Asbestos is a set of six naturally occurring silicate minerals, which all have in common their eponymous asbestiform habit: i.e. long crystals (roughly 1:20 aspect ratio), thin fibrous crystals, with each visible fiber composed of millions of microscopic "fibrils" that can be released by abrasion and other processes. They are commonly known by their colors, as blue asbestos, brown asbestos, white asbestos, and green asbestos.
Asbestos mining existed more than 4,000 years ago, but large-scale mining began at the end of the 19th century, when manufacturers and builders began using asbestos for its desirable physical properties. Some of those properties are sound absorption, average tensile strength, affordability, and resistance to fire, heat, and electricity. It was used in such applications as electrical insulation for hotplate wiring and in building insulation. When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement or woven into fabric or mats. These desirable properties made asbestos very widely used. Asbestos use continued to grow through most of the 20th century until public knowledge (acting through courts and legislatures) of the health hazards of asbestos dust outlawed asbestos in mainstream construction and fireproofing in most countries.
Prolonged inhalation of asbestos fibers can cause serious and fatal illnesses including lung cancer, mesothelioma, and asbestosis (a type of pneumoconiosis). Concern of asbestos-related illness in modern times began in the 20th century and escalated during the 1920s and 1930s. By the 1980s and 1990s, asbestos trade and use were heavily restricted, phased out, or banned outright in an increasing number of countries.
Despite the severity of asbestos-related diseases, the material has extremely widespread use in many areas. Asbestos' continuing long-term use after harmful health effects were known or suspected, and the slow emergence of symptoms decades after exposure ceased, made asbestos litigation the longest, most expensive mass tort in U.S. history and a much lesser legal issue in most other countries involved. Asbestos-related liability also remains an ongoing concern for many manufacturers, insurers and reinsurers.
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Etymology
Asbestos derives from the ancient Greek ????????, meaning unquenchable or inextinguishable. The word is pronounced , or .
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Types and associated fibers
Six mineral types are defined by the United States Environmental Protection Agency (EPA) as "asbestos" including those belonging to the serpentine class and those belonging to the amphibole class. All six asbestos mineral types are known to be human carcinogens. The visible fibers are themselves each composed of millions of microscopic "fibrils" that can be released by abrasion and other processes.
Serpentine
Serpentine class fibers are curly. Chrysotile is the only member of the serpentine class.
Chrysotile
Chrysotile, CAS No. 12001-29-5, is obtained from serpentinite rocks which are common throughout the world. Its idealized chemical formula is Mg3(Si2O5)(OH)4. Chrysotile appears under the microscope as a white fiber.
Chrysotile has been used more than any other type and accounts for about 95% of the asbestos found in buildings in America. Chrysotile is more flexible than amphibole types of asbestos, and can be spun and woven into fabric. The most common use was corrugated asbestos cement roofing primarily for outbuildings, warehouses and garages. It may also be found in sheets or panels used for ceilings and sometimes for walls and floors. Chrysotile has been a component in joint compound and some plasters. Numerous other items have been made containing chrysotile including brake linings, fire barriers in fuseboxes, pipe insulation, floor tiles, residential shingles, and gaskets for high temperature equipment.
Amphibole
Amphibole class fibers are needle-like. Amosite, crocidolite, tremolite, anthophyllite and actinolite are members of the amphibole class.
Amosite
Amosite, CAS No. 12172-73-5, often referred to as brown asbestos, is a trade name for the amphiboles belonging to the cummingtonite-grunerite solid solution series, commonly from South Africa, named as a partial acronym for "Asbestos Mines of South Africa". One formula given for amosite is Fe7Si8O22(OH)2. Amosite is seen under a microscope as a grey-white vitreous fiber. It is found most frequently as a fire retardant in thermal insulation products, asbestos insulating board and ceiling tiles.
Crocidolite
Crocidolite, CAS No. 12001-28-4, is the fibrous form of the amphibole riebeckite, found primarily in southern Africa, but also in Australia and Bolivia. One formula given for crocidolite is Na2Fe2+3Fe3+2Si8O22(OH)2. Crocidolite is seen under a microscope as a blue fiber.
Crocidolite 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 breadths less than 1 micrometer in bundles of very great widths. Asbestos with particularly fine fibers is also referred to as "amianthus".
