Davis v Nolras Pty Ltd

Australian Safeway Stores Pty Ltd v Zaluzna (1987) 162 CLR 479 Bates v Parker [1953] 2 QB 231 Bond v SA Railway Commissioners (1923) 33 CLR 273 Christmas v General Cleaning Contractors [1952] 1 KB 141 Edmonds v Commonwealth (1961) 61 SR (NSW) 527 Felk Industries Pty Ltd v Mallet [2005] NSWCA 111 Ferguson v Welsh [1987] 1 WLR 1553 CASES CITED: Graham Barclay Oysters Pty Ltd v Ryan (2002) 211 CLR 540 Jones v Bartlett (2000) 205 CLR 166 London Graving Dock Ltd v Horton [1951] AC 737 Papatonakis v Australian Telecommunications Commission (1985) 156 CLR 7 Phillis v Daly (1988) 15 NSWLR 65 Roles v Nathan [1963] 1 WLR 1117 Vairy v Wyong Shire Council [2005] HCA 62 Wyong Shire Council v Shirt (1980) 146 CLR 40

Nathan Davis (Appellant) PARTIES: Nolras Pty Ltd (previously known as Sarlon Pty Ltd) (Respondent)

S Norton SC/M Fraser (Appellant) COUNSEL: G Parker (Respondent)

Bryden's Law Office (Appellant) SOLICITORS: Ebsworth & Ebsworth (Respondent)

IN THE SUPREME COURT OF NEW SOUTH WALES COURT OF APPEAL CA 41021/04 DC 1188/03

IPP JA M W CAMPBELL AJA BRERETON J

NATHAN DAVIS v NOLRAS PTY LTD (previously known as SARLON PTY LTD) Judgment 1 IPP JA:

Mr Davis's claim and his appeal 2 This appeal concerns the liability of an occupier for injuries sustained by an employee of a specialist independent contractor who was injured while working on the occupier's premises. 3 The injured worker is the appellant, Mr Nathan Davis. His employer at the time was Pallet Packing Supply Company ("PPSC"), referred to in the evidence as Vertex. Part of PPSC's business was the installation, maintenance and removal of pallet racking systems in factories and warehouses. 4 Mr Davis was injured while he was working for PPSC at a factory owned by the respondent, Nolras Pty Ltd. He contends that his injuries were caused by the negligence of Nolras. He brought a claim against Nolras for the damages he suffered in consequence of those injuries, but Rein DCJ dismissed it. Mr Davis appeals against the dismissal of his claim.

The circumstances under which Mr Davis was injured 5 Nolras was a manufacturer of shade cloth. It stored the shade cloth in racking systems in its factory. At the time Mr Davis was injured, Nolras was intending to move to a new factory and had contracted with PPSC to dismantle its racking systems. PPSC instructed Mr Davis, a co-worker (Mr Howell), and his supervisor (Mr Townend), to perform the contracted task. 6 Shortly before Mr Davis was injured, he and Mr Howell had commenced dismantling a rack of chipboard shelves about six metres high. Their method of work involved removing the top level of shelves first. After they had done this, they began work on the next level of shelves. They were standing on separate shelves at this level, undoing screws that affixed the shelves to horizontal steel members forming part of the racking system. Mr Davis heard a cracking sound. He looked down to see Mr Howell falling. The chipboard on which Mr Howell had been standing had broken in half and one piece had flown into the air. Mr Davis was concerned that this piece of chipboard would land on Mr Howell. To prevent Mr Howell from being injured, Mr Davis dived onto his knees and caught the flying piece of chipboard. In so doing so, he injured his knee. 7 Rein DCJ found that Mr Davis's conduct "was a natural and appropriate response to the danger created by the fracture of the chipboard". 8 The broken chipboard was found to be swollen and affected by water. This caused it to be unable to bear Mr Howell's weight. 9 After Mr Howell had fallen, Mr Davis looked up at the roof above the racking and saw "daylight shining through like little crevices, little particular corners between the sheets". Rein DCJ found that water entering the factory premises during wet weather had affected the chipboard.

