Adjusting Exposure Limits for Atypical Shifts

In most jurisdictions, occupational exposure limits are mandated based on the assumption that workers are engaged in 8-hour shifts per day, or 40-hours of work per week. So what do you do if your workers perform a longer shift, such as the 12-hour shifts common to oil and gas and mining industries, or week on – week off schedules?

Regulatory Requirements

As always, it is best to first consult the occupational health and safety regulations in your area to determine if specific methods of adjusting exposure limits for atypical or unusual shift lengths are already in place.  For example, in the province of Alberta, the OHS Code stipulates that the Brief and Scala model must be followed when adjusting exposure limits for atypical shifts. See below for the applicable excerpt of the Alberta OHS Code:











In contrast, jurisdictions with dated OHS regulations may not explicitly mandate the adjustment method to be used.

Industrial Hygiene Associations

If the OHS authority in your area does not mandate an adjustment method to be followed, industrial hygiene associations are often a great resource for guidance.  For example, the Australian Institute of Occupational Hygienists has produced a position paper, titled Adjustment of Workplace Exposure Standards for Extended Work Shifts, which references four alternative methods for adjusting exposure limits, including the Brief and Scala method, the Quebec model, the OSHA model and Pharmacokinetic models.


While jurisdictional OHS regulations may mandate the adjustment method to be used, it is also critical to check if an adjustment is required for a specific compound or contaminant of concern. For example, if the OSHA model is followed, adjustments are not made for mild irritants or compounds that do not have cumulative effects. Many OHS regulations will also specifically notate individual compounds as not requiring adjustments. See below for an example of a compound-specific notation indicating adjustments are not required.










Further, most adjustment methods are not applicable for ceiling exposure limits or short-term exposure limits (STELs).


Your local OHS authority is your first stop in determining the requirements for adjusting exposure limits for unusual or atypical work shifts. In no specific requirements are in place, several methods are available to you to determine the best path forward.


January 5, 2018

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