Document dYveEZKqyRBBKr8ZNVbDVj1M6

AMERICAN PETROLEUM INSTITUTE 1801 K STREET. NORTHWEST WASHINGTON. D.C. 20006 JAMES M. McNEAMEY. M.P.H. Suff Toiicolocili Ervroc*T**ntl May 29, 1973 (202) 833-5742 TO: Committee on Medicine and Environmental Health SUBJECT: Collaborative Study of the Microscopic Counting of 7Csbestos''-Samples. " Gentlemen: Enclosed is a copy of a report prepared by R. S. Brief, Esso Research and Engineering Company, on a collaborative study by seven COMEH laboratories on a procedure for counting asbestos particles which was specified by NIOSH and endorsed by OSHA. In his cover letter to our office, Mr, Brief summarized: "As you will read, the method produces widely variant results on asbestos samples evaluated by either the same laboratory or different laboratories. As expected, the variation between laboratories is greater than within a laboratory. The results suggest that efforts to control work environments to below 5 fibers greater than 5 jam/cc (and 2 fibers greater than 5 |im/cc after July 1, 1976) will be fraught with difficulty because of the analytical procedure. . The laboratories who participated have been sent a copy of this report with their own laboratory identified. None of the labora tories have been told of the number identification of the others, except laboratory number I which is indicated in the report to be our own, the Medical Research Division of Esso Research and Engi neering Company. Although I have individually thanked the collaborators, I would again wish to express my appreciation to all those who helped bring this project to a successful, albeit disheartening, conclusion." Mr. Brief and the participants in this study are to be commended for this valuable service they have performed for the industry. Sincerely yours. HUT-113903 J s M. McNerney ABS-053903 COLLABORATIVE STUDY OF THE MICROSCOPIC COUNTING OF ASBESTOS SAMPLES By Richard S. Brief Esso Research and Engineering Company Medical Research Division p. 0. Box 45 Linden, New Jersey 07036 May 15, 1973 HUT-113904 o COLLABORATIVE STUDY OF THE MICROSCOPIC COUNTING OF ASBESTOS SAMPLES By Richard S. Brief Esso Research and Engineering Company Medical Research Division P. 0. Box 45 ' Linden, New Jersey 07036 Background Information 1 The term "asbestos" refers to any of six naturally occurring crystalline mineral hydrated silicates: actinolite, amosite, anthophyHite, chrysotile, crocidolice, and tremolite . The degree of hydration varies from approximately 1.5 percent in some deposits of crocidolite to.approxi mately 14.5 percent in the majoricy of the deposits of chrysotile. These minerals display a wide range of chemical compositions, as is indicated in Table 1. The several types of asbestos were formed by the metamorphosis of serpentine and amphibole minerals, both classes of which contain silica. Chrysotile, which is a hydrated silicate of magnesia, is the principal crystalline form of serpentine. Over 9071 of the world's asbestos production comes from chrysotile and it is the asbestos material used almost exclusively in the United States. The remaining five types of asbestos are crystalline forms of amphibole minerals. Crocidolite, frequently called blue asbestos, is associated with riebeckice. Amosite is the only asbestos of grunerite that is of commercial value. Anchophy1lite is thought to be evolved from the metamorphosis of olivine. Tremolite occurs in crystalline, dolomitic limestone and is called actinolite when iron is present in amounts.greater than 2 percent. * . Electron microscopy reveals that the smallest fibrous subdivision of a chrysotile fiber, called a fibril, has an average outside diameter of 0.034 micrometer (pm). Further, it has been shown that the chrysotile fibril is a hollow tube, rather than a solid cylinder, with an average inside dia meter of 0.018 pm. A suggested model views the chrysotile fiber as a cightly packed collection of fibrils, the interiors and interstices of which are filled wich cryscal fragments or amorphous material of the same chemical composition; the incerfibril binding forces are relatively weak so that each "fiber" can usually be subdivided into large numbers of "fibers" of the original length. The elementary crystal structure, or fibril, pf the amphibole asbestoses forms a solid cylinder considerably larger in outside diameter