Final answer:
A lifeguard's zone must be designed to allow for quick recognition and reach of a victim, considering a rescued person can recover well if CPR starts promptly, and there's a critical six-minute window before brain damage escalates.
Step-by-step explanation:
The size and shape of a lifeguard's zone should be such that they can recognize and reach a victim in the furthest and deepest part of their zone within a timeframe that allows for a high chance of recovery. Considering the reality that an unconscious person rescued with an airway still sealed due to the muscular spasm of the larynx stands a good chance of full recovery if they start receiving CPR within minutes, time is of the essence. It's important to note that without water in the lungs, CPR is more effective.
Yet, if the heart has stopped, as in a cardiac arrest, then each second counts, and brain cells begin to die after about six minutes without oxygen. Even so, in certain conditions such as immersion in very cold water, there have been instances where children have been resuscitated without lasting ill effects after extended periods. Therefore, a lifeguard's response time should be quick enough to allow successful resuscitation efforts, especially within the initial minutes following submersion.