Labour & Regulatory Services - Workplace, Safety & Health - Legislation

Occupational Exposure Limits for Airborne Hazardous Substances

In Manitoba, employers must establish occupational exposure limits where the presence of an airborne chemical or biological substance may create a risk to the safety or health of a worker.

Occupational exposure limits outline the amount of a hazardous substance that a person can be exposed to, and are generally set in one of three ways:

  • The average exposure over an eight-hour period (TWA)
  • A short-term 15 minute exposure limit (STEL)
  • The maximum amount that cannot be exceeded at any time (ceiling limit).

Occupational exposure limits set by employers in Manitoba must not exceed the threshold limit values established by the American Conference of Governmental Industrial Hygienists (ACGIH). 

If the ACGIH has not established a threshold limit value for an airborne substance that is found in a workplace, a competent person must establish an occupational exposure limit for the substance that will ensure the safety or health of all workers is not at risk.

Certain workplace conditions, or the health or physical condition of a worker may require the employer to establish a lower occupational exposure limit than the one set by the ACGIH in order to address the additional risk.


Designated Substances

In the case of an airborne designated material (cancer-causing, respiratory sensitizer, reproductive toxin, mutagenic substance), the employer’s occupational exposure limit must be as close to zero as possible. Workplace Safety and Health maintains a convenience table of ACGIH designated substances by chemical name, industry and uses. The International Agency for Research on Cancer (IARC) also publishes designated agents, classified as confirmed human carcinogens (1), probable human carcinogens (2A) and possible human carcinogens (2B).


The American Conference of Governmental Industrial Hygienists (ACGIH)

The ACGIH is a private, not-for-profit, non-governmental corporation consisting of industrial hygienists and other occupational health and safety professionals dedicated to injury and illness prevention in workplaces. Each year in April, the ACGIH publishes an updated reference guide of threshold limit values for more than 700 substances, including a list of new and revised threshold limit values, as well as 0a list of substances under review.

ACGIH New and Revised Substances (Current as of April 1, 2017):

Acetamide (new)
Cadusafos (new)
Ethylene Glycol
Folpet (new)

Furfural alcohol
Hexylene Glycol
Phthalic Anhydride
Tungsten and compounds, in the absence of Cobalt, as W 

ACGIH Substances under Review (Current as of April 1, 2017):
The following substances are being reviewed by the ACGIH and may result in newor revised threshold limit values in the future.

Aldicarb (new)
Allyl methacrylate (new)
Antimony trioxide 
Bendiocarb (new)
Boron trifluoride ethers, as BF3 (new)
tert-Butyl hydroperoxide (new)
Calcium chromate, as Cr 
Carfentrazone-ethyl (new)
Chlorine dioxide
Chromite ore processing, as Cr
Chromyl chloride
Cyanazine (new)
Cyanoacrylates, Ethyl and Methyl (new)

Ethyl cyanoacrylate
Fludioxonil (new)
Isopropyl acetate
Lead Chromate, as Cr(VI)
Methyl 2-cyanoacrylate
Paraquat, as the cation
0-Phthalaldehyde (new)
n-Propyl acetate
Propyl acetate isomers (new)
Strontium Chromate, as Cr
Styrene Oxide (new)
Trimetacresyl phosphate (new)
Triparacresyl phosphate (new)
Zinc chromates, as Cr

WSH Legal Requirements:

See Manitoba Workplace Safety and Health Regulation, MR217/2006, :

  • Part 36: Chemical and Biological Substances

For more information on establishing occupational exposure limits, or to view the ACGIH reference guide:

Call WSH at: 204-957-SAFE (7233), toll-free 1-855-957-SAFE (7233), Select ‘Option 1’.

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