Document ZnkYr0d8q25odEVwVNvjpJ80Z

Improved Techniques of Identification and Determination of Airborne Asbestos , LESLIE BARTOSIEWICZ ' " ' . \ Ford Motor Company, Scientific Research Staff, Dearborn, Michigan 48121 . Colltction, IdtnttflcatioD and data analyzing techniques are presented! for airfcom mineral fibers. The limitations of the techniques are discussed. It is shown that the adaption of a plenum Hi Inches long for sample collection is important, since It leads to a much more uniform particle, collection and distribution. Separation of the asbestos particles from other solid airhorn pollutants with the refractive Index, liquid method Is shown to be accurate, convenient and useful in distinguishing asbestos from other fibrous material. For analysis of this type the Image analyzing micro* scope Is a veiy valuable tool. .. . . .; ' Introduction The need to evaluate the HAZARDS from asbestos inhalation was recognised as early as 1906 but it was more than twenty years before a detailed description of asbestosis was developed. Since then, it has been documented by nu merous studies that inhalation of high con centrations ef asbestos or any prolonged exposure to moderate asbestos dust level can in many instances lead to the development of asbestos connected diseases of the lung.1 In general, the available data and infor mation are only pertinent to the high con centrations caused by occupational exposure, and not to the low asbestos fiber conteat found as background in air. The health problem as posed by the biologically active asbestos fibers has led to the establishment of occupational safety standards.- But, little has been done to develop reliable sample collection, data generation, and identifica tion techniques. This paper deals with these three aspects of analyzing for airborne as bestos pahiclgs. Sampling ' Sample collection is the most important -step in any-analysis for air pollution-There-- fore, one must be sure that the collection mmms $5! E*;*i e'.. d U>\*' Figure I. Non-uniform parti le distribution: of asbestos fibers and dust, collect with an openface filter holder and xiewed at isOOX, phase con trast. (Samplo A). ; - .. SCF-FA-6740 252 8000 0331 HFM - 002035 g&jSfc." American Industrial Hygiene Association Journal technique used gives an unbiased representa tion of those particles which are present. For this study samples were collected by the Ford Motor Industrial Hygiene Unit. Two sample collection methods were used, the approved NIOSH (National Institute for Occupational Safety and Health) and a modified NIOSH technique. All samples were simultaneously obtained at a manufac turing facility of the Ford Motor Company. Approved NIOSH Technique The first group of samples were taken in the timing room of the plant using the. techtuque approved by NIOSH which is to use a start* open-face filter holder with a 37 mm, type AA, millipore filter supported oh a base pad. Ifwo samples were collected with this device: using a 2-liters/minute air sampling flow nate for 48 minutes per sample (a total of 96 IBters of air was sampled). Sample A was oniUected In the casting room and Sample B ia title mixing room. Micrographs show ing dim particle distribution of Samples A and B* were counted with the NIOSH ap proved I microscopy technique (phase con-) hast) atnd are shown in Figures 1 and 2. Various areas of Samples A and B were . ooaaterifl and the data is. presented in Table L Smiles A and B showed that dividing the cfldn Kilters into' three equal parts and . niiwhiiiiljg each segment separately yielded flaw different results on each filter. The fibetiocount for fibers equal to or greater than 5 pnr was 5.2 fibers, m/ of air sampled in One aacea of sample A. while the fiber count -V;4 * > 253 ........ ' . X . iSSRV. Figure 2. Phase contrast micrograph at 500X,. showing the unevenly distributed asbestos* dust particles as collected with an open-face filter holder. (Sample B). /, - was 2.5 and 4.1 fiberi/mf in the other ran-, domly selected areas.: : The values obtained for particles equal to or greater than 5 fan for Sample B were 1.1 fibers/ml in the first segment, 3.5 fibers/mf I "-'1, -X-. TABLE I . Panicle Size Analysis of Samples A and B Sample ' A , . B ; ,' Where Obtained Plenum Length Technique Used Total Air Volume Sampled Analyzed Filter Segments Segment Number 1 Segment Number 2 Segment Number 3 Casting Room . Mixing Roorh Short, Open Face : .' Short. Open Face NIOSH Standard NIOSH Standard 9(5 liters 96 liters ' . 