Surface blackout in freediving: causes and prevention

Surface blackout, or shallow-water blackout, is the most dangerous situation in freediving and can be fully prevented.

What is surface blackout

On ascent from depth, oxygen pressure in the lungs drops sharply. Near the surface it reaches a level that is not enough to maintain consciousness, and the diver suddenly loses consciousness.

Why it happens at the surface, not at depth

At depth, high pressure keeps the oxygen level sufficient. On ascent the air expands and pressure drops, so the oxygen available to the brain decreases.

Factors that increase the risk

• Repeated, fast, deep breathing before the dive (hyperventilation)
• Physical fatigue and little sleep
• Severe hunger or lack of hydration
• Repeated diving without enough rest

Complete prevention

Do not over-breathe before the dive
Two or three normal breaths are enough. Fast, repeated deep breathing reduces carbon dioxide and makes you lose consciousness.

The safety buddy
Your buddy must watch your face as soon as you appear on the surface and be ready to help immediately.

What to do if someone blacks out

• Keep them floating with the head out of the water
• Call for help
• Start rescue breaths if they are not breathing on their own

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Make the rule never dive alone the first and last rule of every dive.