ASBESTOS IN AIR

Method No.:

ID-160

Matrix:

Air

OSHA PEL Tim e W eighted Average: Excursion Level (30 m inutes):

0.1 fiber/cc 1.0 fiber/cc

Procedure:

A known volum e of air is drawn through a 25-m m diam eter cassette containing a m ixed-cellulose ester filter. The cassette m ust be equipped with an electrically conductive 50-m m extension cowl. The sam pling tim e and rate are chosen to give a fiber density of between 100 to 1,300 fibers/m m 2 on the filter. A portion of the sam ple filter is cleared and prepared for asbestos fiber counting by Phase Contrast Microscopy (PCM) at 400X.

Recom m ended Sam pling Rate:

0.5 to 5.0 L/m in

Recom m ended Air Volum es: Minim um :

25 L

Maxim um :

2400 L

5.5 fibers/m m 2 or 0.001 fibers/cc (2400 L Air Volum e)

Detection Lim it:

Precision CV:

0.12 (at 100 fibers/m m 2)

Status of Method:

Fully Validated

Date: July 1988 (Revised: July 1997)

Physical Scientist: Daniel T. Crane

Branch of Physical Measurem ents and Analysis OSHA Salt Lake Technical Center Sandy UT 84070-6406

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For assistance with accessibility problem s in using figures and illustrations presented in this m ethod, please contact Salt Lake Technical Center (SLTC) at (801) 233-4900. These procedures were designed and tested for internal use by OSHA personnel. Mention of any com pany nam e or com m ercial product does not constitute endorsem ent by OSHA. 1. Introduction This m ethod describes the collection of airborne asbestos fibers using calibrated sam pling pum ps with m ixed-cellulose ester (MCE) filters and analysis by phase contrast m icroscopy (PCM). Som e term s used are unique to this m ethod and are defined below: Asbestos: A term for naturally occurring fibrous m inerals. Asbestos includes chrysotile, crocidolite, am osite (cum m ingtonite-grunerite asbestos), trem olite asbestos, actinolite asbestos, anthophyllite asbestos, and any of these m inerals that have been chem ically treated and/or altered. The precise chem ical form ulation of each species will vary with the location from which it was m ined. Nom inal com positions are listed: Chrysotile Mg 3Si2O 5(OH) 4 Crocidolite Na 2Fe 32+Fe 23+Si8O 22(OH) 2 Am osite (Mg,Fe) 7Si8O 22(OH) 2 Trem olite-actinolite series Ca 2(Mg,Fe) 5Si8O 22(OH) 2 Anthophyllite (Mg,Fe) 7Si8O 22(OH) 2 Asbestos Fiber: A fiber of asbestos which m eets the criteria specified below for a fiber. Aspect Ratio: The ratio of the length of a fiber to it's diam eter (e.g. 3:1, 5:1 aspect ratios). Cleavage Fragm ents: Mineral particles form ed by comm inution of m inerals, especially those characterized by parallel sides and a m oderate aspect ratio (usually less than 20:1). Detection Lim it: The num ber of fibers necessary to be 95% certain that the result is greater than zero. Differential Counting: The term applied to the practice of excluding certain kinds of fibers from the fiber count because they do not appear to be asbestos. Fiber: A particle that is 5 :m or longer, with a length-to-width ratio of 3 to 1 or longer. Field: The area within the graticule circle that is superim posed on the m icroscope im age. Set: The sam ples which are taken, subm itted to the laboratory, analyzed, and for which, interim or final result reports are generated. Trem olite, Anthophyllite, and Actinolite: The non-asbestos form of these m inerals which m eet the definition of a fiber. It includes any of these m inerals that have been chem ically treated and/or altered. W alton-Beckett Graticule: An eyepiece graticule specifically designed for asbestos fiber counting. It consists of a circle with a projected diam eter of 100 ± 2 :m (area of about 0.00785 m m 2) with a crosshair having tic-m arks at 3-:m intervals in one direction and 5-:m in the orthogonal direction. There are m arks around the periphery of the circle to dem onstrate the proper sizes and shapes of fibers. This design is reproduced in Figure 2. The disk is placed in one of the m icroscope eyepieces so that the design is superim posed on the field of view. 1.1. History Early surveys to determ ine asbestos exposures were conducted using im pinger counts of total dust with the counts expressed as m illion particles per cubic foot (8.1.). The British Asbestos Research Council (8.2.) recom m ended filter m em brane counting in 1969. In July 1969, the Bureau of Occupational Safety and Health published a filter m em brane m ethod for counting asbestos fibers in the United States (8.3.). This m ethod was refined by NIOSH and published as P & CAM 239 (8.4.). On May 29, 1971, OSHA specified filter m em brane sam pling with phase contrast counting for evaluation of asbestos exposures at work sites in the United States (8.5.). The use of this technique was again required by OSHA in 1986 (8.6.). Phase contrast m icroscopy has continued to be the m ethod of choice for the m easurem ent of occupational exposure to asbestos (8.7.).

