Multi-Employer Construction Worksites and the Reality of Shared OHS Duties

Construction has always been different under occupational health and safety law. Even people outside the industry sense it. More hazards. More trades. More movement. More uncertainty. 

What is often underestimated is how fundamentally different construction is from a legal and enforcement perspective. 

On a multi-employer construction worksite, health and safety duties do not line up neatly with payroll, contracts, or job titles. Responsibility is shared, overlapping, and heavily influenced by who controls the work, the site, and the sequencing of activities. In Canada, that reality has been reinforced repeatedly through legislation, inspections, and prosecutions. 

For employers, supervisors, and project owners, this creates a dangerous gap between assumption and enforcement reality. Many still believe that OHS responsibility ends with their own workers. On a construction site, that belief rarely survives first contact with an inspector. 

This article looks at how shared OHS duties operate on Canadian multi-employer construction worksites, why enforcement routinely cuts across contractual boundaries, and what organizations must do to stay defensible in 2026 and beyond. 

Why Construction Is Treated Differently Under Canadian OHS Law 

Canadian OHS legislation recognizes that construction sites are not static workplaces. They are temporary, dynamic, and layered with multiple employers operating simultaneously. Because of that complexity, most jurisdictions impose additional duties that do not exist in single-employer environments. 

Concepts such as constructor, prime contractor, controlling employer, or project coordinator exist for one reason. Someone must be responsible for coordinating safety when hazards overlap and activities interact. 

Without that coordination, everyone becomes exposed. 

Regulators are explicit about this. When multiple employers operate on the same site, OHS duties do not fragment neatly. They stack. 

The Myth of Contractual Distance 

One of the most persistent myths in construction safety is that contracts define OHS responsibility. They do not. 

Contracts may allocate responsibilities between parties, but they do not override statutory duties. Canadian regulators and courts consistently prioritize actual control over contractual wording. 

If an organization controls the site, sequences the work, or has authority to correct unsafe conditions, it may attract OHS obligations regardless of how contracts are written. This principle is applied repeatedly in enforcement decisions across Canada. 

Inspectors do not ask first who signed which agreement. They ask who knew, who controlled, and who could have acted. 

A Common Scenario After a Serious Incident 

Consider a familiar construction scenario. 

A subcontractor employee is seriously injured after being struck by moving equipment. Multiple trades are working in the same area. The site is busy. Schedules are tight. The injured worker's employer followed its own safety procedures, but site-wide traffic control was inconsistent. 

During the investigation, inspectors examine far more than the subcontractor's program. They look at who coordinated site safety, who controlled access, who scheduled overlapping activities, and who had authority to stop unsafe work. 

Orders are issued not only to the injured worker's employer, but also to the constructor or prime contractor. In some cases, project owners are drawn into the investigation if they exercised sufficient control. 

From an enforcement perspective, shared risk creates shared responsibility. 

Constructor and Prime Contractor Duties in Practice 

In provinces such as Ontario and British Columbia, the constructor or prime contractor carries explicit responsibility for overall site safety. This does not mean other employers are relieved of their duties. It means someone has an added obligation to coordinate. 

That coordination duty is where many organizations fail. 

Being named constructor or prime contractor is not symbolic. It creates expectations around hazard identification, communication between trades, traffic control, scheduling, emergency response, and enforcement of site rules. 

Inspectors routinely test whether coordination exists in practice. Is there evidence that hazards created by one trade were communicated to others? Were conflicting activities managed? Were unsafe practices corrected regardless of which employer's workers were involved? 

When coordination exists only on paper, enforcement follows. 

Employers Cannot Outsource Their Own Duties 

While constructors and prime contractors carry heightened responsibilities, individual employers retain their own obligations to protect their workers. 

This dual responsibility often surprises employers. They assume that once a prime contractor is in place, their own OHS obligations shrink. They do not. 

Employers must still ensure their workers are trained, supervised, and equipped appropriately. They must still assess hazards specific to their tasks. They must still intervene when unsafe conditions exist, even if those conditions were created by others. 

Canadian enforcement makes this clear. Regulators frequently issue orders to both the constructor and individual employers following the same incident. Responsibility is not divided. It is shared. 

Supervisors Caught in the Middle 

Supervisors on multi-employer sites often face conflicting pressures. They answer to their employer but operate within a site controlled by someone else. They are expected to meet production targets while navigating site rules, changing conditions, and overlapping hazards. 

From a legal standpoint, supervisors remain agents of their employer. What they know, tolerate, or fail to correct can be attributed to the organization. 

