Asbestos (a misapplication of Latin: asbestos "quicklime" from Greek ἄσβεστος: a-, "not"; sbestos, "extinguishable") describes any of a group of fibrous metamorphic minerals of the hydrous magnesium silicate variety. 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. Asbestos was used in fabrics such as Egyptian burial cloths and Charlemagne's tablecloth which according to legend, he threw in a fire to clean. Asbestos occurs naturally in many forms (see below); it is mined from metamorphic rocks.

When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement or woven into fabric or mats. Asbestos is used in brake shoes and gaskets for its heat resistance, and in the past was used on electric oven and hotplate wiring for its electrical insulation at elevated temperature, and in buildings for its flame-retardant and insulating properties, tensile strength, flexibility, and resistance to chemicals. The inhalation of some kinds of asbestos fibers, however, causes various serious illnesses, including cancer. Thus, most uses of asbestos are banned in many countries. Fiberglass has been found to be a suitable substitute for thermal insulation, and woven ceramic fiber performs as well as or better than asbestos as an insulator of high-temperature electrical conductors.

Most respirable asbestos fibers are invisible to the unaided human eye because their size is about 3.0-20.0 µm in length and can be as thin as 0.01 µm. Human hair ranges in size from 17 to 181 µm.[1] Fibers ultimately form because when these minerals originally cooled and crystallized, they formed by the polymeric molecules lining up parallel with each other and forming oriented crystal lattices. These crystals thus have three cleavage planes, just 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. The released fibers being heavier than air will eventually settle in quiescent conditions only to be resuspended over and over again by any kind of activity or air currents over a period of time. This cyclic re-entrainment has consequences. Consistent with the tenets of the Second Law of Thermodynamics, the smallest sizes of easily mobile asbestos fibers move away from their initial source location in an ever-broadening manner. They disperse both by simple spontaneous airborne diffusion and through mass transport of the fibers. This latter is an energy-driven process that can occur through directed air currents or by "pickup and release" along a pathway of directed movement by persons, mechanical equipment or vehicles.

For these reasons, asbestos contamination does not tend to remain localized at its initial release point but will eventually spread throughout all available accessible areas of buildings, even into areas that don't have their own asbestos-containing products. Eventually asbestos from virtually all products that were manufactured from this mineral will invade each and every space within an affected building. This is because during the lifecycle of each asbestos product, microscopic fibers and larger particles or pieces of these products are typically produced during their residency. The lifecycle of an asbestos containing product begins from the initial delivery of the product to the building, followed by its installation, normal usage forces, age-related deterioration, physical or chemical damage that often occurs, to finally its removal either for replacement or demolition. Any small impact or damage to a typical asbestos containing product can easily release billions to trillions of fibers of asbestos into the immediate environment which then add to the pool of similar fibers and particles from other asbestos containing products within that building.

Friability of an asbestos containing product means that it is so soft and weak in structure that it can be broken with simple finger crushing pressure. Friable materials are of the most initial concern due to their ease of damage. But non-friable asbestos containing materials are not necessarily safe. The forces or conditions of usage that come into intimate contact with most non-friable asbestos containing materials are substantially higher than finger pressure. Because of this, non-friable asbestos products can and do release substantial quantities of free asbestos fibers into their environments as well. During normal usage, initially non-friable products slowly change into a quasi-friable condition. Asphalt asbestos floor tiles are typically worn down through a sanding action of the normal floor grit under foot traffic on such floor coverings. Asbestos shingles, siding and roofing materials are eroded through drying, weathering, embrittlement, acid rain leaching and other deteriorative changes to their binder matrix resulting in release of asbestos fibers ("chalk dust") when simple contact is made with their surface or when the wind blows across them. Most government regulations treat such products with much less care than they do when addressing more friable products.

Confusingly, the Modern Greek word άσβεστος means quicklime.

Types of asbestos

• Chrysotile, or white asbestos, CAS No. 12001-29-5, is obtained from 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. There is some evidence that this form of asbestos is not as harmful when inhaled. However it should be noted that there is also evidence that this type of asbestos is harmful, although not perhaps as harmful as other forms (refer to UK Health & Safety Commission report Asbestos: Effects on health of exposure to asbestos, 1985). One formula given for Chrysotile is Mg₃(Si₂O₅)(OH)₄.

• Amosite, CAS No. 12172-73-5, also known as Grunerite or brown asbestos, is an amphibole from Africa, named as an acronym from Asbestos Mines of South Africa. One formula given for Amosite is Fe₇Si₈O₂₂(OH)₂.

• Crocidolite, or blue asbestos, CAS No. 12001-28-4, 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). One formula given for Crocidolite is Na₂Fe²⁺₃Fe³⁺₂Si₈O₂₂(OH)₂.

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. Asbestos with particularly fine fibers is also referred to as "amianthus".

