Document rx4Qe5EVmL7bdR8aZ3vzNrDxr

ASBESTOS FIBERS IN AIR Nation! Institute for Occupational Safety and Health Analytical Method Analyte: Matrix: Procedure: Date Issued: Date Revised: Asbestos fibers Air Filter coliectihn, microscopic count 3/30/77 Method No.: P&CAM 239 Range: 0.1-60 fibers/em* Precision (C V ^: 0.24 to 0.38 Classification: D (Operational) 1. Principle a t the Method 1.1 This method describes the equipment and procedures for collecting, mounting, and counting asbestos fibers on cellulose ester membrane filters in the evaluation of personal samples of airborne asbestos fibers. The purpose of the method is to determine an employee's index a t exposure to airborne asbestos fibers. The method is primarily a personal monitoring tech nique, but can be used for area monitoring. 1.2 The sample is collected by drawing air through a membrane filter by means of a battery powered personal sampling pump. The filter is transformed from an opaque solid membrane^ to a transparent optically homogeneous gel. The fibers are sized and counted using a phasecontrast microscope at 400-450X magnification. 1.3 Definitions. Asbestos fiber, for counting purposes, means a particulate which has a physical dimension longer than 3 micrometers and with a length to diameter ratio of 3 to 1 tn greater. Asbestos includes chrysotije, cummingtonite-grunerite (amosite), crocidolite, fibrous tremoUte, fibrous anthophyllite. and fibrous actinoiite. 1.4 Any laboratory attempting to use this procedure should have at least one counter attend a training course conducted by an experienced, proficient laboratory. Novice, untutored counters, using cmly published instructions, can easily obtain counts of half thoso performed by experi enced, proficient counters. Large differences between laboratories can be caused by: 1) dif ferences in technique and observing ability among counters and 2) smatl, but significant, dif ferences between microscopes meeting the basic specifications of Section 6.2. The following procedures are recommended: 1.4.1 All miciDscopists who perfotm asbestos counting should meet together for an "asbestos counting workshop" at least quarterly. This is best accomplished with counters from several laboratories using their own microscopes. 1.4.2 Each microscopist should count the same series of slides and with the results being ' compared. 1.4.3 Differences between counters should be resolved with side-by-side counting of the fields by the different counters. 1.4.4 Individuals who are found to be persistent outliers over several sessions should ha encouraged to seek other tasks in their respective laboratories. 239-1 PLAINTIFF'S EXHIBIT WCD-187 2. Rrajf*' and Sensitivity 2.1 The usable range is primarily a function o f sample volume, microscope count field area, and background airborne particulate. The influence of these variables is discussed in 8.1.3. For a microscope count field area of 0.003 mm2 (see Figure i) and a pump flow rate o f 1.7 lpm, the optimal fiber densities would be produced over the range of 0.4 fiber/cm* (8-hour sam ple) to about 60 fibers/eni* (13-minute sample). F o r a field area of 0.006 mm3 (see Figure 2) and a pump flow rate of 1.7 lpm, the optimal range is 0.2 fiber/cm3 (8-hour sample) to about 30 fibera/cm" (15-minute sample). In each case, the optimal detection limits are in versely proportional to pump flow rate. The upper detection limit can be extended by using sample times less than 15 minutes or using lower flow rates. The lower detection limit can be extended by increasing the flow rate up to about 2.5 lpm. Filter surface fiber densities less than optimal (less than about 0.5 to 1.0 fiber per count field) are still adequate, but will lead to decreased precision for the method (in creased coefficient of variation, see Section 4). The minimum total fiber count in 100 fields considered adequate for reliable quantitation is 10 fibers. Thus, the lower limit of reliable quantitation is 0.1 fiber/cm3 (100,000 fibers/ m8). F o r this level, a flow rate of about 2.5 lpm is recommended. For k field area of 0.003 mm2, the minimum sample time would be about 2 hours. For a field area of 0.006 ram8, the minimum sample time would be about 1 hour. 2.2 This method considers only fibers with a length to diameter ratio of 3 to 1 or greater and a length greater than 5 micrometers. 3. Interferences In an atmosphere known to contain asbestos, all particulate with a length to diameter ratio of 3 to 1 o r greater, and a length greater than 5 micrometers should, in the absence of other information, be considered to be asbestos fibers and counted as such. 4. Precisian and Accuracy 4.1 lln the past decade, there have appeared a number of articles examining sources of variation in the asbestos sampling and counting procedure. These include: Lynch et al. (11.1), Weidaer and Ayer (11.2), Conway and Holland (11.3), Leidel and Busch (11<4), Beckett and Attfield (11.5), and Rajhans and Bragg (11.6). The sources of variation will be discussed by stages in the membrane filter evaluation procedure. 4.2 Sources of Variation in the Sampling Process. These include variations in pump flow rate, proximity of the filter to the employee's body, and filter location (left to right) in the em ployee's breathing zone. 4.2.1 Section 9.1 requires that the personal sampling piimp be calibrated with sufficient accuracy such that ti 95% confidence limits on the flow rate are : 10% . This is equivalent to a coefficient of variation (CV) of about 5% . However, this CV makes a negligible contribution to the total CV for the method due to the relatively large CV of the counting procedure. 4.2.2 Conway and Holland (11.3) concluded that positioning of the filter cassette on the wearer (regarding th angular portions o f the filter and their proximity to the wearer) is not a significant factor in determining the fiber distribution on filters. 4.2.3 Weidner and A yer (11.2) concluded that there is no appreciable difference between samples collected on either the right o r left sides of a breathing zone or between samples collected side-by-side, especially for samples with concentrations less than 2 5 fib e ra /c m 3. WCD 001730 239-2 : 4.3 Sources ol Variation in the Counting Procedure 4.3.1 Random variations exist in the fiber distribution on a filter wedge (intra-wedge vari ability). The industrial hygiene literature has seen considerable debate in the last 20 years concerning whether or not the distribution ol mineral dust or asbestos fibers on a filter surface is adequately described by a Poisson distribution probability density function. Leidel and Busch (11.4) found excellent agreement between empirical error variance and theoretical variance calculated from the assumption of Poisson dis tributed true counts. They concluded that there was not excessive variation among count fields for a filter wedge and that clumping of fibers (non-random coalescence) did not occur. 