Freediving safety: one up one down, blackout, samba and why not to hyperventilate

TUREFF• •0

Freediving is safe when it is done properly and very unforgiving when it is not. The main danger is not running out of air in the way most people imagine. It is losing consciousness without warning, often near or at the surface, with nobody close enough to help. Every safety rule in the sport exists to make sure someone is always there when that happens.

Never dive alone

This is the rule that matters more than all the others. A diver who blacks out underwater with no one watching will usually drown. A diver who blacks out with a trained buddy beside them is normally brought to the surface, recovers within moments and is fine. The difference between the two is simply whether someone was watching. That applies to shallow water too. Blackouts happen in swimming pools and in water you could stand up in.

One up, one down

Freedivers dive in pairs, and only one of the pair dives at a time:

The diver prepares and dives while the buddy stays at the surface, watching the whole dive.
On deeper dives, the buddy usually swims down to meet the diver on the way up, through the last stretch of the ascent where blackouts are most likely.
When the diver surfaces, the buddy stays within arm's reach and keeps watching. Many training agencies teach watching for at least 30 seconds after the diver surfaces.
Only when the diver has recovered fully do they swap roles.

A buddy who is also diving, or resting with their face out of the water looking elsewhere, is not a buddy.

Why blackouts happen where they do

Your urge to breathe is triggered mostly by rising carbon dioxide, not by falling oxygen. Oxygen can drop low enough to switch you off before you feel desperate for air. On a depth dive, water pressure squeezes the lungs and keeps the oxygen in them at a higher pressure. As you come back up, that pressure falls quickly, and so does the oxygen available to the brain. That is why a blackout is most likely in the last few metres of the ascent or just after surfacing, sometimes after the diver has given an OK sign.

Loss of motor control (the samba)

A loss of motor control, or LMC, nicknamed the samba, is a milder hypoxic event, usually after surfacing. The diver stays conscious but loses control of their body for a few seconds: shaking, twitching, the head lolling, difficulty speaking. It is a warning that they were on the edge of a blackout, and it can turn into one. A buddy should support the diver's head and keep their airway clear of the water, talk to them and encourage them to breathe. The dive was too long; it is a reason to stop for the day, not to try again.

What a buddy does for a blackout

This is exactly what a course trains, and you should practise it until it is automatic:

bring the diver to the surface, keeping their airway out of the water
remove their mask, and talk to them while encouraging them to breathe, with gentle stimulation such as blowing across the face
if they do not start breathing quickly, call for help and follow the rescue breathing you were taught
anyone who has blacked out should stop diving for the day and be checked, and get medical help for any breathing difficulty afterwards

Why hyperventilating is dangerous

Taking a series of fast, deep breaths before a dive feels as if it loads you up with oxygen. It does not do much for oxygen, because normal breathing already saturates the blood. What it does is blow off carbon dioxide, which delays the urge to breathe. You stay down longer than your oxygen supply allows, and the warning signal that should bring you up arrives late or not at all. Divers' medical organisations warn that hyperventilation alone can be enough to cause a blackout. Courses teach a slow, relaxed breathe-up instead, and recovery breaths after surfacing. Learn those from an instructor rather than from a video.

Other habits that keep you safe

Never push a maximum attempt without a trained buddy ready to rescue you.
Do not dive when you are tired, cold, unwell, hungover or after a large meal.
Use a buoy and a line in open water so your buddy knows where you are, and boats can see you.
Do not freedive in the hours after a scuba dive.
Turn back when it feels wrong. The dive will still be there tomorrow.

Have you seen a samba or a rescue on a course, or got a question about buddy procedures? Share it in the comments below.