California Code of Regulations › Title 8 - Industrial Relations › Division 1 - Department of Industrial Relations › Chapter 4 - Division of Industrial Safety › Subchapter 4 - Construction Safety Orders › Article 4 - Dusts, Fumes, Mists, Vapors, and Gases › Appendix B - Sampling and Analysis (Non-Mandatory)

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
Matrix Air:
OSHA Permissible Exposure Limits:
..........................Time Weighted
								Average
0.1 fiber/cc
..........................Excursion Level
								(30 minutes)
1.0 fiber/cc
Collection Procedure:
A known volume of air is drawn through a 25-mm diameter
						cassette containing a mixed-cellulose ester filter. The cassette must be
						equipped with an electrically conductive 50-mm extension cowl. The sampling
						time and rate are chosen to give a fiber density of between 100 to 1,300
						fibers/mm2 on the filter.
..........................Recommended
								Sampling Rate
0.5 to 5.0 liters/ minute (L/min)
Recommended Air Volumes:
..........................Minimum
25 L
..........................Maximum
2,400 L
Analytical Procedure:
A portion of the sample filter is cleared and prepared
						for asbestos fiber counting by Phase Contrast Microscopy (PCM) at 400X.
						Commercial manufacturers and products mentioned in this method are for
						descriptive use only and do not constitute endorsements by USDOL-OSHA. Similar
						products from other sources can be substituted.
1. Introduction
This method describes the collection of airborne asbestos
						fibers using calibrated sampling pumps with mixed-cellulose ester (MCE) filters
						and analysis by phase contrast microscopy (PCM). Some terms used are unique to
						this method and are defined below: Asbestos: A term for naturally occurring
						fibrous minerals. Asbestos includes chrysotile, crocidolite, amosite
						(cummingtonite-grunerite asbestos), tremolite asbestos, actinolite asbestos,
						anthophyllite asbestos, and any of these minerals that have been chemically
						treated and/or altered. The precise chemical formulation of each species will
						vary with the location from which it was mined. Nominal compositions are
						listed:
..........................Chrysotile
Mg3Si2O5(OH)4
..........................Crocidolite
Na2Fe32+Fe23+Si8O22(OH)2
..........................Amosite
(Mg,Fe)7Si8O22(OH)2
..........................Tremolite-actinolite
Ca2(Mg,Fe)5Si8O22(OH)2
..........................Anthophyllite
(Mg,Fe)7Si8O22(OH)2
Asbestos Fiber: A fiber of asbestos which meets the
						criteria specified below for a fiber.
Aspect Ratio: The ratio of the length of a fiber to it's
						diameter (e.g. 3:1, 5:1 aspect ratios).
Cleavage Fragments: Mineral particles formed by
						comminution of minerals, especially those characterized by parallel sides and a
						moderate aspect ratio (usually less than 20:1).
Detection Limit: The number 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 [MICRO]m or longer, with a
						length-to-width ratio of 3 to 1 or longer.
Field: The area within the graticule circle that is
						superimposed on the microscope image.
Set: The samples which are taken, submitted to the
						laboratory, analyzed, and for which, interim or final result reports are
						generated.
Tremolite, Anthophyllite, and Actinolite: The
						non-asbestos form of these minerals which meet the definition of a fiber. It
						includes any of these minerals that have been chemically treated and/or
						altered.
Walton-Beckett Graticule: An eyepiece graticule
						specifically designed for asbestos fiber counting. It consists of a circle with
						a projected diameter of 100 plus or minus 2 [MICRO]m (area of about 0.00785
						mm2) with a crosshair having tic-marks at 3-[MICRO]m
						intervals in one direction and 5-[MICRO]m in the orthogonal direction. There
						are marks around the periphery of the circle to demonstrate the proper sizes
						and shapes of fibers. This design is reproduced in Figure 1. of this appendix.
						The disk is placed in one of the microscope eyepieces so that the design is
						superimposed on the field of view.
