Asbestos is the name for a group of naturally occurring silicate minerals that can be separated into fibers. The fibers are strong, durable, and resistant to heat and fire. There are several types of asbestos fibers, three of which are used for commercial applications:
chrysotile, or white asbestos, comes mainly from Canada, and has been very widely used in the United States—it is white-gray in color and found in serpentine rock;
amosite, or brown asbestos, comes from southern Africa;
crocidolite, or blue asbestos, comes from southern Africa and Australia.
Amosite and crocidolite are called amphiboles. This term refers to the nature of their geologic formation. Other asbestos fibers that have not been used commercially are tremolite, actinolite, and anthophyllite, although they are sometimes contaminants in asbestos-containing products. In addition to asbestos mines, asbestos is found as a contaminant mineral in the host rock in non-asbestos mining operations.
Asbestos has long been recognized as a human carcinogen. (Refer to the U.S. Department of Health and Human Services, Public Health Service, the National Toxicology Program report of December 2002, "10th Report on Carcinogens," at http://ehp.niehs.nih.gov/roc/tenth/profiles/s016asbe.pdf.) OSHA estimates that 1.3 million employees in construction and general industry have significant asbestos exposure on the job—those workers involved in construction, renovation, and demolition have the most risk of exposure. Other high-risk jobs include manufacture of asbestos products (such as building materials and insulation) and performing automotive brake and clutch repair. Of particular utility is a list of suspected asbestos-containing materials prepared by the Environmental Protection Agency (EPA), which can be found in Table 3 of this chapter and at http://www.epa.gov/Region06/6pd/asbestos/asbmatl.htm. Construction employers whose projects involve materials of the types listed should anticipate potential asbestos exposure and carefully review their obligations under applicable OSHA, EPA, and/or state standards.
Asbestos, or fibrous dust, is created and released into the ambient air by the breaking, crushing, grinding, drilling, or general abrasive handling of a solid material that has fibrous components. Chrysotile is the type of asbestos most commonly found in commercial products. Amosite and crocidolite are generally considered to be the most toxic. Fibrous dust particles do not readily settle out of the air, but can remain suspended for long periods of time. As a result, accumulations of fibrous dust can continue to present an inhalation hazard when they are stirred up by vehicular traffic, by persons walking through them, or by the wind.