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Asbestos.
29 CFR 1910.1001 (2023-06-05)
This content is from the eCFR and is authoritative but unofficial.
Title 29 —Labor
Subtitle B —Regulations Relating to Labor
Chapter XVII —Occupational Safety and Health Administration, Department of Labor
Part 1910 —Occupational Safety and Health Standards
Subpart Z —Toxic and Hazardous Substances
Authority: 29 U.S.C. 653, 655, 657; Secretary of Labor's Order No. 12–71 (36 FR 8754), 8–76 (41 FR 25059), 9–83 (48 FR
35736), 1–90 (55 FR 9033), 6–96 (62 FR 111), 3–2000 (65 FR 50017), or 5–2007 (72 FR 31159), 4–2010 (75 FR 55355) or
1–2012 (77 FR 3912), as applicable; and 29 CFR part 1911. All of subpart Z issued under 29 U.S.C. 655(b), except those
substances that have exposure limits listed in Tables Z–1, Z–2, and Z–3 of § 1910.1000. The latter were issued under 29
U.S.C. 655(a). Section 1910.1000, Tables Z–1, Z–2 and Z–3 also issued under 5 U.S.C. 553, but not under 29 CFR part 1911
except for the arsenic (organic compounds), benzene, cotton dust, and chromium (VI) listings. See Subpart Z of Part 1910 for
more
Source: 39 FR 23502, June 27, 1974, unless otherwise noted. Redesignated at 40 FR 23072, May 28, 1975.
Source: 39 FR 23502, June 27, 1974, unless otherwise noted.
Editorial Note: Nomenclature changes to part 1910 appear at 84 FR 21597, May 14, 2019.
§ 1910.1001 Asbestos.
(a) Scope and application.
(1) This section applies to all occupational exposures to asbestos in all industries covered by the
Occupational Safety and Health Act, except as provided in paragraph (a)(2) and (3) of this section.
(2) This section does not apply to construction work as defined in 29 CFR 1910.12(b). (Exposure to
asbestos in construction work is covered by 29 CFR 1926.1101).
(3) This section does not apply to ship repairing, shipbuilding and shipbreaking employments and
related employments as defined in 29 CFR 1915.4. (Exposure to asbestos in these employments is
covered by 29 CFR 1915.1001).
(b) Definitions. Asbestos includes chrysotile, amosite, crocidolite, tremolite asbestos, anthophyllite asbestos,
actinolite asbestos, and any of these minerals that have been chemically treated and/or altered.
Asbestos-containing material (ACM) means any material containing more than 1% asbestos.
Assistant Secretary means the Assistant Secretary of Labor for Occupational Safety and Health, U.S.
Department of Labor, or designee.
Authorized person means any person authorized by the employer and required by work duties to be present
in regulated areas.
Building/facility owner is the legal entity, including a lessee, which exercises control over management and
record keeping functions relating to a building and/or facility in which activities covered by this
standard take place.
Certified industrial hygienist (CIH) means one certified in the practice of industrial hygiene by the American
Board of Industrial Hygiene.
Director means the Director of the National Institute for Occupational Safety and Health, U.S. Department
of Health and Human Services, or designee.
29 CFR 1910.1001(b) “Director” (enhanced display)
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29 CFR 1910.1001 (up to date as of 6/05/2023)
Asbestos.
29 CFR 1910.1001(b) “Employee exposure”
Employee exposure means that exposure to airborne asbestos that would occur if the employee were not
using respiratory protective equipment.
Fiber means a particulate form of asbestos 5 micrometers or longer,with a length-to-diameter ratio of at
least 3 to 1.
High-efficiency particulate air (HEPA) filter means a filter capable of trapping and retaining at least 99.97
percent of 0.3 micrometer diameter mono-disperse particles.
Homogeneous area means an area of surfacing material or thermal system insulation that is uniform in
color and texture.
Industrial hygienist means a professional qualified by education, training, and experience to anticipate,
recognize, evaluate and develop controls for occupational health hazards.
PACM means “presumed asbestos containing material.”
Presumed asbestos containing material means thermal system insulation and surfacing material found in
buildings constructed no later than 1980. The designation of a material as “PACM” may be rebutted
pursuant to paragraph (j)(8) of this section.
Regulated area means an area established by the employer to demarcate areas where airborne
concentrations of asbestos exceed, or there is a reasonable possibility they may exceed, the
permissible exposure limits.
Surfacing ACM means surfacing material which contains more than 1% asbestos.
Surfacing material means material that is sprayed, troweled-on or otherwise applied to surfaces (such as
acoustical plaster on ceilings and fireproofing materials on structural members, or other materials
on surfaces for acoustical, fireproofing, and other purposes).
Thermal System Insulation (TSI) means ACM applied to pipes, fittings, boilers, breeching, tanks, ducts or
other structural components to prevent heat loss or gain.
Thermal System Insulation ACM means thermal system insulation which contains more than 1% asbestos.
(c) Permissible exposure limit (PELS) —
(1) Time-weighted average limit (TWA). The employer shall ensure that no employee is exposed to an
airborne concentration of asbestos in excess of 0.1 fiber per cubic centimeter of air as an eight (8)hour time-weighted average (TWA) as determined by the method prescribed in appendix A to this
section, or by an equivalent method.
(2) Excursion limit. The employer shall ensure that no employee is exposed to an airborne concentration
of asbestos in excess of 1.0 fiber per cubic centimeter of air (1 f/cc) as averaged over a sampling
period of thirty (30) minutes as determined by the method prescribed in appendix A to this section,
or by an equivalent method.
(d) Exposure monitoring —
(1) General.
(i)
Determinations of employee exposure shall be made from breathing zone air samples that are
representative of the 8-hour TWA and 30-minute short-term exposures of each employee.
29 CFR 1910.1001(d)(1)(i) (enhanced display)
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29 CFR 1910.1001 (up to date as of 6/05/2023)
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29 CFR 1910.1001(d)(1)(ii)
(ii) Representative 8-hour TWA employee exposures shall be determined on the basis of one or
more samples representing full-shift exposures for each shift for each employee in each job
classification in each work area. Representative 30-minute short-term employee exposures
shall be determined on the basis of one or more samples representing 30 minute exposures
associated with operations that are most likely to produce exposures above the excursion limit
for each shift for each job classification in each work area.
(2) Initial monitoring.
(i)
Each employer who has a workplace or work operation covered by this standard, except as
provided for in paragraphs (d)(2)(ii) and (d)(2)(iii) of this section, shall perform initial monitoring
of employees who are, or may reasonably be expected to be exposed to airborne
concentrations at or above the TWA permissible exposure limit and/or excursion limit.
(ii) Where the employer has monitored after March 31, 1992, for the TWA permissible exposure
limit and/or the excursion limit, and the monitoring satisfies all other requirements of this
section, the employer may rely on such earlier monitoring results to satisfy the requirements of
paragraph (d)(2)(i) of this section.
(iii) Where the employer has relied upon objective data that demonstrate that asbestos is not
capable of being released in airborne concentrations at or above the TWA permissible exposure
limit and/or excursion limit under the expected conditions of processing, use, or handling, then
no initial monitoring is required.
(3) Monitoring frequency (periodic monitoring) and patterns. After the initial determinations required by
paragraph (d)(2)(i) of this section, samples shall be of such frequency and pattern as to represent
with reasonable accuracy the levels of exposure of the employees. In no case shall sampling be at
intervals greater than six months for employees whose exposures may reasonably be foreseen to
exceed the TWA permissible exposure limit and/or excursion limit.
(4) Changes in monitoring frequency. If either the initial or the periodic monitoring required by
paragraphs (d)(2) and (d)(3) of this section statistically indicates that employee exposures are below
the TWA permissible exposure limit and/or excursion limit, the employer may discontinue the
monitoring for those employees whose exposures are represented by such monitoring.
(5) Additional monitoring. Notwithstanding the provisions of paragraphs (d)(2)(ii) and (d)(4) of this
section, the employer shall institute the exposure monitoring required under paragraphs (d)(2)(i) and
(d)(3) of this section whenever there has been a change in the production, process, control
equipment, personnel or work practices that may result in new or additional exposures above the
TWA permissible exposure limit and/or excursion limit or when the employer has any reason to
suspect that a change may result in new or additional exposures above the PEL and/or excursion
limit.
(6) Method of monitoring.
(i)
All samples taken to satisfy the monitoring requirements of paragraph (d) of this section shall
be personal samples collected following the procedures specified in appendix A.
(ii) All samples taken to satisfy the monitoring requirements of paragraph (d) of this section shall
be evaluated using the OSHA Reference Method (ORM) specified in appendix A of this section,
or an equivalent counting method.
29 CFR 1910.1001(d)(6)(ii) (enhanced display)
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29 CFR 1910.1001(d)(6)(iii)
(iii) If an equivalent method to the ORM is used, the employer shall ensure that the method meets
the following criteria:
(A) Replicate exposure data used to establish equivalency are collected in side-by-side field
and laboratory comparisons; and
(B) The comparison indicates that 90% of the samples collected in the range 0.5 to 2.0 times
the permissible limit have an accuracy range of plus or minus 25 percent of the ORM
results at a 95% confidence level as demonstrated by a statistically valid protocol; and
(C) The equivalent method is documented and the results of the comparison testing are
maintained.
