Equivalent Air Depth question

[boulderjohn]

In this post from a thread from nearly 5 years ago, Dr. Simon Mitchell posts a link to research indicating that nitrox may well be less narcotic than air, and he says he agrees with that research. Here is the research:

Objective vs. Subjective Evaluation of Cognitive Performance During 0.4-MPa Dives Breathing Air or Nitrox - PubMed

The results suggest that EANx could protect against decreased neuro-cognitive performance induced by inert gas narcosis. It was not possible for blinded divers to identify which gas they were breathing and differences in postdive fatigue between air and EANx diving deserve further...

pubmed.ncbi.nlm.nih.gov

If true, the benefit is not great.

 

[Bob DBF]

The second occurs at more limited depth (even less than 30m) in muddy, cold water, nothing nice to see, with current or heavy work to be carried on.

I am assuming that you mean to say the effects of a CO2 hit can start a shallower depth, because it certainly can happen at deeper depths as well.

I think the conditions play a roll, but it's more about what one is used to. I was well on my way to a CO2 hit the first time I dove carribian waters and could see so far it took my breath away. I noticed my breathing change, and corrected before it had too bad an effect. Having an understanding of one's breathing breathing patterns, how to control them, and how much air one needs to breathe while working to avoid a CO2 hit or recover when one starts is priceless information, and more important the deeper one dives.

 

[Akimbo]

As far as I understood, helium may cause HPNS. I believe hydrogen doesn't (or at least causes fewer symptoms).

I don't know how anyone would really know. Saturation compression rates are slow to control compression arthralgia as much as HPNS. Not many Hydrox bounce dives have been done, mainly due to fire/explosion issues. The same is true for hyperbaric research on Hydrox, but that may change if Helium availability continues to dwindle.

Oxygen levels for sat diving breathing mixes are well below the fire risk zone, like 0.3-0.8 PPO2 (Edit: deeper than around 500'/150M) The problem is leaks on deck putting the entire DSV at risk.

Remember that Helium is a Noble gas. It is very likely that HPNS is entirely caused by relatively rapid compression because there can't be a direct biochemical reaction. However, never discount the possibility of dozens of indirect biochemical reactions conspiring to kill divers.

 

[Esprise Me]

This is all very interesting to me. I feel the way nitrogen narcosis was taught about in OW training is completely at odds with the idea of N2 and O2 being equally narcotic (which if they are then I can see why EAD wouldn't have any bearing on narcosis management).

I see that you did your OW in 2020, and you have certifications from SSI, SDI, and TDI. I'm surprised that whichever one provided your OW curriculum differs from PADI in this way. My OW manual was last updated in 2016 and states "At one time, it was thought that narcosis was only caused by nitrogen, and it was common to call gas narcosis nitrogen narcosis. Today, it is known that oxygen is similarly narcotic (hence, EANx doesn't have a gas narcosis advantage.)" It does then mention helium and tec diving briefly. This point was easy to miss (I had to check the book to see if it was covered at all, as I didn't remember), but they really hammered it in my Nitrox class (which I do remember.)

 

[Mr. Dooley]

I see that you did your OW in 2020, and you have certifications from SSI, SDI, and TDI. I'm surprised that whichever one provided your OW curriculum differs from PADI in this way. My OW manual was last updated in 2016 and states "At one time, it was thought that narcosis was only caused by nitrogen, and it was common to call gas narcosis nitrogen narcosis. Today, it is known that oxygen is similarly narcotic (hence, EANx doesn't have a gas narcosis advantage.)" It does then mention helium and tec diving briefly. This point was easy to miss (I had to check the book to see if it was covered at all, as I didn't remember), but they really hammered it in my Nitrox class (which I do remember.)

SSI was the agency for my OW. I was actually going over my SSI coursework again last night for the hell of it and while there have been many mentions of nitrogen narcosis, I don't think I've come across anything that mentions the narcotic properties of O2. My OW materials do not suggest any narcosis advantage of EAN, but they way they explain it makes it seem quite clear that N2 is the thing to worry about regarding narcosis.

If N2 and O2 are both similarly narcotic, than the term nitrogen narcosis seems to be a complete misnomer. It should be called nitrox narcosis when discussing the effects of N2/O2 mixes (I've also seen Wikipedia mentions the term inert gas narcosis).

