Document Ne1zDJMbNe8QBNMmJQdYGVRKb

FILE NAME: Ford (FD) DATE: 1975 Feb DOC#: FD213 DOCUMENT DESCRIPTION: Journal Article - Recommended Procedures for Sampling and Counting Asbestos Fibers y Recommended Procedures for Sampling and Counting Asbestos Fibers Procedure* for (he Evaiuatio# W Occupational E x p u arti to Airborne AabeaCos Joint A tH A-AC G IH Aerosol Hazards Evaluation Committee Fibrous a s IDENTIFIED be a st the o s has cautativc been agent o( asbestoais and hai been associated with an increased cancer incidence. The American Conference of Governmental Industrial Hy gienists (ACGIH) has established (1974) a Threshold lim n Value (TuV) lot asbestos of 5 fibers greater than 5 micrometers is length per milliliter ot air. A TLV footnote specifies tbe determination shall be made by the membrane filter method at 400 x to 450 x magnification and with phase contrast illuminatioa. These procedures dine a standard ot sampling and ot processing the colketed samples in order to evaluate occu pational exposure to asbestos libers. 1*1 Airborne samples of asbestos must be collected on membrane filters which retain at the surface essentially all ot the particles an escess of O.S ptn in diameter. Tbe filter must be rendered transparent by the mount ing medium. The filter should be packed in a sealed holder which is capable of being readily opened (or sampling purposes and o f being rescaled after the sample has been collected. The niter must be fully expos during sampling (Recommended filters and fihar boiden are listed under Sspptias). The filter must be practically dust-free with an aw rafe background count of less than 2.5 * -- * -- anMW an n u a x < punas m sM b i the I n a l i ti Is S ie d a B r a * k u r t l m . SS Sa* M ro. a-- t, At-M. ( U f s u n m r o nm m em C m Ji m w T O m 'it-- MHf U d i t i * llpgiialm t.O. -- MIS. CUlUaat. OSS* MUTI ana b Stas pa> aa*._ , _ fibers per square centimeter. At least 2% to 4% of the filters intended for collccung samples should be set aside to determine the background count. (See Co-- Hug and Cab entatioa* tocuoai). In addition. the filter reaiatance should not exceed ) mm of mer cury when filtering air at tbe rate of 0.3 liters per minute (Ipts) per square centimeter of filter. When collecting the sample, care most be taken to prevent dust from falling or from being projected onto the open filter. Ib is may be accomplished by pointing tbe filter bead downward. A guard or shroud should be attached .to the filter holder to further protect the open filter from coouminatton as well u optimize uniform deposition on the filter. Its diameter should be about the same as the holder so that it can be attached tightly so it and it should project at least l t d times the fitter diameter in (root of it. A protective device is particularly important if the filter head is to rest oa contaminated clothing. (Sec Figure I.) The filter holder may be stored for a limit of six months once it is resexled. The sample should not be too dense, since sampies in which panicles overlap must be rejected as uncountable. Similarly, a targe enough voiuroe of air should be sampled so that there art sufficient numbers of fibers u each field. Experience indicates that more that 150 particles per field, including noc- fibrous background, may interfere with counting the cample. It it desirable that there be no more than 10 fibers per field. Tiro ot throe samples should be collected at each sampling Vocation. The teauhi should 8 0 0 2 OOflfs r bolder. T to akrowt may be owtnxtod from pfcaCk hotlb by atftfef off tto Mck Md drilliai ft hole to tho bottom. To me, pmh the fitter bofctor thmifh the bolt urf m ch toi thnoatb ih* top to fMKnt the boldrr cap. To remote Che bolder, re* phce the cap m i pmth tto (ilto hoi<tor"forward through the hole. lie averaged. to obtain the fiber concentra* lion. Breathing rone sample ihould reflect the n x k e t'i e s tire oorm il work day. They n tn t be collected aa cloee to the worker'! "KMC and over aa long a dine period at ^possible. Calibrated battery powered per^ tonal p a p a (aee Appendix HI, Pump CaH^ tcad o u ) are aadafactory air moveri. They ^ <ao be worn by the worker and aupporsed * K the belt by m eant of a clip. The eamptiag head, which can be pinned to the cel lar, la cooDocfied to the pump by flexible tubing. Sach pompa can be operated continootaly for about eight bouta and recharged overnight. If a i l -m m filter la used to collect the ample, the pump ibould be adjusted to sam ple betwee n 1 and 2 liter* per minute. The volume of air tampled should be adjusted so that aa optimum density of dust h col lected oo the fitter. Since the dust concentra tion is not known before ssmpiing, the op tima! sampling period must be determined by trial and error. It is suggested that, unless etperience indicates otherwise, the first sam ple should be collected from 20 liters of air. lie second from 4 0 and the third from 80 February. t 9?s liters. If a filter other than 3?