Not diving to greater than 30m/100ft unless with helium

[Kevrumbo]

I'd like to hear people's thoughts on this but *not* tying back to TSandM as she was not unique in her approach of when to use helium.

DD's claim is that reluctance to dive to depths of greater than 30m/100ft without helium indicates unusually low tolerance for narcosis and therefore represents a weakness in a diver.

I'd like to know people's thoughts on the use of helium to mitigate the effects of narcosis and whether or not this is a "weakness" in a diver. I'd also like to know what alternative would be suggested.

Again, it wasn't a low tolerance or "weakness" for narcosis per se --Just a prudent choice in hindsight if she would have decided to use Recreation Trimix 25/25 as an easier breathing gas to mitigate Exertion CO2 Retention in a physically challenging environment (e.g. strong currents); as well as a providing a better recovery/contingency safety margin (a deeper MOD & CO2 narcosis moderation with the 25/25 Trimix than with Nitrox32), should she suffer another episode of Vertigo during a dive. She would only be "tasked" with overcoming the vertigo and staying with her buddy (as difficult as that turned out to be). . .

IMHO, the motivation & rationale behind this was implied here in this prior incident, in her own words:

http://www.scubaboard.com/forums/ne...-learned/318124-vertigo-deco.html#post4948568

 

[walkonmars]

This discussion is familiar. Another question is whether or not oxygen is a significant contributor to narcosis.
In a text I'm reading ("Recreational Trimix Diving", Kevin Evans) oxygen is stated by the Meyer-Overton hypothesis as having 1.7 times narcotic potential as nitrogen. The text also stated that the hypothesis is incorrect but the contribution to narcosis is still significant. I assume it is less because it is metabolized constantly, as well.
Does anyone have a more definite estimate and references to the narcotic values of oxygen relative to nitrogen?
My goal is to arrive at a mix that accounts for the narcotic weights of both gases and would help me tailor a trimix recipe.
We never got agreement from contributors here as to if and how much oxygen contributes to narcosis. Sorry to bring this up, again.

 

[AfterDark]

This discussion is familiar. Another question is whether or not oxygen is a significant contributor to narcosis.
In a text I'm reading ("Recreational Trimix Diving", Kevin Evans) oxygen is stated by the Meyer-Overton hypothesis as having 1.7 times narcotic potential as nitrogen. The text also stated that the hypothesis is incorrect but the contribution to narcosis is still significant. I assume it is less because it is metabolized constantly, as well.
Does anyone have a more definite estimate and references to the narcotic values of oxygen relative to nitrogen?
My goal is to arrive at a mix that accounts for the narcotic weights of both gases and would help me tailor a trimix recipe.
We never got agreement from contributors here as to if and how much oxygen contributes to narcosis. Sorry to bring this up, again.

No mention of O2, but it would be reduced anyway for deep dives. Hope you don’t plan on reducing it too much!?
As you can see nature has it just about right with N2 dead center, and it won’t catch fire or make you talk funny!

A Practical Discussion of Nitrogen Narcosis | Gilliam
At any rate, the best explanation appears to be the Meyer-Overton hypothesis relating the narcotic effect of an inert gas to its solubility in the lipid phase or fat. This is postulated to act as a depressant to the nervous system proportional to the gas amount going into solution. Mount (1979) has expressed the narcotic effect as determined by multiplying the solubility by the partition coefficient. By examining tables of various inert gases compared by solubility and partition coefficient it becomes abundantly clear that nitrogen is one of the least desirable gases in a breathing mixture for divers at depth. The “relative narcotic potency” is expressed as a number value with the highest number reflecting the least narcotic effect. Argon is extremely narcotic with a value of .43; Nitrogen is rated at 1.0 with Helium one of the least narcotic at 4.26.

Table: Relative Narcotic Potencies
Helium (He) 4.26 (least narcotic)
Neon (Ne) 3.58
Hydrogen (H2) 1.83
Nitrogen (N2) 1.00
Argon (A) 0.43
Krypton (Kr) 0.14
Xenon (Xe) 0.039 (most narcotic)

 

[100days-a-year]

Even if 02 is as narcotic as nitrogen(which I don't buy)the relative percentage change from air or lean nitrox to HE based gasses at depth is minor compared to the fraction of nitrogen displaced.

 

[ScubaInChicago]

Nitrogen is evil. Too much O2 is evil. Helium is your friend. Any questions?

 

[Akimbo]

Nitrogen is evil. Too much O2 is evil. Helium is your friend. Any questions?

I have passed out, almost instantly, too many times from testing masks during pre-dives when gas lines weren’t adequately purged of HeO2 deep mix. Yes, too much Helium (not enough Oxygen really) is about as deadly and fast acting as you put in a cylinder.

As with all gasses, you can have too much or too little of a good thing — including CO2.

 

[ScubaInChicago]

I have passed out, almost instantly, too many times from testing masks during pre-dives when gas lines weren’t adequately purged of HeO2 deep mix. Yes, too much Helium (not enough Oxygen really) is about as deadly and fast acting as you put in a cylinder.

As with all gasses, you can have too much or too little of a good thing — including CO2.

Co2 = evil... Well, except that it drives ventilation.

 

[Akimbo]

Co2 = evil... Well, except that it drives ventilation.

Not a big fan of CO either, but we breathe a little of it all the time.

 

[Centrals]

Nitrogen is evil. Too much O2 is evil. Helium is your friend. Any questions?

Are you sure? A true friend should never cost an arm and a leg!
Took couple of breath of my back gas(15/55) on land and nearly pass-out!!
Too little or too much is NO good in anything.

 

[markmud]

I have passed out, almost instantly, too many times from testing masks during pre-dives when gas lines weren’t adequately purged of HeO2 deep mix. Yes, too much Helium (not enough Oxygen really) is about as deadly and fast acting as you put in a cylinder.

As with all gasses, you can have too much or too little of a good thing — including CO2.

Hi Akimbo,

Thank you for your involvement with this thread. Your experience and knowledge has made this thread truly interesting.

I have read that a small percentage of helium in a mix can make for safer diving (for recreational divers venturing between 100 fsw and 130 fsw). I believe I read this in the synopsis for a certification course named Trimix for Recreational Divers. I was interested in this class even though my opportunities to dive trimix are slim to none. The topic is interesting (to me anyway).

The goal for this class was to teach rec divers to keep their Nitrogen to a 3.16 PP or less. Also, they wanted rec divers to keep their oxygen percentage lower. As I recall, the oxygen percentage goal was 25% to 28% max. This would allow a decent buffer from a 1.4 ATA of oxygen at recreational depths to a 1.6 ATA (you know, as a contingency...a contingency that I believe is being hypothesized on this thread regarding TSandM's last dive).

As I recall, the mixes discussed were 25/15, or 25/20. With a 28% oxygen percentage, the mix could be 28/10 and still achieve the same parameters.

Question, would the NDL with such a trimix gas change the NDL from EANx 32 to make much of a difference (because of the helium)?

Thanks,

markm

---------- Post added October 10th, 2015 at 01:56 PM ----------

I agree, and from everything we have heard, she was very much "by the book" with regard to safety. My point being, that a momentary exposure to 1.6 ATM of oxygen or a quick bounce and ascent from 130 would not be expected to cause oxygen toxicity or (obviously) residual narcosis, but she was probably "not happy" about it either.

Hi Dumpster,

I got the feeling that some people thought you could have worded the paragraphs that were used to start this thread off with a bit more sensitivity. I thought what you wrote was perfect--no problem from my perspective.

Thanks for writing what you did and getting this thread started.

markm