The racking system, its use, and PPSC's method of dismantling it 10 Rein DCJ described the racking system from which Mr Howell fell as: "[A] steel structure bolted together about six metres high with each level approximately two metres high. On each level was a chipboard or particle board panel laying across the metal beams and being screwed in at the corners to the frame. The system also had chipboard panel at the top of the structure." 11 In other words, the structure consisted of a steel frame about six metres high with chipboard shelving (about 18 millimetres thick) affixed to the frame. The steel frame consisted of uprights and horizontal members. Each chipboard shelf rested on four steel horizontal members forming part of the framework. Each end of each shelf rested on a horizontal member. Two other horizontal members "roughly a foot apart" passed under the length of each shelf. Each corner of the shelves was secured by a "wingtek" screw to the horizontal member underneath. 12 The rolls of shade cloth that had been stacked on the shelving were from four metres to about six metres long and about "a foot, a foot and a half" in diameter. Generally, they extended across the full length of each chipboard shelf. 13 Mr Davis had been involved in the installation and dismantling of pallet racking for about two years and three months before his accident. He explained: "Generally with dismantling a pallet rack we'll generally start from the top of the pallet racking. When dislocating the pallet racking on a rack that is 6 metres high we would generally start from the top dismantling the beams and anything that's on top of those beams so that there was nothing left above us therefore working our way to the ground level by level." 14 According to Mr Davis it was necessary to walk on each chipboard shelf to unscrew the wingtek screws before removing the shelves. Once the screws had been removed, a forklift operated by another PPSC employee would remove the loosened shelf. 15 Walking on the chipboard shelves was a risky business. Mr Davis said that if a shelf was damaged "it would be vulnerable to cracking and falling through". It was difficult to detect whether a shelf had indeed been damaged. The PPSC employee charged with dismantling a racking system would first make a visual inspection of the system while standing on the ground. He would then inspect the front face and sides but only at the first level. He could not inspect the other levels while standing on the ground. He would have to make a visual inspection of those as he was "going along". 16 The purpose of the inspection was to make sure "that the rack was secure at the base and that the beams weren't going to pop out as we walked on them". Mr Davis said that he would look for "usage damage" which he could "spot". He said that water damage was "something that's not easily seen". 17 Mr Davis made it plain that, whatever visual inspection occurred, the risk of a shelf cracking or breaking was ever-present. For that reason, when walking on upper chipboard shelving, he would proceed one step at a time, and attempt to place his feet on that part of the shelf that crossed the two central horizontal steel members (although this was not easily accomplished). He said that if he heard "cracks or creaks" he would know that there was a danger. If he did not hear a crack or creak he would keep going.

Mr Davis's main arguments as to liability 18 Before Rein DCJ, Mr Davis presented two main arguments on the question of liability. 19 Firstly, he submitted that Nolras was negligent in failing to maintain or repair the roof and in allowing rainwater to enter the factory premises. In consequence, water had fallen onto the chipboard shelving of the racking system and weakened the shelf on which Mr Howell had stood. This led to Mr Davis injuring his knee. 20 Secondly, Mr Davis submitted that Nolras, in discharge of the duty of care it owed him, should have warned him - prior to him commencing work - that on previous occasions chipboard shelves had been made wet by rain penetrating through the roof and had thereby, possibly, been weakened. 21 As I have indicated, the trial judge rejected both these arguments and dismissed Mr Davis's claim. On appeal Mr Davis raised the same arguments.

