Nitrox CNS causes

[Me2aswell]

Now that the rabbit seems to have gone we can continue disscussions about
diving.

The Nitrox debate turned (again) into a flame war with Idiot flaming anyone
who dissagreed with him about Co2 causing death in a CNS hit.

Now I have just been certified for Nitrox so I would like to restart the
debate.

Why is it that Nitrox is limited to a depth when Heliox and Trimix isnt...or
is that an incorrect statment?

[rnf2]

Nitrogen Nark i would guess, there isn't that prob in heliox since theres no
nitrogen.

rhys

Post by Me2aswell
Now that the rabbit seems to have gone we can continue disscussions about
diving.
The Nitrox debate turned (again) into a flame war with Idiot flaming anyone
who dissagreed with him about Co2 causing death in a CNS hit.
Now I have just been certified for Nitrox so I would like to restart the
debate.
Why is it that Nitrox is limited to a depth when Heliox and Trimix isnt...or
is that an incorrect statment?

[David Scarlett]

Post by Me2aswell
Why is it that Nitrox is limited to a depth when Heliox and Trimix
isnt...or is that an incorrect statment?

Heliox and trimix do have MODs (Maximum Operating Depth). Trimix with
30% O2 has the same MOD (36m) as 30% Nitrox.

It's the oxygen content that determines it. The MOD is to prevent the
Oxygen partial pressure from getting too high and causing oxygen
toxicity.

[rnf2]

What about techies with 3% Heliox?
I know of one guy who dives OC to deep, with multiple tanks with 3 mixes,
32% Nitrox first, then 12% heliox when the PPO2 is high enough to breathe,
finally 3% Heliox for the actual bottom down deep.
Not sure how deep he was going, but wouldn't 3% allow a much deeper diev
than air allows?

rhys

Post by David Scarlett

Post by Me2aswell
Why is it that Nitrox is limited to a depth when Heliox and Trimix
isnt...or is that an incorrect statment?

Heliox and trimix do have MODs (Maximum Operating Depth). Trimix with
30% O2 has the same MOD (36m) as 30% Nitrox.
It's the oxygen content that determines it. The MOD is to prevent the
Oxygen partial pressure from getting too high and causing oxygen
toxicity.
--
David Scarlett
_ _ _ _ _ optusnet.com.au

[David Scarlett]

Post by rnf2
Not sure how deep he was going, but wouldn't 3% allow a much
deeper diev than air allows?

Following the rule of max ppO2 of 1.4atm, the MOD for that gas would be
456m.

[DavidM]

Post by rnf2
What about techies with 3% Heliox?
I know of one guy who dives OC to deep, with multiple tanks with 3 mixes,
32% Nitrox first, then 12% heliox when the PPO2 is high enough to breathe,
finally 3% Heliox for the actual bottom down deep.
Not sure how deep he was going, but wouldn't 3% allow a much deeper diev
than air allows?

Correct. The deeper you want to go, the less O2 (and N2) you should have in
your mix. The theory with, say trimix, is that this O2 and N2 that you
don't want, you replace with helium. The theory with heliox is that you
replace ALL the N2 with helium - and the main reason more people don;t dive
this way is that the helium is very expensive.

3% would allow you do dive very deeply, in fact if it just came down to
ppO2 you could theoretically talk about 500m or so. At that depth though,
HPNS and other physiological issues would definitely be a factor, as would
the sheer logistics of such a dive. It's not impossible, in fact it's been
done on Drager rebreather from a bell in the North Sea almost 20 years ago,
but in the rec diving context it'd pretty much be an impossibility.

Cheers
David M

[Jason]

Post by DavidM
replace ALL the N2 with helium - and the main reason more people don;t dive
this way is that the helium is very expensive.

That's not the only reason. There's also HPNS, or High Pressure Nervous
Syndrome which kicks in at about 120m if you're on heliox. Have a look at
http://www.scuba-doc.com/HPNS.html for some details.

Jason

[DavidM]

Post by Me2aswell
Now that the rabbit seems to have gone we can continue disscussions about
diving.
The Nitrox debate turned (again) into a flame war with Idiot flaming anyone
who dissagreed with him about Co2 causing death in a CNS hit.
Now I have just been certified for Nitrox so I would like to restart the
debate.
Why is it that Nitrox is limited to a depth when Heliox and Trimix isnt...or
is that an incorrect statment?

Everything is limited in depth. EANx might be best though of as a shallow
gas, not a deep one. As you go deeper then the fO2 has to be decreased from
40% downward until eventually you're diving EAN21 (air).

Cheers
David M

[Me2aswell]

OK then someone metioned Narking...to the best of my
knowledge....None....Narking and CNS hits are completely different.

To what I have seen Narking almost looks like someone on NOS (Nitrous
Oxide). Where as someone who has had a CNS hit looks ...well dead really.

[DavidM]

Post by Me2aswell
OK then someone metioned Narking...to the best of my
knowledge....None....Narking and CNS hits are completely different.
To what I have seen Narking almost looks like someone on NOS (Nitrous
Oxide). Where as someone who has had a CNS hit looks ...well dead really.

That's right - "narking" aka nitrogen narcosis is like a state of drunkeness
that's induced by the nitrogen. "CNS hits" refers to the effects of the
toxicity of elevated levels of oxygen on the central nervous system, and can
manifest itself in the way of a seizure and unconsciousness.

CNS hits usually/often result in death, simply because a seized diver will
not have the conscious skills to keep the reg in their mouth - there are
some examples of survival, but only by those who had a very skilled and
attentive buddy, and were very lucky.

Cheers
David M