Ratio Decidendi
Where a disease is caused by cumulative exposure, it is sufficient for the claimant to show that the defendant's breach made a material contribution to the injury. The claimant need not show that the breach was the sole or dominant cause.
Facts
Wardlaw contracted pneumoconiosis from inhaling silica dust at work. The dust came from two sources: swing grinders (for which adequate extraction was not provided, in breach of duty) and pneumatic hammers (for which there was no known precaution). Both sources contributed to the disease.
Judgment Summary
The House of Lords held that the employer was liable. The dust from the swing grinders (the negligent source) materially contributed to the disease, even though the dust from the pneumatic hammers also contributed. The claimant did not need to prove which source caused the disease.
Key Quotes
"What is a material contribution must be a question of degree. A contribution which falls outside the de minimis range is material."
— Lord Reid
Subsequent Treatment
Leading authority on material contribution to injury. Distinguished from material contribution to risk (Fairchild v Glenhaven [2002]).