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freediving on nitrox 40% o2

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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Well-Known Member
Aug 2, 2003
in the past their was a thread about free diving on oxygen .which would be crazy. but i think 40% to a max of 20 metres would be safe but im not sure . has anyone tried this .i know there where a few people here keen to try this.if anyone has tryed this please let me know. im thinking about trying this buti need alot more info. i know about oxtox and all that stuff but its not an isue if you stay within the limits for a particular gas, {eg 40% o2 no deeper than 20 metres} it is co2 blackout that has me worried. but can you still black out on co2 if the dive doesnt exceed 3 minutes. any information from some better informed people than myself would be much appriciated. i want to know what im getting myself into before i do something stupid.
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actually 40 % o2 would be safe from oxygen toxticity till a depth of 25 metres with a ppo2 of 1.4 bar. so thats ok .it co2 blackout really an issue if you keep dives limited to no longer than 3 minutes .this would be great for aspetto spearfishing. three minutes at 20 metres
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To gain benefit from 40% O2, you would have to hyperventilate a LOT before you go down. But, it is still possible to hyperventilate too much (and then have a SWB). So, the only way to figure it out would be to do MANY (40-100) dives (over several days) with a good buddy/safety system, as you RE-LEARN how to breathe before the dive, and RE-LEARN what it feels like on the bottom, and so on.

Further, if you are NOT hyperventilating enough on each dive, then you will be accumulating CO2 from one dive to the next. This means that a CO2 blackout could hit you on the 30th dive of the day, even on a SHORT dive....

So, it is dangerous.... be careful....
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iv done some more research on nitrox free diving .and found out that a mix of oxygen hellium would abolish the risk of co2 retainsion leeding to co2 blackout. so co2 black out and oxygen toxicty should not be a problem. but now the introduction of hellium could be a problem after multiple dives. the helium in the mix will ad to the risk of dsc after multiple dives. sine hillium is a fine gas and is absorbed into the system faster than nitrogen. please correct me if im wrong :)
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No way would I try any kind of a helium mix with the kind of ascent rates we use in freediving. :head

Proper acent rates are much more critical with helium based diving vs. air/nitrox based diving.

I can see playing around with pure 02 while doing a basic static, with close supervison, in a pool; but, mixing compressed gases and freediving doesn't seem too safe to me- unless your talking about offgasing at the end of a long day of diving by breathing off of a deco bottle.

Just my $0.02

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