When is it necessary to designate someone to be 'in charge'?

The correct answer emphasizes the necessity of designating someone to be 'in charge' particularly when the Assistant Fire Marshal is off duty. This ensures that there is a clear chain of command and that responsibilities are clearly assigned during times when the usual leadership is unavailable. Having a designated individual in charge helps maintain operational effectiveness, ensures the safety of personnel, and allows for efficient decision-making in their absence.

In the context of the other options, while having someone in charge during regular shifts and in emergencies is important, the specific need highlighted in this question focuses on the circumstances when key leadership is absent. The choice about being 'in charge' all the time may suggest unnecessary duplication of leadership roles when such delegation is not required. By focusing on the need for designation during the absence of the Assistant Fire Marshal, the policies underscore the significance of leadership continuity.