1.1. History
Early surveys to determine asbestos exposures were
						conducted using impinger counts of total dust with the counts expressed as
						million particles per cubic foot. The British Asbestos Research Council
						recommended filter membrane counting in 1969. In July 1969, the Bureau of
						Occupational Safety and Health published a filter membrane method for counting
						asbestos fibers in the United States. This method was refined by NIOSH and
						published as P & CAM 239. On May 29, 1971, OSHA specified filter membrane
						sampling with phase contrast counting for evaluation of asbestos exposures at
						work sites in the United States. The use of this technique was again required
						by OSHA in 1986. Phase contrast microscopy has continued to be the method of
						choice for the measurement of occupational exposure to asbestos.
1.2. Principle
Air is drawn through a MCE filter to capture airborne
						asbestos fibers. A wedge shaped portion of the filter is removed, placed on a
						glass microscope slide and made transparent. A measured area (field) is viewed
						by PCM. All the fibers meeting defined criteria for asbestos are counted and
						considered a measure of the airborne asbestos concentration.
1.3. Advantages and Disadvantages
There are four main advantages of PCM over other
						methods:
(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 performed on-site
						for rapid determination of air concentrations of asbestos fibers.
(4) The technique has continuity with historical
						epidemiological estimates of expected disease can be inferred from long-term
						determinations of asbestos exposures.
The main disadvantage of PCM is that it does not
						positively identify asbestos fibers. Other fibers which are not asbestos may be
						included in the count unless differential counting is performed. This requires
						a great deal of experience to adequately differentiate asbestos from
						non-asbestos fibers. Positive identification of asbestos must be performed by
						polarized light or electron microscopy techniques. A further disadvantage of
						PCM is that the smallest visible fibers are about 0.2[MICRO]m in diameter while
						the finest asbestos fibers may be as small as 0.02[MICRO]m in diameter. For
						some exposures, substantially more fibers may be present than are actually
						counted.
1.4. Workplace Exposure
Asbestos is used by the construction industry in such
						products as shingles, floor tiles, asbestos cement, roofing felts, insulation
						and acoustical products. Non-construction uses include brakes, clutch facings,
						paper, paints, plastics, and fabrics. One of the most significant exposures in
						the workplace is the removal and encapsulation of asbestos in schools, public
						buildings, and homes. Many workers have the potential to be exposed to asbestos
						during these operations.
About 95% of the asbestos in commercial use in the United
						States is chrysotile. Crocidolite and amosite make up most of the remainder.
						Anthophyllite and tremolite or actinolite are likely to be encountered as
						contaminants in various industrial products.
1.5. Physical Properties
Asbestos fiber possesses a high tensile strength along
						its axis, is chemically inert, non-combustible, 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 matted into asbestos
						papers, felts, or mats.
2. Range and Detection Limit
2.1. The ideal counting range on the filter is 100 to
						1,300 fibers/mm2 With a Walton-Beckett graticule
						this range is equivalent to 0.8 to 10 fibers/field. Using NIOSH counting
						statistics, a count of 0.8 fibers/field would give an approximate coefficient
						of variation (CV) of 0.13.
2.2. The detection limit for this method is 4.0 fibers
						per 100 fields or 5.5 fibers/mm2. This was
						determined using an equation to estimate the maximum CV possible at a specific
						concentration (95% confidence) and a Lower Control Limit of zero. The CV value
						was then used to determine a corresponding concentration from historical CV vs
						fiber relationships. As an example:
Lower Control Limit (95% Confidence) = AC --
						1.645(CV)(AC)
Where:
AC = Estimate of the airborne fiber concentration
						(fibers/cc) Setting the Lower Control Limit = 0 and solving for CV:
0 = AC - 1.645(CV)(AC)
CV = 0.61
This value was compared with CV vs. count curves. The
						count at which CV = 0.61 for Leidel-Busch counting statistics or for an OSHA
						Salt Lake Technical Center (OSHA-SLTC) CV curve (see Appendix A for further
						information) was 4.4 fibers or 3.9 fibers per 100 fields, respectively.