-mm is used, fee volume of sir 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 aH cases the count should be sdjusted with regard to time, so that the exposure is expressed as an 8-hour timeweighted average exposure. For compliance evaluations with short term exposures, 37m filter* samples ihould be collected fot 15 minutes at a minimum of 2 1pm. Sample FVepasatfou A solution one-to-one by volume of di methyl pfithalate and diethyl oxylate in which has been dissolved 50 milligrams of membrane filter material per milliliter of sotutkm is the preferred counting medium. The chemicals used to prepare the medium should be examined microsoopicaily to be certain that they are dust free. The fiber materia) to be dissolved should not be marked and should hive a maximum back ground count of 25 fibers per square centi meter of filter. T he counting medium may be stored in a wide-mouthed Wheaton Bal sam bottle aod should be applied with a glaaa rod. The counting medium has a re fractive index of T.46! at 25*C. The m tdiam. should be made in small quantities aiooe 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 7 inch) glass microscope slide. The slide should be cleaned o f dust before it is used A drop or two of counting medium is placed oo the slide and the filter wedge is placed dust side tip on top of the medium. The wedge oovered by a No. TVi coverslip. Care must be taken while Towering the coverslip 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 cire must be taken to avoid B O tV 0 0 0 5 A 9 t + i m r f r l m t H rgir^r ntfinr U m r**t too much pressure, since (bis causes diator(ton sod stretching in (he filter. The wedge is usually cleared within minutes; however, a residual backgntend granularity may be noted. This will disap pear within a day. Count must he com pleted within two days since there n a tendency for fiber migration and crystal growth. The prepared medium should be chocked periodically for a background count. (Sec C a a S h f and C d f l a l u i sections.) An alternate medium may be used when the samples must be counted immediately. It is prepared in the same manner as the preferred viscous medium, except that the added membrane filter is omitted Since thi\ medium is much less viscous it should be stored in narrow-mouthed bottles This me dium is applied with a glass dropper after the filter wedge Hus been placed dust side up on the slide. However, a drop should be placed on the slide adjacent to but not on top of each corner of the wedge. T his me dium acts very rapidly and the No. IVi covcrglass should be lowered within a min ute. Slides made up with this Alternate medium*' arc ready for counting within five minutes and the count must be completed within two hours after preparation. Filters which have been used to collect u m p i and which have beer* reseated in a holder should be removed on'y in a clear environment. They should not be field with the fingers. They may be held with tweezers and cut with cither 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 m ust be thoroughly cleaned and dried. Tweezer*, scissors, scalpels, etc. should be set aside for this purpose exclusively. Although slides and coversfips arc purchased pre-cleaned, they should he wiped lightly with clean lens tisuc to remove traces of dust. !>*> no ,*itemp to reuse slides covrrsfips Microscope A microscope equipped with a phase con- as trust subaUgc condenser. * 4 mm "high dry** phajz-cootrast objective (40 x to 45 x ) and lOX eyepiecc is used to count the sample. !t should have either a prc-focuscd built-in Illuminator supplied with an Iris diaphragm o r be lighted by a separate bright illuminator* Hut mirror combination. If a separate illu minator is used it should be equipped with a condensing lens, iris diaphragm, and roe* for adjusting both the illuminator level and the distance between (he condensing fens and the bulb. Zoom micr$copcs may be used for counting asbestos fibers, provided that the tolPl magnification is within the 41X1-450 X range. The illuminator should be equipped with an adjustable constant voltage transformer. Both the microscope condenser and stage require close adjustment and N*th should be rack and pinion mounted. The stage must move alobg two