3 ' . 3 - 5.2 t ml' 1.1 t/ml 2.5 tin1 3.5 f/ml 4.1 {/ml 6.8 f/ml -5-^im-or-grealer.- ff-.' * 8000.0332 HFM - 002036 in the second, and 6.8 ftbers/nii in the third section. It can be seen from Figures 1 and 2 and the data in Table I that the particles are not uniformly distributed-on the millipore filters and, therefore, these samples cannot be assumed to be representative of the sam pled working area. For this reason it is almost impossible to avoid a biased area selection for the particle counting. f From these typical results, it is deducted that the samples collected with an open-face filter holder do not present a reliable or reproducible base for the analysis. Other aspects of reliability of this method will be discussed later. Modified NIOSH Technique The collection method for the second group of samples was modified so that the filter holders were fitted with a plenum 146 inches high over the base of the filters. The air inlet on the top of the plenum was die standard size 0.150 inch opening and all other parameters were kept the same. Fig ure 3 shows this modified sample collector with the 1%-inch long plenum, and the T's-ineb long lower chamber behind the filter assembly. Preliminary calculations predicted that the 1% -inch long plenum with the %-inch long Lower Chamber Plenum Tube Fitting % Air : Inlet U50"0ial Filter & Pad 37mm millipore (AA) Figure 3. Overall view of modified sample collector. lower chamber would create a condition that . ' would satisfy the desired air flow properties of this small system. Not only does the plenum lengthen the particle path but it creates a low grade air turbulance which helps to uhiforinly! distribute particles oyer the entire filter surface. The air stream is accelerated (pressure higher) through the orifice (air inlet) O^ut behind the orifice in side the plenum thg pressure drops immedi ately and the air flbw decelerates. This dir minution of the airi velocity is die result of the sudden increase in the cross-sectional dimension of the Jplehum; The. particles, upon entering the plenum, become turbulent but the turbulance decays3 within a distance of 2 to 4ft of the plenum. Uniform collecrion over the entire filter areas is accom plished by placing tl)e filter assembly at {east a distance d = 2Hj upstream4 from the air.s inlet where d? and; d are respectively the radius and the dianfeter of the plenum. The elevated orifibe pressure with the con sequently higher air Velocity is necessary to overcome the gravitational force of the larger particles in order dt collect them on the filter. Therefore, representative ocllectkm of the large particle^ with the "open-face" filter is not. reliable, j Translating into prac tical terms, the complicated aeromechanics of the modified sampje collector, the follow ing consideration mu^t be made in order to design a properly functioning system: The filter assembly should be located at a distance that is at Idast one plenum diam eter from the air inlet,|and one plenum radius from the air outlet. (The sample Collection improvement with thijs modified collector is twofold: (1) uniform collection over the whole filter area, and (2) representative collection of large par- . tides. '. . :-.V : . Experience has shcjwn that a sampling , rateof 2 litcrsperminute for either 48 min utes as was the case for Sample C, or the 38 minutes collection time used for Sample 8000. 0333 HFM - 002037 American Industrial Hygiene A lUKt'aiion Journal TABLE U Particle Size Analysis of Samples C and D Sample C "... D -. ; Where Obuiced . Casting Room Plenum Length . . lVi inches long Technique Used . Modified Total Air Volume Sampled ' .96 Liters Analyzed Filar Segments 3 Segment Number 1 . 5.6 f 'm/" Segment Number 2 4.9 fmi Segment Number 3 : 5.8 t ml . Mixing Room - . 134 inches long ' Modified f 76 liters >. 3 10.5 f/ml 11.2 t/ml 9.8 f/mf "Fiber coca: per mi; fibers 5 >mi or greater. ' ; 255 O will produce an adequate, moderately dense and very' uniform particle distribution, as shown in Figures 4 and 5 and in Table II. An analysis corresponding to that used in Sample A and B was made on these speci- ' jv-V > a-'} . rJh- 4'-V mens. It was found that; the particle count of these samples with :the'evaluation method as outlined by the NIOfiH, yielded results with much less scatter between the filter segments. ; ; ' ./ ';. '. An evaluation of Sample C taken in the ; -,^.5 a. * wTt.vT _TV.,_ --' *-S' ' ifl^:-k-V-t*. . -1 . *' - * ' - ':\.v miJTi wnvftvI.T*- . * . *-'V7t'. '1I- '--v :* ..N ,,g^ , . : gfe . :>* " ';* >: - $+$& -* * 5 -V ` *' yi ."