Freediving Blackout

The human body needs a continuous supply of oxygen to function properly and to survive. Changes in this supply, and thus in levels of oxygen, trigger certain physiological responses to allow the body to continue to function and/or to increase its chances of survival in these various degrees of temporary hypoxia. This is why we can work, walk, swim, exercise, and also hold our breath and freedive. Our bodies are hardwired to cope with levels of hypoxia. Freediving blackout is a part of this coping mechanism. Contrary to popular belief, freediving blackout does not happen when a freediver runs out of oxygen. It happens well before that. It is our body’s way of giving our brain and heart a better chance for survival when oxygen levels are very low. During freediving blackout all the bodily functions that are not necessary for survival are shut down, in order for the remaining oxygen to be distributed where necessary. A freediver experiencing blackout cannot see, talk, feel, etc. because that person is not conscious, but their heart is still beating and their blood, with remaining oxygen, is still being pumped into their brain. They are alive and the blackout state extends the time for how long they stay that way and recover without damage. It is not the blackout that kills freedivers. It is the absent formally trained freedive/spearfishing buddy who can follow freediving safety protocols that leads to the drowning of blackout victims.

Who’s at risk?
Every freediver, regardless of age, experience, depth, or type of diving is at risk. There are many variables and factors in breath-hold diving, human physiology, and environment that can contribute to a blackout. These can be from how well you slept to your stress levels to nutrition. We must always be alert and have proper safety protocols in place when freediving and spearfishing.

What about if I dive shallow and safely within my limits?
Depth is only one of the many variables that defines how oxygen taxing a dive can be. Most people strive to dive within their limits; however, one of the first symptoms of even mild hypoxia is confusion and faulty judgment. In other words, you never really know for sure if you are within your limits while freediving.

How can I minimize the risk of freediver blackout?
Follow proper post-dive evaluation to determine the adequate duration/depth of the following dive, and most importantly, stick with that plan during your dive. However, statistically speaking, it is not matter of if but when.

Does the water temperature or other stresses put you more at risk?
Yes. While facial immersion in cold water strongly initiates a diving reflex, cold water can also be a significant stressor that can cause the opposite effects such as tachycardia (increase of heart rate), muscle shivers, and tension. Similarly to other stresses, these increase the oxygen consumption and can contribute to a higher chance of hypoxic events such as blackout or LMC.

What is LMC?
LMC stands for “loss of motor control,” often referred to as a “near blackout” or “samba.” LMC is a physiological state of severe hypoxia when, upon surfacing, the freediver is attempting to breathe but due to a lack of oxygen cannot fully control their motoric functions. LMC is perhaps more dangerous than a blackout. There are no protective reflexes present during LMC, while the victim’s ability to control their own airway is severely compromised, making water aspiration very likely to happen without proper freediving safety.

What should I do if my buddy blacks out?
Always strive to be within arm’s reach of your surfacing diver, as this allows you to immediately support them should they display hypoxic symptoms. You must keep their airway out of the water and open for the air exchange. Remove their mask and blow across it to stimulate their breathing response. Gently tap their face and calmly speak to the diver. These techniques, when applied correctly, speed up the recovery.

Can a blackout diver continue diving that day?
No. The diving day is over, as they are more likely to blackout again. 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. Newer research suggests the possibility of certain damage from blackout; however, the extent of it can be compared to damage suffered during other widely accepted activities such as playing soccer, contact sports, and alcohol consumption.

What is the difference between drowning and freediver blackout?
Freediving blackout can be seen as an oxygen conservation state where the victim still has a heartbeat and therefore some oxygen is still being supplied to the brain. The victim is unconscious but with dry lungs protected by laryngospasm (cramping of the vocal cords). If left unattended, eventually all oxygen will get depleted. Laryngospasm will relax and terminal gasp (inhalation attempt) will occur. This will lead to water aspiration and drowning.

Is freediving safe?
It is probably safer than driving a car or scuba diving. However, just like the mentioned activities, to minimize the risks associated with freediving one should get formally trained in safe practices and emergency procedures and follow the “rules of the road.”

These are some freediving safety protocols

1. Never dive alone.
2. Remember the rule: “one buddy up, one buddy down.”
3. Keep within arm’s reach of your surfacing diver.
4. Observe your diver for a minimum of 30 seconds before starting your dive.
5. At minimum, make sure you are positively buoyant on the surface (ideally neutral at 33'/10m).
6. Get formal freediving training before participating in any freediving or spearfishing activities.