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 K - Polarized Light Microscopy of Asbestos Non-Mandatory

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
Method number: ID-191
Matrix: Bulk
Collection Procedure: Collect approximately 1 to 2 grams
						of each type of material and place into separate 20 mL scintillation vials.
						Analytical Procedure: A portion of each separate phase is analyzed by gross
						examination, phase-polar examination, and central stop dispersion
						microscopy.
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 may be substituted.
1. Introduction
This method describes the collection and analysis of
						asbestos bulk materials by light microscopy techniques including phase-polar
						illumination and central-stop dispersion microscopy. Some terms unique to
						asbestos analysis are defined below:
Amphibole: A family of minerals whose crystals are formed
						by long, thin units which have two thin ribbons of double chain silicate with a
						brucite ribbon in between. The shape of each unit is similar to an "I beam".
						Minerals important in asbestos analysis include cummingtonite-grunerite,
						crocidolite, tremolite-actinolite and anthophyllite.
Asbestos: A term for naturally occurring fibrous
						minerals. Asbestos includes chrysotile, cummingtonite-grunerite asbestos
						(amosite), anthophyllite asbestos, tremolite asbestos, crocidolite, actinolite
						asbestos and any of these minerals which have been chemically treated or
						altered. The precise chemical formulation of each species varies with the
						location from which it was mined. Nominal compositions are listed:
Chrysotile
						Mg3Si2O5(OH)4
Crocidolite (Riebeckite asbestos)
						Na2Fe32+Fe23+Si8O22(OH)2
Cummingtonite-Grunerite asbestos (Amosite)
						(Mg,Fe)7Si8O22(OH)2
Tremolite-Actinolite asbestos
						Ca2(Mg,Fe)5Si8O22(OH)2
Anthophyllite asbestos
						(Mg,Fe)7Si8O22(OH)2
Asbestos Fiber: A fiber of asbestos meeting the criteria
						for a fiber. (See section
						3.5. of this Appendix)
Aspect Ratio: The ratio of the length of a fiber to its
						diameter usually defined as "length : width", e.g. 3:1.
Brucite: A sheet mineral with the composition
						Mg(OH)(2).
Central Stop Dispersion Staining (microscope): This is a
						dark field microscope technique that images particles using only light
						refracted by the particle, excluding light that travels through the particle
						unrefracted. This is usually accomplished with a McCrone objective or other
						arrangement which places a circular stop with apparent aperture equal to the
						objective aperture in the back focal plane of the microscope.
Cleavage Fragments: Mineral particles formed by the
						comminution of minerals, especially those characterized by relatively parallel
						sides and moderate aspect ratio.
Differential Counting: The term applied to the practice
						of excluding certain kinds of fibers from a phase contrast asbestos count
						because they are not asbestos.
Fiber: A particle longer than or equal to 5 [MICRO]m with
						a length to width ratio greater than or equal to 3:1. This may include cleavage
						fragments. (see section
						3.5 of this appendix).
Phase Contrast: Contrast obtained in the microscope by
						causing light scattered by small particles to destructively interfere with
						unscattered light, thereby enhancing the visibility of very small particles and
						particles with very low intrinsic contrast.
Phase Contrast Microscope: A microscope configured with a
						phase mask pair to create phase contrast. The technique which uses this is
						called Phase Contrast Microscopy (PCM).
Phase-Polar Analysis: This is the use of polarized light
						in a phase contrast microscope. It is used to see the same size fibers that are
						visible in air filter analysis. Although fibers finer than 1 [MICRO]m are
						visible, analysis of these is inferred from analysis of larger bundles that are
						usually present.
Phase-Polar Microscope: The phase-polar microscope is a
						phase contrast microscope which has an analyzer, a polarizer, a first order red
						plate and a rotating phase condenser all in place so that the polarized light
						image is enhanced by phase contrast.
Sealing Encapsulant: This is a product which can be
						applied, preferably by spraying, onto an asbestos surface which will seal the
						surface so that fibers cannot be released.
Serpentine: A mineral family consisting of minerals with
						the general composition Mg(3)(Si(2)O(5)(OH)(4) having the magnesium in brucite
						layer over a silicate layer. Minerals important in asbestos analysis included
						in this family are chrysotile, lizardite, antigorite.
1.1. History
Light microscopy has been used for well over 100 years
						for the determination of mineral species. This analysis is carried out using
						specialized polarizing microscopes as well as bright field microscopes. The
						identification of minerals is an on-going process with many new minerals
						described each year. The first recorded use of asbestos was in Finland about
						2500 B.C. where the material was used in the mud wattle for the wooden huts the
						people lived in as well as strengthening for pottery. Adverse health aspects of
						the mineral were noted nearly 2000 years ago when Pliny the Younger wrote about
						the poor health of slaves in the asbestos mines. Although known to be injurious
						for centuries, the first modern references to its toxicity were by the British
						Labor Inspectorate when it banned asbestos dust from the workplace in 1898.
						Asbestosis cases were described in the literature after the turn of the
						century. Cancer was first suspected in the mid 1930's and a causal link to
						mesothelioma was made in 1965. Because of the public concern for worker and
						public safety with the use of this material, several different types of
						analysis were applied to the determination of asbestos content. Light
						microscopy requires a great deal of experience and craft. Attempts were made to
						apply less subjective methods to the analysis. X-ray diffraction was partially
						successful in determining the mineral types but was unable to separate out the
						fibrous portions from the non-fibrous portions. Also, the minimum detection
						limit for asbestos analysis by X-ray diffraction (XRD) is about 1%.
						Differential Thermal Analysis (DTA) was no more successful. These provide
						useful corroborating information when the presence of asbestos has been shown
						by microscopy; however, neither can determine the difference between fibrous
						and non-fibrous minerals when both habits are present. The same is true of
						Infrared Absorption (IR).
When electron microscopy was applied to asbestos
						analysis, hundreds of fibers were discovered present too small to be visible in
						any light microscope. There are two different types of electron microscope used
						for asbestos analysis: Scanning Electron Microscope (SEM) and Transmission
						Electron Microscope (TEM). Scanning Electron Microscopy is useful in
						identifying minerals. The SEM can provide two of the three pieces of
						information required to identify fibers by electron microscopy: morphology and
						chemistry. The third is structure as determined by Selected Area Electron
						Diffraction -- SAED which is performed in the TEM. Although the resolution of
						the SEM is sufficient for very fine fibers to be seen, accuracy of chemical
						analysis that can be performed on the fibers varies with fiber diameter in
						fibers of less than 0.2 [MICRO]m diameter. The TEM is a powerful tool to
						identify fibers too small to be resolved by light microscopy and should be used
						in conjunction with this method when necessary. The TEM can provide all three
						pieces of information required for fiber identification. Most fibers thicker
						than 1 [MICRO]m can adequately be defined in the light microscope. The light
						microscope remains as the best instrument for the determination of mineral
						type. This is because the minerals under investigation were first described
						analytically with the light microscope. It is inexpensive and gives positive
						identification for most samples analyzed. Further, when optical techniques are
						inadequate, there is ample indication that alternative techniques should be
						used for complete identification of the sample.
