The expression "reasonable and practicable" is taken to mean that a company must take steps which are both reasonable ones to take and also practical ones to prevent any given accident. Clearly if the accident was something very minor, a cut finger for example, then it would be not deemed to be reasonable to spend a lot of time, money, manpower, resources and so on simply to stop it happening. If, on the other hand, the outcome of an accident could result in very serious or even fatal injury then there is no limit on the sort of actions a company must undertake in order to prevent it. In the event of a prosecution it would be for a company to prove that they had indeed taken all reasonable, practicable steps in order to prevent the accident.
Using the graph above: suppose the left hand side represents a minor injury such as a cut finger than maybe a pair of safety gloves might be all a company needs to do in order to take "all reasonable, practicable" precautions. The right hand side of the graph represents a fatal accident and where this is a possibility, every resource that the company possesses should be employed to stop it happening.