Asbestos exposure becomes a health concern when high concentrations of asbestos fibres are inhaled over a long time period.

People who become ill from asbestos are almost always those who are exposed on a day-to-day basis in a job where they work directly with the material.

As a person's exposure to fibres increases, either by breathing more fibres or by breathing fibres for a longer time, that person's risk of disease also increases. Disease is very unlikely to result from a single, high-level exposure, or from a short period of exposure to lower levels.

However, breathing in asbestos fibres has been linked to three respiratory diseases, all of which can be fatal:

• Asbestosis is a chronic lung disease that can lead to respiratory impairment and to diseases such as lung cancer. People with extensive occupational exposure to the mining, manufacturing, handling or removal of asbestos are at risk of developing asbestosis.
• Mesothelioma is a cancer in two forms - pleural which is a tumour of the lung; and peritoneal, which is a cancer of the abdominal cavity. It has been observed in people who were occupationally exposed to chrysotile, family members of the occupationally exposed, and residents who lived close to asbestos factories and mines.
• Lung cancer caused by asbestos cannot be distinguished from those cancers that are caused by other agents such as tobacco smoke. There is a synergistic effect between tobacco smoking and asbestos in the formation of lung cancer.

The link between asbestos and lung disease was known in the early 1900s. Yet, despite warnings from health authorities, mining companies allowed their workers to be exposed to it, and industries that used asbestos in their manufacturing processes did nothing to protect their workers from its dangers.