(iv) To satisfy the monitoring requirements of paragraph (d) of this section, employers must use the
results of monitoring analysis performed by laboratories which have instituted quality
assurance programs that include the elements as prescribed in appendix A of this section.
(7) Employee notification of monitoring results.
(i)
The employer must, within 15 working days after the receipt of the results of any monitoring
performed under this sections, notify each affected employee of these results either individually
in writing or by posting the results in an appropriate location that is accessible to affected
employees.
(ii) The written notification required by paragraph (d)(7)(i) of this section shall contain the
corrective action being taken by the employer to reduce employee exposure to or below the
TWA and/or excursion limit, wherever monitoring results indicated that the TWA and/or
excursion limit had been exceeded.
(e) Regulated Areas —
(1) Establishment. The employer shall establish regulated areas wherever airborne concentrations of
asbestos and/or PACM are in excess of the TWA and/or excursion limit prescribed in paragraph (c)
of this section.
(2) Demarcation. Regulated areas shall be demarcated from the rest of the workplace in any manner that
minimizes the number of persons who will be exposed to asbestos.
(3) Access. Access to regulated areas shall be limited to authorized persons or to persons authorized by
the Act or regulations issued pursuant thereto.
(4) Provision of respirators. Each person entering a regulated area shall be supplied with and required to
use a respirator, selected in accordance with paragraph (g)(2) of this section.
(5) Prohibited activities. The employer shall ensure that employees do not eat, drink, smoke, chew
tobacco or gum, or apply cosmetics in the regulated areas.
(f) Methods of compliance —
(1) Engineering controls and work practices.
(i)
The employer shall institute engineering controls and work practices to reduce and maintain
employee exposure to or below the TWA and/or excursion limit prescribed in paragraph (c) of
this section, except to the extent that such controls are not feasible.
29 CFR 1910.1001(f)(1)(i) (enhanced display)
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29 CFR 1910.1001(f)(1)(ii)
(ii) Wherever the feasible engineering controls and work practices that can be instituted are not
sufficient to reduce employee exposure to or below the TWA and/or excursion limit prescribed
in paragraph (c) of this section, the employer shall use them to reduce employee exposure to
the lowest levels achievable by these controls and shall supplement them by the use of
respiratory protection that complies with the requirements of paragraph (g) of this section.
(iii) For the following operations, wherever feasible engineering controls and work practices that
can be instituted are not sufficient to reduce the employee exposure to or below the TWA and/
or excursion limit prescribed in paragraph (c) of this section, the employer shall use them to
reduce employee exposure to or below 0.5 fiber per cubic centimeter of air (as an eight-hour
time-weighted average) or 2.5 fibers/cc for 30 minutes (short-term exposure) and shall
supplement them by the use of any combination of respiratory protection that complies with
the requirements of paragraph (g) of this section, work practices and feasible engineering
controls that will reduce employee exposure to or below the TWA and to or below the excursion
limit permissible prescribed in paragraph (c) of this section: Coupling cutoff in primary
asbestos cement pipe manufacturing; sanding in primary and secondary asbestos cement
sheet manufacturing; grinding in primary and secondary friction product manufacturing;
carding and spinning in dry textile processes; and grinding and sanding in primary plastics
manufacturing.
(iv) Local exhaust ventilation. Local exhaust ventilation and dust collection systems shall be
designed, constructed, installed, and maintained in accordance with good practices such as
those found in the American National Standard Fundamentals Governing the Design and
Operation of Local Exhaust Systems, ANSI Z9.2–1979.
(v) Particular tools. All hand-operated and power-operated tools which would produce or release
fibers of asbestos, such as, but not limited to, saws, scorers, abrasive wheels, and drills, shall
be provided with local exhaust ventilation systems which comply with paragraph (f)(1)(iv) of
this section.
(vi) Wet methods. Insofar as practicable, asbestos shall be handled, mixed, applied, removed, cut,
scored, or otherwise worked in a wet state sufficient to prevent the emission of airborne fibers
so as to expose employees to levels in excess of the TWA and/or excursion limit, prescribed in
paragraph (c) of this section, unless the usefulness of the product would be diminished thereby.
(vii) [Reserved]
(viii) Particular products and operations. No asbestos cement, mortar, coating, grout, plaster, or
similar material containing asbestos, shall be removed from bags, cartons, or other containers
in which they are shipped, without being either wetted, or enclosed, or ventilated so as to
prevent effectively the release of airborne fibers.
(ix) Compressed air. Compressed air shall not be used to remove asbestos or materials containing
asbestos unless the compressed air is used in conjunction with a ventilation system which
effectively captures the dust cloud created by the compressed air.
(x) Flooring. Sanding of asbestos-containing flooring material is prohibited.
(2) Compliance program.
29 CFR 1910.1001(f)(2) (enhanced display)
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(i)
29 CFR 1910.1001(f)(2)(i)
Where the TWA and/or excursion limit is exceeded, the employer shall establish and implement
a written program to reduce employee exposure to or below the TWA and to or below the
excursion limit by means of engineering and work practice controls as required by paragraph
(f)(1) of this section, and by the use of respiratory protection where required or permitted under
this section.
(ii) Such programs shall be reviewed and updated as necessary to reflect significant changes in the
status of the employer's compliance program.
(iii) Written programs shall be submitted upon request for examination and copying to the Assistant
Secretary, the Director, affected employees and designated employee representatives.
(iv) The employer shall not use employee rotation as a means of compliance with the TWA and/or
excursion limit.
(3) Specific compliance methods for brake and clutch repair:
(i)
Engineering controls and work practices for brake and clutch repair and service. During
automotive brake and clutch inspection, disassembly, repair and assembly operations, the
employer shall institute engineering controls and work practices to reduce employee exposure
to materials containing asbestos using a negative pressure enclosure/HEPA vacuum system
method or low pressure/wet cleaning method, which meets the detailed requirements set out in
appendix F to this section. The employer may also comply using an equivalent method which
follows written procedures which the employer demonstrates can achieve results equivalent to
Method A in appendix F to this section. For facilities in which no more than 5 pair of brakes or 5
clutches are inspected, disassembled, repaired, or assembled per week, the method set forth in
paragraph [D] of appendix F to this section may be used.
(ii) The employer may also comply by using an equivalent method which follows written
procedures, which the employer demonstrates can achieve equivalent exposure reductions as
do the two “preferred methods.” Such demonstration must include monitoring data conducted
under workplace conditions closely resembling the process, type of asbestos containing
materials, control method, work practices and environmental conditions which the equivalent
method will be used, or objective data, which document that under all reasonably foreseeable
conditions of brake and clutch repair applications, the method results in exposures which are
equivalent to the methods set out in appendix F to this section.
(g) Respiratory protection —
(1) General. For employees who use respirators required by this section, the employer must provide each
employee an appropriate respirator that complies with the requirements of this paragraph.
Respirators must be used during:
(i)
Periods necessary to install or implement feasible engineering and work-practice controls.
(ii) Work operations, such as maintenance and repair activities, for which engineering and workpractice controls are not feasible.
(iii) Work operations for which feasible engineering and work-practice controls are not yet sufficient
to reduce employee exposure to or below the TWA and/or excursion limit.
(iv) Emergencies.
(2) Respirator program.
29 CFR 1910.1001(g)(2) (enhanced display)
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(i)
29 CFR 1910.1001(g)(2)(i)
The employer must implement a respiratory protection program in accordance with 29 CFR 134
(b) through (d) (except (d)(1)(iii)), and (f) through (m), which covers each employee required by
this section to use a respirator.
(ii) Employers must provide an employee with a tight-fitting, powered air-purifying respirator (PAPR)
instead of a negative pressure respirator selected according to paragraph (g)(3) of this
standard when the employee chooses to use a PAPR and it provides adequate protection to the
employee.
(iii) No employee must be assigned to tasks requiring the use of respirators if, based on their most
recent medical examination, the examining physician determines that the employee will be
unable to function normally using a respirator, or that the safety or health of the employee or
other employees will be impaired by the use of a respirator. Such employees must be assigned
to another job or given the opportunity to transfer to a different position, the duties of which
they can perform. If such a transfer position is available, the position must be with the same
employer, in the same geographical area, and with the same seniority, status, and rate of pay
the employee had just prior to such transfer.
(3) Respirator selection. Employers must:
(i)
Select, and provide to employees, the appropriate respirators specified in paragraph (d)(3)(i)(A)
of 29 CFR 1910.134; however, employers must not select or use filtering facepiece respirators
for protection against asbestos fibers.
(ii) Provide HEPA filters for powered and non-powered air-purifying respirators.
(h) Protective work clothing and equipment —
(1) Provision and use. If an employee is exposed to asbestos above the TWA and/or excursion limit, or
where the possibility of eye irritation exists, the employer shall provide at no cost to the employee
and ensure that the employee uses appropriate protective work clothing and equipment such as, but
not limited to:
(i)
Coveralls or similar full-body work clothing;
(ii) Gloves, head coverings, and foot coverings; and
(iii) Face shields, vented goggles, or other appropriate protective equipment which complies with
1910.133 of this part.
(2) Removal and storage.
(i)
The employer shall ensure that employees remove work clothing contaminated with asbestos
only in change rooms provided in accordance with paragraph (i)(1) of this section.
(ii) The employer shall ensure that no employee takes contaminated work clothing out of the
change room, except those employees authorized to do so for the purpose of laundering,
maintenance, or disposal.
