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Causation in Mesothelioma Claims: Stretching the Definition

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About The Author

Samuel Cuthbert (Private Law Manager)

Sam read Philosophy at Durham University, followed by the GDL funded by the Lord Brougham Scholarship and a Hardwicke Scholarship from Lincoln's Inn. Sam is now spending a year, prior to undertaking the BPTC, to develop his legal interests in a paralegal capacity. His legal career is starting in a M&A paralegal role at a large Viennese firm. He is a passionate speaker and has his sights set firmly on a career at the bar.

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Image © David Samuel

In order for a tortious claim to succeed, a number of elements need establishing. Mostly, these consist of ascertaining a duty of care, highlighting the standard of that duty, breaching that standard, and that breach causing the loss suffered. However, the legal tests for establishing causation in asbestos claims do not cohere with the every-day construction of it. This article explores that distinction.

Of the four main diseases caused by inhalation of asbestos - namely asbestosis, mesothelioma, plural thickening and lung cancer - this article will focus on mesothelioma because, arguably, the most interesting causational arguments can be raised in its context.

How Do We Understand Causation?

For more on this, see ‘The Metaphysics of Causation’, a philosophical approach.

When the cue ball knocks the nine ball into the corner pocket, in virtue of what is this a case of causation? When I say something hurtful and someone else becomes upset, in virtue of what is this a case of causation? If someone inhales a small amount of poisonous dust and it is extremely difficult to ascertain exactly how much (if any) of the cancer they developed in later life was a result of that inhalation, in virtue of what is this a case of causation?

The short answer is the presence of a causal chain. A’s occurrence has a resultant effect on B, which has a subsequent effect on C, and so on. Causation is understood in the context of those events which interact to precede another event such that if they had not occurred, that event would also not have occurred. This is largely the understanding of causation upon which standard tortious claims turn. Much academic ink has been spilled over this topic in a legal setting, but I suggest that inkwells be replenished for further discussion of issues of causation in mesothelioma claims and, in particular, of causal overdetermination.

The premise of the debate questions whether one happening can legitimately be said to have been caused by two separate, simultaneous events. An oft-cited example is the prisoner facing death by firing squad. Two bullets from different guns enter the same critical organ, at precisely the same time and have the same critical effect of killing the convicted man. Which bullet killed him? The death may be said to be causally overdetermined in virtue of its being caused by two events. The difficulty with such a thought experiment is that the impossible hypothesis depends upon the literal dying of the individual and so starts to lose focus. Arguments concerning which part of the critical organ was penetrated by which bullet, and, if the bullets met at the critical point, which had born the more destructive path in getting there, seem to suggest that two bullets both individually and cumulatively causing the same death is an impossibility.

Suppose that I had had plans with my mother to bake a cake. However, she decided to walk the dog instead, and I decided to read a book. There appear to be two causes of the same occurrence, namely the failure to bake the cake could be said to be a result of our two separate alternative activities. However, this notion of causation doesn’t correlate with the commonplace, everyday alternative: the lack of mixing eggs with sugar, butter, milk and flour and then placing the mixture in a tin in the oven until cooked was the more obvious cause of the cake not being baked; it did not concern dog walking or reading at all. The illuminating point is that typical understandings of causation in real life do not incorporate the scope for multiple simultaneous causes of the same occurrence.

The causal overdetermination debate is much farther reaching than the small vignette I have afforded it here would suggest, but discussion of it in this context serves the purpose of forcing us to consider the causal process on a more fundamental level. The real question born out of such a thought experiment, and one of particular relevance to industrial disease claims, is how closely linked must happening X be to happening Y in order to justify the assertion that there is a causal link between them?

McDonald v National Grid Electricity Transmission PLC (‘McDonald’)

In McDonald, Percy McDonald suffered and died from mesothelioma, which, as Lord Kerr explains in the introduction to his judgment, is:

a form of cancer that develops from cells of the mesothelium, the protective lining that covers many of the internal organs of the body [… ] It is most commonly caused by exposure to asbestos. Symptoms or signs of mesothelioma may not appear until 50 years (or more) after exposure.

The deceased, whose wife brought the claim on his behalf, worked for Building Research Establishment in the 1950s, and in the course of his employment would attend Battersea Power Station to collect pulverised fuel ash. During his frequent visits to the power station he would pass through areas in which asbestos dust was generated by lagging work. As such, the deceased was subject to inhalation of the asbestos dust, something claimed to be the cause of his illness and subsequent death.

The claim brought against the National Grid contended a breach of the duty of care set out in s63 Factories Act 1963 (s47 Factories Act 1937, NB this provision was effectively replaced by the Asbestos Regulation 1969) which provides strict guidance on the removal of dust or fumes in a factory:

In every factory in which, in connection with any process carried on, there is given off any dust or fume or other impurity of such a character and to such extent as to be likely to be injurious or offensive to the persons employed, or any substantial quantity of dust of any kind, all practicable measures shall be taken to protect the persons employed against inhalation of the dust or fume or other impurity and to prevent its accumulating in any workroom, and in particular, where the nature of the process makes it practicable, exhaust appliances shall be provided and maintained, as near as possible to the point of origin of the dust or fume or other impurity, so as to prevent it entering the air of any workroom.

