Document KzJpJ28KNzOnZL21bk3n8D95x

HccOintucndcd Procedures for Smnpling and Counting Asbestos Fibers Procedures for the Evahmtion o( Occupationall~xposures to Airborne Asbestos Joi111 Alf/A-ACGIH Aerosol Ha;;urds. Evuluutio11 Commitlec FIBROUS ASBESTOS HAS BEEN IDENTIFIED as the causative agent of asbestosis and has been associated with an "increased cancer incidence. The American Conference of Governmental Industrial Hygienists (ACGIH) has established (1974) a Threshold Limit Value (TLV) for asbestos of 5 fibers greater than 5 micrometers in length per milliliter of air. A TLV footnote specifies the determination shall be made by the membrane filter method at 400 X to 450 X magnification and with phase contrast illumination. These procedures define a standard of sampling and of processing the collected samples in order to evaluate occupational exposure to asbestos fibers. Sampling Airborne samples of asbestos must be collected on membrane filters which retain at the surface essentially all of the particles in excess of 0.5 ~m in diameter. The filter must be rendered transparent by the mounting medium. The filter should be packed in a sealed holder which is capable of being readily opened for sampling purposes and of being rescaled after the sample has been collected. The filter must be fully exposed during sampling. (Recommended filters and filter holders arc listed under Supplies). The filter must be practically dust-free. with an average background count of less than 25 . Reprints of lhis anlde are available for purchase from ehhcr the American Industrial Hyp:icnc AasociACh.ln, 66 South Miller Ru~<l. Akrun. Ohio "--JIJ or the American Conf~rcnce or Governmental lndu1trial Hy1lenhts, P.O. Box 19J7, CIIKinnall, Ohio 45201. Tha coal It $1.00 per . C>Opy. fibers per square centimeter. At least 2% to 4% of the filters intended for collecting samples should be set aside to determine the background count. (Sec Counting and Calculations sections). In addition, the filter resistance should not exceed 3 mm of mercury when filtering air at the rate of 0.3 liters per minute (lpm) per square centimeter of filter. When collecting the sample, care must be taken to prevent dust from falling t;>r. from being projected onto the open filter. This may be accomplished by pointing the filter head downward. A guard or shroud should be attached to the filter holder to further protect the open filter from contamination , as well as optimize uniform deposition on the filter. Its diameter should be about the same as the holder so that it can be~attachcd tightly to it and it should project at least I 'h times the filter diameter in front of it. A protective device is particularly important if the filter head is to rest on contaminated clothing. (See Figure 1.) The filter holder may be stored for a limit of six months once it is resealed. The sample should not be too dense, since samples in which particles overlap must be rejected as uncountable. Similarly, a large enough volume of air should be sampled so that there arc sufficient numbers of fibers in each field. Experience indicates that more than 150 particles per ,field, including non- fibrous background, may interfere with counting the sample. It is desirable that 'there be no more than 10 fibers per field. Two or three samples should be collected at each sampling location. The results should 13 .J' ~' ..I '~ 'I I. "~I t ~ i I lu 1f ik ~ r J l l' { I t. i ~ ~ ~ i .! I l c i I . ,, FMSI 07191 ,, : 84 Frbruary, 197$ tFFIILLTTEERR APANDD UJD U; 1-J~t__,_l_. -CAP Figure I. Diagram of shroud for membrane filter holder. The shroud may be constructed from a plastic bQttle by culling off the neck and drilling a hole in the bottom. To use, push the filter holder through the hOle and reach in through the top to remove the holder cap. To remove' the holder, repl:~ce the cap and push the filter holder forward through the hole. be averaged to obtain the fiber concentration. Breathing zone samples should reflect the worker's entire normal work day. They must be collected ~s close to the worker's nose and over as long a time period as possible. Calibrated battery powered personal pumps (sec Appendix IH, Pump Calibration) are satisfactory air movers. They can be worn by the worker and supported at the belt by means of a clip. The sampling head, which can be pinned to the collar, is connected to the pump by flexible tubing. Such pumps can be operated continuously for about eight hours and recharged overnight. If a 37-mm filter is used to collect the sample, the