(iii) Contaminated work clothing shall be placed and stored in closed containers which prevent
dispersion of the asbestos outside the container.
(iv) The employer shall ensure that containers of contaminated protective devices or work clothing,
which are to be taken out of change rooms or the workplace for cleaning, maintenance or
disposal, bear labels in accordance with paragraph (j) of this section.
29 CFR 1910.1001(h)(2)(iv) (enhanced display)
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29 CFR 1910.1001(h)(3)
(3) Cleaning and replacement.
(i)
The employer shall clean, launder, repair, or replace protective clothing and equipment required
by this paragraph to maintain their effectiveness. The employer shall provide clean protective
clothing and equipment at least weekly to each affected employee.
(ii) The employer shall prohibit the removal of asbestos from protective clothing and equipment by
blowing or shaking.
(iii) Laundering of contaminated clothing shall be done so as to prevent the release of airborne
fibers of asbestos in excess of the permissible exposure limits prescribed in paragraph (c) of
this section.
(iv) Any employer who gives contaminated clothing to another person for laundering shall inform
such person of the requirement in paragraph (h)(3)(iii) of this section to effectively prevent the
release of airborne fibers of asbestos in excess of the permissible exposure limits.
(v) The employer shall inform any person who launders or cleans protective clothing or equipment
contaminated with asbestos of the potentially harmful effects of exposure to asbestos.
(vi) The employer shall ensure that contaminated clothing is transported in sealed impermeable
bags, or other closed, impermeable containers, and labeled in accordance with paragraph (j) of
this section.
(i)
Hygiene facilities and practices —
(1) Change rooms.
(i)
The employer shall provide clean change rooms for employees who work in areas where their
airborne exposure to asbestos is above the TWA and/or excursion limit.
(ii) The employer shall ensure that change rooms are in accordance with 1910.141(e) of this part,
and are equipped with two separate lockers or storage facilities, so separated as to prevent
contamination of the employee's street clothes from his protective work clothing and
equipment.
(2) Showers.
(i)
The employer shall ensure that employees who work in areas where their airborne exposure is
above the TWA and/or excursion limit, shower at the end of the work shift.
(ii) The employer shall provide shower facilities which comply with 1910.141(d)(3) of this part.
(iii) The employer shall ensure that employees who are required to shower pursuant to paragraph
(i)(2)(i) of this section do not leave the workplace wearing any clothing or equipment worn
during the work shift.
(3) Lunchrooms.
(i)
The employer shall provide lunchroom facilities for employees who work in areas where their
airborne exposure is above the TWA and/or excursion limit.
(ii) The employer shall ensure that lunchroom facilities have a positive pressure, filtered air supply,
and are readily accessible to employees.
29 CFR 1910.1001(i)(3)(ii) (enhanced display)
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29 CFR 1910.1001(i)(3)(iii)
(iii) The employer shall ensure that employees who work in areas where their airborne exposure is
above the PEL and/or excursion limit wash their hands and faces prior to eating, drinking or
smoking.
(iv) The employer shall ensure that employees do not enter lunchroom facilities with protective
work clothing or equipment unless surface asbestos fibers have been removed from the
clothing or equipment by vacuuming or other method that removes dust without causing the
asbestos to become airborne.
(4) Smoking in work areas. The employer shall ensure that employees do not smoke in work areas where
they are occupationally exposed to asbestos because of activities in that work area.
(j)
Communication of hazards to employees—Introduction. This section applies to the communication of
information concerning asbestos hazards in general industry to facilitate compliance with this standard.
Asbestos exposure in general industry occurs in a wide variety of industrial and commercial settings.
Employees who manufacture asbestos-containing products may be exposed to asbestos fibers.
Employees who repair and replace automotive brakes and clutches may be exposed to asbestos fibers. In
addition, employees engaged in housekeeping activities in industrial facilities with asbestos product
manufacturing operations, and in public and commercial buildings with installed asbestos containing
materials may be exposed to asbestos fibers. Most of these workers are covered by this general industry
standard, with the exception of state or local governmental employees in non-state plan states. It should
be noted that employees who perform housekeeping activities during and after construction activities are
covered by the asbestos construction standard, 29 CFR 1926.1101, formerly 1926.58. However,
housekeeping employees, regardless of industry designation, should know whether building components
they maintain may expose them to asbestos. The same hazard communication provisions will protect
employees who perform housekeeping operations in all three asbestos standards; general industry,
construction, and shipyard employment. As noted in the construction standard, building owners are often
the only and/or best source of information concerning the presence of previously installed asbestos
containing building materials. Therefore they, along with employers of potentially exposed employees, are
assigned specific information conveying and retention duties under this section.
(1) Hazard communication—general.
(i)
Chemical manufacturers, importers, distributors and employers shall comply with all
requirements of the Hazard Communication Standard (HCS) (§ 1910.1200) for asbestos.
(ii) In classifying the hazards of asbestos at least the following hazards are to be addressed:
Cancer and lung effects.
(iii) Employers shall include asbestos in the hazard communication program established to comply
with the HCS (§ 1910.1200). Employers shall ensure that each employee has access to labels
on containers of asbestos and to safety data sheets, and is trained in accordance with the
requirements of HCS and paragraph (j)(7) of this section.
(2) Installed Asbestos Containing Material. Employers and building owners are required to treat installed
TSI and sprayed on and troweled-on surfacing materials as ACM in buildings constructed no later
than 1980 for purposes of this standard. These materials are designated “presumed ACM or PACM”,
and are defined in paragraph (b) of this section. Asphalt and vinyl flooring material installed no later
than 1980 also must be treated as asbestos-containing. The employer or building owner may
demonstrate that PACM and flooring material do not contain asbestos by complying with paragraph
(j)(8)(iii) of this section.
29 CFR 1910.1001(j)(2) (enhanced display)
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29 CFR 1910.1001(j)(3)
(3) Duties of employers and building and facility owners.
(i)
Building and facility owners shall determine the presence, location, and quantity of ACM and/or
PACM at the work site. Employers and building and facility owners shall exercise due diligence
in complying with these requirements to inform employers and employees about the presence
and location of ACM and PACM.
(ii) Building and facility owners shall maintain records of all information required to be provided
pursuant to this section and/or otherwise known to the building owner concerning the
presence, location and quantity of ACM and PACM in the building/facility. Such records shall be
kept for the duration of ownership and shall be transferred to successive owners.
(iii) Building and facility owners shall inform employers of employees, and employers shall inform
employees who will perform housekeeping activities in areas which contain ACM and/or PACM
of the presence and location of ACM and/or PACM in such areas which may be contacted
during such activities.
(4) Warning signs —
(i)
Posting. Warning signs shall be provided and displayed at each regulated area. In addition,
warning signs shall be posted at all approaches to regulated areas so that an employee may
read the signs and take necessary protective steps before entering the area.
(ii) Sign specifications:
(A) The warning signs required by paragraph (j)(4)(i) of this section shall bear the following
legend:
DANGER
ASBESTOS
MAY CAUSE CANCER
CAUSES DAMAGE TO LUNGS
AUTHORIZED PERSONNEL ONLY
(B) In addition, where the use of respirators and protective clothing is required in the regulated
area under this section, the warning signs shall include the following:
WEAR RESPIRATORY PROTECTION AND PROTECTIVE CLOTHING IN THIS AREA
(C) Prior to June 1, 2016, employers may use the following legend in lieu of that specified in
paragraph (j)(4)(ii)(A) of this section:
DANGER
ASBESTOS
CANCER AND LUNG DISEASE
29 CFR 1910.1001(j)(4)(ii)(C) (enhanced display)
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29 CFR 1910.1001(j)(4)(ii)(D)
HAZARD
AUTHORIZED PERSONNEL ONLY
(D) Prior to June 1, 2016, employers may use the following legend in lieu of that specified in
paragraph (j)(4)(ii)(B) of this section:
RESPIRATORS AND PROTECTIVE CLOTHING ARE REQUIRED IN THIS AREA
(iii) The employer shall ensure that employees working in and contiguous to regulated areas
comprehend the warning signs required to be posted by paragraph (j)(4)(i) of this section.
Means to ensure employee comprehension may include the use of foreign languages,
pictographs and graphics.
(iv) At the entrance to mechanical rooms/areas in which employees reasonably can be expected to
enter and which contain ACM and/or PACM, the building owner shall post signs which identify
the material which is present, its location, and appropriate work practices which, if followed, will
ensure that ACM and/or PACM will not be disturbed. The employer shall ensure, to the extent
feasible, that employees who come in contact with these signs can comprehend them. Means
to ensure employee comprehension may include the use of foreign languages, pictographs,
graphics, and awareness training.
(5) Warning labels —
(i)
Labeling. Labels shall be affixed to all raw materials, mixtures, scrap, waste, debris, and other
products containing asbestos fibers, or to their containers. When a building owner or employer
identifies previously installed ACM and/or PACM, labels or signs shall be affixed or posted so
that employees will be notified of what materials contain ACM and/or PACM. The employer
shall attach such labels in areas where they will clearly be noticed by employees who are likely
to be exposed, such as at the entrance to mechanical room/areas. Signs required by paragraph
(j) of this section may be posted in lieu of labels so long as they contain the information
required for labeling.
