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16. Gardiner v Motherwell Machinery and Scrap Co Ltd  1 WLR 1424, another Scottish case, concerned a pursuer who had worked for the defenders for a period of some three months, demolishing buildings, and had contracted dermatitis. In an action against the defenders he claimed that they should have provided him with washing facilities but had failed to do so and that their failure had caused him to suffer from dermatitis. This contention was upheld by the Lord Ordinary (Lord Kilbrandon) who awarded him damages. The defenders did not on appeal challenge the finding of breach but contended that the pursuer had failed to prove any connection between his disease and the work which he had been doing. The First Division accepted this argument and found for the defenders, a decision against which the pursuer appealed. In his leading opinion in the House, Lord Reid considered at some length the conflict of medical evidence at the trial and its treatment by the First Division, and expressed his conclusion (at p 1429):
"In my opinion, when a man who has not previously suffered from a disease contracts that disease after being subjected to conditions likely to cause it, and when he shows that it starts in a way typical of disease caused by such conditions, he establishes a prima facie presumption that his disease was caused by those conditions. I think that the facts proved in this case do establish such a presumption. That presumption could be displaced in many ways. The respondents sought to show, first, that it is negatived by the subsequent course of the disease and, secondly, by suggesting tinea pedis as an equally probable cause of its origin. I have found the case difficult, but on the evidence as it stands I have come to the opinion that they have failed on both points. If the appellant's disease and consequent loss should be attributed to the work which he was doing in the respondents' service, it was not argued that they are not liable."
Lord Cohen and Lord Guest agreed, as did Lord Hodson although with some initial hesitation. Lord Guest described the question as a pure question of fact whether on the balance of probabilities the dermatitis had arisen from the pursuer's employment (p 1431). The House would seem to have regarded the pursuer as establishing a prime facie case which the defenders had failed to displace.
17. In the course of the present appeals much argument was directed to the decision of the House in McGhee v National Coal Board  1 WLR 1. The earlier stages of that case are reported at 1973 SC(HL) 37 and are important in understanding what the House decided. Mr McGhee had been employed by the National Coal Board for about 15 years, almost always working in pipe kilns. For some 4½ days he then worked at a brick kiln, giving up because of a dermatitic condition which had by then developed. The work inside the kiln was very hot and very dusty. The heat made men sweat profusely and the operation of the fan caused them to be covered in dust and grit. The pursuer contended that his dermatitis had been caused by his period of working in the brick kiln, short though it had been. The employers contended that his work had not caused the dermatitis and that it was non-occupational in origin. There was at the trial a conflict of medical evidence but the Lord Ordinary (Lord Kissen) held that the pursuer had contracted the dermatitis in the course of his work at the brick kiln and as a result of his exposure to dust and ashes when working there (p 39). Counsel for the pursuer accepted at trial that he could not establish a breach of statutory duty nor a breach of common law duty based on a failure to ventilate, but relied on two alleged breaches by the employers: of a duty to take care that the kiln had cooled sufficiently before men went in to work in it and of a duty to take reasonable care to provide adequate showers to enable men to remove dust from their bodies. The Lord Ordinary rejected the first of these complaints on a number of grounds, including the lack of proof that the breach of duty, even if established, had caused or materially contributed to the dermatitis: it was not enough that a reduction of heat would have lessened the risk (p 41). The Lord Ordinary concluded that the employers were at fault in failing to provide showers (p 42) but found against the pursuer on the basis of evidence given by two expert dermatologists, Dr Hannay and Dr Ferguson, called by the pursuer and the employers respectively. He said (at pp 42-43):
"As I have maintained earlier, the pursuer, in order to succeed, must also establish, on a balance of probabilities, that this fault on the part of the defenders 'caused or materially contributed to his injury', that is to his contracting dermatitis. Dr Hannay's evidence was that he could not say that the provision of showers would probably have prevented the disease. He said that it would have reduced the risk materially but he would not go further than that. Dr Ferguson said that washing reduces the risk. Pursuer's counsel maintained that a material increase in the risk of contracting a disease was the same as a material contribution to contracting the disease and that Dr Hannay established this by his evidence. I think that defenders' counsel was correct when he said that the distinction drawn by Dr Hannay was correct and that an increase in risk did not necessarily mean a material contribution to the contracting of the disease. The two concepts are entirely different. A material increase in risk may refer only to possibilities and may not make a possibility into a probability. It may strengthen the possibility but that cannot mean that in all such cases the possibility has become a probability. What the pursuer has to show is that, as he avers, he would not have contracted the disease but for the defenders' breach of duty. He has to show that this was probable and the degrees of risk have no relevance unless they make the contraction of the disease more probable than not contracting the disease. He cannot succeed if the only inference from the evidence is that lack of shower baths is a possibility as a cause of his having contracted the disease and the provision of shower baths would have increased the possibility but not made it a probability. That is the only inference which I can draw from Dr Hannay's evidence and that was the best evidence for the pursuer. Causal connection between fault and the contraction of the disease has not been established."
