Jurisdiction : WORKERS' COMPENSATION ARBITRATION SERVICE

Appeal - Workers compensation - Whether previous employer is liable to reimburse another employer for compensation for a disease - Whether delayed post-traumatic stress disorder was contracted during employment with previous employer

Workers Compensation and Injury Management Act 2023 (WA), s 6, s 34

Bonnington Castings Ltd v Wardlaw [1956] UKHL 1; [1956] AC 613

Streamline Smash Repairs v Griffiths (Unreported, CM-223/02 (Brown IG) 7 July 2003)

1. On 26 November 2022 Ms Jacobsen, the second respondent, was involved in a truck accident in the course of her employment with Thiess, the first respondent. Ms Jacobsen claimed workers compensation for post-traumatic stress disorder (PTSD).
2. It is not in issue in this appeal that for the purposes of s 6(1) of the Workers Compensation and Injury Management Act 2023 (WA) (WCIMA 2023), her PTSD constitutes an injury from employment in the nature of a disease as defined in s 5.
3. Pursuant to s 34(5)(a) of the WCIMA 2023, Thiess joined the appellant, BHP Nickel West Pty Ltd (BHP), by whom Ms Jacobsen had previously been employed, on the basis that her PTSD was caused by an earlier truck accident in which she was involved during the course of her employment with BHP (first accident).
4. The learned arbitrator observed in his reasons for decision at [164] that each employer submitted that it was an 'all or nothing case', each attributing the cause of Ms Jacobsen's PTSD to the other. Accepting, on the basis of the expert evidence, that each accident contributed to the disorder, the arbitrator found that Thiess was liable to Ms Jacobsen and that BHP was liable to reimburse Thiess to the extent of 50% of the income compensation and health expenses compensation payable to her.
5. The proposed appeal is from the order for reimbursement. Ms Jacobsen's award is not challenged, and she did not wish to be heard in the appeal.
6. At the hearing of the appeal, BHP applied for and was granted leave to amend ground 3 of the appeal notice.
7. As will become clear in the course of these reasons, the appeal gives rise to questions of law with respect to the definition of 'disease' and the construction and application of s 6 and s 34 of the WCIMA 2023. Leave to appeal should be granted, the court being satisfied that it is in the interests of justice to do so.
8. By s 391(5) of the WCIMA 2023, the appeal is by way of a review of the decision appealed from.

1. The appeal notice as amended pleads the questions of law as follows:
   1. For the purposes of sections 6 and 34 of the WCIMA 2023 can a previous employer be liable to pay compensation for a disease which would not have occurred absent an event which takes place subsequently in the course of the worker's employment with a different employer.
   2. Can a psychiatric disease be found to have been caused in the primary sense in the course of employment with an employer where the criteria for that disease could not be established absent an event which occurs in the course of employment with a different and subsequent employer.
2. The grounds of appeal as amended are as follows:
   1. Having found that the Second Respondent sustained a disease being a Post-Traumatic Stress Disorder ('PTSD') in the primary sense as defined in section 6(1)(b) of the WCIMA 2023 and therefore an 'injury', which was not a recurrence of a pre-existing disease, in the course of her employment with the First Respondent, the Learned Arbitrator erred in finding that pursuant to section 34 of the WCIMA 2023 the Appellant, a previous employer of the Second Respondent, was partly liable to compensate the Second Respondent for her injury:

(a) The Learned Arbitrator found at paragraphs [34] and [79] of his reasons that the Second Respondent did not meet the criteria for PTSD until after she had left employment with the Appellant and after an incident in the course of her employment with the First Respondent;

(b) The Learned Arbitrator found at paragraph [95] of his reasons that the Second Respondent's employment with the First Respondent which post-dated employment with the Appellant significantly contributed to the contraction of the Second Respondent's PTSD which was an injury from her employment with the First Respondent;

(c) Implicit in the Learned Arbitrator's findings as to the contraction of the Second Respondent's PTSD, being the assessed injury for the purposes of compensation being payable pursuant to section 17 of the WCIMA 2023, is that the PTSD would not have occurred absent her employment with the First Respondent.

1. Having found at paragraph [149] of his reasons that the Appellant could only have exposure to liability pursuant to WCIMA 2023 section 34 if the Second Respondent sustained an injury from her employment with the Appellant as defined in section 6 of the WCIMA 2023, the Learned Arbitrator erred in finding that the Second Respondent's PTSD was an injury that resulted from her employment with the Appellant.