(ii) Label specifications. In addition to the requirements of paragraph (j)(1), the employer shall
ensure that labels of bags or containers of protective clothing and equipment, scrap, waste, and
debris containing asbestos fibers include the following information:
DANGER
CONTAINS ASBESTOS FIBERS
MAY CAUSE CANCER
CAUSES DAMAGE TO LUNGS
DO NOT BREATHE DUST
AVOID CREATING DUST
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(iii) Prior to June 1, 2015, employers may include the following information on raw materials,
mixtures or labels of bags or containers of protective clothing and equipment, scrap, waste, and
debris containing asbestos fibers in lieu of the labeling requirements in paragraphs (j)(1)(i) and
(j)(5)(ii) of this section:
DANGER
CONTAINS ASBESTOS FIBERS
AVOID CREATING DUST
CANCER AND LUNG DISEASE HAZARD
(6) The provisions for labels and for safety data sheets required by paragraph (j) of this section do not
apply where:
(i)
Asbestos fibers have been modified by a bonding agent, coating, binder, or other material
provided that the manufacturer can demonstrate that during any reasonably foreseeable use,
handling, storage, disposal, processing, or transportation, no airborne concentrations of fibers
of asbestos in excess of the TWA permissible exposure level and/or excursion limit will be
released or
(ii) Asbestos is present in a product in concentrations less than 1.0%.
(7) Employee information and training.
(i)
The employer shall train each employee who is exposed to airborne concentrations of asbestos
at or above the PEL and/or excursion limit in accordance with the requirements of this section.
The employer shall institute a training program and ensure employee participation in the
program.
(ii) Training shall be provided prior to or at the time of initial assignment and at least annually
thereafter.
(iii) The training program shall be conducted in a manner which the employee is able to understand.
The employer shall ensure that each employee is informed of the following:
(A) The health effects associated with asbestos exposure;
(B) The relationship between smoking and exposure to asbestos producing lung cancer:
(C) The quantity, location, manner of use, release, and storage of asbestos, and the specific
nature of operations which could result in exposure to asbestos;
(D) The engineering controls and work practices associated with the employee's job
assignment;
(E) The specific procedures implemented to protect employees from exposure to asbestos,
such as appropriate work practices, emergency and clean-up procedures, and personal
protective equipment to be used;
(F) The purpose, proper use, and limitations of respirators and protective clothing, if
appropriate;
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(G) The purpose and a description of the medical surveillance program required by paragraph
(l) of this section;
(H) The content of this standard, including appendices.
(I)
The names, addresses and phone numbers of public health organizations which provide
information, materials, and/or conduct programs concerning smoking cessation. The
employer may distribute the list of such organizations contained in appendix I to this
section, to comply with this requirement.
(J) The requirements for posting signs and affixing labels and the meaning of the required
legends for such signs and labels.
(iv) The employer shall also provide, at no cost to employees who perform housekeeping
operations in an area which contains ACM or PACM, an asbestos awareness training course,
which shall at a minimum contain the following elements: health effects of asbestos, locations
of ACM and PACM in the building/facility, recognition of ACM and PACM damage and
deterioration, requirements in this standard relating to housekeeping, and proper response to
fiber release episodes, to all employees who perform housekeeping work in areas where ACM
and/or PACM is present. Each such employee shall be so trained at least once a year.
(v) Access to information and training materials.
(A) The employer shall make a copy of this standard and its appendices readily available
without cost to all affected employees.
(B) The employer shall provide, upon request, all materials relating to the employee
information and training program to the Assistant Secretary and the training program to
the Assistant Secretary and the Director.
(C) The employer shall inform all employees concerning the availability of self-help smoking
cessation program material. Upon employee request, the employer shall distribute such
material, consisting of NIH Publication No. 89–1647, or equivalent self-help material,
which is approved or published by a public health organization listed in appendix I to this
section.
(8) Criteria to rebut the designation of installed material as PACM.
(i)
At any time, an employer and/or building owner may demonstrate, for purposes of this
standard, that PACM does not contain asbestos. Building owners and/or employers are not
required to communicate information about the presence of building material for which such a
demonstration pursuant to the requirements of paragraph (j)(8)(ii) of this section has been
made. However, in all such cases, the information, data and analysis supporting the
determination that PACM does not contain asbestos, shall be retained pursuant to paragraph
(m) of this section.
(ii) An employer or owner may demonstrate that PACM does not contain asbestos by the following:
(A) Having a completed inspection conducted pursuant to the requirements of AHERA (40
CFR 763, subpart E) which demonstrates that no ACM is present in the material; or
(B) Performing tests of the material containing PACM which demonstrate that no ACM is
present in the material. Such tests shall include analysis of bulk samples collected in the
manner described in 40 CFR 763.86. The tests, evaluation and sample collection shall be
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conducted by an accredited inspector or by a CIH. Analysis of samples shall be performed
by persons or laboratories with proficiency demonstrated by current successful
participation in a nationally recognized testing program such as the National Voluntary
Laboratory Accreditation Program (NVLAP) or the National Institute for Standards and
Technology (NIST) or the Round Robin for bulk samples administered by the American
Industrial Hygiene Association (AIHA) or an equivalent nationally-recognized round robin
testing program.
(iii) The employer and/or building owner may demonstrate that flooring material including
associated mastic and backing does not contain asbestos, by a determination of an industrial
hygienist based upon recognized analytical techniques showing that the material is not ACM.
(k) Housekeeping.
(1) All surfaces shall be maintained as free as practicable of ACM waste and debris and accompanying
dust.
(2) All spills and sudden releases of material containing asbestos shall be cleaned up as soon as
possible.
(3) Surfaces contaminated with asbestos may not be cleaned by the use of compressed air.
(4) Vacuuming. HEPA-filtered vacuuming equipment shall be used for vacuuming asbestos containing
waste and debris. The equipment shall be used and emptied in a manner which minimizes the
reentry of asbestos into the workplace.
(5) Shoveling, dry sweeping and dry clean-up of asbestos may be used only where vacuuming and/or
wet cleaning are not feasible.
(6) Waste disposal. Waste, scrap, debris, bags, containers, equipment, and clothing contaminated with
asbestos consigned for disposal, shall be collected, recycled and disposed of in sealed impermeable
bags, or other closed, impermeable containers.
(7) Care of asbestos-containing flooring material.
(i)
Sanding of asbestos-containing floor material is prohibited.
(ii) Stripping of finishes shall be conducted using low abrasion pads at speeds lower than 300 rpm
and wet methods.
(iii) Burnishing or dry buffing may be performed only on asbestos-containing flooring which has
sufficient finish so that the pad cannot contact the asbestos-containing material.
(8) Waste and debris and accompanying dust in an area containing accessible ACM and/or PACM or
visibly deteriorated ACM, shall not be dusted or swept dry, or vacuumed without using a HEPA filter.
(l)
Medical surveillance —
(1) General —
(i)
Employees covered. The employer shall institute a medical surveillance program for all
employees who are or will be exposed to airborne concentrations of fibers of asbestos at or
above the TWA and/or excursion limit.
(ii) Examination by a physician.
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(A) The employer shall ensure that all medical examinations and procedures are performed by
or under the supervision of a licensed physician, and shall be provided without cost to the
employee and at a reasonable time and place.
(B) Persons other than licensed physicians, who administer the pulmonary function testing
required by this section, shall complete a training course in spirometry sponsored by an
appropriate academic or professional institution.
(2) Pre-placement examinations.
(i)
Before an employee is assigned to an occupation exposed to airborne concentrations of
asbestos fibers at or above the TWA and/or excursion limit, a pre-placement medical
examination shall be provided or made available by the employer.
(ii) Such examination shall include, as a minimum, a medical and work history; a complete physical
examination of all systems with emphasis on the respiratory system, the cardiovascular system
and digestive tract; completion of the respiratory disease standardized questionnaire in
appendix D to this section, part 1; a 14- by 17-inch or other reasonably-sized standard film or
digital posterior-anterior chest X-ray; pulmonary function tests to include forced vital capacity
(FVC) and forced expiratory volume at 1 second (FEV1); and any additional tests deemed
appropriate by the examining physician. Classification of all chest X-rays shall be conducted in
accordance with appendix E to this section.
(3) Periodic examinations.
(i)
Periodic medical examinations shall be made available annually.
(ii) The scope of the medical examination shall be in conformance with the protocol established in
paragraph (l)(2)(ii) of this section, except that the frequency of chest X-rays shall be conducted
in accordance with Table 1 to this section, and the abbreviated standardized questionnaire
contained in part 2 of appendix D to this section shall be administered to the employee.
Table 1 to § 1910.1001—Frequency of Chest X-ray
Years since first exposure
Age of employee
15 to 35
35 + to 45
45 +
0 to 10
Every 5 years
Every 5 years
Every 5 years.
10 +
Every 5 years
Every 2 years
Every 1 year.
(4) Termination of employment examinations.
(i)
The employer shall provide, or make available, a termination of employment medical
examination for any employee who has been exposed to airborne concentrations of fibers of
asbestos at or above the TWA and/or excursion limit.
(ii) The medical examination shall be in accordance with the requirements of the periodic
examinations stipulated in paragraph (l)(3) of this section, and shall be given within 30 calendar
days before or after the date of termination of employment.
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(5) Recent examinations. No medical examination is required of any employee, if adequate records show
that the employee has been examined in accordance with any of paragraphs ((l)(2) through (l)(4)) of
this section within the past 1 year period. A pre- employment medical examination which was
required as a condition of employment by the employer, may not be used by that employer to meet
the requirements of this paragraph, unless the cost of such examination is borne by the employer.