perpendicular axes ft a horizontal plane, while the condenser must move up and down in a vertical plane. Lighting must be adjusted for optimum bal ance. The Knhtcr method of illumination is recommended. (See Append* I for pro cedures required to establish Kohler Illu minator.) The counting field is defined by a reticle mounted at the level of the field-limiting di aphragm in the 10 X eyepiece. The Porton reticle {Figure 2) is recommended However any reticle which contain* marking* which in addition to outlining an area of about 0.005 square millimeters, as determined by M the c a n M u litn of eyepiece and objective, and which define linear distance* th at may K fve is mrsaurfng aids. |> satisfactory: The reticle a u n t he calibrated p rio r to us* ad .recalibrated each lime it fe removed from the microacopc cycplace or whet the micro* tcope tube length or Interpupillary distance ft changed. Zoom microscopes must be se- .caiH m ed cich time the zoom position * ... changed. (Set Appendix If (or recommended ' callfcndoprocedures.) ' ;' , r" * $ * C aaat^ t A fiber it defined a t i particle whose length ia at least three times greater than Its diameter. All fibers loafer than 5 am vithia the area delineated by the reticle, or which cater it from either of to o adjacent tides, are counted. Fiber entering the area Irom either of the other two tides, Le.. those not arbitrarily chores as "Hinting" Ides ire hot counted, nor fiber* in excess of 5 an in diameter. Touching fiber. I f . , ooc if whose ends touch another fiber regardleu ot the resulting angle, are considered as one. Fibers that cross each other arc counted Inilividaafiy. Fibers that pass through the de lineated area are counted provided Ibat they ' moss it least One of the arbitrarily cboicn counting" sides. (See Figure 3.) Fiber length should be determined by measuring against standards such as a circle or a space defined by markings oo the cali brated reticle. If the fiber is curved o r wavy die total length should be estimated by meas uring along the curve. Once sufficient eaperience has been gained in judging length, only fibers whose length or diameter arc in question need be measured. A routine for cboosiog counting fields must be selected so that fields are not count ed more than once and that a representative fraction of the tola! filter area is viewed. A convenient procedure wha-h may be used h to select a series of microscope slewing fields along a radial line extending from the apex of the filter to the outer edge o ' the Simple wedge. The viewing fields must be February, t 97t chosen without preference to a particular area and should be Approximately equally paced along the line. The first field should be located a little bit in from the point at which matter is deposited on' the filter. If the required number of viewing fields canaor be located on a single radial line, tdditsooal lines parallel to the first should be rhnaua. Preferably 100 fibers should be counted but all tbc fibers la 20 fields should be counted even if there are more than 100 fibers. The counting may be terminated after 100 fields hive been searched even i f ' 100 fibers have not been counted. The concentration of asbestos fibers in sir can be expressed si Asbestos Cone. Fibers xR Fields x VoT Parson reticle. T he lop and left side o f the lrc to e have been chosen as "counting sides". Circle 6 a 5 in ehametet. (A ) fiber A criases the top of the ho* and is c io o e i , therefoee. One end of Fiber A , touches Fiber A and thus tt considered M p art of it and is not counted separately <B) Fi ber B h a bundle conraininp many sp tlcv It pnsstth ro u sb th e bos .reusing bsittom ansi t,p It is loom ed ns am fiber 1C) Fiber ( posse- through the bsix hoe il enr-ses ehe right sale and l-ilin i" ll is aeil enemies! ( O l Fiher I) is entirely within the bus nns! vrsrs-ei sis er Fiber A ll is nsl p.m u f I iber A. Iherefnre il is sneinlrd as a separate fiber i l l Fiber F is less ihao s pm in lenglh It is nut ctunl. ed. 8 n02 00 0 6 A m e r ic a n twA m strM H yg ien e A %<** where: Fibers tot! number of Oben counted Fields m total number of field counted R K fihritio-f-l -r-e--s- -..... area o fa counting field Vol * samp!tog rate (Ipm ) x time (min) xlO> . " ample volume In ml of air Since both tbe nitration area on the mem brane Ctltct and the aiea of the counting field are normally constant, the ratio o f areas. R. is constant for the given conditions. To illustrate: Air is sampled at 1 liter/ minute for SO minutes on a 37-mm mem brane filter (filtration area 855 mm-*). A total o f fibers each longer than 5 pm are counted