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DANGER - No Prolonged Breath Holding Underwater - Australian Safety Signs

About SWB

This site was established in order to raise awareness of Shallow Water Blackout in Australia following the tragic death of Jack MacMillan in January 2013.

The below is information regarding Shallow Water Blackout (SWB) and you can also learn more by clicking on the tabs above or by following our Facebook Page “Shallow Water Blackout SWB”.

WHO: It can affect anyone that is breath-holding, even the physically fit swimmer. It is especially seen in competitive swimmers, Navy, 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.

HOW IT HAPPENS: Shallow Water Blackout typically occurs because of false lower than normal 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/exhaustion 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: SWB frequently occurs, without any warning of its onset. In fact, due to the hypoxia, a condition where the tissues are not oxygenated adequately, usually due to
an insufficient concentration of oxygen in the blood 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 minutes before brain damage and/or death occurs with SWB. The brain has already been oxygen deprived coupled with warm water as in swimming pools, hastening brain death.

WHERE: SWB can occur in any pool, bath, spa, lake, ocean or body of water when breath-holding, regardless of water depth, with or without lifeguards present. SWB is hard to detect from above the water.

WHY: Shallow Water Blackout deaths occur because of lack of education and understanding of the dangers of breath-holding. Lack of safety training for swimmers,
freedivers, snorkelers, and spearfishermen also contribute to the frequency of Shallow Water Blackout drowning deaths.  The breath-holders do not understand how to prevent Shallow Water Blackout or how to survive if it happens to them or a mate.  Unfortunately, training does not inoculate one against SWB.  All too often, trained freedivers succumb to Shallow Water Blackout. Active Supervision and an understanding of the dangers can assist to prevent


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 and no warning. This phenomenon is commonly referred to as shallow water blackout (SWB) and Hypoxic Blackout in some countries and is the result of a SEVERE LACK OF OXYGEN TO THE BRAIN due to falsely lower than normal carbon dioxide levels which is our trigger to breathe at high levels as our oxygen levels become low. It is our bodies natural built in mechanism.

SWB is thought to be the leading cause of competent swimmer drowning deaths in some countries where there is no other obvious reason.  The number of deaths that can be attributed to SWB is not fully known, as these deaths are often misdiagnosed and reported as a general drowning.  When coroners rule what should be 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. Since Jack’s death in 2013, Australia has seen many more incidents and tragically more deaths from SWB. As we learn more and message becomes more familiar, unfortunately we will hear and learn of more deaths, and less will be incorrectly ruled.

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 unconscious and that they will be vulnerable to death within minutes and becomes an unintentional suicide.

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. Hypoxic training or drill sets, can lead and have led to blackouts, non fatal drownings and  and drowning deaths in Australia and all around the world.



  • 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/divers 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


  • Do not prcatice prolonged breath-holding. The ARC, YMCA and USA Swimming now ban hypoxic training and prolonged underwater swimming although far too many still practice it. (make sure your swimming coach is aware of the dangers and is fully qualified before participating in hypoxic drills. Shallow Water Blackout Australia does not condone hypoxic training and would like to see this practice banned in Australia)
  • 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, Once Only, Rest (taking a 5 minute rest break to help your Co2 & O2 levels return to normal).
  • 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.

This information was used with permission from

To download our colour DL Brochure (PDF) to have as a handy guide or to distribute, please click here: Shallow Water Blackout Brochure. The brochures are available for ordering also, please email Sharon at to place your order and arrange shipment. or Download attached.

To order a yellow “NO LONG BREATH HOLDING” sign, email Yellow signs are $44 plus postage for a 15”x15”. Discount are available when purchasing in bulk.

To read an article by international SWB professional Dr Tom Griffiths on Shallow Water Blackout Click Here (this will take you to Get Out There site)

Shallow Water Blackout Australia encourages all aquatic centres to install a Poseidon Drowning Detection Alarm System – contact Dan or Chris today at:



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