Asbestos is an interesting and challenging substance to assess in terms of exposure. Current asbestos-related disease is associated with exposures that occurred 10 to 40 years ago, and the exposure sources were very different at that time than they are now. Exposure from more widespread mining and milling, in addition to primary use of asbestos in manufactured products and buildings was most important. In contrast, the vast majority of exposure that occurs today is due to contact with older asbestos-containing products, and doing renovation work on buildings and in industrial plants. These exposures can be considered as a kind of secondary exposure from contact with those products and building materials that were made or put in place more than 35 years ago. Indeed many of the workers currently expected to be exposed work in the construction sector, where exposure occurs from poor exposure control during renovation and refurbishing of old buildings. In addition, exposure may commonly occur among maintenance workers in industries where substantial amounts of asbestos were used in the past (such as smelting, petroleum refining and pulp and paper), as well as automotive brake repair workers, and people that repair and maintain ships.
In some cases, we expect to see exposure today in the same or similar occupational groups as we did in the 1970s (i.e. construction workers, plumbers and pipefitters), albeit at lower exposure levels. In other cases, such as in mining, exposure has been almost completely phased out. Further, the abatement and asbestos remediation industry is an entire category of business with potential for exposure to asbestos that did not exist as a separate profession until the early 1980s.
Using an approach that considered historical uses of exposure in Canada to guide exposure assessments for the present day, results indicate that approximately 152,000 Canadians are currently exposed to asbestos in their workplaces, and are primarily male. This estimate includes people with the potential for exposure at work to any form of asbestos likely to exceed the non-occupational background level in dwellings or urban air (usually below 0.001 f/cm3). The largest industrial groups exposed are construction-related (specialty trades and building construction contribute about 88% of all exposed workers). Other important industries are automotive repair and maintenance, ship and boat building, and remediation work (which is captured under remediation & waste management, and also under scientific and consulting services, for a total of 2,300 workers).
When examining exposure to asbestos by occupation, the largest exposed groups are carpenters and cabinetmakers (exposed during renovations; 34,000 workers exposed). Construction trades helpers and labourers are the second largest group (28,000 workers). Other important job groups which may be exposed are electricians, plumbers, plaster and drywall installers, and auto mechanics.
Level of Exposure
Data Sources & Methods
Data used in developing the occupational estimates for asbestos were collected from several sources:
- The Canadian Workplace Exposure Database (CWED) contains approximately 6,700 measurements for asbestos exposure. These measurements were collected during the years 1981 to 2004 in Ontario and British Columbia workplaces.
- Canadian and US scientific peer reviewed publications that addressed asbestos exposure in Canada and the United States.
- Grey literature including technical reports from governments and international bodies.
Prevalence Estimate Method
CAREX defines exposure to asbestos as inhalation at work to levels significantly exceeding non-occupational background levels.
To determine the number of workers potentially exposed to asbestos at work, CAREX occupational exposure experts used methods previously established in other peer-reviewed CAREX projects in Europe. A series of steps were taken to assign exposure proportions to occupations and industries at risk of exposure to asbestos.
- Occupations and industries at risk of possible exposure to asbestos were identified using any combination of data sources described above.
- The total number of workers in each identified occupation and industry intersection was obtained from Statistics Canada 2006 census data.
- A percentage of workers exposed was assigned to that occupation and industry intersection. Percentages were determined by consultation with existing evidence in the data sources, previously established methods from the Europe CAREX estimates and the expert judgement of CAREX occupational hygienists.
- The number of workers in the identified group is multiplied by the assigned percentage to calculate the prevalence estimate of workers exposed to asbestos.