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breath holding with nitrox

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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New Member
Aug 23, 2002

I am new to the forum and wish everyone great diving. I am curious... has anyone besides myself attempted freediving on nitrox? I have been experimenting with taking nitrox 32,36 breaths at the surface and freediving. The point is to curb shallow water blackout due to the fact that although CO2 levels can rise before the PO2 drops too far. This should prompt you to get to the surface before you run out of O2. (at least for those who have not conditioned themselves to not respond to rising CO2.

Hold on while I brace myself for the wave of criticism...:D
My opinion

There are several issues with freediving on nitrox:

1. You would still have to follow the scuba tables for the max depth to avoid O2 toxicity
2. There are reports that breath-holding on any elevated oxygen mixture causes strange physiological changes which decrease your ability to hold your breath on regular air. If you are not worried about your ability to hold your breath on regular air, then maybe you are willing to continue the nitrox.
3. The elevated O2 will suppress the breathing reflex even more, so that even the CO2 will not cause a breathing reflex. This puts you in danger of A) CO2 narcosis, B) CO2 blackout. In other words, even though you have minimized the risk of shallow water blackout, now you risk a blackout at the bottom due to extreme CO2 levels. (Imagine a scuba diver performing skip-breathing on nitrox--he would blackout very quickly)

So, an experienced freediver diving on nitrox might experience something like this:
- He starts the dive, and feels great. After several minutes on the bottom, he still feels great. Soon, his CO2 is massively elevated, but the extreme O2 inhibits his breathing reflex. Soon he starts getting confused and disoriented due to CO2 narcosis. Suddenly he realizes something is really wrong and he starts for the surface. The few hard kicks to get off the bottom generate enough CO2 to cause a CO2 blackout. He loses consciousness and promptly sinks back down to the bottom. Out of range of his surface freedivers, the grim reaper awaits him....

The risk of CO2 blackout, for me, would be enough to say no to nitrox.

Eric Fattah
BC, Canada
To Eric

When you say "opinion" do you mean the points you describe in your reply are based on first hand experience with freediving on nitrox or are they personal theory?
As for point 1, oxygen toxicity would occur at 235 ft. on air... are the tables valid for a bounce to depth?
As for point 2, I personally have not experienced changes in my ability to hold on air; but that may be due to procedure. I hyperventilate with air and the nitrox is used only for the dive.
As for point 3, I have not experienced the confusion or approached the feeling of blackout, in fact, I have the urge to breathe and return without the shallow dizziness and with the benefit of increased bottom time.
Thanks for the comments, I'll see if I become aware of those side effects next time I dive.

would the use of nitrox be good for static training?

i mean, when CO2 levels are high but there's no reflex because of high O2, does the body adapt itself to that situation (without the person feeling it) just as it adapts to low O2 levels (at high altitudes for example)

and if it does, will it affect your ability for for not blacking out at low O2. In other words : nitrox training would have the opposite effect of high altitude adaptations (less red bloodcells...)

would there be an optimum nitrox% for training on (22%, 25%???)

bruno :confused:
02 toxicity would occur at 235' on air.....:confused:

Where are you getting that number from???

The old idea of 2.0 PP02 would be at 297' on air.

The old idea of 1.6 PP02 would be at 218' on air.

The more commonly accepted 1.4 PP02 would be around 187' on air.

If I am using any type of nitrox or trimix while scuba diving I limit myself to 1.4 PP02 on the bottom and 1.6 at deco. 235' doesn't come up anywhere. I wouldn't want to push that number anywhere, let alone in the cold water around here.

After the explanation that Eric just gave I have no more interest in trying any type of nitrox freediving. Skip breathing on nitrox would be very easy and C02 blackouts would seem to be pretty easy to happen since most experienced divers are C02 retainers to begin with.

I guess that if I really wanted to try and cheat the system I would just build a sled instead.

check your math jon

you forgot to add the atmospheric to that ppO2...
2.1 is the ppO2 at 297'.

1.705 is the atm at 235'.
The point was that such a short duration of O2 exposure does not cause problems.

I don't know what "system" you may be cheating but good luck with building your sled... remember measure twice, cut once.:duh
I don't facy the idea for the reasons mentioned above, plus the fact that for me freediving is all about freedom, ease of movement, and not having to carry a ton of equipment with me. If I'm in the mood for carrying diving cylinders around, I'll do some scuba. Freediving is, for me, about seeing what I can do by pushing my normal life sustaining functions, using normal air, much more natural that way.

how about on pure O2?

I totally agree with narked.

I've read somewhere that using pure O2 (hyperventilating) could add 5 to 6 minutes on your dry static time and that there where records up to 15.

Has anyone tried this? How long did it increase your hold? Is this bad?

Still learning...thanks in advance!

Okay, just read the "Breathing Oxygen" thread, answered a few questions. Should have seen that before I clicked reply, hehehe.
Umberto has done a breathold more then 20 minutes on pure O2. Forget what it was exactly, somewhere between 20-22 minutes.

That was more then 4 years back when he did it.

If the you are using nitrox is to minimize SWB. There are more effective ways to minimize risk of SWB.

1. Dive with a buddy and learn what your personal signposts are so that you never come close to blacking out.

2. If you are getting any "uh-oh" signposts, stir the unused air from your throat and bronchials by pumping your mask or cheeks and then relax on your way up.

3. Develop the habit of exhaling underwater. Time your exhale so you are almost done when you surface. This reduces the vacuum effect in the lungs and ensures your first major O2 burnin' activity at the surface is an inhale rather than an exhale.

Humans are well adapted to apnea. Seems to me that screwing with gas mixtures will throw off our 'hard-wired' genetic abilities.

How is GA doin' anyhow? I spent alot of time in DeCalb County as a kid. My grandpappy grew up in Macon. PM me and we will chat.
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