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Proposed Changes Affecting the Protection of Workers from Exposures to Hazardous Biological or Chemical Agents under the Occupational Health and Safety Act

Updating of occupational exposure limits - American Conference of Governmental Industrial Hygienists recommendations

Occupational Exposure Limits (OELs) restrict the amount and duration of worker exposure to hazardous workplace substances such as asbestos, benzene and lead.

Consultation on the annual revised limits recommended by the American Conference of Governmental Industrial Hygienists (ACGIH) is the foundation of the Ministry of Labour (MOL)’s OEL update process. Through this process, the MOL has successfully updated OELs for over 200 hazardous substances since 2004. This is the MOL’s 12th consultation under the OEL update process. The proposed changes are based on the ACGIH’s recommended changes to OELs for the years 2016 and 2017.

Additional regulatory changes proposed

This year, in addition to consulting on new or revised OELs for a number of substances, the MOL is proposing to:

  • Provide for the use of Quebec’s Institut de recherche Robert Sauvé en santé et en sécurité du travail (IRSST) model for calculating exposures to hazardous biological or chemical agents for irregular work shifts.
  • Add a new listing and OEL for diesel particulate matter in the Ontario Table (Table 1) in Regulation 833.
  • Include a reference to “substitution” of less hazardous agents in the hierarchy of controls in section 3 of Regulation 833 – Control of Exposure to Biological or Chemical Agents.

Details on all proposals are provided below.

Proposed OEL changes

The tables posted on the MOL’s website contain new or revised OELs or listings proposed for 38 substances resulting from changes recommended by the ACGIH. Further information about the ACGIH’s OEL development process and intended changes and how stakeholders can comment is available at the ACGIH’s site "Notice of Intended Changes".

Proposed changes based on the 2016 ACGIH recommendations include the following:

  • Addition of listings for 4 substances in regulation: Boron trichloride, Calcium silicate, naturally occurring as Wollastonite, Hard metals, containing Cobalt and Tungsten carbide, and Simazine.
  • Revisions to exposure limits or listings for 11 substances currently regulated: Boron tribromide, Boron trifluoride, Butyl acetates (all isomers) (Note: Separate listings for three isomers combined into single listing), Cyanogen, Propoxur, Toluene diisocyanate, Triorthocresyl phosphate, and Warfarin.
  • Removal of listing and OELs for one substance: Calcium silicate (synthetic nonfibrous).

Proposed changes based on the 2017 ACGIH recommendations include the following:

  • Addition of listings for 3 substances to regulation: Acetamide, Cadusafos, and Folpet,
  • Revisions to exposure limits and/or listings for 10 substances currently regulated: Captafol, β-Chloroprene, Ethylene glycol, Formaldehyde, Furfural, Furfuryl alcohol, Hexylene glycol, Phthalic anhydride, Stearates and Tungsten.
  • Addition/removal of notations for 9 substances: Acetylene, Butane (all isomers), 2,4-D, Ethane, Hydrogen, L.P.G. (Liquefied petroleum gas), Methyl acetylene, Methyl acetylene-propadiene mixture, and Propane.

Note: Information on the proposed new listing and OEL for diesel particulate matter in Regulation 833 is discussed separately later in the paper.

Irregular work shifts

Irregular work shifts are now commonplace in a range of industries, including mining, service industries such as healthcare, oil and gas, processing, and manufacturing. The standard eight‐hour work day, the basis for setting OELs for airborne contaminants, no longer exists in many of these workplaces. Irregular work shifts can take many forms, but they generally involve a worker working shifts of greater than 8 hours in length, or a work week greater than 40 hours.

To address this change, exposure standard adjustments have increasingly become an essential component in workplace exposure assessments. The MOL’s current approach for calculating daily and weekly exposures and adjusting for irregular work shifts is set out in the schedules found in Regulation 833 and O. Reg. 490/09 - Designated Substances. It reduces the OEL proportionately based on the increased exposure time. This model is simple to use, however, a disadvantage is that all agents, regardless of toxicity, are treated the same.

An increase in scientific research on exposures and toxicity has led to the development of OEL adjustment methods that take into consideration an agent’s activity in the body. One such method, referred to as the “Quebec Model”, developed by the University of Montreal and Institut de recherche Robert Sauvé en santé et en sécurité du travail (IRSST) is set out in Quebec’s Guide for the adjustment of permissible exposure values (PEVs) for unusual work schedules (the Guide).

This method, used in the Province of Quebec and referenced by the ACGIH and other health and safety organizations, considers toxicological information such as sensitization, irritation, organ toxicity, reproductive system toxicity and teratogenicity, in addition to exposure and recovery times.

Considering the benefits of this method, it is proposed that the schedules in Regulations 833 and O. Reg. 490/09 addressing ‘Airborne Measurement and Calculation of Exposure’ be amended to provide for the use of the Quebec Model. Due to the difference in OELs between the jurisdictions, it is proposed that the exposure adjustment calculations be adopted with the proviso that Ontario’s OELs be used in the calculations. Note: This would mean that the ‘exposure adjustment calculator’ referenced in the Guide cannot be used where the OELs for that substance are different between Ontario and Quebec.