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1.2. Principle Air is drawn through a MCE filter to capture airborne asbestos fibers. A wedge shaped portion of the filter is rem oved, placed on a glass m icroscope slide and m ade transparent. A m easured area (field) is viewed by PCM. All the fibers m eeting defined criteria for asbestos are counted and considered a m easure of the airborne asbestos concentration. 1.3. Advantages and Disadvantages There are four m ain advantages of PCM over other m ethods: 1) The technique is specific for fibers. Phase contrast is a fiber counting technique which excludes non-fibrous particles from the analysis. 2) The technique is inexpensive and does not require specialized knowledge to carry out the analysis for total fiber counts. 3) The analysis is quick and can be perform ed on-site for rapid determ ination of air concentrations of asbestos fibers. 4) The technique has continuity with historical epidem iological studies so that estim ates of expected disease can be inferred from long-term determ inations of asbestos exposures. The m ain disadvantage of PCM is that it does not positively identify asbestos fibers. Other fibers which are not asbestos m ay be included in the count unless differential counting is perform ed. This requires a great deal of experience to adequately differentiate asbestos from non-asbestos fibers. Positive identification of asbestos m ust be perform ed by polarized light or electron m icroscopy techniques. A further disadvantage of PCM is that the sm allest visible fibers are about 0.2 :m in diam eter while the finest asbestos fibers m ay be as sm all as 0.02 :m in diam eter. For som e exposures, substantially m ore fibers m ay be present than are actually counted. 1.4. W orkplace Exposure Asbestos is used by the construction industry in such products as shingles, floor tiles, asbestos cem ent, roofing felts, insulation and acoustical products. Non-construction uses include brakes, clutch facings, paper, paints, plastics, and fabrics. One of the m ost significant exposures in the workplace is the rem oval and encapsulation of asbestos in schools, public buildings, and hom es. Many workers have the potential to be exposed to asbestos during these operations. About 95% of the asbestos in com m ercial use in the United States is chrysotile. Crocidolite and am osite m ake up m ost of the rem ainder. Anthophyllite and trem olite or actinolite are likely to be encountered as contam inants in various industrial products. 1.5. Physical Properties Asbestos fiber possesses a high tensile strength along its axis, is chem ically inert, non-com bustible, and heat resistant. It has a high electrical resistance and good sound absorbing properties. It can be weaved into cables, fabrics or other textiles, and also m atted into asbestos papers, felts, or m ats. 1.6. Toxic Effects Information contained in this section is a synopsis of current know ledge of the physiological effects of asbestos and is not intended as a basis for OSHA policy. Som e possible physiologic results of respiratory exposure to asbestos are m esotheliom a of the pleura or peritoneum , interstitial fibrosis, asbestosis, pneum oconiosis, or respiratory cancer (8.8.). The possible consequences of asbestos exposure are further detailed in reference 8.8 or in the asbestos standard pream ble (8.6.).

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2. Range and Detection Lim it 2.1. The ideal counting range on the filter is 100 to 1,300 fibers/m m 2. W ith a W alton-Beckett graticule this range is equivalent to 0.8 to 10 fibers/field. Using NIOSH counting statistics (8.9.), a count of 0.8 fibers/field would give an approxim ate coefficient of variation (CV) of 0.13. 2.2. The detection lim it for this m ethod is 4.0 fibers per 100 fields or 5.5 fibers/m m 2. This was determ ined using an equation to estim ate the m axim um CV possible at a specific concentration (95% confidence) and a Lower Control Lim it of zero. The CV value was then used to determ ine a corresponding concentration from historical CV vs fiber relationships. As an exam ple: Lower Control Lim it (95% Confidence) = AC - 1.645(CV)(AC) W here: AC = Estim ate of the airborne fiber concentration (fibers/cc) Setting the Lower Control Lim it = 0 and solving for CV: 0 = AC - 1.645(CV)(AC) CV = 0.61 This value was com pared with CV vs. count curves. The count at which CV = 0.61 for Leidel-Busch counting statistics (8.9.) or for an OSHA Salt Lake Technical Center (OSHA-SLTC) CV curve (see Appendix A for further inform ation) was 4.4 fibers or 3.9 fibers per 100 fields, respectively. Although a lower detection lim it of 4 fibers per 100 fields is supported by the OSHA-SLTC data, both data sets support the 4.5 fibers per 100 fields value. 3. Method Perform ance - Precision and Accuracy Precision is dependent upon the total num ber of fibers counted and the uniform ity of the fiber distribution on the filter. A general rule is to count at least 20 and not m ore than 100 fields. The count is discontinued when 100 fibers are counted, provided that 20 fields have already been counted. Counting m ore than 100 fibers results in only a sm all gain in precision. As the total count drops below 10 fibers, an accelerated loss of precision is noted (8.9.). At this tim e, there is no known m ethod to determ ine the absolute accuracy of the asbestos analysis. Results of sam ples prepared through the Proficiency Analytical Testing (PAT) Program and analyzed by the OSHA-SLTC showed no significant bias when com pared to PAT reference values. The PAT sam ples were analyzed from 1987 to 1989 (N=36) and the concentration range was from 120 to 1,300 fibers/m m 2. 4. Interferences Fibrous substances, if present, m ay interfere with asbestos analysis. Som e com m on fibers are: fiber glass anhydrite gypsum m em brane structures m icroorganism s