1.2. Principle
Minerals consist of atoms that may be arranged in random
						order or in a regular arrangement. Amorphous materials have atoms in random
						order while crystalline materials have long range order. Many materials are
						transparent to light, at least for small particles or for thin sections. The
						properties of these materials can be investigated by the effect that the
						material has on light passing through it. The six asbestos minerals are all
						crystalline with particular properties that have been identified and cataloged.
						These six minerals are anisotropic. They have a regular array of atoms, but the
						arrangement is not the same in all directions. Each major direction of the
						crystal presents a different regularity. Light photons travelling in each of
						these main directions will encounter different electrical neighborhoods,
						affecting the path and time of travel. The techniques outlined in this method
						use the fact that light traveling through fibers or crystals in different
						directions will behave differently, but predictably. The behavior of the light
						as it travels through a crystal can be measured and compared with known or
						determined values to identify the mineral species. Usually, Polarized Light
						Microscopy (PLM is performed with strain-free objectives on a bright-field
						microscope platform. This would limit the resolution of the microscope to about
						0.4 [MICRO]m. Because OSHA requires the counting and identification of fibers
						visible in phase contrast, the phase contrast platform is used to visualize the
						fibers with the polarizing elements added into the light path. Polarized light
						methods cannot identify fibers finer than about 1 [MICRO]m in diameter even
						though they are visible. The finest fibers are usually identified by inference
						from the presence of larger, identifiable fiber bundles. When fibers are
						present, but not identifiable by light microscopy, use either SEM or TEM to
						determine the fiber identity.
1.3. Advantages and Disadvantages
The advantages of light microcopy are:
(a) Basic identification of the materials was first
						performed by light microscopy and gross analysis. This provides a large base of
						published information against which to check analysis and analytical
						technique.
(b) The analysis is specific to fibers. The minerals
						present can exist in asbestiform, fibrous, prismatic, or massive varieties all
						at the same time. Therefore, bulk methods of analysis such as X-ray
						diffraction, IR analysis, DTA, etc. are inappropriate where the material is not
						known to be fibrous.
(c) The analysis is quick, requires little preparation
						time, and can be performed on-site if a suitably equipped microscope is
						available.
The disadvantages are:
(a) Even using phase-polar illumination, not all the
						fibers present may be seen. This is a problem for very low asbestos
						concentrations where agglomerations or large bundles of fibers may not be
						present to allow identification by inference.
(b) The method requires a great degree of sophistication
						on the part of the microscopist. An analyst is only as useful as his mental
						catalog of images. Therefore, a microscopist's accuracy is enhanced by
						experience. The mineralogical training of the analyst is very important. It is
						the basis on which subjective decisions are made.
(c) The method uses only a tiny amount of material for
						analysis. This may lead to sampling bias and false results (high or low). This
						is especially true if the sample is severely inhomogeneous.
(d) Fibers may be bound in a matrix and not
						distinguishable as fibers so identification cannot be made.
1.4. Method Performance
1.4.1. This method can be used for determination of
						asbestos content from 0 to 100% asbestos. The detection limit has not been
						adequately determined, although for selected samples, the limit is very low,
						depending on the number of particles examined. For mostly homogeneous, finely
						divided samples, with no difficult fibrous interferences, the detection limit
						is below 1%. For inhomogeneous samples (most samples), the detection limit
						remains undefined. NIST has conducted proficiency testing of laboratories on a
						national scale. Although each round is reported statistically with an average,
						control limits, etc., the results indicate a difficulty in establishing
						precision especially in the low concentration range. It is suspected that there
						is significant bias in the low range especially near 1%. EPA tried to remedy
						this by requiring a mandatory point counting scheme for samples less than 10%.
						The point counting procedure is tedious, and may introduce significant biases
						of its own. It has not been incorporated into this method.
1.4.2. The precision and accuracy of the quantitation
						tests performed in this method are unknown. Concentrations are easier to
						determine in commercial products where asbestos was deliberately added because
						the amount is usually more than a few percent. An analyst's results can be
						"calibrated" against the known amounts added by the manufacturer. For
						geological samples, the degree of homogeneity affects the precision.
1.4.3. The performance of the method is analyst
						dependent. The analyst must choose carefully and not necessarily randomly the
						portions for analysis to assure that detection of asbestos occurs when it is
						present. For this reason, the analyst must have adequate training in sample
						preparation, and experience in the location and identification of asbestos in
						samples. This is usually accomplished through substantial on-the-job training
						as well as formal education in mineralogy and microscopy.
1.5. Interferences
Any material which is long, thin, and small enough to be
						viewed under the microscope can be considered an interference for asbestos.
						There are literally hundreds of interferences in workplaces. The techniques
						described in this method are normally sufficient to eliminate the
						interferences. An analyst's success in eliminating the interferences depends on
						proper training.
Asbestos minerals belong to two mineral families: the
						serpentines and the amphiboles. In the serpentine family, the only common
						fibrous mineral is chrysotile. Occasionally, the mineral antigorite occurs in a
						fibril habit with morphology similar to the amphiboles. The amphibole minerals
						consist of a score of different minerals of which only five are regulated by
						federal standard: amosite, crocidolite, anthophyllite asbestos, tremolite
						asbestos and actinolite asbestos. These are the only amphibole minerals that
						have been commercially exploited for their fibrous properties; however, the
						rest can and do occur occasionally in asbestiform habit.
In addition to the related mineral interferences, other
						minerals common in building material may present a problem for some
						microscopists: gypsum, anhydrite, brucite, quartz fibers, talc fibers or
						ribbons, wollastonite, perlite, attapulgite, etc. Other fibrous materials
						commonly present in workplaces are: fiberglass, mineral wool, ceramic wool,
						refractory ceramic fibers, kevlar, nomex, synthetic fibers, graphite or carbon
						fibers, cellulose (paper or wood) fibers, metal fibers, etc.
Matrix embedding material can sometimes be a negative
						interference. The analyst may not be able to easily extract the fibers from the
						matrix in order to use the method. Where possible, remove the matrix before the
						analysis, taking careful note of the loss of weight. Some common matrix
						materials are: vinyl, rubber, tar, paint, plant fiber, cement, and epoxy. A
						further negative interference is that the asbestos fibers themselves may be
						either too small to be seen in Phase contrast Microscopy (PCM) or of a very low
						fibrous quality, having the appearance of plant fibers. The analyst's ability
						to deal with these materials increases with experience.
