpq7JyqkMMJxLMyrOOa

^ftlS^Sl'yfiri'i 'J8g5S85Sfe^J; i^pr SRiMS` iglglf:- ^V-'v'/fe:.'-'!';' Iff' j^^'. Efe #: f p.C---*'' "VJ DISTRIBUTION frrison _ DEC 151913 -R=rWaisBfi?"S'iR. J. Kronkhyte E" J.M. Anderson uScrrY,CA' A. A. Andrade C. F. Grogan Q R. L. Grogan R. O. Hopper Q AIRBORNE ASBESTOS FIBER CONCENTRATIONS IN ASBESTOS H. L. Soay B. E. Usrey MINES AND MILLS IN THE UNITED STATES D. E. Clark D. J. Garcia G. L. Vessels M. K. Wes by File L. A. Schutz, Walter Bank, and George Weems ft ') Denver Technical Support Center, Denver, Colo. r* T ri- Bureau of Mines Health and Safety Program Technical Progress Report 72 June 1973 Wm:- >, >v . - v`j*?. >.V->(r--. Wv . :Uv. : ftiiiftl:;. sSS*6JW**fr V1X* -V.PSStS' U.S. DEPARTMENT OF THE INTERIOR A088 3\ * EXHIBIT 1 UC-1450 I I zr-W3-:-~' J ...................... , - .. i i . , m- CONTENTS ;m. > t.ri*;- 2sse -Abstract....................................................................................................................................................... 1 Introduction.............................................................................................................................................. SjU: Description of survey........................................................................................................................ 1 3 f-.y Discussion of survey results....................................................................................................... 5 Conclusions................................................................................................................................................ 7 Appendix A.--Occurrence of asbestos with associated basic rock formations in the United States............................................................................................ 9 Appendix B.--Sampling methodsand evaluation procedures........................................... 11 ILLUSTRATIONS 1. 2. .f fc.-1. V.;-. 1. 'y'-iW.: 2. 1", Asbestos fiber exposures (daily weighted averages) in mills...................... Asbestos fiber exposures (daily weighted averages) in mines...................... TABLES Asbestos mines and mills surveyed, with listing of employment and sampling data..................................................................................................................... Average of asbestos fiber exposures (daily weighted averages) in mills and mines.......................................... ......................................................................... 6 7 4 5 V": . -i . - >-V .*.*/ - i&ltt-rr*.- >':rr : * ; .v : '-y'w $*, ' 608832 M'l . .r V AIRBORNE ASBESTOS FIBER CONCENTRATIONS IN ASBESTOS MINES AND MILLS IN THE UNITED STATES by L. A. Schuti,1 Walter Bank,^ and George Weems* ABSTRACT =!': Personnel of the Bureau of Mines have conducted investigations in the 7^.principal asbestos mines and mills in the United States, to determine the cony^centration of airborne asbestos fibers in the workplace, and to establish the ^`.exposure of workers to such fibers. The surveys were conducted using the -^sampling and evaluation method recommended by the National Institute for -^'Occupational Safety and Health. The method consists of collecting the air'borne sample.oh filters and, after appropriate sample preparation, counting .7* the fibers utilizing phase contrast microscopy. The results of the lnvestiga.>?7tion show that fiber concentrations are low in the asbestos mines but high in .fj-Tthe asbestos mills, ranging well above 5 fibers/ml of air based on a count of T-^-fibers greater than 5 um in length. INTRODUCTION ..vX'7 ' Asbestos is a generic term that applies to a number of naturally occuring, hydrated mineral silicates incombustible in air and separable into fila- ^7ments. The most widely used in industry in the United States is chrysotile t^7(3MgO - 2SiOa 2Hg0), a fibrous form of serpentine. The other principal minerii-_al6gic type, amphibole, includes amosite [(FeMg)Si03]; crocidolite l5:[NaFe(Si03)a FeSiO- Ha0]; tremolite [Ca8MgsSie0a2 (0H)S ]; anthophyllite ^--(MgFe)7Si8022 (0H)a j; and actinolite [CaO 3(MgFe)0 4SiOa]. '%4-'';J:-v:`Chrysotile asbestos occurs chiefly in serpentinized peridotite and is jv.`,4Mtributed in the United States in two principal belts; the eastern belt :J':e2tends from Maine to Alabama, and the western belt extends from Washington to ; ..^palifornia, where numerous masses of ultramafic rocks were intruded in .