The term "asbestos" refers to a family of naturally occurring fibrous (asbestiform) hydrated silicates divided on the basis of mineralogical features into two groups: serpentines and amphiboles. The important and distinguishable property of asbestos, compared with non-asbestiform minerals, is the presence of long, thin fibres that can be easily separated.Although, according to some definitions, there are as many as 30 varieties of asbestos, however, only six are of commercial importance. These six are listed in the asbestos definition in section 1 of the regulation: antinolite, amosite, anthophylite, chrysotile, crocidolite, and tremolite.
Chrysotile is the only asbestiform member of the serpentine group of minerals. Although commonly termed "white asbestos," chrysotile fibres may also be green, grey, amber or pink in colour. Chrysotile fibres have high tensile strength, high resistance to alkalise, high flexibility and good spin ability. About 90 per cent of world asbestos production is chrysotile.
Amphibole asbestos fibres differ from the flexibility, curly chrysotile fibres in that they are straight and needle-like. These fibre characteristics appear to give amphibole asbestos a greater tendency to become airborne, which is important to the control of exposure. Two types of amphibole asbestos have been widely used: crocidolite of "blue asbestos" and amosite or "brown asbestos." Anthophylite, tremolite, and antinolite asbestos have been rarely used commercially.
The largest single use of asbestos is as a reinforcing agent in cement products. Asbestos-cement products include flat and corrugated sheets, pipes and shingles. Another major use is friction materials, including linings for drum and disc brakes as well as clutch facings. Other asbestos-containing products are vinyl asbestos flooring, gaskets and curtains, roofing felts, coatings and mastics, and asbestos paper products.
One use of asbestos deserves special mention, and that is its use as an insulating material. Asbestos is an effective insulator against heat, cold, electricity and noise. In the late 1960s and the early 1970s insulation was the largest use of asbestos. Amosite and Chrysotile in combination and, to a lesser extent, crocidolite were widely used in sprayed insulation as fireproofing for steel structures. In some cases, the insulation was exposed to provide a decorative architectural finish. Elsewhere, it doubled as acoustical insulation. Asbestos pipe and boiler insulation was used on heating systems in buildings, including homes, and in industrial processes. In 1973 the spray application of asbestos insulation ceased when new regulations were introduced under the Ontario Construction Safety Act. Also in 1973 the major Ontario suppliers of pipe and boiler insulation stopped using asbestos in their products. Both of these asbestos applications are prohibited by the new asbestos regulation.
To cause disease, asbestos fibres must be inhaled into the lungs. The lung is a system of branching airways that end in tiny air sacs, called alveoli. There are about 300 million of them in the lungs. It is from these air sacs that oxygen from inhaled air enters the bloodstream. This is also where inhaled asbestos fibres do their damage. However, only those fibres within a certain size range can gain access to the lung alveoli. Fibres with a diameter greater than three microns are too large and impact with the upper branches of the respiratory system and then are eliminated. Fibres that can enter the lung and cause disease are too small to be visible to the naked eye.
It is not clear how asbestos fibres cause disease after they enter the lung. For each disease there is a period of latency, usually more than ten years, between first exposure to asbestos and the appearance of the disease. It is this characteristic that makes asbestos disease so insidious; exposure can continue for many years without any outward evidence of harm while disease develops silently within.
Asbestosis is characterized by a fibrosis of the lung tissue, which makes breathing difficult. The most prominent symptom is breathlessness. Early detection of asbestosis is possible by x-ray examination and lung function testing. However, the disease is irreversible and will continue to progress even after exposure has stopped. Rarely a cause of death itself, asbestosis results in an appreciable reduction in life expectancy due to deaths from related illnesses.
This is a rare cancer arising from the cells of the pleura and the peritoneum. The development of mesothelioma is characterized by a long latency period, usually lasting about 15 years and sometimes more than 40. There is no effective treatment of mesothelioma. Large portions of Mesothelioma patients die within a year of diagnosis; few survive longer than five years. Although asbestos was once thought to be responsible for all mesothelioma, other causes have now been identified. Still, the chance of getting mesothelioma in the absence of asbestos exposure is considered to be extremely remote.
- Lung Cancer
Unlike asbestosis and mesothelioma, lung cancer is not associated only with asbestos exposure. Furthermore, there is no basic difference between lung cancer caused by asbestos and that due to other causes. In general, the risk of getting lung cancer increases with the extent of asbestos exposure, in terms of both intensity and duration. This risk is also greatly enhanced by smoking; most asbestos workers who develop lung cancer are also smokers. The prognosis for persons diagnosed with lung cancer is poor. Only about one in twenty survives longer than five years after it is diagnosed.
- Other Asbestos-Related Cancers
The relationship between asbestos exposure and asbestosis, mesothelioma and lung cancer has been clearly established and is beyond argument. Several other cancers have also been associated with the inhalation of asbestos. Although the evidence is not as good as for the diseases discussed above, these cancers should be noted. They are, gastrointestinal cancer affecting all sites in the gastrointestinal tract and cancer of the larynx.
- Other Asbestos-Related Conditions
A number of less serious effects have been associated with asbestos exposure, such as pleural plaques, asbestos bodies and warts. Pleural plaques are areas of scarring of the pleural surfaces. In general, they are not associated with any functional abnormality and are merely an indicator of asbestos exposure. Occasionally, they can become so widespread that they restrict lung function. Asbestos bodies, also known as "ferruginous bodies," result when asbestos fibres become coated with a substance containing protein and iron. The asbestos bodies are not harmful and, like pleural plaques, serve as evidence of asbestos exposure. Asbestos warts are harmless skin growths that occur when asbestos fibres penetrate the skin.
Department of Health and Safety
Asbestos Management Program
Industrial Hygiene Survey Program
Asbestos Removal Projects
Asbestos Abatement Plan for the Ross Building and Complex 1
Asbestos Air Sampling Protocol
Ontario Government Strengthens Protection for People Working With Asbestos