4.3.2 Variations exist in the fiber distribution on the total filter surface (inter-wedge vari ability) due to the random or non-random distribution of fibers across the total sur face of the filter. This type of variation is easily confused whh intra-wedge variations. The count procedure does not requite counting of multiple sectors of the filter. There may be significant differences between average counts for different wedges, or the fiber distribution variations for the total filter surface may be greater than the variations of the Poisson distribution. If either of these occur experimentally, one must use the experimental variations to estimate the minimum precision of the count procedure. The minimum precision is governed by the variations of the fiber distribution on the total surface of the filter. Conway and Holland (11.3) concluded the distribution of fibers on filters is not uni form and the distribution of fiber counts is more disperse than Poisson. For their filters which had significant variations in fiber concentrations between sectors (as much as 50-60% of the total filter mean), they described the following relation for the standard deviation o f the total number of fibers counted on a wedge (N) empirical s(N) - 1.6 (N)1,a where N is about 100. The Poisson standard deviation would be: Poisson o (N) -- (N)' ,! Rajhans and Bragg (11.6) in Series I of their study found significant variation between filter segments and rejected the Poisson distribution for the total filter surface. How ever, in Series n of their study, utilizing various experimental modifications, they found no significant variation between filter segments and no reason to reject tbe assumption of Poisson distributed fiber counts. 4.3.3 Systematic variations due to differences between microscopes were studied by Leidel and Busch (11.4). In their study using five different brands of microscopes, they found no significant differences among four, but the fifth gave counts approximately 43% higher on the average than the other four. 4.3.4 Variations due to differences between counters should be examined at three levels: experienced counters occasionally counting, experienced counters routinely counting, and inexperienced (new or untutored) counters. Leidel and Busch (11.4) studied five experienced counters, with one counting only occasionally. There were no significant differences among three of the counters, but a fourth was 16% lower than the first three. The fifth, who occasionally counted, averaged 27% higher than the first three. Conway and Holland (11.3) studied three experienced counters and three Inexperienced counters. They found statistically significant differences between the means of both the experienced and inexperienced counters that typically were in the range plus or minus 5 to 13% . They concluded that experience as a fiber counter is not a significant param eter affecting intercounter variations. 239-3 Rajhans and Bragg (11.6) found no significant differences among means of five experi enced counters in Series I o f their study. But in their carefully controlled Series 11, an analysis of variance showed significant variations between counters that were plus or minus L to 15% . 4 5 ,5 Variations between laboratories arc most likely due to systematic biases and are not a significant additional source of random variations. Any additional variations are most likely due to differences in counting technique. Beckett and Attfield (11.5) ob served that standard counters improved greatly after personal instruction; also new counters, after instruction, tended to overcompensate and get exceedingly high counts. Additionally, they found that counts from an experienced laboratory that had not had contact with other laboratories performing the same analysis were as far from the standard values as were the counts by new counters. 4.4 Sources of variations between samples taken at different times on one employee during one work shift can affect the exposure estimate for that employee. These are primarily due to a) differences in exposure concentrations during the day, b) differences in location of the employee within the plant, and c) differences in work operation performed by the employee during the day. These sources of variation can be controlled by proper choice of sampling strategy. Refer to Leidel and Busch (11.7) and Leidel, Busch, and Lynch (11.8) for an extended discussion of sampling strategies. Interday temporal variations can affect the ex posure estimates obtained on different days. Refer to Leidel, Busch, and Crouse (11.9) For a discussion of this type of variation. 4 5 Until recently, the total coefficient of variation (CVT) for the sampling and counting procedixe was best estimated from the work of Conway and Holland (11.3). The conclusions of their study included: 4 5 .1 The precision of their procedure for filters not containing an abundance of fine fibers can be estimated by a coefficient of variation of 16.2% . This value includes variation among counters and observed interaction effects. 4 5 -2 The accuracy of the procedure for similar filters may be estimated for a 100-fiber count by a coefficient of variation of 21.4% , This assumes that the contribution of the overall variance from die nonuniform fiber distribution is additive. 