^*a^-e020:i-c and Mesozoic time, respectively. The principal mine in the United 1.7 ^t^tes is located at Belvidere Mountain in Vermont. Minor amounts of asbestos teen produced from other deposits in these belts and from scattered occurof chrysotile elsewhere. Recently, increased activity toward develop- Vv.PPPV'fpr short-fiber chrysotile has occurred in California. " - VL epgineer. 1 ^0i'7iv?jyi8ory chemist. A0883 2 Chrysotile also occurs in bedded limestone, metamorphosed close to intru sions of diabase. The principal occurrences of this type are in Arizona, where small quantities of long-fiber, low-iron chrysotile have been mined from numerous small deposits. Several species of amphibole occur in fibrous forms; in the United States only anthophyllite and tremolite are known to have commercial importance. As both the anthophyllite and tremolite occur in ultramafic rocks, associated greenstone, and amphibolite, the overall distribution of amphibole asbestos in the United States is like that of chrysotile. The deposits are generally small and erratic in distribution; a list of States identifying known asbestos deposits with associated basic rock formations is presented in appendix A. The occurrence of asbestos and/or asbestiform fibers is relatively widespread throughout the United States and, while the asbestos is not recovered for com mercial purposes, the fibers can be present in the mine or mill atmosphere and may constitute a potential health hazard to miners and mill workmen. '3 The fact that asbestos or asbestiform fibers may be associated with the mining of other minerals complicates the problem of evaluating the health hazard of dusts. Almost 1 million tons of asbestos is used in the United States each year. Analysis of production data indicates that approximately 74 percent of the asbestos produced (532,300 tons) was used in the construction industry, while 26 percent (187,400 tons) was used in the nonconstruction industries. Approx imately 92 percent of the 532,300 tons used in the construction industry is firmly bonded, in such products as floor tiles, asbestos cements, roofing felts, and shingles; die remaining 8 percent is friable or in powder form present in insulation materials, asbestos cement powders, and acoustical prod ucts.3 The 187,400 tons of asbestos used in nonconstruction industries in 1965 was utilized in such products as textiles, friction material including brake linings and clutch facings, paper, paints, plastics, roof coatings, floor tiles, and other miscellaneous products. Mining and milling of asbestos in the United States is a small industry, employing fewer than 1,000 workers, and produces 125,300 short tons of asbestos, or approximately 17 percent of the total asbestos used in the United States. .v. :k.*# Based on the results of asbestos surveys completed, the principal health hazards occur in the milling process with only minor problems existing in the mines. The National Institute for Occupational Safety and Health (NIOSH) has developed criteria for a recommended standard for occupational exposure to asbestos. The criteria include consideration of the following factors: environmental, medical, labeling, personal protective equipment and clothing, apprisal of employees of hazards from asbestos work practices, and monitoring and recordkeeping requirements. 3Hendry, N. W. The Geology, Occurrences, and Major Uses of Asbestos. Ann. N.Y. Acad. Sci., v. 132, Art. 1, 1965, pp. 1-766. A 088 3 4 z+sz*** :ru:rom ices As s in >Cos iad :omand ie aar. ile roxs -od- cos S, Lth :he ig* .ng /'"iV ' ' /.The occupational safety and health aspects of the mining and milling of v'./yasbestos ores are covered by provisions of the Federal Metal and Nonmetallic //^Mine Safety Act (30 U.S.C. 725 et seq.)> under vhich provisions the Bureau of .///Mines has promulgated applicable regulations. In 1967, the published Threshold Limit Value4 was 5 million particles per cubic foot (mppcf) for dusts containing asbestos when collected conventionally '.'K'cwith. the impinger or midget impinger and counted with the standard light-field ///counting method. The number concentration represented the visible fragments ////-(small) of asbestos fibers, plus the many associated mineral dust particles. s, K In 1968, the published "Notice of Intended Changes" proposed that (1) the .mppcf be reduced to 2 mppcf and (2) an alternative figure of 12 fibers per //'milliliter of air (fibers/ml) based on a count of fibers greater than 5 ;/;.(micrometers) in length be adopted. This figure was based on the membrane filter method at 430X magnification phase contrast illumination. " The aforementioned intended changes were retained in 1969; in 1970, the Vj>f' \published proposed changes (1) eliminated entirely the midget impinger sam- ^..