(a) The Learned Arbitrator failed to consider his finding that the criteria for the Second Respondent's determined PTSD was not established as a result of her employment with the Appellant and was only established after a subsequent event which occurred in the course of her employment with the First Respondent;

(b) Accordingly, the PTSD 'injury' as found could not be established as an injury from the Second Respondent's employment with the Appellant where its contraction was conditional on her subsequent employment with the First Respondent.

1. The Learned Arbitrator erred in finding that the PTSD contracted by the Second Respondent, a disease in the primary sense, constituted an 'injury' as defined by section 6 of the WCIMA 2023 which was contracted in the course of her employment with the Appellant.

1. In 2021 Ms Jacobsen was employed by BHP as a dump truck driver on a mine site when she was involved in the first accident. She made a claim for workers compensation against BHP for relatively minor physical injuries from which she recovered. She returned to work after three weeks, but her employment was terminated for unrelated reasons a month later.
2. In 2022 while working for Thiess as a dump truck driver Ms Jacobsen was involved in another truck accident (second accident), as a result of which she suffered symptoms that were later diagnosed as PTSD. She suffered no physical injury as a result of the second accident. By the time of the arbitration, she had not recovered and was not working.
3. In the course of the arbitration proceedings, Thiess denied that Ms Jacobsen had suffered any compensable injury from her employment but pleaded that if it were liable for workers compensation, such liability should be apportioned between it and BHP.

1. BHP's position is that Ms Jacobsen did not suffer an injury from employment for the purpose of s 6(1) of the WCIMA 2023 while employed with BHP because her PTSD was not contracted in the course of that employment. The error for which BHP contends is that the learned arbitrator's factual finding that Ms Jacobsen did not meet the criteria for a diagnosis of PTSD until after the second accident precluded a conclusion that it was contracted during her employment with BHP so as to render BHP liable to a contribution. The learned arbitrator is said to have erred in law by misconstruing or failing to apply s 6(3) in this respect.
2. Thiess's position is that the learned arbitrator was correct to find on the evidence that Ms Jacobsen exhibited symptoms of PTSD after the first accident and prior to the second. Thiess submits that even though all the diagnostic criteria for PTSD were not met until after the second accident, the first accident was causative. Thiess contends that the learned arbitrator found correctly on the expert evidence that the diagnosed PTSD was caused by both the first accident and the second.
3. Thiess has submitted that the grounds of appeal argue no more than an error of fact, that no error of law is disclosed and that the appeal should be dismissed.
4. I propose to set out the relevant legislative provisions and the rationale for the learned arbitrator's decision before addressing the grounds of appeal.

1. Section 17(1) of the WCIMA 2023 provides:

An employer is liable for compensation if a worker suffers an injury from employment with the employer.

1. Section 6 provides:
   1. Injury

injury means an injury from employment that is -

(b) a disease, or the recurrence, aggravation or acceleration of a pre-existing disease.

(2) A personal injury by accident is an injury from employment if the injury arises out of or in the course of the employment or while the worker is acting under the employer's instructions.

(3) Unless otherwise provided in this Act, a disease, or the recurrence, aggravation or acceleration of a pre-existing disease, is an injury from employment if -

(a) the disease is contracted, or the recurrence, aggravation or acceleration is suffered, in the course of the employment, whether at or away from the place of employment; and

(b) the employment contributed to a significant degree to the contraction of the disease, or the recurrence, aggravation or acceleration of the pre-existing disease.

(4) In determining whether particular employment contributed to a significant degree to the contraction of a disease, or to the recurrence, aggravation or acceleration of a pre-existing disease, account must be taken of the following -

(b) the nature of, and particular tasks involved in, the employment;

(c) the likelihood of the disease, or the recurrence, aggravation or acceleration of a pre-existing disease, occurring despite the employment;

(d) the existence of any hereditary factors relating to the occurrence of the disease;

(e) matters affecting the worker's health generally;

(f) activities of the worker not related to the employment.

1. Section 5 defines 'disease' as including 'any ailment, disorder, defect or morbid condition whether physical or mental and whether of sudden or gradual development'.
2. Section 34 of the WCIMA 2023 provides, relevantly:
   1. Claiming compensation when question as to liability or apportionment between employers

(1) Except as provided in subsection (8), this section applies when -

(a) a worker makes a claim under section 25 for compensation from the employer who last employed the worker in employment in which the worker claims the worker's injury was suffered (the last employer); and

(b) the last employer's insurer or the self-insurer gives the worker a liability decision notice under section 28 or 29 accepting that the employer is or may be liable to compensate the worker for the injury to which the claim relates but indicating there are 1 or more liability questions in relation to the acceptance.