1.6. Uses and Occupational Exposure
Asbestos is ubiquitous in the environment. More than 40%
						of the land area of the United States is composed of minerals which may contain
						asbestos. Fortunately, the actual formation of great amounts of asbestos is
						relatively rare. Nonetheless, there are locations in which environmental
						exposure can be severe such as in the Serpentine Hills of California.
There are thousands of uses for asbestos in industry and
						the home. Asbestos abatement workers are the most current segment of the
						population to have occupational exposure to great amounts of asbestos. If the
						material is undisturbed, there is no exposure. Exposure occurs when the
						asbestos-containing material is abraded or otherwise disturbed during
						maintenance operations or some other activity. Approximately 95% of the
						asbestos in place in the United States is chrysotile.
Amosite and crocidolite make up nearly all the
						difference. Tremolite and anthophyllite make up a very small percentage.
						Tremolite is found in extremely small amounts in certain chrysotile deposits.
						Actinolite exposure is probably greatest from environmental sources, but has
						been identified in vermiculite containing, sprayed-on insulating materials
						which may have been certified as asbestos-free.
1.7. Physical and Chemical Properties
The nominal chemical compositions for the asbestos
						minerals were given in Section
						1. Compared to cleavage fragments
						of the same minerals, asbestiform fibers possess a high tensile strength along
						the fiber axis. They are chemically inert, noncombustible, and heat resistant.
						Except for chrysotile, they are insoluble in Hydrochloric acid (HCl).
						Chrysotile is slightly soluble in HCl. Asbestos has high electrical resistance
						and good sound absorbing characteristics. It can be woven into cables, fabrics
						or other textiles, or matted into papers, felts, and mats.
1.8. Toxicology (This Section is for Information Only and
						Should Not Be Taken as OSHA Policy)
Possible physiologic results of respiratory exposure to
						asbestos are mesothelioma of the pleura or peritoneum, interstitial fibrosis,
						asbestosis, pneumoconiosis, or respiratory cancer. The possible consequences of
						asbestos exposure are detailed in the NIOSH Criteria Document or in the OSHA
						Asbestos Standards 29 CFR
						1910.1001,
						29 CFR
						1926.1101, and
						29 CFR
						1915.1001.
2. Sampling Procedure
2.1. Equipment for sampling
(a) Tube or cork borer sampling device
(b) Knife
(c) 20 mL scintillation vial or similar vial
(d) Sealing encapsulant
2.2. Safety Precautions
Asbestos is a known carcinogen. Take care when sampling.
						While in an asbestos-containing atmosphere, a properly selected and fit-tested
						respirator should be worn. Take samples in a manner to cause the least amount
						of dust. Follow these general guidelines:
(a) Do not make unnecessary dust.
(b) Take only a small amount (1 to 2 g).
(c) Tightly close the sample container.
(d) Use encapsulant to seal the spot where the sample was
						taken, if necessary.
2.3. Sampling Procedure
Samples of any suspect material should be taken from an
						inconspicuous place. Where the material is to remain, seal the sampling wound
						with an encapsulant to eliminate the potential for exposure from the sample
						site. Microscopy requires only a few milligrams of material. The amount that
						will fill a 20 mL scintillation vial is more than adequate. Be sure to collect
						samples from all layers and phases of material. If possible, make separate
						samples of each different phase of the material. This will aid in determining
						the actual hazard. DO NOT USE ENVELOPES, PLASTIC OR PAPER BAGS OF ANY KIND TO
						COLLECT SAMPLES. The use of plastic bags presents a contamination hazard to
						laboratory personnel and to other samples. When these containers are opened, a
						bellows effect blows fibers out of the container onto everything, including the
						person opening the container.
If a cork-borer type sampler is available, push the tube
						through the material all the way, so that all layers of material are sampled.
						Some samplers are intended to be disposable. These should be capped and sent to
						the laboratory. If a non-disposable cork borer is used, empty the contents into
						a scintillation vial and send to the laboratory. Vigorously and completely
						clean the cork borer between samples.
2.4. Shipment
Samples packed in glass vials must not touch or they
						might break in shipment.
(a) Seal the samples with a sample seal over the end to
						guard against tampering and to identify the sample.
(b) Package the bulk samples in separate packages from
						the air samples. They may cross-contaminate each other and will invalidate the
						results of the air samples.
(c) Include identifying paperwork with the samples, but
						not in contact with the suspected asbestos.
(d) To maintain sample accountability, ship the samples
						by certified mail, overnight express, or hand carry them to the
						laboratory.
3. Analysis
The analysis of asbestos samples can be divided into two
						major parts: sample preparation and microscopy. Because of the different
						asbestos uses that may be encountered by the analyst, each sample may need
						different preparation steps. The choices are outlined below. There are several
						different tests that are performed to identify the asbestos species and
						determine the percentage. They will be explained below.
3.1. Safety
(a) Do not create unnecessary dust. Handle the samples in
						HEPA- filter equipped hoods. If samples are received in bags, envelopes or
						other inappropriate container, open them only in a hood having a face velocity
						at or greater than 100 fpm. Transfer a small amount to a scintillation vial and
						only handle the smaller amount.
(b) Open samples in a hood, never in the open lab
						area.
(c) Index of refraction oils can be toxic. Take care not
						to get this material on the skin. Wash immediately with soap and water if this
						happens.
(d) Samples that have been heated in the muffle furnace
						or the drying oven may be hot. Handle them with tongs until they are cool
						enough to handle.
(e) Some of the solvents used, such as THF
						(tetrahydrofuran), are toxic and should only be handled in an appropriate fume
						hood and according to instructions given in the Safety Data Sheet (SDS).
3.2. Equipment
(a) Phase contrast microscope with 10x, 16x and 40x
						objectives, 10x wide-field eyepieces, G-22 Walton-Beckett graticule, Whipple
						disk, polarizer, analyzer and first order red or gypsum plate, 100 Watt
						illuminator, rotating position condenser with oversize phase rings, central
						stop dispersion objective, Kohler illumination and a rotating mechanical stage.
						(see Figure 1. of this appendix)
(b) Stereo microscope with reflected light illumination,
						transmitted light illumination, polarizer, analyzer and first order red or
						gypsum plate, and rotating stage.
(c) Negative pressure hood for the stereo
						microscope
(d) Muffle furnace capable of 600 deg.C
(e) Drying oven capable of 50 -- 150 deg.C
(f) Aluminum specimen pans
(g) Tongs for handling samples in the furnace
(h) High dispersion index of refraction oils (Special for
						dispersion staining.)
n = 1.550
n = 1.585
n = 1.590
n = 1.605
n = 1.620
n = 1.670
n = 1.680
n = 1.690
(i) A set of index of refraction oils from about n=1.350
						to n=2.000 in n=0.005 increments. (Standard for Becke line analysis.)