\pling method and its number concentration figure and (2) recommended that the //..--alternative value be changed from 12 fibers/ml greater than 5 microns in ^///length to 5 fibers/ml greater than 5 microns in length. -; .-n_ _. . .. , /'ic In 1971 and 1972, the "Notice of Intended Changes" retained the 1970 pro- //Vi-posal and specified the membrane filter method with 400-450X magnification /`///phase contrast illumination. t To evaluate the degree of the health hazard, the sample results included /.'//.in this report were compared with the value of 5 fibers per milliliter '/(fibers/ml) as defined by N10SH in the document "Criteria for a Recommended //./'Standard . . . Occupational Exposure to Asbestos." '-'It appears that control practices in current mining and milling opera////tions can be modified to meet the "5 fibers/ml greater than 5 urn in length" ///^standard. However, in order to meet a standard of "2 fibers/ml greater than in length," the asbestos industry will probably have to develop new pro* Z`;`Vv cesVes, or drastically modify present dust control measures. Meeting the lat- ter'.standard will be more difficult for mills and processing plants than for ////oineaV'' DESCRIPTION OF SURVEY a//-VVf. During the latter part of 1971, a program was instituted to conduct investigations in all the active asbestos mines and mills in the United States. ,Three of the four known active mills and two of the six open-pit mines in California were surveyed. Total employment at the four active mills and the aix/open-pit mines was reported to be 294. '^rican Conference of Governmental Industrial Hygienists. Threshold Limit Values for 1967, Recom&ended and Intended Changes. 1967. A0883h i I I I I i'.ll I ' I ! R'1S >K\VJ.;t. V v aw In Arizona, two of the three known active underground mines and one of the tl\ree active mills were surveyed. Total employment at the three mines and three mills was reported to be 25. i1 The single active open-pit mine and mill in Vermont was surveyed. Total employment in the asbestos mine and mill was 201. The only known active asbestos open pit in North Carolina was surveyed. Total employment was four. Irv Maryland, the one known asbestos mill was surveyed, Total employment was eight. Total employment for all known active asbestos mines and mills was 541. Of this total, 488 were employed at the mines and mills surveyed. A total of 656 samples was collected and evaluated in these surveys. Table 1 lists asbestos mines and mills surveyed in the United States, their location by city, and State, employees at each, and samples collected during the survey at each location. Table 2 lists the average asbestos fiber exposures for the job classifications that were found at the mines and mills. TABLE 1. - Asbestos mines and mills surveyed, with listing of employment and sampling data Number of mines Number Number of samples collected Location Open pit Under of Employees Breathing General Total ground mills zone atmosphere Mines: Burnsville, N.C........................ 1 - - 4 17 Hyde Park, Vt.. 1 - - 58 10 0 17 - 10 Coalinga, Calif................... 1 - - 7 41 0 41 Copperopolis, Calif................... 1 - - 36 55 0 55 Total, open pxts 4 - - 105 123 Globe, Ariz.... - 1 - 11 15 Do........................ - 1 - 2 2 0 123 0 15 02 Total, underground - 2 - 13 17 Total, mines 4 2 - 118 140 0 17 . 0 140 Mills: Baltimore, Md.. - - 1 Hyde Park, Vt. - - 1 King City, 8 143 ' 59 55 1 60 2 57 Calif................... Coalinga, 1 50 50 - 9 59 Calif................... - - 1 31 47 10 57 Copperopolis, - Calif................... - - 1 135 205 57 262 Globe, Ariz.... - - 1 3 20 Total, mills - - 6 370 436 1 21 80 516 Grand total. mines and mills. 4 2 6 488 576 80 656 1 A08836 asb< UT ind il it ty h 3d al j+v-v;..; ...... . %: .'4; i -' 5 -il r"'-J- --i' -.'-".fir' - <VS. fv------- TABLE 2. - Average of asbestos fiber exposures i' 1 (daily weighted averages) j i' in mills and mines J - } *. ! :| i1 Occupation i [i ` i '.Mill; ; j1 sr Blender, bagger, and packer... Palletizer and car ! loader..... .ujt.-;. Crusher and dryer operator.... Foreman. .1................. J..............J.... ' Laboratory technician................... Laborer. .1................. ............................ *31 Maintenance man...j........................ ` *Mill operator..........,...............j... . Other.... 1................. J..............J.... Mine: 1 11 i Driller. .1..............................J........................ J.... Explosives man.. . . J.......................... Heavy equipment operator..................... *y- Maintenance man...................................................... .... K K'- Truck driver.............................................. ... .................... Other.................................................................................................... Total samples ,132 31 ! 32 | 32 ` 33 ! 37 ! 50 501 1 39 1 ! 31 16 55 7 20 21 Asbestos fibers/ml (>5 Lita in length) Highest exposure .Lowest exposure Average exposure 24.8 18.1 20.3 15.8 17.4 17.3 16.9 17.9 10.5 ! 2.7 ' 1.2 i 7.1 ! 4.3 i 4`5 1 8.2 l 3.8 1 4.7 1 2.3 11.3 10.0 11.0 8.3 8.8 12.1 8.4 11.5 6.0 7.8 ; l.o .6 ! .1 1.7 .5 .5 .1 .8 .2 .8 .04 2.8 .3 1.1 .3 .5 .5 It. > xijA Sampling methods and evaluation procedures employed in the surveys of asbestos mines and mills are described in appendix B. vr DISCUSSION OF SURVEY RESULTS -vi- - A summary of the surveys of asbestos mines -and mills is presented in figures 1 and 2. Only daily weighted average exposures are listed in these tables. An analysis of figure 1 indicates the "Laborer" occupation has the highest average exposure with 12.1 fibers/ml. (This is due in part to the cleanup work being done by sweeping.) ' /,V;- Following closely in order are mill operators at 11.5 fibers/ml, ;Vblenders, baggers, and packers at 11.3 fibers/ml, crusher and dryer operators ^A-T-with 11.0 fibers/ml, palletizers and car loaders with 10.0 fibers/ml, laboratory technicians with 8.8 fibers/ml, maintenance men with 8.4 fibers/ml, ^foremen with 8.3 fibers/ml, and the lowest average exposure of 6.0 fibers/ml, including the miscellaneous category. Averages for all the occupational '^^classifications were above 5 fibers/ml. :' Figure 2 lists exposures of the various occupations in open-pit and ^'``^-underground mines. None of the averages were above 5 fibers/ml. -V While a few of the individual samples in some mills were extremely high A tO more than 550 fibers/ml), the average of the highest were recorded at the ending, bagging, and packing operations where controls were not well 408837 L.HWHS TOT *I,U* .m J 1^ L 6 Blender,bagger and packer MW nr Palletizer i car loader and ii i.iriimVairmTiTHi sffr! CVNN Crusher and dryer operator Fo reman 22SI MP UaCGIH intended chc nge i n Threshold Limit Value! 'I Laboratory technician JITOMrfnmnrrn La bo r e r muMiZZ23 Mo i n t e nance ma n U'J.JJ.PUJ I*"" m vMFjTM Mill operator mr Other HW 05 ASBESTOS FIBERS 10 PER 15 20 Ml LLI LITER (>5vm in 25 LENGTH) Highest exposure Average exposure Lowe st exposure FIGURE 1. * Asbestos fiber exposures (daily weighted averages) in mills. designed and maintained. Crushing and drying operations were second, with palletizer and car loader operations running third; mill operators, fourth; laboratory technicians, fifth; laborers, sixth; maintenance workers, seventh; foremen, eighth; and miscellaneous operations, ninth. All were well above the value of 5 fibers/ml. In the mines, dry-drilling, without dust collection, resulted in one high average exposure of 7.8 fibers/ml. . Exp M Tr 408838 C( TH) a; che FIGURE 2. Asbestos fiber exposures (daily weighted averages) in mines. CONCLUSIONS I. Some operators are adequately controlling the amount of asbestos 7 fibers in the breathing zone of workmen; however, many are using inadequate control measures and practices which result in workmen being exposed to asbestos fiber concentrations above 5 fibers/ml. ;*v 2. The fact that asbestos or asbestiform fibers may be associated with i-the mining of other minerals complicates the problem of evaluating the health $$ hazards of dusts in mines and mills throughout the United States. (Dust sux- veys are now routinely including sampling procedures to determine whether this -hazard exists.) .iv yV`-* * * '5'%^-* 3. believed that operators of most mills and mines should be able M`to meet a "5 fibers/ml of fibers greater than 5 um in length" standard by fol- lowing practices such as, but not limited to, those listed below: V'f '-r '. a. Installing and using effective and efficient control systems and .collectors to prevent dust from becoming airborne. b. Establishing a rigid maintenance program for process and dust yjV!*control equipment. >r ` v !.' * A08839 S' 8 ^ c. Packaging the finished product in airtight containers. d. Modifying processing machinery or replacing it with equipment designed to achieve adequate dust control. e. Enclosing all conveyor belts, screens, crushers, and other opera tions, and using exhaust ventilation and. collectors to minimize airborne dust. , i 'Jj? f. Using vacuum cleaning systems for,cleanup work to eliminate air- 3? borne dust from sweeping. ^ g. Following established recommended practices.for the use of respiratory protective equipment. ; h. Using accepted permissible methods for controlling dust when drilling in pits and mines. , ........................ i. Implementing methods for keeping dust at stockpiles, roads, millyards, and plant areas from becoming airborne. j. Providing enclosed cabs with filtered air systems for operators of mobile equipment used in mill and mine surface areas. .31 || ^L 4. New techniques such as the wet-milling process presently being inves-'v/^l tigated by some operators should be evaluated as a possible aid in complying ^ ^ '* with lower standards being considered. 3 * 068 Jr,; ^ V*'.' ' . iaV;. v-".: -*:* 9 APPENDIX A.--OCCURRENCE OF ASBESTOS WITH ASSOCIATED .nyr" BASIC ROCK FORMATIONS IN THE UNITED STATES * The following listing of States indicates known asbestos deposits, with baBC rock formations:1 peradust. air- ill- . Alabama.--Short-fiber amphibole asbestos: associated basic intrusive tSck&s. r if a'.'.'Ari.zona.--Chrysotile in serpentine. California.--Chrysotile in serpentine and in peridotite; tremolite and ^-amphibole and anthophyllite asbestos in serpentine, greenstone, and schist. ; r`i*vSome short-fiber and unknown varieties of asbestos in serpentine. Cross-fiber v;:<chrysotile in ultrabasic intrusion, in serpentinized saxonite, serpentinized [.'^limestone, and chloritized shale. Slip-fiber tremolite and amphibole and Vactinolite in quartz schists, in serpentine, and in limestone and dolomite. 'V'-'f ' " Connec ticut. --Slip- and cross-fiber chrysotile and some pyrophyllite '^asbestos associated with serpentine. Z V V.v.. .. -~r Georgia.--Long-fiber anthophyllite asbestos associated with peridotite, Hwith talcose and chloritic schist, with pyroxenite, and with biotite-granite '/'gneiss. Cross-, slip-, and mass-fiber amphibole asbestos with biotite granite T;?;ind hornblende gneiss, and talcose rock associated with granite. Anthophyl" riite" asbestos associated with harzburgite. Idaho.--Slip-fiber and brittle mass-fiber anthophyllite asbestos in faltered harzburgite and in altered dunite. *'V- .+ - .'-.Z'rV'' ` ""Maine. --Slip- and cross-fiber chrysotile in serpentine. \<.mt -j / * V > a nthoMpahryyllalinted.-a-nSd lilpow-fi-bqeuar littryemamoplihteiboalessaoscbiaetsetdosw. ith basic igneous rocks; also a*-Massachusetts.--Chrysotile asbestos in ultramafic rock; amphibole asbesrr^Jtos; fibrous anthophyllite in blocks of saxonite, enclosed in granite; also {amphibole asbestos. *&. L.-1 Montana.--Brittle tremolite asbestos associated with vermiculite in dike- &j*like masses of pyroxenite; woodlike-fiber anthophyllite in altered peridotite dikes in Precambrian schist and gneiss; chrysotile asbestos in limestone simi- ^jlar to Arizona deposits. New York.--Chrysotile asbestos veins in serpentinized zones in dolomite; /v-rslip- and cross-fiber chrysotile in serpentine. r'Wiy-:- S .V^Chidester, A. H., and A. F. Shride. Asbestos in the United States (Exclusive 5 ;.i'rj;: of Alaska and Hawaii). U.S. Geol. Survey, 1962, 11 pp., with accompanying v.i map MR-17. 4 vt. -.V- 4088 4 -m North Carolina.--Chrvsotile asbestos associated with ultramafic igneous $ rock^ and with dunite and with a large mass of enstatite and in peridotite; 'v 2 anthophyllite asbestos and mass-fiber anthophyllite asbestos associated with '&. $ altered dunite, with serpentinized dunite, and with chlorite in an amphibolite. Oregon.--Chrvsotile asbestos veins in serpentine; short cross-fiber chrysotile asbestos in serpentine; anthophyllite and weak slip- and crossfiber anthophyllite asbestos along shear zones in schists and greenstones; slip-fiber and iron-free tremolite asbestos in dunite. : Pennsylvania.--Unknown variety of asbestos associated with ultramafic igneous rocks. Rhode Island.--Crocidolite asbestos. South Carolina.--Asbestos of unknown variety associated with dikes of pyroxenite altered to amphibolite, in magnesian rocks, in basic igneous rocks,,,^{ in partly metamorphosed amphibolite, in aphanitic hornblende slates. Texas.--Tremolite and long brittle tremolite asbestos fibers in the shear zone between homblendite and mica-quartz schist, in serpentine; small vein- lets of chrysotile and small deposits of amphibole asbestos. i Vermont.--Cross- and slip-fiber chrysotile asbestos in serpentine and in unserpentinized dunite and peridotite. j Virginia.--Asbestos of unknown variety associated with ultramafic rocks; asbestiform anthophyllite occurring with tremolite; amphibole asbestos and slip-fiber amphibole asbestos; slip-fiber anthophyllite asbestos associated with hornblende and olivine. Washington.