If a diver is unconscious and not breathing, what is the most common reason?

The most common reason for a diver being unconscious and not breathing is airway obstruction. When a diver is underwater and becomes unconscious, their ability to protect the airway can be compromised. Various factors can lead to airway obstruction, including water entering the throat, a loss of muscle tone, or foreign body obstruction. If the airway is blocked, oxygen cannot reach the lungs, resulting in the diver not being able to breathe effectively.

In diving scenarios, the effects of water and the physical state of the diver contribute significantly to this risk. It's crucial to assess the airway immediately in such emergencies because restoring the airway and enabling breathing is essential for survival. Addressing airway issues is often the first step in any emergency response protocol, especially in a diving context where rapid recognition and intervention are vital.