Causation in WHS Litigation: 'But For' and Material Contribution Tests

Why Causation Is Often the Hardest Element in WHS Claims

In many WHS matters, breach of the duty of care is relatively straightforward to establish once the expert evidence is before the court. What proves harder is causation: demonstrating that the breach actually caused the injury, not just that a breach existed. A duty holder who failed to implement a control may argue that the injury would have occurred even if the control had been in place. Where that argument has any traction, the causation element becomes the central battleground.

Causation in WHS claims involves both legal causation tests applied by the court and expert analysis addressing the factual connection between the breach and the injury. The WHS expert addresses the factual causation question: given what happened, would adequate controls have prevented the injury or materially reduced the risk that the injury occurred?

The 'But For' Test in Workplace Injury

The primary causation test applied in negligence and breach of statutory duty claims is the 'but for' test: but for the defendant's breach, would the plaintiff's injury have occurred? If the answer is no, the breach caused the injury. If the answer is yes, even with the breach, the injury would have occurred, the 'but for' test is not satisfied.

In WHS matters, the 'but for' question is often framed as: if the employer had implemented the control that was missing, would the incident have been prevented? Where the missing control would clearly have prevented the incident, for example edge protection preventing a fall from an unguarded edge, the 'but for' causation is straightforward. Where the connection is less direct, the analysis becomes more complex.

Material Contribution to Risk

Where the 'but for' test cannot be strictly satisfied, courts have accepted the material contribution to risk test in appropriate circumstances. This test asks whether the breach materially contributed to the risk of injury materialising, even if it cannot be proved that the breach was the sole or primary cause of the injury. The material contribution test is particularly relevant in cumulative exposure cases, disease claims and psychological injury matters where the causal chain is complex.

In psychosocial injury claims, for example, it may be impossible to prove that any single workplace failure was the 'but for' cause of a psychological condition. But where multiple failures each contributed to the cumulative psychosocial hazard exposure that caused the condition, the material contribution framework allows the court to find causation where each failure materially contributed to the risk.

Multiple Contributing Factors and Apportionment

Most serious workplace injuries involve multiple contributing factors. The incident may have involved a combination of an inadequate risk assessment, inadequate training, a defective piece of equipment and the worker's own momentary inattention. Expert analysis identifies each contributing factor, assesses its relative contribution to the incident and addresses whether any factor was so dominant as to break the chain of causation from the earlier failures.

Where the worker's own conduct contributed to the injury, contributory negligence may reduce the damages awarded. Expert analysis can address whether the worker's conduct was itself the product of inadequate training or inadequate supervision, which may limit the contributory negligence reduction. Multiple defendant matters raise apportionment questions between duty holders with concurrent obligations.

Documents That Strengthen Causation Evidence

• The employer's own incident investigation report, particularly any root cause analysis
• Regulator investigation reports where SafeWork or WorkSafe investigated the incident
• Risk assessments conducted before the incident, showing the hazard was or should have been identified
• Records of prior similar incidents or near misses at the same workplace
• Maintenance and inspection records showing the known condition of equipment
• Training records showing what the worker was or was not trained to do
• Workplace photographs and CCTV footage capturing the physical conditions

For the causation analysis service, see causation analysis. For the broader breach and liability framework, see breach analysis and liability. The foreseeability threshold that precedes causation is addressed in foreseeability in WHS litigation.