Other asbestos minerals, such as tremolite, CAS No. 77536-68-6, Ca₂Mg₅Si₈O₂₂(OH)₂; actinolite (or smaragdite), CAS No. 77536-66-4, Ca₂(Mg, Fe)₅Si₈O₂₂(OH)₂; and anthophyllite, CAS No. 77536-67-5, (Mg, Fe)₇Si₈O₂₂(OH)₂; 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 vermiculite. In 1989, In the United States, the Environmental Protection Agency (EPA) passed the Asbestos Ban and Phase Out Rule which was subsequently overturned in 1991. This ruling leaves many consumer product that can still legally contain asbestos. For a clarification of products which legally contain asbestos visit the EPA's clarification statement: http://www.epa.gov/asbestos/pubs/asbbans2.pdf

Uses

Historic usage

Items made of asbestos were held in so great an esteem as to be of equal value with gold; none but emperors and kings had napkins made of it. Some antiquaries have believed that ancients made shrouds of asbestos, wherein they burnt the bodies of their kings, in order to entirely preserve their ashes, and prevent their being mixed with those of wood, or other combustible materials commonly used in building funeral piles.^[1]

Others assert that the ancients used asbestos to make perpetual wicks for sepulchral lamps. In more recent centuries, asbestos was indeed used for this purpose. Although asbestos causes skin to itch upon contact, ancient literature indicates that it was prescribed for diseases of the skin, and particularly for the itch. It is possible that they used the term asbestos for alumen plumosum, because the two terms have often been confused throughout history.^[1]

Modern usage

Serpentine group

Chrysotile is the form of asbestos from the serpentine group that has been used commercially.

In the United States, chrysotile has been the most commonly used type of asbestos. Chrysotile is often present in a wide variety of materials, including but not limited to:

• sheetrock taping
• mud and texture coats
• vinyl floor tiles, sheeting, adhesives and ceiling tiles
• plasters and stuccos
• roofing tars, felts, and shingles
• "transite" panels, siding, countertops, and pipes
• acoustical ceilings
• fireproofing
• putty
• caulk
• gaskets
• brake pads and shoes
• clutch plates
• stage curtains
• fire blankets

Amphibole group

Amosite and crocidolite were used in many products until the early 1980s. The use of all types of asbestos in the amphibole group was banned in the mid-1980s. These products were mainly:

• Low density insulation board and ceiling tiles
• asbestos cement sheets and pipes for construction, casing for water and electrical/telecommunication services
• thermal and chemical insulation (i.e., fire rated doors, limpet spray, lagging and gaskets)

Asbestos-related diseases

Diseases caused by asbestos

As early as 1898 the Chief Inspector of Factories of the United Kingdom reported to 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. Many American injuries from asbestos exposure came from shipbuilders working during World War II.[2]

The problem with asbestos arises when the fibers become airborne and are inhaled. Because of the size of the fibers, the lungs cannot expel them. [Casarrett & Doull's Toxicology (2001), pp 520-522]

Diseases caused by asbestos include[3][4]:

• Asbestosis – A lung disease first found in naval shipyard workers, asbestosis is a scarring of the lung tissue from an acid produced by the body's attempt to dissolve the fibers. The scarring may eventually become so severe that the lungs can no longer function. The latency period ( meaning the time it takes for the disease to develop) is often 10-20 years.

• Mesothelioma – A cancer of the mesothelial lining (pleura) of the lung. The only known cause is from asbestos exposure. The latency period for mesothelioma may be 20-50 years. The prognosis for mesothelioma is grim, with most patients dying within 12 months of diagnosis.

• Cancer – Cancer of the lung, gastrointestinal tract, kidney and larynx have been linked to asbestos. The latency period for cancer is often 15-30 years. [5]

In the United States alone, ten thousand people die each year of asbestos-related diseases, such as mesothelioma, asbestosis, lung cancer, and gastrointestinal cancer. Asbestos also 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 generally become malignant or cause other 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.

Litigation

Asbestos litigation is the longest, most expensive mass tort in U.S. history, involving more than 6,000 defendants and 600,000 claimants.[6] Current trends indicate that the rate at which people are diagnosed with the disease will likely increase though the next decade. Analysts have estimated that the total costs of asbestos litigation in the USA alone will eventually reach $200 billion.

While there is no medical dispute about the dangers of inhaled asbestos, the sheer volume of the liability has alarmed the manufacturers and insurance industry. The amounts and method of allocating compensation have been the source of many court cases, and government attempts at resolution of existing and future cases.

Removal of asbestos

Many buildings contain asbestos, which was used in spray-applied flame retardant, thermal system insulation, and in a variety of other materials. Typically, asbestos was "flocked" above false ceilings, inside technical ducts, and in many other small spaces where firefighters would have difficulty gaining access. Structural components like asbestos panels were also used. In residences, it was often a component of a type of flocked acoustic ceiling called "popcorn ceiling", until its production was banned in the U.S. in 1978. However, the ban allowed installers to use up remaining stocks, so houses built as late as 1986 could still have asbestos in their acoustic ceilings. The only way to be sure is to remove a sample and have it tested by a competent laboratory.