4.5.3 A high percentage of very fine fibers on the filter can significantly ,affect the standard deviation and confidence limits for counts by different ccuaters. After combining variations in fiber concentrations over the entire filter with those for different counters, it was concluded: a. F o r filters with a low concentration of fine fibers, the coefficient of variation is estimated at 21% and the 95% confidence interval is 43% . b. F o r filters with a high concentration of fine fibers, the coefficient of variation is estimated at 25% and the 9S% confidence interval is 50% . Lynch, Kronoveter, and Leidel (l t . l ) have also reported on variations of the method. Their intralaboratory study utilized the data from a large number of dust counts made by different methods by experienced counters over a period of years in an epidemiologic study of the asbestos products industry. They concluded that the standard deviation of counts of fibers longer than 5 micrometers on membrane filters could be estimated from the relation <r = (N)0 *"1. Thus for counts of about 100 fibers, the coefficient of variation could be estimated at about 15.2% and the 9$% confidence limits at - 30.4% . These values are lower than the values reported by Conway and Holland (11.3). Recently, the Johns-Manyille Corporation conducted an in-house Investigation of the asbestos count method (11,10). The study data contained total fiber counts for over 239-4 WCD 001732 too filters with each filter counted by two to five counters. From the Johos-Manville data, NIOSH calculated over 100 estimates of the count CV for the method (11.11). The NIOSH CV estimates included random intrafilter variations and intercountcr variations, but did not include random pump Bow rate variations. It was found that th e count coefficient of variation (all random variations except for pump variations) was a function of the total fiber count. NIOSH then included a CV of 0.05 for ran dom pump variations (sec Section 9.1) in the CV-estimator equation to obtain a C V restim ator. The CVx-estimator line is plotted on Figure 3 for total fiber counts in the range 10 to 100 fibers. Or the following equation can be used: CVT - [antik>gio(--0.215 - 0.203 (log,FB)) + 0.0025P where FB is total fiber count as discussed in Section 10. Figure 3 demonstrates that for a total fiber count of 100, the best CVT is attainable with the appropriate sampling times given in 8.1.3 and the count rules in S.3.9. When malting decisions regarding compliance with the OSHA asbestos exposure standards in 29 CFR 1910.1001, the statistical procedures given in Leidel et al. (11.11) should be followed. The procedures are based on statistical theory and assumptions given in References 11.12, 11.13. Because of the possibility of systematic biases due to differences between microscopes, counters, and laboratories as discussed above, it is strongly recommended that any laboratory counting asbestos should participate in an interlaboratory quality control program that includes the counting of standard reference filters. These standard fitters are available from NIOSH through the Proficiency Analytical Testing (PAT) Pro gram. The PA T Program is used by the American Industrial Hygiene Association (A1HA) as part of its Laboratory Accreditation Program. Each laboratory's quality control program must include protocols for routinely adjustihg and calibrating sampling and counting equipment plus training and evaluation programs for counters. 5. Advantages and Disadvantages of the Method 5.1 The method is intended to give an index of employee exposure to airborne asbestos fibers of specified dimensional characteristics. 5.2 It is not meant to count all asbestos fibers in all size ranges or to differentiate asbestos from other fibrous particulates. 6. Apparatus 6.1 Sampling Equipment The personal sampling equipment train consists of 1) persona] sampling pump, 2) tubing, 3) clothing spring clip, 4) tubing-to-field monitor metai adaptor, and 5) field monitor (filter and holder). 6.1.1 Personal Sampling Pump. The pump must be capable of sampling at 1.0 to 2.5 liters per minute (Ipm) against a flow resistance of 7.5 inches of water (1.4 cm Hg) tor S continuous hours on a fully charged battery. 6.1.2 Tubing. Laboratory tubing such as rubber or plastic with 6:mm bore and about 100 cm length. 6.1.3 Clothing Spring Clip. The clip attaches the rubber tubing to the lapel or shirt o f the individual being monitored, 6.1.4 Tubing-to-field Monitor Adaptor. A short metal adaptor with ridges on one end to grip the inside of the tubing. The other end is designed for a pressure fit into the field monitor. 6.1.5 Field Monitor (Filter and Holder). The only field monitor currently considered acceptable by NIOSH is manufactured by the Millipore Corporation. The unit con- 239-5 -- sti of 1) a three section styrene plastic case designated Millipore Aerosol Monitor Case, 2) a 37-ram diameter plain white cellulose ester membrane filter designated Millipore AA (pore size of 0.8 micrometer), 3) a support pad, and 4) two plastic sealing caps. If a large number of samples are to be taken, it may be less expensive to reuse the plastic cases. Great care must be taken in the cleaning and reassembly process. The outside mating surfaces of the field monitors may be covered with a "shrink-fit" band to provide proper sealing and a writing surface for fitter identifica tion. 6.2 Optical Equipment and Microscope Features 6.2.1 Microscope body with binocular head. 6.2.2 10X Huygenian eyepieces are recommended. Other eyepieces can be substituted if necessary. Wide field eyepieces can be used; however, wide field eyepieces may yield a count field area less than 0.003 mm* with the Porton reticle This is not always desirable from the standpoint of obtaining optimum sampling times (see Sec tion 8.1.3). If wide field eyepieces are used, it is preferable to use the Patterson Globe and Circle reticle to obtain a larger count field area. 6.2.3 Koehler illumination (preferably built-in with provisions for adjusting light intensity). 6.2.4 A Porton reticle is recommended. Others such as the Patterson Globe and Circle can be substituted. 6.2.5 Mechanical stage. 6.2.6 Phase-Contrast condenser with a numerical aperture (N.A.) equal to or greater than the N.A. of the objective. 6.2.7 40-45X phase contrast achromatic objective (N.A. 0.65 to 0.7S). 6.2.8 Phase-ring centering telescope o r Bertrand lens. 6.2.9 Green o r blue filter, if recommended by microscope manufacturer. 6.2.10 Stage micrometer with 0.01 mm subdivisions. 6.2.11 F o r general guidance on phase contrast microscopy, consult Needham (11.12), Clark (11.15) and McCrone (11.14). 6.3 Filter Mounting Equipment. Experience has shown that certain equipment is useful for efficient sample mounting. The following items are recommended for extracting and mount ing a portion of the filter for counting. 6.3.1 Microscope slides. 2.5 by 7.5 cm glass slides are most commonly used. Sample number, data, initials, etc., can be conveniently written on a frosted end riide. 6.3.2 Cover Slips. Cover slips are a necessary part of the slide mount and optical system. The shape should be appropriate for the size o f the filter wedge The appropriate covec slip depends upon the objective to be used. Ordinarily, objectives are optically cor rected for a # 1 Vi (0.17 millimeter) thickness cover slip. Improper cover glass thick ness will detract from the final image quality. 