Allianz Australia Ltd v Sim [2012] NSWCA 68


In this case, the NSW Court of Appeal considered the admissibility of expert evidence relevant to causation of lung cancer and, based upon that evidence, whether the findings of causation against four successive tortfeasors were legitimate.

The case is significant in that it is the first appellate consideration of an alternative theory of causation of lung cancer to the theory rejected by the High Court of Australia in Amaca Pty Ltd v Ellis.


Mr Sim was exposed to substantial quantities of asbestos dust and fibre in the course of four successive employments. He developed asbestosis and lung cancer.

It was uncontroversial that each of the employers was in breach of the duty of care owed to the plaintiff and that the exposure to asbestos dust and fibre in the course of the successive employment periods each caused a portion of the asbestosis. Further, it was uncontroversial that the collective exposure to asbestos dust and fibre was a cause of the lung cancer.

The question was whether the exposure in each period of employment was causative of the lung cancer.

Mr Sim took a different approach to proving causation than that considered by the High Court of Australia in Amaca v Ellis. Ellisproceeded on an analysis of the relative increases in risk of the development of lung cancer as a consequence of relatively modest levels of asbestos exposure by comparison to inhalation of a large quantity of carcinogens through smoking.

In Ellis the High Court held that in consideration of a case based upon epidemiological analysis it was necessary for the plaintiff to establish that the risk associated with the negligent exposure had 'come home'.

It was necessary for the breach of duty by each defendant to have approached doubling the risk of the development of the lung cancer by comparison to the risk arising from exposure to other carcinogens.

Sim called evidence which the trial judge accepted established a direct cause rather than an increase in risk.

Expert evidence

Sim relied upon the opinion of Professor Henderson, a pathologist, Professor Bryant, a respiratory physician, and Dr Yates.

The thrust of the opinions expressed by the plaintiff's medical witnesses was encapsulated in the conclusion of Professor Henderson as follows:

'Because the likelihood and pathogenesis of lung cancer are governed by a dose-response relationship, it also follows on a probabilistic basis that each of Mr Sim's asbestos exposures ... made a significant and substantial causal contribution to the development of his lung cancer.'

The defendants did not tender expert evidence to contradict these conclusions. Rather, the defendants argued that the opinions to that effect expressed by Sim's experts were inadmissible as the evidence did not satisfy the opinion expert exception prescribed by the Evidence Act 1995 (NSW) (the 'Evidence Act').In any event, when properly considered, the expert evidence even if admissible, did not establish causation against each employer in a legal sense but rather only went to establish that each exposure resulted in an increase in risk of the development of cancer.


The Court of Appeal unanimously dismissed the appeals.

The court held that Professor Henderson, Professor Bryant and Dr Yates were all qualified to give opinions as to the causation of lung cancer and that the opinions which were given arose from the specialist training and expertise of the witnesses. Ultimately, the court also unanimously held that the basis on which the opinions were expressed by the witnesses was sufficiently explained in the reports. Accordingly, the evidence was admissible as contemplated by s79 of the Evidence Act.

The court then turned to consideration of the specific evidence of the witnesses to analyse whether the evidence satisfied the legal causation test. In short, to consider the submission by the employers that the expert evidence went no higher than to say that the exposure in each of their respective employment periods made an increase in risk that Mr Sim may develop lung cancer but fell short of establishing legal causation because the evidence did not satisfy the requirement that the risk had 'come home'.

It is evident from the evidence that the pathogenesis of lung cancer is not perfectly understood by medical science. However, the thrust of the finding of the Court of Appeal, was that the hypothesis proffered by Professor Henderson and endorsed by Professor Bryant and Dr Yates amounted to a reasoned scientific analysis of the condition which went beyond mere assertion of an increase in risk and concluded that the exposure arising from each of the employments was directly causally related to Mr Sim's lung cancer.

Thus, different from Ellis, the evidence as analysed by the trial judge and the Court of Appeal was held to be sufficient to identify a direct causative link between each of the exposures and the lung cancer.

It is helpful to note that once admissible the evidence is available to the trial judge in legitimately supporting a factual finding giving rise to causation. Allsop P noted that it may well be that the hypothesis of Professor Henderson is wrong, however, critically, he said that:

'The question here is whether Professor Henderson's views, which, in the context of mesothelioma, have been the foundation of the Tribunal's factual findings, are admissible insofar as he proffers them in respect of lung cancer.

For the reasons that I have expressed, I think they are. They may be wrong. The experience and multidisciplinary training of others, scientists and legal scholars included, may suffice beyond a lay analysis to criticise the acceptability of Professor Henderson's views. With that I do not quarrel. But that was not attempted by the appellant. His views do not suffer the characterisation capable of being made by a judge without expert assistance of unreasoned ipse dixit.'

In short, the trial judge was entitled to rely upon the only expert evidence available to support the finding of causation. The result may have been different had compelling alternative expert evidence been tendered by the employers because the trial judge may have preferred a different hypothesis as to the development of lung cancer or, alternatively, rejected the hypothesis proffered by Professor Henderson as being unreliable. In either event, Mr Sim would have failed to discharge the onus of proof in relation to causation and his case would have failed.

After accepting the evidence that each of the exposures cumulatively impacted upon the plaintiff so as to be directly causative of the lung cancer, the question of whether each made a material cause became irrelevant. The Court of Appeal took the same type of approach as accepted by the High Court of Australia in Amaca v Booth (that all exposure beyond a trivial level is causative). Again, it is a question of fact informed by expert evidence as to what amounts to trivial exposure in the circumstances of any case. Expert minds may differ on the point and it is a matter for a trial judge to consider competing opinions to ultimately reach a factual conclusion on that type of issue.


Allianz v Sim provides the framework by which a person suffering lung cancer arguably as a consequence of exposure to asbestos by successive tortfeasors can succeed. Absent compelling expert opinion contradicting the approach by Professor Henderson, the Tribunal will, in the writer's view, now accept that all exposure beyond trivial exposure is directly causative.

By operation of provisions peculiar to practice in the NSW Dust Diseases Tribunal, the expert evidence supporting that finding (being the evidence of Professor Henderson, Professor Bryant and Dr Yates in Sim, together with the factual findings which followed) will be available to plaintiffs (by dint of ss25(3) and 25B of the Dust Diseases Tribunal Act 1989).

Defendants who have caused limited exposure may argue that their exposure was relevantly trivial and thus not a material cause, or, in the event that compelling alternative expert evidence is available contradicting the hypothesis accepted in Sim, seeking leave to reargue the factual basis on which Sim has been decided.

The difference in approach between Sim and Ellis as to requiring evidence to establish the breach in each successive employment period in itself made a material contribution is interesting. It remains to be seen as to whether an application for special leave will be filed. In the writer's view, it is unlikely that an appeal to the High Court of Australia will succeed bearing in mind that the expert evidence is likely to be accepted as admissible and similar opinion evidence was held to be legitimate to support factual findings on causation in Booth.

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