Washington Administrative Code › Title 296 - Labor and Industries, Department of › Chapter 296-62 - General occupational health standards › Part I-1 - ASBESTOS, TREMOLITE, ANTHOPHYLLITE, AND ACTINOLITE › Section 296-62-07737 - Appendix B - Detailed procedure for asbestos sampling and analysis - Nonmandatory

Current through Register Vol. 24-14, July 15, 2024
Air
Matrix:
WISHA 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 4.0 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 WISHA.
				  Similar products from other sources can be substituted.
Introduction.
This method describes the collection of airborne asbestos
				  fibers using calibrated sampling pumps with mixed-cellulose ester (MCE) filters
				  and analysis by phase contrast microscopy (PCM). Some terms used are unique to
				  this method and are defined below:
Asbestos:
A term for naturally occurring fibrous
				  minerals. Asbestos includes chrysotile, crocidolite, amosite
				  (cummingtonite-grunerite asbestos), tremolite asbestos, actinolite asbestos,
				  anthophyllite asbestos, and any of these minerals that have been chemically
				  treated and/or altered. The precise chemical formulation of each species will
				  vary with the location from which it was mined. Nominal compositions are
				  listed:
Chrysotile
Mg3Si2O5(OH)4
Crocidolite
Na2Fe32+Fe23+Si8O22(OH)2
Amosite
(Mg,Fe)7Si8O22(OH)2
Tremolite-actinolite
Ca2(Mg,Fe)5Si8O22(OH)2
Anthophyllite
(Mg,Fe)7Si8O22(OH)2
Asbestos Fiber:
A fiber of asbestos which meets
				  the criteria specified below for a fiber.
Aspect Ratio:
The ratio of the length of a fiber
				  to it's diameter (e.g. 3:1, 5:1 aspect ratios).
Cleavage Fragments:
Mineral particles formed by
				  comminution of minerals, especially those characterized by parallel sides and a
				  moderate aspect ratio (usually less than 20:1).
Detection Limit:
The number of fibers necessary
				  to be 95% certain that the result is greater than zero.
Differential Counting:
The term applied to the
				  practice of excluding certain kinds of fibers from the fiber count because they
				  do not appear to be asbestos.
Fiber:
A particle that is 5 µm or longer,
				  with a length-to-width ratio of 3 to 1 or longer.
Field:
The area within the graticule circle that
				  is superimposed on the microscope image.
Set:
The samples which are taken, submitted to
				  the laboratory, analyzed, and for which, interim or final result reports are
				  generated.
Tremolite, Anthophyllite, and Actinolite:
The
				  non-asbestos form of these minerals which meet the definition of a fiber. It
				  includes any of these minerals that have been chemically treated and/or
				  altered.
Walton-Beckett Graticule:
An eyepiece graticule
				  specifically designed for asbestos fiber counting. It consists of a circle with
				  a projected diameter of 100 ± 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. The disk is placed in one of the microscope eyepieces so
				  that the design is superimposed on the field of view.
1.History.
(a) 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 worksites 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.
(b) 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 a
				defined criteria for asbestos are counted and considered a measure of the
				airborne asbestos concentration.
(c) Advantages and Disadvantages
(i) There are four main advantages of PCM
				over other methods:
(A) The technique is
				specific for fibers. Phase contrast is a fiber counting technique which
				excludes non-fibrous particles from the analysis.
(B) The technique is inexpensive and does not
				require specialized knowledge to carry out the analysis for total fiber
				counts.
(C) The analysis is quick
				and can be performed on-site for rapid determination of air concentrations of
				asbestos fibers.
(D) The technique
				has continuity with historical epidemiological studies so that estimates of
				expected disease can be inferred from long-term determinations of asbestos
				exposures.
(ii) 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.
(d) 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.
(e) 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.