The failure to maintain and repair the roof 22 In my view, the argument that Nolras breached its duty of care by failing to maintain and repair the roof is without merit. While Nolras, as occupier, owed Mr Davis a general duty of care, the content or scope of that duty did not extend to repairing the roof. Put in another way, Nolras did not breach that duty by failing to maintain and repair the roof. 23 In Jones v Bartlett (2000) 205 CLR 166 Gummow and Hayne JJ pointed out (at [166] to [167], 213) that in determining the content of a duty of care in a particular case it is "of no utility merely to conclude that the duty is to be expressed simply as one to take reasonable care to avoid a foreseeable risk of injury to a person in the situation of the appellant". Their Honours observed: "That would be to leave unanswered the critical questions respecting the content of the term 'reasonable' and hence the content of the duty of care, matters essential for the determination of this case, for without them the issue of breach cannot be decided." 24 In Graham Barclay Oysters Pty Ltd v Ryan (2002) 211 CLR 540 Gummow and Hayne JJ at [192], 611 to 612 emphasised the importance of the need "to identify with the necessary precision, by reference to considerations of the nature of those indicated in Wyong Shire Council v Shirt (1980) 146 CLR 40, the reasonable response to the risk of harm that existed". 25 The risk of harm in this case was the risk of injury to a person falling from a water-affected chipboard shelf. It is that risk that had to be eliminated. What is reasonable has to be determined by looking at the situation before the accident, not after: Vairy v Wyong Shire Council [2005] HCA 62 at [49] and [126]. 26 One way in which the risk of injury from falling from the weakened chipboard shelf could have been eliminated would have been to place appropriate warning signs at appropriate places in the vicinity of the shelving. Another way would have been by identifying and removing the affected shelving. 27 It is not clear, on the evidence, whether maintenance and repair of the roof by Nolras would have eliminated the risk. The evidence did not establish for how long the roof had been leaking, for how long Nolras had occupied the premises, for how long the water had come into contact with the shelf from which Mr Howell fell, and whether the shelf only became affected by water after Nolras occupied the factory. Had the shelf been weakened before Nolras became the occupier, the maintenance and repair of the roof would have been pointless. 28 There are also difficulties in inferring, on the evidence, that Nolras should have foreseen that a failure to maintain and repair the roof would lead to a person being injured by a structurally weakened chipboard shelf. This requires knowledge by persons, whose knowledge is to be attributed to Nolras, that water in quantities that might damage the shelving was falling or might fall on to the shelving, and that someone might walk on that shelving. Apart from the fact that at the time Mr Davis was injured, Nolras employees were working in the vicinity (and the evidence does not identify who the employees were, or their level of authority or experience, or the particular nature of their work) there was no evidence of this kind. 29 Moreover, no attempt was made in evidence to lay the foundation for the evaluative process required by Wyong Shire Council v Shirt to be undertaken. There was, as I have said, no evidence of the relevant period over which the failure to maintain and repair the roof led to the shelf being damaged. The cost of maintenance and repair may well have been more than the identification and replacement of any defective shelves. Common sense leads to the conclusion that the cost of maintaining and repairing the roof would have been far more than the cost of erecting warning signs. 30 In my opinion, repairing and maintaining the roof was not a reasonable response to the risk of harm that existed. 31 Accordingly, I would reject the argument that Nolras breached its duty of care as occupier by failing to repair and maintain the roof.

The failure to warn: proof of Nolras's relevant knowledge 32 It was submitted on Mr Davis's behalf, that Nolras knew or should have known, firstly, that water had affected the chipboard shelf from which Mr Howell fell, secondly, that, in consequence, the shelf had been weakened to the extent that it might not be able to bear the weight of a man, and thirdly, that a visitor to the factory premises might stand on the shelf and, because of the defect in it, fall. These submissions underpinned Mr Davis's argument that Nolras breached its duty of care by failing to warn him that rainwater had come into contact with the shelving and had affected it. 33 In examination in chief it was put to Mr Davis that, prior to his injuries, he had been to the factory as a PPSC worker, doing work for Nolras, "maybe three times" over a period of a couple of years and he replied in the affirmative. It may be accepted from this evidence that Nolras occupied the factory for a period of at least "a couple of years". 34 According to Mr Davis, on one of the days in which he had so visited the factory, the weather had been wet and he had to move electrical leads because of puddles on the floor. He said that the water he observed on this prior occasion was not in the particular area where he fell. He said: "We hadn't really worked much in that particular spot". Nevertheless, this evidence, together with Mr Davis's evidence as to the gaps in the roof and the position of those gaps (over the racking system), leads to the inference that, on occasions during the period of Nolras's occupation, water penetrated the factory from the roof and came into contact with the shelf that caused Mr Howell's fall. This leads in turn, I think, to the inference that Nolras knew or should have known that from time to time water must have come into contact with that shelf. 35 The next question is whether Nolras knew or should have known that the water would have affected the chipboard shelving of the racking to the extent that some of the shelves were substantially weakened and not safe to stand on. 36 Rein DCJ said that, assuming that Nolras knew that water had leaked onto the chipboard, "it would not follow that it was aware that the effect of such rainwater would be to produce an effect on the structure and integrity of the chipboard, which effect would not be visible upon inspection by those dismantling and would present a danger to experienced dismantlers in proceeding with their task". I agree with this observation. 37 There was no evidence as to the kind of chipboard used on the racking, the degree of compression of the woodchips of which it was constituted, its strength, its permeability and resistance to water, and whether it was more or less susceptible to the effects of water than other chipboard. In the absence of evidence as to any knowledge on the part of Nolras as to the quality and characteristics of the chipboard, and the extent to and frequency with which water came into contact with it, it is not possible to find that Nolras knew or should have known that the leaking rainwater might cause the shelves to crack when stood upon. It was submitted on Mr Davis's behalf that this was a matter of common knowledge of which judicial notice should be taken, but I do not accept that. I think it is common knowledge that there are various kinds of chipboard materials which have different characteristics and different degrees of water resistance, but no more than that is common knowledge. 38 Thus, in my view, Mr Davis did not establish that Nolras knew or should have known that water might have destroyed the weight-bearing capacity of the shelf from which Mr Howell fell. Accordingly, I would dismiss the appeal as to liability on this ground alone.