than the chrysotile fibril; the average outside diameter ranges from 0.1 to 0.2 pm. Although the majoricy of dry-milled asbestos fibers each contain many fibrils, smaller numbers of fibers composed of only one or two fibrils are always present; a considerable number of these fibers of smaller diameter are found in asbestos dust . HUT-113905 ABS-058910 n 0 GO sO E 3 - i-? C3l -2 - r*+> J--L o cl ^. o --e -* c *n vi co e3 .oc aj -r< > 3 Ea u CO *34 cCD u ua 2: U <3 <9 -- E ci 3 to U *o cSOm OfO I/O O o st a> 0 0 0*0 *J AJ iJ * 4J O qi t: n -* 3 -c* H3o vJW4 LV4 flJ H3 to 00 >1 -3 u o >S O6f +1 >o JZ fct 'Zt Cl C o jE vv4 Cl .vcr c to 3 c --oe M3 Q CO V &' >s oO 13 C V X. (c5 o-- cfl tC/O"t -m* --CM* %o oo <o V~l CM Uo uo (oJ 3 Cl O 4J Vl -rJ -C 3 3 J* O J3 +1 3-- X Oci av un 4 oB --41 aX 3 r- ^ CL Vi X a3 O >o-- nu 3 - cCiL 3 Ow a (Q v* jz u3 W 4J -- 3 3 T> ^ c <y OQ o ci E to u3 Cl tuo -O -uc u. O ^ H si 3 <0 O c co OflOO i/'l CM CM CO oo C\ O po r<r --4 rW oo O O M"'* U"* lf\ s-3*j ^ s> vO -- O OOG O *j i-> Cl o fM oCM* PLJ. r-> m o O O --* <0 CO uo a OC -EQ L-=* ci n 3 <4 t<0J 3e= %- eO c Xc_> o -*tf4l j dtcol oeCl o o uidl CCOl uC <C4l Ccl uu CEl .oc -l*~~ti a 0 oe o C--<PMoCO V3 X oCl pO tO&/pm--Q<rC:cmoC-: O r: 21 ac 3 O OPM a 2: a01. Voo o u a >s a O JZ u no o o CD CO m o Cl Vu3-* K41 ^ -s. i (.0 m < 3 t- J HUT-113906 Workmen handling or working with asbestos and asbescos-concaining materials have experienced adverse health effects. Inhalation of the asbestos fibers has been found to be .eciology of disease. Thus, to minimize the effects resulting from exposure, ic is essential to control the release of fibers into the breathing zone- Assessment of airborne concentrations of asbestos fibers is necessary to assure that controls are effective and workmen are not exces sively expc;ed. Of the various ways to sample and analyze suspended asbestos fibers in air, with particular relation to the respiracory hazard they create, the generally recognized best method today is collection on membrane filters and analysis by microscopic counting at 400-450X magnifications under phase-contrast illumination. This procedure was collaboratively tested and is the subject of this report. Health Experience and Exposure Limits -- Asbestos fibers can cause asbestosis (a form of lung fibrosis), lung cancer, and mesothelioma of the pleura and peritoneum (a form of cancer of the lining of the lung or abdominal cavity). This knowledge has arisen from studies of asbestos miners in South Africa and from asbestos fabricators in Great Britain. Epidemiologic studies of unionized asbestos workers in the United States also reveal an increased incidence of these diseases among chose workers. It is important to recognize, however, that working with asbestos-containing materials per se does not necessarily produce the conditions noted. For example,in the petroleum industry a medical evaluation of over one hundred insulators, with 20 or more years experience, revealed that they showed no lung impairment of any type. This continuing study covers approximately 3000 man-years of exposure to asbestos fibers and suggests that there must be a threshold dose for producing asbestos created disease^. As a result of Che untoward experience with asbestos, limits'for airborne concentration have been set by various grours. In the United States, Che present Limit established by the Occupational Safety and Healch Admin istrat ion3 (OSHA) is related to fibers longer than 5 um (a fiber traditionally relates to a structure which has a length to width ratio greater than 3:1). According to OSHA, Che permissible exposure to airborne concentrations of asbestos fibers are shown in Table 2. TABLE 2 OSHA EXPOSURE LIMITS Effective Dace Until June 30, 1976 After July 1, 1976 Fibers Greater Than 5 pm Per Cubic Centimecer of Air 8-Hour Average Ceiling 5 10 2 10 HUT-113907 ABS-058912 -4 - The method of measurement requires that air samples be collected on membrane filters and that-the fiber counts be done at 400-450X magnifi cations (with a 4 mm objective) using phase contrast illumination. The Asbestos Textile Institute^ and the National Institute for Occupational Safety and Health (NIOSK)^ have described this optical method in detail.