perlite veins plant fibers som e synthetic fibers sponge spicules and diatom s wollastonite

The use of electron m icroscopy or optical tests such as polarized light, and dispersion staining m ay be used to differentiate these m aterials from asbestos when necessary.

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5. Sam pling 5.1. Equipm ent 5.1.1.

Sam ple assem bly (The assem bly is shown in Figure 3): Conductive filter holder consisting of a 25-m m diam eter, 3-piece cassette having a 50-m m long electrically conductive extension cowl. Backup pad, 25-m m , cellulose. Mem brane filter, m ixed-cellulose ester (MCE), 25-m m , plain, white, 0.4- to 1.2-:m pore size.

NOTES:

a) DO NOT RE-USE CASSETTES. b) Fully conductive cassettes are required to reduce fiber loss to the sides of the cassette due to electrostatic attraction. c) Purchase filters which have been selected by the manufacturer for asbestos counting or analyze representative filters for fiber background before use. Discard the filter lot if more than 4 fibers/100 fields are found. d) To decrease the possibility of contam ination, the sampling system (filter-backup pad-cassette) for asbestos is usually preassembled by the manufacturer. e) Other cassettes such as the Bell-m outh® may be used within the limits of validation.

5.1.2.

Gel bands for sealing cassettes.

5.1.3

Sam pling pum p: Each pum p m ust be a battery operated, self-contained unit sm all enough to be placed on the m onitored em ployee and not interfere with the work being perform ed. The pum p m ust be capable of sam pling at the collection rate for the required sam pling tim e.

5.1.4.

Flexible tubing, 6-m m bore.

5.1.5.

Pum p calibration: Stopwatch and bubble tube/burette or electronic m eter.

5.2. Sam pling Procedure 5.2.1.

Seal the point where the base and cowl of each cassette m eet (see Figure 3) with a gel band or tape.

5.2.2.

Charge the pum ps com pletely before beginning.

5.2.3.

Connect each pum p to a calibration cassette with an appropriate length of 6-m m bore plastic tubing. Do not use luer connectors - the type of cassette specified above has built-in adapters.

5.2.4.

Select an appropriate flow rate for the situation being m onitored. The sam pling flow rate m ust be between 0.5 and 5.0 L/m in for personal sam pling and is com m only set between 1 and 2 L/m in. Always choose a flow rate that will not produce overloaded filters.

5.2.5.

Calibrate each sampling pum p before and after sam pling with a calibration cassette in-line (Note: This calibration cassette should be from the sam e lot of cassettes used for sam pling). Use a prim ary standard (e.g. bubble burette) to calibrate each pum p. If possible, calibrate at the sam pling site.

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NOTE: If sampling site calibration is not possible, environmental influences may affect the flow rate. The extent is dependent on the type of pum p used. Consult with the pump m anufacturer to determine dependence on environm ental influences. If the pump is affected by tem perature and pressure changes, use the formula in Appendix B to calculate the actual flow rate. 5.2.6.

Connect each pum p to the base of each sam pling cassette with flexible tubing. Rem ove the end cap of each cassette and take each air sam ple open face (see Figure 3). Assure that each sam ple cassette is held open side down in the em ployee's breathing zone during sam pling. The distance from the nose/m outh of the em ployee to the cassette should be about 10 cm . Secure the cassette on the collar or lapel of the em ployee using spring clips or other sim ilar devices.

5.2.7.

A suggested m inim um air volum e when sam pling to determ ine TW A com pliance is 25 L. For Excursion Lim it (30 m in sam pling tim e) evaluations, a m inim um air volum e of 48 L is recom m ended.

5.2.8.