The failure to warn: the principle in Papatonakis 39 There is another obstacle that faces Mr Davis in regard to his failure to warn argument. This is the principle expressed by Brennan and Dawson JJ in Papatonakis v Australian Telecommunications Commission (1985) 156 CLR 7 at 30: "[W]here an independent contractor carrying on a particular trade is engaged by an occupier to work on his premises, the occupier is not under a duty to give warning of a defect in the premises if tradesmen of that class are accustomed to meeting and safeguarding themselves against defects of that kind."

This observation was qualified by their Honours' subsequent statement (also at 30) that: "It is one thing to leave it to an independent contractor to decide for himself how to do his work; it is another thing to leave him in ignorance of a fact that is material to his decision if he, using reasonable care, might not discover that fact." 40 PPSC was an expert in the business of dismantling racking systems of the kind from which Mr Howell fell. Nolras had entered into a contract with PPSC where PPSC undertook to dismantle the racking system at the factory. The question therefore arises whether the water-affected shelf constituted a defect in the factory which PPSC, as an expert in dismantling racking systems, was accustomed to meeting and safeguarding its employees against. Put in another way, was it reasonable for Nolras to rely solely on PPSC and its employees, as experts in the field, to take appropriate steps to safeguard themselves against water-affected shelves and not warn them that rainwater had come in contact with the shelving. 41 Part of Mr Davis's work had been to replace damaged chipboard shelves found in other factories. He testified that he had previously seen chipboard that had been affected by water. He was asked, in evidence-in-chief, how, in the course of dismantling racking systems, he would determine whether a shelf was so water-damaged that it needed to be discarded. He explained that, in that event, the shelf would be removed so that could be examined. On closer inspection, he would look down "the edge" of the shelf as that would give "an indication as to the swelling". He said that that was "generally the only indication you can get". Mr Davis testified that, while damage to shelving caused by "usage" was a "visible thing", water damage could not be detected by ordinary inspection of a racking system. The tenor of his evidence was that the presence of a water-damaged shelf was not a surprising phenomenon. 42 Mr Davis agreed that in the course of his work he would not infrequently "come across racking systems which had been damaged in some way". This included damage to "the chipboard material used in the middle". He said that this was a common experience in his employment. When PPSC employees realised that a shelf was damaged they would have adopt a procedure different to the one they usually used. Mr Davis said, "We'd take an hour longer but we would deal with it." 43 The following exchange occurred in the course of Mr Davis's cross-examination: "Q. It was quite common for pieces of chipboard to be damaged by water, is that right? A. Generally if it was on the outside perspective, yes, but in a warehouse the only generally [sic] damages we look for are a usage damage [sic] and they're quite noticeably [sic]. You can see them quite well and truly. Q. You say, generally, but they're occasions when the chipboard would be damage[d] wouldn't it? A. From water damage? Yes. Q. Inside the warehouse? A. That's correct. Q. Other than this occasion? A. Yes." 44 I would interpose the comment that it seems from this exchange that chipboard could be used as shelving in racking systems that were "outside" and not under cover; this reinforces the proposition that some kinds of chipboard would be able better to withstand water than others (otherwise chipboard shelving could not be used outdoors). 45 Significantly, this exchange also confirms Mr Davis's other evidence that on occasions he would find chipboard shelving, used internally, that had been damaged by water. 46 Mr Davis confirmed that he knew that water-damaged chipboard shelving might be unable to support a person's weight. He accepted that one of the hazards of his occupation was that the shelves might have a defect "that couldn't be detected and may not support a weight". I have referred to the method adopted by PPSC employees to cope with such a hazard, namely, when walking on an upper shelf, they would traverse the shelf gradually, one step at a time, and would attempt to place their feet where the shelf was supported by the two central horizontal steel members. If they heard cracks or creaks they would stop and investigate. If they did not hear a crack or creak, they would keep going. 47 This does not appear to be a safe method of work, but it was adopted by PPSC and Nolras bore no responsibility for it. Nolras had contracted with PPSC to dismantle its racks and it was entitled to assume that it would take appropriate care for the safety of its employees, subject to any unusual or unexpected risks on the premises. 48 The evidence establishes that PPSC and its employees were accustomed to meeting and safeguarding themselves against the possibility of shelves being structurally damaged by water. The fact that water-damaged shelving may have been encountered relatively infrequently did not make the existence of such a defect unusual in the sense of being a fact that a PPSC employee, "using reasonable care, might not discover". Having to deal with a water-damaged shelf from time to time was not an unexpected phenomenon. It was simply part of the job which PPSC, as a specialist racking system dismantler, had contracted to undertake. 49 Therefore, in my opinion, in the circumstances of this case it was reasonable for Nolras to rely on PPSC's employees to take reasonable care for their own safety should they encounter water-affected shelving. In my opinion, a warning by Nolras was not a reasonable response to the risk of harm that should have been perceived by it. In my opinion, the principle expressed in Papatonakis applies. 50 Accordingly, I would not uphold Mr Davis's failure to warn argument.

