In Petroleum Company of Trinidad and Tobago Ltd v Ryan  UKPC 30, the claimants had been diagnosed with pulmonary fibrosis and reactive airways disease. They attributed these conditions to emissions of hydrocarbon gases from a disused oil well on land under the control of the defendants and adjacent to their dwellings. They sought damages from the defendants on the basis of negligence and nuisance. Their claim was dismissed in the Trinidad and Tobago High Court but allowed (by a majority of 2 to 1) in the Court of Appeal. The Privy Council restored the decision of the High Court.
Rajkumar J, in the High Court, accepted that the defendants were under a duty to ensure that oil or other substances on their land did not emit noxious gases to such an extent as to cause harm to adjoining landowners, and it would be sufficient for the claimants to show that such emissions had materially contributed to their illnesses. In this case, despite remedial measures undertaken by the defendants in 1999, there was evidence of seepage of hydrocarbons from the area around the well up to 2006, when the defendants took additional measures to eliminate further emissions. Rajkumar J concluded (i) that there was insufficient evidence as to the extent of the emissions, and (ii) that in any event the medical evidence did not establish a causal link between the alleged emissions and the claimants’ ill health.
In the Court of Appeal, Mendonca JA (dissenting) agreed with Rajkumar J’s reasoning, but Smith JA (Moosai JA concurring) held that the claimants had proved on the balance of probabilities the causative link between their illnesses and the hydrocarbon emissions for which the defendants were responsible. The basis of Smith JA’s reasoning was that the evidence relating to the well and its surroundings lay exclusively within the control of the defendants and,accordingly, little affirmative evidence was required for the claimants to establish a prima facie case of negligence. The onus then lay on the defendants to rebut the prima facie case against them by, for instance, evidence of tests establishing the non-existence of harmful emissions pre-2006, but no such evidence had been produced.
Lord Carnwath, delivering the judgment of the Privy Council, disagreed with Smith JA’s approach and preferred Mendonca JA’s view that the trial judge’s conclusions were reasonably open to him on the evidence, and that there was no basis for an appellate court to intervene. The claim failed principally because “the problem for all the medical experts was not the diagnosis but the lack of any evidence, in their combined experience or in the literature, of a causative link between hydrocarbon emissions associated with an oil well and the claimants’ conditions.”
What would at first sight appear to be a ‘hard’ decision from the claimants’ perspective, as they did contract lung-related illnesses and there was some evidence of seepage from the defendants’ well, is actually a straightforward application of the ‘but-for’ test of causation. Since the claimants could not show that hydrocarbon emissions were, according to medical science, a known cause of the diseases they had contracted, they had failed to satisfy the ‘but-for’ test, and it would not have been legally justifiable to require the defendants to compensate them.