“The impossible dream in pursuit of the indefinable standard.”

A safety case is a reasoned argument that should conclude that you are safe. But what do we mean by safe? We mean ALARP but what does that mean? So my topic is when risk is to be reduced to "as low as reasonably practical" when is enough enough? Perhaps what the law requires is an environment where risk is eliminated. Hence my title the impossible dream in pursuit of the indefinable standard.