The Online Encyclopedia and Dictionary







Structures containing asbestos are marked
Structures containing asbestos are marked

Asbestos (Greek a-, "not"; sbestos, "extinguishable") is a group of fibrous metamorphic minerals. The name is derived for its historical use in lamp Wicks; the resistance of asbestos to fire has long been exploited for a variety of purposes. It was used in fabrics such as Egyptian burial cloths and Charlemagne's tablecloth, which, according to legend, he threw in a fire to clean.

When asbestos is used for its resistance to fire or heat, the fibers are typically mixed with cement or woven into fabric or mats. It was used in brake shoes and gaskets for its heat resistance, and in buildings for its flame-retardant and insulating properties, its tensile strength, flexibility, and resistance to chemicals. However, the inhalation of asbestos fibers is now known to cause various illnesses, including cancer, and thus most uses of asbestos are banned in many countries.

Most respirable asbestos fibers are invisible to the unaided human eye because their size is about 3.0-20.0 Ám in length and can be as thin as 0.01 Ám. Fibers ultimately form because when these minerals originally cooled and crystallized, they formed by the polymeric molecules lining up parallel with eachother and forming oriented crystal lattices. These crystals thus have three cleavage planes as other minerals and gemstones have. But in their case, there are two cleavage planes that are much weaker than the third direction. Thus when sufficient force is applied they tend to break along their weakest directions, resulting in a linear fragmentation pattern and hence a fibrous form. This fracture process can keep occurring over and over until they have been broken down to their smallest unit dimensions. For this reason, one larger asbestos fiber can ultimately become the source of hundreds of much thinner and smaller fibers in a normal environment over the course of time. As they get smaller and lighter, they become more mobile and more easily entrained (wafted) into the air, where human respiratory exposures typically result.

Confusingly, the Modern Greek word asbestos means quicklime.


Types of asbestos

  • Chrysotile, or white asbestos, is obtained from Canadian serpentine rocks. It is less friable (and therefore less likely to be inhaled) than the other types and is the type most often used industrially. Chrysotile should not be confused with chrysolite, a synonym of olivine.
  • Amosite, or brown asbestos, is an amphibole from Africa.
  • Crocidolite, or blue asbestos, is an amphibole from Africa and Australia. It is the fibrous form of riebeckite. Blue asbestos is commonly thought of as the most dangerous type of asbestos (see above and below).

Notes: Serpentine rocks are those with curled fibres. Amphiboles have straight, needle-like fibres.

The amphiboles, in their fibrous form, are friable and therefore the most carcinogenic, although they also exist in safer non-fibrous forms.

Other asbestos minerals, such as tremolite, actinolite and anthophyllite are less-used industrially but can still be found in a variety of construction materials and insulations and occur in a few consumer products, such as talcum powders and vermicullite. In the United States, any asbestos content of 1% or greater in construction and other friable (easily crushed by finger pressure) products is banned by the United States Environmental Protection Agency (EPA).

Asbestos-related diseases

Asbestosis and cancer

Strong concerns about the health hazards associated with asbestos had been described many times over the years. As early as 1898 the Chief Inspector of Factories of the United Kingdom reported to the Parliament in his Annual Report about the "evil effects of asbestos dust". He reported the "sharp, glass like nature of the particles" when allowed to remain in the air in any quantity, "have been found to be injurious, as might have been expected" (Report of the Select Committee 1994). In 1906 a British Parliamentary Commission confirmed the first cases of asbestos deaths in factories in Britain and recommended better ventilation and other safety measures. In 1918 a US insurance company produced a study showing premature deaths in the asbestos industry in the United States and in 1926 the Massachusetts Industrial Accidents Board processed the first successful compensation claim by a sick asbestos worker.