Other materials
Other regulated asbestos minerals, such as tremolite asbestos, CAS No. 77536-68-6, Ca2Mg5Si8O22(OH)2; actinolite asbestos, CAS No. 77536-66-4, Ca2(Mg, Fe)5(Si8O22)(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 used in a few consumer products.
Other natural asbestiform minerals, such as richterite, Na(CaNa)(Mg, Fe++)5(Si8O22)(OH)2, and winchite, (CaNa)Mg4(Al, Fe3+)(Si8O22)(OH)2, though not regulated, are said by some to be no less harmful than tremolite, amosite, or crocidolite. They are termed "asbestiform" rather than asbestos. Although the U.S. Occupational Safety and Health Administration (OSHA) has not included them in the asbestos standard, NIOSH and the American Thoracic Society have recommended them for inclusion as regulated materials because they may also be hazardous to health.
Production
In late 2011, Canada's remaining two asbestos mines, both located in the Province of Quebec, halted operations. In September 2012, the government in the Province of Quebec halted asbestos mining. In 2009, about 9% of world's asbestos production was mined in Canada.
In 2015, 2 million tonnes of asbestos were mined worldwide. The Russian Federation was the largest producer with about 55% world share followed by China (20%), Brazil (15.6%), and Kazakhstan (10.8%).
History of use
Early uses
Asbestos use dates back at least 4,500 years, when the inhabitants of the Lake Juojärvi region in East Finland strengthened earthenware pots and cooking utensils with the asbestos mineral anthophyllite (see Asbestos-ceramic). One of the first descriptions of a material that may have been asbestos is in Theophrastus, On Stones, from around 300 BC, although this identification has been questioned. In both modern and ancient Greek, the usual name for the material known in English as "asbestos" is amiantos ("undefiled", "pure"), which was adapted into the French amiante and Portuguese amianto. In modern Greek, the word ???????? or ???????? stands consistently and solely for lime.
The term asbestos is traceable to Roman naturalist Pliny the Elder's manuscript Natural History, and his use of the term asbestinon, meaning "unquenchable". While Pliny or his nephew Pliny the Younger is popularly credited with recognising the detrimental effects of asbestos on human beings, examination of the primary sources reveals no support for either claim.
Wealthy Persians amazed guests by cleaning a cloth by exposing it to fire. For example, according to Tabari, one of the curious items belonging to Khosrow II Parviz, the great Sassanian king (r. 531-579), was a napkin (Persian: ???????) that he cleaned simply by throwing it into fire. Such cloth is believed to have been made of asbestos imported over the Hindu Kush. According to Biruni in his book, Gems, any cloths made of asbestos (Persian: ????????, ?zarshost) were called shostakeh (Persian: ???????). Some Persians believed the fiber was the fur of an animal, called the samandar (Persian: ???????), which lived in fire and died when exposed to water, which was where the former belief that the salamander could tolerate fire originated.
Charlemagne, the first Holy Roman Emperor (800-814), is said to have had a tablecloth made of asbestos.
Marco Polo recounts having been shown, in a place he calls Ghinghin talas, "a good vein from which the cloth which we call of salamander, which cannot be burnt if it is thrown into the fire, is made ..."
Some archaeologists believe that ancients made shrouds of asbestos, wherein they burned the bodies of their kings, in order to preserve only their ashes, and prevent them being mixed with those of wood or other combustible materials commonly used in funeral pyres. Others assert that the ancients used asbestos to make perpetual wicks for sepulchral or other lamps. A famous example is the golden lamp asbestos lychnis, which the sculptor Callimachus made for the Erechtheion. 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 soapstone, because the two terms have often been confused throughout history.
Industrial era
The large scale asbestos industry began in the mid-19th century. Early attempts at producing asbestos paper and cloth in Italy began in the 1850s, but were unsuccessful in creating a market for such products. Canadian samples of asbestos were displayed in London in 1862, and the first companies were formed in England and Scotland to exploit this resource. Asbestos was first used in the manufacture of yarn, and German industrialist Louis Wertheim adopted this process in his factories in Germany. In 1871, the Patent Asbestos Manufacturing Company was established in Glasgow, and within the following decades, the Clydebank area became a centre for the nascent industry.