(2) A liability question is a question as to any of the following -

(a) whether another employer (a relevant employer) is wholly or partly liable to compensate the worker because the injury is or may be from employment during a period with another employer or more than 1 other employer;

(b) how the liability to compensate the worker is to be apportioned between employers;

(c) which insurer is liable to indemnify an employer liable to compensate the worker.

(3) The last employer is liable to deal with the claim and make payments of compensation as if the last employer were wholly liable and the last employer's insurer must indemnify the last employer for the payments.

(4) Each relevant employer is liable to make to the last employer any contributions as, in default of agreement, may be determined by an arbitrator.

(5) If the worker or last employer applies for determination by an arbitrator of a liability question -

(a) the last employer may join as a party to the dispute any employer who may be wholly or partly liable to pay the compensation; and

(b) the arbitrator may determine that an employer who is a party to the dispute is wholly or partly liable to compensate the worker; and

(c) the arbitrator may make 1 or more of the following orders -

(i) an order requiring the payment of compensation by the last employer or a relevant employer;

(ii) an order requiring reimbursement of compensation paid by the last employer or a relevant employer;

(iii) an order for the apportionment of liability for compensation between employers.

1. Before dealing with the rationale of the decision of the learned arbitrator, I should note that there is no issue in this appeal, as there was before the learned arbitrator, as to whether the liability questions between Thiess and BHP were properly joined pursuant to s 34(1) so as to empower the learned arbitrator to make a reimbursement order under s 34(5)(c).
2. The learned arbitrator rejected BHP's contention that because Thiess had not complied with the procedural requirement of s 34(1)(b) to give a liability decision notice to Ms Jacobsen indicating that there was one or more liability questions for the purposes of s 34(2), that he did not have s 34 jurisdiction. The learned arbitrator observed that it was a technical objection that overlooked the procedural history and the fact the claim had been made pursuant to s 58 of the Workers' Compensation and Injury Management Act 1981 (WA) (WCIMA 1981) and was subject to the transitional provisions in the WCIMA 2023, noting at [137] that BHP was joined under s 73 of the WCIMA 1981, the purpose of which was to ensure that all 'interested' parties were joined so that the questions of liability and apportionment could be heard and determined at the same time, citing Streamline Smash Repairs v Griffiths (Unreported, CM-223/02 (Brown IG) 7 July 2003).
3. By the transitional provisions, Ms Jacobsen's claim under s 58 became a s 30 claim. Although there was no direction given that Thiess's claim against BHP be decided in accordance with s 34, the learned arbitrator observed that the parties had assumed that s 34 applied in the circumstances. It is unnecessary to deal with the learned arbitrator's reasons for that finding in full as there is no appeal from that part of his decision.
4. To understand the learned arbitrator's substantive findings as to injury and causation it is necessary to have reference to the diagnostic criteria for PTSD as set out in the Diagnostic and Statistical Manual of Mental Disorders (5th ed, 2013) (DSM-V) that the learned arbitrator annexed to his reasons for decision, and that are reproduced at Annexure A of these reasons.
5. In his reasons at [31] the learned arbitrator noted that Ms Jacobsen's evidence was that prior to the second accident she did not experience any of the symptoms set out in criterion B. At [32] he held:

In my view, the cross-examination is capable of giving rise to an inference that had Ms Jacobsen been assessed by a forensic psychiatrist after the 2021 BHP MVA but before the 2022 Thiess MVA, she probably would not have been clinically diagnosed with PTSD at that time because criteria B might not have been met. But such an inference is of low probative value because the claimed injury is PTSD. As an inner limit, Criteria F means a diagnosis of PTSD cannot be made within 1 month of relevant event(s). There is no outer limit on when PTSD can be diagnosed, merely that if the criteria are not all met until more than 6 months after the event(s), the PTSD is of 'delayed expression'. Because there is no outer limit on when PTSD can express, the inference above does not get us very far in resolving the actual issues to fall to be determined in this case. Put another way, just because Ms Jacobsen might not have had clinically diagnosable PTSD after the 2021 BHP MVA, does not mean the 2021 BHP MVA was incapable of being a traumatic event (by itself or in combination with other traumatic events) for a subsequently expressed PTSD.

