Advance freediving at big depths is an exciting but risky sport. Erika Schagaty, philosophy doctor in zoophysiology and research scientist at the diving laboratory of Zoo physiological Institute in Lund, tells us here about the risks and how to avoid them.

There are several risks in real deep freediving. As in all freediving its very dangerous to hyperventilate before diving (breath deeper and faster than normally). This could otherwise seem to be the right thing to do because the diver experience it as easier to hold the breath for a longer time before the reflex makes the diver breath again.

The risks depend on that large amounts of carbon dioxide are weathered out of the blood keeping the oxygen pressure at a normal.

Normally the carbon dioxide pressure gives the first signals for the diver/person to start breathing again at an individual point. This occurs normally in good time before the oxygen pressure lowers to a level that makes the diver unconscious.

But with hyperventilating this signal comes too late: just after the point when the oxygen pressure has passed the level where the diver is conscious. The person looses consciousness without any warning and when the high carbon dioxide pressure starts the breathing reflex again there is great risk that the diver breathes in water instead of air. Only alert persons in the surrounding area can prevent the diver from drowning of "hyperventilation blackout".

Shallow water blackout

Another great risk that is directly linked to the pressure of the breathing gases, and is therefore greater as the diver reaches greater depths is called "shallow water blackout". With increasing depths the oxygen pressure in the lungs will rise which leads to that the blood can take up more oxygen. With ascending to the surface the oxygen pressure lowers dramatically, and if the pressure in the lungs becomes lower than in the blood the oxygen will pass from the blood into the lungs instead.

Sudden unconsciousness can follow. At the same time the carbon dioxide pressure in the lungs sinks with ascending to the surface and carbon dioxide will pass from the blood to the lungs. A lower carbon dioxide pressure is registered in the blood and the breathing reflex weakens. This gives the diver a faked signal to be able to stay down for a much longer time just before unconsciousness occurs. The continuous development is the same as in hyperventilating blackout with inhaling of water and drowning.

The risk with "shallow water blackout" increases if the diver exhales slowly when diving or stops on the way up from maximal depth. The hyperventilating- and shallow water-risks increase together with real deep freediving and urges for great caution.

Other risks in freediving

With infections and difficulty in pressurizing, diving should be avoided. A sinuse sqeeze and eardrum explosion is always unpleasant and could give future detriment. This risk increases with depth and if the sense of balance is effected, and the diver looses orientation, down at 30 meters of depth, it is much more dangerous than if it happens in 2-3 meters depth.

Theoretically and practical maximal deep.

Many divers have learned to calculate their maximum freediving depth with help of the largest and smallest lung volume the lungs can willingly take. In some case reports of records breaks every rule. Clearly it is so that the results is strictly individual and it is wise not to stretch the personal limits of yourself. How record makers make this without destroying their lungs is not fully understood, but it seems that blood fills out the lung compensating the loss of lung volume.

The above mentioned risks could be avoided just if the freediver would remember that:
-Never dive alone
-Never hyperventilate before a dive.
-Never exhale under the dive (ATTENTION! For Scuba divers this is just the opposite! ).
-Rise from maximal depth to the surface. Dont stop.
-Not to dive with an infection or other disease.
-Increase depth in steps and "begin from the beginning", after a break in diving.