18. The pursuer appealed to the First Division against the dismissal of his claim. The medical evidence given at the trial was reviewed in detail, and in particular an exchange between cross-examining counsel and Dr Hannay ( pp 43-44, 47, 50):
"Q. Do I understand you to say you are not in a position to say that the provision of showers would probably have prevented his contracting this skin trouble?
A. No one could say that that would prevent that man developing the condition. It would be likely to reduce the chances."
In answer to further questions the doctor repeated his opinion that he could only say that the provision of showers would have reduced the chances of the pursuer contracting dermatitis and that that was as far as he was able to go. In the course of his judgment the Lord President, Lord Clyde, considered the pneumoconiosis cases and expressed his conclusion (at p 44):
"But in contrast to the pneumoconiosis cases, the present case is essentially concerned with proof of the causal connection between the fault alleged (i.e. inadequate washing facilities) and the development of dermatitis. Even if the pursuer had established (as he did not) that the absence of washing facilities increased the risk of the pursuer getting dermatitis, that would clearly not prove that the absence of these facilities caused the disease, nor indeed would it go any distance towards proving it. For risk of dermatitis and causation of dermatitis are two quite separate matters."
Lord Migdale was of the same opinion (at pp 47-48):
"Counsel for the pursuer contended that as it was now accepted that the failure to provide a shower was a breach of the duty which the defenders owed to the pursuer to take reasonable steps for his well-being, the doctors' evidence that it would have materially reduced the risk of dermatitis is enough to link the failure with the injury. Counsel for the defenders, on the other hand, contended that the test of causal connection between the breach and the injury is whether the provision of a shower would, on a balance of probabilities, have prevented the dermatitis. The Lord Ordinary says an increase in risk does not mean a material contribution to the contracting of the disease. A material increase in risk may refer only to possibilities and it does not make a possibility into a probability. 'What the pursuer has to show is that, as he avers, he would not have contracted the disease but for the breach of duty'. He has to show this on a balance of probabilities.
In my opinion this is correct. Unless the pursuer can point to evidence that shows that a shower would more probably have avoided the disease than not, he cannot succeed and I do not find that evidence in this case."
Lord Johnston was more hesitant, but in view of the other opinions did not feel inclined to take the view that the evidence was sufficient to allow him to hold that the test of the balance of probability had been satisfied (p 50).
19. On appeal to the House counsel for the pursuer faced the problem, as he had at trial and in the First Division, that his own evidence precluded a finding that the absence of a shower had probably caused the pursuer's dermatitis. Mr Davidson QC accordingly relied on the evidence that provision of a shower would have materially reduced the risk to contend that he had made out a prima facie case. The contrary argument for the employers was advanced by Mr James Mackay QC, as reported at p 51:
"It was accepted that [the provision of washing facilities] would have been a reasonable precaution, but it did not follow that this would have eliminated the risk. The employee might have developed dermatitis in any event. If the precaution would not have prevented the disease, the appellant was not entitled to damages. In the case of pneumoconiosis the inhalation of dangerous dust inevitably created a basis for the disease by accumulation, whereas in the case of dermatitis a particle of grit would cause the disease only if there were an abrasion which opened up the layer below the horny outer layer of the skin. In the case of pneumoconiosis all the particles could be blamed. It was not so in the case of dermatitis. The mere fact that shower baths would have reduced the chances of the contraction of the disease did not mean that what was probable would thereby have been rendered improbable."