The m ost significant problem when sam pling for asbestos is overloading the filter with non-asbestos dust. Suggested m axim um air sam ple volum es for specific environm ents are: Environm ent Asbestos rem oval operations (visible dust) Asbestos rem oval operations (little dust) Office environm ents

Air Vol. (L) 100 240 400 to 2400

CAUTION: Do not overload the filter w ith dust. High levels of non-fibrous dust particles may obscure fibers on the filter and low er the count or make counting impossible. If more than about 25 to 30% of the field area is obscured w ith dust, the result may be biased low. Smaller air volumes may be necessary w hen there is excessive non-asbestos dust in the air. W hile sam pling, observe the filter with a sm all flashlight. If there is a visible layer of dust on the filter, stop sam pling, rem ove and seal the cassette, and replace with a new sam pling assem bly. The total dust loading should not exceed 1 m g. 5.2.9.

Blank sam ples are used to determ ine if any contam ination has occurred during sam ple handling. Prepare two blanks for the first 1 to 20 sam ples. For sets containing greater than 20 sam ples, prepare blanks as 10% of the sam ples. Handle blank sam ples in the sam e m anner as air sam ples with one exception: Do not draw any air through the blank sam ples. Open the blank cassette in the place where the sam ple cassettes are m ounted on the em ployee. Hold it open for about 30 seconds. Close and seal the cassette appropriately. Store blanks for shipm ent with the sam ple cassettes.

5.2.10. Im m ediately after sam pling, close and seal each cassette with the base and plastic plugs. Do not touch or puncture the filter m em brane as this will invalidate the analysis. 5.2.11. Attach a seal (OSHA-21 or equivalent) around each cassette in such a way as to secure the end cap plug and base plug. Tape the ends of the seal together since the seal is not long enough to be wrapped end-to-end. Also wrap tape around the cassette at each joint to keep the seal secure.

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5.3. Sam ple Shipm ent 5.3.1.

Send the sam ples to the laboratory with paperwork requesting asbestos analysis. List any known fibrous interferences present during sam pling on the paperwork. Also, note the workplace operation(s) sam pled.

5.3.2.

Secure and handle the sam ples so that they will not rattle during shipm ent nor be exposed to static electricity. Do not ship sam ples in expanded polystyrene peanuts, verm iculite, paper shreds, or excelsior. Tape sam ple cassettes to sheet bubbles and place in a container that will cushion the sam ples without rattling.

5.3.3.

To avoid the possibility of sam ple contam ination, always ship bulk sam ples in separate m ailing containers.

6. Analysis 6.1. Safety Precautions 6.1.1.

Acetone is extrem ely flam m able and precautions m ust be taken not to ignite it. Avoid using large containers or quantities of acetone. Transfer the solvent in a ventilated laboratory hood. Do not use acetone near any open flam e. For generation of acetone vapor, use a spark free heat source.

6.1.2.

Any asbestos spills should be cleaned up im m ediately to prevent dispersal of fibers. Prudence should be exercised to avoid contam ination of laboratory facilities or exposure of personnel to asbestos. Asbestos spills should be cleaned up with wet m ethods and/or a High Efficiency Particulate-Air (HEPA) filtered vacuum . CAUTION: Do not use a vacuum without a HEPA filter - It will disperse fine asbestos fibers in the air.

6.2. Equipm ent 6.2.1.

Phase contrast m icroscope with binocular or trinocular head.

6.2.2.

W idefield or Huygenian 10X eyepieces (NOTE: The eyepiece containing the graticule m ust be a focusing eyepiece. Use a 40X phase objective with a num erical aperture of 0.65 to 0.75).

6.2.3.

Kohler illum ination (if possible) with green, blue filter, or PLM illum ination.

6.2.4.

W alton-Beckett Graticule, type G-22 with 100 ± 2 :m projected diam eter. See Appendix C for further inform ation regarding ordering the graticule.

6.2.5.

Mechanical stage. A rotating m echanical stage is convenient for use with polarized light.

6.2.6.

Phase telescope.

6.2.7.

Stage m icrom eter with 0.01-m m subdivisions.

6.2.8.

Phase-shift test slide, m ark II (Available from PTR optics Ltd., and also McCrone).

6.2.9.

Precleaned glass slides, 25 m m X 75 m m . O ne end can be frosted for convenience in writing sam ple num bers, etc., or paste-on labels can be used.

6.2.10. Cover glass #1½. 6.2.11. Scalpel (#10, curved blade). 6.2.12. Fine tipped forceps. 7 of 20

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6.2.13. Alum inum block for clearing filter (see Appendix D and Figure 4). 6.2.14. Autom atic adjustable pipette, 100- to 500-:L. 6.2.15. Micropipette, 5 :L. . 6.2.16. Polarizer, analyzer and first order red plate (optional). 6.3. Reagents 6.3.1.