- The NIOSH procedure is appended. t ___ Evaluation of the Method Early efforts Co standardize this method among government agencies suggested wide variation between resulcs obtained by operators in different laboratories^- This was disquieting since the OSHA standard could be vio lated by the variability of the measurement scheme This could create a health problem if the asbestos count was in error on the low side and an excessive requirement for controls if the counts erred on the high side-. Methodology which is required as part of regulations should proper!y-Mre tested to understand the variance to be expected so that this information could be incorporated in implementation plans. A review of the possible reasons for the variation suggests chat the errors could reflect operator capabilities with microscopic counting procedures. In addition, different microscopes and optics, including the filters and magnification, could affect results. The operator is required to make judgments during the counting procedure to define the fibers to be included in the count. The rules of counting are not clearly defined by Che regulations; but we offer some below, based on cotunents made by Scheinbaum . 1. The fibers must fit inside or pass through two predesignated sides of the viewing area formed by a counting reticle. If the fibers pass through either of the undesignated .sides chey are not included in the count. When the fiber count is very low a full field count is also acceptable pro vided a flat field objective is used so chat aberrations at the edges are-' min i miz ed . 2. Fibers which just meet at the end or along one length so that they appear to be "L", "T" or "Y" shaped are counted as one fiber. However, fibers which cross so that four ends can be seen are counted as two separate fibers . 3. A clump or mass from which several fibers emanate are counted as one fiber . During counting, when it is possible to separate non-asbestos fibers from the count this should be done. Glass, mineral wool, synthetics, and natural fibers if included would bias the overall count upward. Typically, these other fibers have a different appearance chan asbestos and where it is obvious that they are not asbestos fibers, chey should not be included. For HUT-113908 A3S-053S13 5 example, fiberglass fibers are long and straight with a uniform diameter, typically larger than asbestos, and with ends which appear to be firepolished glass tubing. Mineral wool fibers show an uneven diameter along their length and often have a bulbous center from which numerous fibers, emanate. Because the regulations refer to 5 pn or greater in size, the selection of this length requires another judgment. For the Porton reticle used in our laboratory, a size greater than Porton Reticle number 6 was used to determine those fibers greater than 5 pm. Background counts must be considered because the membrane filters can contain fibers which may be subsequently counted. However, this is usually a minor problem. It has been mentioned that the materials once mounted, should be promptly counted to avoid changes in the sample with time resulting from such things as crystal growth, particle migration, evaporation of mounting material, and the like. Sometimes it is difficult to make prompt counts and here is where further work was indicated. Finally, the calculation relating the count to the air concen tration involves definitive measurements of the counting area related to the filtering area and a knowledge of the total air volume of the sample. A stage micrometer is usually used to accurately define the optical counting area and the filter area must be carefully measured. The accuracy of the rotometer used during sampling must also be checked by suitable calibration mechods. Because of the uncertainties described above, it was deemed worthwhile to establish a collaborative test among several industrial laboratories who were actively involved in assessment of asbestos fiber concentrations in air. The technique involved mounting 9 actual asbestos samples plus one blank membrane filter on slides and distributing them to the participants on a random schedule- The mounting media contained 0.05 grams of membrane filter per ml of 1:1 solution of dimethyl phthalate and diethyl oxalate . The samples were prepared by cutting a wedge-shaped piece of the membrane filter (Millipore Filter Paper Type AA) while in che filter holder (a