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3.1.3 Causation Lecture - Hands on Example


Jack works for the Buoy Company - an organisation which specialises in the production of maritime safety gear. He has been working for the organisation for 20 years. During this time, he has worked with vulcanised rubber, used in the production of high quality sea buoys.

Ten years ago, following a government study into the long-term health effects of working with vulcanised rubber, a law was passed requiring factories which work with rubber to have sufficient ventilation systems in place to protect their employees - it emerges that unventilated exposure can lead to a lung-condition which can lie dormant for many years before becoming fatal. This is novel medical research - those companies which have been working with rubber had no way of knowing about the condition up until this government announcement and subsequent legislation. Unfortunately, the Buoy Company failed to take note of this new law, and has not put a sufficient ventilation system in place to date, exposing their employees to unsafe levels of rubber by-products.

Jack notices that he has developed a significant cough, and goes to visit his GP. He is sent for an MRI scan, and it is revealed that Jack has developed bouncy lung - a condition which occurs when an individual is exposed to vulcanised rubber without proper ventilation. Jack’s GP is unable to tell him exactly when he developed the condition, only that it must have been at some point during his career with the Buoy Company, and that the only possible cause of the condition would have been his exposure to rubber within the factory. Jack takes time off work as required, and informs the Buoy Company of his condition. They immediately install a new ventilation system for the benefit of the other employees working there.

Jack is prescribed a specialised medicine designed to take care of his condition. Unfortunately, his pharmacist misreads the prescription whilst distracted by another customer, and sends Jack away with the wrong medicine. This mistake is only discovered three months later when Jack goes for a check-up with his GP: unfortunately, because Jack has not been taking his medicine, his condition has worsened in such a way as to be fatal within the next five years.

Jack is understandably upset, and seeks legal advice. As part of this advice, a medical expert is consulted, and it is established that had Jack been taking the correct medicine, he would have had a 40% chance of surviving the disease completely, but this has now diminished to a 0% chance.

Advise Jack as to the validity of his claim against both the Buoy Company and his pharmacist, concentrating on issues of causation.


Jack’s claim against the Buoy Company is based on the illegitimate exposure to unventilated vulcanised rubber Jack experienced whilst under their employment. However, the length of Jack’s career somewhat complicates things. Whilst Jack was exposed to the rubber in an unventilated environment for 20 years, it has only been in the last 10 years that his exposure has been illegitimate, since that was when the law regarding ventilation was passed. In turn, this means that when Jack acquired bouncy lung is important - if in the last 10 years, then it will likely be actionable, because his employer should have been ventilating the dangerous rubber from Jack’s workplace. If the exposure occurred in the first 10 years, however, then this will not give rise to an action - the factory was not aware of the risks, and had to statutory obligation to ventilate. Unfortunately, it is impossible to tell when the dangerous exposure actually occurred. This means Jack’s situation is arguably analogous to the one in Bonnington Castings Ltd v Wardlaw [1956] AC 613 - there are two different possible causes for his ailment, but it is impossible to tell which is which. He has been exposed to ‘legitimate rubber’ for the first 10 years of his career, and ‘illegitimate rubber’ for the last 10 years. Since it is impossible to tell which caused his condition, there is a 50% likelihood that Buoy Company was responsible for his illness, and a 50% chance it is not. As per Bonnington, Jack does not need to demonstrate that his disease was definitely caused by the illegal exposure over the last 10 years, but simply that the Buoy Company made a material contribution to his illness. Since there is a 50% likelihood that his illness was caused by an illegal exposure to vulcanised rubber, this is a sufficiently large contribution - indeed, it was 50% likely in Bonnington that the claimant’s illness was illegitimately caused by his employer.

Regarding the negligence of Jack’s pharmacist, this is a matter of lost chance, and thus, Hotson v East Berkshire Area Health Authority [1987] AC 750. As per this case, the courts will examine what would have happened had Jack’s pharmacist provided him with the correct medicine in order to work out the effects of the pharmacist’s negligence.

According to expert evidence, if properly treated Jack would have had a 40% chance of surviving, which means that the most likely outcome for Jack would still have been death, at a 60% chance.

This will mean Jack does not have a claim against his pharmacist: with negligence, Jack’s health outcome is death. Even if that negligence had not occurred, Jack’s likely health outcome is still death. This means that causation cannot be established on the balance of probabilities. To confirm this reading of the case, Gregg v Scott [2005] 2 WLR 268 is founded on similar facts - a medical failing caused the claimant to lose a (near) 40% chance at survival. Nevertheless, this was regarding as inactionable for the same reason as in Hotson.

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