--Cross-fiber chrysotile asbestos in serpentine and in diopside and serpentine; cross-fiber and slip-fiber asbestos of unknown vari ety in serpentine and in peridotite; silky fibers of amphibole asbestos, fibrous soapstone with amphibole asbestos in shear zones cutting greenstone, short fibers of amphibole asbestos; talcose asbestos in serpentine dike; anthophyllite asbestos in biotite gneiss; tremolite asbestos in dolomite. Wisconsin.--Cross-fiber chrysotile asbestos veins in peridotite.<- Wyoming.--Slip-fiber chrysotile and amphibole asbestos in veins associ ated with serpentine cut by metadiabase dikes and surrounded by granite gneiss; brittle-fiber amphibole asbestos and talc in a sequence of metamorphic rocks and amphibole asbestos in serpentine. ^08642 11 ous m APPENDIX B.--SAMPLING METHODS AND EVALUATION PROCEDURES1 e; ith m. Air Sampling Methods 1w4";,'.,' In the study of asbestosis conducted%by Dreessen, midget impinger count '%f<jata were used as an estimate of dust exposure. All of the dust particles .S'iv'een, both grains and fibers, were counted since too few fibers were seen to *-^:give an accurate measurement. The resulting count concentration was a measure .6':of overall dust levels rather than a specific measurement of the asbestos con- I .S^fcentration. This method was satisfactory at that time since exposures were j massive and the control measures installed to reduce overall dust levels also ! reduced the asbestos dust levels. c icks, 'hear n- in ks; i i-' As dust levels were reduced, it became necessary to measure the biologi- cally appropriate attribute of the dust cloud. At equal levels of overall !' dustiness, the concentration of asbestos could vary considerably from textile manufacture (75-85 percent) to insulation (5-15 percent). Furthermore, if the limit were lowered below the 5 mppcf used previously and dust counts were 'US--, taken by the impinger technique, it would be necessary to consider the effect of background dust, which could be as high as 1 mppcf. <jPl *-4 A number of methods for measurement of asbestos dust concentrations have j; been used in the NIOSH epidemiological study of the asbestos product industry. Based on these data, the preferred index of asbestos exposure is the concen I: tration of fibers longer than 5 um counted on membrane filters at 430X magnifi cation with phase contrast illumination. This index is utilized in the method adopted as the standard field sampling method by the Public Health Service. Fibers longer than 5 urn are counted in preference to counting all fibers seen in order to minimize observer and/or microscope resolving power variability. Furthermore, the British define a "fibre" as a particle, "of length between <. 5 um and 100 um and having a length-to-breadth ratio of at least 3:1, observed by transmitted light by means of a microscope at a magnification of approxi- j Ms'- mately 500X. " : tP: Although the British have refrained from standardizing on a single method Si-')-- of measurement, recent measurements have been performed by a method essen- '.I'Vtially identical to the fiber-count method described in detail below, and the British hygiene standards for use with their asbestos regulations are stated in these terms. Principles of Sampling iss; 3 A dust sampling procedure must be designed so that samples of actual dust ^ v concentrations are collected accurately and consistently. The results of the analysis of these samples will reflect, realistically, the concentrations of dust at the place and time of sampling. *_________________________________ U.S. Department of Health, Education, and Welfare. Criteria for Recommended Standard, Occupational Exposure to Asbestos. Publication HSM 72-10267, sec. VIII, appendix I, 1972, pp. VIII-1 through VIII-8. A 08843 V-v i.* 12 To collect a sample representative of airborne dust that is likely to enter the subject's respiratory system, it is necessary to position a collec tion apparatus near the nose and mouth of the subject or in his "breathing zone. The concentration of dust in the air to which a worker is exposed will vary, depending upon the nature of the operation and upon the type of work performed by the operator and the position of the operator relative to the source of the dust. The amount of dust Inhaled by a worker can vary daily, seasonally, and with the weather. To obtain representative samples of workers' exposures, it is necessary to collect samples under varying condi tions of weather, on different days, and at different times during a shift. M The percentage of working time spent on different tasks will