.png)
Freediving Blackouts Explained
- Curtis Tredway
- Aug 19
- 9 min read
This week, one of our posts about freediving safety went viral.
And while it reached far more people than we expected, what interested me most was the comment section.
There were hundreds of opinions about blackouts - including comments from scuba divers, experienced water people and even people working in medical fields - and it became pretty obvious just how misunderstood freediving blackouts still are.
Some people seemed to believe that a blackout automatically means drowning.
So let's clear a few things up.
I've worked professionally in the diving industry for close to a decade, across both freediving and scuba. I've worked as a competition safety diver supporting athletes at the 2025 Freediving World Cup, as a scuba safety diver for Helicopter Underwater Escape Training (HUET), and on safety teams supporting film and television crews underwater.
One thing all of these environments have in common is that underwater safety depends on understanding what can go wrong before it happens.
And in freediving, one of the most important things to understand is hypoxic blackout.
What is a freediving blackout?
A freediving blackout is a temporary loss of consciousness caused by the brain no longer receiving enough oxygen to maintain consciousness.
The medical term for low oxygen is hypoxia.
During a breath-hold, your body is continuously consuming oxygen while producing carbon dioxide. Eventually oxygen levels can become sufficiently low that the body engages a fail safe and switches off to conserve oxygen.
This doesn't necessarily happen when you feel the strongest urge to breathe.
The urge to breathe is driven heavily by rising carbon dioxide, whereas blackout is primarily associated with falling oxygen. These are related, but they are not the same thing.
That distinction is incredibly important.
In many instances that 'urge to breathe' will take place long before you are hypoxic. Meaning you have a natural guage of where you are at in your breathhold.
Why does a blackout happen?
Every second you hold your breath, your body continues using oxygen.
Swimming, kicking, fighting current, being cold, feeling stressed or exerting yourself all increase oxygen consumption.
Eventually, if the breath-hold continues for long enough, oxygen availability can become too low to maintain consciousness.
Depth adds another factor.
When a freediver descends, increasing pressure temporarily increases the partial pressure of oxygen in the lungs. During ascent that process reverses.
As the diver approaches the surface, ambient pressure decreases rapidly. The partial pressure of oxygen can therefore fall very quickly during the final part of the ascent.
This is why many freediving blackouts occur close to the surface or shortly after the diver reaches it.
You've probably heard this referred to as shallow-water blackout.
However, "hypoxic blackout" is often the more useful term because blackouts are not restricted to deep freediving. They can occur during pool dynamics, static breath-holds, spearfishing, repeated shallow diving and other breath-hold activities.
"There’s no warning before a blackout": Signs and Symptoms of Hypoxia
This one needs a little nuance.
Non-freedivers think that a freediving blackout happens without any warning whatsoever.
That isn’t completely accurate.
Hypoxia can produce signs and symptoms before unconsciousness. However, inexperienced divers may not recognise them clearly.
So while there can be warning signs, you should never rely on feeling a blackout coming as your safety system.
Signs and symptoms of hypoxia
As oxygen levels fall, a diver may experience things such as:
Changes in vision - tunnel vision, narrowing vision, greying out or visual disturbances
Cyanosis - blue lips and ears
Dizziness or light-headedness
Tingling or unusual sensations
Feeling unusually warm or euphoric
Confusion or difficulty thinking clearly
Poor judgement or unusual decision-making
Loss of coordination and strange movements
Weakness or difficulty maintaining swimming technique
Slowing down or speeding up unexpectedly
Difficulty responding appropriately to a buddy
Spaced out look
Loss of motor control
Ultimately, loss of consciousness
The difficult part is that hypoxia can also affect the brain's ability to recognise that something is wrong.
A diver may genuinely feel that they're fine while their ability to make good decisions, coordinate their movements or assess the situation is already deteriorating.
This is one of the reasons why saying "I'll just come up when I start feeling hypoxic" isn't a reliable safety strategy.