(original emphasis)

1. At [34] the learned arbitrator found that while working for Thiess prior to the second accident Ms Jacobsen experienced hypervigilance as 'a symptom of what would develop into PTSD, although the PTSD Criteria were not yet met before the 2022 Thiess MVA'. At [38] the learned arbitrator held that Ms Jacobsen's hypervigilance about workplace safety that emerged after the first accident 'ramped up considerably' after the second.
2. At [42] the learned arbitrator found that the symptoms that led to a diagnosis of PTSD largely emerged after the second accident. He said:

These are symptoms such as low mood, nightmares and bed-wetting, ruminations about the 2021 BHP MVA and 2022 Thiess MVA incidents, anxiety, difficulty leaving the house, and fear of driving.

1. At [54] the learned arbitrator found that all three psychiatrists whose reports were received in evidence were of the opinion that Ms Jacobsen had PTSD related to both the first accident and the second. He said:

Dr Cheng's views on the part each event played in causing PTSD differs slightly from Dr Shub and Dr Lee although the difference is explainable by Dr Cheng assuming a fact that I have not found proven, and I prefer Dr Shub and Dr Lee's opinion on that discreet [sic] issue.

1. Dr Shub's opinion, accepted by the learned arbitrator, was that Ms Jacobsen's PTSD was caused by both accidents, the second triggering latent psychological issues caused by the first ([57]). Dr Shub in a medical report dated 26 June 2024 opined:

... the serious accident that occurred on 22 July 2021 was the precipitant for the development of her psychiatric condition however in Ms Jacobsen's case, the full expression of her symptoms was delayed and she remained functional for quite some time after this incident.

1. Dr Shub went on to state that the first accident appeared to cause significant psychological injury. He said that overt post-trauma symptoms such as flashbacks and nightmares were not present following the first accident, but Ms Jacobsen did exhibit hypervigilance and a preoccupation with safety. He said the second accident appeared to have been the 'tipping point' at which Ms Jacobsen's pre-existing pathology was unmasked and she 'began experiencing flagrant post-trauma symptoms (with re-experiencing phenomena related to the initial incident of 2021)'. Importantly, he observed in his report at [57]:

It is impossible to speculate upon the trajectory of her clinical state in the absence of the second accident at Thiess, however it is possible that this could have improved over time, such that she was less vulnerable to re-traumatisation or aggravation of her symptoms. Thus it could be argued that it was her employment at Thiess (and the accident encountered there) that was the cause of her psychopathology and associated functional impairment.

1. The learned arbitrator at [60] then dealt with the evidence of Dr Cheng who had reviewed Ms Jacobsen at the request of Thiess. Dr Cheng found that Ms Jacobsen was suffering from PTSD. The learned arbitrator observed that Dr Cheng's opinion that this condition was caused by the first accident and aggravated by the second differed from the opinions of Dr Shub and Dr Lee who each found that the PTSD was caused by both accidents. The learned arbitrator found that Dr Cheng appeared to have assumed incorrectly that Ms Jacobsen was incapacitated for work after the first accident because of her psychological condition. For that reason, the learned arbitrator did not accept Dr Cheng's opinion in that respect.
2. From [69] of his reasons, the learned arbitrator dealt with the evidence of the third psychiatrist, Dr Lee, which he accepted. Dr Lee provided a report to BHP. The learned arbitrator found at [72]:

Dr Lee's opinion was that there was an isolated symptom of PTSD following the 2021 BHP MVA, being hypervigilance around safety, and then a significant escalation of symptoms following the 2022 Thiess MVA resulting in a diagnosis of PTSD. That opinion led Dr Lee to conclude that:

I am of the same view as Dr Shub in terms of causation being from both incidents; that had she not experienced one or the other of 2021 or 2022 incident that she unlikely would have developed the PTSD and therefore unlikely to suffer from sequalae which has caused the major depression.

1. The learned arbitrator's critical finding is found at [79] where he stated:

I accept Dr Shub and Dr Lee's opinion and that [sic] I find that the relevant traumatic events for the DSM-V Criteria are the 2021 BHP MVA and the 2022 Thiess MVA. I find that Ms Jacobsen did not meet the DSM-V Criteria for PTSD until after the 2022 Thiess MVA, but once she did, the symptoms listed in the Criteria relate to both the 2021 BHP and 2022 Thiess MVA.

One of the causes of the PTSD was the 2021 BHP MVA but PTSD didn't express itself until after another of the causes, being the 2022 Thiess MVA, occurred. The DSM-V Criteria for PTSD was not met until after the 2022 Thiess MVA, but once the Criteria was [sic] met, the diagnosable PTSD related to both accidents.

