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Residual lung capacity

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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Simon Blampied

New Member
Oct 16, 2001
I remember reading somewhere, I seem to recall it being in the PADI manual, that the average human reaches residual lung capacity at 40 metres. This is to say that any deeper the average mans lungs are in danger of collapse. I myself noticed a considerable increase of pressure on my chest at 40 metres compared to the 35s, 36s and 37s I'd done previously.

It therefore seems obvious that any further requires specialist training. Anyway, the general consensus seems to be that free diving is 90% physchological. So a man who starts with a below average lung capacity and trains hard (only bringing himself to average capacity) feels he's now capable of attempting 42 metres and due to pyschological training is able to push himself that little bit further, reaches his target depth and doesn't return.

Is this a real danger?? If so how do the no limits divers get so deep - are their lung capacities that big?? And if this is an issue should people discover their capacities before attempting any depths, say 30 metres plus??

Just a thought :p


Many years ago, when Enzo Maiorca was trying to brake all records, his physician warned him about going deeper than 50 meters, because that pressure will make his lung volume go below the residual functional capacity and he can suffer a total lung collapse that will be fatal. He reached 50 meters with his hand and pulled him self to 52 meters. Nothing happened. Since that time we are trying to explain how the human being can go so deep without "implosion" of his chest.
First, we have to forget the idea that the thorax is a gas bottle, we have arteries, veins, blood, heart, cartilade, bones, lympha,etc.
When a freediver starts a descent the enviromental pressure diminishes his thorax volume (boyle law), but it has a limit because you can´t compress the costal ribs, when the freedivers continues his descent and the pressure increases without effect on the thorax, the intratoracic pressure become negative and the blood flow is deviated to the pulmonary sistem. At this moment the alveolar capilaries are full of blood and the total component of thorax is mainly liquid (blood) that can get compressed. The phenomenon is called "Blood-Shift".
I can´t tell you if this is a "normal" reflex of the human being because the experiments have been done in freedivers, but I believe it´s part of every human, like the diving reflex, it has to be discovered.
There are some respiratory exercises that you can use to improve the blood shift previous to the inmersion.
The principal risk is that we don´t know where the enviromental pressure will overcome the strength of our costal ribs and at that depht we will have a rib fracture and maybe a lung lesion. It´s seem to be beyond 200 meters.
Hope this help

Frank Pernett
lung collapse thread

Anyone interested in this topic would also benefit from reading the Lung Collapse thread in the general discussion section from last summer when a similar question was raised.
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