Hidden in today's CA decision in Howmet Ltd v Economy Devices Ltd & Ors [2016] EWCA Civ 847, is something that could be an important development in product liability. 

H's factory, as part of its process of making turbine blades, heated difficult chemicals in polypropylene tanks. It was vital that the heaters not be on when the tanks were empty, since otherwise there was a big fire-risk. For that reason H had thermosensors made by EDL installed to prevent this happening. A badly-designed thermosensor failed to work: after the resulting fire there was little left of the factory. Before this happened, employees of H had had every reason to know, from a previous incident, that the thermosensor might well be dodgy (and indeed H had bought but not yet fitted a replacement device); but H had continued to use the bad thermosensor.

H sued EDL in good old-fashioned Donoghue v Stevenson. Edwards-Stuart J decided against H. He found that it had not been shown that if the thermosensor had been properly made the fire would have been avoided. He thought it was a case on the lines of The Popi M [1985] 1WLR 948: i.e. a situation where a judge who hasn't really got a clue about the cause of the damage is not allowed to cut the Gordian knot by simply seizing on the least implausible answer. However, he rejected the alternative argument that H's knowledge broke the chain of causation: that merely went to contributory negligence.

On appeal, a majority (Jackson and Arden LJJ) thought this wasn't a Popi M case, though the minority (Akenhead J) thought the judge was right. But H still lost. The reason was that Jackson LJ, with whom Akenhead J this time explicitly agreed, thought that once a person had knowledge of the defectiveness of a product, he had to fail outright in negligence, as he would in contract. This was on the basis of causation: despite the possibility of applying apportionment in negligence but not in contract, it was not a case where the contributory negligence rule should be applied. Arden LJ disagreed: she thought that this was a classic case for the application of apportionment (though she decided for EDL on unconnected causation grounds, thus making the result unanimous).

It seems to me that Jackson LJ and Akenhead J's view, if it prevails elsewhere, is highly significant, and likely to make product liability claims a good deal more awkward to pursue in future. In other words, watch this space ...

Andrew