Asbestos is a broad term applied to a number of substances falling into two chief varieties, chrysotile and amphiboles. These substances are naturally occurring iron, sodium, calcium and magnesium hydrated silicates. They have a fibrous structure and are incombustible.
Chrysotile asbestos (white asbestos) is a hydrated magnesium silicate found in serpentine rock. It is widely distributed in nature and accounts for some 93% of the world’s asbestos production. Amphibole asbestos varieties include amosite, crocidolite, anthophyllite, tremolite and actinolyte. The last two substances have few industrial applications but are sometimes found as impurities in talc.
Pathological effects of exposure to asbestos
The risks to health result from the inhalation of the fibrous dust and its subsequent dispersion within the lung and other parts of the body. This may occur in those extracting the fibre and processing same, and subsequent manufacture and application of products. In practice, exposure to asbestos alone is uncommon. Other mineral dusts are frequently inhaled along with the asbestos and may influence its effects. The effect of these and other pollutants, especially cigarette smoke, may adversely influence the type and severity of disease produced by asbestos.
Several types of diseases may result from the inhalation of asbestos:
- asbestosis, a fibrous (thickening and scarring) of the lung itself and of its outer surface, and the pleura, which may become calcified;
- cancer of the bronchial tubes; and
- cancer of the pleural surface (diffuse mesothelioma), which may also occur in the abdominal cavity (peritoneal mesothelioma).
There is also some evidence that cancers in other sites of the body may occasionally become asbestos-linked. These types of disease have a long latent period in that they first become evident as long as 20 years after the first exposure to the fibres.
Control of exposure
Exposure to all forms of asbestos should be reduced to the minimum level reasonably practicable. In addition, the personal exposure of workers should not exceed the current action levels and control limits. Action levels refer to cumulative exposures over a continuous 12 week period. Control limits refer to concentrations of asbestos in the atmosphere.
They do not represent safe levels which, once attained, make further improvements in dust control unnecessary. They represent the upper level of permitted exposure, for each form of asbestos, above which the risk to health is unacceptable.