Thus the issue, as presented to the House, was whether the pursuer could succeed despite his inability to show that he would probably not have suffered dermatitis but for the defenders' failure to provide the showers which they should have provided.
20. In the House, opinions were given by all five members of the Appellate Committee which heard the appeal and the appeal was allowed:  1 WLR 1. Lord Reid, giving the first opinion, described the pursuer's complaint based on the failure to provide shower facilities as raising "a difficult question of law" (p 3). He pointed out that the breach of duty in relation to showers was admitted, and it was admitted that the disease was attributable to the work which the pursuer had performed in the brick kiln, but it was contended that the pursuer had not proved that the defenders' failure to carry out the admitted duty had caused the onset of the disease (p 3). Lord Reid's understanding of the evidence, and his view of the proper approach to it, appear from the following passage of his opinion (at pp 4-5):
"In the present case the evidence does not show - perhaps no one knows - just how dermatitis of this type begins. It suggests to me that there are two possible ways. It may be that an accumulation of minor abrasions of the horny layer of the skin is a necessary precondition for the onset of the disease. Or it may be that the disease starts at one particular abrasion and then spreads, so that multiplication of abrasions merely increases the number of places where the disease can start and in that way increases the risk of its occurrence.
I am inclined to think that the evidence points to the former view. But in a field where so little appears to be known with certainty I could not say that that is proved. If it were, then this case would be indistinguishable from Wardlaw's case. But I think that in cases like this we must take a broader view of causation. The medical evidence is to the effect that the fact that the man had to cycle home caked with grime and sweat added materially to the risk that this disease might develop. It does not and could not explain just why that is so. But experience shows that it is so. Plainly that must be because what happens while the man remains unwashed can have a causative effect, though just how the cause operates is uncertain. I cannot accept the view expressed in the Inner House that once the man left the brick kiln he left behind the causes which made him liable to develop dermatitis. That seems to me quite inconsistent with a proper interpretation of the medical evidence. Nor can I accept the distinction drawn by the Lord Ordinary between materially increasing the risk that the disease will occur and making a material contribution to its occurrence.
There may be some logical ground for such a distinction where our knowledge of all the material factors is complete. But it has often been said that the legal concept of causation is not based on logic or philosophy. It is based on the practical way in which the ordinary man's mind works in the everyday affairs of life. From a broad and practical viewpoint I can see no substantial difference between saying that what the defender did materially increased the risk of injury to the pursuer and saying that what the defender did made a material contribution to his injury."
Lord Wilberforce acknowledged the need for the pursuer to establish both a breach of duty and a causal connection between the default and the disease complained of (p 5), and also the difficulties of proof which the pursuer faced (pp 5-6):
"[The pursuer's medical expert] could not do more than say that the failure to provide showers materially increased the chance, or risk, that dermatitis might set in."
Lord Wilberforce accepted that merely to show that a breach of duty led to an increase of risk was not enough to enable a pursuer to succeed, but continued (at page 6):
"But the question remains whether a pursuer must necessarily fail if, after he has shown a breach of duty, involving an increase of risk of disease, he cannot positively prove that this increase of risk caused or materially contributed to the disease while his employers cannot positively prove the contrary. In this intermediate case there is an appearance of logic in the view that the pursuer, on whom the onus lies, should fail - a logic which dictated the judgments below. The question is whether we should be satisfied, in factual situations like the present, with this logical approach. In my opinion, there are further considerations of importance. First, it is a sound principle that where a person has, by breach of a duty of care, created a risk, and injury occurs within the area of that risk, the loss should be borne by him unless he shows that it had some other cause. Secondly, from the evidential point of view, one may ask, why should a man who is able to show that his employer should have taken certain precautions, because without them there is a risk, or an added risk, of injury or disease, and who in fact sustains exactly that injury or disease, have to assume the burden of proving more: namely, that it was the addition to the risk, caused by the breach of duty, which caused or materially contributed to the injury? In many cases, of which the present is typical, this is impossible to prove, just because honest medical opinion cannot segregate the causes of an illness between compound causes. And if one asks which of the parties, the workman or the employers, should suffer from this inherent evidential difficulty, the answer as a matter of policy or justice should be that it is the creator of the risk who, ex hypothesi must be taken to have foreseen the possibility of damage, who should bear its consequences."
