On 14 December 2011, the High Court of Australia handed down its decision in Amaca Pty Ltd v Booth  HCA 53. The decision has been anticipated by practitioners in dust disease matters, as it deals with the difficult issue of liability for mesothelioma as between multiple defendants. The result of the decision is that it will be easier for plaintiffs with mesothelioma, whose history of asbestos exposure presents them with multiple defendants, to succeed in recovering damages from all of them.
The appellants, Amaca Pty Ltd (Amaca) and Amaba Pty Ltd (Amaba), were the manufacturers of asbestos used in brake linings, which the trial judge found to have constituted 70% of the asbestos that the plaintiff inhaled over the course of his life. It was not in issue that inhalation of asbestos fibres was the cause of his mesothelioma.
Mr Booth had succeeded against Amaca and Amaba in the NSW Dust Diseases Tribunal (DDT). the NSW Court of Appeal upheld the trial judge's findings, and the defendants appealed to the High Court, presenting this as a test case.
Causation in mesothelioma cases where a plaintiff has been exposed to different types of asbestos at different times, produced by different defendants, has caused some difficulty for common law rules of causation.
For a defendant to be legally liable for causing a plaintiff's injury, it must be proved that it is more probable than not that the defendant's negligent conduct caused or materially contributed to the plaintiff's injury. There are two elements to this test: the defendant's negligent conduct must be a cause or make a material contribution to the injury; and, this factual causation must be proved on the balance of probabilities.
The difficulty for this legal test in mesothelioma cases is that medical science is not certain as to the mechanism by which mesothelioma is caused. This causes problems of factual causation, and proof to the required standard.
To understand this problem, it is helpful to look at how the UK courts have dealt with it. Lord Bingham of Cornhill summed up the state of medical opinion in the UK in 2000 in Fairchild v Glenhaven Funeral Services  1 AC 32 in these terms: "the condition may be caused by a single fibre, or a few fibres, or many fibres: medical opinion holds none of these possibilities to be more probable than any other, and the condition once caused is not aggravated by further exposure". If this is the accepted expert opinion on causation, the difficulty for a plaintiff who was exposed to asbestos while working for three employers, for example, in holding any of them liable is clear: it cannot be proved to be more probable than not that any particular exposure caused their injury. The UK courts therefore adopted a special rule of causation in such cases, which said that if a defendant's negligent conduct materially increased the risk of injury, then they may be liable. in this way, a plaintiff could succeed against all three employers.
Such a rule has not been adopted in Australia. The test is: is it more probable than not that the negligence of the defendant was a cause of the plaintiff's injury: Amaca Pty Ltd v Ellis (2010) 240 CLR 111 at .
The trial judge in Mr Booth's case found that all exposure to chrysotile asbestos, other than trivial or de minimis exposure, materially contributed to the cause of the plaintiff's mesothelioma. On this basis, he held both Amaca and Amaba liable.
In the High Court, Amaca and Amaba contended that by so finding, the trial judge had introduced into Australian law a de facto test of causation that holds a defendant liable if their conduct increases the risk of injury, not if their conduct was proved to have caused or materially contributed to the injury.
The High Court found 4 to 1 against Amaca and Amaba the appellants, and upheld the trial judge's finding in favour of the plaintiff.
The majority did not, however, adopt any special rule of causation in mesothelioma cases. They resolved the appeal by finding that the trial judge's finding of fact was open on the evidence. As they saw it, the case turned on the acceptance by the trial judge of the evidence of Dr Leigh and Professor Henderson that the 'single fibre theory' of causation is discredited, and that all exposure to asbestos contributes to the causation of mesothelioma.
Chief Justice French agreed with Gummow, Hayne and Crennan JJ, but wrote a separate opinion. He gave detailed consideration to the link between causation and proof based on epidemiology. He said (at ):
The Chief Justice appears to be saying here that where epidemiology provides statistical support for a correlation between conduct and injury at the population level, and medical science supports factual causation between the same conduct and the same injury at the biological level, an appropriate expert can draw the inference that the particular defendant's conduct caused the particular plaintiff's injury that satisfies the test for legal causation.
Justice Heydon, in dissent, considered that the trial judge had adopted a test of causation based on risk: at . He said that "[e]ach exposure to asbestos increased his risk of developing mesothelioma. it does not follow that each exposure caused the mesothelioma": at .
Mr Booth was awarded damages of $326,640 at first instance in the DDT, against Amaca and Amaba. The result of the High court decision is that Mr Booth's judgment stands.
More broadly, however, this is a significant result for plaintiffs in mesothelioma cases, and certainly puts them in a better position than plaintiffs that seek damages for asbestos-induced lung cancer who have a history of smoking. It will make it easier to succeed against multiple defendants, as it can no longer be contended that a plaintiff must prove which defendant's negligent conduct was the cause of the mesothelioma.
In the DDT, in particular, it means that Judge Curtis' finding that "all exposures to chrysotile asbestos, other than trivial or de minimis exposure, occurring in a latency period of between 25 and 56 years, materially contributes to the cause of mesothelioma" stands for the purposes of section 25B of the Dust Diseases Tribunal Act 1989 (NSW), which means that this issue may not be re-litigated without leave of the tribunal. This eases the burden of proof on future claimants in a similar position to Mr Booth.
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