(j) Glass slides with painted or frosted ends 1x3 inches
						1mm thick, precleaned.
(k) Cover Slips 22x22 mm, #1 ½
(
l
) Paper clips or dissection
						needles
(m) Hand grinder
(n) Scalpel with both #10 and #11 blades
(o) 0.1 molar HCl
(p) Decalcifying solution (Baxter Scientific
						Products)
Ethylenediaminetetraacetic Acid, Tetrasodium 0.7
						g/l
Sodium Potassium Tartrate 8.0 mg/liter
Hydrochloric Acid 99.2 g/liter
Sodium Tartrate 0.14 g/liter
(q) Tetrahydrofuran (THF)
(r) Hotplate capable of 60 deg.C
(s) Balance
(t) Hacksaw blade
(u) Ruby mortar and pestle
3.3. Sample Pre-Preparation
Sample preparation begins with pre-preparation which may
						include chemical reduction of the matrix, heating the sample to dryness or
						heating in the muffle furnace. The end result is a sample which has been
						reduced to a powder that is sufficiently fine to fit under the cover slip.
						Analyze different phases of samples separately, e.g., tile and the tile mastic
						should be analyzed separately as the mastic may contain asbestos while the tile
						may not.
(a) Wet Samples
Samples with a high water content will not give the
						proper dispersion colors and must be dried prior to sample mounting. Remove the
						lid of the scintillation vial, place the bottle in the drying oven and heat at
						100 deg.C to dryness (usually about 2 h). Samples which are not submitted to
						the lab in glass must be removed and placed in glass vials or aluminum weighing
						pans before placing them in the drying oven.
(b) Samples With Organic Interference -- Muffle
						Furnace
These may include samples with tar as a matrix, vinyl
						asbestos tile, or any other organic that can be reduced by heating. Remove the
						sample from the vial and weigh in a balance to determine the weight of the
						submitted portion. Place the sample in a muffle furnace at 500 deg.C for 1 to 2
						h or until all obvious organic material has been removed. Retrieve, cool and
						weigh again to determine the weight loss on ignition. This is necessary to
						determine the asbestos content of the submitted sample, because the analyst
						will be looking at a reduced sample.
NOTE: Heating above 600 deg.C will cause the sample to
						undergo a structural change which, given sufficient time, will convert the
						chrysotile to forsterite. Heating even at lower temperatures for 1 to 2 h may
						have a measurable effect on the optical properties of the minerals. If the
						analyst is unsure of what to expect, a sample of standard asbestos should be
						heated to the same temperature for the same length of time so that it can be
						examined for the proper interpretation.
(c) Samples With Organic Interference -- THF
Vinyl asbestos tile is the most common material treated
						with this solvent, although, substances containing tar will sometimes yield to
						this treatment. Select a portion of the material and then grind it up if
						possible. Weigh the sample and place it in a test tube. Add sufficient THF to
						dissolve the organic matrix. This is usually about 4 to 5 mL. Remember, THF is
						highly flammable. Filter the remaining material through a tared silver
						membrane, dry and weigh to determine how much is left after the solvent
						extraction. Further process the sample to remove carbonate or mount
						directly.
(d) Samples With Carbonate Interference
Carbonate material is often found on fibers and sometimes
						must be removed in order to perform dispersion microscopy. Weigh out a portion
						of the material and place it in a test tube. Add a sufficient amount of 0.1 M
						HCl or decalcifying solution in the tube to react all the carbonate as
						evidenced by gas formation; i.e., when the gas bubbles stop, add a little more
						solution. If no more gas forms, the reaction is complete. Filter the material
						out through a tared silver membrane, dry and weigh to determine the weight
						lost.
3.4. Sample Preparation
Samples must be prepared so that accurate determination
						can be made of the asbestos type and amount present. The following steps are
						carried out in the low-flow hood (a low-flow hood has less than 50 fpm
						flow):
(1) If the sample has large lumps, is hard, or cannot be
						made to lie under a cover slip, the grain size must be reduced. Place a small
						amount between two slides and grind the material between them or grind a small
						amount in a clean mortar and pestle. The choice of whether to use an alumina,
						ruby, or diamond mortar depends on the hardness of the material. Impact damage
						can alter the asbestos mineral if too much mechanical shock occurs. (Freezer
						mills can completely destroy the observable crystallinity of asbestos and
						should not be used). For some samples, a portion of material can be shaved off
						with a scalpel, ground off with a hand grinder or hack saw blade.
The preparation tools should either be disposable or
						cleaned thoroughly. Use vigorous scrubbing to loosen the fibers during the
						washing. Rinse the implements with copious amounts of water and air-dry in a
						dust-free environment.
(2) If the sample is powder or has been reduced as in (1)
						above, it is ready to mount. Place a glass slide on a piece of optical tissue
						and write the identification on the painted or frosted end. Place two drops of
						index of refraction medium n=1.550 on the slide. (The medium n=1.550 is chosen
						because it is the matching index for chrysotile. Dip the end of a clean
						paper-clip or dissecting needle into the droplet of refraction medium on the
						slide to moisten it. Then dip the probe into the powder sample. Transfer what
						sticks on the probe to the slide. The material on the end of the probe should
						have a diameter of about 3 mm for a good mount. If the material is very fine,
						less sample may be appropriate. For non-powder samples such as fiber mats,
						forceps should be used to transfer a small amount of material to the slide.
						Stir the material in the medium on the slide, spreading it out and making the
						preparation as uniform as possible. Place a cover-slip on the preparation by
						gently lowering onto the slide and allowing it to fall "trapdoor" fashion on
						the preparation to push out any bubbles. Press gently on the cover slip to even
						out the distribution of particulate on the slide. If there is insufficient
						mounting oil on the slide, one or two drops may be placed near the edge of the
						coverslip on the slide. Capillary action will draw the necessary amount of
						liquid into the preparation. Remove excess oil with the point of a laboratory
						wiper.
Treat at least two different areas of each phase in this
						fashion. Choose representative areas of the sample. It my be useful to select
						particular areas or fibers for analysis. This is useful to identify asbestos in
						severely inhomogeneous samples.
When it is determined that amphiboles may be present,
						repeat the above process using the appropriate high-dispersion oils until an
						identification is made or all six asbestos minerals have been ruled out. Note
						that percent determination must be done in the index medium 1.550 because
						amphiboles tend to disappear in their matching mediums.
3.5. Analytical procedure
NOTE: This method presumes some knowledge of mineralogy
						and optical petrography.
The analysis consists of three parts: The determination
						of whether there is asbestos present, what type is present and the
						determination of how much is present. The general flow of the analysis
						is:
(1) Gross examination.
(2) Examination under polarized light on the stereo
						microscope.
