Asbestos (Greek ?sίest??: a-, "not"; sbestos, "extinguishable") is a group of fibrous metamorphic minerals. 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. It was used in fabrics such as Egyptian burial cloths and Charlemagnes tablecloth, which, according to legend, he threw in a fire to clean.
When asbestos is used for its resistance to fire or heat, the fibers are typically mixed with cement or woven into fabric or mats. It was used in brake shoes and gaskets for its heat resistance, on electric oven and hotplate wiring for its electrical insulation at elevated temperature, and in buildings for its flame-retardant and insulating properties, its tensile strength, flexibility, and resistance to chemicals. However, the inhalation of some kinds of asbestos fibers is now thought to cause various illnesses, including cancer, and thus most uses of asbestos are banned in many countries. Fiberglass has been found to be a suitable substitute for thermal insulation and woven ceramicG fiber performs as well or better as an insulator of high-temperature electrical conductors.
Most respirable asbestos fibers are invisible to the unaided human eye because their size is about 3.0-20.0 ΅m in length and can be as thin as 0.01 ΅m. Human hair ranges in size from 17 to 181 ΅m. Fibers ultimately form because when these minerals originally cooled and crystallized, they formed by the polymeric molecules lining up parallel with each other andforming oriented crystal lattices. These crystals thus have three cleavage planes as other minerals and gemstones have. But in their case, there are two cleavage planes that are much weaker than the third direction. Thus 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 over and over until they have been broken down to their smallest unit dimensions. For this reason, one larger asbestos fiber can ultimately become the source of hundreds of much thinner and smaller fibers in a normal environment over the course of time. As they get smaller and lighter, they become more mobile and more easily entrained (wafted) into the air, where human respiratory exposures typically result.
Types of Asbestos
- Chrysotile, or white asbestos, is obtained from Canadian serpentine rocks. It is less friable (and therefore less likely to be inhaled) than the other types and is the type most often used industrially.
- Chrysotile should not be confused with chrysolite, a synonym of olivine. There is some evidence that this form of asbestos is not actually harmful when inhaled. However it should be noted that there is also evidence that this type of asbestos is harmful, although not perhaps as harmful as other forms.
- Amosite, or brown asbestos, is an amphibole from Africa, from the initials Asbestos Mines of South Africa.
- Crocidolite, or blue asbestos, is an amphibole from Africa and Australia. It is the fibrous form of riebeckite. Blue asbestos is commonly thought of as the most dangerous type of asbestos.
- Serpentine rocks are those with curled fibres. Amphiboles have straight, needle-like fibers.
- The amphiboles, in their fibrous form, are friable and therefore the most carcinogenic, although they also exist in safer non-fibrous forms.Other asbestos minerals, such as tremolite, actinolite and anthophyllite are less-used industrially but can still be found in a variety of construction materials and insulations and occur in a few consumer products, such as talcum powders and vermiculite. In the United States, the U.S. Environmental Protection Agency (EPA) has banned all construction-related products that have asbestos content of 1% or greater. It has also banned asbestos in all other friable (easily crushed by finger pressure) products.
Asbestos related diseases
Asbestosis and cancer
Strong concerns about the health hazards associated with asbestos had been described many times over the years. As early as 1898 the Chief Inspector of Factories of the United Kingdom reported to Parliament in his Annual Report about the "evil effects of asbestos dust". He reported the "sharp, glass like nature of the particles" when allowed to remain in the air in any quantity, "have been found to be injurious, as might have been expected" (Report of the Select Committee 1994). In 1906 a British Parliamentary Commission confirmed the first cases of asbestos deaths in factories in Britain and recommended better ventilation and other safety measures.
In 1918 a US insurance company produced a study showing premature deaths in the asbestos industry in the United States and in 1926 the Massachusetts Industrial Accidents Board processed the first successful compensation claim by a sick asbestos worker. Many American injuries from asbestos exposure came from shipbuilders working during World War II.
The fine asbestos fibres are easily inhaled, and can cause a number of respiratory complaints, including a potentially serious lung fibrosis called asbestosis. Exposure to asbestos has also been determined to cause a very serious form of cancer, mesothelioma, that occurs in the chest and abdominal cavities. This aggressive disease is not properly referred to as a lung cancer, as the malignant cells are derived from the mesothelium, a tissue found on the inner walls of the chest and abdominal cavities and on the outer surface of the lungs rather than in the lung itself.
When inhaled, asbestos is carcinogenic. In the United States alone, it is estimated that ten thousand people die each year of asbestos-related diseases, such as mesothelioma, asbestosis, lung cancer, and gastrointestinal cancer. Asbestos has a synergistic effect with tobacco smoking in the causation of lung cancer.
Other asbestos related diseases
- Asbestos warts
Caused when the sharp fibres 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 nor normally cause any 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.