Conclusion 51 I would not uphold Mr Davis's arguments as to liability. In the circumstances, there is no need to address the arguments advanced as to quantum. 52 I would dismiss the appeal with costs. 53 M W CAMPBELL AJA: I have had the advantage of reading in draft the judgments of Ipp JA and Brereton J. I agree with the orders proposed by Ipp JA with which Brereton J agreed. 54 Subject to what follows I agree substantially with the reasons given for those orders. 55 Ipp JA did not regard the circumstance that the defective chipboard was indoors rather than outdoors as a distinguishing feature in considering whether it was, in the relevant sense, an unusual danger [45], [49]. On the other hand, Brereton J did so regard it [68] to [71]. 56 This distinction led to somewhat different approaches to the disposition of the appeal so far as it was based on an allegation of failure to warn. 57 If it be assumed that the circumstance referred to is not a distinguishing feature I agree with Ipp JA's reasons in relating to the alleged failure to warn. If, on the other hand, it be assumed that it is a distinguishing feature I agree with Brereton J. 58 It does seem to me that the facts that the building was "very, very old", had a roof which showed light through crevices and that there were puddles of water on the floor in wet weather at times when employees of PPSC were present rather support the view taken by Ipp JA. However, it is not necessary for me to reach a conclusion on the point for either alternative leads to the same result. 59 BRERETON J: The appellant Nathan Davis was an employee of Pallet Packing Supply Company ("PPSC"), whose business included the installation and removal of pallet racking systems. The respondent Nolras Pty Ltd contracted PPSC to dismantle and remove a pallet racking system, the shelves of which were made of chipboard, from factory premises occupied by Nolras. While Mr Davis and his co-worker Mr Howell were dismantling the racking, a shelf on which Mr Howell was standing fractured and he fell to the ground. Mr Davis saw that one fragment of the chipboard had flown into the air and, fearing that it would land on and injure Mr Howell, he dived onto his knees and caught it, injuring his knees in the process. The chipboard shelf was unable to support Mr Howell's weight because it had been affected by water which had entered the factory during wet weather, through holes in the roof.

60 At trial, Rein DCJ, while acknowledging that an occupier owed a general duty of care to entrants, in respect of which the ordinary principles of negligence applied, held that given the expertise of PPSC and the ordinary risks incidental to the works which it contracted to perform, either Nolras owed Mr Davis no relevant duty of care or, if it did, there was no relevant breach. Mr Davis appeals to this court, contending that: · Nolras owed him a duty to keep the roof in good repair, breach of which resulted in water damage to the chipboard shelving and thus to his injury, and · Nolras owed him a duty to warn him and his co-workers that the chipboard has been exposed to water and thus had possibly been damaged. Did Nolras owe Mr Davis a duty to maintain the roof in good repair?

61 I am unable to accept that Nolras owed entrants such as Mr Davis - an employee of a specialist contractor engaged to dismantle a racking system on the premises - a duty to maintain the roof in good repair, even assuming that it was foreseeable that the ingress of water affecting the chipboard would create a risk of injury to persons engaged to dismantle it.

