Shallow water blackout in freediving

What shallow water blackout means

In freediving, blackout can occur when oxygen available to the brain falls too low. The final part of an ascent deserves particular attention because pressure is decreasing quickly and the partial pressure of oxygen also falls.

Why the surface can be deceptive

A diver may feel that the dive is almost finished, but safety continues through the ascent, surface arrival and recovery breaths. A buddy should stay close and attentive until the diver is clearly recovered.

Hyperventilation increases risk

Excessive pre-dive hyperventilation lowers carbon dioxide and can delay the urge to breathe. It does not create a proportionate increase in oxygen reserve, so the diver may lose an important warning signal.

The buddy system

An effective buddy knows the plan, meets the diver during the final part of the ascent, watches the airway and face closely at the surface and is prepared to respond immediately to loss of motor control or blackout.

Prevention is procedural

Safe freediving relies on conservative planning, appropriate recovery, active supervision, no solo water apnea, and a culture where turning early is considered good judgement rather than failure.

Learn with an instructor

Educational articles can help you understand the concepts, but equalization and safety skills should be developed progressively with direct feedback in an appropriate training environment.