Turning Legal Responsibility into Documented Due Diligence
Ontario’s Occupational Health and Safety Act (OHSA) Part III assigns clear legal duties to employers, supervisors, and owners.
The Act requires due diligence by the employer. That means taking every reasonable precaution in the circumstances for the protection of workers — and being able to demonstrate that you did.
For many organizations, the gap is not intent. It is documentation, technical assessment, and defensibility.
This guide explains what Part III requires and how duty-holders can translate those obligations into practical, defensible action.
Who Has Duties Under OHSA Part III?
OHSA does not assign responsibility to “the company” in a general sense. It assigns duties directly to specific roles.
Employers (Sections 25 and 26)
If you employ workers in Ontario, you are responsible for:
- Providing information and instruction regarding workplace hazrds and supervision to workers
- Ensuring equipment, materials, and protective devices are provided and maintained in good condition, have proper fit and are used as prescribed
- Taking every reasonable precaution in the circumstances
- Complying with applicable regulations (e.g., designated substances, noise, chemical exposure limits)
Where Employers Commonly Face Risk
- Exposure monitoring is outdated or never formally conducted
- Indoor air quality complaints are handled informally
- Health and safety programs exist but are not supported by technical assessments
- Medical surveillance requirements are unclear or undocumented
Due diligence requires more than having a policy. It requires evidence.
Owners and Project Owners (Sections 29–30)
Owners have independent obligations under OHSA. These duties apply even if contractors are retained.
These duties include:
- Ensuring required assessments are completed before work begins
- Identifying designated substances prior to tendering and provide this information as part of the tender process
- Providing contractors with accurate hazard information
A Common Misunderstanding
Hiring a contractor does not transfer liability.
If hazardous building materials are missed in a pre-tender assessment, the owner may still face regulatory scrutiny.
Defensibility begins before the project starts.
Supervisors (Section 27)
Supervisors have personal statutory duties, including:
- Ensuring workers comply with OHSA and regulations
- Advising workers of known hazards
- Ensuring that workers wear equipment, protective devices and clothing as required by the employer
- Taking reasonable precautions in the circumstances
Supervisors are often placed in a position of responsibility without having access to specialized technical expertise.
When ventilation performance, airborne exposure, or hazardous materials are involved, “reasonable precautions” may require professional input from third-party experts.
What Does “Every Precaution Reasonable” Actually Mean?
This phrase is central to OHSA enforcement.
In practice, inspectors evaluate whether:
- Hazards were formally identified
- Risks were measured where appropriate
- Controls were selected based on recognized standards
- Documentation supports decisions made
After an incident or inspection, the question becomes:
Was the organization able to demonstrate due diligence?
If the above items were not assessed and documented, due diligence would be difficult to defend.
Where Technical Assessments Support Due Diligence
Many OHSA obligations intersect with areas requiring specialized expertise.
Examples include:
Occupational Hygiene Monitoring
Airborne contaminants (e.g., silica, asbestos), noise, and other exposures require measurement — not assumption.
Indoor Air Quality and Ventilation Assessments
Complaints about odours, comfort, or ventilation performance can escalate into regulatory review if not properly evaluated.
Designated Substance Surveys
Before renovation or demolition, designated substances must be identified and documented.
Health and Safety Programs and Training
Programs must reflect actual site conditions and risks, not generic environments.
Technical assessment strengthens the defensibility of your health and safety framework.
Documentation Is Not Administrative — It Is Legal Protection
In an inspection or investigation, documentation demonstrates:
- Hazard identification
- Engineering and administrative controls implemented by the employer
- Professional evaluation of risks and controls
- Reasoned decision-making
Documentation is evidence that the owner, employer and supervisor are doing their due diligence in order to protect workers from hazards.
A Practical Approach to OHSA Part III Compliance
Rather than reacting to inspections or complaints, many organizations take a structured approach:
- Identify legal duties by role (Employer, Owner, Supervisor)
- Conduct gap assessments against regulatory requirements
- Perform technical evaluations where necessary
- Update policies and training to reflect real findings
- Maintain defensible documentation
This approach shifts compliance from reactive to proactive.
How THEM Supports Ontario Duty-Holders
THEM works with employers, owners, and supervisors across Ontario to translate OHSA duties into practical, defensible action.
Our services include:
- Occupational hygiene exposure monitoring
- Indoor air quality and ventilation assessments
- Designated Substance Surveys
- Health and safety program development and review
- Supervisor-focused compliance support
We focus on clarity, documentation, and defensibility — not alarmism.
Next Step: Evaluate Your Current Position
If you are unsure whether your current programs would withstand regulatory scrutiny, the first step is a structured review.
Contact THEM to:
- Discuss your obligations under OHSA Part III
- Review your current documentation
- Identify gaps before they become issues
Call us or email our team to start the conversation.