Types of Asbestos
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Share ArticleAsbestos is a group of six minerals that occur naturally in the environment and can be mined. The word asbestos is actually a name that was given commercially and applied to this group of minerals. Asbestos consists of hydrogen, oxygen, silicon and other metal cations (a positively charged ion).
Asbestos shares many qualities with cloth, but is also resistant to heat and fire and is very strong. Characteristics like these made it a popular and prevalent material in many industrial processes from the late 1800's through the end of the twentieth century. Industries that involve exposure to asbestos include: aluminum plants; chemical plants; oil refineries; power plants; shipyards; steel mills; and construction sites. Asbestos has also been used in the production of many common household items, such as hair dryers. One study estimated that asbestos has been used in over 3,000 products.
However, when asbestos is damaged, its fibers become airborne and can be inhaled or swallowed. At this point, asbestos becomes very dangerous. Over time, it can cause both chronic lung conditions and fatal forms of asbestos cancer.
Asbestos occurs naturally as a group of fibers. These fibers can be pulled apart into separate threads. There are two main types of asbestos: amphibole asbestos and serpentine asbestos. A fiber must be examined under a microscope to determine its type. Amphibole fibers are straight and shaped like rods or poles; it develops in a structure that looks like a chain. Types of amphibole fibers are: amosite actinolite, anthophyllite, crocidolite, and tremolite asbestos. Because it stays in the lungs for longer, amphibole is considered more dangerous and more likely to lead to the development of mesothelioma. All uses of amphibole asbestos have been banned in the United States. Serpentine fibers are, as their name suggests, curly and snake-like in shape. It develops in layers. The most common type of serpentine fiber is chrysolite.
Overall, the most common types of asbestos are:
- Chrysolite: this white fiber is the most commonly-used form of asbestos. It consists of magnesium silicate. Because of its curly shape, it can be woven into fabrics. This type of asbestos is used in the United States on a very limited basis. It has been used to make roofing shingles, caulk, fire blankets, and pipe insulation. Any exposure to it is considered dangerous;
- Amosite: these fibers are brown or gray in color and contain iron and magnesium; and
- Crocidolite (or Riebeckite): this fiber is straight and blue. It is composed of a sodium iron magnesium silicate. This is considered the most dangerous form of asbestos.
Other types include:
- Anthophyllite can be white, gray or brown. It consists of magnesium iron silicate hydroxide;
- Tremolite: this white, gray or green fiber is composed of calcium magnesium iron silicate. It is found in metamorphic rocks; and
- Actinolite is similar in its composition to tremolite, but has a darker green color.
Asbestos can also be found in a mineral called vermiculite that was mined at the W.R. Grace Mine in Libby, Montana. This mine provided approximately 80% of the world's vermiculite until it was shut down in 1990 because of the asbestos contamination. When it is heated, vermiculite expands and is resistant to fire. It is mined throughout the world and, to date, the Libby Mine is the only place where it has been found to contain asbestos. Vermiculite is used in insulation and certain garden products. The Environmental Protection Agency has issued recommendations that people limit the use of vermiculite, use it outdoors and take measures to prevent excessive exposure to vermiculite dust.
The shape and dimensions of the asbestos fiber determines what part of the body it reaches when it is inhaled or ingested. Fibers which are thinner and longer travel into the lower parts of the airways and lungs. Wider particles do not typically travel further than the upper respiratory tract and do not make it to the lungs. Those who directly inhale asbestos fibers can also "carry" the risk with them into other environments. There are documented cases, for instance, of the family members of a worker being exposed to asbestos through fibers in clothing. This is called secondary, or limited, exposure.
Once asbestos fibers are lodged in the lungs, pleura or abdomen, it can take anywhere between 15 and 50 years for a medical condition to develop. During this period, the asbestos fibers constantly aggravate the tissue that they are lodged in. They can cause a buildup of scar-like tissue that impedes breathing and limit blood flow into and out of the lungs. They can also lead to development and growth of cancerous cells in the lungs or in the mesothelium, a membrane which covers most of the body's internal organs.
Malignant mesothelioma is a particularly aggressive form of cancer that is often fatal. The disease can be treated with surgery, chemotherapy, radiation and experimental therapies. These treatments may slow the progress of the disease and alleviate symptoms, such as shortness of breath, to increase comfort. However, they do not represent a cure for the disease. Rising mesothelioma rates are responsible for drawing increased attention to the risks of asbestos during the past several decades.
The many risks associated with asbestos exposure led to its reduced use and to its use being banned in most cases in the United States. By the late 1970's, the U.S. Consumer Product Safety Commission had banned several uses of asbestos and some industries stopped using asbestos voluntarily. In 1989, the Environmental Protection Agency passed a ban on any new uses of asbestos, although this ban allows uses that predate 1989. In 2000, domestic producers of crayons eliminated talc from the production process because of the risk of asbestos exposure to children. According to the National Cancer Institute, the consumption of asbestos in the United States was about 2,400 metric tons in 2005 compared to 803,000 metric tons in 1973. Growing numbers of countries around the world are also limiting or banning asbestos use.
- National Institute for Occupational Safety and Health. “ Asbestos.”
Accessed: 27 July 2007. - National Cancer Institute. “Asbestos Exposure: Questions and Answers.” 1 February 2007.
Accessed: 27 July 27, 2007. - Environmental Protection Agency. “Asbestos.” 12 July 2007.
Accessed: 27 July 2007. - Agency for Toxic Substances and Disease Registry. “Asbestos: Health Effects.” 20 March 2007.
Accessed: 27 July 2007.
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