(6) Information provided to the physician. The employer shall provide the following information to the
examining physician:
(i)
A copy of this standard and Appendices D and E.
(ii) A description of the affected employee's duties as they relate to the employee's exposure.
(iii) The employee's representative exposure level or anticipated exposure level.
(iv) A description of any personal protective and respiratory equipment used or to be used.
(v) Information from previous medical examinations of the affected employee that is not otherwise
available to the examining physician.
(7) Physician's written opinion.
(i)
The employer shall obtain a written opinion from the examining physician. This written opinion
shall contain the results of the medical examination and shall include:
(A) The physician's opinion as to whether the employee has any detected medical conditions
that would place the employee at an increased risk of material health impairment from
exposure to asbestos;
(B) Any recommended limitations on the employee or upon the use of personal protective
equipment such as clothing or respirators;
(C) A statement that the employee has been informed by the physician of the results of the
medical examination and of any medical conditions resulting from asbestos exposure that
require further explanation or treatment; and
(D) A statement that the employee has been informed by the physician of the increased risk of
lung cancer attributable to the combined effect of smoking and asbestos exposure.
(ii) The employer shall instruct the physician not to reveal in the written opinion given to the
employer specific findings or diagnoses unrelated to occupational exposure to asbestos.
(iii) The employer shall provide a copy of the physician's written opinion to the affected employee
within 30 days from its receipt.
(m) Recordkeeping —
(1) Exposure measurements.
Note: The employer may utilize the services of competent organizations such as industry
trade associations and employee associations to maintain the records required by this
section.
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(i)
29 CFR 1910.1001(m)(1)(i)
The employer shall keep an accurate record of all measurements taken to monitor employee
exposure to asbestos as prescribed in paragraph (d) of this section.
(ii) This record shall include at least the following information:
(A) The date of measurement;
(B) The operation involving exposure to asbestos which is being monitored;
(C) Sampling and analytical methods used and evidence of their accuracy;
(D) Number, duration, and results of samples taken;
(E) Type of respiratory protective devices worn, if any; and
(F) Name and exposure of the employees whose exposure are represented.
(iii) The employer shall maintain this record for at least thirty (30) years, in accordance with 29 CFR
1910.20.
(2) Objective data for exempted operations.
(i)
Where the processing, use, or handling of products made from or containing asbestos is
exempted from other requirements of this section under paragraph (d)(2)(iii) of this section, the
employer shall establish and maintain an accurate record of objective data reasonably relied
upon in support of the exemption.
(ii) The record shall include at least the following:
(A) The product qualifying for exemption;
(B) The source of the objective data;
(C) The testing protocol, results of testing, and/or analysis of the material for the release of
asbestos;
(D) A description of the operation exempted and how the data support the exemption; and
(E) Other data relevant to the operations, materials, processing, or employee exposures
covered by the exemption.
(iii) The employer shall maintain this record for the duration of the employer's reliance upon such
objective data.
(3) Medical surveillance.
(i)
The employer shall establish and maintain an accurate record for each employee subject to
medical surveillance by paragraph (l)(1)(i) of this section, in accordance with 29 CFR
1910.1020.
(ii) The record shall include at least the following information:
(A) The name of the employee;
(B) Physician's written opinions;
(C) Any employee medical complaints related to exposure to asbestos; and
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(D) A copy of the information provided to the physician as required by paragraph (l)(6) of this
section.
(iii) The employer shall ensure that this record is maintained for the duration of employment plus
thirty (30) years, in accordance with 29 CFR 1910.1020.
(4) Training. The employer shall maintain all employee training records for one (1) year beyond the last
date of employment of that employee.
(5) Availability.
(i)
The employer, upon written request, shall make all records required to be maintained by this
section available to the Assistant Secretary and the Director for examination and copying.
(ii) The employer, upon request shall make any exposure records required by paragraph (m)(1) of
this section available for examination and copying to affected employees, former employees,
designated representatives and the Assistant Secretary, in accordance with 29 CFR 1910.1020
(a) through (e) and (g) through (i).
(iii) The employer, upon request, shall make employee medical records required by paragraph (m)(3)
of this section available for examination and copying to the subject employee, to anyone having
the specific written consent of the subject employee, and the Assistant Secretary, in
accordance with 29 CFR 1910.1020.
(6) Transfer of records. The employer shall comply with the requirements concerning transfer of records
set forth in 29 CFR 1910.1020(h).
(n) Observation of monitoring —
(1) Employee observation. The employer shall provide affected employees or their designated
representatives an opportunity to observe any monitoring of employee exposure to asbestos
conducted in accordance with paragraph (d) of this section.
(2) Observation procedures. When observation of the monitoring of employee exposure to asbestos
requires entry into an area where the use of protective clothing or equipment is required, the
observer shall be provided with and be required to use such clothing and equipment and shall
comply with all other applicable safety and health procedures.
(o) Appendices.
(1) Appendices A, C, D, E, and F to this section are incorporated as part of this section and the contents
of these Appendices are mandatory.
(2) Appendices B, G, H, I, and J to this section are informational and are not intended to create any
additional obligations not otherwise imposed or to detract from any existing obligations.
Appendix A to § 1910.1001—OSHA Reference Method—Mandatory
This mandatory appendix specifies the procedure for analyzing air samples for asbestos and specifies quality
control procedures that must be implemented by laboratories performing the analysis. The sampling and
analytical methods described below represent the elements of the available monitoring methods (such as
appendix B of their regulation, the most current version of the OSHA method ID–160, or the most current
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version of the NIOSH Method 7400). All employers who are required to conduct air monitoring under paragraph
(d) of the standard are required to utilize analytical laboratories that use this procedure, or an equivalent
method, for collecting and analyzing samples.
Sampling and Analytical Procedure
1. The sampling medium for air samples shall be mixed cellulose ester filter membranes. These shall be
designated by the manufacturer as suitable for asbestos counting. See below for rejection of blanks.
2. The preferred collection device shall be the 25-mm diameter cassette with an open-faced 50-mm electrically
conductive extension cowl. The 37-mm cassette may be used if necessary but only if written justification for
the need to use the 37-mm filter cassette accompanies the sample results in the employee's exposure
monitoring record. Do not reuse or reload cassettes for asbestos sample collection.
3. An air flow rate between 0.5 liter/min and 2.5 liters/min shall be selected for the 25-mm cassette. If the
37-mm cassette is used, an air flow rate between 1 liter/min and 2.5 liters/min shall be selected.
4. Where possible, a sufficient air volume for each air sample shall be collected to yield between 100 and 1,300
fibers per square millimeter on the membrane filter. If a filter darkens in appearance or if loose dust is seen on
the filter, a second sample shall be started.
5. Ship the samples in a rigid container with sufficient packing material to prevent dislodging the collected
fibers. Packing material that has a high electrostatic charge on its surface (e.g., expanded polystyrene) cannot
be used because such material can cause loss of fibers to the sides of the cassette.
6. Calibrate each personal sampling pump before and after use with a representative filter cassette installed
between the pump and the calibration devices.
7. Personal samples shall be taken in the “breathing zone” of the employee (i.e., attached to or near the collar
or lapel near the worker's face).
8. Fiber counts shall be made by positive phase contrast using a microscope with an 8 to 10× eyepiece and a
40 to 45× objective for a total magnification of approximately 400× and a numerical aperture of 0.65 to 0.75.
The microscope shall also be fitted with a green or blue filter.
9. The microscope shall be fitted with a Walton-Beckett eyepiece graticule calibrated for a field diameter of 100
micrometers (±2 micrometers).
10. The phase-shift detection limit of the microscope shall be about 3 degrees measured using the HSE phase
shift test slide as outlined below.
a. Place the test slide on the microscope stage and center it under the phase objective.
b. Bring the blocks of grooved lines into focus.
Note: The slide consists of seven sets of grooved lines (ca. 20 grooves to each block) in
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descending order of visibility from sets 1 to 7, seven being the least visible. The requirements
for asbestos counting are that the microscope optics must resolve the grooved lines in set 3
completely, although they may appear somewhat faint, and that the grooved lines in sets 6
and 7 must be invisible. Sets 4 and 5 must be at least partially visible but may vary slightly in
visibility between microscopes. A microscope that fails to meet these requirements has either
too low or too high a resolution to be used for asbestos counting.
c. If the image deteriorates, clean and adjust the microscope optics. If the problem persists, consult the
microscope manufacturer.
11. Each set of samples taken will include 10% field blanks or a minimum of 2 field blanks. These blanks must
come from the same lot as the filters used for sample collection. The field blank results shall be averaged and
subtracted from the analytical results before reporting. A set consists of any sample or group of samples for
which an evaluation for this standard must be made. Any samples represented by a field blank having a fiber
count in excess of the detection limit of the method being used shall be rejected.
12. The samples shall be mounted by the acetone/triacetin method or a method with an equivalent index of
refraction and similar clarity.
13. Observe the following counting rules.
a. Count only fibers equal to or longer than 5 micrometers. Measure the length of curved fibers along the curve.
b. In the absence of other information, count all particles as asbesto that have a length-to-width ratio (aspect
ratio) of 3:1 or greater.
c. 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 the count of one half (1⁄2). 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.
d. Count bundles of fibers as one fiber unless individual fibers can be identified by observing both ends of an
individual fiber.
e. Count enough graticule fields to yield 100 fibers. Count a minimum of 20 fields; stop counting at 100 fields
regardless of fiber count.