						Although a lower detection limit 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 Performance -- Precision and Accuracy
Precision is dependent upon the total number of fibers
						counted and the uniformity of the fiber distribution on the filter. A general
						rule is to count at least 20 and not more than 100 fields. The count is
						discontinued when 100 fibers are counted, provided that 20 fields have already
						been counted. Counting more than 100 fibers results in only a small gain in
						precision. As the total count drops below 10 fibers, an accelerated loss of
						precision is noted.
At this time, there is no known method to determine the
						absolute accuracy of the asbestos analysis. Results of samples prepared through
						the Proficiency Analytical Testing (PAT) Program and analyzed by the OSHA-SLTC
						showed no significant bias when compared to PAT reference values. The PAT
						samples were analyzed from 1987 to 1989 (N=36) and the concentration range was
						from 120 to 1,300 fibers/mm(2).
4. Interferences
Fibrous substances, if present, may interfere with
						asbestos analysis.
Some common fibers are:
fiberglass
anhydrite
plant fibers
perlite veins
gypsum
some synthetic fibers
membrane structures
sponge spicules
diatoms
microorganisms
wollastonite
The use of electron microscopy or optical tests such as
						polarized light, and dispersion staining may be used to differentiate these
						materials from asbestos when necessary.
5. Sampling
5.1. Equipment
5.1.1. Sample assembly. Conductive filter holder
						consisting of a 25-mm diameter, 3-piece cassette having a 50-mm long
						electrically conductive extension cowl, Backup pad, 25-mm, cellulose. Membrane
						filter, mixed-cellulose ester (MCE), 25-mm, plain, white, 0.4- to 1.2-[MICRO]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 contamination, the
						sampling system (filter-backup pad-cassette) for asbestos is usually
						preassembled by the manufacturer.
(e) Other cassettes, such as the Bell-mouth, may be used
						within the limits of their validation.
5.1.2. Gel bands for sealing cassettes.
5.1.3. Sampling pump. Each pump must be a battery
						operated, self-contained unit small enough to be placed on the monitored
						employee and not interfere with the work being performed. The pump must be
						capable of sampling at the collection rate for the required sampling
						time.
5.1.4. Flexible tubing, 6-mm bore.
5.1.5. Pump calibration.
Stopwatch and bubble tube/burette or electronic
						meter.
5.2. Sampling Procedure
5.2.1. Seal the point where the base and cowl of each
						cassette meet with a gel band or tape.
5.2.2. Charge the pumps completely before
						beginning.
5.2.3. Connect each pump to a calibration cassette with
						an appropriate length of 6-mm 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 monitored. The sampling flow rate must be between 0.5 and 5.0 L/min for
						personal sampling and is commonly set between 1 and 2 L/min. Always choose a
						flow rate that will not produce overloaded filters.
5.2.5. Calibrate each sampling pump before and after
						sampling with a calibration cassette in-line (Note: This calibration cassette
						should be from the same lot of cassettes used for sampling). Use a primary
						standard (e.g. bubble burette) to calibrate each pump. If possible, calibrate
						at the sampling site.
NOTE: If sampling site calibration is not possible,
						environmental influences may affect the flow rate. The extent is dependent on
						the type of pump used. Consult with the pump manufacturer to determine
						dependence on environmental influences. If the pump is affected by temperature
						and pressure changes, correct the flow rate using the formula shown in the
						section "Sampling Pump Flow Rate Corrections" at the end of this
						appendix.
5.2.6. Connect each pump to the base of each sampling
						cassette with flexible tubing. Remove the end cap of each cassette and take
						each air sample open face. Assure that each sample cassette is held open side
						down in the employee's breathing zone during sampling. The distance from the
						nose/mouth of the employee to the cassette should be about 10 cm. Secure the
						cassette on the collar or lapel of the employee using spring clips or other
						similar devices.
5.2.7. A suggested minimum air volume when sampling to
						determine TWA compliance is 25 L. For Excursion Limit (30 min sampling time)
						evaluations, a minimum air volume of 48 L is recommended.
5.2.8. The most significant problem when sampling for
						asbestos is overloading the filter with non-asbestos dust. Suggested maximum
						air sample volumes for specific environments are:
Environment
Air Vol. (L)
Asbestos removal operations (visible
								dust)
100.
Asbestos removal operations (little dust)
240.
