Keoghs Insight


David Pugh

David Pugh


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Asbestos lung cancer, causation and contributory negligence

Disease Aware Issue 6

The complex issues of causation in asbestos lung cancer claims are well known to insurers. Where a claimant has smoked and been exposed to asbestos how does a court decide which caused their cancer?

In most asbestos lung cancer (ALC) cases both parties accept that the test to use is whether a claimant’s asbestos exposure - when considered in isolation - more than doubled the risk of his developing cancer.

The legal basis for that formula is at best uncertain but it strikes a balance. It is a far more difficult test for claimants to overcome than the Fairchild test in mesothelioma.

Some claims will still succeed. The alternative arguments would either stop compensation for all asbestos exposed smokers with lung cancer, or allow all of them to succeed. So far neither claimants nor insurers have felt like taking that gamble.

In Blackmore, the defendant also accepted this doubling of the risk test, yet many of the facts underlying the primary causation issues were still debated. This was because the defendant used those facts to argue for a very high deduction for contributory negligence.


Mr Blackmore was exposed to asbestos while both removing it and sweeping up after others’ activities. It was relatively heavy exposure. This exposure occupied about five years of his employment.

He was also a moderate but long term smoker, with a 20 a day habit for around 60 years, tailing off a little in his final few years.

The defendant’s expert used epidemiological evidence to argue that the deceased’s smoking was the overwhelmingly more significant contributor to the risk of his cancer.

Even after stripping out the first 25 years of smoking (as he would not then be regarded as knowing the dangers) it caused 90% of his cancer risk. The remaining 10% was due to asbestos. The defendant used this to argue for a correspondingly large deduction for contributory negligence - either 85 or 90%.


The court rejected the defendant’s arguments in two ways - by criticising the basis for the defendant’s figures and by a more fundamental consideration of the law of contributory negligence. The judge accepted criticism levelled by the claimant’s expert that the defendant’s figures were unreasonably precise.


Cancer is a complex disease and its causes in a given case are still very poorly understood. Even where an individual has smoked and been exposed to asbestos, other factors will play their part. The causes of cancer are not susceptible to proof by a simple statistical analysis drawn from a cohort of other unrelated cases. This is obviously right - but it is less obvious why this should automatically lead to a reduction in the role played by smoking.

Perhaps a stronger point was that the defendant’s expert had not weighted the smoking history to reflect the likely greater contribution to lifetime risk of the earlier smoking years.


The judge used these aspects to find that the negligent smoking was between two and three times more potent a cause of the claimant’s cancer than his asbestos exposure. Even given the judge’s criticisms of the defendant’s approach this seems a substantial reduction.

The judge then emphasised that assessment of contributory negligence is a jury question rather than one which relied on attempting to establish a precise degree of contribution to injury.

The exercise principally rested on two separate analyses - the level of causative potency of the claimant’s actions, and their relative blameworthiness. The defendant’s arguments had been all about the first, and not the second.

The court emphasised the policy driven considerations behind imposing statutory duties on employers and the fact that these had been (repeatedly) breached by the defendant. The claimant’s actions were morally less blameworthy.

Deduction the new normality?

In all the circumstances, the court made a finding of 30% deduction for contributory negligence. This should now be regarded as the norm, superseding authorities such as Badger (25%) and Shortell (20%).

The judge was specifically critical of the latter authority - rightly pointing to the logical fallacy of its reference to, “the synergistic effect of asbestos,” - which tends to overlook what synergy actually means.

What does this mean?

On its face then, this is a defeat for defendants. The reality however, is that it should be helpful.

The judge’s rejection of a close analysis of the precise potency of competing causative factors means that factual variations in asbestos exposure and smoking history in other cases should not disturb the 30% deduction - itself an improvement over earlier findings.

This case may also bring closer the day when insurers may take the causation gamble. If smoking is so powerful a contributor to the lung cancer, why are these claims being paid at all?