What is shallow water blackout? You need to know.

What is shallow water blackout? You need to know.

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.

WHERE: Shallow Water Blackout can occur in any pool, lake, ocean or body of water when breath-holding, regardless of water depth. Even if lifeguards are on duty there is still a great risk because it is hard to detect from above the water.

WHY: Shallow Water Blackout occurs because of the LACK OF EDUCATION and understanding of the dangers of breath-holding. It also occurs because of the lack of safety training for swimmers, free divers, snorkelers, and spear fishermen. The breath-holders do not understand how to prevent Shallow Water Blackout or how to survive if it happens to them. Unfortunately, training does not inoculate one against SWB. All too often trained freedivers succumb.


People who hold their breath while swimming or practicing breath-holding underwater in pools are at risk of “passing out” due to lack of oxygen. This phenomenon is commonly referred to as shallow water blackout (SWB) and it is the result of a SEVERE LACK OF OXYGEN TO THE BRAIN.

SWB may be the leading cause of swimmer death. The number of deaths that can be attributed to SWB is not fully known, as these deaths are often misdiagnosed as traditional drowning. When coroners rule a SWB death as “drowning” only, it masks the real problem: hyperventilation combined with competitive, repetitive breath-holding. For this reason, SWB is not well known or understood by many of those who are most at risk.

When oxygen levels fall to critical levels, blackout is instantaneous and frequently occurs without warning. Most of the time, underwater swimmers have no clue they are about to be rendered unconscious and that they will be vulnerable to death within minutes.

Swimmers who hyperventilate to excess before breath-holding are in particular danger. Hyperventilation is simply an increase in the amount of air moving in and out of the lungs. It may be due to rapid, shallow breathing, but deep slow breathing can also result in hyperventilation. Paradoxically, hyperventilation does not increase the amount of oxygen in the body, but it does decrease the amount of circulating carbon dioxide. Carbon dioxide levels in the blood are primarily responsible for the swimmer’s desire to breathe. When the level of carbon dioxide in the blood is driven to artificially low levels as a result of hyperventilation, the desire to breathe is diminished. This artificial method of fooling the body into thinking it does not need oxygen is deadly, as it lures the breath-holder into believing he can hold his breath longer than he safely can.



Underwater breath-holding and underwater swimming have been practiced for decades.

Coaches and military trainers teach hypoxic training and breath-holding, which can be deadly without professional, one-on-one monitoring.

Lifeguards typically do not have training to monitor breath-holding.

Lifeguards and parents routinely accept and encourage breath-holding drills conducted in swimming pools.


Swimming athletes who train and perform in swimming pools, particularly those who practice hyperventilation.

Swimmers who are physically exerted.

Swimmers who are not closely observed while engaged in breath-holding.

Swimmers who consecutively perform a repeated hyperventilation/breath-holding routine.

Breath-holding swimmers who have unknown and underlying medical causes, i.e. long Q-T, RyR2, seizures, etc.

People who practice holding their breath in a pool while floating face down or sitting on the bottom. Since the individual is already in a state of relaxation, SWB becomes nearly impossible for an observer to detect.

Freedivers and spearfishermen (please see www.divewise.org).


DO NOT PRACTICE prolonged breath-holding. The ARC, YMCA and USA Swimming now ban hypoxic training and prolonged underwater swimming although far too many still practice it.

Never swim alone.

Underwater breath-holding should never be encouraged, but if practiced the rule of thumb for safety is: One Breath-hold, One Time, One Lap, ONLY.

Never Hyperventilate.

Repetitive breath-holding Increases risk of SWB. If Breath-holding under water, a buddy must be next to you tapping you on your shoulder so you can signal that you are OK. Their total focus needs to be you and your safety. They should never breath-hold with you. Do not rely on lifeguards. SWB is difficult to detect above water.

For freediving and spearfishing safety guidelines and safety courses visit www.DiveWise.org and www.immersionfreediving.com.