three-piece plastic container obtained from the Millipore Corporation, Bedford, Massachusetts). The piece was removed from the filter with a scalpel and forceps and placed dusc-side up on a drop of che mounting media, which in turn, had been placed on a freshly cleaned, standard (35 mm x 75 irnn), micro scopic slide, a number 1-1/2 cover slip, carefully cleaned with lens tissue, was placed over the filter wedge. Slight pressure on the cover slip achieved contact between it and the mounting media. The specimen was rendered trans parent by absorption and transfer of the mounting media into che filter. The ten specimens were prepared and counted in our laboratory within one day after preparation. The technique used was chat described in che Appendix. HUT-113909 A33-053914 -6 The specimens were then sent by mail to each of six other parti cipants for their count of these samples- A repeat count was made in. our laboratory at the completion of the round-robin test- Air filtration data was provided and each laboratory was requested to calculate the respective number of fibers greater than 5 fim per cubic centimeter of air- ..Details on the microscope and opcics used was also requested. Elapsed time betveen measurements was obtained. The results were statistically analyzed at the Esso Research and Engineering Company. HUT'113910 ABS-C5S915 O '7" STATISTICAL EVALUATION The fiber concentrations obtained by the seven laboratories on the ten samples are shown in Table 3 in terms of the number of the. fibers greater chan 5- pm per cubic centimeter of air. As shown in the bottom of Table 3, the standard deviation appears to be a function of the mean value. A direct analysis of the data wouJ.d, therefore, be over whelmed by the greater magnitude of variation for the higher concentra tions. To minimize this effect, a logarithmic transformation of the data was made with the following adjustments: 1) data from sample 2 were eliminated (this was the blank sample); and 2) the data for sample number 3 from laboratory number 5 was changed from zero to the equivalent con centration for one counted fiber (viz. 0.48 fibers/cc). Zero values are not permissible if a log transform is used and these adjustments were considered reasonable. Table 4 shows the transformed data (natural logarithms were used). TABLE 3 Overall Results Laboratory 1 Number 2 3 4 5 6 7 Mean Standard Deviation 12 Fibers > 5 um/cc air Sample Number 3456 7 8 9 10 53.7 29-3 28.4 28.0 43-2 45 .9 42 .4 .48 .07 2.54 .00 .00 .39 . 19 -95 .66 3.0 2.1 .-00 .39 38 33-7 19-3 17.9 19.0 23-1 18.7 33 -0 .95 .84 3.0 1.6 .95 .20 .66 43 .2 17.6 33.3 39.0 22.8 26.5 54.1 8.6 3.5 5-1 4.7 2.4 1.6 4.6 21.9 8-2 13.5 9 .5 20.4 11 .0 9-6 28.5 18.4 19 .2 19-0 18.1 23-6 29.7 50.7 25.8 26 .4 28.0 22 .3 53.1 38.7 .55 1.1 23-5 1.2 33.8 4.4 13.4 22 .4 33.3 10.2 .90 l.l 6.9 .9 12.7 2.7 5.5 5-0 12.9 HUT-113911 '\ 'x _ yJ ABS-05B91S 8 TABLE 4 Log Transformed Daca 134 Sample Number 56 7 .8 9 io Laboratory 1 Number 2 3 4 5 6 7 3.98341 3-37759 3.34639 3.33220 3.76584 3-82647 3.74715 -.05129 -.41552 1.09861 .74194 -.73397* -.94161 -.96768 3.51750 2.96011 2.88480 2 .94444 3.13983 2.92852 3.49651 -.05129 -.17435 1.09861 .47000 -.05129 -1.60944 -.41552 3.76584 2.86790 3.50556 3.66356 3.12676 3.27714 3.99083 2.15176 1.25276 1.62924 1.54756 .87547 .47000 1.52606 3.08649 3.34990 2.10413 2.91235 2.60269 2.95491 2.25129 2 .94444 3.01553 2.89591 2.39790 3-16125 2.26176 '3-39115 3 -92593 3.25037 3-27336 3.33220 3 10459 3.27714 3-97218 Mean 3.62558 -.18135 3.12453 -.10475 3.45680 1.35041 2.53140 3.08713 3-44797 Standa rd Deviation .26720 .82301 .27337 .83163 .39026 .54770 .38711 .21289 .34959 * In 0.48 In Table 4, the standard deviation ts now less affected by the value of the mean so that the analysis of variance can properly include all the data tabulated. Table 5 shows the analysis of variance (2-way classification) for the data in Table 4. Note that the total degrees of freedom were'diminished by one to account for the substitution of 0.48 fibers/cc in place of 0.00 for sample 3, laboratory 5- The conclusions that can be drawn from Table 5, are as follows: 1- Different laboratories give significantly different results on the same sample. 2. Gross differences in sample concentration are observed with high probability. 