6.3.3 Scalpel. A scalpel is needed to cut out a portion of the filter to be examined. A num ber-ten curved blade scalpel is recommended. 6.3.4 Tweezers. A pair of fine-tipped tweezers is used to remove the membrane filter slice from the field monitor and place it upon the slides 6.3.3 Lens Tissue. To insure cleanliness, a lint-free tissue is recommended. This tissue should also be used for wiping mounting tools and for cleaning slides and cover slips. 6.3.6 Glass Rod. A fire-polished glass rod may be used to spread the mounting solution cm the slide. 239-6 WCD 001734 : i * 6.3.7 W heaton Balsam Bottle. This special glass container has a glass top which prevents contamination of the mounting solution. A glass rod is included for dispensing the solution. 7 Reagents Chemicals should be reagent grade, free from particles and color, conforming to the speci&cations of the Committee on Analytical Reagents of the American Chemical Society, where such specifi cations are available. 7.1 Dimethyl phthalate 7.2 Diethyl oxalate Avoid getting the mounting solution on the skin. Wash skin promptly with soap and water if skin contact occurs. 8. Procedure 8.1 Sampling 8.1.1 General Information Guidelines for the monitoring of employee exposures to industrial atmospheres are given in Reference 11.8. The Federal requirements for monitoring employee expo sure to airborne asbestos are found in 29 C FR 1910.1001. 8.1.2 Mounting the Sampling Pump on the Worker Fasten the sampling pump to the worker's belt and fasten the field monitor to the lapel or shin front (as close to the breathing zone as is practical). Remove the top cover of the plastic monitor, then invert the monitor making certain the exposed filter is facing downward. Turn the pump on and adjust to the calibrated Sow rate (1.0 to 2.5 1pm). Record the following information in a logbook. 1. Filler number 2. Pump stan time and date 3. Flow rate 4. Subject's name and job title 5. Type of operation or process 6. Ventilation controls and is tbe worker wearing a respirator approved for asbestos? The pump should be checked periodically during the sampling period for proper oper ation and flow rate. 8.1.3 Optimum Sampling Times The requirement for the minimum count of 100 fibers or 20 fields in 8.3.9 was determined to be the best compromise to achieve adequate precision for the airborne fiber estimate and reasonable counting times. An optimum fiber density of about I to 5 fibers per microscope count field is recommended. To estimate appropriate sampling times for feasible counting and optimal counting, one must consider the following constraints'. 1. microscope count field area (generally 0.003 to 0.006 mm3) 2. pump flow rate (typically 2.5 1pm maximum) 3. average airborne fiber concentrations 4. counting rule range of 20 to 100 fields 5. adequate fiber density to obtain a minimum count of 10 fibeis in 100 fields, whicb is the least total fiber count that yields an acceptable count precision 6. background airborne particulate levels that can reduce the count precision due an obscuring of fibers on the filter surface 239-7 The preceding constraints were considered in drawing Figures 1 and 2. These figures were developed (tom the following relationship: ______________(F B /F L ) (ECA /M FA ) sampling time *" (FR) (A Q ~ (i 000) mrautes where; F B /F L -- l to 5 fibers/fiekJ ECA effective collecting area of filters (855 mm* for 37-mm fiilter with effec tive diameter of 33 mm) M FA -- microscope field area (generally 0.003 to 0.006 mm*) F R * Pump flow rate (generally 1.0 to 2.5 Ipm) AC = A ir concentration of fibers in fibers/cm*. Figure 1 (microscope field area -- 0.003 mm1) and Figure 2 (microscope field area = 0.006 mm2) show optimum and feasible sampling times for a pump flow rate of 1.7 1pm. Each individual responsible for sampling asbestos should prepare a similar chart for his particular pump flow rate and microscope field area before sampling is per formed to aid in estimating proper sampling times;. O n Figures 1 and 2, the areas with solid shading lines are generally the optimum conditions for counting. The broken shading lines are for conditions very close to optimal. However, feasible counting conditions may extend down to about 0.1 fiber/field and and above 5 fibere/field. Recommended sampling times are most strongly influenced by background airborne particulate levels, once all the other constraints have been estimated. For heavy particulate levels, it may be necessary to limit each filter to about 60 to ISO minutes sampling duration. Each individual responsible for sampling should work closely with the microscopist to attain as high as possible filter surface fiber densities (up to about 5 fibcrs/field), while avoiding filter surface background particulate levels that create very difficult o r impossible counting conditions. If one has very little idea of airborne fiber and particulate levels, the best procedure is to take several long samples (as one 8-hour o r two consecutive 4-hour samples) in con junction with several short samples (as four consecutive 2-hour or eight consecutive 1-hour samples). If the longer samples prove very difficult to count, the microscopist will have the shorter samples to fall back on. From Figures 1 and 2, it can be seen that there are certain sampling times which will yield optimum fiber densities on the filter, for almost all airborne fiber concen trations from 1 to 10 fibers/cm3. These optimum times have been calculated and are presented in Figure 4. Note that the optimum times given by Figure 4 are approxi mate and can be varied by as much as rfc 25% . The nomogram is intended as' a guide to be used where no prior knowledge of the air concentration is available. 0.1.4 End of Sampling Period Remove the field monitor, replace the plastic top cover and the small end caps, and store the monitor. Always shut off the pump when changing monitors to avoid contaminating o r damaging the pump. Record the pump shutoff time and flow rate in the logbook. .1.5 Blanks With each batch (25 to 50 filters) of samples sent for analysis, submit two unopened field monitors which have been subjected to the same treatment as the samples except that they were not exposed to the sampling environment. Label these as Wanks. If the blanks yield fiber counts greater than 5 fibers/100 fields, then the entire sam pling procedure should be examined carefully for the cause of contamination. The 239-8 WCD 001736  I \ i I mounting solution of Section 8.2.1 should also be examined for contamination and/or crystal growth. 8.1.6 Shipping The field monitors in which the samples are collected should be shipped in a rigid container with sufficient packing material to prevent crushing. 