The largest industrial groups exposed include dry cleaning and laundry services, printing and related support activities, and traveller accommodation. The largest occupational groups exposed to tetrachloroethylene include dry cleaning, laundry and related occupations, printing press operators, metalworking and forging machine operators, and labourers in metal fabrication. Workers performing metal degreasing, producing fluorocarbons, and producing chemicals are also at risk of exposure totetrachloroethylene.[2]

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 tetrachloroethylene were collected from several sources:

1. The Canadian Workplace Exposure Database (CWED) contains approximately 5,000 measurements for tetrachloroethylene 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 tetrachloroethylene 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 tetrachloroethylene as inhalation exposure at work to levels above those expected in the general environment (this may not include people who live above dry-cleaning establishments that use PERC, however).

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

1. Occupations and industries at risk of possible exposure to tetrachloroethylene 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 tetrachloroethylene.

Exposure Level Method

CAREX uses available workplace exposure measurements in the CWED to create exposure level categories by industry and occupation. For tetrachloroethylene (PERC), 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: Moderate 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 12.5 ppm (which is ½ of the current occupational exposure limit for tetrachloroethylene),

OR

1. There are at least 10, but less than 25, individual samples in the CWED, AND
2. 20% or more samples have a value higher than 25 ppm (which is the current occupational exposure limit for tetrachloroethylene).

Category 3: 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 25 ppm (which is the current occupational exposure limit for tetrachloroethylene).