Industrial scale mining began in the Thetford hills, Quebec from the 1870s. Sir William Edmond Logan was the first to notice the large deposits of chrysotile in the hills in his capacity as head of Geological Survey of Canada. Samples of the minerals from here were displayed in London, and excited much interest. With the opening up of the Quebec Central Railway in 1876, mining entrepreneurs, such as Andrew Stuart Johnson established the asbestos industry in the province. The 50 ton output of the mines in 1878 rose to over 10,000 tons in the 1890s with the adoption of machine technologies and expanded production. For a long time, the world's largest asbestos mine was the Jeffrey mine in the town of Asbestos, Quebec.
Asbestos production began in the Urals of the Russian Empire in the 1880s, and in the Alpine regions of Northern Italy with the formation in Turin of the Italo-English Pure Asbestos Company in 1876, although this was soon swamped by the greater production levels from the Canadian mines. Mining also took off in South Africa from 1893 under the aegis of the British businessman Francis Oates, the Director of the De Beers company. It was in South Africa that the production of amosite began in 1910. The U.S. asbestos industry had an early start in 1858, when fibrous anthophyllite was mined for use as asbestos insulation by the Johns Company, a predecessor to the current Johns Manville, at a quarry at Ward's Hill on Staten Island, New York. US production began in earnest in 1899, with the discovery of large deposits in the Belvidere Mountain.
The use of asbestos became increasingly widespread towards the end of the 19th century, when its diverse applications included fire retardant coatings, concrete, bricks, pipes and fireplace cement, heat, fire, and acid resistant gaskets, pipe insulation, ceiling insulation, fireproof drywall, flooring, roofing, lawn furniture, and drywall joint compound. In 2011 it was reported that over 50% of UK houses still contained asbestos, despite a ban on asbestos products some years earlier.
In Japan, particularly after World War II, asbestos was used in the manufacture of ammonium sulfate for purposes of rice production, sprayed upon the ceilings, iron skeletons, and walls of railroad cars and buildings (during the 1960s), and used for energy efficiency reasons as well. Production of asbestos in Japan peaked in 1974 and went through ups and downs until about 1990, when production began to drop dramatically.
Discovery of toxicity
In 1899, Dr. Montague Murray noted the negative health effects of asbestos. The first documented death related to asbestos was in 1906.
In the early 1900s researchers began to notice a large number of early deaths and lung problems in asbestos-mining towns. The first such study was conducted by Dr. H. Montague Murray at the Charing Cross Hospital, London, in 1900, in which a postmortem investigation of a young man who had died from pulmonary fibrosis after having worked for 14 years in an asbestos textile factory, discovered asbestos traces in the victim's lungs. Adelaide Anderson, the Inspector of Factories in Britain, included asbestos in a list of harmful industrial substances in 1902. Similar investigations were conducted in France and Italy, in 1906 and 1908, respectively.
The first diagnosis of asbestosis was made in the UK in 1924. Nellie Kershaw was employed at Turner Brothers Asbestos in Manchester, England from 1917, spinning raw asbestos fibre into yarn. Her death in 1924 led to a formal inquest. Pathologist Dr William Edmund Cooke testified that his examination of the lungs indicated old scarring indicative of a previous, healed, tuberculosis infection, and extensive fibrosis, in which were visible "particles of mineral matter ... of various shapes, but the large majority have sharp angles." Having compared these particles with samples of asbestos dust provided by Dr S.A. Henry, His Majesty's Medical Inspector of Factories, Cooke concluded that they "originated from asbestos and were, beyond a reasonable doubt, the primary cause of the fibrosis of the lungs and therefore of death".
As a result of Cooke's paper, parliament commissioned an inquiry into the effects of asbestos dust by Dr E. R. A. Merewether, Medical Inspector of Factories, and C. W. Price, a factory inspector and pioneer of dust monitoring and control. Their subsequent report, Occurrence of Pulmonary Fibrosis & Other Pulmonary Affections in Asbestos Workers, was presented to parliament on 24 March 1930. It concluded that the development of asbestosis was irrefutably linked to the prolonged inhalation of asbestos dust, and included the first health study of asbestos workers, which found that 66% of those employed for 20 years or more suffered from asbestosis. The report led to the publication of the first Asbestos Industry Regulations in 1931, which came into effect on 1 March 1932. These regulated ventilation and made asbestosis an excusable work-related disease. The term mesothelioma was first used in medical literature in 1931; its association with asbestos was first noted sometime in the 1940s. Similar legislation followed in the U.S. about ten years later.