in 100 fields each 0 003 mm*' m area: 855 mm? x 10-* mm-' 2.8 x t0 ' and Asbestos Cone. J 2.8 x 10 x 6 0 Fibers______ 100 Fields x ---- -- x 50 mm mm 3.4 Fibers/m! Since the precision of this method is limited, the averaged results of the several samples should be reported to the nearest significant figure. Appendix I Rrcotnmemtrd PrtKedurt- ft n f.ytahltshm? Kohler Illumination The microscope is set on a level surface at a convenient height and in strh position that sighting through the eyepiece* is possible without undue strain or discomfort. The illuminator placed directly in front of and aligned with the microscope. If he illuminator is equipped with a coil filament * btilb. tts ffii should be ten inches from Hu* mirror If a ribbon filament bulb is used, the front of the filter holder should he at least seven inches from the mirror. Only the plane surface of the mirror shouU be used. All filters should be removed hunt 17 the system except that K desired, neutral daasity filters cnay be used to reduce the light iatansity. If the nsicroacope la equipped with a buUi-ln Htumiruitor. proper Illuminator positioning h a t already been accomplished and need not be of further concern. Fix a mounted sample o n the stage and rechcck the alignment. Raise the subatage condenser until it nearly touebes the bottom of the aide. Turn on the HlaniM tor and use the tilt controls to ditact the light to the center of the mirror. Tilt the mirror, direct ing the beam upward into the stage condenser. Close the microscope substage irK and the illuminator iris. Use the Illuminator focus control to focus the image of the fWamem on the bottom of the substage iris. The reflection ofVhc iris m ay be vie m the mirror by leaning over the microscope. After adjusting the illuminator condenser 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 then put the objective in place and focus sharply on the samp!. It im*y he necessary to open the sobstage iris during lorusing. After the sample is in focus, fully close the iris. Readjust the condenser height at that the edge of the tri* leaves are in sharp focus and there is a bright spot within the rs Readjust the mirror to obtain rmumuivn brightness If the color around the iris is not uniform, recheck he illuminator tilt and focus. If t!e color is uniform and maximum brightness has been achieved, open the field iris until the blades just pass out of the field of view. The proper phase stop is inserted or ro tated into place in the substage condenser. The phase objective is rotated into place. The eyepiece is replaced with the phase ring centering telescope. The telescope is ad justed for sighting The location of the phase ring is observed through the telescope. It may be adjusted by using the two rotating shafts provided with tin.* phase condenser. When the ring is centered it appears as a bright annular ring mounted on top of a F rb rm ry . / 97) p u ycteg. The center IMask. TtercahouU it related in terms of L units of length in t* no.pvcrtap c< (Ac bright xiqg^lreto the accordance with the formula: t c p w u Wptm Ui flate iiagi t f y i toypd j tke D - L WF te n O ia the diameter a t the circle or tbc uWth of the space and Af is the number of : * *+Kj \t +. tec drtfc. or space. -> The unit L Is detersniaod by measurement. -'^a^^^b -..''fc P "i-'* ,,#*'rfl,' ,, A Mage micrometer b the primary ruler. A u y o m o rm o rccf the definitive linear di- i ''Mi*iftTtwi t fttIeitttofffoi't-fthottote*.:bxan-.;il;igybyfty - nj ia'aUrr../J>a. : atMthrfeoalasrgaaeayrechteanmglseutburosadr. asIufretdhethleenngtLh h dh btebrtte he y ptoca I Web It 1o equals I/200th o f that value. betead.'- H fbs tete he tete m b M d te K the stage micrometer b marled In hun- flana at (ha ly p lin ( b o l pote by apring dtadtht o f millimeters the value of L is in prnaaair.' The fecal pofat la usarfced by tn hundredths of millimeters. If the left square bteraal collar wbich prevente he ratkb b uard aa a counting area, its area is equal Item poate( farthar hato he tuba. Sotae to -- a fu f is lcate he focal potet ja ttefe* te collar teta odam p este a potat teatodbtoly abo**. Tbus W f a y be aeo- (100 x 0.01 L Y mm-' The filtering area of a 37-mm filter is 855 aum: and thus - and the collar oa c a t micropope aad below the collar oa another, to ekhcr caac the projected Im aft o f the rotkb oa the (bte mutt ba d ear aad abaip. The reticle muat project a eotaataat e oaai lac an a as ell aa proride a itlo g s for aieta(. M any types of rctJcte arc satbfactory. The Potion retlcte illuatrated In Figure 2 it raoomtneoded. It outline* a large rec tangle that fits