3. A 95% confidence interval for fiber concentrations can be derived from the error mean square (.20655) as follows: 1-96 \/.20655 = .89078 .89078 e 2.437 HUT-113912 ABS-053917 9 The 95'i confidence interval for results is, therefore, Lower .Limit = X 2.437 Upper Limit = 2.437 X where X = fibers > 5 um/cc. For example, a fiber concentration of 5 fibers > 5 um/cc measured in one laboratory could be reported (957. of the time) as 2.1 to 12.2 fibers > 5 /jm/cc in other laboratories; and a fiber count of 2 fibers > 5 um/cc could be reported as 0.8 to 4.8 fibers > 5 um/cc. To assure that the. ceiling value of 10 fibers > 5 pn/cc is not exceeded, these data also sugg&&t that no value should exceed 10/2.437 or 4.I fibers > 5 um/cc. TABLE 5 Analysis of Variance On Log Transformed Data Without Sample 2 and Adjustment of Sample 3 (Laboratory 5) Source of Variation Laboratories Samples Error -Total _ Sum of Squares 3.93353 130.29369 9.70773 143.93495 Degrees of Freedom 6 8 47 61 Mean Square .65559 16 .28671 .20655 F 3.1 7 -78.8** -*4 *Significant at > 957. Probability. **Significant at > 997. Probability. In an attempt to separate the random error within the laboratory, repeat counts were made in Laboratory l on the cen samples after 149 days had elapsed. The replicate results taken by the same operator in Laboratory i are shown in Table 6 . a non-parametric sign-rank test of these results showed that the amount of time between anaLyses did not influence results. In addition, a parametric analysis of these paired results was done after a logarithmic transformation of the data and rejection of sampLe number 2. HUT-113913 ABS-058913 10 TABLE 6 Repeat Results in Laboratory Sample I 2 3 4 5 6 7 8 9 10 Fibers > 5 pm/cc. On On Day 1 Day 149 53.8 .48 .95 33.7 .95 43.2 8.6 21.9 28.5 50.7 49.8 .48 1.9 31.7 2.9 50.3 5.0 20.9 35.4 37.6 The analysis of variance ts shown in Table 7.. As anticipated the effect of time is seen to be nonsignificant. (The sample differences are significant, as expected.) The error term is related to one operator in one laboratory and, therefore, does not constitute a uniform result for all laboratories. However, using the same interpretive method described previously, the results in this laboratory, at least, are considered to fall within a 957, confidence interval when results are multiplied and divided by 2.0. The geometric methodology for determining acceptable limits of fiber concentrations seems reasonable, although disheartening, because of its magnitude. TABLE 7 Analysis of Variance on Replicate Sample s Source of Variation' Sum of Squares Degrees of Freedom Time Samples Error Tota 1 .07371 33.21484 1.02202 34.31057 1 8 8 17 **Significant at > 997. Probability Mean Square -07371 4.15186 .12775 F -58 32.50** HUT-113914 A3S-Q58919 The blank filter reported as sample number 2 (if one excludes the results from laboratory number 3) would be, on average, about 6.2 fibers per cc. It follows, then, that the sealed filters from Mil 1ipore do not contribute significantly to the evaluation of asbestos fiber concentrations in air'. '_ Conclusions Microscopic examination of asbestos fibers > 5 fim at 400-450X magnifications with phase contrast illumination was collaboratively tested in 7 industrial laboratories using mounted specimens of 9 asbestos samples collected on membrane filter paper and one blank filter. An analysis of variance shows that different laboratories can be expected to get significantly different results on the same sample. " A geometric methodology for determining confidence limits of fiber concentration suggest that 95% of the time a result in one laboratory multiplied and divided by 2-437 wouLd be the expected.range of results reported on the same sample in other Laboratories. Even within one laboratory, although this factor was not extensively tested, the 95% confidence interval would be expected to fall within the measurement result multiplied and divided by 2.0. The blank filter (Millipore Type AA three-piece filter assembly) contributes little to the overall count, averaging about 0.2 fibers greater than 5 um per cubic centimeter of air. HUT-113915 REFERENCES 1. Environmenta1 Protection Agency. Control Techniques for Asbestos Air Pollutants. AP-117. U. S- Government Printing Office, Washington, 0. C. February 1973- 2. Weaver, N-, M.D. Personal Communication. May 14, 1973. 