Approximately 100,000 people in the United States have died, or are terminally ill, from asbestos exposure related to ship building. In the Hampton Roads area, a shipbuilding center, mesothelioma occurrence is seven times the national rate. Thousands of tons of asbestos were used in World War II ships to insulate piping, boilers, steam engines, and steam turbines. There were approximately 4.3 million shipyard workers in the United States during WWII; for every 1,000 workers about 14 died of mesothelioma and an unknown number died from asbestosis.
The United States government and asbestos industry have been criticized for not acting quickly enough to inform the public of dangers, and to reduce public exposure. In the late 1970s, court documents proved that asbestos industry officials knew of asbestos dangers since the 1930s and had concealed them from the public.
In Australia, asbestos was widely used in construction and other industries between 1946 and 1980. From the 1970s there was increasing concern about the dangers of asbestos, and its use was phased out. Mining ceased in 1983. The use of asbestos was phased out in 1989 and banned entirely in December 2003. The dangers of asbestos are now well known in Australia and there is help and support for sufferers from asbestosis or mesothelioma.
Usage by industry and product type
Serpentine group
Serpentine minerals have a sheet or layered structure. Chrysotile is the only asbestos mineral in the serpentine group. In the United States, chrysotile has been the most commonly used type of asbestos. According to the U.S. EPA Asbestos Building Inspectors Manual, chrysotile accounts for approximately 95% of asbestos found in buildings in the United States. Chrysotile is often present in a wide variety of products and materials, including:
- Chlor Alkali diaphragm membranes used to make chlorine (currently in the USA)
- Drywall and joint compound
- Plaster
- Gas mask filters pre-1960s
- Mud and texture coats
- Vinyl floor tiles, sheeting, adhesives
- Roofing tars, felts, siding, and shingles
- "Transite" panels, siding, countertops, and pipes
- Popcorn ceilings, also known as acoustic ceilings
- Fireproofing
- Caulk
- Industrial and marine gaskets
- Brake pads and shoes
- Stage curtains
- Fire blankets
- Interior fire doors
- Fireproof clothing for firefighters
- Thermal pipe insulation
- Filters for removing fine particulates from chemicals, liquids and wine
- Dental cast linings
- HVAC flexible duct connectors
- Drilling fluid additives
In the European Union and Australia it has recently been banned as a potential health hazard and is not used at all. Japan is moving in the same direction, but at a slower pace.
Amphibole group
Amphiboles including amosite (brown asbestos) and crocidolite (blue asbestos) were formerly used in many products until the early 1980s. Tremolite asbestos constituted a contaminant of many if not all naturally occurring chrysotile deposits. The use of all types of asbestos in the amphibole group was banned in much of the Western world by the mid-1980s, and in Japan by 1995. Some products that included amphibole types of asbestos included the following:
- Low density insulating board (often referred to as AIB or asbestos insulating board) and ceiling tiles;
- Asbestos-cement pipe (made until the early 1990s by at least one manufacturer);
- Asbestos-cement sheets and pipes for construction, casing for water and electrical/telecommunication services;
- Thermal and chemical insulation (e.g., fire rated doors, limpet spray, lagging and gaskets).
Cigarette manufacturer Lorillard (Kent's filtered cigarette) used crocidolite asbestos in its "Micronite" filter from 1952 to 1956.
While mostly chrysotile asbestos fibers were once used in automobile brake pads, shoes, and clutch discs, contaminants of amphiboles were present. Since approximately the mid-1990s, brake pads, new or replacement, have been manufactured instead with linings made of ceramic, carbon, metallic and aramid fiber (Twaron or Kevlar--the same material used in bulletproof vests).
Artificial Christmas snow, known as flocking, was previously made with asbestos. It was used as an effect in films including The Wizard of Oz and department store window displays and it was marketed for use in private homes under brand names that included "Pure White", "Snow Drift" and "White Magic".
Construction
Developed countries
The use of asbestos in new construction projects has been banned for health and safety reasons in many developed countries or regions, including the European Union, Australia, Hong Kong, Japan, and New Zealand. A notable exception is the United States, where asbestos continues to be used in construction such as cement asbestos pipes. The 5th Circuit Court prevented the EPA from banning asbestos in 1991 because EPA research showed the ban would cost between $450 and 800 million while only saving around 200 lives in a 13-year timeframe, and that the EPA did not provide adequate evidence for the safety of alternative products. Until the mid-1980s, small amounts of white asbestos were used in the manufacture of Artex, a decorative stipple finish, however, some of the lesser-known suppliers of Artex were still adding white asbestos until 1999.
