Facts
- The claimant, a worker (C), developed pneumoconiosis, a lung disease caused by inhaling silica dust during employment at Bonnington Castings Ltd.
- C was exposed to silica dust from two sources: unavoidable dust generated by pneumatic hammers (non-negligent), and dust from swing grinders, attributable to the employer’s negligent maintenance.
- The disease resulted from a gradual accumulation of silica particles in the lungs.
- Only part of the exposure was due to the employer’s negligence.
- The dispute centered on whether the employer was liable given that the negligent exposure was only a portion of the total dust inhaled.
Issues
- Whether the employer could be held liable for negligence when the claimant’s exposure to harm arose from both negligent and non-negligent sources.
- Whether the defendant’s actions needed to be the sole or primary cause of harm, or if a material contribution sufficed to establish causation.
- Whether application of the traditional “but for” test or the “material contribution test” was appropriate in the context of cumulative causes.
Decision
- The House of Lords held the employer liable, finding that their negligence made a material (more than negligible) contribution to C’s pneumoconiosis.
- It was not necessary to determine that the negligent exposure was the probable or main cause of harm.
- The court departed from the strict “but for” test, holding that a significant contribution was sufficient where injury resulted from cumulative causes.
- Full compensation was awarded to the claimant because the employer’s breach materially contributed to the injury.
Legal Principles
- The “material contribution test” applies where injury arises from cumulative exposures, and the defendant’s tortious conduct is a more than negligible factor.
- The test differs from the “material increase in risk” approach, which applies where individual contributions to an indivisible injury cannot be identified.
- The material contribution test is appropriate for divisible injuries (e.g., pneumoconiosis) where additional exposure increases severity, but not for indivisible injuries (e.g., lung cancer).
- Proportional damages may now apply in similar factual contexts due to later case law development.
- Employers are responsible for ensuring that avoidable harmful exposures in the workplace are minimized, even where some level of exposure is unavoidable.
Conclusion
Bonnington Castings Ltd v Wardlaw established that an employer can be held liable if their negligence materially contributes to a claimant’s divisible injury, even where non-negligent factors are also present. This case created a key distinction between cumulative causation and increased risk, clarifying the legal framework for causation in occupational disease claims and delineating the proper use and limits of the material contribution test.