8.1.7 Numbers of Samples When sampling for the Federal ceiling standard of 10 fibers (> 5 (u n )/c tn \ [29 CFR 1910.1001(b) (3), effective July 7, 1972], only one sample (15 minutes maximum duration) is necessary, theoretically. However, several samples should be taken dur ing expected periods of peak air concentrations to allow for detection of gross sam pling or counting errors. When sampling for determination of noncompliance with the Federal 8-hour TWA standard of 2 fibers (> 5 /im )/cm a, [29 C FR 1910.1001(b) (2 )]. one should contin uously sample as large a portion of the work day as is feasible for airborne concen trations of about 2 to 10 fibers/cm*. However, for a lower airborne concentration such as 0.5 fiber/cm*, one sample might require 4 to 8 hours sampling time in order to get the proper filter fiber density (Section 8.1.3). For this situation, the 8-hour TWA exposure would be determined from One 8-hour or two 4-hour samples as ap propriate. 8.2 Sample Preparation 8.2.1 Preparation of Mounting Solution A very important part o f the sample evaluation is the mounting process. This proc ess involves a special mounting medium of prescribed viscosity. The proper viscosity is important in order to expedite filter dissolving and still minimize particle migration. After the sample has been mounted, an elapsed time of approximately sixty minutes is needed before the sample is ready for evaluation. Combine the dimethyl phthalate and diethyl oxalate in a one to one ratio by volume and pour into a W heaton balsam bottle. Add approximately 0.05 (tfc 0.005) grams of new membrane filter per milliliter of sedation to reach the necessary viscosity. The mixture must be stirred periodically until the filters have dissolved and a homogeneous mixture is formed. The normal shelf life of the mounting solution is about three months. Twenty milliliters of mounting solution will prepare approximately 300 samples. 8.2.2 Sample Mounting Cleanliness is important! A dirty working area may result in sample contamination and erroneous counts. The following steps should be followed when mounting a sample. 1. Clean the slides and cover stips with lens tissue. Lay each slide down on a dean surface with the frosted end up. If is a good practice to rest one edge of the cover slip on the slide and the other edge on the working surface. By doing this, you keep the bottom surface (the one which contacts the filter) from becoming contaminated. 2. Wipe ail the mounting tools clean with lens tissue and place them on a clean surface (such as lens tissue). All tools should be wiped dean prior to mounting each sample. 3. Using the glass rod supplied with the Wheaton balsam bottle, apply a drop of mounting solution onto the center of tbe slide. It may be necessary to adjust the quantity of solution so that after the cover slip has been placed on top, the solu tion extends only slightly beyond the filler boundary, if the quantity is greater than this, particle migration may occur. 239-9 -4. Cbbtg another g t a s ro d , spread irhemtourtting media into a triangular shape. The ease <tif this triangle should oeoincide 'With -the dimension ot the filter wedge. 3 . S rju tu iu she anUBfc sand tomtom rotions o f the field monitor case to expose the Shoe. C m mwmgiiler wedge ifsom th e center to the edge of the filter using the axaitpel. T he s k e it 'the wetigevihouidapproximate one-eighth of the filter surface. T h e filter o n h e very ra re fully -removed -from the cassette for cutting, but this *anld only h e ideate with great care. 6. -Grasp th filter wedge with the tweezers on the perimeter of the filter which was d a m p e d between d ie monitor case sections. Do not touch the filter with your fiqgers. Place th e wedge, sample side =op, upon the mounting medium. 7 . Pick up a d e a n sev er d ip w ith tweezers an d carefully place it on the filter wedge. O nce this contact has been made, do mot reposition the cover slip. 8. Label the slide with the sample number and current date before proceeding to the n ex t filter. On the bottom (backside) of the slide, trace the perimeter of the filter wedge with a felt tip marking pen. This will enable the counter, after the filter has become transparent, to stay "within the filter perimeter when counting. 9. T h e sample should become transparent within fifteen minutes. If the filter appears eioudy. it m ay b e w cem sry to -press very lightly on the cover slip. This is rarely necessary; however, counting hostel s o t be started until an hour after the mount ing. This allows th e microscopic msctcretof the filter to become invisible to micro scope viewing. 10. Discard the mande. m om s after two days If it bas not been counted. Crystals appearing similar to asbestos fibers m ay begin to grow at tbe mounting m edia/ait interfaces. T hey seldom prsent any problems if tbe slide is examined before two d ays. l a any case, stay aw ay from .rite fitter's edges when counting and sizing. 413 Grunting of f h n 8.3.1 Place the slide an tb e m r i m i n l stage tsf fibs microscope and position the center o f th e wedge under tbe objective leas ro d brass upon the sample. Start counting from o n e end o f the wedge and progress a io tg a radial line to the other end (count in eith er direct from perimeter to wedge rip). Random fields are selected, without looking into the eyepieces, by slifhdy advancing the slide in one direction with the mechanical stage control. 8.3.2 It is essential to continually scan over a range of focal planes (generally the upper 10 to IS micrometers o f th e filter surface) with the fine focus control during each field comte. This is especially necessary' for asbestos fibers due to their impaction Into the filter matrix. J 3 O n most airborne samples, asbestos fibers will generally have fiber diameters less than one micrometer. Therefore, it is necessary to look carefully for faint fiber images. J6 3 A Regularly check phase ring alignment. S.3.5 W hen an agglomerate (mass of material) covers a significant portion of the field of view (approx 1 /6 o r greater) reject the field and select another. (Do not include it in the number o f fields counted.) However, report tbe fact as it may have meaning o n other data collection. 8 3 .6 Bundles of fibers are counted as one fiber unless both ends of the fiber can be clearly resolved. < 3 .7 C ount only fibers with a length to width ratio greater than or equal to 3:1. 