(3) Examination by phase-polar illumination on the
						compound phase microscope.
(4) Determination of species by dispersion stain.
						Examination by Becke line analysis may also be used; however, this is usually
						more cumbersome for asbestos determination.
(5) Difficult samples may need to be analyzed by SEM or
						TEM, or the results from those techniques combined with light microscopy for a
						definitive identification.
Identification of a particle as asbestos requires that it
						be asbestiform. Description of particles should follow the suggestion of
						Campbell. (Figure 1 of this appendix)
Click
						here to view image
Figure 1. Particle definitions showing mineral growth
						habits. From the U.S. Bureau of Mines
For the purpose of regulation, the mineral must be one of
						the six minerals covered and must be in the asbestos growth habit. Large
						specimen samples of asbestos generally have the gross appearance of wood.
						Fibers are easily parted from it. Asbestos fibers are very long compared with
						their widths. The fibers have a very high tensile strength as demonstrated by
						bending without breaking. Asbestos fibers exist in bundles that are easily
						parted, show longitudinal fine structure and may be tufted at the ends showing
						"bundle of sticks" morphology. In the microscope some of these properties may
						not be observable. Amphiboles do not always show striations along their length
						even when they are asbestos. Neither will they always show tufting. They
						generally do not show a curved nature except for very long fibers. Asbestos and
						asbestiform minerals are usually characterized in groups by extremely high
						aspect ratios (greater than 100:1). While aspect ratio analysis is useful for
						characterizing populations of fibers, it cannot be used to identify individual
						fibers of intermediate to short aspect ratio. Observation of many fibers is
						often necessary to determine whether a sample consists of "cleavage fragments"
						or of asbestos fibers.
Most cleavage fragments of the asbestos minerals are
						easily distinguishable from true asbestos fibers. This is because true cleavage
						fragments usually have larger diameters than 1 [MICRO]m. Internal structure of
						particles larger than this usually shows them to have no internal fibrillar
						structure. In addition, cleavage fragments of the monoclinic amphiboles show
						inclined extinction under crossed polars with no compensator. Asbestos fibers
						usually show extinction at zero degrees or ambiguous extinction if any at all.
						Morphologically, the larger cleavage fragments are obvious by their blunt or
						stepped ends showing prismatic habit. Also, they tend to be circular rather
						than filiform.
Where the particles are less than 1 [MICRO]m in diameter
						and have an aspect ratio greater than or equal to 3:1, it is recommended that
						the sample be analyzed by SEM or TEM if there is any question whether the
						fibers are cleavage fragments or asbestiform particles. Care must be taken when
						analyzing by electron microscopy because the interferences are different from
						those in light microscopy and may structurally be very similar to asbestos. The
						classic interference is between anthophyllite and biopyribole or intermediate
						fiber. Use the same morphological clues for electron microscopy as are used for
						light microscopy, e.g. fibril splitting, internal longitudinal striation,
						fraying, curvature, etc.
(1) Gross examination:
Examine the sample, preferably in the glass vial.
						Determine the presence of any obvious fibrous component. Estimate a percentage
						based on previous experience and current observation. Determine whether any
						prepreparation is necessary. Determine the number of phases present. This step
						may be carried out or augmented by observation at 6 to 40 x under a stereo
						microscope.
(2) After performing any necessary pre-preparation,
						prepare slides of each phase as described above. Two preparations of the same
						phase in the same index medium can be made side-by-side on the same glass for
						convenience. Examine with the polarizing stereo microscope. Estimate the
						percentage of asbestos based on the amount of birefringent fiber
						present.
(3) Examine the slides on the phase-polar microscopes at
						magnifications of 160 and 400x. Note the morphology of the fibers. Long, thin,
						very straight fibers with little curvature are indicative of fibers from the
						amphibole family. Curved, wavy fibers are usually indicative of chrysotile.
						Estimate the percentage of asbestos on the phase-polar microscope under
						conditions of crossed polars and a gypsum plate. Fibers smaller than 1.0
						[MICRO]m in thickness must be identified by inference to the presence of
						larger, identifiable fibers and morphology. If no larger fibers are visible,
						electron microscopy should be performed. At this point, only a tentative
						identification can be made. Full identification must be made with dispersion
						microscopy. Details of the tests are included in the appendices.
(4) Once fibers have been determined to be present, they
						must be identified. Adjust the microscope for dispersion mode and observe the
						fibers. The microscope has a rotating stage, one polarizing element, and a
						system for generating dark-field dispersion microscopy (see Section
						4.6. of this appendix). Align a
						fiber with its length parallel to the polarizer and note the color of the Becke
						lines. Rotate the stage to bring the fiber length perpendicular to the
						polarizer and note the color. Repeat this process for every fiber or fiber
						bundle examined. The colors must be consistent with the colors generated by
						standard asbestos reference materials for a positive identification. In
						n=1.550, amphiboles will generally show a yellow to straw-yellow color
						indicating that the fiber indices of refraction are higher than the liquid. If
						long, thin fibers are noted and the colors are yellow, prepare further slides
						as above in the suggested matching liquids listed below:
Type of
								asbestos
Index of refraction
Chrysotile
n = 1.550.
Amosite
n = 1.670 or
								1.680.
Crocidolite
n = 1.690.
Anthophyllite
n = 1.605 and
								1.620.
Tremolite
n = 1.605 and
								1.620.
Actinolite
n = 1.620.
Where more than one liquid is suggested, the first is
						preferred; however, in some cases this liquid will not give good dispersion
						color. Take care to avoid interferences in the other liquid; e.g., wollastonite
						in n=1.620 will give the same colors as tremolite. In n=1.605 wollastonite will
						appear yellow in all directions. Wollastonite may be determined under crossed
						polars as it will change from blue to yellow as it is rotated along its fiber
						axis by tapping on the cover slip. Asbestos minerals will not change in this
						way.
Determination of the angle of extinction may, when
						present, aid in the determination of anthophyllite from tremolite. True
						asbestos fibers usually have 0 deg. extinction or ambiguous extinction, while
						cleavage fragments have more definite extinction.
Continue analysis until both preparations have been
						examined and all present species of asbestos are identified. If there are no
						fibers present, or there is less than 0.1% present, end the analysis with the
						minimum number of slides (2).
(5) Some fibers have a coating on them which makes
						dispersion microscopy very difficult or impossible. Becke line analysis or
						electron microscopy may be performed in those cases. Determine the percentage
						by light microscopy. TEM analysis tends to overestimate the actual percentage
						present.
(6) Percentage determination is an estimate of occluded
						area, tempered by gross observation. Gross observation information is used to
						make sure that the high magnification microscopy does not greatly over- or
						underestimate the amount of fiber present. This part of the analysis requires a
						great deal of experience. Satisfactory models for asbestos content analysis
						have not yet been developed, although some models based on metallurgical
						grain-size determination have found some utility. Estimation is more easily
						handled in situations where the grain sizes visible at about 160x are about the
						same and the sample is relatively homogeneous.
