Asbestos
Asbestos (/æsˈbɛstəs, æz-, -tɒs/ ass-BES-təs, az-, -toss)[1] is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre (particulate with length substantially greater than width)[2] being composed of many microscopic "fibrils" that can be released into the atmosphere by abrasion and other processes. Inhalation of asbestos fibres can lead to various dangerous lung conditions, including mesothelioma, asbestosis, and lung cancer. As a result of these health effects, asbestos is considered a serious health and safety hazard.[3]
For other uses, see Asbestos (disambiguation).Asbestos
09.ED.15
71.01.02d.03
277.11 g
Green, red, yellow, white, gray, blue
Amorphous, granular, massive
Fibrous
2.5.6.0
Silky
White
2.4–3.3
Biaxial
1.53–1.72
0.008
20° to 60°
Relatively weak
Parallel or oblique
Non-fluorescent
400 to 1,040 °C (752 to 1,904 °F)
Archaeological studies have found evidence of asbestos being used as far back as the Stone Age to strengthen ceramic pots,[4] but large-scale mining began at the end of the 19th century when manufacturers and builders began using asbestos for its desirable physical properties. Asbestos is an excellent thermal and electrical insulator, and is highly fire resistant, so for much of the 20th century, it was very commonly used across the world as a building material, until its adverse effects on human health were more widely acknowledged in the 1970s.[5][6] Many buildings constructed before the 1980s contain asbestos.[7]
The use of asbestos for construction and fireproofing has been made illegal in many countries.[3] Despite this, at least 100,000 people are thought to die each year from diseases related to asbestos exposure. In part, this is because many older buildings still contain asbestos; in addition, the consequences of exposure can take decades to arise. The latency period (from exposure to the diagnosis of negative health effects) is typically 20 years.[7][8] The most common diseases associated with chronic asbestos exposure are asbestosis (scarring of the lungs due to asbestos inhalation) and mesothelioma (a type of cancer).[9]
Many developing countries still support the use of asbestos as a building material, and mining of asbestos is ongoing, with the top producer, Russia, having an estimated production of 790,000 tonnes in 2020.[10]
Etymology[edit]
The word "asbestos", first used in the 1600s, ultimately derives from the Ancient Greek: ἄσβεστος, meaning "unquenchable" or "inextinguishable".[11][12][13][14] The name reflects use of the substance for wicks that would never burn up.[11]
It was adopted into English via the Old French abestos, which in turn got the word from Greek via Latin, but in the original Greek, it actually referred to quicklime. It is said by the Oxford English Dictionary to have been wrongly used by Pliny for asbestos, who popularized the misnomer. Asbestos was referred to in Greek as amiantos, meaning "undefiled",[15] because it was not marked when thrown into a fire. This is the source for the word for asbestos in many languages, such as the Portuguese amianto and the French amiante. It had also been called "amiant" in English in the early 15th century, but this usage was superseded by "asbestos".[16] The word is pronounced /æsˈbɛstəs/ or /æsˈbɛstɒs/.[17]
Chrysotile asbestos
Asbestos fibers
Asbestos
Blue asbestos, teased to show the fibrous nature of the mineral
Substitutes for asbestos in construction[edit]
Fiberglass insulation was invented in 1938 and is now the most commonly used type of insulation material. The safety of this material has also been called into question due to similarities in material structure.[157] However, the International Agency for Research on Cancer removed fiberglass from its list of possible human carcinogens in 2001.[158] A scientific review article from 2011 claimed epidemiology data was inconsistent and concluded that the IARC's decision to downgrade the carcinogenic potential of fiberglass was valid, although this study was funded by a sponsored research contract from the North American Insulation Manufacturer's Association.[159]
In 1978, a highly texturized fiberglass fabric was invented by Bal Dixit, called Zetex. This fabric is lighter than asbestos but offers the same bulk, thickness, hand, feel, and abrasion resistance as asbestos. The fiberglass was texturized to eliminate some of the problems that arise with fiberglass, such as poor abrasion resistance and poor seam strength.[160]
In Europe, mineral wool and glass wool are the main insulators in houses.
Many companies that produced asbestos-cement products that were reinforced with asbestos fibers have developed products incorporating organic fibers. One such product was known as "Eternit" and another "Everite" now use "Nutec" fibers which consist of organic fibers, portland cement and silica. Cement-bonded wood fiber is another substitute. Stone fibers are used in gaskets and friction materials.
Another potential fiber is polybenzimidazole or PBI fiber. Polybenzimidazole fiber is a synthetic fiber with a high melting point of 760 °C (1,400 °F) that also does not ignite. Because of its exceptional thermal and chemical stability, it is often used by fire departments and space agencies.