14. Blind recounts shall be conducted at the rate of 10 percent.
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Quality Control Procedures
1. Intralaboratory program. Each laboratory and/or each company with more than one microscopist counting
slides shall establish a statistically designed quality assurance program involving blind recounts and
comparisons between microscopists to monitor the variability of counting by each microscopist and between
microscopists. In a company with more than one laboratory, the program shall include all laboratories and shall
also evaluate the laboratory-to-laboratory variability.
2.a. Interlaboratory program. Each laboratory analyzing asbestos samples for compliance determination shall
implement an interlaboratory quality assurance program that as a minimum includes participation of at least
two other independent laboratories. Each laboratory shall participate in round robin testing at least once every
6 months with at least all the other laboratories in its interlaboratory quality assurance group. Each laboratory
shall submit slides typical of its own work load for use in this program. The round robin shall be designed and
results analyzed using appropriate statistical methodology.
2.b. All laboratories should also participate in a national sample testing scheme such as the Proficiency
Analytical Testing Program (PAT), or the Asbestos Registry sponsored by the American Industrial Hygiene
Association (AIHA).
3. All individuals performing asbestos analysis must have taken the NIOSH course for sampling and evaluating
airborne asbestos dust or an equalivalent course.
4. When the use of different microscopes contributes to differences between counters and laboratories, the
effect of the different microscope shall be evaluated and the microscope shall be replaced, as necessary.
5. Current results of these quality assurance programs shall be posted in each laboratory to keep the
microscopists informed.
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Appendix B to § 1910.1001—Detailed Procedures for Asbestos Sampling
and Analysis—Non-mandatory
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 mixedcellulose 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
Mg3 Si2 O5(OH)4
Crocidolite
Na2 Fe32 + Fe23 + Si8 O22 (OH)2
Amosite
(Mg,Fe)7 Si8 O22 (OH)2
Tremolite-actinolite
Ca2(Mg,Fe)5 Si8 O22 (OH)2
Anthophyllite
(Mg,Fe)7 Si8 O22 (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).
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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 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. 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:
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(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 studies so that estimates of expected disease
can be inferred from long-term determinations of asbestos exposures.
The main disadvantage of PCM is that it does not positively identify asbestos fibers. Other fibers which are not
asbestos may be included in the count unless differential counting is performed. This requires a great deal of
experience to adequately differentiate asbestos from non-asbestos fibers. Positive identification of asbestos
must be performed by polarized light or electron microscopy techniques. A further disadvantage of PCM is that
the smallest visible fibers are about 0.2 µm in diameter while the finest asbestos fibers may be as small as
0.02 µm 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:
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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
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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 (The assembly is shown in Figure 3). 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 padcassette) for asbestos is usually preassembled by the manufacturer.
(e) Other cassettes, such as the Bell-mouth, may be used within the limits of their validation.
5.1.2. Gel bands for sealing cassettes.
5.1.3. Sampling pump.
Each pump must be a battery operated, self-contained unit small enough to be placed on the monitored
employee and not interfere with the work being performed. The pump must be capable of sampling at the
collection rate for the required sampling time.
5.1.4. Flexible tubing, 6-mm bore.
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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.
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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.
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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 ±2 µm 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 × 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 #11⁄2.
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).
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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 °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 onesixth 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.
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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 °C
to hasten clearing. The top of the hot block can be used if the slide is not heated too long.
6.5.9. Counting may proceed immediately after clearing and mounting are completed.
6.6. SAMPLE ANALYSIS
Completely align the microscope according to the manufacturer's instructions. Then, align the microscope
using the following general alignment routine at the beginning of every counting session and more often if
necessary.
6.6.1. Alignment
(1) Clean all optical surfaces. Even a small amount of dirt can significantly degrade the image.
(2) Rough focus the objective on a sample.
(3) Close down the field iris so that it is visible in the field of view. Focus the image of the iris with the
condenser focus. Center the image of the iris in the field of view.
(4) Install the phase telescope and focus on the phase rings. Critically center the rings. Misalignment of the
rings results in astigmatism which will degrade the image.
(5) Place the phase-shift test slide on the microscope stage and focus on the lines. The analyst must see line
set 3 and should see at least parts of 4 and 5 but, not see line set 6 or 6. A microscope/microscopist
combination which does not pass this test may not be used.
6.6.2. Counting Fibers
(1) Place the prepared sample slide on the mechanical stage of the microscope. Position the center of the
wedge under the objective lens and focus upon the sample.
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(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 1⁄2. 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 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.
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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:
where:
AC = Airborne fiber concentration
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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 = π(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 × MFA) = 49. The previous equation
simplifies to:
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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:
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), US Treasury Dept., Washington, DC, 1938.
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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. DC: 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 = antilog110[A(log10(x))2 + B(log10(x)) + C]
where:
x = the number of fibers/mm2
Application of least squares gave:
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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.
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.
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(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:
Example: If PL = 108 µm, AL = 2.93 mm and D = 100 µm, then,
(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±2 µm) with a stage micrometer upon receipt of the graticule from the manufacturer. Determine the field
area (mm2).
Field Area = Δ(D/2)2
If D = 100 µm = 0.1 mm, then
Field Area = Δ(0.1 mm/2)2 = 0.00785 mm2
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.
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Counts for the Fibers in the Figure
Structure No.
1 to 6
7
Count
Explanation
1 Single fibers all contained within the circle.
1⁄
2
Fiber crosses circle once.
8
0 Fiber too short.
9
2 Two crossing fibers.
10
0 Fiber outside graticule.
11
12
0 Fiber crosses graticule twice.
1⁄
2
Although split, fiber only crosses once.
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Appendix C to § 1910.1001 [Reserved]
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Appendix D to § 1910.1001—Medical Questionnaires; Mandatory
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Appendix E to § 1910.1001—Classification of Chest X-Rays—Mandatory
(a) Chest X-rays shall be classified in accordance with the Guidelines for the use of the ILO International
Classification of Radiographs of Pneumoconioses (revised edition 2011) (incorporated by reference, see §
1910.6), and recorded on a classification form following the format of the CDC/NIOSH (M) 2.8 form. As a
minimum, the content within the bold lines of this form (items 1 through 4) shall be included. This form is not
to be submitted to NIOSH.
(b) All X-rays shall be classified only by a B-Reader, a board eligible/certified radiologist, or an experienced
physician with known expertise in pneumoconioses.
(c) Whenever classifying chest X-ray film, the physician shall have immediately available for reference a
complete set of the ILO standard format radiographs provided for use with the Guidelines for the use of the ILO
International Classification of Radiographs of Pneumoconioses (revised edition 2011).
(d) Whenever classifying digitally-acquired chest X-rays, the physician shall have immediately available for
reference a complete set of ILO standard digital chest radiographic images provided for use with the Guidelines
for the Use of the ILO International Classification of Radiographs of Pneumoconioses (revised edition 2011).
Classification of digitally-acquired chest X-rays shall be based on the viewing of images displayed as electronic
copies and shall not be based on the viewing of hard copy printed transparencies of images.
Appendix F to § 1910.1001—Work Practices and Engineering Controls for
Automotive Brake and Clutch Inspection, Disassembly, Repair and
Assembly—Mandatory
This mandatory appendix specifies engineering controls and work practices that must be implemented by the
employer during automotive brake and clutch inspection, disassembly, repair, and assembly operations. Proper
use of these engineering controls and work practices by trained employees will reduce employees' asbestos
exposure below the permissible exposure level during clutch and brake inspection, disassembly, repair, and
assembly operations. The employer shall institute engineering controls and work practices using either the
method set forth in paragraph [A] or paragraph [B] of this appendix, or any other method which the employer
can demonstrate to be equivalent in terms of reducing employee exposure to asbestos as defined and which
meets the requirements described in paragraph [C] of this appendix, for those facilities in which no more than 5
pairs of brakes or 5 clutches are inspected, disassembled, reassembled and/or repaired per week, the method
set forth in paragraph [D] of this appendix may be used:
[A] Negative Pressure Enclosure/HEPA Vacuum System Method
(1) The brake and clutch inspection, disassembly, repair, and assembly operations shall be enclosed to cover
and contain the clutch or brake assembly and to prevent the release of asbestos fibers into the worker's
breathing zone.
(2) The enclosure shall be sealed tightly and thoroughly inspected for leaks before work begins on brake and
clutch inspection, disassembly, repair, and assembly.
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(3) The enclosure shall be such that the worker can clearly see the operation and shall provide impermeable
sleeves through which the worker can handle the brake and clutch inspection, disassembly, repair and
assembly. The integrity of the sleeves and ports shall be examined before work begins.
(4) A HEPA-filtered vacuum shall be employed to maintain the enclosure under negative pressure throughout
the operation. Compressed-air may be used to remove asbestos fibers or particles from the enclosure.
(5) The HEPA vacuum shall be used first to loosen the asbestos containing residue from the brake and clutch
parts and then to evacuate the loosened asbestos containing material from the enclosure and capture the
material in the vacuum filter.
(6) The vacuum's filter, when full, shall be first wetted with a fine mist of water, then removed and placed
immediately in an impermeable container, labeled according to paragraph (j)(5) of this section and disposed of
according to paragraph (k) of this section.