View all of the area under the cover slip to make the
						percentage determination. View the fields while moving the stage, paying
						attention to the clumps of material. These are not usually the best areas to
						perform dispersion microscopy because of the interference from other materials.
						But, they are the areas most likely to represent the accurate percentage in the
						sample. Small amounts of asbestos require slower scanning and more frequent
						analysis of individual fields. Report the area occluded by asbestos as the
						concentration. This estimate does not generally take into consideration the
						difference in density of the different species present in the sample. For most
						samples this is adequate. Simulation studies with similar materials must be
						carried out to apply microvisual estimation for that purpose and is beyond the
						scope of this procedure.
(7) Where successive concentrations have been made by
						chemical or physical means, the amount reported is the percentage of the
						material in the "as submitted" or original state. The percentage determined by
						microscopy is multiplied by the fractions remaining after pre-preparation steps
						to give the percentage in the original sample. For example:
Step 1. 60% remains after heating at 550 deg.C for 1
						h.
Step 2. 30% of the residue of step 1 remains after
						dissolution of carbonate in 0.1 m HCl.
Step 3. Microvisual estimation determines that 5% of the
						sample is chrysotile asbestos.
The reported result is:
R = (Microvisual result in percent) x (Fraction remaining
						after step 2) x (Fraction remaining of original sample after step 1)
R = (5) x (.30) x (.60) = 0.9%
(8) Report the percent and type of asbestos present. For
						samples where asbestos was identified, but is less than 1.0%, report "Asbestos
						present, less than 1.0%." There must have been at least two observed fibers or
						fiber bundles in the two preparations to be reported as present. For samples
						where asbestos was not seen, report as "None Detected." Auxiliary Information
						Because of the subjective nature of asbestos analysis, certain concepts and
						procedures need to be discussed in more depth. This information will help the
						analyst understand why some of the procedures are carried out the way they
						are.
4.1. Light
Light is electromagnetic energy. It travels from its
						source in packets called quanta. It is instructive to consider light as a plane
						wave. The light has a direction of travel. Perpendicular to this and mutually
						perpendicular to each other, are two vector components. One is the magnetic
						vector and the other is the electric vector. We shall only be concerned with
						the electric vector. In this description, the interaction of the vector and the
						mineral will describe all the observable phenomena. From a light source such a
						microscope illuminator, light travels in all different direction from the
						filament.
In any given direction away from the filament, the
						electric vector is perpendicular to the direction of travel of a light ray.
						While perpendicular, its orientation is random about the travel axis. If the
						electric vectors from all the light rays were lined up by passing the light
						through a filter that would only let light rays with electric vectors oriented
						in one direction pass, the light would then be POLARIZED.
Polarized light interacts with matter in the direction of
						the electric vector. This is the polarization direction. Using this property it
						is possible to use polarized light to probe different materials and identify
						them by how they interact with light. The speed of light in a vacuum is a
						constant at about 2.99 x 10(8) m/s. When light travels in different materials
						such as air, water, minerals or oil, it does not travel at this speed. It
						travels slower. This slowing is a function of both the material through which
						the light is traveling and the wavelength or frequency of the light. In
						general, the more dense the material, the slower the light travels. Also,
						generally, the higher the frequency, the slower the light will travel. The
						ratio of the speed of light in a vacuum to that in a material is called the
						index of refraction (n). It is usually measured at 589 nm (the sodium D line).
						If white light (light containing all the visible wavelengths) travels through a
						material, rays of longer wavelengths will travel faster than those of shorter
						wavelengths, this separation is called dispersion. Dispersion is used as an
						identifier of materials as described in Section
						4.6.
4.2. Material Properties
Materials are either amorphous or crystalline. The
						difference between these two descriptions depends on the positions of the atoms
						in them. The atoms in amorphous materials are randomly arranged with no long
						range order. An example of an amorphous material is glass. The atoms in
						crystalline materials, on the other hand, are in regular arrays and have long
						range order. Most of the atoms can be found in highly predictable locations.
						Examples of crystalline material are salt, gold, and the asbestos
						minerals.
It is beyond the scope of this method to describe the
						different types of crystalline materials that can be found, or the full
						description of the classes into which they can fall. However, some general
						crystallography is provided below to give a foundation to the procedures
						described.
With the exception of anthophyllite, all the asbestos
						minerals belong to the monoclinic crystal type. The unit cell is the basic
						repeating unit of the crystal and for monoclinic crystals can be described as
						having three unequal sides, two 90 deg. angles and one angle not equal to 90
						deg.. The orthorhombic group, of which anthophyllite is a member has three
						unequal sides and three 90 deg. angles. The unequal sides are a consequence of
						the complexity of fitting the different atoms into the unit cell. Although the
						atoms are in a regular array, that array is not symmetrical in all directions.
						There is long range order in the three major directions of the crystal.
						However, the order is different in each of the three directions. This has the
						effect that the index of refraction is different in each of the three
						directions. Using polarized light, we can investigate the index of refraction
						in each of the directions and identify the mineral or material under
						investigation. The indices alpha, beta, and gamma are used to identify the
						lowest, middle, and highest index of refraction respectively. The x direction,
						associated with alpha is called the fast axis. Conversely, the z direction is
						associated with gamma and is the slow direction. Crocidolite has alpha along
						the fiber length making it "length-fast". The remainder of the asbestos
						minerals have the gamma axis along the fiber length. They are called
						"length-slow". This orientation to fiber length is used to aid in the
						identification of asbestos.
4.3. Polarized Light Technique
Polarized light microscopy as described in this section
						uses the phase-polar microscope described in Section
						3.2. A phase contrast microscope is
						fitted with two polarizing elements, one below and one above the sample. The
						polarizers have their polarization directions at right angles to each
						other.
Depending on the tests performed, there may be a
						compensator between these two polarizing elements. A compensator is a piece of
						mineral with known properties that "compensates" for some deficiency in the
						optical train. Light emerging from a polarizing element has its electric vector
						pointing in the polarization direction of the element. The light will not be
						subsequently transmitted through a second element set at a right angle to the
						first element. Unless the light is altered as it passes from one element to the
						other, there is no transmission of light.
4.4. Angle of Extinction
Crystals which have different crystal regularity in two
						or three main directions are said to be anisotropic. They have a different
						index of refraction in each of the main directions. When such a crystal is
						inserted between the crossed polars, the field of view is no longer dark but
						shows the crystal in color. The color depends on the properties of the crystal.
