What is the most efficient way to provide oxygen to a breathing, injured diver?

Using a continuous flow with a nonrebreather mask is considered the most efficient way to provide oxygen to a breathing, injured diver because it allows for the delivery of high concentrations of oxygen directly to the patient. The nonrebreather mask is designed with a one-way valve that prevents the inhalation of exhaled gases, ensuring that the injured diver receives fresh oxygen from the tank without dilution from room air.

This method is particularly effective in emergency situations where the diver may be hypoxic or experiencing difficulties with their airway or respiratory function. The design of the nonrebreather mask maximizes oxygen supply while minimizing the risk of carbon dioxide retention, which is crucial for maintaining the diver's conscious state and overall stability.

In contrast, other methods listed may not provide the same level of oxygen concentration or may be more suitable for different circumstances. For instance, a demand valve system and a positive pressure resuscitator are generally used for non-breathing patients or in scenarios where controlled ventilation is required, which does not apply to a diver who is still breathing. A pocket mask is also less efficient in providing concentrated oxygen compared to the nonrebreather mask, as it primarily focuses on ventilating the patient rather than supplying pure oxygen.