Ontario Occupational Health and Safety: Employer Duties, OHSA, and Workplace Investigations

March 2026 · 14 min read

Ontario's Occupational Health and Safety Act, RSO 1990, c O.1 (OHSA) is the primary statute governing workplace health and safety. It imposes obligations on employers, supervisors, owners, constructors, and workers, and creates significant enforcement and liability exposure. Employment lawyers advising on workplace injuries, harassment investigations, and regulatory compliance must understand the full OHSA framework.

1. Scope and Application

The OHSA applies to virtually all Ontario workplaces — manufacturing, construction, offices, healthcare, retail, and hospitality. Certain sectors have sector-specific regulations that elaborate on the general OHSA framework:

• Industrial Establishments Regulation (O. Reg. 851)
• Construction Projects Regulation (O. Reg. 213/91)
• Health Care and Residential Facilities Regulation (O. Reg. 67/93)
• Mines and Mining Plants Regulation (O. Reg. 854)

Federal undertakings (banks, airlines, telecommunications, interprovincial transport) are governed by the Canada Labour Code, Part II, not OHSA.

2. Core Employer Duties — Section 25

Section 25 of the OHSA imposes broad duties on employers. The most important:

• s. 25(1)(a): Provide and maintain equipment, materials, and protective devices as prescribed.
• s. 25(1)(b): Ensure equipment, materials, and protective devices are used as prescribed.
• s. 25(2)(a): Provide information, instruction, and supervision to a worker to protect health and safety.
• s. 25(2)(h) — the overarching duty: Take every precaution reasonable in the circumstances for the protection of workers. This is the residual "catch-all" duty and is frequently the basis for Ministry of Labour prosecutions.

The "take every precaution reasonable" standard is objective — the employer is measured against what a reasonable employer in similar circumstances would have done. Ignorance of a hazard is not a defence if the hazard was reasonably foreseeable.

3. Supervisor Duties — Section 27

Supervisors bear personal duties under s. 27. A supervisor must:

• Ensure workers comply with the OHSA and regulations
• Ensure workers use required equipment and protective devices
• Advise workers of actual and potential hazards
• Take every precaution reasonable in the circumstances

Supervisors can be personally prosecuted. Individual convictions of supervisors — resulting in fines up to $100,000 or 12 months imprisonment (or both) — are not uncommon following serious workplace injuries.

4. Worker Rights

4.1 Right to Know

Workers have the right to know about actual and potential hazards in the workplace. This includes WHMIS (Workplace Hazardous Materials Information System) labelling and Safety Data Sheets for hazardous materials.

4.2 Right to Participate

Workers have the right to participate in identifying and resolving workplace health and safety concerns — primarily through the Joint Health and Safety Committee (JHSC).

4.3 Right to Refuse Unsafe Work — Sections 43–45

A worker may refuse work where they have reasonable grounds to believe the work is likely to endanger themselves or another worker. The refusal procedure:

1. Worker notifies supervisor or employer of the refusal and the reasons
2. Supervisor and worker (and JHSC worker member or worker health and safety representative, if any) investigate
3. If the matter is not resolved, the worker may continue the refusal
4. Either party may request a Ministry of Labour inspector to investigate (s. 44)
5. The inspector investigates and issues a decision in writing

Pending investigation, the employer may assign the refusing worker to other reasonable work. The employer may direct another worker to perform the work — but must first inform that worker of the refusal and the reasons.

5. Joint Health and Safety Committee (JHSC)

Workplaces with 20 or more regularly employed workers must have a JHSC under s. 9. The JHSC:

• Must include at least two members — at least one management and one worker representative
• Worker members must be certified under s. 9(12) — must complete a Ministry-approved certification training program
• Must meet at least quarterly (monthly if the workplace had a lost-time injury rate above average)
• Must conduct workplace inspections at least monthly (rotating portions of the workplace)
• Must investigate serious accidents (critical injuries or fatalities)
• Has the right to make recommendations to the employer — the employer must respond in writing within 21 days

Workplaces with fewer than 20 workers but at least 6 must have a health and safety representative (s. 8) with similar but reduced functions.

6. Critical Injury and Fatality Reporting

Section 51 requires immediate notification to the Ministry of Labour when a worker is killed or critically injured at a workplace. "Critical injury" is defined in O. Reg. 834 and includes: fracture of the skull, spine, pelvis, arm, leg, or wrist; amputation; loss of sight; internal haemorrhage; burns; loss of consciousness from any cause.

Section 51 also requires preserving the scene: the employer must ensure the scene is not disturbed except to rescue a worker, prevent further injury, or comply with an order of an inspector. Tampering with a scene after a critical injury or fatality is a serious offence.

A written report must follow within 48 hours describing the accident. The employer must also notify the JHSC co-chairs.