						The light acts as if it travels through the crystal along the optical axes. If
						a crystal optical axis were lined up along one of the polarizing directions
						(either the polarizer or the analyzer) the light would appear to travel only in
						that direction, and it would blink out or go dark. The difference in degrees
						between the fiber direction and the angle at which it blinks out is called the
						angle of extinction. When this angle can be measured, it is useful in
						identifying the mineral. The procedure for measuring the angle of extinction is
						to first identify the polarization direction in the microscope. A commercial
						alignment slide can be used to establish the polarization directions or use
						anthophyllite or another suitable mineral. This mineral has a zero degree angle
						of extinction and will go dark to extinction as it aligns with the polarization
						directions. When a fiber of anthophyllite has gone to extinction, align the
						eyepiece reticle or graticule with the fiber so that there is a visual cue as
						to the direction of polarization in the field of view. Tape or otherwise secure
						the eyepiece in this position so it will not shift.
After the polarization direction has been identified in
						the field of view, move the particle of interest to the center of the field of
						view and align it with the polarization direction. For fibers, align the fiber
						along this direction. Note the angular reading of the rotating stage. Looking
						at the particle, rotate the stage until the fiber goes dark or "blinks out".
						Again note the reading of the stage. The difference in the first reading and
						the second is an angle of extinction.
The angle measured may vary as the orientation of the
						fiber changes about its long axis. Tables of mineralogical data usually report
						the maximum angle of extinction. Asbestos forming minerals, when they exhibit
						an angle of extinction, usually do show an angle of extinction close to the
						reported maximum, or as appropriate depending on the substitution
						chemistry.
4.5. Crossed Polars with Compensator
When the optical axes of a crystal are not lined up along
						one of the polarizing directions (either the polarizer or the analyzer) part of
						the light travels along one axis and part travels along the other visible axis.
						This is characteristic of birefringent materials.
The color depends on the difference of the two visible
						indices of refraction and the thickness of the crystal. The maximum difference
						available is the difference between the alpha and the gamma axes. This maximum
						difference is usually tabulated as the birefringence of the crystal.
For this test, align the fiber at 45 deg. to the
						polarization directions in order to maximize the contribution to each of the
						optical axes. The colors seen are called retardation colors. They arise from
						the recombination of light which has traveled through the two separate
						directions of the crystal. One of the rays is retarded behind the other since
						the light in that direction travels slower. On recombination, some of the
						colors which make up white light are enhanced by constructive interference and
						some are suppressed by destructive interference. The result is a color
						dependent on the difference between the indices and the thickness of the
						crystal. The proper colors, thicknesses, and retardations are shown on a
						Michel-Levy chart. The three items, retardation, thickness and birefringence
						are related by the following relationship:
R = t (n gamma - n alpha)
R = retardation, t = crystal thickness in [MICRO]m,
						and
n alpha, gamma = indices of refraction.
Examination of the equation for asbestos minerals reveals
						that the visible colors for almost all common asbestos minerals and fiber sizes
						are shades of gray and black. The eye is relatively poor at discriminating
						different shades of gray. It is very good at discriminating different colors.
						In order to compensate for the low retardation, a compensator is added to the
						light train between the polarization elements. The compensator used for this
						test is a gypsum plate of known thickness and birefringence. Such a compensator
						when oriented at 45 deg. to the polarizer direction, provides a retardation of
						530 nm of the 530 nm wavelength color. This enhances the red color and gives
						the background a characteristic red to red-magenta color. If this "full-wave"
						compensator is in place when the asbestos preparation is inserted into the
						light train, the colors seen on the fibers are quite different. Gypsum, like
						asbestos has a fast axis and a slow axis. When a fiber is aligned with its fast
						axis in the same direction as the fast axis of the gypsum plate, the ray
						vibrating in the slow direction is retarded by both the asbestos and the
						gypsum. This results in a higher retardation than would be present for either
						of the two minerals. The color seen is a second order blue. When the fiber is
						rotated 90 deg. using the rotating stage, the slow direction of the fiber is
						now aligned with the fast direction of the gypsum and the fast direction of the
						fiber is aligned with the slow direction of the gypsum. Thus, one ray vibrates
						faster in the fast direction of the gypsum, and slower in the slow direction of
						the fiber; the other ray will vibrate slower in the slow direction of the
						gypsum and faster in the fast direction of the fiber. In this case, the effect
						is subtractive and the color seen is a first order yellow. As long as the fiber
						thickness does not add appreciably to the color, the same basic colors will be
						seen for all asbestos types except crocidolite. In crocidolite the colors will
						be weaker, may be in the opposite directions, and will be altered by the blue
						absorption color natural to crocidolite. Hundreds of other materials will give
						the same colors as asbestos, and therefore, this test is not definitive for
						asbestos. The test is useful in discriminating against fiberglass or other
						amorphous fibers such as some synthetic fibers. Certain synthetic fibers will
						show retardation colors different than asbestos; however, there are some forms
						of polyethylene and aramid which will show morphology and retardation colors
						similar to asbestos minerals. This test must be supplemented with a positive
						identification test when birefringent fibers are present which cannot be
						excluded by morphology. This test is relatively ineffective for use on fibers
						less than 1 [MICRO]m in diameter. For positive confirmation TEM or SEM should
						be used if no larger bundles or fibers are visible.
4.6. Dispersion Staining
Dispersion microscopy or dispersion staining is the
						method of choice for the identification of asbestos in bulk materials. Becke
						line analysis is used by some laboratories and yields the same results as does
						dispersion staining for asbestos and can be used in lieu of dispersion
						staining. Dispersion staining is performed on the same platform as the
						phase-polar analysis with the analyzer and compensator removed. One polarizing
						element remains to define the direction of the light so that the different
						indices of refraction of the fibers may be separately determined. Dispersion
						microscopy is a dark-field technique when used for asbestos. Particles are
						imaged with scattered light. Light which is unscattered is blocked from
						reaching the eye either by the back field image mask in a McCrone objective or
						a back field image mask in the phase condenser. The most convenient method is
						to use the rotating phase condenser to move an oversized phase ring into place.
						The ideal size for this ring is for the central disk to be just larger than the
						objective entry aperture as viewed in the back focal plane. The larger the
						disk, the less scattered light reaches the eye. This will have the effect of
						diminishing the intensity of dispersion color and will shift the actual color
						seen. The colors seen vary even on microscopes from the same manufacturer. This
						is due to the different bands of wavelength exclusion by different mask sizes.
