Designated substances Ontario list, surveys and Regulation 833
Ontario has 11 designated substances under O. Reg. 490/09. The list, exposure limits, when a designated substance survey is needed and the Reg. 833 link.
Designated substances in Ontario, the survey and Regulation 833
Designated substances in Ontario are 11 chemical agents: acrylonitrile, arsenic, asbestos, benzene, coke oven emissions, ethylene oxide, isocyanates, lead, mercury, silica and vinyl chloride. Section 2 of O. Reg. 490/09 (Designated Substances) lists them under the Occupational Health and Safety Act (OHSA).
Construction projects work differently. Owners must list designated substances before work starts. Regulation 833 controls worker exposure, except where O. Reg. 278/05 covers asbestos.
The 11 designated substances and their limits
Table 1 of O. Reg. 490/09 sets these limits. TWA means time-weighted average. Where the short-term column says none, no short-term limit is set; the TWA still applies.
| Substance | TWA | STEL, ceiling or notation |
|---|---|---|
| Acrylonitrile | 2 ppm | C 10 ppm, Skin |
| Arsenic and inorganic compounds, as As | 0.01 mg/m³ | 0.05 mg/m³ |
| Asbestos, all forms | 0.1 f/cc | none |
| Benzene | 0.5 ppm | 2.5 ppm, Skin |
| Coke oven emissions | 0.15 mg/m³ | none |
| Ethylene oxide | 1 ppm | 10 ppm |
| Isocyanates (TDI, MDI, HDI, IPDI) | 0.005 ppm | C 0.02 ppm |
| Lead and compounds, as Pb (except tetraethyl lead) | 0.05 mg/m³ | none |
| Mercury, all forms except alkyl | 0.025 mg/m³ | none |
| Mercury, alkyl compounds | 0.01 mg/m³ | 0.03 mg/m³ |
| Silica, quartz and tripoli (respirable) | 0.10 mg/m³ | none |
| Silica, cristobalite (respirable) | 0.05 mg/m³ | none |
| Vinyl chloride | 1 ppm | none |
Table 1 also lists other isocyanates and tetraethyl lead separately. Under section 16, benzene, coke oven emissions, lead and mercury must stay within Table 1. The other seven must be cut to the lowest practical level and still not exceed it.
What O. Reg. 490/09 asks of employers
Sections 3 to 13 apply substance by substance. Presence alone does not trigger the regulation, except ethylene oxide, which applies wherever it is present. The ministry overview also excludes farming operations. Most other sections use a likely-exposure test. Where O. Reg. 490/09 applies, employers must:
- carry out a written assessment of the exposure or likelihood of exposure (s. 19)
- put a control program in place if a worker is likely to be exposed and their health may be affected (s. 20), covering engineering controls, work practices, hygiene, monitoring, records and training
- include employer-paid medical surveillance in control programs for asbestos, benzene, coke oven emissions, isocyanates, lead, mercury and silica, using the Code for Medical Surveillance for pre-placement, periodic, acute exposure and exit exams
- when control-program monitoring results come in, post them for at least 14 days, give a copy to the joint health and safety committee and keep them for at least 5 years (s. 25)
When a designated substance survey is required
You need one before a construction project begins. The duty comes from section 30 of the OHSA, not from O. Reg. 490/09. Section 30(1) reads: "Before beginning a project, the owner shall determine whether any designated substances are present at the project site and shall prepare a list of all designated substances that are present at the site."
The Act asks for a list, not a document titled "designated substance survey" or "designated substances report". If work is tendered, the person issuing tenders includes the list. The owner gives it to prospective constructors before a binding contract, and the constructor passes it to prospective contractors and subcontractors before theirs.
An owner who leaves off a substance they ought reasonably to have known of is liable for the resulting losses (s. 30(5)). A constructor who fails to pass on a listed substance is liable to contractors and subcontractors (s. 30(6)). Section 30 sets no survey format. Scope the survey to the planned work.
Asbestos has extra rules under O. Reg. 278/05. Under section 10, before tenders or work, the owner must have an examination done and a report prepared on asbestos-containing material. Section 2(4) excludes owner-occupied private residences and owner-occupied residential buildings with 4 or fewer dwelling units.
How designated substances relate to Regulation 833
O. Reg. 490/09, section 14 excludes employers engaged in construction at a project. The ministry guide sends those exposures to Regulation 833, except asbestos covered by O. Reg. 278/05.
Regulation 833 does not apply to an agent already covered by 490/09, or to asbestos where 278/05 applies (s. 2(2)). Its Table 1 marks designated substances with an asterisk and uses the same key values, such as benzene at 0.5 ppm and quartz at 0.10 mg/m³. The default excursion limits, 3 times the TWA for 30 minutes and 5 times at any time, don't apply to them (s. 4).
On construction, Reg. 833 sets the same silica limits, and section 3 puts substitution and engineering controls ahead of PPE. Section 6 requires air monitoring by or under a person qualified in industrial hygiene, and section 8 requires medical exams at the employer's expense where health may be affected. See the ministry's silica construction guidance.
Recent changes
From July 1, 2026, O. Reg. 114/26, 113/26 and 115/26 added CSA respirator approval and filter codes in 490/09, Reg. 833 and 278/05. Exposure limits did not change.
See the RegAffairs AI answer on Ontario designated substances.