Plainly, several questions arise from the application of this statutory provision to the claimant’s case. As discussed in the judgment, the most significant of these ask what constitutes a process and a person employed? How much dust is a substantial quantity? Does that substantial quantity of dust need to be so at the point of inhalation? If not, what are the ramifications for the concept of causation and can they be reconciled with the intuitive understanding of it discussed above? These questions are intrinsically linked, so I will go through each in turn in order to contextualise the causation discussion.

What is a Process/Person Employed?

It was held in McDonald that, unlike as in Brophy, in order for the above statute to apply, the process in question does not have to be part of the business of the factory as long as it is ‘a normal feature of the factory’s activity’ (Lord Kerr at 64). Further, the wording ‘persons employed’ is taken to mean:

Those employed persons liable to be affected by the dust or fume, not merely to those employees who were responsible for producing those substances. (Lord Kerr at 70).

The rationale for establishing this focuses on the notion that it would run contrary to the intentions of the statute if only those working within the process and not those working close by, were owed a duty of care. This discussion necessarily precedes that concerning the inhalation of dust and the ensuing causation of serious illness.

The Quantity of Dust at Inhalation

The debate here concerns whether, in order for the statute to apply, a) a substantial quantity of dust needs inhaling, or b) whether only the quantity of dust given off at source needs to be substantial. Lord Kerr, with whom Lady Hale and Lord Reed agreed, established (at 76) that the answer to this question was that:

The duty to take practicable measures arises whenever a significant quantity of dust is given off and that the activation of the duty is not dependent on is given off and that the activation of the duty is not dependent on its being shown that the quantity of dust was considerable at the moment of inhalation.

This is the interesting causal point. Whilst it remains a question for the jury to determine quite what is meant by ‘substantial’, this much we can draw from the judgments of Bonnington and Ebbs: the amount of dust actually inhaled is not considered material to establishing the claim. All that remains important is that some dust is inhaled and that, at the source of the dust, the quantity is substantial.


As such, the legal position currently directs that the aforementioned statute is engaged equally when a single particle of asbestos dust is inhaled as when large amounts are inhaled on a frequent basis. Moreover, mesothelioma claims (as this was) are subject to the Fairchild exception in proving causation. This exception provides that:

defendants whose breaches of their duty of care 'materially increase the risk' of mesothelioma are jointly and severally liable for the damage suffered if mesothelioma does in fact develop. This rule relaxes the usual requirement that a claimant must show that it is more likely than not that the harm he has suffered has been caused by the defendant's breach.

The reason for the exception is that it is often not possible to determine which asbestos fibre caused the mesothelioma to develop and as such, causation needs to be determined in this way in order to protect potential claimants and furnish them with an avenue of redress. It is my contention that this is wholly right, and that the law does an excellent job of ensuring this.

What is of interest though, is the different construction of causation that this industrial disease claim adheres to, in comparison with the previously cited examples of establishing a causal chain. To suggest that quantity of dust inhaled is not important in establishing a claim is akin to claiming that a person is equally liable for the deterioration of an object who used it once, as the person who used it regularly. Or to suggest that causing a material increase in the risk of something happening is enough to prove actual causation, is akin to suggesting that leaving my valuables in plain sight is as much a cause of their loss as the person who smashed the window to steal them.

Further, mesothelioma can develop decades after the initial inhalation of asbestos fibres. It is conceivable that, within the interim period of time, the suffering person could have also been party to decades of exposure to other asbestos and carcinogens. Thus, on a normal tortious understanding of causation, it would be impossible to pathologically locate the instant someone developed cancer. Owing to the impossibility of highlighting the exact moment at which the fiber that caused the mesothelioma was inhaled, the construction of causation needs to be different so that the law provides sufficient protection for the vulnerable. Were it not to be, all persons responsible for exposing staff to any carcinogenic dust would escape liability, something that is plainly wrong. Such a construction, centered on the Fairchild exception, is recognizable in the context of the aforementioned causal overdetermination. That is to say that joint and several liability can be apportioned to any defendant who breaches the standard set out in the statute and thusly materially increases the risk of contracting the illness. However, because there is no way in which we may highlight the fatal fiber, multiple events are seen to have caused the same occurrence. In legal terms then, there is scope for causal overdetermination.


I finish this article by stating once more that I do not intend to provide a critique of the McDonald judgment, nor of the current legal position directing causation in mesothelioma claims. This article is solely intended to draw attention to the distinct and different construction of causation that is wholly necessary in order for these claims to be fairly heard, and for claimants to be sufficiently protected: the legal construction of causation allows the law to justly punish and compensate in cases of irreducible complexity. The law regulates and mirrors life, but at times, as in the above discussion, the latter needs bending and reconstructing in order for the former to work as well as it might.

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Tagged: Personal Injury, Tort Law

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