1. At [95] and [96] the learned arbitrator found that Ms Jacobsen's employment with Thiess contributed to a significant degree to the contraction of her PTSD and that accordingly, PTSD was an injury from her employment with Thiess. As mentioned earlier, there is no challenge to that conclusion in this appeal.
2. The learned arbitrator went on to consider, for the purposes of s 34 of the WCIMA 2023, whether Ms Jacobsen's PTSD was an injury from employment with BHP. At [156] he stated:

To be compensable, s 6(3) requires Ms Jacobsen's PTSD to be contracted in the course of employment (with BHP), whether at or away from the place of employment, and for the employment to have contributed to a significant degree to the contraction of the PTSD.

1. He then considered the matters that he was required to take into account by virtue of s 6(4). At [157] he stated:

Taking into account all the above matters, I determine that Ms Jacobsen's employment with BHP contributed to a significant degree to the contraction of her PTSD because the 2021 BHP MVA materially contributed to the contraction of PTSD.

1. The learned arbitrator made no finding, however, that the PTSD was contracted in the course of employment with BHP. Indeed, at [156(c)], he made an express finding that Ms Jacobsen did not have PTSD before the second accident and probably would not have developed PTSD had the second accident not occurred.
2. Notwithstanding this finding, at [159] the learned arbitrator concluded that the PTSD 'is an injury from her employment with BHP (as well as being an injury from her employment with Thiess)'. As I have noted, the learned arbitrator stated clearly at [156] that to be compensable by BHP the PTSD had to be 'contracted' in the course of that employment.

1. By ground 1 of the appeal, BHP contends that having found that Ms Jacobsen contracted PTSD as an injury in the nature of a disease (which was not a re-occurrence of a pre-existing disease) in the course of her employment with Thiess, the learned arbitrator erred by finding that BHP was partially liable for compensation. This contention is particularised by reference to the learned arbitrator's findings at [34] and [79] that: Ms Jacobsen did not meet the criteria for PTSD until after the second accident; his finding at [95] that Ms Jacobsen's employment with Thiess significantly contributed to the contraction of PTSD, such that it was an injury by way of disease from her employment with Thiess; and by implication his finding that Ms Jacobsen would not have contracted PTSD but for her employment with Thiess.
2. BHP contends by ground 2 that having found that BHP could only be liable for compensation pursuant to s 34 if Ms Jacobsen sustained an injury from employment, the learned arbitrator erred in finding that the PTSD was an injury that resulted from her employment with BHP. The particulars of ground 2 point to the learned arbitrator's findings that the criteria for PTSD were not established until after the second accident and that accordingly, PTSD as an injury could not be found to be from the employment with BHP.
3. By ground 3 BHP contends that the learned arbitrator erred in finding that Ms Jacobsen's PTSD was contracted in the course of her employment with BHP. In its outline of submissions at par 23, BHP submits that s 34(2)(a) does not contemplate circumstances where:

(a) an injury is not established during a period of employment with one employer; but

(b) where that employment might be seen as a causative factor in any injury which is established after further events with a subsequent employer; and

(c) where the determined injury would not have been contracted absent further events occurring during the 'subsequent employment'.

1. In BHP's submission, for liability to arise pursuant to s 34, it must be determined that the injury was from employment with the relevant employer. Thus, where the injury is a disease, the disease must have been contracted in the course of that employment, as indeed the learned arbitrator held at [156]. The learned arbitrator made no finding that Ms Jacobsen contracted PTSD in the course of her employment with BHP. It is further submitted that his actual findings preclude that conclusion.
2. Thiess in its submissions merely reiterates the learned arbitrator's uncontroversial findings to the effect that the onset of PTSD after the second accident was due in part to the first accident to support his conclusion that the first accident which occurred in the course of Ms Jacobsen's employment with BHP was a cause of that disease. In Thiess's submission, having found that the PTSD was attributable in a causative sense to the first accident, the learned arbitrator did not err in law by finding BHP partly liable. Thiess does not accept that the learned arbitrator's finding that Ms Jacobsen did not suffer PTSD until after the second accident precludes a finding that she suffered an injury in her employment with BHP.
3. The submission by Thiess suggested that s 34 should be construed as permitting what might be termed the common law approach to causation such as would be taken in a case involving tortious conduct. Thiess's position seemed to be that if the first accident caused, in the sense of materially contributed to the onset of PTSD after the second, BHP was liable to contribute to compensation.
4. At common law, whether the conduct in question caused the harm suffered is to be determined as a matter of common sense, bearing in mind that a number of factors may contribute materially to the harm such that a defendant in an action for negligence may be liable for the harm suffered even though it cannot be said that, but for the conduct of the defendant, the plaintiff would not have suffered such harm: Bonnington Castings Ltd v Wardlaw [1956] UKHL 1; [1956] AC 613.

