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Asbestos is a group name given to a groupd of naturally occurring minerals that had widespread use in many commercial, domestic and industrial products until the mid 1980's (New Zealand).
The three most common forms of asbestos within New Zealand are:
Chrysotile or "white" asbestos (CAS No : 12001-29-5), the most common form of
asbestos material found in many domestic, commercial and industrial
applications. The chemical composition of Chrysotile asbestos is {Mg3(Si2O5)
(OH)4}n
Amosite or "brown" asbestos (CAS No: 12171-73-5) is considered particularly
hazardous. The chemical composition of Amosite asbestos is
{(Mg,Fe)7SiO22(OH)2}n
Crocidolite or "blue" asbestos (CAS No: 12001-28-4)is highly fibrouse. The
chemical composition of Crocidolite asbestos is Na2Fe3+Si8O22(OH)2.
Exposure to asbestos fibres will occur when materials containing asbestos are sanded, sawn, drilled, or handled during maintenance or removal tasks. Most of the larger fibres are deposited in the nose and major airways, and are cleared by normal physiological processes. Smaller fibres may be deposited in the airspaces deep in the lung or migrate to other parts of the body. Three main disease states have been associated with the inhalation of asbestos fibre: asbestosis, lung cancer and mesothelioma.
Forms of cancers associated with the inhalation of asbestos are lung cancer and mesothelioma. In addition, recent studies have also identified that cancers of the larynx, oropharynx, gastrointestinal tract and kidneys can also be caused by exposure to asbestos. Generally, fibres below 0.3 micrometres in diameter and greater than 0.5 micrometres in length are potentially carcinogenic, and the risk of cancer increases as fibre size decreases.
It is important to remember that the risk of cancer also increases with the dose and there is no safe lower limit for exposure.
There is a long delay between exposure and the development of mesothelioma or lung cancer, which in the majority of cases ranges from 15 to 50 years. There is some suggestion that children exposed to asbestos have a greater susceptibility to disease. In addition there has been conclusive evidence of the risk to non workers from exposure, such as in the laundering of contaminated clothing.
Asbestos-related disease, therefore, has the potential to continue to occur long after the exposure to asbestos has been controlled.
Further information on asbestos exposure risk and disease states can be found at:
United Kingdom HSE Asbestos Guidance is available here
Approved Code of Practice for the Management and Removal of Asbestos is available here
NZDAA asbestos guidance notes can be found here
Loose fibre broken down from the mined rock material is used in the manufacture of a variety of products. Asbestos is often mixed with other materials and is rarely encountered in its rare form, making identification based on visual examination unreliable. Asbestos has been incorporated in a number of materials for the construction, cladding, thermal or acoustic insulation of offices, factories, manufacturing plants and residential dwellings.
Asbestos properties of heat resistance and mechanical strength have been exploited in these applications, and many substitutes have been found for the above applications.
New Zealand Amosite and Crocidolite asbestos importations were banned in 1974 under the Customs Import Prohibition (Asbestos) Order 1984 and this was extended to Chrysotile imports in 1999. In November 2016, products containing asbestos were prohibited from import unless under special license.