Acetone (HPLC grade).

6.3.2.

Triacetin (glycerol triacetate).

6.3.3.

Lacquer or nail polish.

6.4. Standard Preparation A way to prepare standard asbestos sam ples of known concentration has not been developed. It is possible to prepare replicate sam ples of nearly equal concentration. This has been perform ed through the PAT program . These asbestos sam ples are distributed by the AIHA to participating laboratories. Since only about one-fourth of a 25-m m sam ple m em brane is required for an asbestos count, any PAT sam ple can serve as a "standard" for replicate counting. 6.5. Sam ple Mounting Note: See Safety Precautions in Section 6.1. before proceeding. The objective is to produce sam ples with a sm ooth (non-grainy) background in a m edium with a refractive index of approxim ately 1.46. The technique below collapses the filter for easier focusing and produces perm anent m ounts which are useful for quality control and interlaboratory com parison. An alum inum block or sim ilar device is required for sam ple preparation. A drawing is shown in Figure 4. 6.5.1.

Heat the alum inum block to about 70°C. The hot block should not be used on any surface that can be dam aged by either the heat or from exposure to acetone.

6.5.2.

Ensure that the glass slides and cover glasses are free of dust and fibers.

6.5.3.

Rem ove the top plug to prevent a vacuum when the cassette is opened. Clean the outside of the cassette if necessary. Cut the seal and/or tape on the cassette with a razor blade. Very carefully separate the base from the extension cowl, leaving the filter and backup pad in the base.

6.5.4.

W ith a rocking m otion cut a triangular wedge from the filter using the scalpel. This wedge should be one-sixth to one-fourth of the filter. Grasp the filter wedge with the forceps on the perim eter of the filter which was clam ped between the cassette pieces. DO NOT TOUCH the filter with your finger. Place the filter on the glass slide sam ple side up. Static electricity will usually keep the filter on the slide until it is cleared.

6.5.5.

Place the tip of the m icropipette containing about 200 :L acetone into the alum inum block. Insert the glass slide into the receiving slot in the alum inum block. Inject the acetone into the block with slow, steady pressure on the plunger while holding the pipette firm ly in place.

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W ait 3 to 5 seconds for the filter to clear, then rem ove the pipette and slide from the alum inum block. 6.5.6.

Im m ediately (less than 30 seconds) place 2.5 to 3.5 :L of triacetin on the filter (NOTE: W aiting longer than 30 seconds will result in increased index of refraction and decreased contrast between the fibers and the preparation. This m ay also lead to separation of the cover slip from the slide).

6.5.7.

Lower a cover slip gently onto the filter at a slight angle to reduce the possibility of form ing air bubbles. If m ore than 30 seconds have elapsed between acetone exposure and triacetin application, glue the edges of the cover slip to the slide with lacquer or nail polish.

6.5.8.

If clearing is slow, warm the slide for 15 m in on a hot plate having a surface tem perature of about 50°C to hasten clearing. The top of the hot block can be used if the slide is not heated too long.

6.5.9.

Counting m ay proceed im m ediately after clearing and m ounting are com pleted.

6.6. Sam ple Analysis Com pletely align the m icroscope according to the m anufacturer's instructions. Then, align the m icroscope using the following general alignm ent routine at the beginning of every counting session and m ore often if necessary. 6.6.1.

Alignm ent 1) Clean all optical surfaces. Even a sm all am ount of dirt can significantly degrade the im age. 2) Rough focus the objective on a sam ple. 3) Close down the field iris so that it is visible in the field of view. Focus the im age of the iris with the condenser focus. Center the im age of the iris in the field of view. 4) Install the phase telescope and focus on the phase rings. Critically center the rings. Misalignm ent of the rings results in astigm atism which will degrade the im age. 5) Place the phase-shift test slide on the m icroscope stage and focus on the lines. The analyst m ust see line set 3 and should see at least parts of 4 and 5 but, not see line set 6 or 7. A m icroscope/m icroscopist com bination which does not pass this test m ay not be used. 6) If used, align the polarizer and analyzer at right angles to each other, and with the first order red com pensator at 45 degrees to the polarization directions, as for PLM analysis. (If PLM is used, do not insert either a green of blue filter.)

6.6.2.

Counting Fibers 1)

Place the prepared sam ple slide on the m echanical stage of the m icroscope. Position the center of the wedge under the objective lens and focus upon the sam ple.

2)

Start counting from one end of the wedge and progress along a radial line to the other end (count in either direction from perim eter to wedge tip). Select fields random ly, without looking into the eyepieces, by slightly advancing the slide in one direction with the m echanical stage control.

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3)

Continually scan over a range of focal planes (generally the upper 10 to 15 :m of the filter surface) with the fine focus control during each field count. Spend at least 5 to 15 seconds per field.