pump should be adjusted to sample between I and 2 liters per minute. The volume of air sampled should be adjusted so that an optimum density of dust is collected on the filter. Since the dust concentration is not known before sampling, the optimal sampling period must be determined by trial and error. It is suggested that, uniess experience indicates otherwise, the first sample should be collected from 20 liters of air, the second from 40 and the third from 80 liters. If a filter other than 37-mm is used, the volume of air sampled should be altered in direct proportion to the open filter area. Samples collected during short- periods of exposure should be collected at a high flow rate and if necessary, for the entire exposure period. In all cases the count should be adjusted with regard to time, so that the exposure is expressed as an 8-hour timeweighted average exposure. For compliance evaluations with short term exposures, 37mm filters samples should be collected for 15 minutes at a mi~imum of 2 lpm. Sample Preparation I! I A solution one-to-one by volume of dimethyl phthalate and diethyl oxylate in which has been dissolved 50 milligrams of membrane filter material per milliliter of solution is the preferred counting medium. The chemicals used to prcpard the medium should be examined microscopically to be certain that they are dust free. The fiber r I' i material to be dissolved should not be marked and should have a maximum background count of 25 fibers per square centimeter of filter. The counting medium may be stored in a wide-mouthed Wheaton Balsam bottle and should be applied with a glass rod. The counting medium has a refractive index of 1.461 at 25C. The medium should be made in small quantities since it has a 6 month shelf life. Asbestos fibers are counted on wedge shaped sections cut from the filter. The wedge should be reasonably sized so that it can be mounted on a 25 x 75 mm (1 x 3 inch) glass microscope slide. The slide should be cleaned of dust before it is used. A drop or two of counting medium is placed on the slide and the filter wedge is placed dust side up on top of the medium. The wedge is covered by a No. 11/.z coverslip. Care must be taken while lowering the cover- slip to avoid trapping air under it. Air bub- bles may be forced .out by exerting slight pressure on the cover slip with a pencil eraser. Extreme care must be taken to avoid fMS\ 07192 ""'. I l ifmrricllll''lllrlll.\'ll'illllly~:il'm ~l.t.mdttlimt lmtrttnl l too much pressure, since this causes distortion and 5trctching in the filter. The wedge is usually cleared within 15 i minutes; however, a residual background j granularity may be noted. ,This will disap- pear within a day. Counts must he cum- plcted within two days since there is a ! tendency for fiber migration ami crystal I growth. The prepared medium should be ! 1I checked periodically for a background count. (See Counting and Cnlculufions sections.) An alternate medium may be used when i the samples must be counted immediately. ! It is prepared in the same manner as the I preferred viscous medium, except that the addd membrane filter is omitted. Since this l medium is much less viscous it should be I I stored in narrow-mouthed bottles. This medium is applied with a glass dropper .after the filter wedge has been placed dust side up Il on the slide. However, a drop should be placed on the slide adjacent to but not on l top of each corner of the wedge. This me- dium acts very rapidly and the No. Jlh coverglass should be lowered within a min- ute. Slides made up with this "alternate medium" arc ready for counting within five 1I minutes and the count must be completed within two hours after preparation. .I Filters which have been used to collect samples and which have been resealed in a ,I, holder should be removed only in a clean environment. They should not be held with the fingers. They may be held with tweezers and cut with either a scalpel. or scissors. Bottles containing media must be tightly closed except during use. All bottles, tools used for handling and cutting filters, and containers used for storing tools must be thoroughly cleaned and dried. Tweezers, scissors, scalpels, etc. should be set aside for this purpose exclusively. Although slides and coverslips arc purchased pre-cleaned, they should be wiped lightly with clean lens tisuc to remove traces of dust. Do not at- tempt to reuse slides or covcrslips. Microscope A microscope equipped with a phase con- 85 trast suhslagc cumlcnscr, a 4 111111 "high dry" phase-cuntrm:;t