Office environments. 400 to 2,400.
CAUTION: Do not overload the filter with dust. High
						levels of nonfibrous dust particles may obscure fibers on the filter and lower
						the count or make counting impossible. If more than about 25 to 30% of the
						field area is obscured with dust, the result may be biased low. Smaller air
						volumes may be necessary when there is excessive non-asbestos dust in the
						air.
While sampling, observe the filter with a small
						flashlight. If there is a visible layer of dust on the filter, stop sampling,
						remove and seal the cassette, and replace with a new sampling assembly. The
						total dust loading should not exceed 1 mg.
5.2.9. Blank samples are used to determine if any
						contamination has occurred during sample handling. Prepare two blanks for the
						first 1 to 20 samples. For sets containing greater than 20 samples, prepare
						blanks as 10% of the samples. Handle blank samples in the same manner as air
						samples with one exception: Do not draw any air through the blank samples. Open
						the blank cassette in the place where the sample cassettes are mounted on the
						employee. Hold it open for about 30 seconds. Close and seal the cassette
						appropriately. Store blanks for shipment with the sample cassettes.
5.2.10. Immediately after sampling, close and seal each
						cassette with the base and plastic plugs. Do not touch or puncture the filter
						membrane as this will invalidate the analysis.
5.2.11. Attach and secure a sample seal around each
						sample cassette in such a way as to assure that the end cap and base plugs
						cannot be removed without destroying the seal. 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.
5.3. Sample Shipment
5.3.1. Send the samples to the laboratory with paperwork
						requesting asbestos analysis. List any known fibrous interferences present
						during sampling on the paperwork. Also, note the workplace operation(s)
						sampled.
5.3.2. Secure and handle the samples in such that they
						will not rattle during shipment nor be exposed to static electricity. Do not
						ship samples in expanded polystyrene peanuts, vermiculite, paper shreds, or
						excelsior. Tape sample cassettes to sheet bubbles and place in a container that
						will cushion the samples in such a manner that they will not rattle.
5.3.3. To avoid the possibility of sample contamination,
						always ship bulk samples in separate mailing containers.
6. Analysis
6.1. Safety Precautions
6.1.1. Acetone is extremely flammable and precautions
						must 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 flame. For generation of acetone vapor, use a spark free
						heat source.
6.1.2. Any asbestos spills should be cleaned up
						immediately to prevent dispersal of fibers. Prudence should be exercised to
						avoid contamination of laboratory facilities or exposure of personnel to
						asbestos. Asbestos spills should be cleaned up with wet methods 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. Equipment
6.2.1. Phase contrast microscope with binocular or
						trinocular head.
6.2.2. Widefield or Huygenian 10X eyepieces (NOTE: The
						eyepiece containing the graticule must be a focusing eyepiece. Use a 40X phase
						objective with a numerical aperture of 0.65 to 0.75).
6.2.3. Kohler illumination (if possible) with green or
						blue filter.
6.2.4. Walton-Beckett Graticule, type G-22 with 100 plus
						or minus 2[MICRO]m projected diameter.
6.2.5. Mechanical stage. A rotating mechanical stage is
						convenient for use with polarized light.
6.2.6. Phase telescope.
6.2.7. Stage micrometer with 0.01-mm subdivisions.
6.2.8. Phase-shift test slide, mark II (Available from
						PTR optics Ltd., and also McCrone).
6.2.9. Precleaned glass slides, 25 mm X 75 mm. One end
						can be frosted for convenience in writing sample numbers, etc., or paste-on
						labels can be used.
6.2.10. Cover glass #1 ½.
6.2.11. Scalpel (#10, curved blade).
6.2.12. Fine tipped forceps.
6.2.13. Aluminum block for clearing filter (see Appendix
						D).
6.2.14. Automatic adjustable pipette, 100-to
						500-[MICRO]L.
6.2.15. Micropipette, 5 [MICRO]L.
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 samples of known
						concentration has not been developed. It is possible to prepare replicate
						samples of nearly equal concentration. This has been performed through the PAT
						program. These asbestos samples are distributed by the AIHA to participating
						laboratories.