4)

Most sam ples will contain asbestos fibers with fiber diam eters less than 1 :m . Look carefully for faint fiber im ages. The sm all diam eter fibers will be very hard to see. However, they are an im portant contribution to the total count.

5)

Count only fibers equal to or longer than 5 :m . Measure the length of curved fibers along the curve.

6)

Count fibers which have a length to width ratio of 3:1 or greater.

7)

Count all the fibers in at least 20 fields. Continue counting until either 100 fibers are counted or 100 fields have been viewed; whichever occurs first. Count all the fibers in the final field.

8)

Fibers lying entirely within the boundary of the W alton-Beckett graticule field shall receive a count of 1. Fibers crossing the boundary once, having one end within the circle shall receive a count of ½. Do not count any fiber that crosses the graticule boundary m ore than once. Reject and do not count any other fibers even though they m ay be visible outside the graticule area. If a fiber touches the circle, it is considered to cross the line.

9)

Count bundles of fibers as one fiber unless individual fibers can be clearly identified and each individual fiber is clearly not connected to another counted fiber. See Figure 2 for counting conventions.

10) Record the num ber of fibers in each field in a consistent way such that filter non-uniform ity can be assessed. 11) Regularly check phase ring alignm ent. 12) W hen an agglom erate (m ass of m aterial) covers m ore than 25% of the field of view, reject the field and select another. Do not include it in the num ber of fields counted. 13) Perform a "blind recount" of 1 in every 10 filter wedges (slides) 6.7. Fiber Identification As previously m entioned in Section 1.3., PCM does not provide positive confirm ation of asbestos fibers. Alternate differential counting techniques should be used if discrim ination is desirable. Differential counting m ay include prim ary discrim ination based on m orphology, polarized light analysis of fibers, or m odification of PCM data by Scanning Electron or Transm ission Electron Microscopy. A great deal of experience is required to routinely and correctly perform differential counting. It is discouraged unless it is legally necessary. Then, only if a fiber is obviously not asbestos should it be excluded from the count. Further discussion of this technique can be found in reference 8.10. If there is a question whether a fiber is asbestos or not, follow the rule: "W HEN IN DOUBT, COUNT" 6.8. Analytical Recom m endations - Quality Control System 6.8.1.

All individuals perform ing asbestos analysis m ust have taken the NIOSH course for sam pling and evaluating airborne asbestos or an equivalent course.

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6.8.2.

Each laboratory engaged in asbestos counting shall set up a slide trading arrangem ent with at least two other laboratories in order to com pare perform ance and elim inate inbreeding of error. The slide exchange occurs at least sem iannually. The round robin results shall be posted where all analysts can view individual analyst's results.

6.8.3.

Each laboratory engaged in asbestos counting shall participate in the Proficiency Analytical Testing Program , the Asbestos Analyst Registry or equivalent.

6.8.4.

Each analyst shall select and count prepared slides from a "slide bank". These are quality assurance counts. The slide bank shall be prepared using uniform ly distributed sam ples taken from the workload. Fiber densities should cover the entire range routinely analyzed by the laboratory. These slides are counted blind by all counters to establish an original standard deviation. This historical distribution is com pared with the quality assurance counts. A counter m ust have 95% of all quality control sam ples counted within three standard deviations of the historical m ean. The analyses done by the counters to establish the slide bank m ay be used for an interim quality control program if the data are treated in a proper statistical fashion.

7. Calculations 7.1. Calculate the estim ated airborne asbestos fiber concentration on the filter sam ple using the following form ula:

where: AC FB FL BFB BFL ECA FR MFA

= = = = = = = =

T = 1000 = NOTE:

Airborne fiber concentration Total num ber of fibers greater than 5 :m counted Total num ber of fields counted on the filter Total num ber of fibers greater than 5 :m counted in the blank Total num ber of fields counted on the blank Effective collecting area of filter (385 m m 2 nom inal for a 25-m m filter.) Pum p flow rate (L/m in) Microscope count field area (m m 2). This is 0.00785 m m 2 for a W alton-Beckett Graticule. Sam ple collection tim e (m in) Conversion of L to cc The collection area of a filter is seldom equal to 385 m m 2. It is appropriate for laboratories to routinely monitor the exact diameter using an inside micrometer. The collection area is calculated according to the formula: Area = B(d/2) 2

7.2. Short-cut Calculation Since a given analyst always has the sam e interpupillary distance, the num ber of fields per filter for a particular analyst will rem ain constant for a given size filter. The field size for that analyst is constant (i.e. the analyst is using an assigned m icroscope and is not changing the reticle). For exam ple, if the exposed area of the filter is always 385 m m 2 and the size of the field is always 0.00785 m m 2, the num ber of fields per filter will always be 49,000. In addition it is necessary to convert liters of air to cc. These three constants can then be com bined such that ECA/(1,000 X MFA) = 49. The previous equation sim plifies to:

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7.3. Recount Calculations As m entioned in step 13 of Section 6.6.2., a "blind recount" of 10% of the slides is perform ed. In all cases, differences will be observed between the first and second counts of the sam e filter wedge. Most of these differences will be due to chance alone, that is, due to the random variability (precision) of the count m ethod. Statistical recount criteria enables one to decide whether observed differences can be explained due to chance alone or are probably due to system atic differences between analysts, m icroscopes, or other biasing factors. The following recount criterion is for a pair of counts that estim ate AC in fibers/cc. The criterion is given at the type-I error level. That is, there is 5% m axim um risk that we will reject a pair of counts for the reason that one m ight be biased, when the large observed difference is really due to chance. (8.11.) Reject a pair of counts if:

W here: AC 1 = lower estim ated airborne fiber concentration AC 2 = higher estim ated airborne fiber concentration CV FB = Pooled average CV for the two concentration estim ates:

CV 1 CV 2

= Coefficient of variation associated with the lower count = Coefficient of variation associated with the higher count

Coefficients of variation (CV) m ay be determ ined as in Appendix A of this m ethod (ID-160) or as discussed in NIOSH Method 7400. If a pair of counts are rejected by this criterion then, recount the rest of the filters in the subm itted set. Apply the test and reject any other pairs failing the test. Rejection shall include a m em o to the industrial hygienist stating that the sam ple failed a statistical test for hom ogeneity and the true air concentration m ay be significantly different than the reported value. 7.4. Reporting Results Report results to the industrial hygienist as fibers/cc. Use two significant figures. If m ultiple analyses are perform ed on a sam ple, an average of the results is to be reported unless any of the results can be rejected for cause.

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8. References 8.1.

Dreesen, W .C., et al, U.S. Public Health Service: A Study of Asbestosis in the Asbestos Textile Industry, (Public Health Bulletin No. 241), US Treasury Dept., W ashington, DC, 1938.

8.2.

Asbestos Research Council: The Measurement of Airborne Asbestos Dust by the Membrane Filter Method (Technical Note), Asbestos Research Council, Rockdale, Lancashire, Great Britain, 1969.

8.3.

Bayer, S.G., Zumw alde, R.D., Brow n, T.A., Equipment and Procedure for Mounting Millipore Filters and Counting Asbestos Fibers by Phase Contrast Microscopy, Bureau of Occupational Health, U.S. Dept. of Health, Education and W elfare, Cincinnati,OH,1969.

8.4.

NIOSH Manual of Analytical Methods, 2nd ed., Vol. 1 (DHEW /NIOSH Pub. No. 77-157-A). National Institute for Occupational Safety and Health, Cincinnati, OH, 1977.pp.239-1-239-21.

8.5.

Asbestos, Code of Federal Regulations 29 CFR 1910.1001. 1971.

8.6.

Occupational Exposure to Asbestos, Tremolite, Anthophyllite, and Actinolite. Final Rule, Federal Register 51: 119 (20 June 1986). pp.22612-22790.

8.7.

Asbestos, Tremolite, Anthophyllite, and Actinolite, Code of Federal Regulations 1910.1001. 1988. pp 711-752.

8.8.

Criteria for a Recommended Standard -- Occupational Exposure to Asbestos (DHEW /NIOSH Pub. No. HSM 72-10267), National Institute for Occupational Safety and Health NIOSH, Cincinnati,OH, 1972. pp. III-1-III-24.

8.9.

Leidel, N.A., Bayer,S.G., Zumw alde, R.D.,Busch, K.A., USPHS/NIOSH Membrane Filter Method for Evaluating Airborne Asbestos Fibers (DHEW /NIOSH Pub. No. 79-127). National Institute for Occupational Safety and Health, Cincinnati, OH, 1979.

