Abstract: This case concerns three appeals, heard together, which resulted from actions brought by employees who had developed the mesothelioma disease as a result of being exposed at work to asbestos dust. In these actions, the claimants sought compensation against employers who had exposed them to substantial inhalation of asbestos dust or fibres. At first instance, two of the claims were dismissed on the basis that the claimants could not establish, on a balance of probabilities, which of the defendants had exposed the employee to the asbestos dust which caused the disease. In the third case the judge found that, by exposing the claimant to asbestos fibres, the defendant had materially contributed to, and thus caused, the occurrence of mesothelioma. He accordingly apportioned liability between the defendants. The claimants in the first two actions, and the defendants in the third, appealed. Before the Court of Appeal it was common ground that (a) the mechanism initiating the genetic process which culminated in mesothelioma was unknown, (b) the factor triggering off the disease might, with an equal degree of probability, be a single, a few or many fibres, and (c) the condition, once caused, was not aggravated by further exposure – however, the greater the quantity of fibres inhaled the greater the risk of developing the disease. This caused the Court of Appeal to conclude that, since mesothelioma was an indivisible disease triggered on a single unidentifiable occasion by one or more fibres on a single unidentifiable occasion, it could not be proved on a balance of probabilities which period of exposure had caused the disease. The Court accordingly held that the claimant in each case had failed to establish causation against any of the defendants. It accordingly dismissed the appeals in the first two cases and allowed the appeal in the third case.
The claimants appealed to The House of Lords, which overturned these decisions. The Law Lords held that, where an employee had been exposed by different defendants, during different periods of employment, to inhalation of asbestos dust, in breach of each defendant’s duty to protect him from the risk of contracting mesothelioma, and where that risk had arisen but, in current medical knowledge, the onset of the disease could not be attributed to any particular or cumulative wrongful exposure, a modified approach to proof of causation was justified. In such cases, evidence that each defendant’s wrongdoing had materially increased the risk of contracting the disease was sufficient to satisfy the causal requirements for his liability. Accordingly, applying that approach and in the circumstances of each case, the claimants could prove, on a balance of probabilities, the required causal connection to establish the defendants’ liability.European Review of Private Law