Low level asbestos exposure — what constitutes “a material increase in risk”?

In a judgment handed down by His Honour Judge Simon on 13 December 2023, the High Court considered whether a comparatively low level of occupational exposure to asbestos “materially increased the risk” of the deceased developing mesothelioma — the relaxed causation test previously laid down by both the House of Lords in Fairchild [2003] and the Supreme Court in Sienkiewicz v Grief [UK] Limited [2011].

The court heard from a number of experts in the disciplines of respiratory medicine, occupational hygiene, epidemiology and toxicology. Weightmans LLP (Steve Phillips), represented the successful defendant.

Factual background

The deceased was previously employed at the defendant’s garage between 1982/1983 and 1989/1990 as a clerk in the accounts office.

It was the claimant’s case that the deceased’s exposure to asbestos arose from the activities of a mechanic servicing brakes and clutches in a workshop opposite the office — with dust containing a small proportion of asbestos fibres being blown from the use of an airline on average one day a week.

Exposure arose from dust blowing into the office and when the deceased crossed the yard to access the office.

The defendant admitted breach of duty and called no factual witnesses. Causation remained in dispute. The claimant did not allege any other occupational exposure to asbestos.

The issues and findings

The judge was required firstly to consider the extent of the deceased’s exposure to asbestos, having heard both lay and expert witnesses and in the context of published studies and meta-analyses broadly relating to those working with asbestos-containing products.

Declining to apply a straightforward comparison of occupational and environmental exposure in the consideration of what constituted a material increase in risk, the judge assessed the deceased’s exposure in the range of 0.001 to 0.002 fibre/ml/years — preferring the evidence and calculations of Marin Stear, the defendant’s occupational hygienist.

The judge was secondly required to assess whether that exposure constituted a material increase in risk. To do so, the judge considered the evidence given by both Professor Norrie, the claimant’s epidemiologist, and the defendant’s toxicologist, Professor Jones, alongside the medical experts, Doctors Twort and Moore-Gillon.

The judge also assessed the deceased’s exposure (albeit with appropriate caution) by reference to the Hodgson and Darnton model of estimating the risks associated with low levels of asbestos exposure, which had previously been accepted by the court in the case of Bannister v Freemans Plc.

To recap, the court in Bannister held that the test for materiality was: “a dose of asbestos which was properly capable of being neglected (and) could be defined as a dose which a medical practitioner who is aware of the medical risks would define as something that the average patient should not worry about”.

In Bannister, the estimated incidence of those so exposed was 0.2 deaths per 100,000 (lifetime risk) or 1 in 50 million (annual risk). The court in Bannister concluded that that risk was not material and was therefore “de minimis”.

The judge concluded in Johnstone that the deceased’s occupational exposure had increased the risk of her developing mesothelioma in the order of 0.1 %. He did not consider this to be a material increase in risk and the claimant’s case was dismissed.

Commentary

This case usefully highlights the importance of both the medical and epidemiological assessment of risk in low dose cases and for a case by case approach to be taken to determine what constitutes “a material increase in risk”.

The judge’s findings here that exposure equating to 0.001 to 0.002 fibre/ml/years was not material, is higher than the court had assessed in Bannister — 0.0004 fibre/ml/years but lower than the court in Sienkiewicz had considered to be material — 0.013 fibre/ml/years.

The judgment also highlights that even in cases where breach of duty can be established, the relaxed causation test laid down by Fairchild [2003] and Sienkiewicz [2011] may not in certain ‘low dose’ cases be satisfied.

Following the judge’s refusal of permission to appeal, it is understood that the claimant will seek leave from the Court of Appeal.