Free diving on EAN Nitrox?

[MarineMammal]

I'm an experienced scuba diver and also a spearfisherman. I used to spearfish on scuba, but am beginning to prefer spearfishing while freediving instead. After reading about SWB (shallow water blackout) being the number one pressure related injury to free divers, I'm thinking about trying EAN 36 or EAN 40 to prevent SWB and maybe increase my bottom time.

As I understand it SWB is caused by a rapid drop in pO2 as the freediver ascends. Because pO2 is increased at depth, it may be possible to feel like you have enough oxygen at depth and starve yourself of it when you ascend causing unconsciousness.

If instead I dived with 36 or 40% O2, I should feel the urge to breathe far earlier than my oxygen reserves burn out even with decreasing pressure because the accumulation of breath-reflex inducing CO2 will still accumulate at the normal rate.

In any case it seems to me that freediving on enriched air will help me stay safe as long as I follow the MODs for 1.4 pO2.

This is what I'm thinking, but what do you think? Am I missing anything?

 

[snowflake4727]

Ummm..... I am thinking that free diving takes place without tanks and regs.

I am also thinking that dragging a heavy tank and regs will eat into your O2.
I may be wrong, so please let me know.

 

[Michael_Lambert]

I have seen some free diving spear fisherman move around with a small inflatable boat to keep there gear and catch in, So keeping a AL80 with 40% could be easily done.

 

[Cave Diver]

Ummm..... I am thinking that free diving takes place without tanks and regs.

I think he may be talking about breathing nitrox at the surface before diving, rather than just air.

 

[MarineMammal]

Yeah I'm talking about bringing a Nitrox tank out with me on my modified boogie board when I go spearfishing. I'd take a few breaths of Nitrox then go down holding my breath rather than breathing air.

 

[fdog]

There is little in the literature regarding working breath hold dives using nitrox as a surface breathing gas. Most of what I've read indicates the possibility of CO2 retention; this could lead to a hypercapnic blackout under exercise. As deep technical divers know, hypercapnic blackouts are a very bad thing.

The phenomena you describe - blackout on ascent - is what is now known as a Deep Water Blackout. Shallow Water Blackout refers to excess CO2 blowoff during a breathold dive exclusively in shallow water, such as Dynamic Apnea in a pool.

Freediving apnea is a complex series of physiological responses. By using Nitrox, you may be "fixing" one potential problem at the risk of introducing another....

The best fix for what you're trying to avoid (Deep Water Blackout) is a good buddy that escorts you to the surface from 10 meters.


All the best, James

 

[JPENDERGRAST]

As deep technical divers know, hypercapnic blackouts are a very bad thing.

I'm pretty sure that I don't want to have anything to do with something that has the word "hypercapnic" in it. So much for my freediving ambitions.....

 

[fdog]

John, please don't pass up on the beauty of freediving just because of this thread, which is an extremely unusual application of freediving (and certainly not the norm).

Please take a look at this review, and consider signing up for a class.



All the best, James

 

[MauiScubaSteve]

If you use a 40% EAN tank at the surface it may be breath hold diving but it sure isn't FREE diving!

 

[JPENDERGRAST]

If you use a 40% EAN tank at the surface it may be breath hold diving but it sure isn't FREE diving!

touche'