Asbestos is a naturally occurring mineral. However, it differs from other minerals in its crystal development. The crystal formation of asbestos is in the form of long thin fibers. Asbestos is divided into two mineral groups --- Serpentine and Amphibole. The division between the two types of asbestos is based upon the crystalline structure. Serpentines have a sheet or layered structure where amphiboles have a chain-like structure.
In the amphibole group, there are five types of asbestos. As an acronym for the Asbestos Mines of South Africa, Amosite is the second most prevalent type of asbestos found in building materials. Amosite is also known as "brown asbestos." Next, there is Crocidolite or "blue asbestos," which is an asbestos found in specialized high temperature applications. The other three types (Anthophyllite, Tremolite, and Actinolite) are rare and found mainly as contaminants in other minerals. Asbestos deposits can be found throughout the world and are still mined in Australia, Canada, South Africa, and the former Soviet Union.
Asbestos has been used in more than 5,000 products, including roofing, thermal and electrical insulation, cement pipe and sheet, flooring, gaskets, friction materials, coatings, plastics, textiles, and paper products. Chrysotile, amosite, and particularly crocidolite all have extremely high-tensile strengths and are used extensively as reinforcers in cements, resins, and plastics. Chrysotile fibers are soft and flexible, whereas crocidolite and amosite fibers are hard and brittle. Although chrysotile is most adaptable to industrial use, crocidolite and amosite are particularly useful in combination with chrysotile for adding specific properties, such as rigidity. Due to its flexibility and softness, chrysotile can be more readily spun into textiles than the amphiboles (amosite, anthophyllite, and crocidolite).
Domestically used asbestos fibers are technically classified into seven quality categories or grades. Grades 1, 2, and 3 include the longer, maximum-strength fibers and are generally used in the production of textiles, electrical insulation, and pharmaceutical and beverage filters. Grades 4, 5, and 6 are medium-length fibers used in the production of asbestos-cement (A/C) pipe, A/C sheet, clutch facings, brake linings, asbestos paper, packaging, gaskets, and pipe coverings. Grade 7 includes short fibers generally used as a reinforcer in plastics, floor tiles, coatings and compounds, some papers, and roofing felts.
The primary routes of potential human exposure to asbestos are dermal contact, inhalation, and ingestion. Because asbestos fibers are naturally occurring and aerodynamic, virtually everyone is exposed to asbestos. Asbestos fibers are released into the environment from the natural occurrence of asbestos in the earh and as a result of wear and deterioration of asbestos products. Asbestos minerals are emitted into the atmosphere and water systems from the mining and milling of asbestos ores.
To be a significant health concern, asbestos fibers must be inhaled at high concentrations over an extended period of time. Asbestos fibers then accumulate in the lungs. As exposure increases, the risk of disease also increases. Therefore, measures to minimize exposure and consequently minimize accumulation of fibers will reduce the risk of adverse health effects.
Asbestos is only dangerous if it becomes airborne. As long as asbestos containing materials are not damaged, the asbestos fibers do not become airborne and do not pose a health threat to the building occupants. During an asbestos building survey, inspectors assess the condition of asbestos containing materials. These conditions do deteriorate over time.
The next type of disease attributed to asbestos exposure is Mesothelioma. It is a cancer of the pleural lining. It is considered to be exclusively related to asbestos exposure. By the time it is diagnosed, it is almost always fatal. Similar to other asbestos related diseases, mesothelioma has a longer latency period of 30 to 40 years.
Lung Cancer is a malignant tumor of the bronchi covering. The tumor grows through surrounding tissue, invading and often obstructing air passages. The time between exposure to asbestos and the occurrence of lung cancer is 20 to 30 years. It should be noted that there is a synergistic effect between smoking and asbestos exposure, which creates an extreme susceptibility to lung cancer.
Airborne Fiber Concentrations
FDA regulates, under the Food, Drug, and Cosmetic Act, the use of asbestos in indirect food additives, adhesives, components of coatings and polymers. FDA has also taken action concerning asbestos, restricting the utilization of asbestos filters in the manufacture of drugs and drug ingredients.
The Occupational Safety and Health Administration (OSHA) has set a Permissible Exposure Limit (PEL) at 0.1 fibers per cubic centimeter (f/cc) for an 8 hour time weighted average.
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Did You Know?
None of the original soldier huts remain. The huts that you see in the park today are reproductions based on the model that General Washington wanted the soldiers to follow. Despite a lack of tools and the relative haste in which they were built, most served as decent shelters for the troops.