UPDATE - just checked on my SSI Nitrox course online, which states -

The fact that diving nitrox exposes divers to less nitrogen, suggests the use of nitrox should result in less nitrogen narcosis. Studies have not been able to verify this, however. A possible reason why is that oxygen itself can be narcotic, and exposure to greater concentrations of oxygen, such as occurs when diving nitrox, may also cause impairment.

Until such time as researchers can verify what impact, if any, nitrox has on narcosis, you should not count on experiencing less narcosis or impairment when diving nitrox than you do when diving air at comparable depths.

So SSI is basically taking the "we don't know much about it so don't count on it" which is a different position than "O2 has narcotic properties similar to N2".

This sort of "who knows?" approach, combined with usage of the term nitrogen narcosis for the effects felt when breathing nitrox - which explicitly connotes N2 as the narcotic agent (and suggesting O2 isn't narcotic) - is odd to me, if there really is near-consensus to the contrary.

 

[tursiops]

The more time you spend at depth, the more you are likely to experience narcosis.

This has not been my experience. I am, I believe, only sensitive to depth, not to time at depth. If I am going to be narced at (say) 45m, it happens as I approach 45m; it doesn't require me to be at 45m for any amount of time. Unless I am working hard at 45m, in which case I'm building CO2 and changing the experiment.

 

[Esprise Me]

So SSI is basically taking the "we don't know anything about it so don't count on it" which is a very different position than "O2 has narcotic properties similar to N2".

This sort of "who knows?" approach, combined with usage of the term nitrogen narcosis for the effects felt when breathing nitrox - which explicitly connotes N2 as the narcotic agent (and suggesting O2 isn't narcotic) - is odd to me, if there really is near-consensus to the contrary.

Interesting. I agree with your take, and I think PADI's phrasing more accurately characterizes the current understanding. I've never taken an SSI course, but I remember being bothered by a similar phrasing issue on a different subject in my SDI Deep Diver course. When PADI covered the same subject in my Wreck Diving course, I thought they said it better. Explaining things clearly is harder than it looks.

 

[tursiops]

If N2 and O2 are both similarly narcotic, than the term nitrogen narcosis seems to be a complete misnomer. It should be called nitrox narcosis when discussing the effects of N2/O2 mixes (I've also seen Wikipedia mentions the term inert gas narcosis).

Most folks today call it gas narcosis, or just narcosis. Anybody -- or any agency -- still calling it nitrogen narcosis is out of date.

Don't assume everything told to you in your OW c;ass -- no matter which agency -- is 100% true. It may have been true at some point in the past (like telling you to turn your tank valve back off 1/4 turn after opening it) but is no longer valid. Other things told to you (like a mask on your forehead means you are panicked) were never true; it is a misinterpretation of the statement that if you are panicked, you might put your mask on your forehead. there are a lot of myths in scuba. Be skeptical.

 

[ginti]

This has not been my experience. I am, I believe, only sensitive to depth, not to time at depth. If I am going to be narced at (say) 45m, it happens as I approach 45m; it doesn't require me to be at 45m for any amount of time. Unless I am working hard at 45m, in which case I'm building CO2 and changing the experiment.

I was trying to understand the post from @mac64... I have the same experience of you

 

[Mr. Dooley]

Don't assume everything told to you in your OW c;ass -- no matter which agency -- is 100% true.

Agreed. There are definitely a couple things that I've come across in OW material that seem pretty illogical.

Explaining things clearly is harder than it looks.

No doubt about that! Even in my technical training texts from TDI (technical diving!) they didn't seem to have an editor for the text. Grammatical errors, misspellings, missing punctuation. Very strange to be taking instruction on how not to kill yourself from a textbook that doesn't know where a period should go in a sentence.

Furthermore, the more I've dived and learned about diving, the more I find myself thinking "I could teach OW theory better than I was taught" (assuming I were one day trained and qualified to instruct). Not because my instructors weren't good divers or didn't know how to keep us safe, just because I feel they were unexceptional teachers. There's nuance into breaking down foreign concepts to the uninitiated, to making things "click" (vs. simple memorization of facts) for people. A lot of things about scuba aren't intuitive ("why would I let air OUT of the BC when ascending?? I'm trying to go up - I'll just smash the button!") out of the gates necessarily. Maybe I'll have to get an instructor cert one day after all to give it a shot.