The situation can also change particularly quickly during the final section of an ascent. As pressure decreases, the partial pressure of oxygen in the lungs falls with it, meaning a diver who felt relatively comfortable deeper in the dive can become critically hypoxic close to the surface.
And importantly, the urge to breathe isn't the same thing as a warning of blackout.
The urge to breathe is influenced heavily by rising carbon dioxide. Blackout happens when oxygen falls too low to maintain consciousness.
This is why hyperventilation is so dangerous. It lowers carbon dioxide and can delay the urge to breathe without adding a meaningful amount of extra oxygen. A diver can therefore feel surprisingly comfortable while their oxygen level continues to fall.
So the myth isn't really that there are no signs of hypoxia.
The more accurate statement is:
There is no reliable warning sign that tells you exactly when you are about to blackout.
That is why freediving safety is built around conservative diving, appropriate recovery, avoiding hyperventilation and most importantly having a trained buddy actively supervising the dive.
You shouldn't need to recognise your own blackout.
Your buddy should already be there before it happens.
The biggest avoidable risk: hyperventilation
This is one of the most important misconceptions we still see.
Taking lots of big breaths before diving doesn't meaningfully load your body with huge amounts of additional oxygen.
What it can do very effectively is lower your carbon dioxide.
That matters because carbon dioxide is one of the primary things creating your urge to breathe.
Hyperventilate before a breath-hold and you can delay that warning signal while your oxygen continues falling.
In other words, you can feel more comfortable while actually moving closer to hypoxia.
DAN specifically identifies excessive pre-dive hyperventilation as a major contributor to breath-hold blackout risk.
That is why proper freediving education spends so much time differentiating relaxation and normal breathing from hyperventilation.
A blackout does NOT automatically mean someone has drowned
This was probably the biggest misunderstanding in the comments on our post.
Loss of consciousness and drowning are not the same event.
A blackout means the diver has lost consciousness because of hypoxia.
Drowning involves respiratory impairment resulting from submersion or immersion.
A freediver can therefore blackout, be immediately supported by their buddy, have their airway protected above the surface and regain consciousness without progressing to drowning.
An Amazing Blackout Response
One of the many remarkable responses our body can have during a breath-hold occurs around loss of consciousness itself. Following a blackout, the airway may initially remain closed and a laryngospasm - an involuntary closure of the vocal cords can occur. This can temporarily limit water entering the airway.
This is why an attentive buddy is so important: a blackout needs to be recognised immediately, with the diver brought to the surface and their airway kept clear of the water as quickly as possible.
In competitive freediving, this is exactly why trained safety divers are positioned where an athlete is most likely to experience trouble.
The moment there is a problem, the diver is supported to the surface.
The airway comes out of the water.
The mask is removed.
The safety diver stimulates the person and encourages breathing.
The situation is dealt with immediately.
In 2025 I performed a number of real blackout rescues from competition divers going 100m and beyond. Some of the rescues happened as deep as 30m, and took approximately 30-45 seconds to get them to the surface. In every instance the competitors were back to normal, and able to dive within a couple of days.
That doesn't make blackout harmless.
It means blackout and drowning need to be understood as two different stages of an emergency.
An unmanaged blackout underwater can absolutely progress to drowning.
And that is exactly why we never freedive alone.
What does a freediving rescue actually look like?
At a basic level, the priorities are simple:
Protect the airway. Get the diver to the surface. Keep their face out of the water. Remove facial equipment obstructing the airway. Stimulate them and encourage them to breathe.
Freediving organisations train divers in specific blackout and loss-of-motor-control rescue procedures for exactly this reason. Even junior freediving education includes blackout rescue and buddy skills.
A freediving blackout will often resolve quickly once the diver is at the surface, the airway is protected and breathing resumes.
However, if the diver does not resume normal breathing, the situation has escalated.
Emergency services should be activated and appropriate rescue breathing/CPR and oxygen should be provided by trained rescuers according to current resuscitation protocols. Because drowning is fundamentally a hypoxic emergency, ventilation is particularly important in drowning resuscitation.
