What is a material increase in risk?

Notwithstanding Lord Brown's dismissive comment in...

Sienkiewicz v Grief (UK) Ltd [2011] UKSC 10 ("… mesothelioma claims must now be considered from the defendant's standpoint a lost cause…") there have been a number of mesothelioma cases successfully defended in recent years, many on the basis of low exposure and the claimant not proving causation.  The latest of these is Johnstone v Fawcett’s Garage (Newbury) Ltd [2025] EWCA 467.

The late Mrs Elaine Johnston was employed by the defendant, a vehicle garage business located in Newbury in Berkshire, from 1982/83 to 1989/90. She worked in the accounts department in an office situated to the side of the garage forecourt. She developed malignant pleural mesothelioma from which she sadly died on 31 August 2019. It was alleged that she had exposure to asbestos during her employment with the garage that materially increased her risk of the disease, satisfying the ‘special rule of causation’ introduced by The House of Lords in Fairchild v Glenhaven Funeral Services Ltd [2002] UKHL 22. Her alleged exposure to asbestos had been from work carried out at the garage on asbestos brake and clutch linings. The extent of any exposure was undeniably limited and predominantly to chrysotile (white) asbestos.

The defendant admitted breach of duty but argued causation, disputing that the admitted breach involved exposure to asbestos that created a material increase in the risk of the late Mrs Johnstone developing mesothelioma. The judge at first instance accepted the evidence of the garage’s expert occupational hygienist who estimated occupational asbestos exposure of between 0.001 – 0.002 f/ml years. On the basis of this low level of exposure, the trial judge preferred the evidence of the garage’s epidemiological and medical experts that such exposure gave rise to an increase in risk of no more than some 0.1%. He concluded that this was not a ‘material’ increase and he therefore dismissed the claim.

There were five separate grounds of appeal, all of which were ultimately dismissed. For present purposes, the focus will be on the grounds of appeal relating to application of the test of material increase in risk. It is noticeable on this point that the garage served a notice which sought to support the judge’s conclusions by reference to the third of 3 alternative methods of application of the special rule (each of which were re-named by the Court of Appeal as in italics below). 

The 3 potential methods put forward to assess material increase in risk were:-

• Method 1 - the "exposure/risk" approach, as argued for by the claimant. This was so labelled as the increase in risk expressed as a percentage is calculated by dividing the occupational asbestos exposure in breach of duty by the estimated lifetime environmental exposure. This was said to amount to an increased risk of between 2% and 4.3% in this case, which the claimant’s representatives argued was material.
• Method 2 - the "direct risk assessment” approach, involving a comparison of the risk to Mrs Johnson of contracting mesothelioma from her work at the garage to her background risk.  This was the approach advocated by the garage and adopted by the judge.
• Method 3 - the "absolute risk” approach, being the garage’s alternative option, in which the estimated risk from the occupational exposure in question is the subject of medical opinion as to whether it is ‘medically significant’.  This was most notably seen (and accepted, obiter) in Bannister v Freemans plc [2020] EWHC 1256 (QB). 

The direct risk assessment approach more specifically involves assessing the ‘workplace’ risk of developing mesothelioma on the one hand as indicated in ‘The Quantitative Risks of Mesothelioma and Lung Cancer in Relation to Asbestos Exposure’ by Hodgson & Darnton (2000) and then comparing the background risk from any other source on the basis of ‘Occupational, domestic and environmental mesothelioma risks in the British population: a case-control study’ by Peto, Rake, et al (2009).  The application of this method led the judge to conclude that the increase in risk was 0.1% or less and was de minimis (i.e. not material).

The appellant argued that the judge had failed to explain why he had rejected the exposure/risk approach and had preferred the direct risk assessment approach. The Court of Appeal was able to deal quickly with this “challenge to an absence of reasons” in the following terms. “As is clear from the judgment, the judge did adjudicate upon the two approaches and he did so by preferring the evidence of Professor Jones as to the reliability of the direct risk assessment approach.” The inevitable and direct consequence was that “There is nothing in this ground of appeal which is dismissed.”

The Court of Appeal stressed that the appeal was not about deciding whether the direct risk assessment approach is generally a valid and appropriate method of assessing causation, highlighting that this is heavily dependent on the evidence of experts in various fields of study, including statistics, epidemiology, toxicology and medicine. It was stressed that the question on the appeal was whether the judge’s conclusions were open to him on the basis of the evidence that was before him. The Court of Appeal dismissed the claimant’s complaints in this respect and upheld the trial judge’s findings and judgment. The Court of Appeal therefore reached no general conclusions as to which of the exposure/risk or the direct risk assessment approaches was the appropriate methodology of assessing the increase in risk, or whether or not it is material, although its rejection of the claimant’s criticisms of the direct risk assessment approach in itself provides some support for this methodology.

The judge did not reach a conclusion on the absolute risk approach, which was reliant upon the expert evidence of Dr Moore-Gillon on behalf of the garage, who adopted Hodgson & Downton's description of a lifetime risk of contracting mesothelioma of less than 1 in 100,000 as "insignificant". By its respondent’s notice, the garage contended that this approach supported the judge's conclusion that there was no material increase in risk.

The Court of Appeal was however critical of the absolute risk approach, expressing the view (albeit obiter) that this approach was not appropriate in assessing material increase in risk in mesothelioma cases and observing that: “Comparison of the tortious and non-tortious risk provides a basis for attribution as the impact of the tortious risk on the total risk can be considered and assessed. The absolute risk approach does not assist in attribution [and] would make the word "increase" within the Fairchild exception otiose.” The Court of Appeal noted in any event that the acceptance of the absolute risk approach in Bannister was obiter and therefore not binding and furthermore pointed out that Bannister “was concluded in circumstances where no epidemiological expert evidence was before the judge. Such evidence was available in this case.”

The Court of Appeal also pointed out in respect of the absolute risk approach that it would mean that even if there was a large material increase in risk of developing mesothelioma caused by a defendant, a claimant would not have a cause of action if their risk of developing disease was deemed "medically insignificant." As an illustration, it was stated that a tortious dose representing a ninefold increase in lifetime risk (the example given was a risk of 0.9 in 100,000, increased from a background risk of 0.1 in 100,000) would be clearly ‘material’ but nevertheless ‘medically insignificant’. This was said to fly in the face of the reasons for introducing the Fairchild exception.

There are two points that justify specific consideration as regards this issue. Firstly, as regards the contention that the absolute risk approach is contrary to the decision in Fairchild, the fifth out of the six factors set out by Lord Bingham in Fairchild to justify the special rule of causation read: "… any cause of the victim’s mesothelioma other than the inhalation of asbestos dust at work could be effectively discounted”. However, when the levels of exposure and therefore risk are so low, it is difficult to see how any potential idiopathic or environmental causes of mesothelioma can be ‘effectively discounted’.

The second point is that the illustration that the Court of Appeal relied upon, whilst constituting a ninefold increase in risk, represents an increase in risk of 0.8 in 100,000 which, expressed in percentage terms, is 0.0008%. As Lord Toulson stated when addressing the ‘doubling of risk’ test of causation in Williams v The Bermuda Hospitals Board [2016] UKPC 4, “A doubled tiny dose will still be very small."  With due respect to the Court of Appeal, it is difficult to see how such a minuscule percentage increase can be ‘material.’