Freediving Hypoxia and Approaches to Safety | Freedive Earth

Freediving Hypoxia and Approaches to Safety

According to the Diver’s Alert Network (DAN), around 40 freediving-related deaths occur every year. The overwhelming majority of these deaths involve new or untrained freedivers who don’t know how to avoid dangerous situations, or what to do when they occur. We’ve put together this short guide to help to introduce you to some concepts of safety, or to refresh your memory from your most recent freediving course. Remember, the most important thing is Never, Ever, Freedive Alone .

Hypoxia, Blackout and LMC in Freediving

As a novice or recreational freediver, by far the biggest risk you’ll face is hypoxia, that is, low stores of oxygen in the blood. This condition can cause loss of consciousness (also known as “blackout”) and loss of motor control, also known as a “samba” or LMC. Blackouts and LMCs occurring in the water are extremely dangerous. They occur because the brain has been so badly starved of oxygen that it shuts down. A diver suffering a blackout or LMC will be unable to make purposeful movements, may struggle to reach the surface and even if they do, will almost certainly not manage to keep their airway clear of the water.

A blackout isn’t the same thing as drowning. Drowning occurs when water enters the lungs, and very often during blackout, laryngospasm, an automatic closing of the glottis (vocal cords), protects the airway. 


If the diver isn’t rescued, however, drowning will quickly follow. This is because after around 30 seconds of unconsciousness, the laryngospasm will typically release and breathing will resume automatically. Clearly, if the airway is still submerged, water will be inhaled. Another important point to remember is that simply ascending to the surface can cause you to lose consciousness as the partial pressure of oxygen drops in response to the fall in surrounding water-pressure. This is a phenomenon known as shallow water blackout, and is the leading cause of blackout in almost all freediving accidents.


Subdmind Freediving


What are the Signs of Freediving Hypoxia?

The onset of serious hypoxia is usually quite obvious if you know what to look for. Always always dive with a buddy and keep a very close eye on them. The indications can be divided up into symptoms that you might (or might not) notice yourself and signs that you might notice in someone else:


  1. Light-Headedness
  2. Disorientation
  3. Visual disturbance (tunnel vision etc)
  4. Sudden Fatigue
  5. Tingling of hands and feet
  6. Strong urge to breathe
  7. Reduced urge to breathe!
  8. Feeling of euphoria
  9. Nothing at all


  1. Loss of coordination
  2. Disorientation
  3. Diver stops moving or slows right down
  4. Blue lips and face (Cyanosis)
  5. Blurred-looking eyes
  6. Abnormal movements/twitches/fitting (LMC)
  7. Air escaping from the lungs
  8. Poor attempts to breathe at the surface

It's important to understand that you may very well not be aware of the onset of hypoxia yourself or, if you are, you may get the wrong information about how far away you are from blackout. In all likelihood hypoxia will make you feel euphoric and overconfident which, combined with disorientation as your brain begins to shut down, is a recipe for disaster. I’ve heard a lot of people say “it’s ok for me to dive by myself because I know my limits and I know the signs…” but this, frankly, is rubbish. The women’s world record-holder, Natalia Molchanova died this year whilst diving recreationally, much shallower than her personal best depths, without a buddy. If it can happen to her, it can certainly happen to you.

Always dive with a buddy

Don't have a buddy? We can help!


Have a look at our article on freediving blackout for more information about how to avoid hypoxia and a more in-depth look at the causes.

How to Rescue a Blacked-Out Diver

We’ve put together a quick reference guide to performing a freediving rescue at depth, in the pool and during static apnea. Have a look here to see the details.

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