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Mesothelioma, De minimis Exposure and Causation


Johnstone v Fawcett’s Garage (Newbury) Ltd 2023 EWHC 3010 (KB)

“In… mesothelioma a stage must be reached at which exposure is too insignificant to be taken into account, having regard to the overall exposure which has taken place… This must be a question of fact for the judge on the facts of the particular case.” Lord Phillips, Sienkiewicz v Greif (UK) Ltd [2011] UKSC 10.

Having contracted mesothelioma, Mrs Johnstone died in August 2019. She had worked for the defendant from 1982/83 to 1989/90 in an office close to where airlines were used to blow out brake shoes and clutch plates. These items contained chrysotile asbestos. The defendant admitted breach as vacuums should have been used. The defendant argued that the level of Mrs Johnstone’s exposure had not made a material contribution to her risk of mesothelioma.

The court heard evidence from six separate experts – two occupational hygienists, an epidemiologist, a Professor of Environmental Toxicology, and two chest physicians. All their evidence was directed at one question – what exactly is ‘material’?

The first issue was how much exposure Mrs Johnstone had experienced. This was what the occupational hygienists tried to answer. This meant first trying to establish how much exposure had been experienced by the operator of the airline and then projecting that finding on to Mrs Johnstone’s position. Both aspects involved careful examination of the factual evidence and any relevant studies before coming to the best achievable conclusion. Every stage involved making valid assumptions to navigate the many variables – how much dust was created, how close was Mrs Johnstone, what effect did that have, how often did the work take place?

This sort of analysis is very familiar to asbestos practitioners, but it is not a simple exercise – each case will differ. In the end the court preferred the defendant’s expert, Martin Stear to the claimant’s expert Chris Chambers. Mrs Johnstone, it decided, had experienced between 0.001 and 0.002 f/ml years of exposure at the garage.

This figure was used to inform the court’s assessment of the epidemiological and toxicology evidence about the contribution to the risk of mesothelioma. This evidence in turn relied on trying to make the best use of the available studies. Again, the court preferred the defendant’s expert evidence. It decided that the defendant’s breach of duty had increased Mrs Johnstone’s risk of mesothelioma by 0.1%.

The court appears to have used the chest physicians’ evidence to inform and conform the validity of its conclusions about the epidemiological/toxicology evidence.

The court rejected the claimant’s argument that the increase in risk must only be assessed by reference to Mrs Johnstone’s occupational exposure. The assessment of material increase in risk had also to take into account both the risk from background exposure and that from naturally occurring (“idiopathic”) mesothelioma. The court then decided that a 0.1% increase in risk was not enough to be material and the claim failed.

Comparisons are going to be made with the only other de minimis exposure mesothelioma case: Bannister v Freeman. There are differences, and most of them are in defendants’ favour:

  • The Bannister decision about causation was technically in obiter. This case was just about causation.
  • The court in Bannister only considered a possible single episode of exposure. This case assesses causation against the backdrop of all the risk factors. That is far more typical of mesothelioma claims.
  • The dosage here was significantly higher than in Bannister – up to five times greater.
  • The judge in this case relied on a numerical assessment of risk. The Bannister decision drew more heavily on the chest physicians’ evidence and their clinical experience.

Insurers and their advisers have to be quite brave to take mesothelioma cases to trial, especially with the 100% costs uplift if the claimant wins – but cases like Johnstone are going to become more frequent. If the evidence is right, they should be contested. As Lord Phillips tells us, it is all about the facts.

David Pugh

David Pugh


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