- Asbestos is the common name for a group of fibrous, mineral silicates, having unique properties.
- These properties include:
- a. Noncombustible
- b. High tensile strength
- c. Good noise absorption
- d. Thermal insulator
- e. Condensation control
- f. Resistant to the effects of corrosive chemicals
- g. Resistant to the effects of friction
- The various types of asbestos, their characteristics, and uses are given in Table I.
B. Historical Uses
- Asbestos has been used for over two thousand years. The meaning stemmed from the Greek word "quenchable" - derived from the observation that the material would not burn.
- Marco Polo reported the use of asbestos in gun powder by the Chinese.
- A tablecloth belonging to Charlemagne was woven with asbestos.
- In 1729, Benjamin Franklin sold a purse fabricated with asbestos to his British benefactor.
C. Modern Uses
- The unique characteristics of asbestos have resulted in a very diverse use of the material over the years. The asbestos industry reports that currently over 3,600 products contain asbestos.
- Asbestos-containing products can be divided into two categories:
- Category I - Friable Material and Asbestos Textile Products
- Category II - Nonfriable Matrix-Bonded Composite Products
- Table II lists categories, product uses, and approximate dates of use
D. Trade Names
- Listed in Table III are the types of application and the associated trade names of some asbestos-containing products
E. Methods of Application
- Asbestos was sprayed onto structures in auditoriums, hallways, and classrooms for fireproofing, noise absorption, condensation control, and decorative purposes.
- Sprayed-on asbestos is usually friable.
- Two methods were used to spray-apply asbestos:
- Wet Method
- Generally, a mixture might have consisted of a slurry of one or more of the following: asbestos (5-30%), mineral wool, and/or fiberglass, and Portland cement, gypsum, pearlite and vermiculite.
- This material was more dense and less friable than that applied by the dry method (described below).
- The thickness of the application usually ranged from 1/2 to 1 inch.
- Chrysotile was usually used in the formulation.
- The surfaces were often trowelled after application, resulting in a harder, more dense material.
- Dry Method
- Generally, a mixture consisted of a dry blend of asbestos fibers (5-90%) and one or more of the following: mineral wool or fiberglass, Portland cement or gypsum, water-soluble resins, starches, and other additives.
- The mixture was applied with a sprayer and wetted as it passed through the nozzle. The water activated the water-soluble resins, producing a wet fiber matrix, which readily adhered to the application surface.
- The thickness of the application was usually 1/2 to 2 inches.
- Amosite, chrysotile, or both were often used; Crocidolite was used infrequently.
- Because of the method, the asbestos content can vary greatly within the same application.
- Wet Method
2. Pipe and Boiler Insulation
- a. This insulation is usually applied by pasting preformed blocks or sheets or by applying wetted asbestos-containing compounds.
- b. Generally, three types of insulation were used:
- Preformed sections, blocks or siabs
- Insulating cement for values, elbows or over fiberglass ducts
- Asbestos paper products (flat sheets or corrugated).
F. Airborne Asbestos
- Unlike many man-made fibers, asbestos as it is mined and used in manufacturing rarely is in single-fiber form. It can continue to split into smaller and smaller fiber bundles.
- The average fiber diameter ranges from 0.11 to 0.24 micrometers. However, asbestos can split into even smaller bundles,which cannot be seen with an optical microscope.
- These fine fibers settle from the air very slowly. In completely still air, fibers of the size usually found in overhead spray insulation in a occupied 8' or 10' office take approximately 80 hours to settle.
|Chrysotile||White asbestos; fine silky fibers; flexible and high tensile strength; accounts for over 90% of the uses of asbestos.||Canada
|Amosite||Brown asbestos; brittle fibers; bonds well with plastics and is used in heat insulation materials.||South Africa|
|Crocidolite||Blue asbestos; strongest of the asbestos fibers; brittle fibers; usually found in combination with chrysotile in pipes and sheeting; also occasionally found with amosite or chrysotile in pipe and boiler wrap; also used as decorative material.||South Africa|
|These three are types of asbestos most often found in construction materials and commercial products. Tremolite, actinolite, and anthophyllite are also asbestos minerals, but rarely found in building and commercial products.|
|Surfacing Material||sprayed-on or troweled-on||1-95||1935-1970||Sodium silicate, portland cement, organic biners.|
|Preformed thermal insulating products||batts blocks and pipe covering
|felts: blue stripe||80||1920-present||cotton|
|felts: red stripe||90||1920-present||cotton|
|felts: green stripe||95||1920-present||cotton|
|Cementitious: concrete-like products||extrusion panels||8||1965-1977||portland cement|
|flexible perforated||30-50||1930-present||portland cement|
|roof tiles||20-30||1930-present||portland cement|
|siding shingles||12-14||unknown-present||portland cement|
|roofing shingles||20-32||unknown-present||portland cement|
|Paper Products||corrugated: high temp.||90||1935-present||sodium silicate|
|corrugated: moderate temp.||35-70||1910-present||starch|
|indented||98||1935-present||cotton and organic binder|
|millboard||80-85||1925-present||starch, lime, clay|
|Roofing felts||smooth surface||10-15||1910-present||asphalt|
|Asbestos containing compounds||caulking putties||30||1930-present||linseed oil|
|adhesive (cold applied)||5-25||1945-present||asphalt|
|asphalt tile cement||13-25||1959-present||asphalt|
|spackles||3-5||1930-1975||starch, casein, synthetic resins|
|sealanis fire water||50-55||1935-present||caster oil or polyisobutylene|
|cement magnesia||15||1926-1950||magnesium carbonate|
|Flooring tile and Sheet Goods||vinyl asbestos tile||21||1950-present||poly(vinyl)chloride|
|asphalt asbestos tile||26-33||1920-present||asphalt|
|sheet good/resilient||30||1950-present||dry oils|
|Paints and Coatings||roof coating||4-7||1900-present||asphalt|
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