What causes shallow water blackout in freediving?
Shallow water blackout is a loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive in shallow water. It is typically caused by hyperventilating just before a dive, which lowers the carbon dioxide (CO2) level and delays the diver’s urge to breathe. Deep water blackout occurs as the surface is approached following a breathe-hold dive of over ten metres and typically involves deep, free-divers practicing dynamic apnoea depth diving usually at sea. The immediate cause of deep water blackout is the rapid drop in the partial pressure of oxygen in the lungs on ascent.If the diver inhaled any water, they must seek immediate medical attention. Does freediver blackout cause brain damage? Several studies have been conducted on this topic and evidence suggests that no brain damage occurs from freediving blackout.The Golden Rule: Never Dive Alone One of the biggest take-home messages we are informed of is “never dive alone. Shallow water blackout is a potentially fatal outcome while freediving, and if you don’t have a buddy to rescue you, the event will likely end in death.The victim of hypoxic blackout may have been seen to be hyperventilating before the dive, and typically the blackout will have occurred some time after immersion, often without surfacing, and usually close to the surface. The victim is subsequently found unconscious or dead at the bottom of the water.Freediving to depth may increase the risk of blackout due to the decreasing hydrostatic pressure while ascending to the surface, causing “shallow water blackout” (Lanphier and Rahn 1963). Here, oxygen exchange may cease or even be reversed, moving oxygen from the blood back into the lungs (Lanphier and Rahn 1963).
How deep for shallow water blackout?
A shallow water blackout happens when you lose consciousness while swimming and diving in water less than about 15 feet deep. It can also happen at deeper depths when you black out due to hyperventilation before a dive. The term shallow water backout has been commonly used as a term for drowning, particularly when preceded by hyperventilation.