Freediving Ascent

[cpe111]

well, this isnt strictly scuba - but here goes anyway.

Does a freediver need to exhale during ascent and if yes, why?

I assumed that a free diver takes a lungful of air at the surface, dives, then surfaces again, they will still only have a lungful of air - so why exhale?

I came across this article http://www.deeperblue.net/article.php/281 which states they need to exhale to prevent overexpansion injuries - what i want to know is where does the extra air volume come from ? or is this article inaccurate?

 

[roakey]

As far as I can tell, that article is completely wrong. A full breath at the surface will only expand to a full breath upon surfacing, no more.

There are reasons for exhaling upon ascent, psychological and physiological, that allow you to "hold" your breath longer.

Can anyone out there explain that article?

Roak

 

[crazyitalian]

Unless the author knows something the rest of us don't, the article is horse@&^%. Those injuries listed happen as a result of breathing compressed air and not exhaling during ascent. However, if one's breathing compressed air then it's not exactly freediving, is it? There may well be valid reasons to exhale upon ascent during a freedive, but a pulmonary barotrauma wouldn't be one of them.

 

[boulderjohn]

I am mystified as well. All the physics the guy cites about expansion as you ascend assumes that the lungs are already at capacity at depth, which would only be true if you had filled them with pressurized gas at depth.

He says, "Using the same example, a breath-hold ascent from 33 feet would result in the lung volume doubling, almost guaranteeing barotrauma if breath were held at or near the diver's total lung capacity."

If the diver held air at near total lung capacity by means of a full breath at the surface before descending, that lungs would be at 1/2 volume at 33 feet. The most it could expand to would be its initial volume.

 

[boulderjohn]

I could not believe that the article had not been commented upon in the three years since it was written, so I did a search of the site and, sure enough, there was a follow-up article.

http://www.deeperblue.net/article.php/291

In it, he says,

Since the publication of the "Risks of Ascent" article on 2nd December I have receiveda few e-mails questioning the risk of barotraumas during freediving. In the article I should have emphasized that under normal conditions the risk of barotrauma is slim to non-existent. Theoretically however, there is still a chance that it may occur.​

He goes on to give some examples, but, hey, I'm sure not going to worry about what he describes could "theoretically" happen.

 

[freediver]

I exhale when I am ascending simply to avoid a conflict between inspiration/expiration at the surface. Esp with deeper dives I would rather not have to exhale at surface and then begin inhalation.

 

[Gary D.]

I’m surprised he didn’t mention the need for a 20’ 3 minute safety stop for free divers as well.

Gary D.

 

[wardric]

If you change the word "free" for "scuba" or "compressed air", his article seems at first glance relatively accurate. However if the author maintain that he's talking about free diving, then he really should consider revewing parts of his OW course

Air in lungs will compress at descent and expand at ascent and at the same rate. P1V1=P2V2 P*V=C, as in constant

The only "air" or gaz that can be a problem in free diving would be if you eat beans or pea soup before going down and produce it and I sure hope It would'nt come out your lung system

someone should e-mail him this thread

 

[hvulin]

well you can actually exhale a little (when close to surface and using a snorkel) and twist your neck so your head looks up and as you surface your snorkel will be free of water

this will also shorten the time for you to exhale what is left in your lungs and start another breath (I typically completly exhale some 10cm before surface so I can start the next breath as soon as possible)

 

[dpbishop]

Major reason to exhale when free diving is to vent CO2. It is CO2 loading, not lack of oxygen, that causes the impulse to breathe that you have to suppress while under water.