8.3.8 Count only fibers greater than 5 micrometers in length. (Be as accurate as passible m accepting fibers near this length.) Measure curved fibers along the curve to esti m ate the total length. 239-10 WCD 001738 ! r i 8.3.9 Count as many fields as necessary to yield a total count of at least 100 fibers. Ex ceptions: a) count at least 20 fields even if you count more than 100 fibers, and b) stop at 100 fields even if you haven't reached 100 fibers. 8.3.10 For fibers that cross either one or two sides of the counting field, the following pro cedure is used to obtain a representative count. COUNT any fiber greater than 5 micrometers in length, that lies entirely within the counting area. COUNT as fiber" any fiber with only one end lying within the counting area. DO NOT COUNT any fiber crossing any two sides. Reject and do not count all other fibers. Refer to Figures 5 through 10. Note that the fibers in Figures 5 through 10 are not representative of the appearance of most as bestos fibers. Most fibers have a very faint image. 9. Calibration and Standards 9.1 Sampling Train Calibration Th accurate calibration of the sampling pump is essential to the correct calculation of the air volume sampled. The frequency of calibration is dependent on the use, care, and hand ling to which the pump is subjected. Pumps must be recalibrated if they have just been repaired, misused, or received from the manufacturer. If the pump receives hard usage, more frequent calibration may be necessary. Ordinarily, pumps should be calibrated in the labora tory 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 upon the type of instrument used as a reference. The choice of a calibration instrument will depend largely on where the calibration is per formed. For laboratory testing, a 1-liter burnt used as a soap bubble flow meter or wet-test meter is recommended. Other standard calibrating instruments, such as a spirometer, Mar riott's bottle, o r dry gas meter can be used. The calibration should be of sufficient precision that the 95% confidence limits on the flow rate are 10% (95% of the flow rates will 1 fall within * 10% of the calibrated value). I 3 Instructions for calibration with the soap bubble flow meter follow. The sampling train used (pump, hose, filter cassette) in the pump calibration should be the same as the one used In the field. 9.1.1 Check the voltage of the pum p battery with a voltmeter both with the pnmp off and while it is operating to assure adequate voltage for calibration. If necessary, charge the battery to manufacturer's specifications. 9.1.2 Fill a beaker with 10 ml of soap solution. 9.1.3 Connect the filter cassette inlet to the top of the buret with a length of hose. 9.1.4 Turn the pump on and moisten the inside of the soap bubble meter by Immersing the open end of the buret into the soap solution and drawing bubbles up the inside of the buret. Perform this task until the bubbles are able to travel the entire length of the buret without breaking. 9.1.5 Adjust the pump rotameter to provide a flow between 1.5 to 2.5 1pm. 9.1.6 With a water manometer, check that the pressure drop across the filter is less than 13 inches of water (about 1 inch of mercury). 9.1.7 Start a soap bubble up the buret and measure the tim it takes for the bubble to travel a minimum volume of 1 liter. 9.1.8 Repeat the procedure in 9.1.7 at least three times, average the results, and calculate the calibrated flow rate by dividing the volume traveled by the soap bubble by the elapsed time. If the range between the highest and lowest of the three flow rates is greater than about 0.33 1pm, then the calibration should be repeated since it is likely that the precision is not adequate. WCD 001739 239-11 1.1.9 D ata required for the calibration include the volume measured, elapsed time, pressure .drop, air temperature, atmospheric pressure (or elevation), pump serial number, date, and name of person performing the calibration. '9.1.10 Corrections to the flow rate for pumps with rotameters may be necessary if the pres sure (elevation) o r temperature where the samples are collected factual flow rate) differs significantly from that where the calibration was performed (indicated flow rate;. Actual flow rates at time of sampling may be calculated for a linear scale rotameter by using the following correction formula: where both pressure (P) and temperature (T) are in absolute units such as: psia = psig + 14.7 deg Rankin = deg Fahrenheit + 460 deg Kelvin = deg Celsius + 273 9.2 Microscope Setup 9-2.1 Porton Reticle and the Counting Field The asbestos fiber count procedure consists of comparing fiber length to the diam eters of calibrated circles of a Porton reticle, and counting all fibers greater than J micrometers m length lying within a given counting field area. The Porton reticle is a glass plate inscribed with a series of circles and rectangles. The left half of the reticle is divided into six rectangles constituting the counting field. The counting field is illustrated in Figures S through 10. '!Kk2 ; Placement in Eyepiece '(T h e Porton reticle is placed inride the Huygenian eyepiece where it rests on the fieldhlimiting diaphragm. If other types of eyepieces are used, ft may be necessary to insert a counting collar for retaining the reticle. The reticle should always be kept clean, since dirt on the reticle is in focus and could complicate the counting and sizing r>process. ( .2 .3 '.StageMicrometer The Porton reticle cannot be used for counting until it has been properly calibrated with a stage micrometer. Most stage micrometer scales are approximately two millimeters long and are divided into units of one-hundredth of a millimeter (ten >micrometers). : ).2.4 Microscope Adjustment .When adjusting the microscope, follow the manufacturer's instructions while observing the following guidelines. .1, <The light source image must be in focus and centered on the condenser iris or : annular diaphragm. 2 . : The particulate material to be examined must be in focus. 3. i The illuminator field iris must be in focus, centered on the sample, and opened oni> to (he point where the field of view is illuminated. 