SWB — Shallow Water Blackout

A shallow water blackout occurs when a diver loses consciousness while ascending near the surface. This happens because oxygen levels in the blood drop too low to support brain function. It primarily affects freedivers or those performing breath-hold safety stops. During an ascent from 20 m, the partial pressure of oxygen drops rapidly as ambient pressure decreases. This sudden shift often causes a blackout between 5 m and 10 m depths. Many people mistake the urge to breathe for a sign that they are safe. In reality, you might feel fine until the very last moment. Never practice breath-holding alone in a pool or open water. Always use a trained safety diver who watches your eyes during the final 5 m of your ascent.