Further to the trial and judgment for the plaintiff, while the negligence of the employer was not in issue, the Court of Appeal allowed the defendant’s appeal on factual causation under s 305D Workers’ Compensation and Rehabilitation Act2003 (WCRA) because the plaintiff could not establish that the employer’s breach was a “necessary condition” for the injury claimed.
The facts were unremarkable. The plaintiff worked as a community support worker at a residential care facility for a 15 year old boy, who had a “history of drug use and aggressive, sometimes criminal, behaviour, including conduct directed towards support workers”. On the evening of the injury the boy was verbally abusive and physically aggressive towards the plaintiff:
 On that evening, the boy became verbally abusive and physically aggressive towards the respondent. He threw a phone at her and pushed her out of his way as he searched for keys to a car which was used by staff at the facility. He started to hyperventilate and threatened to kill himself by jumping through a window. He kicked the window of his room breaking a pane of glass. He then picked up a large shard of glass which he held in front of him, saying to the respondent that he could “fuck someone up with this”.
 The respondent felt threatened and frightened. But she was able to calm him down and disarm him and she was then able to talk to him about his behaviour. She believed that the boy was under the influence of glue at the time and gave him some medication and got him to go to bed for the night in his room.
The plaintiff telephoned her supervisor Mr Mafulu:
 During this incident the respondent had telephoned a Mr Mafulu, who was employed by the appellant as the respondent’s supervisor. Mr Mafulu could hear the commotion that was occurring. He was told by the respondent that the boy had managed to get inside the staff room, that she wanted to get off the phone so that she could deal with the situation and that she would call him back. After the boy had gone to bed, the respondent rang Mr Mafulu and reported what had occurred. There were differences between the recollections of the respondent and Mr Mafulu about this conversation, but it was common ground that he made no offer to then relieve the respondent from the rest of her shift, which was not to finish until the following morning, or to come to the house or send another worker to support her. Nor did the respondent ask for any of those things. The trial judge found that this was because the respondent thought that Mr Mafulu did not think that the incident was serious and she did not want to appear to him to be unable to manage the situation. The trial judge found that they discussed who the respondent should call and that Mr Mafulu told her to call a glazier, someone from the relevant government department and the boy’s aunt. The respondent asked Mr Mafulu whether the police should be called and he said that there was no need to do so because she had deescalated the situation. The boy was then on bail and staff had been instructed to call the police if he absconded or they were unaware of his whereabouts.
The plaintiff alleged her post-traumatic stress disorder (PTSD) arose from the employer’s failure to intervene after the plaintiff had telephoned her supervisor.
The trial judge found:
“ It is common ground the traumatic incident itself was a major contributor to Ms Greenway’s injury. She says that being required to stay alone with her assailant overnight without any support was also a cause of her injury. There is also evidence that her feelings of being let down and unsupported contributed to her injury.
 Ms Greenway does not need to prove that Anglicare’s breach of duty was the sole cause of her injury, provided it was a necessary condition of the injury being caused. In some cases where there are multiple factors which have contributed to an injury, it is not possible to disentangle them. This is one of those cases. It involves the cumulative operation of factors in the occurrence of the total harm in circumstances in which the contribution of each factor to that harm is unascertainable.”
… “Had he [Mr Mafulu] visited that night her perception about his attitude may well have been different and she may well have asked to be relieved. What she might or might not have said or done if Mr Mafulu had responded differently is too speculative for the court to draw an inference about it.”
“ Further, Anglicare’s breach of duty is failing to adopt the precautions outlined at  of these reasons: i.e. guidelines for and training of on call Team Leaders in assessing the welfare of workers subjected to traumatic incidents. Had Mr Mafulu been adequately equipped to assess Ms Greenway’s welfare, he would, on Ms Lloyd’s evidence, have asked a series of prompting questions and drawn on his observations (whether by phone or in person). He would not have relied solely on the self-assessment of a person who had so recently been through a traumatic incident.
 The question of causation is a legal not a medical enquiry, but, in this case, it is informed by the evidence of the psychiatrists called by the parties. In a concurrent evidence session, Dr Chalk and Dr de Leacy agreed that Ms Greenway had not been so overwhelmed by the incident itself that it was inevitable she would develop PTSD. That was demonstrated by her actions in de-escalating and disarming the young person.
 They also agreed that for Ms Greenway, staying in the house with the young person overnight and without support added an additional level of anxiety and this “would be seen as a contributing factor” to the injury. Although Ms Greenway’s feelings were connected to Mr Mafulu’s response on the night, it is the ongoing exposure to the potential of further harm which contributed to her injury.
 Given that evidence and accepting Ms Greenway’s evidence about her circumstances that night and how she felt at the time, it is more probable than not that Anglicare’s breach of duty was a necessary condition of her injury. Anglicare accepted that, if that was my finding, it is appropriate for the scope of its liability to extend to this injury.”
