Asbestos

Asbestos (a misapplication of Latin: asbestos "quicklime" from Greek ἄσβεστος: a, "not" and sbestos, "extinguishable") describes any of a group of minerals that can be fibrous, many of which are metamorphic and are hydrous magnesium silicates.

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 asbestos fibers, however, can cause a number of serious illnesses, including cancer. Since the mid 1980s, many uses of asbestos are banned in multiple countries.


"White" asbestos
Chrysotile, CAS No. 12001-29-5, is obtained from serpentine rocks. Chrysotile, along with other types of asbestos, have been banned in dozens of countries and is only allowed in the United States and Europe in very limited circumstances. Applications where Chrysotile might be used include the use of joint compound. There is no safe level of exposure to crysotile that is recognized. It is more flexible than amphibole types of asbestos; it can be spun and woven into fabric. Chrysotile does not persist in the lungs after inhalation; but is transferred to the pleura (the lining of the lungs) where mesothelioma, a fatal asbestos related cancer develops. Over 90% of the asbestos used in the United States is Chrysotile asbestos, making it one of the major causes of asbestos-related diseases in the U.S.
"Brown" asbestos
Amosite, CAS No. 12172-73-5, is a trade name for the amphiboles belonging to the Cummingtonite - Grunerite solid solution series, commonly from Africa, named as an acronym from Asbestos Mines of South Africa. One formula given for Amosite is Fe7Si8O22(OH)2. This type of asbestos, like all asbestos, is very hazardous.
"Blue" asbestos
Riebeckite, CAS No. 12001-28-4, also known under the variety name of Crocidolite, is an amphibole from Africa and Australia. It is the fibrous form of the amphibole 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. This type of asbestos is very hazardous.
Notes: chrysotile commonly occurs as soft friable fibers. Asbestiform amphibole may also occur as soft friable fibers but some varieties such as amosite are commonly straighter. All forms of asbestos are fibrillar in that they are composed of fibers with widths less than 1 micrometer that occur in bundles and have very long lengths. Asbestos with particularly fine fibers is also referred to as "amianthus". Amphiboles such as tremolite have a sheetlike crystalline structure. Serpentine (chrysotile) has a stringlike crystalline structure.(Inorganic Chemistry, E. de Barry Barnett and C. L. Wilson). Crysotile asbestos is often contaminated with tremolite, creating an additional hazard.

Other asbestos
Other regulated asbestos minerals, such as tremolite asbestos, CAS No. 77536-68-6, Ca2Mg5Si8O22(OH)2; actinolite asbestos (or smaragdite), CAS No. 77536-66-4, Ca2(Mg, Fe)5Si8O22(OH)2; and anthophyllite asbestos, CAS No. 77536-67-5, (Mg, Fe)7Si8O22(OH)2; are less commonly used industrially but can still be found in a variety of construction materials and insulation materials and have been reported in the past to occur in a few consumer products.
Other natural and not currently regulated asbestiform minerals, such as richterite, Na(CaNa)(Mg,Fe++)5[Si8O22](OH)2, and winchite, [ ](CaNa)Mg4(Al,Fe3+)Si8O22(OH)2, may be found as a contaminate in products such as the vermiculite containing Zonolite insulation manufactured by W.R. Grace and Company. These minerals are thought to be no less harmful than tremolite, amosite, or crocidolite, but since they are not regulated, they are referred to as "asbestiform" rather than asbestos although may still be reltated to diseases and hazardous.

In 1989 the United States Environmental Protection Agency (EPA) passed the Asbestos Ban and Phase Out Rule which was subsequently overturned in the case of Corrosion Proof Fittings v. U.S. Environmental Protection Agency, 1991. This ruling leaves many consumer products that can still legally contain trace amounts of asbestos. For a clarification of products which legally contain asbestos visit the EPA's clarification statement.[1]


[edit] Production trends

Asbestos output in 2005In 2005, Russia was the largest producer of asbestos with about 40% world share followed by China and Kazakhstan, reports the British Geological Survey.


[edit] Uses

[edit] 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. Supposedly, Charlemagne had a tablecloth made of asbestos. Cleaning an asbestos cloth was simple–it was simply thrown into a fire. Some archeologists have believed that ancients made shrouds of asbestos, wherein they burned the bodies of their kings, in order to preserve only their ashes, and prevent their being mixed with those of wood or other combustible materials commonly used in funeral pyres.[2]

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.[2]

Asbestos fibers were once used in automobile brake pads and shoes. Since the mid-1990s, a majority of brake pads, new or replacement, have been manufactured instead with Aramid fiber (Twaron or Kevlar) linings (the same material used in bulletproof vests).