** ,, sV?'" L .. j*'. i* r -':''* > ,:?&> : .* *...'.;Vsa!' *. rt. ,ri *a- *''' i., , ' ^aw-'V .- .. . -ai /*. CfV * s r ' I?:' !"**'. I-. .*.. .-afei^^fea..;. Figure 4. Uniform distribution of asbestos fibers and dust particles as collected with the modified fitter holder ( Rj " long plenum and viewed at ' 500X~pbise_contrastr'(Sample7QT ^ " Figure 5. Even distribltion pf asbestos and nonasbcsios particles as collected with the modified filter holder (IV1" long plerjum) and viewed at 500X phase contrasLTSamplb D).... . i-| 9000 0334- HFM - 002038 2J6 casting room, revealed that there were 5.6 fibers 'to! present for fibers 5 pm or greater in length in the first segment of the filter while. 4.9 fibers 'ml were found in the sec ond and 5.8 fibers/mf were counted in the third segment. Sample D. taken in the mix ing room, shows an equally good distribution between the three segmen ts of the. filter. In the first filter segment 10.5 fibers/m! were counted for fibers 5 pm or longer in length, whfle 11.2 fibers m! were found in the second, and 9.8 fibers m/ were found in the third segment. \ Comparing the results of the analysis of. Sample C with Sample A, the superiority of the long plenum collection method is appar ent. The difference between the high and the low fiber count of Sample C is only 0.9 fiber, while Sample A shows a three times higher discrepancy or 2.7 fibers. The rela tionship between Sample D and B is even worse. Sample D shows only a 1.4 fiber count difference between the individual filter segments, while a 5.7 fiber count difference exists between the three filter segments of Sample B. The fiber count discrepancy of Sample B is slightly more than four times that of Sample D. The previously described modified sample collector with the 0.150-inch size air inlet' was found acceptable for all other flow rates as specified by the NIOSH standards. Since . the recommended flow rate of air is between 1 and 2.5 liters per minutes and the calcula- lions for the lengthened plenum were made for 2 liters per minute of air flow, no differ- cnce is expected at either end of the flow rate range. It should be pointed out that the uniform distribution of heavier particles as seen hefe (/.<. > 5 pm) insures the uniform distribution of smaller particles (i.e. < 5 pm): Sample Preparation for Identification Since the index of refraction (ND) of most asbestos fibers is near to the refractive index of the chemically cleared membrane filter,: it becomes necessary to eliminate the pres- June, 197J ence of the filter. This can best be accom plished using a low tetjiperature asher. This method uses a very slpw oxidizing process, that will neither harm; nor disturb even the finest particles of asbestos or other non- . oxidizable material. Tjhis instrument allows the oxidation reaction to occur at a low temperature by converting approximately 20% of the molecular. oxygen to atomic oxygen5 with the use of a radio frequency field. The atomic oxygen reacts with the oxidizable materials id the specimen chamr ber. A mechanical vacuum pump then re moves the voltatile oxidation products. This method also eliminate^ many other bxidiz- able airborn particles! commonly found in industrial operations. ; Approximately four hours are required to lash" the filter. Sam- ., pies C and D were prepared by this ! tech nique. The pressure ojE the specimen cham-: < ber was maintained at (a pressure of 0.6 nim \ of mercury and 300 watos of power was used. ' The flow rate of thejoxygen was 150 pc/ : minute. " . ! . " . Identification and Measurements of Asbestos Fibers '' An extremely convenient and easy method of measuring particles;is with an image an alyzing microscope (IAM). With the aid of an IAM it is not difficult to measure 50 to 100 fields in a relatively short time. The particles can be bracketed in various size groups, and the measuring of a previously mapped out area can be accomplished. Data collected from 50 fields requires approxi mately 15 minutes. In order to determine the number and size of asbestos particles present on a filter, using