(7) Any spills or releases of asbestos containing waste material from inside of the enclosure or vacuum hose
or vacuum filter shall be immediately cleaned up and disposed of according to paragraph (k) of this section.
[B] Low Pressure/Wet Cleaning Method
(1) A catch basin shall be placed under the brake assembly, positioned to avoid splashes and spills.
(2) The reservoir shall contain water containing an organic solvent or wetting agent. The flow of liquid shall be
controlled such that the brake assembly is gently flooded to prevent the asbestos-containing brake dust from
becoming airborne.
(3) The aqueous solution shall be allowed to flow between the brake drum and brake support before the drum
is removed.
(4) After removing the brake drum, the wheel hub and back of the brake assembly shall be thoroughly wetted to
suppress dust.
(5) The brake support plate, brake shoes and brake components used to attach the brake shoes shall be
thoroughly washed before removing the old shoes.
(6) In systems using filters, the filters, when full, shall be first wetted with a fine mist of water, then removed
and placed immediately in an impermeable container, labeled according to paragraph (j)(4) of this section and
disposed of according to paragraph (k) of this section.
(7) Any spills of asbestos-containing aqueous solution or any asbestos-containing waste material shall be
cleaned up immediately and disposed of according to paragraph (k) of this section.
(8) The use of dry brushing during low pressure/wet cleaning operations is prohibited.
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[C] Equivalent Methods
An equivalent method is one which has sufficient written detail so that it can be reproduced and has been
demonstrated that the exposures resulting from the equivalent method are equal to or less than the exposures
which would result from the use of the method described in paragraph [A] of this appendix. For purposes of
making this comparison, the employer shall assume that exposures resulting from the use of the method
described in paragraph [A] of this appendix shall not exceed 0.016 f/cc, as measured by the OSHA reference
method and as averaged over at least 18 personal samples.
[D] Wet Method.
(1) A spray bottle, hose nozzle, or other implement capable of delivering a fine mist of water or amended water
or other delivery system capable of delivering water at low pressure, shall be used to first thoroughly wet the
brake and clutch parts. Brake and clutch components shall then be wiped clean with a cloth.
(2) The cloth shall be placed in an impermeable container, labelled according to paragraph (j)(4) of this section
and then disposed of according to paragraph (k) of this section, or the cloth shall be laundered in a way to
prevent the release of asbestos fibers in excess of 0.1 fiber per cubic centimeter of air.
(3) Any spills of solvent or any asbestos containing waste material shall be cleaned up immediately according
to paragraph (k) of this section.
(4) The use of dry brushing during the wet method operations is prohibited.
Appendix G to § 1910.1001—Substance Technical Information for
Asbestos—Non-Mandatory
I. SUBSTANCE IDENTIFICATION
A. Substance: “Asbestos” is the name of a class of magnesium-silicate minerals that occur in fibrous form.
Minerals that are included in this group are chrysotile, crocidolite, amosite, tremolite asbestos, anthophyllite
asbestos, and actinolite asbestos.
B. Asbestos is used in the manufacture of heat-resistant clothing, automative brake and clutch linings, and a
variety of building materials including floor tiles, roofing felts, ceiling tiles, asbestos-cement pipe and sheet, and
fire-resistant drywall. Asbestos is also present in pipe and boiler insulation materials, and in sprayed-on
materials located on beams, in crawlspaces, and between walls.
C. The potential for a product containing asbestos to release breatheable fibers depends on its degree of
friability. Friable means that the material can be crumbled with hand pressure and is therefore likely to emit
fibers. The fibrous or fluffy sprayed-on materials used for fireproofing, insulation, or sound proofing are
considered to be friable, and they readily release airborne fibers if disturbed. Materials such as vinyl-asbestos
floor tile or roofing felts are considered nonfriable and generally do not emit airborne fibers unless subjected to
sanding or sawing operations. Asbestos-cement pipe or sheet can emit airborne fibers if the materials are cut
or sawed, or if they are broken during demolition operations.
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D. Permissible exposure: Exposure to airborne asbestos fibers may not exceed 0.2 fibers per cubic centimeter
of air (0.1 f/cc) averaged over the 8-hour workday.
II. HEALTH HAZARD DATA
A. Asbestos can cause disabling respiratory disease and various types of cancers if the fibers are inhaled.
Inhaling or ingesting fibers from contaminated clothing or skin can also result in these diseases. The
symptoms of these diseases generally do not appear for 20 or more years after initial exposure.
B. Exposure to asbestos has been shown to cause lung cancer, mesothelioma, and cancer of the stomach and
colon. Mesothelioma is a rare cancer of the thin membrane lining of the chest and abdomen. Symptoms of
mesothelioma include shortness of breath, pain in the walls of the chest, and/or abdominal pain.
III. RESPIRATORS AND PROTECTIVE CLOTHING
A. Respirators: You are required to wear a respirator when performing tasks that result in asbestos exposure
that exceeds the permissible exposure limit (PEL) of 0.1 f/cc. These conditions can occur while your employer
is in the process of installing engineering controls to reduce asbestos exposure, or where engineering controls
are not feasible to reduce asbestos exposure. Air-purifying respirators equipped with a high-efficiency
particulate air (HEPA) filter can be used where airborne asbestos fiber concentrations do not exceed 2 f/cc;
otherwise, air-supplied, positive-pressure, full facepiece respirators must be used. Disposable respirators or
dust masks are not permitted to be used for asbestos work. For effective protection, respirators must fit your
face and head snugly. Your employer is required to conduct fit tests when you are first assigned a respirator
and every 6 months thereafter. Respirators should not be loosened or removed in work situations where their
use is required.
B. Protective clothing: You are required to wear protective clothing in work areas where asbestos fiber
concentrations exceed the permissible exposure limit.
IV. DISPOSAL PROCEDURES AND CLEANUP
A. Wastes that are generated by processes where asbestos is present include:
1. Empty asbestos shipping containers.
2. Process wastes such as cuttings, trimmings, or reject material.
3. Housekeeping waste from sweeping or vacuuming.
4. Asbestos fireproofing or insulating material that is removed from buildings.
5. Building products that contain asbestos removed during building renovation or demolition.
6. Contaminated disposable protective clothing.
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B. Empty shipping bags can be flattened under exhaust hoods and packed into airtight containers for disposal.
Empty shipping drums are difficult to clean and should be sealed.
C. Vacuum bags or disposable paper filters should not be cleaned, but should be sprayed with a fine water mist
and placed into a labeled waste container.
D. Process waste and housekeeping waste should be wetted with water or a mixture of water and surfactant
prior to packaging in disposable containers.
E. Material containing asbestos that is removed from buildings must be disposed of in leak-tight 6-mil thick
plastic bags, plastic-lined cardboard containers, or plastic-lined metal containers. These wastes, which are
removed while wet, should be sealed in containers before they dry out to minimize the release of asbestos
fibers during handling.
V. ACCESS TO INFORMATION
A. Each year, your employer is required to inform you of the information contained in this standard and
appendices for asbestos. In addition, your employer must instruct you in the proper work practices for handling
materials containing asbestos, and the correct use of protective equipment.
B. Your employer is required to determine whether you are being exposed to asbestos. You or your
representative has the right to observe employee measurements and to record the results obtained. Your
employer is required to inform you of your exposure, and, if you are exposed above the permissible limit, he or
she is required to inform you of the actions that are being taken to reduce your exposure to within the
permissible limit.
C. Your employer is required to keep records of your exposures and medical examinations. These exposure
records must be kept for at least thirty (30) years. Medical records must be kept for the period of your
employment plus thirty (30) years.
D. Your employer is required to release your exposure and medical records to your physician or designated
representative upon your written request.
Appendix H to § 1910.1001—Medical Surveillance Guidelines for Asbestos
Non-Mandatory
I. ROUTE OF ENTRY INHALATION, INGESTION
II. TOXICOLOGY
Clinical evidence of the adverse effects associated with exposure to asbestos is present in the form of several
well-conducted epidemiological studies of occupationally exposed workers, family contacts of workers, and
persons living near asbestos mines. These studies have shown a definite association between exposure to
asbestos and an increased incidence of lung cancer, pleural and peritoneal mesothelioma, gastrointestinal
cancer, and asbestosis. The latter is a disabling fibrotic lung disease that is caused only by exposure to
asbestos. Exposure to asbestos has also been associated with an increased incidence of esophageal, kidney,
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laryngeal, pharyngeal, and buccal cavity cancers. As with other known chronic occupational diseases, disease
associated with asbestos generally appears about 20 years following the first occurrence of exposure: There
are no known acute effects associated with exposure to asbestos.
Epidemiological studies indicate that the risk of lung cancer among exposed workers who smoke cigarettes is
greatly increased over the risk of lung cancer among non-exposed smokers or exposed nonsmokers. These
studies suggest that cessation of smoking will reduce the risk of lung cancer for a person exposed to asbestos
but will not reduce it to the same level of risk as that existing for an exposed worker who has never smoked.
III. Signs and Symptoms of Exposure-Related Disease
The signs and symptoms of lung cancer or gastrointestinal cancer induced by exposure to asbestos are not
unique, except that a chest X-ray of an exposed patient with lung cancer may show pleural plaques, pleural
calcification, or pleural fibrosis, and may also show asbestosis (i.e., small irregular parenchymal opacities).