The fine asbestos fibres are easily inhaled, and can cause a number of respiratory complaints, including a potentially serious lung fibrosis called asbestosis. Exposure to asbestos has also been determined to cause a very serious form of cancer, mesothelioma, that occurs in the chest and abdominal cavities. This aggressive disease is not properly referred to as a lung cancer, as the malignant cells are derived from the mesothelium, a tissue found on the inner walls of the chest and abdominal cavities and on the outer surface of the lungs rather than in the lung itself.

When inhaled, asbestos is carcinogenic. In the United States alone, it is estimated that ten thousand people die each year of asbestos-related diseases, such as mesothelioma, asbestosis, lung cancer, and gastrointestinal cancer. Asbestos has a synergistic effect with tobacco smoking in the causation of lung cancer.

Other asbestos-related diseases

  • asbestos warts – caused when the sharp fibres lodge in the skin and are overgrown causing benign callus-like growths.
  • pleural plaques – discrete fibrous or partially calcified thickened area which can be seen on X-rays of individuals exposed to asbestos. They do not become malignant nor normally cause any lung impairment.
  • diffuse pleural thickening – similar to above and can sometimes be associated with asbestosis. Usually no symptoms shown but if extensive can cause lung impairment.


In the United States, asbestos was one of the first hazardous air pollutants regulated under Section 112 of the Clean Air Act of 1970.

Lawsuits claiming asbestos caused diseases are a gigantic part of the total amount of lawsuits pending in American courts. Since the late 1970s, approximately 6% of all filings in American courts each year were related to asbestos. As of 2004, asbestos cases result in about 600 to 700 appellate opinions per year (that is, including both federal and state courts); this number obviously does not include countless more cases that were not appealed, or were settled or otherwise abandoned before trial. Estimates of total American deaths attributable to asbestos range from 200,000 to 265,000 (according to the March 1991 Report of the Judicial Conference Ad Hoc Committee on Asbestos Litigation).

Asbestos liability is by far the largest issue facing the global insurance industry today, with the industry protesting because many are suing because they have been exposed but have not as yet contracted a disease.

In mid-2004, a huge public outcry across Australia followed revelations at a New South Wales government-sanctioned inquiry into the company James Hardie's handling of its asbestos injury liabilities. See that article for details.

In Brazil, prohibition of extraction and use of asbestos is currently under regulamentation.

Removal of asbestos

Many buildings contain asbestos, which was used as a fire retardant . Typically, asbestos was "flocked" under false ceilings, inside technical ducts, etc. Asbestos panels etc. were also used.

Depending on how and where asbestos was applied, it may not pose any risk to most users of the building: if the fibers cannot dislodge themselves, they cannot be inhaled, and thus the risk is absent. However, with certain ways of applying asbestos, particularly flocking, asbestos fibers may gradually drop off into the air. Furthermore, in all cases, asbestos poses special hazards to maintenance personnel which has to drill holes in walls, install electrical or other cables, etc. Also, even if the workers are protected, such maintenance operation may release fibers into the air, which may be inhaled by other users later. As a consequence, interventions in areas where asbestos is present often have to follow stringent procedures.

The removal of asbestos from a building is uneasy because of the above constraints. If removal is to be performed when users are still present in the building, it is usually necessary to relocate some of them temporarily, because, typically, the part of the building from which asbestos is being removed has to be sealed off in order to prevent contamination of the other areas. Even if the building is closed to normal users, it is necessary to seal it off. Accordingly, asbestos removal works are long and costly. Examples of long asbestos removal enterprises include the Jussieu Campus (begun circa 1996 and still going on as of 2005) and the Tour Montparnasse (in 2005, projected times were 3 years if the tower was emptied from its users, and 10 years if it was not).

An asbestos-containing building that is to be torn down may be required to be sealed and to have its asbestos safely and properly removed first, before ordinary demolition can be performed. The asbestos removal may take longer and cost more than the actual tearing-down of the building.

See also

External links

Last updated: 10-11-2005 20:59:31
The contents of this article are licensed from under the GNU Free Documentation License. How to see transparent copy