the IAM, a multi-process procedure is used. The specimen! is first ashed (as has been outlined) to. eliminate the filter and any oxidizable particles such as lint. The area (or areas) of interest arc mapped out, measured, and all the! particles present are counted. This will give the total number of particles (asbestos and non-asbeStos). A sec ond measurement of tW exact same area is 8000 0335 HFM - 002039 American Industrial Hygiene Association Journal made after a refractive index liquid having the same refractive index as chrysolite6 is placed on the sample. This has the effect of making all the asbestos particles invisible and allows us to determine the number of non-asbestos panicles present in the sample. By this means, an accurate measure of only the asbestos panicles present can be made. Some care must be exercised when using the refractive index liquid, since the threshoM sensitivity of ebe' intsrument's detection system for proper functioning requires ap proximately 10fc difference in contrast. Minute shade variations due to the dose refractive index, similarities cannot be de tected. Consequently, the absolute matching of the vara6us refractive indexes among the different asbestos types is not necessary. For this experiment a refractive index liquid (KD 1.546) was used that very well coin dries with tfhe index of refraction of chrysotie (die mvOst widely used form of asbestos for industrial application) and also accept(Me far serpentine since the contrast prodiced is stSIl a shade below the detection Bait of die (instrument. On the average any ..fBceptible sshade difference produced by! a acfeaaxva imdex difference of ND = 0.010 kncoeptabUe to make proper measurements, ft is also reecognized that substances other dan asbestaos with refraaive indexes within ds nrae will be measured as asbestos. -His soacoeei of error cannot be totally elimfarted. hum. knowing the total material invokemaa: oa( the locality to be tested, and the type ait'rasbestos used, the proper choice of die ne&aacrive index liquid will minimize (Ms pszfl&em. The refractive index liquid usd for 'this study is available from the Gajillle Corporation. It contains aliphatic, ^.faiqgeniated and chlorinated hydrocarbons. ^orrrelattpn of the data is very simple. ^Sitce tlht measurements accumulated in the fits pmrt of the analysis encompass ali par':prresent, the calculated values do not R:rettw aeccurateiv the presence of the asbestos zdlone. Separating the asbestos partifc]-: tEfar freum all other .detectable features by _r - . 2J7 suppressing their visibility Iwith the refractive index liquid in the second portion of the analysis enables the data accumulation of the iion-asbestos content of the sample. Sample C and D were [analyzed with the IAM. Calculations, for. the asbestos fiber' content of the sample were carried out using the formulae published iii the appendix of the "Criteria Document."2 . Filter Area Field Area = K (1) Average Net Count x K Air Volue Sampled Fibers/ml (2) Measurements of Sample! C indicated that; only 0.2% of the particles Were non-asbestos, therefore, the sample wai viewed as being 100% asbestos. The particles were meas ured in six different size groups that ranged from 2 ftm to IS /tm. Qniy 163 particles or 12.7% were counted as being 5 /un or larger in the total partide population of 1,280. Most particles were found in the 2 jtm to 3 /tm range and the calculated average par- tide size was 2.9 /tin. The total fiber count of all sizes was 5.6 fibers jper milliliter, and' 12.7% of this or 0.6 fiber/ml were 5 /tnv or larger. -.. . : The analysis of Sample iD was carried out identically to Sample C.! Micrographs of Sample D are shown in ! Figures 6 and 7 before and after application of the. rtfrac- tive index liquid. It was found: that Sample D contained 31.9% of hon-asbestos parti cles. There was a total j of 53.8 particles counted per milliliter, but ijhe 31.9% or 16.8 particles of non-asbestos origin reduced this count to 37 fibers/mf. The size distribution measurements indicated tjhat 3.3% of the partides were 5 /uh orlarger. Consequently, for these sizes the liber count per milliliter was 1.1. The largest number of partides were again found to be in the 2 /tm to 3 /uh group, and die average particle size measured 2.3 /tm. These data are presented in Table III. 7 !~7"TT: "7 Iitf** "IM 8000 0336 .a m >i :* 3- i HFM- 002040 2J8 ; .V }**,$* > 9 * '* . *i**. 