						The mask may either reside in the condenser or in the objective back focal
						plane. It is imperative that the analyst determine by experimentation with
						asbestos standards what the appropriate colors should be for each asbestos
						type. The colors depend also on the temperature of the preparation and the
						exact chemistry of the asbestos. Therefore, some slight differences from the
						standards should be allowed. This is not a serious problem for commercial
						asbestos uses. This technique is used for identification of the indices of
						refraction for fibers by recognition of color. There is no direct numerical
						readout of the index of refraction. Correlation of color to actual index of
						refraction is possible by referral to published conversion tables. This is not
						necessary for the analysis of asbestos. Recognition of appropriate colors along
						with the proper morphology are deemed sufficient to identify the commercial
						asbestos minerals. Other techniques including SEM, TEM, and XRD may be required
						to provide additional information in order to identify other types of
						asbestos
Make a preparation in the suspected matching high
						dispersion oil, e.g., n=1.550 for chrysotile. Perform the preliminary tests to
						determine whether the fibers are birefringent or not. Take note of the
						morphological character. Wavy fibers are indicative of chrysotile while long,
						straight, thin, frayed fibers are indicative of amphibole asbestos. This can
						aid in the selection of the appropriate matching oil. The microscope is set up
						and the polarization direction is noted as in Section
						4.4. Align a fiber with the
						polarization direction. Note the color. This is the color parallel to the
						polarizer. Then rotate the fiber rotating the stage 90 deg. so that the
						polarization direction is across the fiber. This is the perpendicular position.
						Again note the color. Both colors must be consistent with standard asbestos
						minerals in the correct direction for a positive identification of asbestos. If
						only one of the colors is correct while the other is not, the identification is
						not positive. If the colors in both directions are bluish-white, the analyst
						has chosen a matching index oil which is higher than the correct matching oil,
						e.g. the analyst has used n=1.620 where chrysotile is present. The next lower
						oil (Section
						3.5.) should be used to prepare
						another specimen. If the color in both directions is yellow-white to
						straw-yellow-white, this indicates that the index of the oil is lower than the
						index of the fiber, e.g. the preparation is in n=1.550 while anthophyllite is
						present. Select the next higher oil (Section
						3.5.) and prepare another slide.
						Continue in this fashion until a positive identification of all asbestos
						species present has been made or all possible asbestos species have been ruled
						out by negative results in this test. Certain plant fibers can have similar
						dispersion colors as asbestos. Take care to note and evaluate the morphology of
						the fibers or remove the plant fibers in pre-preparation. Coating material on
						the fibers such as carbonate or vinyl may destroy the dispersion color.
						Usually, there will be some outcropping of fiber which will show the colors
						sufficient for identification. When this is not the case, treat the sample as
						described in Section
						3.3. and then perform dispersion
						staining. Some samples will yield to Becke line analysis if they are coated or
						electron microscopy can be used for identification.
5. References
5.1. Crane, D.T., Asbestos in Air, OSHA method ID160,
						Revised November 1992.
5.2. Ford, W.E., Dana's Textbook of Mineralogy; Fourth
						Ed.; John Wiley and Son, New York, 1950, p. vii.
5.3. Selikoff, I.J., Lee, D.H.K., Asbestos and Disease,
						Academic Press, New York, 1978, pp. 3,20.
5.4. Women Inspectors of Factories. Annual Report for
						1898, H.M. Statistical Office, London, p. 170 (1898).
5.5. Selikoff, I.J., Lee, D.H.K., Asbestos and Disease,
						Academic Press, New York, 1978, pp. 26,30.
5.6. Campbell, W.J., et al, Selected Silicate Minerals
						and Their Asbestiform Varieties, United States Department of the Interior,
						Bureau of Mines, Information Circular 8751, 1977.
5.7. Asbestos, Code of Federal Regulations,
						29 CFR
						1910.1001 and
						29 CFR
						1926.58.
5.8. National Emission Standards for Hazardous Air
						Pollutants; Asbestos NESHAP Revision, Federal Register, Vol. 55, No. 224, 20
						November 1990, p. 48410.
5.9. Ross, M. The Asbestos Minerals: Definitions,
						Description, Modes of Formation, Physical and Chemical Properties and Health
						Risk to the Mining Community, Nation Bureau of Standards Special Publication,
						Washington, D.C., 1977.
5.10. Lilis, R., Fibrous Zeolites and Endemic
						Mesothelioma in Cappadocia, Turkey, J. Occ Medicine, 1981,
						23,(8),548-550.
5.11. Occupational Exposure to Asbestos -- 1972, U.S.
						Department of Health Education and Welfare, Public Health Service, Center for
						Disease Control, National Institute for Occupational Safety and Health,
						HSM-72-10267.
5.12. Campbell,W.J., et al, Relationship of Mineral Habit
						to Size Characteristics for Tremolite Fragments and Fibers, United States
						Department of the Interior, Bureau of Mines, Information Circular 8367,
						1979.
5.13. Mefford, D., DCM Laboratory, Denver, private
						communication, July 1987.
5.14. Deer, W.A., Howie, R.A., Zussman, J., Rock Forming
						Minerals, Longman, Thetford, UK, 1974.
5.15. Kerr, P.F., Optical Mineralogy; Third Ed.
						McGraw-Hill, New York, 1959.
5.16. Veblen, D.R. (Ed.), Amphiboles and Other Hydrous
						Pyriboles -- Mineralogy, Reviews in Mineralogy, Vol 9A, Michigan, 1982, pp
						1-102.
5.17. Dixon, W.C., Applications of Optical Microscopy in
						the Analysis of Asbestos and Quartz, ACS Symposium Series, No. 120, Analytical
						Techniques in Occupational Health Chemistry, 1979.
5.18. Polarized Light Microscopy, McCrone Research
						Institute, Chicago, 1976.
5.19. Asbestos Identification, McCrone Research
						Institute, G & G printers, Chicago, 1987.
5.20. McCrone, W.C., Calculation of Refractive Indices
						from Dispersion Staining Data, The Microscope, No 37, Chicago, 1989.
5.21. Levadie, B. (Ed.), Asbestos and Other Health
						Related Silicates, ASTM Technical Publication 834, ASM, Philadelphia
						1982.
5.22. Steel, E. and Wylie, A., Riordan, P.H. (Ed.),
						Mineralogical Characteristics of Asbestos, Geology of Asbestos Deposits, pp.
						93-101, SME-AIME, 1981.
5.23. Zussman, J., The Mineralogy of Asbestos, Asbestos:
						Properties, Applications and Hazards, pp. 45-67 Wiley, 1979.
1. New
						Appendix K to section
						1529 filed 5-3-96; operative 7-3-96
						(Register 96, No. 18).
2. Change without regulatory effect repealing
						and adopting new Figure 1 filed 5-19-2008 pursuant to section
						100, title 1, California Code of
						Regulations (Register 2008, No. 21).
3. Amendment of subsection
						3.1(e) filed
						5-5-2014; operative 5-6-2014 pursuant to Government Code section
						11343.4(b)(3)
						(Register 2014, No. 19).
Note: Authority cited: Section
						  142.3. Labor
						  Code. Reference: Section
						  142.3, Labor
						  Code.