Since only about one-fourth of a 25-mm sample membrane is
						required for an asbestos count, any PAT sample can serve as a "standard" for
						replicate counting.
6.5. Sample Mounting
NOTE: See Safety Precautions in Section
						6.1. before proceeding. The
						objective is to produce samples with a smooth (non-grainy) background in a
						medium with a refractive index of approximately 1.46. The technique below
						collapses the filter for easier focusing and produces permanent mounts which
						are useful for quality control and interlaboratory comparison.
An aluminum block or similar device is required for
						sample preparation.
6.5.1. Heat the aluminum block to about 70 deg.C. The hot
						block should not be used on any surface that can be damaged 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. Remove 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. With a rocking motion 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 perimeter of the
						filter which was clamped between the cassette pieces. DO NOT TOUCH the filter
						with your finger. Place the filter on the glass slide sample side up. Static
						electricity will usually keep the filter on the slide until it is
						cleared.
6.5.5. Place the tip of the micropipette containing about
						200 [MICRO]L acetone into the aluminum block. Insert the glass slide into the
						receiving slot in the aluminum block. Inject the acetone into the block with
						slow, steady pressure on the plunger while holding the pipette firmly in place.
						Wait 3 to 5 seconds for the filter to clear, then remove the pipette and slide
						from the aluminum block.
6.5.6. Immediately (less than 30 seconds) place 2.5 to
						3.5 [MICRO]L of triacetin on the filter (NOTE: Waiting longer than 30 seconds
						will result in increased index of refraction and decreased contrast between the
						fibers and the preparation. This may 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 forming air bubbles. If more 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 min on
						a hot plate having a surface temperature of about 50 deg.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 may proceed immediately after clearing
						and mounting are completed.
6.6. Sample Analysis
Completely align the microscope according to the
						manufacturer's instructions. Then, align the microscope using the following
						general alignment routine at the beginning of every counting session and more
						often if necessary.
6.6.1. Alignment
(1) Clean all optical surfaces. Even a small amount of
						dirt can significantly degrade the image.
(2) Rough focus the objective on a sample.
(3) Close down the field iris so that it is visible in
						the field of view. Focus the image of the iris with the condenser focus. Center
						the image of the iris in the field of view.
(4) Install the phase telescope and focus on the phase
						rings. Critically center the rings. Misalignment of the rings results in
						astigmatism which will degrade the image.
(5) Place the phase-shift test slide on the microscope
						stage and focus on the lines. The analyst must see line set 3 and should see at
						least parts of 4 and 5 but, not see line set 6 or 6. A microscope/microscopist
						combination which does not pass this test may not be used.
6.6.2. Counting Fibers
(1) Place the prepared sample slide on the mechanical
						stage of the microscope. Position the center of the wedge under the objective
						lens and focus upon the sample.
(2) Start counting from one end of the wedge and progress
						along a radial line to the other end (count in either direction from perimeter
						to wedge tip). Select fields randomly, without looking into the eyepieces, by
						slightly advancing the slide in one direction with the mechanical stage
						control.
(3) Continually scan over a range of focal planes
						(generally the upper 10 to 15 [MICRO]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 samples will contain asbestos fibers with fiber
						diameters less than 1 [MICRO]m. Look carefully for faint fiber images. The
						small diameter fibers will be very hard to see. However, they are an important
						contribution to the total count.
(5) Count only fibers equal to or longer than 5 [MICRO]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
						Walton-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 more than
						once. Reject and do not count any other fibers even though they may 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 1 of this appendix
						for counting conventions.
(10) Record the number of fibers in each field in a
						consistent way such that filter non-uniformity can be assessed.
(11) Regularly check phase ring alignment.
(12) When an agglomerate (mass of material) covers more
						than 25% of the field of view, reject the field and select another. Do not
						include it in the number of fields counted.
(13) Perform a "blind recount" of 1 in every 10 filter
						wedges (slides). Re-label the slides using a person other than the original
						counter.