4. '| The phase rings (annular diaphragm and phase-shifting elements) must be con- licencie. ' '1.2.5 Porton. Reticle Calibration Procedure h B a c h . eyepiece-objective-reticle combination on the microscope must be calibrated. SiSbouid any of the three be changed (disassembly, replacement, zoom adjustment, etc.). thtbe,combination must .be, recalibrated. Calibration may .change if intetpupillary dis- :-2 3 ? -i2 WCD 001740 ! lance is changed. For. proper calibration, the following procedure should be followed closely. With a 10X objective in place, place the stage micrometer on the mechanic1 stage, focus the millimeter scale, and center the image. Change to the 40-45X objec tive and adjust the first millimeter scale division to coincide with the left boundary of the Porton rectangle. Measure the distance between the left and extreme right bound aries of the Porton rectangle, estimating any portion of the final division. This meas urement represents 200 L units. The rectangle is 100 L units on the short vertical dimension. The calculated "L" is inserted into the formula D = H I 51)1'* where "N " is the circle number (indicated on the reticle) and " D " is the circle diameter. Since the circle diameters vary logarithmically, every other circle doubles in diameter. For example, circle number three is twice the diameter of number one; number four is twice the diameter of number two. When the circle sires have been determined, the count ing field area which consists of the left six smaller rectangles can be calculated from the relation 10,000 LJ. This completes the reticle calibration for this specific objec tive-eyepiece-reticle combination. Example for Porton Reticle The following calibration was obtained for a pair of 10X Huygenian eyepieces and a 43X objective; 200 L " 0.148 nun = 148 micrometers 100 L -- 0.074 mm = 74 micrometers One L-unit = 0.74 micrometers Thus Circle #1 has a diameter D = L * )1'* = 0.74(2l) VJ - 0.74 (1.414) - 1.0S micrometers. Then our circle diameter calibration table looks like; Diameter of Circle #1 = 1.05 micrometers # 2 - 1.48 #3 = 2.09 # 4 = 2.96 # 5 4.19 # 6 = 5.92 Field area = (10,000) (L*) = (100 L) (100 L) " (0.074) (0.074) - 0.0055 mm* Thus fibeis with a length greater than a distance halfway between the diameters of the #5 and # 6 circles would be counted. If a Patterson Globe and Circle reticle is used, a different calculation procedure is required. The circle diameters are related as follows. The # 2 5 circle diameter is (0,1) (reticle length). The circle diametets are proportional to the ratio of their numbers. Thus the #20 circle diameter is (20/25) or 0.8 times the #25 circle diameter. 10. Calculations 10.1 The average airborne asbestos fiber concentration estimated by the filter sample may be calculated from the following formula: . ,, K FB/FL) - (BFB/BFL)) (ECA) (1000) (FR) (T) (MFA) 239-13 BFB ** Total number of fibers counted m the BFL fields of the blank o r control filters in fibers > 5 /*m. BFL * Total number of fields counted on the blank or control filters. ECA =* Effective collecting area of filter (855 mm2 for a 37-mm filter with effective di ameter of 33 mm). PR =*= Pump flow rate in Uters/min (1pm). PB * Total number o f fibers counted in the F L fields in fibers > 5 fm. FL m Total number of fields counted on the filter. MFA . Microscope count field area in mma (generally 0.003 to 0.006). T 33 Sample collection time in minutes. Recount criteria. It is very desirable for a counter to conduct a "blind recount" foT about I in every 10 filter wedges (slides) counted. Alternatively, a second counter could perform the blind recount, in training sessions for novice counters, the trainee should conduct a blind recount for filter wedges counted by an experienced, proficient counter, in all cases, we will observe differences between the first and second counts of the same filter wedge. Most of these differences will be due to chance alone, that is, due to the random variability (precision) of the count method. Statistical recount criteria enable us to decide whether observed dif ferences can reasonably be explained due to chance alone or are probably due to systematic differences between counters or microscopes or due to some other biasing factor. The following recount criterion is for a pair of counts that estimate some airborne fiber con centration (AC) in fibers/cm*. The criterion is given at the type-I error level. That is, here is a 5% maximum risk that we will reject a pair of counts for the reason that one might be biased, when the large observed difference is really due to chance. Reject a pair of counts because one might be biased if: (AG s -- A C ,) exceeds 2.77(ACKCVrn) -where: XACi ** lower estimated airborne fiber concentration ACa higher estimated airborne fiber concentration 'AC -** average of the two airborne concentration estimates u3Vr *= average CV for the two concentration estimates which are a function of the total `fiber count (FH) in each case. Use the relation in Section 4 or Figure 3. !For a pair of counts on the same filter, reject the pair because one might be biased if: where: (FBa -- FBi) exceeds 2.77(FB)(CViH) *1?B, = lower fiber count on the filter (total fibers) 1FB-. = higher fiber count on the filter (total fibers) iFB *= average of the two total fiber counts GV,,,, = CVT for the value FB. Use the relation in Section 4 or Figure 3. KrlwtiKB i l ; l Lynch, 7. R., K. J. Kronoveter, and N . A. Lejdel, "Validity of the Poisson Distribution in ;Dust iCounting", unpublished. *L-2 \Wcklner, R. JB. and H. E. Ayer, `*Dust Exposure in Asbestos Processing" , Transactions of the WCD 001742 339-14 American Conference of Governmental Industrial Hygienists, May 1972, pp, 103-121, San Francisco, California. I. 1.3 Conway, R. E. and W. D. Holland, "Statistical Evaluation of the Procedure for Counting Asbestos Fibers on Membrane Filters", L F E Corporation, Richmond, California. Prepared for the Asbestos on Membrane Assoc/North America, New York, 1973. I I . 4 Leidel, N. A. and K. A. Busch, "A n Evaluation of Phase Contrast Microscopes for Asbestos Counting", presented at the 1974 American Industrial Hygiene Conference, Miami Beach, Florida, May 18, 1974, unpublished. 11.5 Beckett, S. T. and M. D. Attfleld, "Inter-Laboratory Comparison of the Counting of Asbestos Fibers Sampled on Membrane Filters", Ann Occup Hyg 17:85-96, 1974. 11.6 Rajhans, G. S. and G. M. Bragg, "A Statistical Analysis of Asbestos Fiber Counting in the Laboratory and Industrial Environment", Am Ind Hyg Assoc J 36(12):909-915,1975. 11.7 Leidel, N . A. and K. A. Busch, "Statistical Methods for the Determination of NoncompBanee with Occupational Health Standards", NIOSH Technical Publication 75-159, 1975. 11.8 Leidel, N. A., K. A. Busch, and J. R. Lynch, "Occupational Exposure Sampling Strategy Manual", NIOSH Technical Publication 77-173, 1977. 11.9 Leidel, N. A., K. A. Busch, and W. E. Crouse, "Exposure Measurement Action Level and Occupational Environmental Variability", NIOSH Technical Publication 76-131, 1975, 11.10 Comments of the Johns-Manville Corporation with Respect to the Notice of Proposed Rulemaking: Occupational Exposure to Asbestos. Federal Register, October 9, 1975. Submitted to the public record at the U. S. Department of Labor, Occupational Safety and Health Ad ministration, April 1976. 