Nitrogen Narcosis, what's up with that?

[tomfcrist]

I generally(despite 1 or 2 interesting episodes) don't feel narced on deep dives. I am acutely aware however that just because I'm not feeling it doesn't mean it's not happening. I look at narcosis as just another level of complexity to the dives mission accomplishment, but not a barrier.
I have considered diving helium mixes past 160 if the goal of the dive is anything but looking around, but the financial barrier is still getting thicker on that one.

 

[Subcooled]

47m/155ft on air (and 1m/4ft visibility):

"Oh sh*t, I though I already did that"

My deco reg was hanging and it got stuck between the line and a tree trunk on the bottom. I remedied the situation and swam further - only to notice that I wasn't free yet. My motor skills and sensation were compromised. I thought I had freed myself but I had not.

Also the short term memory (memorizing to be exact) failed. Logic involves remembering intermediate results so quite naturally reasoning wasn't going tohappen. I have some proof for this from two chamber rides. It was like having all the nervous system slowed down to crawl. My GoPro helped me a bit to memorize what there was on the bottom, meter by meter. I memorized the video on the surface and remembered it on subsequent dives.

One becomes a bit s_l_o_w at 40-50mts(120-150ft). This is true both for memorizing and logic. Also, having eyes out of sync is a wild experience. To wait for the two images to stabilize and align at 40+m overhead/siltout is "interesting".

It never felt scary. It never felt safe. There was too much to focus on. Below 40m narcosis become noticeably intensive. It severely affects my cognitive ability (tested that in a chamber).

But yeah, it kind of felt good.

 

[Subcooled]

Look at the attached test, done at 50mts, 6ATA, dry chamber.

1: What does a cow drink? I answered: water. A biologist answered: milk
2: Connect letter and number with a line (order A-1-B-2) [and so I did: A-1-B-2]. I spent A LOT of time on this one, and decided that it really meant I should ONLY connect those four characters. It said so. A-1-B-2. Nothing more...(?)
3: what is 3*3-1+2?
4: pay attention to the one calculation (4) that I have "corrected". I calculated it. I verified it. I corrected it. I was unable to notice the division. When your short term memory fails due to narcosis, not much is left :|

 

[Akimbo]

Sorry to resurrect an old thread but I thought this article helps round out the discussion on building Narcosis tolerance:

Nitrogen Narcosis: A Critical Conversation | DIVER magazine

 

[joe8mofo]

Unfortunately I am late for the narc party; but I have input. I was born in the 80s so no fun mind-bending drugs for me, but I can always tell when I am narced; most of the time it is pleasant; occasionally it is more of a dark narc. I can feel the narcosis setting in at 72 ft; I can also hear it, bubbles sound increasingly tinny as the narcosis increases (with depth). Luckily I am consistently aware of my impairment; which leads to tasks being executed in a more finite-state-machine manner until shallower.

Recently I had the "pleasure" of dealing with the increased narcosis one receives when CO2 builds up. It was a wreck dive where the deck was at 134' and the current was ripping. After fighting the current to get down the down line to the shelter of the wreck I had built-up a ton of CO2 and felt extra-narced (really-impaired). I slowed my breathing and after about a minute was much more clear-headed and able to continue on with my dive.

My experience with "dark narcs" has revealed that this is really dependent upon my state of mind when executing the dive; meaning don't dive if you aren't mentally prepared for the dive. I dive very often in lakes, so a lack of visibility, ambient light, and cold water are normal conditions for me to experience. So, diving Puget Sound last year in poor vis and dark, cold water did not lead to a dark narc. Thanks again NWGratefulDiver for the opportunity to dive such a unique area.

 

[Akimbo]

…. I can feel the narcosis setting in at 72 ft; I can also hear it, bubbles sound increasingly tinny as the narcosis increases (with depth)…

I wouldn’t blame sound attenuation entirely on narcosis. Changes in gas density also play a part. I hear a change in bubble noise even on open circuit HeO2, though not as pronounced as on air. Sounds over the intercom in a decompression chamber also change. Perceived sound and voices change significantly in a chamber even at 60'.

 

[Stoo]

Here's an experiment I tried once a few years back. Take two buddies, one diving air the other diving a mix with 20-25% helium in it. Dive down to 120-130 feet. Swap regs and take a few breaths.

The great thing about being "muddle-headed" is that you don't know you're muddle-headed. When I am "deeper" on air, my litmus test is my ability to use my camera. Lot's of buttons, lot's of things to remember...

One of the neat things about being in Tobermory, is that we have access to a chamber. Many Instructors will take AOW students on a dry dive in the chamber, typically to (if I recall correctly) 160'. The tender then busts out a bunch of little games from the Dollar Store and some notepads to do a few simple arithmetic questions. It's fascinating to watch... the puzzles are a disaster. The arithmetic is generally correct, but the hand-writing looks like that of a three-year old.

It's important to remember that these "divers" are typically inexperienced divers, and I think it is generally accepted that divers who do lots of deep dives function better at depth than less experienced divers.

I can also say unequivocally that the "narc" varies on occasion. I do a lot of diving in the 120'-170' range on air (almost every dive here is upwards of 100') and I generally have zero feeling of narcosis. Once in a while though, that isn't the case, but it's usually a "dark narc" where I just feel like I need to be "up"... shallower. I don't know why it happens now and again, but it does.