Having referred to Wardlaw's and Nicholson's cases Lord Wilberforce concluded (at page 7):
"The present factual situation has its differences: the default here consisted not in adding a material quantity to the accumulation of injurious particles but by failure to take a step which materially increased the risk that the dust already present would cause injury. And I must say that, at least in the present case, to bridge the evidential gap by inference seems to me something of a fiction, since it was precisely this inference which the medical expert declined to make. But I find in the cases quoted an analogy which suggests the conclusion that, in the absence of proof that the culpable addition had, in the result, no effect, the employers should be liable for an injury, squarely within the risk which they created and that they, not the pursuer, should suffer the consequence of the impossibility, foreseeably inherent in the nature of his injury, of segregating the precise consequence of their default."
Lord Simon of Glaisdale considered that Wardlaw's and Nicholson's cases established a rule (at page 8)
"that where an injury is caused by two (or more) factors operating cumulatively, one (or more) of which factors is a breach of duty and one (or more) is not so, in such a way that it is impossible to ascertain the proportion in which the factors were effective in producing the injury or which factor was decisive, the law does not require a pursuer or plaintiff to prove the impossible, but holds that he is entitled to damages for the injury if he proves on a balance of probabilities that the breach or breaches of duty contributed substantially to causing the injury. If such factors so operate cumulatively, it is, in my judgment, immaterial whether they do so concurrently or successively."
Lord Simon then continued (page 8):
"The question, then, is whether on the evidence the appellant brought himself within this rule. In my view, the failure to take steps which would bring about a material reduction of the risk involves, in this type of case, a substantial contribution to the injury. In this type of case a stark distinction between breach of duty and causation is unreal. If the provision of shower baths was (as the evidence showed) a precaution which any reasonable employer in the respondents' position would take, it means that such employer should have foreseen that failure to take the precaution would, more probably than not, substantially contribute towards injury: this is sufficient prima facie evidence."
Lord Simon regarded "material reduction of the risk" and "substantial contribution to the injury" as mirror concepts. Any other conclusion would mean that the defenders were under a legal duty which they could, on the present state of medical knowledge, ignore (page 9).
Lord Kilbrandon appears to have adopted a more orthodox approach to tortious liability. He said (at page 10):
"When you find it proved (a) that the defenders knew that to take the precaution reduces the risk, chance, possibility or probability of the contracting of a disease, (b) that the precaution has not been taken, and (c) that the disease has supervened, it is difficult to see how those defenders can demand more by way of proof of the probability that the failure caused or contributed to the physical breakdown ... In the present case, the pursuer's body was vulnerable, while he was bicycling home, to the dirt which had been deposited on it during his working hours. It would not have been if he had had a shower. If showers had been provided he would have used them. It is admittedly more probable that disease will be contracted if a shower is not taken. In these circumstances I cannot accept the argument that nevertheless it is not more probable than not that, if the duty to provide a shower had not been neglected, he would not have contracted the disease. The pursuer has after all, only to satisfy the court of a probability, not to demonstrate an irrefragable chain of causation, which in a case of dermatitis, in the present state of medical knowledge, he could probably never do."
In Lord Salmon's opinion the question before the House was whether the pursuer's dermatitis was proved to have been caused or materially contributed to by the defenders' negligence (page 11). He rejected the view, expressed by the Lord President (see paragraph 18 above) that to increase the risk of injury was not, in the circumstances of this case, to cause the injury. In such a case he regarded it as unrealistic and contrary to ordinary common sense to hold that the negligence which materially increased the risk of injury did not materially contribute to causing it (pages 11-12). He observed (at page 12):
"I think that the approach by the courts below confuses the balance of probability test with the nature of causation. Moreover, it would mean that in the present state of medical knowledge and in circumstances such as these (which are by no means uncommon) an employer would be permitted by the law to disregard with impunity his duty to take reasonable care for the safety of his employees."
