What is shallow water blackout?
WHO: It can affect anyone that is breath-holding, even the physically fit swimmer. It is especially seen in competitive swimmers, Navy SEALs, snorkelers, spear fishermen or anyone who free-dives. SWB cuts across the spectrum of freediver training affecting all levels. No one is protected from succumbing to SWB.
WHAT: Shallow Water Blackout typically occurs because of low carbon dioxide (CO2) and low oxygen (O2). Unconsciousness occurs when O2 levels in a swimmer are too low. What triggers us to breathe to get O2 is HIGH CO2 not low O2 as one might think. Hyperventilation done before breath-holding lowers the CO2 abnormally so one can hold their breath longer, however, one may experience Shallow Water Blackout even without hyperventilation before breath-holding. The primary cause of SWB is lack of O2 reaching the brain. The CO2 levels may be high as in extreme exertion or low as in hyperventilation. In each case SWB happens. However with low CO2 levels, our bodies are robbed of their built-in mechanism to protect us and tell us to breathe before unconsciousness happens. One basically "blacks out" in the water. For some, their lungs will take on water leading to drowning while others simply suffocate or die of other causes brought on by the breath-holding. Death can be a result of the prolonged breath-holding even if not from so called "Shallow Water Blackout."
WHEN: Frequently, Shallow Water Blackout occurs WITHOUT ANY WARNING of its onset. In fact, because of the hypoxia and detached mental state one can feel euphoric and empowered to continue breath-holding. Unlike regular drowning where there can be 6-8 minutes before brain damage and death, there is ONLY about 2 ½ minutes before BRAIN DAMAGE then DEATH with SWB because the brain has already been oxygen deprived coupled with warm water as in swimming pools, hastening brain death.