Designated Substances

In Ontario, designated substances are materials that cause severe health impairment from exposure or repeated exposure. The definition used in the Occupational Health and Safety Act is:

“…a biological, chemical or physical agent or combination thereof prescribed as a designated substance to which the exposure of a worker is prohibited, regulated, restricted, limited or controlled…”

The following are designated substances in Ontario:

  • Isocyanates
  • Lead
  • Mercury
  • Silica
  • Vinyl chloride
An assessment is required if any of these substances are present and if there is a risk a worker could be exposed. 

The health effects are generally one or more of the following:

  • Cancer
  • Strong allergic reactions
  • Liver and lung disorders
  • Nervous system damage


Employers in Ontario must assess the use of these materials even if they are adequately controlled as there is potential for the worker to be exposed if the control breaks down or fails. At UW, the supervisor or principal investigator has the responsibility to ensure this has been completed for the spaces they have authority over. The expectation is that if a risk of exposure exists, the supervisor/principle investigator will initiate the designated substance assessment by contacting the Safety Office and requested a review to be completed for the material in question. In order to complete a review the following minimum information will be required: 

  • How the material is stored
  • Proposed use of the material - step by step process that outlines handling procedures
  • The ultimate fate of the material

The designated substances review process requires a cradle to grave understanding of the material's use.

Documentation of the designated substance assessment must be stored by the supervisor/principal investigator and readily available for as long as the designated substance is in their possession.

Control programs

Ontario Regulation 490 specifies that designated substance assessments are used to determine if further control programs are needed to protect the worker.

Control program not required (worker health not affected)

  • If the substance is present in the working environment, but because of the amount used or the physical state in which it is present, it is not possible for a worker's health to be affected by exposure
  • If workers are exposed and some engineering controls exist, but the health of a worker is not likely to be affected because the risk to health would be minimal even if the engineering controls failed

Control program is required (worker health may be affected)

  • If there are no controls in place
  • If the current controls are adequate but may fail or deteriorate
  • If existing controls are not adequate
  • If occupational exposure monitoring results indicate potential exposure of workers
  • If there have been reports of previous health effects from one or more of these substances

Safety Office contacts

  • For any construction-related exposure, such as maintenance, renovation, contact Robert Mullins. At the University of Waterloo, the assessments are based on the material and type of exposure.
  • For any use of a designated substance in a laboratory or office as a result of research work, contact Dhananjai Borwankar.

Additional resources and information