Lord Salmon's conclusion (pages 12-13) was expressed in these terms:
"In the circumstances of the present case, the possibility of a distinction existing between (a) having materially increased the risk of contracting the disease, and (b) having materially contributed to causing the disease may no doubt be a fruitful source of interesting academic discussions between students of philosophy. Such a distinction is, however, far too unreal to be recognised by the common law."
21. This detailed review of McGhee permits certain conclusions to be drawn. First, the House was deciding a question of law. Lord Reid expressly said so (page 3). The other opinions, save perhaps that of Lord Kilbrandon, cannot be read as decisions of fact or as orthodox applications of settled law. Secondly, the question of law was whether, on the facts of the case as found, a pursuer who could not show that the defender's breach had probably caused the damage of which he complained could nonetheless succeed. Thirdly, it was not open to the House to draw a factual inference that the breach probably had caused the damage: such an inference was expressly contradicted by the medical experts on both sides; and once that evidence had been given the crux of the argument before the Lord Ordinary and the First Division and the House was whether, since the pursuer could not prove that the breach had probably made a material contribution to his contracting dermatitis, it was enough to show that the breach had increased the risk of his contracting it. Fourthly, it was expressly held by three members of the House (Lord Reid at page 5, Lord Simon at page 8 and Lord Salmon at pages 12-13) that in the circumstances no distinction was to be drawn between making a material contribution to causing the disease and materially increasing the risk of the pursuer contracting it. Thus the proposition expressly rejected by the Lord Ordinary, the Lord President and Lord Migdale was expressly accepted by a majority of the House and must be taken to represent the ratio of the decision, closely tied though it was to the special facts on which it was based. Fifthly, recognising that the pursuer faced an insuperable problem of proof if the orthodox test of causation was applied, but regarding the case as one in which justice demanded a remedy for the pursuer, a majority of the House adapted the orthodox test to meet the particular case. The authority is of obvious importance in the present appeal since the medical evidence left open the possibility, as Lord Reid pointed out at page 4, that the pursuer's dermatitis could have begun with a single abrasion, which might have been caused when he was cycling home, but might equally have been caused when he was working in the brick kiln; in the latter event, the failure to provide showers would have made no difference. In McGhee, however, unlike the present appeals, the case was not complicated by the existence of additional or alternative wrongdoers.
22. In Wilsher v Essex Area Health Authority a problem of causation arose in a different context. A prematurely-born baby was the subject of certain medical procedures, in the course of which a breach of duty occurred. The baby suffered a condition (abbreviated as RLF) of a kind which that breach of duty could have caused, and the breach of duty increased the risk of his suffering it. But there were a number of other factors which might have caused the injury. In the Court of Appeal ( QB 730 at 771-772) Mustill LJ concluded a detailed review of McGhee by making this statement of principle:
"If it is an established fact that conduct of a particular kind creates a risk that injury will be caused to another or increases an existing risk that injury will ensue; and if the two parties stand in such a relationship that the one party owes a duty not to conduct himself in that way; and if the first party does conduct himself in that way; and if the other party does suffer injury of the kind to which the risk related; then the first party is taken to have caused the injury by his breach of duty, even though the existence and extent of the contribution made by the breach cannot be ascertained."
Omitted from this statement is any reference to condition (5) in the composite question formulated in paragraph 2 at the outset of this opinion. It was on this omission that Sir Nicolas Browne-Wilkinson V-C founded his dissenting opinion (at page 779):
"To apply the principle in McGhee v National Coal Board  1 WLR 1 to the present case would constitute an extension of that principle. In the McGhee case there was no doubt that the pursuer's dermatitis was physically caused by brick dust: the only question was whether the continued presence of such brick dust on the pursuer's skin after the time when he should have been provided with a shower caused or materially contributed to the dermatitis which he contracted. There was only one possible agent which could have caused the dermatitis, viz, brick dust, and there was no doubt that the dermatitis from which he suffered was caused by that brick dust.