7. Workplace Violence and Harassment — Bill 168 (2009)

Ontario's Bill 168 (2009) amended the OHSA to add specific requirements for workplace violence and harassment (ss. 32.0.1–32.0.7). These obligations apply to all Ontario employers:

7.1 Workplace Violence

• Policy required (s. 32.0.1): Employer must prepare and review at least annually a written workplace violence policy.
• Program required (s. 32.0.2): Employer must develop a workplace violence program to implement the policy — including measures and procedures to control identified risks, summoning immediate assistance, and reporting to the employer.
• Risk assessment (s. 32.0.3): Employer must assess the risk of workplace violence from the nature of the workplace, type of work, and conditions of work. The assessment must be reviewed at least annually or when a new circumstance arises.
• Domestic violence disclosure (s. 32.0.4): Where an employer becomes aware — or ought reasonably to be aware — that domestic violence may come into the workplace and expose a worker to physical injury, the employer must take every precaution reasonable.

7.2 Workplace Harassment

Workplace harassment is defined in s. 1 as engaging in a course of vexatious comment or conduct that is known or ought reasonably to be known to be unwelcome. It includes harassment on prohibited grounds under the Human Rights Code and sexual harassment.

Bill 132 (2016) strengthened workplace harassment requirements by requiring employers to:

• Develop a written workplace harassment policy (s. 32.0.1(1)(b))
• Establish a workplace harassment program addressing investigation procedures
• Ensure reported incidents are investigated appropriately (s. 32.0.7)
• Provide written results of the investigation to the complainant and respondent
• Inform the complainant of any corrective action taken

The Ministry of Labour may appoint an investigator if it determines that an employer's investigation was inadequate. This "ministry investigator" mechanism was introduced by Bill 132 and has been used in high-profile cases.

8. Reprisals — Section 50

Section 50 prohibits reprisals against workers who exercise rights under the OHSA — including refusing unsafe work, participating in JHSC activities, seeking enforcement, or giving evidence in proceedings. A reprisal is defined broadly to include dismissal, discipline, penalty, or threat.

The burden of proof is reversed: once a worker establishes that they exercised an OHSA right and suffered an adverse employment action, the employer must prove the action was not a reprisal. This reversal significantly strengthens the worker's position.

Reprisal complaints are filed with the Ontario Labour Relations Board (OLRB) — not the Ministry of Labour. The OLRB may reinstate the worker, award lost wages, and impose civil penalties. The OLRB process is faster and less formal than civil litigation.

9. Ministry of Labour Inspections and Enforcement

Ministry of Labour inspectors have broad powers under s. 54: to enter workplaces without notice, inspect and take samples, examine documents and records, and issue orders.

An inspector may issue:

10. Offences and Penalties — Section 66

OHSA offences are quasi-criminal (regulatory). Convictions carry significant consequences:

• Individual (worker, supervisor): Fine up to $100,000 and/or 12 months imprisonment.
• Corporation: Fine up to $1,500,000.
• Director/officer: Where they directed, authorized, assented to, acquiesced in, or participated in the offence — personally liable to the same fines and imprisonment as an individual.

The Ministry has ramped up prosecutions following serious workplace fatalities. High-profile convictions — including in the construction, mining, and food processing sectors — have resulted in fines in the millions of dollars.

The due diligence defence is available: the defendant must prove they took every precaution reasonable in the circumstances. The burden of establishing due diligence is on the defendant on a balance of probabilities.

11. Practical Considerations for Employment Lawyers

• Scene preservation is critical: Following a critical injury or fatality, advise the employer immediately to preserve the scene and document the condition of equipment, materials, and the work area. Contemporaneous photographs and measurements are essential.
• Privilege considerations: Internal investigation reports prepared in anticipation of OHSA prosecution may attract solicitor-client privilege if counsel is engaged immediately. Engage criminal/regulatory counsel promptly after any serious incident.
• Separate the internal investigation from the regulatory response: The OHSA harassment investigation obligation and a potential HRTO complaint are distinct processes. Ensure the internal investigation is documented and defensible independently of any regulatory proceeding.
• Directors and officers personal liability: Advise directors and officers that "I didn't know" is not a defence if they ought to have known. Strong OHS management systems, documented training programs, and safety audits are the best protection.
• Limitation period for OLRB reprisal complaints: A reprisal complaint under s. 50 must be filed with the OLRB within 60 days of the reprisal. This is a hard deadline with limited ability to extend.

Conclusion

Ontario's OHSA imposes substantial obligations on employers, supervisors, and directors. The combination of regulatory prosecution risk, stop-work orders, JHSC requirements, and the growing enforcement of workplace harassment obligations means that employment lawyers must be well-versed in the Act. The due diligence defence rewards employers who build genuine OHS management systems — not just paper policies.