Symptoms characteristic of mesothelioma include shortness of breath, pain in the chest or abdominal pain.
Mesothelioma has a much longer average latency period compared with lung cancer (40 years versus 15–20
years), and mesothelioma is therefore more likely to be found among workers who were first exposed to
asbestos at an early age. Mesothelioma is a fatal disease.
Asbestosis is pulmonary fibrosis caused by the accumulation of asbestos fibers in the lungs. Symptoms
include shortness of breath, coughing, fatigue, and vague feelings of sickness. When the fibrosis worsens,
shortness of breath occurs even at rest. The diagnosis of asbestosis is most commonly based on a history of
exposure to asbestos, the presence of characteristic radiologic abnormalities, end-inspiratory crackles (rales),
and other clinical features of fibrosing lung disease. Pleural plaques and thickening may be observed on chest
X-rays. Asbestosis is often a progressive disease even in the absence of continued exposure, although this
appears to be a highly individualized characteristic. In severe cases, death may be caused by respiratory or
cardiac failure.
IV. Surveillance and Preventive Considerations
As noted in section III of this appendix, exposure to asbestos has been linked to an increased risk of lung
cancer, mesothelioma, gastrointestinal cancer, and asbestosis among occupationally exposed workers.
Adequate screening tests to determine an employee's potential for developing serious chronic diseases, such
as cancer, from exposure to asbestos do not presently exist. However, some tests, particularly chest X-rays and
pulmonary function tests, may indicate that an employee has been overexposed to asbestos increasing his or
her risk of developing exposure-related chronic diseases. It is important for the physician to become familiar
with the operating conditions in which occupational exposure to asbestos is likely to occur. This is particularly
important in evaluating medical and work histories and in conducting physical examinations. When an active
employee has been identified as having been overexposed to asbestos, measures taken by the employer to
eliminate or mitigate further exposure should also lower the risk of serious long-term consequences.
The employer is required to institute a medical surveillance program for all employees who are or will be
exposed to asbestos at or above the permissible exposure limit (0.1 fiber per cubic centimeter of air). All
examinations and procedures must be performed by or under the supervision of a licensed physician, at a
reasonable time and place, and at no cost to the employee.
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Although broad latitude is given to the physician in prescribing specific tests to be included in the medical
surveillance program, OSHA requires inclusion of the following elements in the routine examination:
(i) Medical and work histories with special emphasis directed to symptoms of the respiratory system,
cardiovascular system, and digestive tract.
(ii) Completion of the respiratory disease questionnaire contained in appendix D of this section.
(iii) A physical examination including a chest X-ray and pulmonary function test that includes measurement of
the employee's forced vital capacity (FVC) and forced expiratory volume at one second (FEV1).
(iv) Any laboratory or other test that the examining physician deems by sound medical practice to be
necessary.
The employer is required to make the prescribed tests available at least annually to those employees covered;
more often than specified if recommended by the examining physician; and upon termination of employment.
The employer is required to provide the physician with the following information: A copy of the standard in this
section (including all appendices to this section); a description of the employee's duties as they relate to
asbestos exposure; the employee's representative level of exposure to asbestos; a description of any personal
protective and respiratory equipment used; and information from previous medical examinations of the
affected employee that is not otherwise available to the physician. Making this information available to the
physician will aid in the evaluation of the employee's health in relation to assigned duties and fitness to wear
personal protective equipment, if required.
The employer is required to obtain a written opinion from the examining physician containing the results of the
medical examination; the physician's opinion as to whether the employee has any detected medical conditions
that would place the employee at an increased risk of exposure-related disease; any recommended limitations
on the employee or on the use of personal protective equipment; and a statement that the employee has been
informed by the physician of the results of the medical examination and of any medical conditions related to
asbestos exposure that require further explanation or treatment. This written opinion must not reveal specific
findings or diagnoses unrelated to exposure to asbestos, and a copy of the opinion must be provided to the
affected employee.
Appendix I to § 1910.1001—Smoking Cessation Program Information For
Asbestos—Non-Mandatory
The following organizations provide smoking cessation information and program material.
1. The National Cancer Institute operates a toll-free Cancer Information Service (CIS) with trained personnel to
help you. Call 1–800–4–CANCER* to reach the CIS office serving your area, or write: Office of Cancer
Communications, National Cancer Institute, National Institutes of Health, Building 31, Room 10A24, Bethesda,
Maryland 20892.
2. American Cancer Society, 3340 Peachtree Road, NE., Atlanta, Georgia 30062, (404) 320–3333.
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The American Cancer Society (ACS) is a voluntary organization composed of 58 divisions and 3,100 local units.
Through “The Great American Smokeout” in November, the annual Cancer Crusade in April, and numerous
educational materials, ACS helps people learn about the health hazards of smoking and become successful exsmokers.
3. American Heart Association, 7320 Greenville Avenue, Dallas, Texas 75231, (214) 750–5300.
The American Heart Association (AHA) is a voluntary organization with 130,000 members (physicians,
scientists, and laypersons) in 55 state and regional groups. AHA produces a variety of publications and
audiovisual materials about the effects of smoking on the heart. AHA also has developed a guidebook for
incorporating a weight-control component into smoking cessation programs.
4. American Lung Association, 1740 Broadway, New York, New York 10019, (212) 245–8000.
A voluntary organization of 7,500 members (physicians, nurses, and laypersons), the American Lung
Association (ALA) conducts numerous public information programs about the health effect of smoking. ALA
has 59 state and 85 local units. The organization actively supports legislation and information campaigns for
non-smokers' rights and provides help for smokers who want to quit, for example, through “Freedom From
Smoking,” a self-help smoking cessation program.
5. Office on Smoking and Health, U.S. Department of Health and, Human Services, 5600 Fishers Lane, Park
Building, Room 110, Rockville, Maryland 20857.
The Office on Smoking and Health (OSH) is the Department of Health and Human Services' lead agency in
smoking control. OSH has sponsored distribution of publications on smoking-realted topics, such as free flyers
on relapse after initial quitting, helping a friend or family member quit smoking, the health hazards of smoking,
and the effects of parental smoking on teenagers.
*In Hawaii, on Oahu call 524–1234 (call collect from neighboring islands),
Spanish-speaking staff members are available during daytime hours to callers from the following areas:
California, Florida, Georgia, Illinois, New Jersey (area code 210), New York, and Texas. Consult your local
telephone directory for listings of local chapters.
Appendix J to § 1910.1001—Polarized Light Microscopy of Asbestos—NonMandatory
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.
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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, cummingtonitegrunerite 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
Crocidolite (Riebeckite asbestos)
Cummingtonite-Grunerite asbestos (Amosite)
Tremolite-Actinolite asbestos
Anthophyllite asbestos
Mg3 Si2 O5(OH)4
Na2 Fe32 + Fe23 + Si8
O22(OH)2
(Mg,Fe)7 Si8 O22(OH)2
Ca2(Mg,Fe)5 Si8 O22(OH)2
(Mg,Fe)7 Si8 O22(OH)2
Asbestos Fiber: A fiber of asbestos meeting the criteria for a fiber. (See section 3.5.)
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.
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Fiber: A particle longer than or equal to 5 µm 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 µm 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 Mg3(Si2O5(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).
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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 µm 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 µm 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 µm. 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 µm 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.
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(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.
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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.
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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, non- combustible, 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
and 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.
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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.
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(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 WaltonBeckett 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.
(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 °C
(e) Drying oven capable of 50–150 °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
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(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 1 × 3 inches 1mm thick, precleaned.
(k) Cover Slips 22 × 22 mm, #11⁄2
(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 °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.
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(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 °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 °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 °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):
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(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
may 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 highdispersion 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.
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(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)
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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 µm. 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
acicular rather than filiform.
Where the particles are less than 1 µm 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 × 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 400 × . 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
µm in thickness must be identified by inference to the presence of larger, identifiable fibers and morphology. If
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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° 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
under- estimate 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
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on metallurgical grain-size determination have found some utility. Estimation is more easily handled in
situations where the grain sizes visible at about 160 × 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 °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) × (Fraction remaining after step 2) × (Fraction remaining of original sample
after step 1)
R = (5) × (.30) × (.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.”
4. 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.
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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 × 108 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° angles and one angle not equal to 90°. The orthorhombic group, of which anthophyllite
is a member has three unequal sides and three 90° 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
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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 α, β, and γ are used to identify
the lowest, middle, and highest index of refraction respectively. The x direction, associated with α is called the
fast axis. Conversely, the z direction is associated with γ and is the slow direction. Crocidolite has α along the
fiber length making it “length-fast”. The remainder of the asbestos minerals have the γ 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. 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.
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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 α and the γ axes. This maximum difference is
usually tabulated as the birefringence of the crystal.
For this test, align the fiber at 45° 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(nγ—nα)
R = retardation, t = crystal thickness in µm, and
nα,γ = 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° 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° 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
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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 can not
be excluded by morphology. This test is relatively ineffective for use on fibers less than 1 µm 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° 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-yellowwhite, 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
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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, DC, 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.
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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, ASTM,
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.
[51 FR 22733, June 20, 1986]
Editorial Note: For FEDERAL REGISTER citations affecting § 1910.1001, see the List of CFR Sections Affected,
which appears in the Finding Aids section of the printed volume and at www.govinfo.gov.
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