ASBESTOS

images of an asbestos element coating


Asbestos is a term used to refer to six naturally occurring silicate minerals. All are composed of long and thin fibrous crystals, each fiber being composed of many microscopic 'fibrils' that can be released into the atmosphere by abrasion and other processes. Asbestos is a well known health hazard, and use of it as a building material is now banned in many countries. Inhalation of the fibres can lead to various lung conditions, including cancer.
Archaeological studies have found evidence of asbestos being used as far back as the Stone Age to strengthen ceramic pots, 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 use was widespread during the 20th century until public recognition of the health hazards, beginning in the 1970s, of asbestos dust led to its outlawing by courts and legislatures in mainstream construction and fireproofing in most countries. Despite this, at least 100,000 people a year are thought to die from diseases related to asbestos exposure.
Despite the severity of asbestos-related diseases, the material has been used widely all around the world, and most pre-1980s buildings are thought to contain asbestos. Many developing countries also still support the use of asbestos as a building material, and mining of asbestos is ongoing, with the top producer Russia producing around one million metric tonnes in 2015

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 during the following decades, the area became a centre for the nascent industry.

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 11, 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.

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, commonly known as blue asbestos, 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 Na2FeII
3
FeIII
2
Si8O22(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,FeII)5(Si8O22)(OH)2; and anthophyllite asbestos, CAS No. 77536-67-5, (Mg,FeII)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,FeII)5(Si8O22)(OH)2, and winchite, (CaNa)Mg4(Al,FeIII)(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.

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. 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.

Recycling and disposal

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.
In the United States, the EPA governs the removal and disposal of asbestos strictly. Companies that remove asbestos must comply with EPA licensing. These companies are called EPA licensed asbestos contractors. Anytime one of these asbestos contractors performs work a test consultant has to conduct strict testing to ensure the asbestos is completely removed.
Asbestos can be recycled by transforming it into harmless silicate glass. A process of thermal decomposition at 1,000–1,250 °C (1,800–2,300 °F) produces a mixture of non-hazardous silicate phases, and at temperatures above 1,250 °C (2,300 °F) 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.
 


Comments

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