objective (4(1 X tn 45 X) and a lOX eyepiece is used tn count the sain~. It should have either a pre-focused built-in ilhnninatur supplied with an iris diaphragm or he lighted hy a separate bright illumimatnrflat mirror combination. If a separate illuminator is used it should he equipped with ll condensing lens, iris diaphrngm, and means for adjusting both the illuminator level and the dishmce between the condensing lens . and the bulb. Zoom microscopes may be used for counting <asbestos fibers, provided that the total magnification is within the 400-450 X range. The illuminator should be equipped with an adjustable constant voltage transformer. Both the microscope condenser and stage require close adjustment and both should be rack and pinion mounted. The stage must move along two perpendicular axes in a horizontal plane, while the condenser must move up and down in a vertical plane. Lighting must be adjusted for optimum balance. The Kohler method of illumination is recommended. (See Appendix I for procedures required to establish Kohler illu- minator.) The counting field is defined by a reticle mounted at the level of the field-limiting diaphragm in the l 0 X eyepiece. The Porton reticle (Figure 2) is recommended. However, any reticle which contains markings which, in addition to .outlining an area of about 0.005 square millimeters, as determined by 11 ,ootoO' 'O, .Q ' tt 11 11 " ..:: Fiaure 1. Porton reticle. "' : ~ FMSI 07193 , 1 J' !~,. 86 l the combination of eyepiece and objective, and which defines linear distances that may serve as 11,1easuring aids, is satisfactory. The :.: ;retide ~lUSt be calibrated prior lo USC and ...": r~callbraicd .each tiinc it is removed from the miCroscope eyepiece. or when the micro- scope tube length or interpupillary distance is changed. Zoom microscopes must be re- calibrated each time the zoom position is changed. (Sec Appendix II. for recommended calibration procedures.) Counting A fiber is defined as a particle whose length is at least three times greater than its diameter. All fibers longer than 5 ~tm within the area delineated by the reticle, or which enter it from either of two adjacent sides, arc counted. Fibers entering the area from either of the other two sides, i.e., those not arbitrarily chosen as "counting" sides arc not counted, nor fibers in excess of 5 ~J-Ill in diameter. Touching fibers, i.e., one of whose ends touch another fiber regardless of the resulting angle, arc considered as one. Fibers that cross each other arc counted individually. Fibers that pass through the delineated area arc counted provided that they cross at least one of the arbitrarily chosen "counting" sides. (Sec Figure 3.) Fiber length should be determined by measuring against standards such as a circle or a space defined by markings on the calibrated reticle. If the fiber is curved or wavy the total length should be cstimatep by measuring along the curve. Once sufficient experience has been gained in judging length, only fibers whose length or uiamctcr arc in question need be incasurcd. A routine for choosing counting riclds must be selected so that fields arc not counted more than once anu that a representative fraction of the total filter area is viewed. A convenient procedure which may be used is to select a series of microscope viewing fields along a radial line cxtcnuing front the apex of the filter t.o the outer edge of the sample wedge. The viewing fields must be Ft'bmary, 197$ chosen without preference to a .particular area and should be approximately equally spaced along the line. The first field should be located a little bit in fronflfie-point at which matter is deposited on the filter. If the required number of viewing fields eannot be located on a single radial line; additional lines parallel to the first should be chosen. Preferably 100 fibers should be counted but all the fibers. in 20 fields should be counted even if there are more than 100 fibers. The counting may be terminated after 100 fields have been searched even if 100 fibers have not been counted. Calculations The concentration of asbestos fibers in air can be expressed as: =Asbestos Cone. Fibers x R Fields x Vol oo 0 Figure 3. Illustration of fiber counting with a Porton reticle. The top and left side of the large box have been chosen as "counting sides". Circle 6 is S ,.m in diameter. (A) Fiber A crosses the top oC the box and is counted, therefore. One end of fiber A1 touches Fiber A and thus is considered as part of it and is not counted separately. (B) Fiber B is a bundle