6.7. Fiber Identification
As previously mentioned in Section
						1.3., PCM does not provide positive
						confirmation of asbestos fibers. Alternate differential counting techniques
						should be used if discrimination is desirable. Differential counting may
						include primary discrimination based on morphology, polarized light analysis of
						fibers, or modification of PCM data by Scanning Electron or Transmission
						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: "WHEN IN DOUBT, COUNT."
6.8. Analytical Recommendations -- Quality Control
						System
6.8.1. All individuals performing asbestos analysis must
						have taken the NIOSH course for sampling and evaluating airborne asbestos or an
						equivalent course.
6.8.2. Each laboratory engaged in asbestos counting shall
						set up a slide trading arrangement with at least two other laboratories in
						order to compare performance and eliminate inbreeding of error. The slide
						exchange occurs at least semiannually. 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 uniformly distributed samples 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 compared with the
						quality assurance counts. A counter must have 95% of all quality control
						samples counted within three standard deviations of the historical mean. This
						count is then integrated into a new historical mean and standard deviation for
						the slide.
The analyses done by the counters to establish the slide
						bank may be used for an interim quality control program if the data are treated
						in a proper statistical fashion.
7. Calculations
7.1. Calculate the estimated airborne asbestos fiber
						concentration on the filter sample using the following formula:
Click
						here to view image
where:
AC = Airborne fiber concentration
FB = Total number of fibers greater than 5 [MICRO]m
						counted
FL = Total number of fields counted on the filter
BFB = Total number of fibers greater than 5 [MICRO]m
						counted in the blank
BFL = Total number of fields counted on the blank
ECA = Effective collecting area of filter (385 mm(2)
						nominal for a 25 - mm filter.)
FR = Pump flow rate (L/min)
MFA = Microscope count field area (mm(2)). This is
						0.00785 mm(2) for a Walton-Beckett Graticule.
T = Sample collection time (min)
1,000 = Conversion of L to cc
NOTE: The collection area of a filter is seldom equal to
						385 mm(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 =
						[PI](d/2)2
7.2. Short-Cut Calculation
Since a given analyst always has the same interpupillary
						distance, the number of fields per filter for a particular analyst will remain
						constant for a given size filter. The field size for that analyst is constant
						(i.e. the analyst is using an assigned microscope and is not changing the
						reticle).
For example, if the exposed area of the filter is always
						385 mm(2) and the size of the field is always 0.00785 mm(2) the number 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 combined such that
						ECA/(1,000 x MFA)=49. The previous equation simplifies to:
Click
						here to view image
7.3. Recount Calculations
As mentioned in step 13 of Section
						6.6.2., a "blind recount" of 10% of
						the slides is performed. In all cases, differences will be observed 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 enables one to decide whether
						observed differences can be explained due to chance alone or are probably due
						to systematic differences between analysts, microscopes, or other biasing
						factors.
The following recount criterion is for a pair of counts
						that estimate AC in fibers/cc. The criterion is given at the type-I error
						level. That is, there is 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 if:
Click
						here to view image
Where:
AC(1) = lower estimated airborne fiber
						concentration
AC(2) = higher estimated airborne fiber
						concentration
AC(avg) = average of the two concentration
						estimates
CV(FB) = CV for the average of the two concentration
						estimates
If a pair of counts are rejected by this criterion then,
						recount the rest of the filters in the submitted set. Apply the test and reject
						any other pairs failing the test. Rejection shall include a memo to the
						industrial hygienist stating that the sample failed a statistical test for
						homogeneity and the true air concentration may 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 multiple analyses are performed on a sample, an
						average of the results is to be reported unless any of the results can be
						rejected for cause.
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), U.S. Treasury Dept., Washington, 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., Zumwalde, R.D., Brown, 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 Welfare, 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., Zumwalde, 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
						Chemistry, edited by D.D. Dollberg and A.W. Verstuyft. Wash. D.C.: American
						Chemical Society, (ACS Symposium Series 120) 1980. pp. 13-41.
Quality Control
The OSHA asbestos regulations require each laboratory to
						establish a quality control program. The following is presented as an example
						of how the OSHA-SLTC constructed its internal CV curve as part of meeting this
						requirement. Data is from 395 samples collected during OSHA compliance
						inspections and analyzed from October 1980 through April 1986.
