Asbestos (Greek a-,“not”; sbestos, “extinguishable”), the fibrous form of several minerals and hydrous silicates of magnesium. The name may also be applied to the fibrous forms of calcium and iron. Asbestos fibers can be molded or woven into various fabrics. Because it is nonflammable and a poor heat conductor, asbestos has been widely used to make fireproof products such as safety clothing for fire fighters and insulation products such as hot-water piping. The first recorded use of the word asbestos is by Pliny the Elder in the 1st century ad, although the substance itself was known as early as the 2nd century bc. The Romans made cremation cloths and wicks from it, and centuries later Marco Polo noted its usefulness as cloth.
Asbestos is of two principal classes, the amphiboles and the serpentines, the former of relatively minor importance. Chrysotile, in the serpentine class, constitutes about 95 percent of the world supply of asbestos, of which three-fourths is mined in Québec. Other large deposits exist in South Africa. In the United States, California, Vermont, and Arizona are the leading asbestos-producing states; however, the majority of United States deposits are of no commercial value.
Asbestos is obtainable by various underground mining methods, but the most common method is open-pit mining. Only about 6 percent of the mined ore contains usable fibers.
The fibers are separated from the ore by crushing, air suction, and vibrating screens, and in the process are sorted into different lengths, or grades. The most widely used method of grading, the Québec Standard Test Method, divides the fibers into seven groups, the longest in group one and the shortest, called milled asbestos, in group seven. The length of the fibers, as well as the chemical composition of the ore, determines the kind of product that can be made from the asbestos. The longer fibers have been used in fabrics, commonly with cotton or rayon, and the shorter ones for molded goods, such as pipes and gaskets.
Asbestos has been used in building-construction materials, textiles, missile and jet parts, asphalt and caulking compounds and paints, and in friction products such as brake linings. Exposure to asbestos fibers and dust, however, can cause asbestosis, a disease of the lungs caused by the inhalation of asbestos particles, and, after a latent period of up to 30 years and more, various cancers, especially lung cancer and mesothelioma, which is an inoperable cancer of the chest and abdominal lining . At present no wholly satisfactory substitutes are available for asbestos in many of its applications; because of health risks posed by asbestos use, however, research into replacements has been accelerated. In 1986 the Environmental Protection Agency proposed an immediate ban on the major uses of asbestos and a complete ban on all asbestos products within the next decade. This proposal was partially overturned by the U.S. Court of Appeals, which limited the ban to asbestos flooring and new products using asbestos.
Asbestos is of two principal classes, the amphiboles and the serpentines, the former of relatively minor importance. Chrysotile, in the serpentine class, constitutes about 95 percent of the world supply of asbestos, of which three-fourths is mined in Québec. Other large deposits exist in South Africa. In the United States, California, Vermont, and Arizona are the leading asbestos-producing states; however, the majority of United States deposits are of no commercial value.
Asbestos is obtainable by various underground mining methods, but the most common method is open-pit mining. Only about 6 percent of the mined ore contains usable fibers.
The fibers are separated from the ore by crushing, air suction, and vibrating screens, and in the process are sorted into different lengths, or grades. The most widely used method of grading, the Québec Standard Test Method, divides the fibers into seven groups, the longest in group one and the shortest, called milled asbestos, in group seven. The length of the fibers, as well as the chemical composition of the ore, determines the kind of product that can be made from the asbestos. The longer fibers have been used in fabrics, commonly with cotton or rayon, and the shorter ones for molded goods, such as pipes and gaskets.
Asbestos has been used in building-construction materials, textiles, missile and jet parts, asphalt and caulking compounds and paints, and in friction products such as brake linings. Exposure to asbestos fibers and dust, however, can cause asbestosis, a disease of the lungs caused by the inhalation of asbestos particles, and, after a latent period of up to 30 years and more, various cancers, especially lung cancer and mesothelioma, which is an inoperable cancer of the chest and abdominal lining . At present no wholly satisfactory substitutes are available for asbestos in many of its applications; because of health risks posed by asbestos use, however, research into replacements has been accelerated. In 1986 the Environmental Protection Agency proposed an immediate ban on the major uses of asbestos and a complete ban on all asbestos products within the next decade. This proposal was partially overturned by the U.S. Court of Appeals, which limited the ban to asbestos flooring and new products using asbestos.
