Exposure limits for hazardous chemicals are critical benchmarks that safeguard human health by controlling the levels of exposure to harmful substances. However, the acceptable exposure limits differ significantly between workers in occupational settings and the general public. This distinction arises from differences in exposure duration, susceptibility, and the environments in which these groups encounter hazardous chemicals. Below, we explore the key differences and the reasoning behind these varying standards, with specific reference to Canadian regulations.

1. Exposure Duration

Workers: Occupational exposure limits (OELs), such as those established by the Ministry of Labour (MOL) in Ontario Canada, are designed for adults in the workforce who are typically exposed to hazardous substances for 8 hours a day, 5 days a week. These limits assume that exposure occurs over a working lifetime (approximately 40 years).

General Public: In contrast, exposure limits for the general population, such as those provided by Health Canada’s guidelines, account for continuous exposure, often 24 hours a day, 7 days a week, over a lifetime. The public’s exposure scenarios include diverse age groups, such as children, the elderly, and individuals with pre-existing health conditions.

2. Health Protection Goals

Workers: OELs aim to prevent acute and chronic health effects, ensuring that workers remain healthy and capable of performing their duties. Since workers are generally healthier and fitter than the average population, OELs may not offer the same level of protection for more vulnerable individuals. These limits are legally enforceable in workplaces.

General Public: Exposure limits for the general public are more stringent, reflecting the need to protect sensitive groups for a prolonged time. Some guidelines are, provided by Health Canada in Indoor Air Reference Levels, Ontario’s Ambient Air Quality Criteria (2012), and in other National and International guidelines.  Unlike the OELs, the guidelines are not legally enforceable but serve as recommendations for maintaining public health. The limits consider individuals who may be more vulnerable due to age, pre-existing medical conditions, or other factors.

3. Assessment and Application

Workers: In occupational settings, exposure assessments involve direct measurement of airborne concentrations, dermal exposure, and other relevant routes. Employers must implement control measures such as ventilation systems, personal protective equipment (PPE), and administrative controls to maintain exposure below OELs. Compliance is mandatory and subject to regulatory inspections and penalties.

General Public: For the public, exposure limits consider multiple sources, including air, water, soil, and food. Regulatory agencies use models and monitoring data to estimate cumulative exposure and recommend actions to mitigate risks. These guidelines are advisory and often implemented voluntarily or through public health initiatives.

4. Examples of Limits

  • Workers:
    • Formaldehyde: The MOL OEL is 1.00 ppm as a 15-min Short Term Exposure Limit in Ontario (2024)
  • General Public:
    • Formaldehyde: Health Canada’s indoor air quality guideline recommends a maximum of 0.04 ppm for continuous exposure.

Avoiding Misapplication of Exposure Limits

From time to time, air quality reports emerge where consultants compare concentrations of chemicals found in residential houses with industrial exposure limits. While this may seem convenient, it is fundamentally misleading.

At LCS Laboratory, we firmly believe that exposure standards should be appropriate for the specific context of the project. Occupational Exposure Limits (OELs) are tailored for industrial settings, where controlled environments and worker protections are in place. Clean air standards, such as those established by Health Canada, are designed for residential and public spaces, taking into account continuous exposure and sensitive populations.

For more information about chemical exposure assessments or to discuss your workplace’s specific needs, contact our team of experts today.

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