3. Occupational Safety and Health Administration. Federal Register. 37(202) .-22102-22356. CFR Title 29-Chapter XVII - Part 1910.93a Asbestos. October 18, 1972. 4. Asbestos Textile Institute. Measurement of Airborne Asbestos _Elber.. by the Membrane Filter Method. Asbestos Textile InstitutePompton Lakes, N. J. 1971. 5. National Institute for Occupational Safety and Health. Criteria for a Recommended Standard -- Occupational Exposure to Asbestos. HSM 72-10267. 1972 . 6. Lynch, J. R. Personal Communication- October 31, 1972. 7. Scheinbaum, M. Asbestos Measurement. Presentation at the American Industrial Hygiene Association Quad Section Meeting., New York, N- Y. December 1, 1972- RSB:ecb 5/15/73 HUT-113916 13 ACKNOMLEDGiENT The assistance and cooperation of the participating laboratories is acknowledged with sincere appreciation for the voluntary efforts of the staff members who represented the following organizations- Name Organization R- G- Confer Esso Research and Engineering Company Linden, New Jersey R- M- Curtis Shell Development Company Houston, Texas E. K. Daniels Mobil Oil Corporation New York, New York --- E. N- Davis Atlantic-Richfield Company Harvey, Illinois R. L. Stoffer Standard Oil Company (Indiana) Naperville, Illinois F. M. Toca Gulf Oil Corporation Pittsburgh, Pennsylvania R. W. Veit Phillips Petroleum Company Bartlesville, Oklahoma Thanks are also due to Messrs. H- T- Oakley, Esso Research and Engineering Company, and R. Spirtas, University of North Carolina for-'' their assistance in evaluating the data. HUT-113917 ABS-058922 APPENDIX Sampling and Evaluation Procedure HUT-113918 o f) 15 APPENDIX Sampling and Evaluation Procedure"* . Principles of Sampling V A dust sampling procedure must be designed so that samples of actual dust 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. In order to collect a sample representative of airborne dust., which is likely to enter the subject's respiratory system, it is.necessary to position a collection 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. In order to obtain representative samples of workers1 exposures, it is necessary to collect samples under varying conditions of weather, on different days, and at different times during a shift . 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 percen tage can be determined from work Schedules and by observation of work routines. The daily average weighted exposure can be determined by using the following formula: (Hours X cone task A) +(Hours X cone, task TS) 8 Hours (or actual hours worked) -+___________ etc . The concentration of any air contaminant resulting from an industrial operation also varies with time- Therefore, a longer sampling time will better approximate the actual average. With the following recommended sampling procedure, ic is possible to collect samples at the workers' breaching 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, dusc exposures of a more normal work pattern result from the use of personal samplers. In evaluating daily exposures, samples should be collected as near as possible to workers' breathing zones. HUT-113919 ABS-058924 16 Collecting Sample The sample should be collected on a 37-mj.llimeter Millipore Type AA filter mounted in an open-face filter holder. The holder should be fastened to the worker's lapel and air drawn through the filcer by means of a battery-powered personal sampler pump.1 The filters .are con tained in plastic filter holders and are 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 face-caps should be removed. Sampling flow rates from 1.0 liter per minute (1pm) up to the maximum flow rate of the personal sampler pump (usually not over 2.5 lpra) and sampling time from 15 minutes to eight hours are acceptable provided the following restraints are considered: (a) 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 distribu tion, a count of 100 fibers in a sample would have a standard deviation of \J 100 or 10 fibers or + 10%. Thus the 95Z confidence limits would be approximately 2 standard deviations or + 20%. Since the 37 mm filter has an effec tive collecting area of 855 and if the projected field area of the Porton reticle is 0.005 tnm^, then each field represents 1/171000 of the sample. Based on this ratio the following number of fields must be counted to measure the various limits in various sampling times: Sampling Time Minut es 10 15 30 90 90 240 240 480 Flow Rate 1pm 2 2 2 1 2 1 2 1 Number of Fields for 100 Fibe'rs 0-2 fibers/ml 2 .0 fibers/mi 10 fibers/ml 4350 2860 1430 1000 500 260 180 180 435 286 143 100 50 26 18 18 9T 58 29 20 10 7 4 4 (b) Do not count a field containing over 20 fibers because in addition to the fibers being counted, chere are also present a number of grains, which interfere with the accuracy of the count. HUT-113920 ABS-058925 17 Based on these restraints, i.e., number of fields to be counted and maximum number of fibers per field, acceptable sampling parameters for the various limits are underlined' in the above table. * The following conclusions may be drawn from this analysis: (1) The short-term limit should be for a period of at least 15 minutes and preferably 30 minutes- (2) The 2.0 fiber/cc limit may be evaluated over periods of from 90 Co 480 minutes. As many fields as required to yield at least 100 fibers'"5hout'd be counted. In general the minimum number of fields should be 20 and the maximum 100. Mounting Sample The mounting medium used in this method is prepared by dissolving 0.05 g 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 the filter with a scalpel and forceps and placed dust-side-up on the drop of mounting solution- A No. 1-1/2 coverslip, carefully cleaned with lens tissue, is placed over the filcer wedge. Slight pressure on'the coverslip achieves contact between it and the mounting medium. The sampLe may be examined as soon as the mount is transparent. The optical homogeneity of the resulting mount is nearly perfect, with only a slight background granularity under phase contrast, which disappears within one day. The sample should be counted within two days after mounting. Evaluation The filter samples mounted in the manner previously, described are evaluated in terms of the concentration of asbestos fibers greater than 5 pm in length. A microscope equipped with phase-contrast optics and a 4-mm "high-dry" achromatic objective is suitable for this determination. 10X eyepices, one of which contains a Porton or other suitable reticle at the level of the field-limiting 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 counced and total asbestos fibers longer than 5 pm are recorded. Any particle having an aspect ratio of three, or greater is considered a fiber. ASS-058926 HUT-113921 () 18 The following formulae are used co determine the number of fibers/mL: 2 U) Filter area (mm ) 2 Field area (mm ) K (2) Average net count X K Air volume sampled (ml) f ibers/tnl For example, assume the-following: area of the filter used was 855 mm^, counting area of one field under the Porton reticle was 0.005 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 mm^ 2 0.005 mm 171,000 (K) 10 fibers x 171,000 2,000 ml/min x 90 min 9.5 fibers/ml 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 co the correct interpretation of an instru ment's indication. The frequency of calibration is somewhat dependent on the use, care, and handling to which the pump is subjected. Pumps should be calibrated if they have been subjected to misuse or if they have just been repaired or received from a manufacturer. If hard usage is given the instrument, 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 instrument used as a reference. The choice of calibration instrument will depend largely upon where the calibration is to be performed. For laboratory testing, a 1-liter burette or wet-test meter should be usedIn the field, a rotameter is the most convenient instrument used. The actual set-up will be the same for all of these instruments. The calibration instrument will be connected in sequence co the filter unit which will be followed by the personal sampler pump. In this way, the calibration instru ment 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 filter with a different pore size. The burette should be set up so that the flow is toward the narrow end of the unit. o ABS-058927 HUT-113922 19 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 condi tions 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 pulsation 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 splrbmeter, Marriott's bottle, or drygas meter. The burette and wet-test meter were selected because of their accuracy, availability, and ease of operation. HUT-113923 ABS-058923