62 The deterioration of the roof was not itself the danger. It was at most a step on the way to the creation of a danger, if water penetrating the roof came into contact with the chipboard. Repairing the roof would not have removed the danger once the strength and integrity of the chipboard had been compromised by exposure to water. As Ipp JA, whose judgment in draft I have had the benefit of reading, points out, there were alternative means of reducing or removing the risk created by the penetration of water affecting the chipboard shelving, including the replacement of any affected shelving, which would probably have been more economical than repairing the roof, or the use of warnings. An occupier's duty will often be sufficiently discharged by notice or a warning which enables the entrant to appreciate and avert or avoid the danger, although there are cases in which physical removal of the danger may be required [London Graving Dock Ltd v Horton [1951] AC 737, 772-773 (Lord MacDermott); Edmonds v Commonwealth (1961) 61 SR (NSW) 527, 531-2; cf Roles v Nathan [1963] 1 WLR 1117, 1124-1125 (Lord Denning MR), 1127-1128 (Harman LJ); Bond v SA Railway Commissioners (1923) 33 CLR 273, 289 (Isaacs J); Phillis v Daly (1988) 15 NSWLR 65 (CA)].

63 In my opinion, in these circumstances reasonable care - even assuming foreseeability of risk to a person such as Mr Davis - did not require maintenance of the roof in good repair.

64 An occupier of premises does not owe to specialist independent contractors engaged to perform work on the premises a duty to warn of defects which such specialist contractors are accustomed to encounter and safeguard themselves against [Papatonakis v Australian Telecommunications Commission (1985) 156 CLR 7, 30 (Brennan and Dawson JJ); Felk Industries Pty Ltd v Mallet [2005] NSWCA 111, [18] (Hunt AJA; Sheller JA and MW Campbell AJA agreeing); Christmas v General Cleaning Contractors [1952] 1 KB 141 (CA); affirmed [1953] AC 180 (HL); Roles v Nathan, 1123 (Lord Denning MR)]. However, this principle does not extend to allowing an occupier to leave such a contractor in ignorance of a fact material to the decision how to perform the work if, using reasonable care, the contractor might not discover it [Papatonakis, 30 (Brennan and Dawson JJ)].

65 The preferable reconciliation of the particular principles in Papatonakis with the now established position that occupier's liability is but one aspect of the general principles of negligence and that the special rules relating to different categories of entrants have been swept away [Australian Safeway Stores Pty Ltd v Zaluzna (1987) 162 CLR 479] is that the Papatonakis principles do not constitute an exception to the normal duty of an occupier to an entrant, but that in the application of those ordinary principles, a specialist contractor may be taken to expect to encounter and safeguard himself or herself against those risks which are ordinarily incidental to performance of his or her specialist function, so that such risks are not regarded as necessitating a warning [cf Papatonakis, 20-21 (Mason J); Bates v Parker [1953] 2 QB 231, 240 (Romer LJ)].

66 Consistently with that approach, if, in that context, a risk remains an unusual one, in the sense that it exceeds what is ordinarily incidental to performance of the contractor's specialist function, and might not be discoverable by the contractor prudently performing his or her function (including making appropriate inspections), there will (subject to any issue of foreseeability) remain a duty to warn the entrant of it. This limitation on the Papatonakis "principle" has two elements: the first is the materiality of the fact to the contractor's decision how to proceed, and the second is that the fact might not be discovered with reasonable care on the part of the contractor. Although in Papatonakis its application was in circumstances where the unusual risk was of the occupier's own making, the linesman having been injured as a result of the occupier having tampered with the cable, it would be inconsistent with the general duty owed by an occupier to an entrant to limit it in that way. If there is a foreseeable risk which exceeds that ordinarily incidental to performance of the contractor's specialist work, it calls for a warning, whether or not it was created by the occupier, because it is outside the scope of what the entrant may be taken to expect to encounter.

67 Water damage to chipboard shelving which was not under cover was a hazard not infrequently encountered by Mr Davis and his colleagues. In the context of shelving located externally, it could not be described as an unusual danger; to the contrary, it was one which PPSC and its employees including Mr Davis were accustomed to encounter and safeguard themselves against, by close inspection and adoption, where necessary, of a method of dismantling which was somewhat slower, but avoided stepping on the shelving - since they knew that, if it had been exposed to water, the chipboard might not retain the strength to support a man's weight.