Kent, the first filtered cigarette on the market, used crocidolite asbestos in its "Micronite" filter from 1952 to 1956.[3]


[edit] Modern usage

[edit] Serpentine group
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 :

joint compound
mud and texture coats
vinyl floor tiles, sheeting, adhesives
roofing tars, felts, siding, and shingles
"transite" panels, siding, countertops, and pipes
fireproofing
caulk
gaskets
brake pads and shoes
clutch plates
stage curtains
fire blankets
interior fire doors
fireproof clothing for firefighters
thermal pipe insulation
In the European Union and Australia it has recently been banned as a potential health hazard[4] and is not used at all.


[edit] Amphibole group
Amosite and crocidolite were formally 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)

[edit] Etiology

Asbestos Warning Sign at Bauer Elementary Miamisburg, Ohio June 2007Health concern associated with asbestos began in the 1970s soon after Dr. Irving Selikoff, of Mt. Sinai School of Medicine, found that some workers, occupationally exposed to certain amphibole (non-serpentine) type asbestos fibers, were at increased risk of lung disease. While Dr. Selikoff's work played a key role in removing amphibole asbestos from industry, the resulting media-driven hysteria and the EPA failed to differentiate between amphibole and chrysotile (serpentine) fibers used for asbestos. Without exception, every human study in the United States showing asbestos etiology is associated with amphibole fiber asbestos, and there is not a single study showing chrysotile etiology.[citation needed]





[edit] Asbestos as a contaminant
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 in width.[5] 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. 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 and one larger asbestos fiber can ultimately become the source of hundreds of much thinner and smaller fibers.

As asbestos fibers get smaller and lighter, the more easily they become airborne and human respiratory exposures can result. Fibers will eventually settle but may be re-suspended by air currents or other movement.

Friability of a product containing asbestos 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. The forces or conditions of usage that come into intimate contact with most non-friable materials containing asbestos are substantially higher than finger pressure.


[edit] Asbestos in the environment
Low levels of asbestos are in the air we breathe and some of the water we drink, including water from natural sources.[6] Studies have shown that members of the general (nonoccupationally exposed) population have tens of thousands to hundreds of thousands of asbestos fibers in each gram of dry lung tissue, which translates into millions of fibers and tens of thousands of asbestos bodies in every person's lungs.[7]

The EPA has proposed a concentration limit of 7 million fibers per liter of drinking water for long fibers (lengths greater than or equal to 5 µm). OSHA (Occupational Safety and Health Administration) has set limits of 100,000 fibers with lengths greater than or equal to 5 µm per cubic meter of workplace air for 8-hour shifts and 40-hour work weeks.[8]

EWG Action Fund estimates that in the United States, about 10,000 people die each year of asbestos-related diseases, such as mesothelioma, asbestosis, lung cancer, and gastrointestinal cancer.[9]


[edit] Abundant Asbestos Construction in Developing Countries
Countries like India, China have continued widespread use of asbestos. The most common is corrugated Asbestos-Cement Sheets or A/C Sheets for roofing and for side walls. Millions of homes, factories, schools or sheds and shelters continue to use asbestos without a second thought on hazards. Eternit Everest, Hyderabad Industries and RamCo are some of the major asbestos products manufacturers in India.

Cutting these sheets to size and drilling for holes to receive 'J' bolts to help secure the sheets to roof framing is done on site. Precaution or protection against asbestos health hazards during such work or while demolition or storage is unheard of.

Asbestos-Cement sheets seems to remain cheap and easy roofing along with Galvanized Iron sheet roofing, Terracota or burnt clay tile roofing. There has been no significant change in production and use of A/C Sheets in developing countries following the widespread restrictions in Developed Nations.


[edit] Other asbestos-related diseases
asbestos warts – caused when the sharp fibers 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 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.

[edit] Litigation
Main article: Asbestos and the law
Asbestos litigation is the longest, most expensive mass tort in U.S. history, involving more than 6,000 defendants and 600,000 claimants.[10] Current trends indicate that the rate at which people are diagnosed with the disease will likely increase through the next decade. Analysts have estimated that the total costs of asbestos litigation in the USA alone is over $250 billion[11]. Due to the prevalence of asbestos, it is normally part of the scope of a Phase I Environmental Site Assessment to inspect for potential asbestos in a building which is being sold.

The volume of the asbestos 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.