By industry, the largest exposed groups are elementary and secondary schools, provincial and territorial public administration, and universities. By occupation, the greatest exposures occur among administrative assistants, general office support workers, receptionists, and elementary school and kindergarten teachers.

Radon levels in confined or underground spaces (particularly in mines) are often elevated compared to outdoor air levels.[1,3] The highest exposed workers are those involved in underground mining, especially for uranium.[4] Other workers who spend time underground (e.g. subway and utility tunnel workers) are also at increased risk in areas where radon is present. Indoor workers of any type may also be exposed, especially if they work in areas and rooms with higher concentrations of radon (e.g. basements).

Other occupations with the potential for exposure to radon include remediation workers (especially of mine sites), phosphate fertilizer producers, researchers who use radon, and construction excavators. There is little information available on the occurrence of radon in Canadian workplaces. There are five active uranium mines in Canada; all are located in Saskatchewan. In 1998, high levels of radon were associated with propane production in British Columbia, with concentrations reaching as high as 4,958 Bq/m³.[5] In Nova Scotia, radon concentrations were collected over a three month period from 21 workplaces that had high potential for radon exposure, including water treatment facilities and coal power stations. The maximum concentration measured was 202 Bq/m³.[6]

Occupational radon exposure measurement is mandated and managed by the Radiation Protection Bureau of Health Canada for uranium miners. This data is held in the National Dose Registry (NDR), which contains exposure data for workers exposed to radiation across Canada.[7]

According to the Burden of Occupational Cancer in Canada project, occupational exposure to radon leads to approximately 190 lung cancers each year in Canada, based on past exposures (1961- 2001).[8,9] This amounts to 0.8% of all lung cancers diagnosed annually. Radon exposure occurs very broadly across workers in many industries. The groups with the largest burden of radon-related cancers are finance, insurance, real estate and leasing; trade; mining and oil and gas extraction; and public administration. Work-related radon exposure resulted in approximately $185 million in costs for newly diagnosed lung cancer cases in 2011.[9]

Our Occupational Approach page outlines the general approach used to calculate prevalence and exposure level estimates for workplace exposures.

Data Sources

Data used in developing the occupational estimates for radon were collected from several sources:

1. The Canadian Federal Building Survey, which has been conducted by Health Canada since 2007, measures radon concentrations in federal work places using alpha track detectors over at least three months. Our federal building data set included approximately 13,000 samples. No federal buildings were surveyed in Nunavut, so:
2. The Cross-Canada Survey of Radon Concentrations (CCRS) was used to calculate radon exposure in Nunavut only. The CCRS is a two year study conducted by Health Canada’s National Radon Program in 2009-2011. Homes in all health regions in Canada were sampled for a minimum of three months using alpha track detectors. Detectors were placed in the room with the lowest elevation in which homeowners occupied at least four hours per day. Individuals who were renting a home, living in high-rise condos that were above the second floor, or living on military bases or on-reserve were not included. The CCRS dataset contains 13,814 samples, with 8,340 (60%) samples collected on the first floor, 4,014 (29%) collected in the basement, and 1,163 (8%) collected on the second floor.
3. Canadian and US scientific peer reviewed publications that addressed radon exposure in Canada and the United States.
4. Grey literature including technical reports from governments and international bodies.

Prevalence Estimate Method

CAREX Canada defines exposure to radon as inhalation exposure at work above the levels expected in the general environment (i.e. in the home, above the Canadian guideline for radon set by Health Canada, which is 200 Bq/m³).

A two-stage process was used to assess prevalence of exposure: 1) estimating prevalence in workers with high probability of radon contact (i.e. underground workers); and 2) estimating prevalence in indoor work environments where exposure to radon occurs incidentally (such as office buildings and schools).

Estimating prevalence of exposure in workers where direct contact to radon is expected

A series of steps were taken to assign exposure proportions to underground workers at risk of high exposure to radon.

1. Occupations and industries at risk of possible exposure to radon were identified via peer reviewed and grey literature.
2. The total number of workers in each identified occupation and industry intersection was obtained from Statistics Canada 2016 census data.
3. A percentage of workers exposed was assigned to each occupation and industry intersection. Percentages were determined through consultation with existing evidence in the data sources, previously established methods from the Europe CAREX estimates and expert judgement of CAREX occupational hygienists.
4. The number of workers in the identified group is multiplied by the assigned percentage to calculate the prevalence estimate of underground workers exposed to radon.

Estimating exposure in indoor workers

To estimate the number of indoor workers exposed to radon in various occupation and industry intersections, we modelled radon concentrations in workplaces and susceptible indoor working populations. Generally:

1. Indoor workers at risk of exposure to radon were identified using Statistics Canada 2006 census data and previous estimates of exposure to solar radiation.
2. The distributions of indoor workplace radon concentrations by Canadian province/territory were calculated using radon measurements from the Canadian Federal Building Survey (and the Cross-Canada Survey of Radon Concentrations for Nunavut only).
3. The distributions of radon concentrations in workplaces and of susceptible populations across different occupations and industries were combined to estimate the prevalence of radon exposure in susceptible indoor working populations.

More specifically, we used previous estimates created by CAREX Canada to identify and exclude outdoor workers (thus creating a subset of the census that only included indoor workers). All occupation-industry matrix cells that were identified and used to estimate prevalence of exposure in underground workers were excluded to avoid double counting.

The distribution of radon concentrations was then applied to the susceptible (indoor) population model to determine the number of workers exposed.

Exposure Level Method

CAREX Canada used distribution parameters from the radon concentration model to calculate the number of workers above exposure level thresholds. Exposure thresholds were >200 to 400 Bq/m³ for low exposure, >400 Bq/m³ to 800 Bq/m³ for moderate exposure, and >800 Bq/m³ for high exposure. Workers were considered to be exposed to “very high” levels of radon if they were identified in the preliminary literature search as being an underground worker with a likely unique exposure scenario.

Category 1: Low Exposure

A group of workers is put in this exposure category if the susceptible working population was exposed to levels between
>200-400 Bq/m³ based on the concentration distributions produced by the radon concentration model.

Category 2: Moderate Exposure

A group of workers is put in this exposure category if the susceptible working population was exposed to levels between
>400-800 Bq/m³ based on the concentration distributions produced by the radon concentration model.

Category 3: High Exposure

A group of workers is put in this exposure category if the susceptible working population was exposed to levels above 800 Bq/m³ based on the concentration distributions produced by the radon concentration model.