68 However, water damage to chipboard shelving installed internally and under cover was exceptional, though not unknown. Mr Davis said that when in a warehouse, as distinct from externally, the only damage for which they generally looked was usage damage, which was quite noticeable; water damage was not easily seen. The adoption of different practices for internal and external shelving is readily understandable: the latter would ordinarily be expected to be exposed to weather, and potentially damaged by rainfall, in a way in which the former ordinarily would not.

69 A useful touchstone for the materiality test is whether the matter in question is one knowledge of which would make a difference to how the tradesman would proceed. Although Mr Davis accepted that there had been occasions on which he had encountered, internally, chipboard which had been damaged by water - and that one of the hazards of his occupation was that a shelf might have a defect which could not be detected and might not support a worker's weight, so that he and his fellow workers adopted a means for mitigating the risk, by moving gradually and cautiously on shelving, using so far as possible those parts which were supported by steel members, and stopping if a crack or creak was heard - this was a case in which the ingress of water had significantly increased the level and degree of risk of damage to the integrity and strength of the chipboard. Mr Davis and his colleagues knew that water-damaged chipboard might be unable to support the weight of a worker standing on it. Had they known that the racking system had been exposed to water, they would have known that the risk of damage to the integrity and strength of the shelving was substantially increased, and (contrary to their usual practice internally) they would have inspected it closely for water damage, and upon discovering any sign of such damage they would have adopted the alternative, slower, system of dismantling which was referred to in the evidence. I cannot escape the conclusion that, had they been warned that there had been exposure to water - and thus appreciated that the risk of damage had been significantly increased about the norm for internal racking - they would have adopted a substantially more cautious, albeit slower, approach. In other words, the fact that the racking system had been exposed to water was material to the workers' decision as to how they would perform their task.

70 The difficulty of detecting water damage, coupled with the unlikelihood of its being encountered in internal shelving, and thus the practice in respect of internal shelving of inspecting only for usage damage, warrants the conclusion that, using reasonable care, workers such as Mr Davis might not discover that internal racking had been exposed to and potentially damaged by water.

71 It follows that in my opinion, the fact that the racking, located as it was internally, had been exposed to water with the result that its strength and integrity might have been compromised, was a fact material to the worker's decision how to proceed, which using reasonable care he might not discover, and accordingly was, in the relevant context, not one which the Papatonakis principle excluded from the occupier's general duty to warn of other than obvious dangers: in the context of internal shelving, it was, from the perspective of Mr Davis and Mr Howell, an unusual danger, exceeding the risks which they would ordinarily anticipate.

72 However, while it is their perspective that is relevant when addressing materiality and discoverability, that is not the relevant perspective when considering foreseeability. A duty to warn, as an incident of a duty of care, assumes knowledge of the risk, and can exist only in respect of dangers of which the occupier knows, or using reasonable care should have known [cf Horton, 766]. There can be no duty to warn of dangers of which a prudent occupier would not have known. Thus, the existence of a duty to warn depends on the actual or constructive knowledge of the occupier, not of the entrant, and the duty to warn entrants of risks attends dangers of which the occupier knows or ought to know. In the context of entrants who are skilled specialist contractors, this means that the duty to warn does not extend to dangers which a reasonable occupier would not have foreseen, or if foreseen would not have thought it reasonably necessary to guard against having regard to the specialist knowledge and skill of those entrants [Papatonakis, 21 (Mason J)].

73 Thus, in deciding what a reasonably prudent occupier "ought to have known" - that is to say, what it should have learnt from inspection - it is relevant to take into account the expertise of the contractor. This is the preferable explanation of the case which was the progenitor of Papatonakis, namely Christmas v General Cleaning Contractors [1952] 1 KB 141 (CA), in which an occupier was held not liable to a window cleaner for the insecurity of a part of premises which he used as a foot or handhold for the purpose of cleaning the exterior of windows. It can hardly be doubted that if the occupier had known that the window cleaner was going to use the hold and that it was insecure, there would have been a duty to warn; but not knowing of it, reasonable care did not require him to interrogate the window cleaner to ascertain how he would proceed, nor to inspect the premises to ascertain whether the holds he would use were satisfactory [cf Bates v Parker, 239 (Morris LJ), 240-241 (Romer LJ)]. Reasonable care does not require that an occupier conduct an interrogation of a specialist contractor to ascertain how the work will be done, and then an inspection (which in any event would be less expert than any the contractor might perform) of the contractor's workplace in order to identify special risks which the contractor might as a result encounter. This is because the specialist contractor is in a superior position to the occupier to make any relevant inspection and judgment.