containing many spike,. It passes through the bolt crossing bottom :md top. It is counted as one fiber. (C) Fiber C p:1s~es through the bolt but it crosses the right side and bottom. It is not counccd. (D) Fiber 0 is entirely wicJ1in the box and crosses over Fiber A. It is not part of Fiber InA, thereft>n: it is counted ns 11 separate fiber. (E) Fiber E is less th11n S ,.m lenath. It is not count cd. ..... "'-\ I~. Ir l I ~ FMSI 07194( :'-,., ' Amtrican lmlustrilllllyKi~n~ As.mcitllioll Jmmml 87 where: =Fibers total number of fibers counted the system except that if desired, neutral density filters may be used to reduce the Fields = total number of fields counted R = filtration area area of a counting field Vol =sampling rate (lpm) x time (min) X 103 = sample volume in ml of air Since both the filtration area on the membrane filter and the area o( the counting field are normally constant, the ratio of areas, R, is constant for the given conditions. To illustrate: Air is sampled at 1 liter/ minute for 50 minutes on a 37-mm membrane filter (filtration area 855 mm2). A total of 60 fibers each longer than 5 p.m are counted in 100 fields each 0.003 mm2 in area: light intensity. If the microscope is equipped with a built-in illuminator, proper ~ht.!Jtjnator positioning has already been accomplished and need not be or further concern. Fix a mounted sample on the stage and recheck the alignment. Raise the substage condenser until it nearly touches the bottom of the slide. Turn on the illuminator and usc the tilt controls to direct the light to the .center of the mirror. Tilt the mirror, directing the beam upward into the stage condenser. Close the microscope substage iris and the illuminator iris. Usc the illuminator focus control to focus the image of the filament on the 'bottom of the substage iris. The reflection of the iris may be viewed in '" = =855 mm2 R 3 x IQ-3 mm2 2.8 x 1()5 the mirror by leaning over the microscope. After adjusting the illuminator condenser and so that there is a sharp image of the filament on the substage iris, open it about halfway._ Recheck proper position of the mirror and Asbestos Cone. 2.8 x 1().\ x 60 Fibers 100 F 1.eldS X r x 1()3 nun ml . X 50. mm. . .. . -~ 3.4 ~ibc~~~~ .~- .-.- . Smce the prec1s1on of th1s mctrlbd-.Js hm1tcd, then put the objective in place and focus sharply on the sample. It may be necessary to open the substage iris during focusing. After the sample is in focus, fully close the iris. Readjust the condenser height so I ~y ~i ti . the averaged results of the se'Veral samples that the edge of the iris leaves are in sharp _/ should be reported to the nearest significant focus and there is a bright spot within the figure. iris. Readjust the mirror to obtain maximum Ibrightness. If the color around the iris is Appendix I Recommended Procedure for Establishing Kohler Illumination not uniform, recheck the illuminator tilt and focus. If the color is uniform and maximum brightness has been achieved,_ open the field i I The microscope is set on a level surface at a convenient height and in such position iris until the biades just pass out of the field of view. that sighting through the eyepieces is possible The proper phase stop is inserted or ro- without undue strain or discomfort. tated into place in the substage condenser. The illuminator is placed dircc~l)_' i.n. f~l,lnt of and aligned with the microscope. ~f the The phase objective is rotated into place. The eyepiece i~ replaced with the phase ring illuminator is equipped with a coil filament centering telescope. The telescope is ad- bulb, its iris should be ten inches from the justed for sighting. The location of the mirror. If a ribbon filament bulb is used, phase ring is observed through the telescope. the front of the filter holder should be at It may be adjusted by using the two rotating least seven inches from the mirror. Only shafts provided with the phase condenser. the plane surface o( .the mirror should be When the ring is centered it appears as a used. All filters should be removed from bright annular ring mounted on top of a .. /.. FMSI 07195 .J. l ' i. 88 F~lmmry, 197S 1 grey ring. ll1e center is hlack. There should is rchttcu in terms of L units of length in be no overlap of the bright ring into the accordance with the formula: center. When the plmse stop is centered the telescope is removed and the eyepiece is i-c- placed. The microscope is now ready for usc. D=LvV where D is the diameter o the circle or the width of the space and N is the number of the circle, or space. Appendix II The unit L is determined by measurement. A stage micrometer is the primary ruler. Recommended Pruceclures for Any one or more of the definitive linear di- Calibrclling Reticle mensions may be measured. If. the length The reticle must be srightly smaller in of the large rectangle is measured then L diameter than the eyepiece in which it is to be used. It fits into tbc tube and is held in place at the eyepiece focal point by spring Ipressure. The focal point" is marked by an I internal collar which prevents the reticle lfrom passing further into the tube. Some I. manufacturers locate the focal point just equals I /200th of that value. 