California Code of Regulations › Title 8 - Industrial Relations › Division 1 - Department of Industrial Relations › Chapter 4 - Division of Industrial Safety › Subchapter 7 - General Industry Safety Orders › Group 16 - Control of Hazardous Substances › Article 110 - Regulated Carcinogens › 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 µm 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 µm (area of about 0.00785
						  mm2) with a crosshair having tic-marks at 3-µm
						  intervals in one direction and 5-µm 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 0.2µm in diameter while
						  the finest asbestos fibers may be as small as 0.02µm 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/mm2.
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-µm
						  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 of 2.5 liters per minute (L/min) 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 non-fibrous 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 2µm 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 and Figure 4).
6.2.14. Automatic adjustable pipette, 100-to
						  500-µL.
6.2.15. Micropipette, 5 µL.
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 µL 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 µL 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 7. 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 µm 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 µm. 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
						  µm. 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:
[(
FB/FL
) -
								  (
BFB/BFL
)] x
ECA
AC
=
___________________________
1000 x
FR x T x
								  FMA
where:
AC = Airborne fiber concentration
FB = Total number of fibers greater than 5 µm
						  counted
FL = Total number of fields counted on the
						  filter
BFB = Total number of fibers greater than 5 µm
						  counted in the blank
BFL = Total number of fields counted on the
						  blank
ECA = Effective collecting area of filter (385
						  mm2 nominal for a 25 - mm filter.)
FR = Pump flow rate (L/min)
MFA = Microscope count field area
						  (mm2). This is 0.00785
						  mm2 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 mm2. 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 = P (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 mm2 and the size of the field is always
						  0.00785 mm2 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:
(
FB/FL
) -
								  (
BFB/BFL
) x 49
AC
=
___________________________
FR x T
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:
AC1 = lower estimated airborne
						  fiber concentration
AC2 = higher estimated airborne
						  fiber concentration
ACavg = average of the two
						  concentration estimates
CVFB = 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:
Qact = actual flow rate
Qcal = calibrated flow rate (if
						  a rotameter was used, the rotameter value)
Pcal = uncorrected air pressure
						  at calibration
Pact = uncorrected air pressure
						  at sampling site
Tact = temperature at sampling
						  site (°K)
Tcal = 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 (µm),
						  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 µm. Calculate the circle
						  diameter, dc(mm), for the Walton-Beckett graticule and
						  specify the diameter when making a purchase:
AL x D
dc
								  =
___________________________
PL
Example: If PL = 108 µm, AL = 2.93 mm and D = 100
						  µm, then,
2.93 x 100
dc
								  =
___________________________
= 2.71mm
108
(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 µm) with a stage micrometer upon receipt of the graticule
						  from the manufacturer. Determine the field area
						  (mm2).
Field Area =
						  [PI](D/2)2
If D = 100 µm = 0.1 mm, then
Field Area = P(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
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
						  5208 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.