McMurdo JA (with whom Morrison JA and Bond J agreed) held the application by the trial judge of s.305D of the WCRA did not accord with the authorities:
 The respondent was required to prove that her injury had been caused by a breach of duty according to the principles prescribed by s 305D of the Workers’ Compensation and Rehabilitation Act 2003 (Qld) (the WCR Act). Section 305D provides as follows:
“(1) A decision that a breach of duty caused particular injury comprises the following elements –
(a) the breach of duty was a necessary condition of the occurrence of the injury (factual causation);
(b) it is appropriate for the scope of the liability of the person in breach to extend to the injury so caused (scope of liability)…
 In the passage from the judgment which I have just set out, the judge did express her conclusion in the terms of s 305D(1)(a), by finding that the appellant’s breach of duty was a necessary condition of the respondent’s injury. However her Honour reached that conclusion by reasoning which was inconsistent with the well-established effect of that provision.
“The determination of factual causation under s 5D(1)(a) is a statutory statement of the ‘but for’ test of causation: the plaintiff would not have suffered the particular harm but for the defendant’s negligence.”
Yet at no point did the trial judge apply the “but for” test: she did not consider whether, but for the acts and omissions which she found constituted the breaches of duty, the injury would not have occurred.
 These provisions, such as that considered in Strong v Woolworths and s 305D of the WCR Act, were enacted upon the recommendations in the Final Report of the Review of the Law of Negligence published in 2002, the so-called Ipp Report. As was discussed in Strong v Woolworths, the Ipp Report instanced two categories of cases which would not pass the “but for” test of causation and for which special legislative provision should be made. The first category was said to be exemplified by Bonnington Castings Ltd v Wardlaw. It was in the description of that category of case that the majority in Strong v Woolworths referred to cases which involve “the cumulative operation of factors in the occurrence of the total harm in circumstances in which the contribution of each factor to that harm is unascertainable”. The majority in Strong summarised that decision as follows:
“In Bonnington Castings Ltd v Wardlaw, the expression ‘material contribution’ was employed in determining the causation of the pursuer’s pneumoconiosis, a disease caused by the gradual accumulation of particles of silica in the lungs. There were several sources of exposure: the pneumatic hammers, the floor grinders and the swing grinders. The employer’s breach of statutory duty lay only in exposing the pursuer to the dust generated by the swing grinders. The greater proportion of the pursuer’s exposure to silica dust had come from the use of the pneumatic hammers. Lord Reid characterised the ‘real question’ as whether the dust from the swing grinders ‘materially contributed’ to the disease. The swing grinders had contributed a quote of silica dust that was not negligible to the pursuer’s lungs and had thus helped to produce the disease.”
 Of that type of case, the majority in Strong also noted that Allsop P (as he then was) in Zanner v Zanner, like the authors of the Ipp Report, had assumed that a case such as Bonnington Castings would not pass the “but for” test. But the majority said:
“However, whether that is so would depend upon the scientific or medical evidence in the particular case, a point illustrated by the decision in Amaca Pty Ltd v Booth with respect to proof of causation under the common law. In some cases, although the relative contribution of two or more factors to the particular harm cannot be determined, it may be that each factor was part of a set of conditions necessary to the occurrence of that harm.”
 Consequently, the trial judge’s categorisation of the case, which used the description in Strong of the facts in Bonnington Castings, did not answer the question of factual causation under s 305D(1)(a). The trial judge had to decide whether the appellant’s breaches of duty were “necessary to complete a set of conditions that [were] jointly sufficient to account for the occurrence of the harm”.
 The question of factual causation was not answered by the judge’s finding that the respondent’s “ongoing exposure to the potential of further harm … contributed to her injury.” The injury of which the respondent complained was, as I have set out above, “a psychiatric injury in the form of a post-traumatic stress disorder [requiring] psychiatric treatment and psychological counselling and [leaving the respondent] with a permanent impairment”. If what happened to the respondent after her conversations with Mr Mafulu did contribute to that injury, it did not follow that absent that experience, the injury would not have occurred.
 At  of her reasons for judgment, the trial judge said that Dr Chalk and Dr de Leacy had agreed that the respondent “had not been so overwhelmed by the incident itself that it was inevitable that she would develop PTSD”. If that was an accurate summary of their evidence, the acceptance of that evidence would not have proved factual causation. To say that the appellant’s PTSD was not inevitable from the incident itself was to recognise the respective possibilities that the injury would or would not have occurred, absent the breach of duty. But the respondent bore the onus of proving that, more probably than not, the injury would not have occurred from the incident alone. The injury may not have been inevitable because there was a “remote possibility” that, absent the breach of duty, it would not have occurred, but that was not proof of causation on a balance of probabilities.
McMurdo JA found after considering the psychiatric evidence that:
 The relevant psychiatric evidence has been set out above. At its highest, that evidence proved no more than a possibility that, but for the breach of duty, the injury, as it was pleaded, would not have occurred. Dr de Leacy agreed with the judge’s suggestion that “there might have been a less severe PTSD”, but as I have just noted, he described the relative likelihood that PTSD might not have developed at all as a “remote possibility”. Dr Chalk agreed with Dr de Leacy that the respondent’s experience after the incident was a contributor, but so was the incident itself. Importantly, the reports by each of these witnesses had attributed the injury to the incident itself, and neither witness said that he had altered that opinion.
David Cormack – Brisbane Barrister & Mediator