easily within the field of vision. T he rectangle it divided brio (wo equal quarts The left square is further divided Into six rectangles. Each side of each square has e length equal to 100 L, then the large rectangle is 200 L units long and the small ones 50 L units long and 33Vi L units high. T o the left of the left sqesre is a scale which divides the side into 20 equal increments of 5 i. units each. The right square is divided horizontally in third corresponding to the small rectangles tnd vertically into 1 series of increasing spaces The distance between each vertical bnc and the center o f the large rectangle correspond, to the diameter of a circle (h r. lor or sires I thruugh 9 arc located aSosc and 1vlov, the large rectangle The diameter ot each cm to If other areas arc used as counting fields or other sued filters arc used, the value of R must be calculated for the individual con dition. I t is wise, to prepare a chart showing each linear dimension and area for ready reference uteile counting Pump Calibration Personal sampling pumps should he cali brated for flowrate frequently. They may be calibrated against a primary meter such as a spirometer or against a previously calibrat ed secondary standard such as a wet gas meter or dry gas meter. The train should be arranged so that tbc pump is operating against the same resistance Hwould normally operate against', and that the calibrating meter is ot atmospheric pressure. Figure 4 illustrates the recommended arrangement Air flow through the filter may be limited by Null resliKting the air flow to the pump as well as by admitting secondary air into I 8 3 0 / 3007 Am erican f/Umstrtsl H ygiene Astactmflan fo u r n el Fifwe 4. Diagram of et-p for calibration ot P^mp. the pump. Moat person! pump rt con structed with adjustment valves that permit both actions. Calibration should be repeated after each 24 to 36 hours of pump use. If the pump has not been used for a prolonged period of time it should be recalibrated. Temperature and attitude corrections should be made. Personal sampling pumps should not be used to such an extent that the batteries arc allowed to run down below normal operating 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 simulated conditions. Supplies Fitte n and Filter Holders Milliporc Corp.* FicM Monitor filter hoWers prclojdcd with 37 mm Type AA filters, cither white plain (catalog 4MA.W P0370) or gridded (4 M A W G 0 3 7 A 0 ) are recom mended These are sold with a guaranteed average particle background and can be used without additional background checks. It is le expensive to purchase unloaded field monitors (4 M A B G 0 3 7 A 0 ) to be loaded with plain or gridded fibers pur chased se p a ra te ly n packages of 100^ f*AAWPO3700, and AAW0037(X>). 7hc * held monitor can then be reloaded after each uve However, it is necessary to care fully clean the empty monitor and to check the background count on filter*, in the re loaded monitor. Type AA fitter* can be aaed hi any diaaflur la any nooleaklng opan type filter hottfac, aa long aa proper adjuatpaeat la Bade la tha calculation for the ck a ^ s iaftticrini area, and periodic bsdegrouad chocks art made. Membrane filters of other typae and m m h` afacturers caanot be recommended at this time, either bacauaa they do not become optically dear h the mounti f aitdlam or because of excessive particle background. Personal Battery Powered Sampling Pump* ( 1 ) Ca*e1!afc MK !i or MK It! Personal Sampler ( 2 ) MSA' Monitairc Sampler, Mode! O. ( 3 ) Bendix* VM 22 o r Micronair Per sonal Sampler or C-M 5. Microscopes: Phase Equipped (7 microscope body wjth a fine focus accuracy of 0.006 mm; (b> 10x eyepiece; (c) mechanical stage; ( d ) illuminator (preferably built in and having provisions for adjusting fight intensity); (c> 4 o x to 45 X (0 6 5 N.A. at least! positive (bright field) phase-contrast objective; f f > snnua! ring condenser diaphragm (corresponding fo rhe objective); ami (g) phase ring centering telescope. (Afore. Moat manufacturers sell a bask body unit and budi-in illumination system as a unit. Phase-contrast accessories can us ually be purchased as a kit consisting of 10 X . 40 X and 90 X phase objectives, a phase condenser containing appropriate an nular ring diaphragms, a phase ring center ing telescope, and a green filter. It is to the microscopijt's advantage to purchase (he kit > A list of manufacturers of phase-contrast rrMcro$c<x*S' and reticles' is given below to aid in selecting a proper instrument. i of. . Uba. iOIU) -w.it... r . I ) . . r o o.. 6" *r*Jw*. r*a (Mil ( I < im IIi A <n I id Rrnfu M.m / R ut..