This is why watching a few videos online isn't a substitute for actually practising a rescue.
On our freediving courses, students physically perform these skills until they understand both what to do and how quickly to do it.
Let's Clear This Up - Freediving Rescues are NOT the Same as SCUBA
We had a lot of comments from scuba divers asking why the weight belt wasn't ditched, whether the diver ascended too quickly, and what happened to the safety stop.
Those are completely valid concerns in scuba diving - but they don't apply in the same way to freediving.
Freedivers are not breathing compressed gas at depth, so the risks associated with rapid ascent, lung overexpansion and decompression are fundamentally different. A freediver does not need to make a safety stop after a normal breath-hold dive, and in a blackout rescue the priority is to get the diver's airway to the surface as quickly and safely as possible.
The weight belt question also needs context. In some emergencies, ditching weight may absolutely be appropriate. But in a controlled freediving rescue, a trained buddy can often support and surface the unconscious diver immediately without first removing equipment. The priority is simple: reach the diver, secure them, get their airway above the water, and begin the appropriate blackout response.
Scuba and freediving share the same environment, but they involve very different physiology, risks and rescue procedures. That distinction matters.
How do we prevent blackouts?
You can't make breath-hold diving completely risk free.
But you can dramatically change the way that risk is managed.
The foundations aren't particularly complicated:
Never freedive alone.
Dive with somebody who actually understands freediving safety and not simply someone who happens to be in the water.
Don't hyperventilate before diving.
Don't deliberately push through warning signs simply to reach a depth, time or distance.
Allow adequate recovery between dives.
Account for current, waves, cold, fatigue and increased exertion.
Weight yourself appropriately.
Have the buddy actively supervise the critical portion of the dive and the recovery at the surface.
Learn how to recognise loss of motor control and blackout.
Practise rescue skills regularly rather than assuming you'll remember them during an emergency.
Formal freediving courses are built around exactly this principle. SSI, for example, specifically describes certified freediving as diving with a buddy, rather than simply teaching people how to hold their breath longer.
What competition safety diving taught me
Working as a safety diver at a Freediving World Cup changed the way I look at this.
You're surrounded by some of the strongest breath-hold athletes in the world.
These are people with extraordinary physical ability, years of experience and highly developed awareness of their bodies, capable of pushing their limits
And yet there is still a dedicated safety team.
Why?
Because being good at freediving doesn't make you immune to physiology.
Competition safety is built around layers.
The athlete is trained.
The dive is monitored.
Safety divers are positioned strategically.
The diver is met during the final section of the ascent.
The surface is supervised.
Emergency equipment is available.
And everyone knows their role before something happens.
I've worked in a similar way as a safety diver on scuba for Helicopter Underwater Escape Training, where people are deliberately placed into demanding underwater emergency scenarios, and supporting film and television crews working around water.
The environments are very different.
The principle isn't.
Even in the worst-case scenarios of the compeitions, the athletes were okay thanks to our safety protocols.
Good safety isn't about pretending incidents can never happen.
It's about building systems so that IF something does happen, it is recognised early and managed correctly.
Blackout shouldn't be normalised — but it shouldn't be sensationalised either
We don't want people walking away from this article thinking blackouts aren't serious.
They are.
An unconscious person underwater is an emergency.
But portraying every freediving blackout as an immediate drowning or assuming the diver was seconds away from death isn't particularly helpful either.
Understanding the difference matters.
A blackout is a physiological consequence of insufficient oxygen reaching the brain. Divers can listen to their body, and take necessary precautions to reduce their risks.
A trained buddy can recognise the signs, and assist their buddy even before loss of conciousness.
The goal isn't simply to teach somebody to dive deeper or hold their breath longer.
The goal is to create divers who understand what their bodies are doing, recognise risk and are capable of looking after the person they're diving with.
Because ultimately the most important piece of freediving equipment you have isn't your fins.
It's your buddy.
Comments