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How do you learn your narcosis depths? Gas switches?

Discussion in 'Diving Physics, Physiology, & Medicine' started by MichaelMc, May 19, 2021.

  1. shurite7

    shurite7 Dive Shop

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    Very plausible for anyone who hasn’t recognized it. In my tech course the instructor stated everyone gets narced, whether or not they realize it is another matter.
     
  2. napDiver

    napDiver ScubaBoard Supporter ScubaBoard Supporter

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    If your looking for a scientific way to measure roughly when you may get narced...

    A guy in Italy told me where they do this test... The test entailed putting you in a hyperbaric chamber and doing a task. I don't remember if it was math problems or a puzzle or what. But basically, they increase "depth" and at each stop. You try to complete the puzzle. The duration it takes should increase with depth and at some point, you may not be able to do it.

    Now, this probably doesn't accurate translate into actual diving. Probably considered a Best case scenario.
     
    MichaelMc likes this.
  3. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

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    @Akimbo where I was going with the unpredictable comment was that you may be narc'd at 90ft in a cold dark river where you are kicking against the current, but not when in 130ft deep warm clear caribbean water where you are coasting in the current on a reef. If you are diving in repeatable conditions then the level of impairment should be pretty predictable.
     
  4. shurite7

    shurite7 Dive Shop

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    There is merit to this. When I lived in the Caribbean and consistently diving in warm clear water narcosis was noticeable at deeper depths compared to diving in a cold murky mountain lake where narcosis was noticeable at shallower depths.
     
    Akimbo and MichaelMc like this.
  5. Akimbo

    Akimbo Just a diver Staff Member ScubaBoard Supporter

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    You bring up a few important variables. Black water is one of the first things that working divers are acclimatized to. Most also have cold water experience. We also aren't concerned with conserving gas. Recreational divers tend to develop bad habits in terms of CO2 retention through the effort to reduce their RMV.
     
  6. MichaelMc

    MichaelMc Working toward Cenotes ScubaBoard Supporter

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    Thanks everyone.

    Both reasons for testing shallow to deep, stopping at moderately affected, and preferring to test both gasses on the same dive and conditions. Getting suddenly narced out of your mind would be unwise. Also I realize the 'results' might have a resolution of only about 20', not some finely marked increase in symptoms, and that effects might start at 80', or shallower.


    But, there are some precautions for switching off a helium mix to a higher nitrogen mix. In my reading there have been different versions of when that is ok with rules of: 1/5 N2/He, about 0.5 bar ppN2, 100', 70', or never.

    A switch from 21/15 to EAN32 at 100' steers clear on most of those rules by having very little N2 change, but the higher He and deeper options do not. I do not see anything that takes the more accurate step of accounting for tissue pressures. Except for the gas loading bar in SubSurface, thought it uses the 1/5 rule for warnings.

    Yet there are also past comments that it is not a concern shallow. But not so much why it is not a concern shallow. A usual caveat is that you would be going to a rich deco gas, so it is not an issue. But what if you are not going to a rich deco gas?

    Current understanding on when such a switch is fine was my interest and the context of why, for plan 2. In the context of 130' and above and non-deco gasses. Because plan 1 has the risk of being narced without a clear headed gas handy to switch back to.
     
  7. Centrals

    Centrals Barangay Pasaway

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    Only speak from my own experience on the topic.
    1. Aware there is inert gas narcosis. So came prepared.
    2. It is a slow process and act accordingly before it is getting serious. Slow the descend first and might recover!!
    3. I have to be cautious on the first dive of the trip especially on depth.
    4. Everyone feels differently so talk over it with close buddies.
     
    MichaelMc likes this.
  8. mac64

    mac64 Contributor

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    If you’re worried about narcosis take the worst case of narcosis you’ve experienced during your diving and adapt your setup to deal with it.
     
    MichaelMc likes this.
  9. mac64

    mac64 Contributor

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    I’d take those tests with a pinch of salt. You can actually get very good at working at depth.
     
    Esprise Me, Akimbo and MichaelMc like this.
  10. MichaelMc

    MichaelMc Working toward Cenotes ScubaBoard Supporter

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    I'd like to skip rehashing the getting good at working on narcotic gases debate! It has been well hashed.

    I'd rather we focus on how you find the depths at which we are affected (for the local conditions, activity level and good respiration rate).

    And what guidance you use in deciding if He to non-He gas switches are safe in doing that, or otherwise. Short of going to 50+ O2 mixes, which seems the typical tech coverage of the topic, and which happens above typical narcotic depths. I have read and been told of switching trimix students to air to demonstrate the narcosis that was prevented by the trimix. Is there guidance for the conditions when that or other switches are fine? Such as the guidance I mentioned above. Several of which would seem to exclude such a trimix to air switch, for likely depths and trimix mixes in a standard trimix class.
     
    Lorenzoid likes this.

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