On 3 March 2010, the High Court delivered an important decision, holding that the asbestos exposure of a smoker who died of lung cancer was not, on its own, a cause of injury, even when the medical and scientific evidence available was unable to definitely attribute the cancer to any particular cause.
Paul Cotton died of lung cancer. He had smoked between 15 and 20 cigarettes a day for over 26 years. He was also exposed to respirable asbestos fibres in the course of his employment with the South Australian Engineering and Water Supply Department (EWSD) and then later with Millennium Inorganic Chemicals Ltd (Millennium). During his employment with EWSD, Mr Cotton worked with asbestos cement pipes manufactured by Amaca (formerly James Hardie & Co Pty Ltd) (Amaca). The executor of Mr Cotton's estate, Teresa Ellis (the plaintiff), sued EWSD, Millenium and Amaca (the defendants) in negligence for a breach of duty to provide safe working conditions for Mr Cotton which caused his death.
The issue for determination by the High Court was causation. The essential question was whether the plaintiff had shown that it was more probable than not that the negligence of each defendant was a cause of Mr Cotton's lung cancer. Ultimately, to show this, the plaintiff had to establish that Mr Cotton's exposure to respirable asbestos fibres was, on its own, more probably than not, a cause of his lung cancer.
No expert evidence was available to say definitively what had caused Mr Cotton's cancer. The only evidence available was of an epidemiological nature.
The evidence showed that the relative risk of cancer due to smoking was greater than that due to exposure to asbestos. None of the expert witnesses assigned a probability of greater than 23 per cent to Mr Cotton's cancer being caused by asbestos exposure (or a combination of asbestos exposure and smoking). However, all expert witnesses assigned not less than a 67 per cent chance to Mr Cotton's cancer being caused by smoking alone.
One of the experts, a consultant occupational physician and epidemiologist, suggested that smoking and asbestos exposure had a synergistic effect by operating interdependently and cumulatively to cause lung cancer. However, he also said it was possible to partition attributability to smoking and asbestos under mathematical risk models. The High Court, reading that expert's opinion as a whole, concluded that the expert did not mean that when a smoker has been exposed to asbestos and develops lung cancer, the asbestos exposure is, or is probably, a cause of that cancer.
In rejecting the approach of looking at the risks to Mr Cotton developing lung cancer in isolation of each other, the trial judge in the Supreme Court had found in favour of the plaintiff. The trial judge accepted the medical evidence that the synergistic effect between smoking and asbestos exposure caused the two to operate cumulatively towards lung cancer. On that basis, it was found that Mr Cotton's asbestos exposure materially contributed to his lung cancer.
The trial judge's approach to establishing a causal connection between the asbestos exposure and the lung cancer was to assume that Mr Cotton's cumulative exposure to asbestos, by the negligence of more than one defendant, was sufficient to establish the relevant nexus between an individual defendant's negligence and the damage suffered. This approach was subsequently found by the High Court as diverting attention from whether individual defendants were to be found liable.
The trial judge also said that the plaintiff would succeed if the evidence established that it was more probable than not that Mr Cotton's lung cancer was caused by asbestos arising from one or both of his periods of occupational exposure to asbestos or if it supported the conclusion, on the probabilities, that his cancer was caused to a material extent by the combined effects of his periods of asbestos exposure with the effects of his chronic smoking.
The majority of the Court of Appeal upheld the trial judge's decision. In dissent, Martin CJ opined that the approach taken by the trial judge in determining the liability of individual defendants was incorrect. Martin CJ was of the view that the plaintiff's claim against each defendant was decided by whether the negligence of that defendant was a cause of Mr Cotton's cancer. His Honour made clear that deciding only whether Mr Cotton's aggregate exposure to asbestos was a cause of his cancer did not answer the question about the particular responsibility of each defendant.
The High Court ultimately found that the evidence did not establish that it was more probable than not that the negligence of any of the defendants, in isolation of each other, was a cause of Mr Cotton's lung cancer because:
- the epidemiological evidence only established that smoking was a more probable cause of Mr Cotton's lung cancer than the asbestos exposure, and
- the evidence did not show that when a smoker has been exposed to asbestos and develops lung cancer, the asbestos exposure is, or is probably, a cause of the cancer.
The High Court further held that material contribution was incorrectly considered by the trial judge as an approach to establishing causal connection. The High Court explained that the question of material contribution is not a test for causal connection and is only relevant to contribution to the damage suffered where more than one cause of damage has already been established.
In making its decision, the High Court made the following observations:
- it is the role of the court to decide legal causation (on the balance of probabilities) even when science and medicine cannot attribute a cause, and
- in determining causation, questions of material contribution do not arise – material contribution of a cause of damage only arises once the connection between the cause of damage and the damage has been established.
The decision highlights issues of causation in cases involving injuries that have no scientifically proven cause. The important lesson here is that causation will only be established if it can be shown, on a balance of probabilities, that the alleged cause is the cause of the damage and not only that it may be a cause of the damage. This is in stark contrast with the position in the United Kingdom, where the required standard for causation is met if it can be shown that the asbestos exposure materially increased the risk of the injury suffered. In such circumstances it would not be necessary to show that the asbestos exposure is a cause of the injury (Fairchild v Glenhaven Funeral Services Ltd ).
The decision underlines the significant difficulty a plaintiff may face in establishing asbestos exposure as a cause of injury where the cancer sufferer has a history of smoking. In such circumstances, the plaintiff's success will turn on the individual facts of the asbestos exposure. At this point, epidemiological evidence alone would seem to fall short as a basis for establishing causation. Causation will remain a significant hurdle in asbestos/smoking cases until further developments in science occur or the standard for causation is relaxed in Australia.
Amaca Pty Ltd v Ellis; The State of South Australia v Ellis; Millennium Inorganic Chemicals Ltd v Ellis (2010) 240 CLR 111
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