8.10. Dixon, W .C., Applications of Optical Microscopy in Analysis of Asbestos and Quartz, Analytical Techniques in Occupational Health Chem istry, edited by D.D. Dollberg and A.W . Verstuyft. W ash. D.C.: Am erican Chem ical Society, (ACS Sym posium Series 120) 1980. pp. 13-41. 8.11. Abell, M . T., et al.,The Quality of Fiber Count Data, Appl. Ind. Hyg. Vol 4 No.11, Novem ber 1989, pp. 273-285

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Appendix A The OSHA asbestos regulations require each laboratory to establish a quality control program . The following is presented as an exam ple of how the OSHA-SLTC constructed its internal CV curve as part of m eeting this requirem ent. Data for the CV curve shown below is from 395 sam ples collected during OSHA com pliance inspections and analyzed from October 1980 through April 1986. Each sam ple was counted by 2 to 5 different counters independently of one another. The standard deviation and the CV statistic was calculated for each sam ple. This data was then plotted on a graph of CV vs. fibers/m m 2. A least squares regression was perform ed using the following equation: CV = antilog 10[A(log 10(x)) 2 + B(log 10(x)) + C] where:

x = the num ber of fibers/m m 2

Application of least squares gave: A B C

= 0.182205 = -0.973343 = 0.327499

Using these values, the equation becom es: CV = antilog 10[0.182205(log 10(x)) 2 - 0.973343(log 10(x)) + 0.327499]

Figure 2: CV curve generated from OSHA Salt Lake Technical Center data.

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Appendix B Sam pling Pum p Flow Rate Corrections This correction is used if a difference greater than 5% in am bient tem perature and/or pressure is noted between calibration and sam pling sites and the pum p does not com pensate for the differences.

W here: Q act = actual flow rate Q cal = calibrated flow rate (if a rotam eter was used, the rotam eter value) P cal = uncorrected air pressure at calibration P act = uncorrected air pressure at sam pling site T act = tem perature at sam pling site (K) T cal = tem perature at calibration (K)

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Appendix C W alton-Beckett Graticule W hen ordering the Graticule for asbestos counting, specify the exact disc diam eter needed to fit the ocular of the m icroscope and the diam eter (m m ) of the circular counting area. Instructions for m easuring the dim ensions necessary are listed: 1. Insert any available graticule into the focusing eyepiece and focus so that the graticule lines are sharp and clear. 2. Align the m icroscope. 3. Place a stage m icrom eter on the m icroscope object stage and focus the m icroscope on the graduated lines. 4. Measure the m agnified grid length, PL (:m ), using the stage m icrom eter. 5. Rem ove the graticule from the m icroscope and m easure its actual grid length, AL (m m ). This can be accom plished by using a m echanical stage fitted with verniers, or a jeweler's loupe with a direct reading scale. 6. Let D = 100 :m . Calculate the circle diam eter, d c (m m ), for the W alton-Beckett graticule and specify the diam eter when m aking a purchase:

Exam ple: If PL = 108 :m , AL = 2.93 m m and D = 100 :m , then,

7. Each eyepiece-objective-reticle com bination on the m icroscope m ust be calibrated. Should any of the three be changed (by zoom adjustm ent, disassem bly, replacem ent, etc.), the com bination m ust be recalibrated. Calibration m ay change if interpupillary distance is changed. Measure the field diam eter, D (acceptable range: 100 ± 2 :m ) with a stage m icrom eter upon receipt of the graticule from the m anufacturer. Determ ine the field area (m m 2). Field Area = B(D/2) 2 If D = 100 :m = 0.1 m m , then Field Area = B(0.1 m m /2) 2 = 0.00785 m m 2 The Graticule is available from : Graticules Ltd., Morley Road, Tonbridge TN9 IRN, Kent, England (Telephone 011-44-732-359061). Also available from PTR Optics Ltd., 145 Newton Street, W altham , MA 02154 [telephone (617) 891-6000] or McCrone Accessories and Com ponents, 2506 S. Michigan Ave., Chicago, IL 60616 [phone (312)-842-7100]. The graticule is custom m ade for each m icroscope.

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Appendix D Alum inum Block Diagram s of the block are provided in Figure 4. For assistance with accessibility problem s in using figures and illustrations presented in this m ethod, please contact Salt Lake Technical Center (SLTC) at (801) 233-4900. These procedures were designed and tested for internal use by OSHA personnel. Mention of any com pany nam e or com m ercial product does not constitute endorsem ent by OSHA. The cartridge therm ostat and heater used for this block have the following dim ensions: Diam eter: Cartridge length:

1/2" 2 3/8"

These heating units were obtained from : Vulcan Electric Com pany Kezar Falls, Maine 04047 (207)-625-3231 Therm ostat part num ber: Heater part num ber:

N1A1C2 C516

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Figure 3: W alton-Beckett Graticule with som e explanatory fibers.

Counts for the fibers in the figure Structure num ber 1 to 6 7 8 9 10 11 12

Count

Explanation

1 ½ 0 2 0 0 ½

single fibers all contained within the circle fiber crosses circle once fiber too short two crossing fibers fiber outside graticule fiber crosses graticule twice although split, fiber only crosses once

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Figure 4: Exploded view of an asbestos sam pling cassette.

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Figure 4: Engineering Drawings for the alum inum "Hot Block" as used at the Salt Lake Technical Center.

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