Depending on how and where asbestos was applied, it might 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 who have to drill holes in walls for installation of cables or pipes.

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 quite difficult 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. 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 from outside atmosphere so that no accessible air is contaminated. Accordingly, asbestos removal projects 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 duration was 3 years if the tower was emptied of its users, and 10 years if it was not).

An asbestos-containing building that is to be torn down may have to be sealed, and to have its asbestos safely 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. For example, the former seat of parliament of East Germany, the Palast der Republik was stripped of most of its asbestos between 1998 and 2001, before it was finally decided to tear it down starting in 2006. The demolition process alone is expected to cost between 20 and 60 million Euros.

Regarding the automotive industry, asbestos linings were once used in brake pads and shoes. Since the mid-1990s, a majority of brake linings, new or replacement, have been manufactured with kevlar linings (the same material used in bulletproof vests).

Controversy

Asbestos has been banned in 60 countries. There have also been calls for an international ban, to "eliminate the burden of disease and death that is caused worldwide by exposure to asbestos." See The Journal of Occupational and Environmental Medicine [7] As with some other environmental prohibitions like DDT and CFCs, this so-called "movement to ban asbestos" has its critics, like "Junk Science" pundit Tim Milloy and the asbestos industry.[8] These critics claim that asbestos is not harmful, or that the ban does more harm than good [9]. However, the dangers of asbestos have been well documented for a hundred years. There is no medical controversy about this. Asbestos fibers are trapped in the lungs, and can be seen on xrays. The pathology of asbestos disease is well settled. Indeed, the EPA points out that asbestos is the only known cause of mesothelioma, a fatal cancer of the lining of the lung. Exposure to asbestos during mining, construction, or when the material ages and flakes, is a health hazard. In the US alone, 10,000 people die every year from asbestos related diseases. [10] See also Asbestos and the law.

Nonetheless, critics raise arguments such as the following:

• Critics claim the shuttle Challenger exploded because the maker of O-ring putty was pressured by the EPA into ceasing production of asbestos-laden putty, prompting replacement with an inferior putty, which could have caused the O-ring leak and subsequent explosion. However, scientists point out that the putty used in Challenger's final flight did contain asbestos, and failures in the putty were not responsible for the failure of the O-ring that led to loss of the shuttle. Jim Norton.

• Critics claim that substitutes for asbestos are often either inferior, or far more expensive, and create a negative impact on society as a whole. No data has been presented to support this claim, and there is ample data that show the toll it has taken on human lives: hundreds of thousands of people have died from asbestos related disease.

• "Junk Science" pundit Tim Milloy suggests that the World Trade Center towers could still be standing or at least would have stood for longer had asbestos lagging not been removed in the years prior to 2001. Scientists and architects flatly refute this claim. Insulation that replaced asbestos had equivalent fire resistance, and any sort of sprayed-on insulation, including asbestos-based material, would have been removed in large areas by the impact of the planes and subsequent explosion (Jim Norton, Cryptome.org).

Substitutes for asbestos in construction

Many companies that produced products that were reinforced with asbestos fibres have developed products incorporating alternative fibres, such as Eternit. See also a report by the Australian government, Hazardous Substances-Chrysotile Asbestos: Technical Assessment of Alternatives.[11]

See also

• Asbestosis
• Mesothelioma
• Asbestos and the law
• Eternit
• Fireproofing
• List of minerals
• Vermiculite
• Asbestine
• Ambler, PA

References

1. ^{^}  This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al. {{cite encyclopedia}}: Missing or empty |title= (help) [12]

External links

• Asbestos Epa Gov
• About Your House — General Series — Asbestos
• Congressional Research Service (CRS) Reports regarding asbestos
• CBC Digital Archives - Asbestos: Magic mineral or deadly dust?

Mineral links

• Parachrysotile (asbestos) at the webmineral.com Mineral Database
• Univ. of Minn.: Asbestos
• Asbestos Newspaper Articles Archive
• Asbestos in the World

Health

• Asbestos and Occupational Health in the World
• Hazards.org
• Case Studies in Environmental Medicine: Asbestos Toxicity
• Health History Source: Article by the SafetyLine Institute - WorkSafe - Western Australian state government
• British Government Health and Safety Executive (HSE)
• An article on the health impact of asbestos from Liverpool's 'Nerve' magazine
• The Wittenoom Tragedy, Asbestos Diseases Society of Australia.

Cleanup and the environment

• U.S. EPA Asbestos Home Page
• Health and Safety - Asbestosis (TUC Resources, UK)
• White Gold Pioneers: Asbestos Mining — The origins of asbestos mining, illustrated with many early photographs