1f the stage micrometer is marked in hun- dredths of millimeters the value of L is in hundredths of millimeters. If the left square is used as a counting area, its area is equal to (100 x 0.01 )2 mm2 below the collar while others prefer a point The filtering area of a 37-mm filter is 855 immediately above it. Thus it may be nec- mm2 and thus essary to insert the reticle between the lens and the collar on one microscope and below the collar on another. In either case the R = 855 2 r projected image of the reticle on the field If other areas arc used as counting fields must be clear and sharp. The reticle must project a constant count- ing area as well as provide markings for sizing. Many types of reticles are satisfactory. The Parton reticle illustrated in Figure or other sized filters are used, the value of R must be calculated for the individual condition. It is wise to prepare a chart showing each lin~ar dime~sion and area for ready reference - I . 2 is recommended. It outlinci.a large. rec- . whtle counting. . , tangle that fits easily within the field of vision. The rectangle is divided into two Appendix HI equal squares. The. left square is further divided into six: rectangles. Each side of Pump Calibration each square has a length equal to 100 L, Personal sampling pumps should be cali- then the large rectangle is 200 L units long brated for flowrate frequently. They may be and the small ones 50 L units long and 33'13 L units high. To the left of the left square is a scale which <.livides the side into 20 equal increments of 5 L units each. The calibrated against a primary meter such as a spirometer or against a previously calibrated secondary standard such as a wet gas meter or dry gas meter. The train should be I right square is Jivil.lcl.l horizontally in thirds arranged so that the pump is operating corresponding to the small rectangles and against the same resistance it would normally vertically into a series of increasing spaces. operate against, and that the calibrating The distance between each vertical line and meter is at atmospheric pressure. Figure 4 the c-:ntcr of the large rcctanp.lc correspond:~ illustrates the rccommemlcd arrangement. to the di;unetcr of <l circle. Circles of sizes Air flow through the filter may be limited 1 through 9 arc loc~ted above and below the by both rcstrictin~c air flow to the pump large rectangle. The diameter of each circle as well as by udmitting-secondary air into I .. '' FMSI 07196  A mt"ricall lmlusll'ial ll)~git'llt' Assoc{afioll Jo11mal I I P1LT!Jt PrOLDEil i ""''III'ET!IIl Figure 4. Din~ram of set-up for c:alibn.tion of I pump. the pump. Most personal pumps arc con- structed with adjustment valves that permit I both actions. Calibration should be repeated after each 24 to 36 hours of pump usc. If the pump has not been used for a prolonged J { period of time it should be recalibrated. i Temperature and altitude corrections should I be made. I Personal sampling pumps should not be t used to such an extent that the batteries arc 1 allowed to run down below normal operating lI' voltage. Since battery life varies, it is wise to occasionally check the life of the battery by allowing the pump to run down to the first indicated change in voltage under timed 1 simulated conditions. l ~ Supplies Filters and Filter Holders Milliporc Corp. Field Monitor filter holders prcloaded with 37-mm Type AA filters, either white plain (catalog #MAW.I?037AO). or griddcd (#MAWG037AO) arc recommended. These are sold with a guaranteed average p.:rticlc background and can be used without additional background checks. It is less expensive to purchase unloaded field monitors ( #MABG037AO) to be loaded with plain or gridJcd filters pur chased separately m packages of 100 (#AAWP03700, and AAWG03700). The field monitor can then be reloaded aflcr each usc. However, it is necessary to carefully clean the empty monitor and to check the background court on filters in the reloaded monitor. 