(II) The magnitude of harm

The Wagon Mound (No. 2) made clear that the seriousness of harm likely to be caused by the neglect of a relevant precaution is relevant to the issue of negligence,¹⁵⁸ but there is a striking absence in the cases of any financial calculation of the ‘value’ of the harm which either would not or could not have occurred. In the hands of English judges, there is no explicit economic calculation of the type which would require the actual estimated cost of precautions to be put against the actual (or potential harm) caused and the statistical probability of the actual (or potential) harm: the balancing of these factors remains at large. Instead, typically there is an implicit assessment of the probability (usually without statistics)¹⁵⁹ and a rough sense of the cost of precautions (often with no figures adduced) as against the harm likely to be caused, but with the harm actually caused to the claimant present in the minds of the judges. This non-mathematical nature of the judicial calculation is important because it allows courts to take into account factors which could not form part of a purely economic calculation, such as the utility of the defendant’s conduct other than in economic terms. As a result, the courts clearly consider that a defendant is justified in taking a greater risk of injury in promoting the interests of personal safety.¹⁶⁰

(P.197) (III) The cost of precautions

The cost of the precautions which a defendant is expected to have undertaken so as to avoid likely harm is an important factor in the assessment of negligence. For example, in Latimer v A.E.C. Ltd.¹⁶¹ where a claimant had suffered minor injuries on slipping at work, it was held that an employer was not negligent in allowing its employees to continue working in its large factory despite the slipperiness of the floor after heavy rain given the drastic nature of closing the factory,¹⁶² though this may be required of a reasonably prudent employer ‘if the peril to his employees is sufficiently grave’.¹⁶³

Three further points arise. The first is the importance of looking at the correct basis on which to assess the cost of precautions. For example, Haley v London Electricity Board¹⁶⁴ concerned the precautions to be undertaken by the defendants to protect blind people from injuring themselves as a result of the excavation which they had constructed in the highway. Here, should the court balance the cost of providing fencing appropriate to protect blind pedestrians for the one excavation where the particular plaintiff had been injured or for all its excavation works in pavements? The answer is that the point of reference of the cost of precautions needs to tally with the point of reference of the probability of harm. So, in a case like Haley, if a court were to focus on the probability of a blind pedestrian walking along the particular street where the defendants were working (a very low probability), then the appropriate cost would be the cost of the one fencing needed for that excavation: but if the probability of blind pedestrians walking in London were taken as the measure of this factor (as it was in Haley itself), then the appropriate cost of precautions should be the cost of preventing such injuries in London.¹⁶⁵

Secondly, while generally the standard of the practicability of precautions is an objective one based on the costs incurred by a reasonable person in the situation of the defendant given the risk of harm, in some situations and especially where a danger has been thrust upon the defendant, a more subjective approach to the cost of precautions has been held appropriate, sometimes referred to as a standard of ‘measured’ negligence.¹⁶⁶ So, for example, in Goldman v Hargrave,¹⁶⁷ lightning struck a tree on the land of the defendant in Western Australia and the fire spread to the plaintiff’s closely neighbouring property. In these circumstances, the Privy Council held that the plaintiff could succeed only on proof of negligence (whether under the tort of negligence itself or in nuisance), and that where a hazard is thrust upon a defendant, negligence must be judged according to ‘what it is reasonable to expect of him in his individual circumstances’.¹⁶⁸ A similar approach has been taken by the majority of the House of Lords to the liability of an occupier for harm done by trespassers to his neighbour’s land: here, the practicability of avoiding a very probable danger must be assessed by the standard of the particular occupier.¹⁶⁹

(p.198) Thirdly, can a defendant escape liability in negligence by arguing that he relied on the skill, judgment or competence of another person? Unsurprisingly, English law’s response is ‘only when it is reasonable to do so’, taking into account the usual balance of risk against precautions: reliance on another person’s competence should be seen as a practical expression (or part of a practical expression) of a defendant’s precautions.¹⁷⁰ So, for example, in Davie v New Merton Board Mills¹⁷¹ it was held that an employer is not liable in negligence for personal injuries caused by a tool which had been negligently manufactured ‘provided that he has been careful to deal with a seller of repute and has made any inspection which a reasonable employer would make’.¹⁷²