This creates a significant risk when supervisors assume that site-wide safety issues are someone else's problem. Regulators do not accept that assumption. 

Supervisors are expected to escalate concerns, refuse unsafe work, and cooperate with site coordination mechanisms. Failure to do so is frequently cited in enforcement actions. 

Control, Not Proximity, Drives Responsibility 

One of the most important enforcement principles in multi-employer construction sites is that responsibility follows control. 

Control can take many forms. Control over the site layout. Control over scheduling. Control over access points. Control over equipment movement. Control over sequencing of work. 

An employer or owner who exercises control cannot ignore the safety consequences of that control. This is particularly relevant for project owners who take an active role in directing work. 

Canadian regulators have repeatedly emphasized that owners who cross the line from oversight into operational control may attract OHS obligations they did not anticipate. 

Shared Hazards Are the Most Dangerous 

The highest-risk hazards on construction sites are often shared hazards. Vehicle and pedestrian interaction. Falls through floor openings created by another trade. Electrical hazards exposed during sequencing. Simultaneous operations that interfere with each other. 

These hazards do not belong to a single employer. They exist because multiple activities intersect. 

This is why coordination is central to construction OHS. When shared hazards are not managed collectively, enforcement risk increases sharply. 

Inspectors consistently ask whether hazards created by one employer were communicated to others and whether corrective action was coordinated across trades. Silence or fragmentation is interpreted as failure. 

Enforcement Focus Has Intensified 

In recent years, Canadian regulators have increased enforcement activity on construction sites, particularly where serious injuries or fatalities occur. Multi-employer sites receive heightened scrutiny because of their inherent complexity. 

Investigations often expand outward from the immediate incident to examine systemic coordination failures. Orders, penalties, and prosecutions may follow even when the injured worker was not employed by the cited organization. 

The rationale is clear. Construction sites are inherently dangerous. The law expects those who benefit from the work to actively manage those dangers. 

Jurisdictional Differences That Matter on Construction Sites 

While core principles are consistent across Canada, some jurisdictional differences affect how shared duties are applied. 

Across jurisdictions, the theme is the same. Multi-employer complexity increases, rather than reduces, OHS expectations. 

Documentation and Communication Are Central to Defence 

One of the most common weaknesses exposed during inspections is poor documentation of coordination efforts. 

Meetings occur but are not recorded. Hazards are discussed but not tracked. Instructions are given verbally but not documented. When incidents occur, there is little evidence of what was known or done. 

In enforcement terms, undocumented coordination may as well not exist. 

Effective documentation does not need to be excessive. What matters is that it demonstrates active management of shared hazards. Site orientations, coordination meetings, hazard alerts, and corrective action records all contribute to a defensible position. 

Integrating Shared Duties Into Safety Systems 

The most effective construction organizations treat shared OHS duties as a core part of their safety system, not an administrative add-on. 

This means aligning internal procedures with site-wide expectations, training supervisors to operate within shared responsibility frameworks, and ensuring that escalation pathways are clear when hazards extend beyond a single employer's control. 

When shared duties are integrated rather than assumed, safety becomes more predictable and enforcement risk decreases. 

A Reality Check for Construction Employers and Owners 

Multi-employer construction sites expose a truth that many organizations resist. Health and safety responsibility cannot be neatly outsourced or contained. 

Canadian OHS law reflects this reality. Responsibility follows influence, control, and knowledge. Where work overlaps, duties overlap. 

For construction employers, supervisors, and owners in 2025, the question is no longer whether shared duties exist. It is whether the organization understands them well enough to act before an inspector forces the issue. 

Constructor and Prime Contractor OHS Checklist 

Managing Shared Duties on Multi-Employer Construction Sites in Canada 

Purpose: This checklist helps constructors and prime contractors assess whether shared occupational health and safety duties are being actively managed on multi-employer construction sites. It reflects Canadian enforcement expectations, not best-case theory. 

Answer based on what actually happens on site, not what contracts say. 

Use the following scale: 

• Yes = Consistently in place and documented. 
• Somewhat = Exists but informal, inconsistent, or undocumented. 
• No = Missing, unclear, or assumed. 