Prior to the ban, asbestos was widely used in the construction industry in thousands of materials. Some are judged to be more dangerous than others due to the amount of asbestos and the material's friable nature. Sprayed coatings, pipe insulation and Asbestos Insulating Board (AIB) are thought to be the most dangerous due to their high content of asbestos and friable nature. Many older buildings built before the late 1990s contain asbestos. In the United States, there is a minimum standard for asbestos surveys as described by ASTM Standard E 2356-04. The U.S. Environmental Protection Agency includes some but not all asbestos-contaminated facilities on the Superfund National Priorities list (NPL). Renovation and demolition of asbestos contaminated buildings is subject to EPA NESHAP and OSHA Regulations. Asbestos is not a material covered under CERCLA's innocent purchaser defense. In the UK, the removal and disposal of asbestos and of substances containing it are covered by the Control of Asbestos Regulations 2006.
U.S. asbestos consumption hit a peak of 804,000 tons in 1973; world asbestos demand peaked around 1977, with 25 countries producing nearly 4.8 million metric tons annually.
In older buildings (e.g. those built prior to 1999 in the UK, before white asbestos was banned), asbestos may still be present in some areas. Being aware of asbestos locations reduces the risk of disturbing asbestos.
Removal of asbestos building components can also remove the fire protection they provide, therefore fire protection substitutes are required for proper fire protection that the asbestos originally provided.
Outside Europe and North America
Some countries, such as India, Indonesia, China, Russia and Brazil, 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. Cutting these sheets to size and drilling holes to receive 'J' bolts to help secure the sheets to roof framing is done on-site. There has been no significant change in production and use of A/C sheets in developing countries following the widespread restrictions in developed nations.
11 September 2001 attacks
As New York City's World Trade Center collapsed following the September 11 attacks, Lower Manhattan was blanketed in a mixture of building debris and combustible materials. This complex mixture gave rise to the concern that thousands of residents and workers in the area would be exposed to known hazards in the air and in the dust, such as asbestos, lead, glass fibers, and pulverized concrete. More than 1,000 tons of asbestos are thought to have been released into the air following the buildings' destruction. Inhalation of a mixture of asbestos and other toxicants is thought to be linked to the unusually high death rate from cancer of emergency service workers since the disaster. Thousands more are now thought to be at risk of developing cancer due to this exposure with those who have died so far being only the 'tip of the iceberg'. Some commentators have criticised authorities for using asbestos in the buildings' construction.
In May 2002, after numerous cleanup, dust collection, and air monitoring activities were conducted outdoors by EPA, other federal agencies, New York City and the state of New York, New York City formally requested federal assistance to clean and/or test residences in the vicinity of the World Trade Center site for airborne asbestos.
Asbestos contaminants in other products
Vermiculite
Vermiculite is a hydrated laminar magnesium-aluminum-iron silicate which resembles mica. It can be used for many industrial applications and has been used as insulation. Some deposits of vermiculite have been found to be contaminated with small amounts of asbestos.
One vermiculite mine operated by W. R. Grace and Company in Libby, Montana exposed workers and community residents to danger by mining vermiculite contaminated with asbestos, typically richterite, winchite, actinolite or tremolite. Vermiculite contaminated with asbestos from the Libby mine was used as insulation in residential and commercial buildings through Canada and the United States. W. R. Grace and Company's loose-fill vermiculite was marketed as Zonolite but was also used in sprayed-on products such as Monokote.
In 1999 the EPA began cleanup efforts in Libby and now the area is a Superfund cleanup area. The EPA has determined that harmful asbestos is released from the mine as well as through other activities that disturb soil in the area.
Talc
Talc can sometimes be contaminated with asbestos due to the proximity of asbestos ore (usually tremolite) in underground talc deposits. By 1973, US federal law required all talc products to be asbestos-free, and today there is strict quality control in the production of talc products, separating cosmetic-grade talc (e.g. talcum powder) from industrial-grade talc (often used in friction products) has largely eliminated this issue for consumers.