74 I agree with Ipp JA that it should be inferred that Nolras knew or ought to have known that, from time to time, water entering though the roof of the factory came into contact with the shelves of the racking system. But as Ipp JA also points out, foreseeability of a risk of harm to persons such as Mr Davis requires more than that: it would be necessary for Nolras also to foresee that persons such as Mr Davis and Mr Howell might stand on the shelving, and that exposure to water might have impaired the strength and integrity of the shelving to the extent that it would not support them.

75 Although Mr Davis knew of the propensity of chipboard to deteriorate when exposed to water, that was knowledge derived from years of experience in the industry. To treat an occupier such as Nolras as having similar knowledge of the properties of chipboard - whether in general, or in respect of the particular type and grade of chipboard installed in the racking system - would in my opinion involve attributing to it a degree of expert knowledge beyond that of the ordinary reasonable occupier. And to attribute to Nolras knowledge that, to dismantle a racking system, PPSC would adopt a system of work which required its employees to stand on the shelving (rather than adopting the slower but safer alternative method referred to in the evidence) would involve attributing to it an understanding of the practices and procedures of specialist contractors which likewise exceeds that of the ordinary reasonable occupier. Moreover, an occupier is not responsible to an employee of a contractor for an unsafe manner of work adopted by the employer [Ferguson v Welsh [1987] 1 WLR 1553 (HL)]. Having engaged PPSC as a specialist contractor, reasonable care for entrants employed by PPSC did not require Nolras to inform itself how PPSC would perform its task and conduct an inspection which would necessarily be less expert than any that PPSC could itself conduct to ascertain whether its employees would encounter any special risks which might arise.

76 Accordingly, in my opinion, notwithstanding that Nolras knew or ought to have known that from time to time water entering though the roof of the factory came into contact with the shelves of the racking system, it was not reasonably foreseeable to an occupier such as Nolras that the shelving might have been compromised by exposure to water, and that persons such as Mr Davis and Mr Howell might stand on it and be injured as a result. It follows that the danger to Mr Howell and Mr Davis, though an unusual one which called for a warning if known to the occupier, was not one of which Nolras knew or ought reasonably to have known, and was therefore not one of which Nolras was obliged to give a warning. The position would be otherwise if Nolras had known that the chipboard had been compromised and how PPSC would perform its task, but given PPSC's function and expertise, Nolras was not required to find out.

77 The defective roof was not itself the relevant danger. Its repair (after the chipboard had been compromised) would not have removed the danger. There were alternative means of reducing or removing the danger created by the penetration of water affecting the chipboard shelving, which would probably have been more economical than repairing the roof. A warning would have been sufficient discharge of any duty owed by the occupier in the circumstances. Accordingly, reasonable care did not require that Nolras maintain the roof in good repair, even assuming foreseeability of risk to a person such as Mr Davis.

78 That the racking, located internally, had been exposed to water, with the result that its strength and integrity might have been compromised, was a fact material to the worker's decision how to proceed, which using reasonable care he might not discover, and accordingly was not one which the Papatonakis principle excluded from the occupier's general duty to warn of other than obvious dangers: in the context of internal shelving, it was, from the worker's perspective, an unusual danger. However, it was not reasonably foreseeable to an occupier such as Nolras that the shelving might have been compromised by exposure to water, and that persons such as Mr Davis and Mr Howell might be required to stand on it and be injured as a result. Having engaged PPSC as a specialist contractor, reasonable care did not require Nolras to inform itself how PPSC would perform its task and conduct an inspection, less expert than any that PPSC could itself conduct, to ascertain whether PPSC's employees would encounter any special risks which might arise. Accordingly, the danger to Mr Howell and Mr Davis, though an unusual one which called for a warning if known to the occupier, was not one of which Nolras knew or ought reasonably to have known, and was therefore not one of which Nolras was obliged to give a warning.

79 It follows that Nolras' general duty of care to Mr Davis as an entrant did not in the circumstances extend to require maintenance of the roof in good repair, nor warnings to persons such as Mr Davis and Mr Howell that the shelving might have been compromised by exposure to water. Nolras did not breach its duty of care by omitting to take those steps.

80 I agree that the appeal should be dismissed with costs.

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