11.11 Leidel, N. A., S. G. Bayer, R. D. Zuniwalde, and K. A. Busch, USPHS/NIOSH Membrane Filter Method for Evaluating Airborne Asbestos Fibers, to be published by NIOSH in 1977. 11.12 Needham, G, H , The Practical Use of the Microscope, Charles C. Thomas Publishing Corporation, Springfield, Illinois, 1958. 11.13 Clark, G. L., The Encyclopedia of Microscopy, Rheinhold Publishing Corporation, New York, 1961. 11.14 McCrone, W. C. and J. G. Delly, I. The Particle Atlas, Edition Two, Atm Arbor Science Publishers, Inc., Ann Arbor, Michigan, 1973. 239-15 AVERAGE FIBERS /c c OF PLANT AIR FIGU R E L, Optimum Sampling H i for airborne asbestos where microscopic field area e 0.003 O mm* D o o 239-26 AVERAGE FIBERS /CC OF PLANT AIR FIG U R E 2. Optimum sampling times for airborne asbestos w hen microscopic field me* = 0.006 mm* 239*17 WCD 001746 I t o l o ftben/oB1 " o L-- 61-6ti FR -PUM P FLOW R A T E, ipm */ IN IV cn / o cn j____ 1____ L___ I___ I--- L j -- 1---I-- i-- 1-- L-- I--1 EXAMPLE 1.7 lpm 100- O PTIM U M /SA M PLIN G T IM E ,minutes CM S MOo 1 i ' 1-- 1. 1.I..1 cn o l.l L 1_1-- 1-- L X> m s - t o 1 81 8 3. 3 | T I I i | I i i r p r i i r r i T r p i1 i h u j j ir r r n r ^ n iT W H A - MICROSCOPE FIELD AREA , mm' zotro 2J9-20 WCD 001748 L IS T O F F IG U R E S (5 through 10) FIG U R E 5. DO NOT COUNT. F iber crosses to p and bottom sides. FIG U R E 6 . COUNT. O ne fiber. FIG U R E 7 . COUNT, O n eh alf fiber. F iber crosses left side and one end lies w ithin count area. FIG U R E 8 . COUNT. O ne-half fiber. F ib er crosses bottom side and one end lies w ithin count area. FIG U R E 9 . DO N O T COUNT. Fiber crosses tw o sides. FIG U R E 10. DO N O T COUNT. F iber crosses tw o skies (bottom left com er). COUNT. O ne-half fiber. Fiber crosses bottom side and one end lies w ithin count area. COUNT. O ne fiber (top right com er). 239-21 Sampling Data Sheet April 23, 1975 t 29.02 Class D Substance: Inert or Nuisance Dust Standard s 8-hcur time-weighted average for respirable dust: 5 mg/nr* 8-hour time-weighted average for total dust: 15 mg/m3 Reference: 29 CFR 1910.93 Analytical Method: The amount of material on a filter is determined by filter weight gain. Before sampling,the filter is pre-veighed to the nearest 0.01 mg. After sampling, the filter is reweighed. The difference in the filters weight is assumed to be the mass of material collected. Sampling Equipment: Pump: A calibrated personal sampling pump whose flow can be determined to an accuracy of + 5%. The pump must have been calibrated, with a representative filter and filter holder in line. If the respirable dust concentration is being measured, the pump must have a pulsation dampener and be certified under 30 CFR 74. Kilter Holder: 2 or 3-piece,37-ram filter holder held together by tape or shrinking band. Filter: 37-mm diameter, 5.0 micrometer pore size polyvinyl chloride filter or equivalent that has been pre-welghed to the nearest 0.01 mg. These filters must be hydrophobic. The filter should be supported with a back-up pad. Cyclone: 10-mm nylon cyclone. When the respirable dust concentration is measured, it is used with a 2-piece filter holder. Sampling Head Assembly: This assembly must hold the filter holder, cyclone, and coupler together rigidly so that air enters only at the cyclone Inlet. Sample Size : A minimum sampling period of 60 minutes is recommended and longer periods up to eight houra are preferable. If the respirable dust concentration is being measured, a flow rate of 1.7 liters per minute must be used. To determine total dust concentration, use a flow rate of 1.5 liters per minute. 29-1 WCD 001750 ; Daca S heet #29,02 Sampling Procedure: 1. Assemble the filter and three-piece filter cassette and close firmly to insure that the center ring seals the edge of the filter. Examine the holder far a good filter seal. If the cassette will not seal tightly, it should be discarded. If respirable dust is being measured, the center ring Is not included In the filter holder. The filter cassette should be held together by a shrinking band or tape. 2. If total nuisance dust is being sampled, remove the filter holder plugs. Attach the filter holder to the sampling pump with a 1/4 inch diameter,3-foot piece of tubing and an adaptor. The adaptor is used to provide a tight connection between the filter holder and tubing. 3. If the respirable dust is being sampled, assemble the two-piece filter holder, coupler, cyclone,and sampling head. The sampling head rigidly holds together the cyclone and filter holder. The outlet of the sampling head is connected to the pump by a 3-foot piece of 1/4 inch flexible tubing. 4. Clip the cassette or cyclone assembly to the worker's lapel. 5. Turn the pump on and begin sample collection. The pump flow rate should be checked periodically and readjusted If necessary. 6. Terminate sampling after the predetermined time and note sample flow rate, collection time,and ambient temperature and pressure. If a pressure reading is unavailable, record the elevation. 7. Collected sample cassette should be firmly sealed with the plugs in both the inlet and outlet. 8. With each batch of samples, submit one filter subjected to exactly the same handling as for the samples except that no air is drawn throw it. Label these as blanks. Special Considerations : 1. Filter holders molded from cellulose-acetate-butyrate,which is commonly known as Tenite plastic,have been shown to cause blank filter weight gains and must not be used. 2. The alignment of the filter holder and cyclone in the sampling head must be checked. If these parts are not aligned properly, leakage can result. 3. Before use, the cyclones grit cap or vortex finder should he removed and the interior of the cyclone should be Inspected. If the Inside of the cyclone is visibly scared, this cyclone should be discarded since the dust separation characteristics of the cyclone might be altered. If It is dirty, the interior of the cyclone should be clean* before use. This will prevent the reentralnment of this dirt. A * WCD 001751 S a ta Sheet #29.02 Shipping : After sampling,the samples and the blank should be shipped in a suitable container designed to prevent damage in transit. Reference: "Sampling and Svaluatlng Respirable Coal Mine Dust", US Bureau of Mines, Pittsburgh, Pa. Information Circular 8503, February, 1971, p. 47. 29-3 WCD 001752 I