In the present case the question is different. There are a number of different agents which could have caused the RLF. Excess oxygen was one of them. The defendants failed to take reasonable precautions to prevent one of the possible causative agents (e.g. excess oxygen) from causing RLF. But no one can tell in this case whether excess oxygen did or did not cause or contribute to the RLF suffered by the plaintiff. The plaintiff's RLF may have been caused by some completely different agent or agents, e.g. hypercarbia, intraventicular haemorrhage apnoea or patent ductus arteriosus. In addition to oxygen, each of those conditions has been implicated as a possible cause of RLF. This baby suffered from each of those conditions at various times in the first two months of his life. There is no satisfactory evidence that excess oxygen is more likely than any of those other four candidates to have caused RLF in this baby. To my mind, the occurrence of RLF following a failure to take a necessary precaution to prevent excess oxygen causing RLF provides no evidence and raises no presumption that it was excess oxygen rather than one or more of the four other possible agents which caused or contributed to RLF in this case.
The position, to my mind, is wholly different from that in the McGhee case  1 WLR 1, where there was only one candidate (brick dust) which could have caused the dermatitis, and the failure to take a precaution against brick dust causing dermatitis was followed by dermatitis caused by brick dust. In such a case, I can see the common sense, if not the logic, of holding that, in the absence of any other evidence, the failure to take the precaution caused or contributed to the dermatitis. To the extent that certain members of the House of Lords decided the question on inferences from evidence or presumptions, I do not consider that the present case falls within their reasoning. A failure to take preventative measures against one out of five possible causes is no evidence as to which of those five caused the injury."
On the defendants' appeal to the House, this passage in the Vice-Chancellor's judgment was expressly approved by Lord Bridge of Harwich, who gave the only opinion, with which Lord Fraser of Tullybelton, Lord Lowry, Lord Griffiths and Lord Ackner concurred, and the appeal was allowed:  AC 1074,1090-1092. It is plain, in my respectful opinion, that the House was right to allow the defendants' appeal in Wilsher, for the reasons which the Vice-Chancellor had given and which the House approved. It is one thing to treat an increase of risk as equivalent to the making of a material contribution where a single noxious agent is involved, but quite another where any one of a number of noxious agents may equally probably have caused the damage. The decision of the Court of Appeal did indeed involve an extension of the McGhee principle, as Mustill LJ recognised:  QB 730, 771-772. Lord Bridge was also, as I respectfully think, right to describe the observations of Lord Wilberforce on reversal of the burden of proof (see paragraph 20 above) as expressing a "minority opinion" (p 1087), if Lord Wilberforce was suggesting more than that the proof of an increased risk can found a prima facie case which casts an evidential burden on the defendant. But much difficulty is caused by the following passage in Lord Bridge's opinion in which, having cited the opinions of all members of the House in McGhee, he said (p 1090):
"The conclusion I draw from these passages is that McGhee v National Coal Board  1 WLR 1 laid down no new principle of law whatever. On the contrary, it affirmed the principle that the onus of proving causation lies on the pursuer or plaintiff. Adopting a robust and pragmatic approach to the undisputed primary facts of the case, the majority concluded that it was a legitimate inference of fact that the defenders' negligence had materially contributed to the pursuer's injury. The decision, in my opinion, is of no greater significance than that and to attempt to extract from it some esoteric principle which in some way modifies, as a matter of law, the nature of the burden of proof of causation which a plaintiff or pursuer must discharge once he has established a relevant breach of duty is a fruitless one."
This is a passage to which the Court of Appeal very properly gave weight ( 1 WLR 1052, 1080, para 103), and in argument on these appeals counsel for the respondents strongly relied on it as authority for their major contention that a claimant can only succeed if he proves on the balance of probabilities that the default of the particular defendant had caused the damage of which he complains. As is apparent from the conclusions expressed in paragraph 21 above, I cannot for my part accept this passage in Lord Bridge's opinion as accurately reflecting the effect of what the House, or a majority of the House, decided in McGhee, which remains sound authority. I am bound to conclude that this passage should no longer be treated as authoritative.
The wider jurisprudence