Diesel engine exhaust

Diesel engine exhaust is a complex mixture of toxic gases and particulates produced from the combustion of diesel fuel. The International Agency for Research on Cancer (IARC) has classified diesel engine exhaust as a definite human carcinogen (Group 1) – a classification that includes asbestos, silica and tobacco smoke – based on sufficient evidence that exposure is associated with an increased risk of lung cancer. At the present time, the ACGIH, the foundation of the MOL’s OEL update process and the primary basis for setting Ontario’s OELs in Regulation 833, has not recommended an OEL for diesel particulate matter (DPM), the component that includes the more hazardous diesel soot particles that are linked to lung cancer.

According to CAREX [1] Canada, approximately 9,100 workers in Ontario’s mining industry are estimated to be exposed to diesel engine exhaust. Worker exposures to DPM in Ontario’s mining industry are regulated under Regulation 854 – Mines and Mining Plants under OHSA. Section 183.1(5) of Regulation 854 sets the time-weighted average limit for DPM in underground mines at 400 µg/m3, total carbon. [2] This OEL is based on the United States Department of Labor’s Mining Safety and Health Administration (MHSA) rule for diesel particulate matter for Metal and Non-metal mines published in 2001. This exposure limit has since been revised by the MSHA to 160 µg/m3, total carbon.

On and off-road diesel engines are widely used in other industries such as construction, transportation and warehousing. As an important first step in minimizing and controlling worker exposures to DPM in these sectors, the MOL is proposing to add a new listing and OEL for DPM measured as total carbon, in the Ontario Table (Table 1) in Regulation 833 based on the revised MSHA limit of 160 µg/m3, total carbon.

In support of this proposal, the Ministry will work with mining stakeholders, including the Mining Legislative Review Committee, regarding the application of this proposal to the mining sector and any regulatory changes that would be proposed with respect to Regulation 854.

The Ministry is seeking feedback on the proposal to introduce a new OEL for DPM in Regulation 833.

  • Do you foresee any implementation challenges? What are they?
  • What type of training or support would assist in implementing this proposed new OEL?


Substitution of hazardous substances with those that are less hazardous is one of the most effective ways of eliminating or reducing exposure to hazardous substances. Other occupational hygiene methods for controlling worker exposure to hazardous substances include isolation, enclosure, local exhaust ventilation, process or equipment modification, good housekeeping, administrative controls and personal protective equipment. All these methods reduce or eliminate the risk of injury or harm by interrupting the path of exposure between the hazardous material and the worker. Substitution removes or reduces the hazard at the source.

While Ontario encourages the substitution of hazardous substances with those that are less hazardous, section 3 of Regulation 833 does not explicitly mention substitution as one of the methods employers must consider to protect workers from exposure. Recognizing the importance of eliminating or reducing exposures to hazardous substances, the MOL is proposing to add “substitution” to the list of controls. This approach is in line with good industrial practice and many other Canadian jurisdictions.

How to participate

Stakeholders are invited to submit comments on any or all of the proposed changes affecting the protection of workers from exposures to hazardous biological and chemical agents under the Occupational Health and Safety Act.

The 45 day consultation period ends May 4, 2018. Submissions may be mailed, faxed, or sent electronically to the following addresses:


2018 Hazardous Substance Review Project
Ontario Ministry of Labour
12th Floor, 400 University Avenue
Toronto, ON M7A 1T7


(416) 326-7650


Notice to Consultation Participants

Submissions and comments provided to the Ministry of Labour are part of a public consultation process to solicit views on proposed revisions to affecting Regulation 833, O. Reg. 490/09 and Regulation 854. This process may involve the Ministry publishing or posting to the internet your submissions, comments, or summaries of them. In addition, the Ministry may also disclose your submissions, comments, or summaries of them, to other parties during and after the consultation period.

Therefore, you should not include the names of other parties (such as the names of employers or other employees) or any other information by which other parties could be identified in your submission.

Further, if you, as an individual, do not want your identity to be made public, you should not include your name or any other information by which you could be identified in the main body of the submission. If you do decide to identify yourself in the body of the submission this information may be released with published material or made available to the public. However, your name and contact information provided outside of the body of the submission, such as found in a cover letter, will not be disclosed by the Ministry unless required by law. An individual who provides a submission or comments and indicates an affiliation with an organization will be considered a representative of that organization and his or her identity may be disclosed.

Personal information collected during this consultation is under the authority of the Occupational Health and Safety Act and is in compliance with section 38(2) of the Freedom of Information and Protection of Privacy Act.

If you have any questions regarding privacy matters, you may contact the Ministry’s Freedom of Information and Privacy Office at 416-326-7786.

[1] CAREX (CARcinogen EXposure) Canada leads an evidence-based carcinogen surveillance program for Canada.

[2] 308 µg/m3 expressed as elemental carbon (EC)