In 2000, tests in a certified asbestos-testing laboratory found the tremolite form of amphibole asbestos in three out of eight bigger brands of children's crayons that are made partly from talc: Crayola, Prang, and RoseArt. In Crayola crayons, the tests found asbestos levels from 0.05% in Carnation Pink to 2.86% in Orchid; in Prang crayons, the range was from 0.3% in Periwinkle to 0.54% in Yellow; in Rose Art crayons, it was from 0.03% in Brown to 1.20% in Orange. Overall, 32 different types of crayons from these brands contained more than trace amounts of asbestos, and eight others contained trace amounts. The Art and Creative Materials Institute, a trade association which tests the safety of crayons on behalf of the makers, initially insisted the test results must be incorrect, although they later said they do not test for asbestos. In May 2000, Crayola said tests by Richard Lee, a materials analyst whose testimony on behalf of the asbestos industry has been accepted in lawsuits over 250 times, found two of its crayons tested negative for asbestos. In June 2000, Binney & Smith, the maker of Crayola, and the other makers agreed to stop using talc in their products, and changed their product formulations in the United States.
The mining company, R T Vanderbilt Co of Gouverneur, New York, which supplied the talc to the crayon makers, states that "to the best of our knowledge and belief" there is no asbestos in its talc. However media reports claim that the United States Mine Safety and Health Administration (MSHA) had found asbestos in four talc samples tested in 2000. The Assistant Secretary for Mine Safety and Health subsequently wrote to the news reporter, stating that "In fact, the abbreviation ND (non detect) in the laboratory report - indicates no asbestos fibers actually were found in the samples", and multiple studies by both mineral studies laboratories and biological cell studies do not report asbestos. These findings have been rejected by other health reports and studies which advocate a "same as" asbestos risk.
Health impact
All types of asbestos fibers are known to cause serious health hazards in humans. Amosite and crocidolite are considered the most hazardous asbestos fiber types; however, chrysotile asbestos has also produced tumors in animals and is a recognized cause of asbestosis and malignant mesothelioma in humans, and mesothelioma has been observed in people who were occupationally exposed to chrysotile, family members of the occupationally exposed, and residents who lived close to asbestos factories and mines.
During the 1980s and again in the 1990s it was suggested at times that the process of making asbestos cement could "neutralize" the asbestos, either via chemical processes or by causing cement to attach to the fibers and changing their physical size; subsequent studies showed that this was untrue, and that decades-old asbestos cement, when broken, releases asbestos fibers identical to those found in nature, with no detectable alteration.
Exposure to asbestos in the form of fibers is always considered dangerous. Working with, or exposure to, material that is friable, or materials or works that could cause release of loose asbestos fibers, is considered high risk. However, in general, people who become ill from inhaling asbestos have been regularly exposed in a job where they worked directly with the material.
The most common diseases associated with chronic exposure to asbestos are asbestosis and mesothelioma.
Substitutes for asbestos in construction
Fiberglass insulation was invented in 1938 and is now the most commonly used type of insulation material. The safety of this material is also being called into question due to similarities in material structure. However, the International Agency for Research on Cancer removed fiberglass from its list of possible human carcinogens in 2001 and 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 (however, this study was funded by sponsored research contract from the North American Insulation Manufacturer's Association).
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.
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 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.
Recycling and disposal
Asbestos alternatives for industrial use include sleeves, rope, tape, fabric, textiles and insulation batt materials made from fiberglass and silica.
In most developed countries, asbestos is typically disposed of as hazardous waste in landfill sites.
The demolition of buildings containing large amounts of asbestos based materials pose particular problems for builders and property developers - such buildings often have to be deconstructed piece by piece, or the asbestos has to be painstakingly removed before the structure can be razed by mechanical or explosive means. One such example is the Red Road Flats in Glasgow, Scotland which used huge amounts of asbestos cement board for wall panelling - here British health and safety regulations stipulate that asbestos material has to be removed to a landfill site via an approved route at certain times of the day in specially adapted vehicles.
Asbestos can be recycled by transforming it into harmless silicate glass. A process of thermal decomposition at 1000-1250 °C produces a mixture of non-hazardous silicate phases, and at temperatures above 1250 °C it produces silicate glass. Microwave thermal treatment can be used in an industrial manufacturing process to transform asbestos and asbestos-containing waste into porcelain stoneware tiles, porous single-fired wall tiles, and ceramic bricks.
The combination of oxalic acid with ultrasound fully degrades chrysotile asbestos fibers.
Source of the article : Wikipedia
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