A serious accident or injury can lead to unconsciousness at the surface or underwater. The leading causes include drowning, lung overexpansion injury, and decompression sickness. No matter what the cause is, you must get the victim to the boat or shore, provide CPR if necessary, and contact emergency services.

If the diver is unconscious underwater, you must get the diver to the surface as soon as possible. To surface an unconscious diver:

1. Check the diver for consciousness by waving your hand in front of his or her mask.
2. Roll the diver onto his or her back, and remove the diver's weight belt.
3. If the regulator is still in the victim's mouth, hold it in place with one hand.
4. Ascend while holding onto the victim. Let go if the victim's buoyancy prevents you from controlling your ascent rate.