Everything You Need to Know about Shallow Water Blackout

What it is, why it happens, and how to avoid it

If there’s one thing people ask about most, it's shallow water blackout

And fair enough. It’s real. It’s serious. But it’s also wildly misunderstood.

This isn’t a scare piece. It’s just a straight explanation, the way I explain it to students in a course.

I spent 14 years diving before I ever saw my first shallow water blackout (I’ll talk more about that later). In 2025, I was asked to work as a Safety Diver at the World Cup, where I saw and assisted with multiple blackouts. When you dive responsibly, shallow water blackout is very unlikely, and if it does occur under proper protocols, it’s manageable and not something to be afraid of.

What shallow water blackout actually is

Shallow water blackout is a loss of consciousness caused by low oxygen, usually happening near the surface or just after you surface.

Not just on deep dives.

Not because you “held too long”.

And not because of CO₂.

CO₂ makes you uncomfortable.

Oxygen keeps you conscious.

That difference matters more than most people realise.

Why it happens near the surface

Pressure is doing you a favour at depth.

When you’re diving, pressure helps keep oxygen available in your blood. As you ascend, that pressure drops fast, especially in the last 10 metres. The partial pressure of oxyge drops with it.

So you can:

• Feel fine on the way up

• Feel fine breaking the surface

• Then suddenly not be fine at all

This is why people say it “came out of nowhere”. It didn’t. It just wasn’t loud.

The biggest causes (this is the important bit)

There are patterns. They show up over and over again.

Hyperventilation

This is the big one.

Hyperventilating lowers CO₂, which delays the urge to breathe. It does not meaningfully increase oxygen.

All it does is remove your warning system.

You feel calm. You feel strong. You feel in control. You're not.

Poor recovery between dives

One of the quickest ways people get into trouble is stacking dives, statics, or dynamics without enough surface interval. Oxygen drops, fatigue builds, and your margin disappears fast.

Pushing when you shouldn’t

Chasing numbers. Chasing mates. Chasing a “good day”. This is where ego sneaks in and decision-making drops. Whether its on the line, or chasing a fish, always stick within your limits.

Lack of surface protocol

No proper recovery breathing. Turning away too early. No one actually watching you.

Most blackouts happen after the dive, not during it.

What a blackout usually looks like

It’s rarely dramatic.

Often it’s:

• Delayed or weak breathing

• Loss of motor control

• Glassy eyes

• Slumping or sinking quietly

• Bubbles

• Out of the ordinary , if something looks off get ready to respond.

A lot of divers don’t even remember it happening.

That’s why buddies matter.

How to avoid it (this is non-negotiable)

Don’t hyperventilate

A calm breathe-up is not hyperventilation. Slow, relaxed tidal breathing is the goal.

Always dive with a buddy who knows what they’re doing

Not just someone nearby. Someone watching you, timing you, and ready to act.

Use proper recovery breathing

Strong inhale, passive release. Repeat until you’re fully stable. Every dive. No shortcuts.

Progress conservatively

Depth and time come with consistency, not forcing it. If you’re fatigued, you’re done. That’s discipline, not weakness.

Get proper training

A good course isn’t about ticking boxes. It’s about learning habits that stay with you when things don’t go to plan.

How to respond to a Shallow Water Blackout

If you ever see a shallow water blackout, the response should be simple, calm, and focused. The goal is always the same: protect the airway and restore breathing.

ThesShallow water blackout rescue response

1. Support the airway immediately

Get the diver’s face out of the water. Support the head, tilt it slightly back, and keep the airway clear at all times.

2. Remove facial equipment

Remove the mask and nose clip if worn. This helps keep the airway open and allows normal breathing to resume.

3. Blow and talk

Blow gently across the diver’s face and speak calmly to them. Encourage breathing as consciousness starts to return. This helps stimulate respiration and orient the diver during recovery.

4. Stay with them

Maintain airway support and close supervision until breathing is strong, regular, and the diver is fully aware. Do not let go too early.

That’s it. No rushing, no panic, no unnecessary movement.

A note on “tap”

You may still hear blow, tap, talk referenced. Over time, and through analysis of real-world rescues and competition footage, tapping showed little correlation with recovery.

Divers recovered due to:

• airway support

• oxygen returning

• blow and verbal cues

  
  

Because it didn’t add value, tap has largely been removed from modern protocols.

The key takeaway

A good blackout response isn’t complicated.

Protect the airway. Blow and talk. Stay calm. Stay present until the diver is fully stable.

Everything else is noise.

The part people don’t like hearing

Shallow water blackout is rarely bad luck.

It’s usually a mix of:

• Behaviour

• Poor habits

• Complacency

The ocean doesn’t shout when you make mistakes. It whispers.

A shallow water blackout does not equal drowning when correct buddy procedures are in place. With proper airway support and a prompt response, a diver can blackout and still have a 2–4 minute rescue window, often with little to no long-term effects.

Final thought

Freediving is incredibly safe when it’s done properly.

The goal isn’t to remove all risk, it’s to understand it well enough that you don’t play games with it.

If something feels off, stop.

If you’re solo, don’t dive.

If you’re tired, call it.

There’s always another day.

Understanding blackout risk is only one side of the equation. The other is learning how to safely improve your hypoxic threshold through structured, progressive training. This is where properly designed CO₂ and O₂ tables come in, teaching your body to tolerate low oxygen in a controlled environment, not by pushing limits in the ocean.

If you want to understand how we approach this safely, you can read our full breakdown here