1. The real issue to emerge from the pleaded questions of law and grounds of appeal is whether a previous employer is liable to contribute to compensation for an injury from employment in the form of a disease where the disease was not contracted in that employer's employment and would not have been contracted but for a further event in the course of employment with a subsequent employer.
2. It is clear from s 6(3) that a disease is an injury from employment if it is contracted in the course of that employment and the employment contributed to a significant degree. The verb 'to contract' does not have a technical meaning. In the context of s 6(3) it should be given its ordinary and natural meaning. According to the New Shorter Oxford Dictionary it means 'to become infected with, catch'. In the case of a non-infectious disease, such as a mental disorder, I take it to mean 'to develop or acquire'.
3. Section 34 deals with the apportionment of liability between employers, affording an arbitrator the power under s 34(6) to order an indemnity or reimbursement. The WCIMA 2023 does not state expressly, in s 34 or elsewhere, on what basis or according to what criteria or considerations an indemnity or reimbursement might be ordered pursuant to s 34(6).
4. Section 34 applies in the circumstances set out in subsection (1) where a liability decision notice indicates that there are one or more liability questions. In this case, however, as explained, the arbitration proceeded without such a liability notice being served. Being a pending dispute, the arbitration had to be decided as if it were a dispute proceeding under s 575 of the WCIMA 2023. The question of apportionment was therefore dealt with according to s 34.
5. Section 34(2) prescribes three liability questions, the first of which is 'whether another employer (a relevant employer) is wholly or partly liable to compensate the worker because the injury is or may be from employment during a period with another employer or more than 1 other employer ...' (underline added).
6. So expressed, the question itself contains the factual premise that leads to it: 'the injury is or may be from employment during a period with another employer'. It follows that that fact, or at least the probability of it ('may be'), must be established before the learned arbitrator has power to decide the question.
7. In that context, there is no reason to construe the meaning of the words 'injury ... from employment' other than in accordance with s 6 which defines an injury from employment as a personal injury by accident or a disease and defines a disease in that context as a disease contracted in the course of employment.
8. On this basis there would be no reason to decide whether an employer, other than the one against whom the claim is made, is 'wholly or partly liable to compensate the worker' unless it were shown, in the case of an injury in the form of a disease, that it was contracted in that other employment.
9. On the facts as found, Ms Jacobsen contracted a disease, PTSD, that constituted such an injury from employment in the course of her employment with Thiess. That disease was not diagnosed until after the second accident. The first accident was found to have contributed to the PTSD, even though it would probably not have been contracted but for the second.
10. It was accepted, on the expert evidence and according to the DSM-V diagnostic criteria, that PTSD may be delayed in expression, such that all the diagnostic criteria may not be met until more than six months after the traumatic incident in question. It was thus open to the learned arbitrator to conclude that as a result of the first accident (and therefore in the course of her employment with BHP), Ms Jacobsen contracted delayed-onset PTSD which found its expression after the second accident, such that each accident could be found to have contributed to the disease. While the learned arbitrator did not make an express finding that PTSD was contracted in the course of employment with BHP, it may be implied from his finding at [81] that '[o]ne of the causes of the PTSD was the 2021 BHP MVA but PTSD didn't express itself until after another of the causes, being the 2022 Thiess MVA'.

1. I conclude, therefore, that the learned arbitrator did not err in apportioning liability between the two employers to reflect the contributions of each accident to the PTSD. The evidence permitted the finding that Ms Jacobsen contracted PTSD in the course of her employment with BHP, notwithstanding the fact that its expression was delayed and may not in fact have occurred but for the second accident. Put another way, I am not satisfied that the learned arbitrator erred in finding that PTSD was caused by the first accident, and in that sense 'contracted', even though all the diagnostic criteria were not met until after the second, delayed onset being a recognised feature of PTSD in some cases.
2. On the facts and circumstances of this case, each question of law posed in the appeal is answered in the affirmative. Each ground of appeal must fail.

I certify that the preceding paragraph(s) comprise the reasons for decision of the District Court of Western Australia.