Industries where the largest numbers of workers are exposed include automotive repair and maintenance, public administration (where firefighters are included), and taxi and limo service. According to the US Department of Labour, benzene exposure is also likely during petrochemical production, petroleum refining, coke and coal chemical manufacturing, tire manufacturing, and storage or transport of benzene and petroleum products containing benzene.[3]

Occupations at risk of benzene exposure include automotive service technicians and mechanics, delivery and courier drivers, taxi and limousine drivers, and firefighters. Other occupations such as steel workers, printers, rubber workers, shoemakers, laboratory technicians, and gas station employees were also identified as exposed.[3]

According to the Burden of Occupational Cancer in Canada project, occupational exposure to benzene leads to approximately 20 leukemia cases, and less than 5 possible multiple myeloma cancers each year in Canada, based on past exposures (1961-2001).[4,5] This amounts to 0.5% of all leukemia and 0.2% of all multiple myeloma cancers diagnosed annually. Most benzene-related cancers occur among workers in the manufacturing, transportation and warehousing, and trade sectors.[5]

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 benzene were collected from several sources:

1. The Canadian Workplace Exposure Database (CWED) contains over 1,500 measurements for benzene exposure. These measurements were collected during the years 1981 to 2004 in Ontario and British Columbia workplaces.
2. Canadian and US scientific peer reviewed publications that addressed benzene exposure in Canada and the United States.
3. Grey literature including technical reports from governments and international bodies.

Prevalence Estimate Method

CAREX defines exposure to benzene as inhalation exposure at work to levels above those encountered in the general environment.

To determine the number of workers potentially exposed to benzene 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 benzene.

1. Occupations and industries at risk of possible exposure to benzene were identified using any combination of data sources described above.
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 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.
4. The number of workers in the identified group is multiplied by the assigned percentage to calculate the prevalence estimate of workers exposed to benzene.

Exposure Level Method

CAREX uses available workplace exposure measurements in the CWED to create exposure level categories by industry and occupation. For benzene, these categories are:

Category 1: Low Exposure

A group of workers (people in the same job category and industry) is put in this exposure category for one of two reasons:

1. The are no valid measurements, but a hygienist identified this group as typically exposed during literature and other reviews;
2. There are valid exposure measurements in the CWED and a hygienist review determined that exposure is plausible; AND EITHER:
   1. There are less than 10 samples available in the CWED, OR
   2. There are ≥10 measurements available but they do not meet the criteria for Moderate Exposure.

Category 2/3: Moderate to High Exposure

A group of workers is put in this exposure category if:

1. There are at least 25 individual samples in the CWED, AND
2. 20% or more samples have a value higher than 0.25 ppm (which is ½ of the current occupational exposure limit for benzene).

OR

1. There are at least 10 individual samples in the CWED, AND
2. 20% or more samples have a value higher than 0.5 ppm (which is the current occupational exposure limit for benzene).

For benzene, the moderate and high exposure categories were combined due to very few workers exposed above 0.5 ppm.