affect the concentration of dust the worker inhales since the different tasks usually result in exposure to different concentrations. The percentage can be deter mined from work schedules and by observation of work routines. :1 i-Stl The daily average weighted exposure can be determined by using the fol lowing formula: (Hours X cone, task A) + (Hours X cone, task B) + etc, 8 hours (or actual hours worked) The concentration of any air contaminant resulting from an industrial operation also varies with time. Therefore, a longer sampling time will bet ter approximate the actual average. With the following recommended sampling procedure, it is possible to col lect samples at the workers' breathing zones for periods from 4 to 8 hours, thus permitting the evaluation of average exposures for a half or full 8-hour shift--a desirable and recommended procedure. Furthermore, dust exposures of a more normal work pattern result from the use of personal samplers. In evalu ating daily exposures, samples should be collected as near as possible to workers' breathing zones. Collecting Sample The method recommended in this report for taking samples and counting fibers is based on a modification of the membrane filter method described by Edwards and Lynch. The sample should be collected on a 37-mm Millipore type AAa filter mounted in an open-face filter holder. The holder should be fastened to the worker's lapel. Air is drawn through the filter by means of a battery-powered personal sampler pump similar to those approved by NIOSH under the provisions of 30 CFR 74. The filters are contained in plastic filter holders and are aMention of commercial products does not constitute endorsement by the Public Health Service, the U.S. Department of Health, Education, and Welfare, or the Bureau of Mines. suppochrou. face (Ip) over provi ax A08844 , / Sfc ii I to >llecng ill rk le -y lit. the y ter- 13 ...................................' $y-- ..................... Supported on pads which also aid in controlling the distribution of air ^through the filter. To yield a more uniform sample deposit, the filter-holder Efface caps should be removed. Sampling flow rates from 1.0 liter per minute ^{Ipm) up to the maximum flow rate of the personal sampler pump (usually not Sover 2.5 1pm) and sampling times from 15 minutes to 8 hours are acceptable ^provided the following restraints are considered: 1 1. In order to obtain an accurate estimate of the number of fibers, the ^^statistical error resulting from the random distribution of the fibers must be ':kept to an acceptably low level. Since fiber counts follow a Poisson distri- TgSbution, a count of 100 fibers in a sample would have a standard deviation of *va0O,or 10 fibers,or 10 percent. Thus, the 95-percent confidence limits 'i&vwould be approximately 2 standard deviations, or 20 percent. Since the ^37-mm filter has an effective collecting area of 855 mma and the projected v^field area of the Porton reticle is 0.005 ram3, each field represents 1/171000 j^r-pf the sample. Based on this ratio, the following number of fields must be ^.-counted to measure the various limits in various sampling times: >1- Sampling Flow Number of fields for 100 fibers time, rate, 0.2 fiber/ml 2.0 fibers/ml 10 fibers/ml minutes 1pm 10 2 4,350 435 91 15 2 2,860 286 58 30 2 1,430 143 29 it- * 90 1 1,000 100 20 90 2 500 50 10 240 1 260 26 7 ol- 240 2 180 18 4 480 1 180 18 4 ir >f lu- .2 Do not count a field containing over 20 fibers because, in addition |;:^.to the fibers being counted, there are also present a number of grains, which interfere with the accuracy of the count. v Based on these restraints--that is, number of fields to be counted and -maximum number of fibers per field--acceptable sampling parameters for the if-. various limits are underlined in the above table. p: ' i'iM&k-" The following conclusions may be drawn from this analysis: 1. The short-term limit should be for a period of at least 15 minutes ; -A-and preferably 30 minutes. 2. The 2.0-fiber/ml limit may be evaluated over periods of from 90 to i . ,480 minutes. ' S' As many fields as required to yield at least 100 fibers should be VS'-counted. In general, the minimum number of fields should be 20 and the maxisi'&r mum 100. A0884h I (; i . n. ( i l iI i 14 Mcji ei .'At v2 Mounting Sample The mounting medium used in this method is prepared by dissolving 0.05 of membrane filter per ml of 1:1 solution of dimethyl phthalate and diethyl oxalate. The index of refraction of the medium thus prepared is ND 1.47. To prepare a sample for microscopic examination, a drop of the mounting medium is placed on a freshly cleaned, standard (25 mm X 75 mm) microscopic slide. A wedge-shaped piece with arc length of about 1 cm is excised from thev* i filter with a scalpel and forceps and placed dust-side-up on the drop of .