Section 1: Constructor / Prime Contractor Designation and Authority 

1. The constructor or prime contractor has been formally designated in writing and communicated to all employers on site.
    Yes  Somewhat  No
   
2. The constructor or prime contractor understands that this role carries statutory duties, not just administrative coordination.
    Yes  Somewhat  No 
3. Authority to enforce safety rules, issue stop-work directions, and correct unsafe conditions is clearly defined and exercised in practice.
    Yes  Somewhat  No 
4. Employers and supervisors on site understand who has overall responsibility for coordination of health and safety.
    Yes  Somewhat  No 

Why This Matters
Inspectors focus early on whether coordination authority exists and whether it is real. A named constructor or prime contractor without practical authority creates immediate exposure. 

Section 2: Site-Wide Hazard Identification and Coordination 

1. Site-wide hazard assessments address hazards created by overlapping trades and activities, not just individual employer tasks.
    Yes  Somewhat  No 
2. Shared hazards such as vehicle-pedestrian interaction, fall openings, energized systems, and simultaneous operations are identified and controlled.
    Yes  Somewhat  No 
3. Hazard information is communicated to all affected employers and workers, not only the trade that created the hazard.
    Yes  Somewhat  No 
4. Changes in work sequencing trigger updated hazard communication.
    Yes  Somewhat  No 

Why This Matters
Most serious construction incidents involve shared hazards. Regulators expect coordination, not fragmentation. 

Section 3: Contractor and Subcontractor Safety Integration 

1. Contractors and subcontractors are reviewed for safety competency before starting work.
    Yes  Somewhat  No 
2. Site-specific safety rules and expectations are communicated through a documented orientation process.
    Yes  Somewhat  No 
3. Contractors understand that site rules apply regardless of their internal policies.
    Yes  Somewhat  No 
4. There is a process to address contractors who do not comply with site safety requirements.
    Yes  Somewhat  No 

Why This Matters
Contracts do not replace oversight. Inspectors assess whether expectations were verified and enforced. 

Section 4: Supervisor Roles and Escalation 

1. Supervisors understand their role in managing shared hazards, not just their own crew's tasks.
    Yes  Somewhat  No 
2. Supervisors know when and how to escalate safety concerns to the constructor or prime contractor.
    Yes  Somewhat  No 
3. Supervisors feel supported when stopping work due to site-wide safety concerns.
    Yes  Somewhat  No 
4. Unsafe conditions created by one employer are addressed even if they do not affect the constructor's own workers directly.
    Yes  Somewhat  No 

Why This Matters
Supervisors are agents of their employers. Regulators do not accept "that was someone else's problem" as a defence. 

Section 5: Site Rules, Traffic Control, and Work Sequencing 

1. Site rules address high-risk activities that affect multiple employers.
    Yes  Somewhat  No 
2. Traffic control plans are site-wide and enforced consistently.
    Yes  Somewhat  No 
3. Work sequencing is planned to reduce interference between trades.
    Yes  Somewhat  No 
4. Changes to schedules consider health and safety impacts, not only production pressure.
    Yes  Somewhat  No 

Why This Matters
Regulators increasingly examine whether scheduling decisions contributed to unsafe conditions. 

Section 6: Incident, Near-Miss, and Hazard Reporting 

1. All incidents and near misses involving shared hazards are reported and reviewed at the site level.
    Yes  Somewhat  No 
2. Investigations examine coordination failures, not just individual worker actions.
    Yes  Somewhat  No 
3. Corrective actions are communicated to all affected employers.
    Yes  Somewhat  No 
4. Repeat hazards trigger broader site-wide controls.
    Yes  Somewhat  No 

Why This Matters
Regulators use near-miss and incident history to establish what the constructor or prime contractor knew before a serious event. 

Section 7: Documentation and Inspection Readiness 

1. Records of site orientations, coordination meetings, and safety communications are maintained.
    Yes  Somewhat  No 
2. Corrective actions and follow-up are documented.
    Yes  Somewhat  No 
3. The constructor or prime contractor can quickly demonstrate how shared hazards are managed.
    Yes  Somewhat  No 
4. There is clarity on who speaks to inspectors and how information is provided.
    Yes  Somewhat  No 

Why This Matters

Undocumented coordination is treated as absent coordination during inspections. 

Scoring and Interpretation 

• 24–28 Yes responses
  Strong coordination and defensible oversight. Maintain consistency and monitor change. 
• 16–23 Yes responses
  Partial compliance. Shared-duty exposure is present and likely during an inspection. 
• Below 16 Yes responses
  High enforcement risk. Shared hazards are not being actively managed. 

This score does not predict incidents. It predicts how regulators will interpret responsibility if one occurs. 

Using This Checklist in OHS Insider 

Each "Somewhat" or "No" should trigger: 

• A corrective action. 
• Supporting documentation or tools. 
• Supervisor coaching or training.