89 Type AA riltcrs can he used in any diameter in any non-leak in~ open-type filter Iholder, as long as proper adjustment is made in the calculations fur the change in filtering area, nnd periodic hackground checks :.re made. Membrane fillers of other types and manufacturers cannot be recommended at this time, either because they do not become optically clear in the mounting medium or because of excessive particle background. Personal Battery Powered SCIIII(Jiing Pumps (I) Casella'' MK II or MK Ill Personal Sampler (2) MSN Monitairc Sampler, Model G. (3) Bendix'' VM 22 or Micronair Personal Sampler or C-1 I 5. Microscopes: Phase Equipped . (a) microscope body with a fine focus accuracy of 0.006 mm; (b) 10 X eyepiece; (c) mechanical stage; (d) illuminator (preferably built in and having provisions for adjusting light intensity); (c) 40X to 45X (0.65 N.A. at least) positive (bright field) phase-contrast objective; (f) annual ring condenser diaphragm (corresponding to the objective); and (g) phase ring centering telescope. (Note: Most manufacturers sell a basic body unit and built-in illumination system as a unit. Phase-contrast accessories can us- ually be purchased as a kit consisting of . I0 X, 40 X and 90 X phase objectives, a phase condenser containing appropriate an- nola~ ring diaphragms, a phase ring center- ing telescope, and a green filter. Jt is to the microscopist's advantage to purchase the kit.) A list of manufacturers of plutsc,ontrast microscopes and reticles' is given below tn aid in selecting a proper instrument. . !t I I l .. "~-. ' I f I I Mllllparc Corr., BeiiC<>rd, Ma._._ 071)0. Wllln PnldU<:IA Dlv., P.O. Dux 622, R<nllln~. Penna. 196413. C. F. Cawlla A (o. l.ld., ll<IICnl lh>to,..,, Britannia -----------~~~ FMSI 07197 90 Walk, Landon, N.l, En1and. e Mine Safety Arrllance Co., 201 Braddock ""' Pill.. hur~h. l'enna. 1520H. Dcndi-NEI, P.O. Bo 5911, Fall River, Ma111. 02722. Hau!!o4:'h nnd Lomb, St.:ientaric lnstruml'nt DiYlslun. 72624 Bousch Street, Rochester, N.Y. 14602.. Olympu~ Microscoptl, MJcro Optlca Company, 2116) Greenricld, Southridd, Mich. 4R075. American Opllcal Corporalion, Rdchen Products, Buf falo, N.Y. 14215. Fdmary, 191S E. Lellz: Inc., Rocklcl~h, N.I. 07647. Nlkon Inc., Instrument Division, Garden CIIJ, N.Y. 115l0. Unilron lntmment Company, Mlc:roscopc Sales DIYlak>n, 66 Needham St~el, Newton Hl1hland, M""- 02161. Carl Zeiss, 444 Fifth Avenue, New York, N.Y. 10011. ' Edmund Sclenllfic Co., 101 Edsorp Blllldlnlo Barrilll- ton, N.l. 07007. BGI, Incorporated, 511 Guinan St, Waltham. M- 02154. Joi11t AIIIA-ACGIH Acro.rol Ha:.ards Etaluation Commlttt. AliiA ACCIII Morton Lippmann, Ph.D., Chairman J. LeRoy Balzer, Ph.D. Douglas K. Craig, Ph.D. -Gr.1ham W. Gibbs, Ph.D. . William C. Janes William H. Krebs, Ph.D. Carl A. Mangold Eric B. Sansone, Ph.D. Marvin Tillery Thomas F. Tomb Rus5ell W, VanHouten Wesley R. VanPelt, Ph.D. Donald l. Webster Howard E. Ayer George Carson, Ph.D. Harry J. Ettinger Murray Jacob'Son Geoffrey Knight Jeremiah R. Lynch 0. Major Owen Moss Milton Scheinbaum Glen W. Sutton J I I l~ I Industrial Hygiene Training in Israel Medical and engineering students at Tel Aviv University will be obligated in the future to undertake training in occupational safety, hygiene and health to inspire them whh an awareness of their obligations for the maintenance of the health of the worker and for the prevention of ill effects from work on man. This has been made possible by the establishment in 1974 by the Faculties of Medicine and Engineering of the University, in collaboration with the Ministry of Labor, of the National Insurance Institute and the Workers Health Insurance (Kupat-Holim) of a Center for Occupational Safety, Hygiene and Health, with four major departments-Physiology of Work and Rehabilitation, Occupational Toxicology, Occupational Hygiene, and Safety Engineering. It comes to fill long-standing gaps in the promotion of safety and health of the working population in Israel and the ubscncc of training facilities for specialists in these fields. The new Center will immediately provide refresher courses for physicians and nurses, but curricula for the training of Occupational Toxicologists, Hygienists and Physiologists arc in preparation. Ultimately the Occupationul Health Physician will also be trained at the Center. Due to lack of suitable personnel' in the country the Center is seeking to recruit specialists ~rom abroad. i .. !'. ' ~ 'lit \'-,. " FMSI 07198