-tH- mounting solution. A No. 1-1/2 coverslip, carefully cleaned with lens tissue**?, is placed over the filter wedge. Slight pressure on the coverslip achieves contact between it and the mounting medium. The sample may be examined as -''Tty soon as the mount is transparent. The optical homogeneity of the resulting mount is nearly perfect, with only a slight background granularity under phased contrast, which disappears within 1 day. The sample should be counted within 2 days after mounting. Evaluation The filter samples mounted in the manner previously described are evalu ated in terms of the concentration of asbestos fibers greater than 5 ym in $ length. A microscope equipped-with phase-contrast optics and a 4-mm "high-dry"^ achromatic objective is suitable for this determination. 10X eyepieces, one of which contains a Porton or other suitable reticle at the level of the fieldlimiting diaphragm, should be used. The left half of the Porton reticle field serves to define the counting area of the field. Twenty fields located at random on the sample are counted, and total asbestos fibers longer than 5 ym are recorded. Any particle having an aspect ratio of three or greater is con sidered a fiber. The following formulae are used to determine the number of fibers per milliliter: Filter area (mm2) Field area (mn^) (1) i Average net count X K (flow rate ml/min) (min sampled) = fibers/ml (2) For example, assume the following: Area of the filter used was 855 mnf1, counting area of one field under the Porton reticle was 0.005 mn?, average net count per field of 20 fields was 10 fibers, and sample was collected at 2 liters per minute for 90 minutes. Then, 855 mn? 0.005 md3 " 171,000 (1) 10 fibers X 171.000 Q Q ... ., 2,000 ml/min X 90 min " 9-5 fibers/,nl (2) A0884 15 Calibration of Personal Sampler \ The accuracy of an analysis can be no greater than the accuracy of the volume of air which is measured. Therefore, the accurate calibration of a sampling device is essential to the correct interpretation of an instrument's indication. The frequency of calibration is somewhat dependent on the use, care, and handling to which the pump is subjected. Pumps should be cali brated if they have been subjected to misuse or if they have just been ie repaired or received from a manufacturer. If hard usage is given the instru ment, more frequent calibration may be necessary. Ordinarily, pumps should be calibrated in the laboratory both before they are used in the field and after they have been used to collect a large number of field samples. The accuracy of calibration is dependent on the type of ;e instrument used as a reference. The choice of calibration instrument will i depend largely upon where the calibration is to be performed. For laboratory testing, a 1-liter burette or wet-test meter should be used. In the field, a rotameter is the most convenient instrument used. The actual setup will be the same for all of these instruments. The calibration instrument will be con nected in sequence to the filter unit which will be followed by the personal sampler pump. In this way, the calibration instrument will be at atmospheric pressure. Connections between units can be made using the same type of tubing used in the personal sampling unit. Each pump must be calibrated separately for each type of filter used, if, for example, it has been decided to use a d- filter with a different pore size. The burette should be set up so that the d flow is toward the narrow end of the unit. Care must be exercised in the assembly procedure to insure adequate seals at the joints and that the length of connecting tubing be kept at a minimum. Calibration should be done under the same conditions of pressure, temperature, and density as will be encountered. The rotameter should be used only in the field as a check if the diaphragm or piston pumps are not equipped with pulsa tion dampeners. The pulsating flow resulting from these type pumps causes the rotameter to give results which are not as accurate as that obtained with a burette or wet-test meter. Calibration can be accomplished with any of the other standard calibrating instruments, such as spirometer, Marriott's bottle, or dry-gas meter. The burette and wet-test meter were selected because of their accuracy, availability, and ease of operation. : v : v -"T, INT.-BU.Or MINES,POM.,PA. 1tl A0884? " V IIU.MIlfl.i