Many of us have heard about this material, but what is asbestos really? Asbestos (pronounced /æs’b?st?s/ or /æz’b?st?s/) is a set of six naturally occurring silicate minerals, which all have in common their eponymous asbestiform habit: long (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.
What is asbestos used for?
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 because of its desirable physical properties: sound absorption, average tensile strength, its resistance to fire, heat, electrical and chemical damage, and affordability. 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 a very widely used material, and its use continued to grow throughout most of the 20th century until the knowledge of carcinogenic effects of asbestos dust caused its effective demise as a mainstream construction and fireproofing material in most countries.
Health issues related to asbestos exposure can be found in records dating back to Roman times. By the beginning of the 20th century concerns were beginning to be raised, which escalated in severity during the 1920s and 1930s. By the 1980s and 1990s asbestos trade and use started to become banned outright, phased out, or heavily restricted in an increasing number of countries.
The severity of asbestos-related diseases, the material’s extremely widespread use in many areas of life, its continuing long-term use after harmful health effects were known or suspected, and fact that asbestos-related diseases can emerge decades after exposure ceases, have resulted in the biggest man-made health disaster in modern time.
Despite being banned in many countries, asbestos is still abundant around the world and can be found in ordinary homes, schools, offices and factories all over the world, sustaining a major global health risk. Also, in many countries, even in the developed nations, the knowledge of asbestos is soon either forgotten or ignored among future generations, who are at high risk of being exposed unknowingly through work activities and home renovations.
This will surely result in a continous plague of deaths for a long time to come. If you know how to protect yourself from asbestos in all situations, you can act wisely and minimize the risk of disease.
What is asbestos: Chemistry
As mentioned, asbestos is a natural mineral in fibrous form. Individual asbestos fibers are invisible to the unaided human eye because their size is about 3–20 µm wide and can be as slim as 0.01 µm. Human hair ranges in size from 17 to 181 µm in breadth. 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, and in this case, there are two cleavage planes which are much weaker than the third. 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.
What is asbestos: Types and associated fibers
Six mineral types are defined by the United States Environmental Protection Agency 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.
All forms of asbestos are fibrillar in that they are composed of fibers with breadths less than 1 micrometer that occur in bundles and have very great widths. Asbestos with particularly fine fibers is also referred to as “amianthus”.
Serpentine class fibers are curly. Chrysotile is the only member of the serpentine class.
Chrysotile, often referred to as white asbestos, is obtained from serpentinite rocks which are common throughout the world. Its 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. Its most common use has been in corrugated asbestos cement roof sheets typically used 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, and gaskets for high temperature equipment.
Amphibole class fibers are needle-like. Amosite, crocidolite, tremolite, anthophyllite and actinolite are members of the amphibole class:
Amosite, 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 an 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, often referred to 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 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.
What is asbestos – Other asbestos minerals
Other regulated asbestos minerals, such as tremolite asbestos, Ca2Mg5Si8O22(OH)2; actinolite asbestos, Ca2(Mg, Fe)5(Si8O22)(OH)2; and anthophyllite asbestos, (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.
What is asbestos – Other natural minerals
Other natural and not regulated asbestiform minerals, such as erionite,(Na2,K2,Ca)2Al4Si14O36·15H2O, richterite, Na(CaNa)(Mg, Fe++)5(Si8O22)(OH)2, and winchite, (CaNa)Mg4(Al, Fe3+)(Si8O22)(OH)2, are thought by some to be no less harmful than tremolite, amosite, or crocidolite. They are referred to as “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 that they be included as regulated materials. Either way, those other minerals should also be treated as very hazardous to human health.