Warne v Vinters-Armstrongs Ltd

Where agreed medical evidence treats a cumulative asbestos exposure level as a bright line for causation, the court should apply that threshold unless there is a proper evidential basis to depart from it. Expert exposure estimates must rest on reliable data and rational methodology. Selecting the highest available figure without establishing its provenance or relevance is unsound. The assessment must also reflect the location, duration and frequency of exposure, including the decay and dispersal of airborne fibres. Where exposure falls significantly below the agreed threshold, causation is not established and the negligence claim fails.

The claimant developed interstitial lung fibrosis after working for the defendant in a machine shop between 1952 and 1966. He alleged that his condition was asbestosis caused by exposure to asbestos powder used to extinguish magnesium fires between 1958 and 1960, and claimed damages for negligence and breach of statutory duty under the Factories Act 1937.

By trial, breach was conceded if substantial asbestos exposure and causation were proved. The medical experts agreed that exposure of 25 fibre/ml-years or more would support a diagnosis of asbestosis, while lower exposure would indicate idiopathic pulmonary fibrosis. The central issue was therefore the extent of the claimant’s cumulative asbestos exposure.

1. The claim was dismissed. The agreed medical evidence treated cumulative exposure of 25 fibre/ml-years as the causation threshold. The claimant accepted that causation would not be established if exposure was significantly below that level.
2. The court preferred the occupational hygienist’s evidence to the claimant’s expert evidence. The claimant’s expert selected a peak concentration of 10,000 f/ml because it was the highest figure available, relying on data of unknown provenance. There was no scientific or rational basis for selecting that figure, and the resulting one-hour mean concentration was likewise unreliable.
3. Reliable observed data from Dr Harries’ study provided a sounder basis for assessment. The court accepted that suppressing a magnesium fire would initially produce a concentration of about 2,000 f/ml, but that this would persist for only about one minute. Exposure from fires at other machines would be materially lower because asbestos dust would disperse in all directions.
4. The court also rejected the assumption that a high mean exposure continued for an hour before cleaning began. The claimant’s evidence showed that cleaning began promptly and lasted about 30 minutes. The calculations therefore had to reflect the actual timing of the work and the subsequent dispersal of dust.
5. The court accepted that expert qualification principally affected the weight, rather than the admissibility, of the evidence, applying the approach in Rogers v Hoyle [2014] EWCA Civ 257. It found cumulative exposure probably no more than 10 f/ml-years and likely well below that figure. Even on a three-year period, exposure would have been below 15 f/ml-years. It was therefore significantly below the agreed threshold, so causation was not proved.