Each sample was counted by 2 to 5 different counters
						independently of one another. The standard deviation and the CV statistic was
						calculated for each sample. This data was then plotted on a graph of CV vs.
						fibers/mm2. A least squares regression was performed
						using the following equation:
CV = antilog10
						[A(log10(x))2+B(log10(x))+C]
where:
x = the number of
						fibers/mm2
Application of least squares gave:
A = 0.182205
B = 0.973343
C = 0.327499
Using these values, the equation becomes:
CV = antilog10
						[0.182205(log10(x))2 +
						0.973343(log10(x)) + 0.327499]
Sampling Pump Flow Rate Corrections
This correction is used if a difference greater than 5%
						in ambient temperature and/or pressure is noted between calibration and
						sampling sites and the pump does not compensate for the differences.
Click
						here to view image
Where:
Q(act) = actual flow rate
Q(cal) = calibrated flow rate (if a rotameter was used,
						the rotameter value)
P(cal) = uncorrected air pressure at calibration
P(act) = uncorrected air pressure at sampling site
T(act) = temperature at sampling site (K)
T(cal) = temperature at calibration (K)
Walton-Beckett Graticule
When ordering the Graticule for asbestos counting,
						specify the exact disc diameter needed to fit the ocular of the microscope and
						the diameter (mm) of the circular counting area. Instructions for measuring the
						dimensions 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 microscope.
(3) Place a stage micrometer on the microscope object
						stage and focus the microscope on the graduated lines.
(4) Measure the magnified grid length, PL ([MICRO]m),
						using the stage micrometer.
(5) Remove the graticule from the microscope and measure
						its actual grid length, AL (mm). This can be accomplished by using a mechanical
						stage fitted with verniers, or a jeweler's loupe with a direct reading
						scale.
(6) Let D = 100 [MICRO]m. Calculate the circle diameter,
						d(c)(mm), for the Walton-Beckett graticule and specify the diameter when making
						a purchase:
Click
						here to view image
(7) Each eyepiece-objective-reticle combination on the
						microscope must be calibrated. Should any of the three be changed (by zoom
						adjustment, disassembly, replacement, etc.), the combination must be
						recalibrated. Calibration may change if interpupillary distance is
						changed.
Measure the field diameter, D (acceptable range: 100 plus
						or minus 2 [MICRO]m) with a stage micrometer upon receipt of the graticule from
						the manufacturer. Determine the field area (mm(2)).
Field Area =
						[PI](D/2)2
If D = 100 [MICRO]m = 0.1 mm, then
Field Area = [PI](0.1
						  mm/2)2 =
						0.00785mm2
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, Waltham, MA 02154 [telephone
						(617) 891-6000] or McCrone Accessories and Components, 2506 S. Michigan Ave.,
						Chicago, IL 60616 [phone (312)-842-7100]. The graticule is custom made for each
						microscope.
Click
						here to view image
Figure 1: Walton--Beckett Graticule with some
						explanatory fibers
.
Counts for the Fibers in the Figure
Structure No.
Count
Explanation
1 to 6
1
Single fibers all
								contained within the Circle.
7
½
Fiber
								crosses circle once.
8
0
Fiber too short.
9
2
Two crossing
								fibers.
10
0
Fiber outside
								graticule.
11
0
Fiber crosses
								graticule twice.
12
½
Although
								split, fiber only crosses once.
1. New
						Appendix B to section
						1529 filed 2-15-91; operative
						2-15-91 pursuant to Government Code section
						11346.2(d)
						(Register 91, No. 19).
2. Editorial correction of HISTORY 1
						(Register 91, No. 45).
3. Editorial correction of Appendix B
						(Register 95, No. 41).
4. Repealer and new appendix and NOTE filed
						5-3-96; operative 7-3-96 (Register 96, No. 18).
5. Change without
						regulatory effect providing more legible Figure 1 filed 1-20-2008 pursuant to
						section 100, title 1, California Code of
						Regulations (Register 2009, No. 4).
Note: Authority cited: Section
						  142.3, Labor
						  Code. Reference: Section
						  142.3, Labor
						  Code.