“The supplier shall – (a) enclose any part of a substation in the open air, containing live apparatus which is not encased, by a fence not less than 2.4 metres high to prevent, so far as is reasonably practicable, danger or unauthorised access;”
““Reasonably practicable” … seems to me to imply that a computation must be made by the owner, in which the quantum of risk is placed on one scale and the sacrifice involved in the measures necessary for averting the risk (whether in money, time or trouble) is placed in the other; and that if it be shown that there is a gross disproportion between them – the risk being insignificant in relation to the sacrifice – the defendants discharge the onus on them.”
“… for the purpose of considering whether the defendant has discharged the onus which rests upon him to establish that it was not reasonably practicable for him, in the circumstances, to eliminate the relevant risk, there has to be taken into account (inter alia) the likelihood of that risk eventuating. The degree of likelihood is an important element in the equation. It follows that the effect is to bring into play forseeability in the sense of likelihood of the incidence of the relevant risk, and that the likelihood of such risk eventuating has to be weighed against the means, including cost, necessary to eliminate it.”