Posted by Gerry Smith on March 10, 2001 at 11:20:03:
In Reply to: Re: Lung Overexpansion posted by Steve on March 10, 2001 at 10:00:40:
Steve, can you clarify your question a bit? The part about a full breath and lungs compressed to half size implies the breath was taken at 1 ATM, a freediver in other words, then dived to 33'.
If a scuba diver fills his lungs at 33' they are essentially normal size because he is breathing air compressed to 2 ATA. If he then closes his airway and ascends he risks a lung overexpansion injury. Lung tissues are delicate and can't take much overpressure. I forget specific numbers and I'm sure the number would vary between divers; but if we assume 10% as a dangerous overpressure, then that would occur in a 7 ft ascent from 33 ft.
That's why NAUI condemns breath holding at any depth, regardless of experience. They use "breath hold" as a synonym for closing the airway (epiglottis.) An experienced photographer or hunter might cease breathing for a few seconds, but the smart ones hold the airway open while doing so. This is putting a pretty fine point on a topic that can kill divers though, so NAUI just says not to hold your breath.
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