4-L ** . -r y-: *r..s >. ' > ' > :,?; .' vvr < .*r ,, r.. ' A ',*' . . - * * , * ' O. : ' ,* = > -- - * :... . . .... -?. ;. ... June, 1973 \ | .; ~*f4sSS^& . V-*?. * ..r\ ;C`: ^ w * .V??e'-*' IN .; *. , . * * \ , <a*r. u,I ^.'^^4 i\ _ /- y v Figure 6. Asbestos and non-asbestos particles before the application of refractive index liquid. JOOX. (Sample D). mmgra r t'* . Figure 7. Same area a^ shown in Figure .6 after; application of the refractive index liquid, 300X. (Sahiple D). ;' :. . TABLE nr . : ' Data from IAM .Analysis Sample . C % of Non-Atbestos. 0 % of Particlei 5 *m or > 12.7 Fiber Gbum. ml 5 iim or > 0.6 Average Panicle Size . 2.9 inn '. D 31.9 3.3 1-1 2.3 itm Discussion The .present use of the "total fiber count" system:' as recommended by the NIOSH for overall evaluation of asbestos concentrations , coupled with the "open-face" filter collection technique can be a source of error in the ; measurement of exposure to asbestos. The --low-number-of total particle xount and an approximately 1/9000 analyzed area of the " total filter surface (as specified by NIOSH) . along with the non-uniform particle distribu tion cannot produce 4 reliable analysis. The presence of asbestos resembling fibers also adds to the problems: : j The accuracy Of the IAM method relies on two important factjs, the large number of particles counted, anijl the large number of areas covered. It is also important that within these areas: aUj particles are counted. These factors will minimize the uncontrolla ble errors: There is no correlation between the results obtained bjy IAM and the micro scope counts of Samples C and D (Tables/ II and III). This is' due to the fact that Sample. D is .composed to .almost one-third of non-asbestos particles.. r- 8000 033? HFM - 002041 American Industrial Hspent Atsociaion Journal Acknowledgements The author is grateful to Dr. E. Eichen for the critical review of the manuscript, and to Dr. C. D. Melvin for the fruitful discuslions. I also wish to thank Mr. J. \V. Sprys and Mr. R. C McCune for their help with the sample preparation using the low tem perature asher. and Mr. H: B. Lick of the In dustrial Hygiene Unit for fabricating the sample holder and collecting the samples. References 1. Gilson. J. C.: Man ar.d Asositos. Ann S.Y. . And. JW.7J2.-9 (Dtc. 196.*.. . -' . ; 2J9 2. National Institute for Occupational Safety, and Health: Occupational Exposure to Asbestos. t.S. Department of Health,. Education; and Welfare. Rockville. Maryland (1972). ?. Tietjens, O. G.: Fundamentals of Hydro and Aeromechanics, p. 243, figure 176, Dover Publications, New York (1957). . V- 4. Ibid. p. 14J, Figures 74-75. ' . . 5. HoUaban; F. R.i Topics in Chemical Inslnir mentation. XXVII. Analytical. Applications of Electrodelessly Discharged Gases. J. Chem. Ed. 43:A401 (1966). , ; ; 6. MtCrune.W.C., R. G. i Drafty, and G. rJ. Delly: The Particle Atiaiy pp.. 154-165 Ann. Arbor Science Publisher^ Inc, Ann Arbor, Michigan.'- .' . .' Received July 26, 1972 ! . Industrial Waste Information Bulletin ;- A unique bulletin on industrial waste is being launched by die Haz- anrdous Wastes Service at A.E.R.E. Harwell (England) with the;support, off the Department of the Environment. Based on research papers,; govern- iment and company reports, the patent, literature, plant and equipment biTochures, other such sources, and the extensive library services ajnd tech nical expertise at Harwell, the Industrial Wastes Information-Bulletin will prrovide a convenient source of useful information oil current developments ini 'the treatment and disposal of industrial wastes. , ; '. Subscribers will, receive the Bulletin and will be entitled to other seirvices as well. A computer-based information service will cover every heem in the Bulletin and actual copies of the documents can be provided at maominal cost. A free assessment service is included as well as aiccess to a vwealth of information through the computerized filing and retrieval ifc syystem. The charge for the Bulletin and services will be nominal. Free ccopies of the hrs: Bulletin will be available in September-Octiober on Request to: : . The Manager, Industrial Wastes Information Bulletin The Hazardous Wastes Service Building 151 ; A.E.R.E. Harwell. Didcot. Berks. OXII ORA . ;' Endand .- . . . ' "ft :i *** ' . , v * HFM - 002042 BiO 00 0338>