Certain legally imposed ‘health and safety duties’ have to be ca ried out in this way. It means that a particular risk can be balanced against the time, trouble, cost and physical difficulty of taking measures to avoid the risk. If the cost and effort are disproportionate to the risk, the parties can run the risk without taking the alternative steps. The greater the risk, the greater must be the effort before it is considered disproportionate. If both the consequences and extent of risk are small, insistence on great expense would not be reasonable. Compare with all practicable steps’ meaning ‘capable of accomplishment regardless of cost but dependent on state of knowledge at time.’ See PROPERLY MAINTAINED.