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I haven't done any dives past 100' in a long time. I definitely can tell that I'm narc-ed at about 110'. That's usually when I start finding the wind-chime tinkling noise that my bubbles make extremely funny. I'd be willing to guess that I begin getting narc-ed at about 90' but am not concious of it. I would need to do some tests at that depth to know for sure.
I don't drink, smoke a couple of cigs a day but am in good shape for a 27 year old adrenaline junkie, lots of spearfishing at all depths which i consider to be a fairly high task load depending on the fish. Fighting pissed off 60# amber jack on air at 150' is not abnormal for me and about as hard as anything Ive personally ever done under water. Things like loading and shooting a gun or working a stringer are burned into my muscle memory and not a good test of unforeseen tasks. However, when that big aj freaks and wraps you up or a 600# jewfish/bull shark decides he doesn't want you to take his fish, that is when you get a real test of your wits at depth.
Never once have "felt" it or seen/heard any evidence of its existence, but i may just have built up a tolerance.
I just started regularly going past 60' and I've been getting a peculiar feeling around 90', which seems a bit shallow for narcosis from what I've read. Maybe it's my imagination?
What is the shallowest depth at which you thought narcosis may have been creeping up on you?
I make a lot of dives in the 30-40 metre range (100-130ft) on air and some in the range from 40-55m (about 180ft).
at 30m/100ft I seldom notice significant narcosis. At about 36m (120ft) I usually notice some degree of impairment. At 45m/ (+/-) 150ft I almost always feel it at at 55m (180) I always feel it. There's a lot a variation to that on a day-to-day basis.
In a chamber, however, it's another matter. During a chamber dive I feel the narcosis starting to come up at about 20m and by the time I'm at 30m it's pretty pronounced.
About 95 feet I start feel narced. Exertion, stress, cold water, and low viz seem to make it worse. A few weeks ago I was diving on the Duane in stiff current off of Key Largo, I went down the line to 104 feet and was badly narced. I slowly went back up to 90 feet until I felt "normal" and slowly went back down to 100 feet and didn't feel as narced. Probably the few second of rest helped.
I tend to grin like an idiot from the moment I put my gear on (unless I'm puking from seasickness) so some might argue 1 atm. To my knowledge I have not yet experienced narc beyond my normal level of goofy though.
I have been fine at 160' on air in warm tropical water...
I have also been narc'd outta my gourd at 100' in cold water in Canada when I was totally fine at 120' the day before...it kind of varies at times.
Anti-Troll Disclaimer
Yes, I am a technical diver.
No, I would not suggest diving that deep on air is a good idea.
No, I would not dive that deep with a single tank, no matter what's in it.
I've also been narc'd bad at about 4"...into a 1.14 liter of Crown, but that's another story...
...that's a great disclaimer James R, I'm gonna borrow that one...
For one of my Mater modules we did a chamber dive and went a little over 150ft. Did feel a little "happy" but performed all my tasks. I was more aware of the "giddiness" around me by my partners in the chamber. LOL! Was really impressed with the rubber glove/lung simulation. The Hyperbaric tech put a tiny breath into a rubber glove and tied it off. By the time we reached the "surface", it was as big as a bowling ball and then burst!!
Ok on the basis that everyone is affected differently, what's some simple tests one can do to see the effects (seeing I have no feeing of degradation of ability).
Maths
Writing
Switch between air and trimix at depth.
And not one Trimix tech diver picked me up on my error, "Switch between air and trimix at depth". In my ignorance, at the time I thought this to be a good test.
It wasn't until I was discussing this with my tech instructor during my Trimix course who replied "That would not be a good idea as you can get bent at depth due to the radical difference in Nitrogen levels between Trimix and Air". He then went on to explain Isobaric counterdiffusion which I had read briefly on previously but hadn't fully comprehended it.
"Perhaps sometimes the story gets lost amongst the words"
Isobaric counterdiffusion (Wikipedia)
DCS can also be caused at a constant ambient pressure when switching between gas mixtures containing different proportions of inert gas. This is known as isobaric counterdiffusion, and presents a problem for very deep dives.For example, after using a very helium-rich trimix at the deepest part of the dive, a diver will switch to mixtures containing progressively less helium and more oxygen and nitrogen during the ascent. Nitrogen diffuses into tissues 2.65 times slower than helium, but is about 4.5 times more soluble. Switching between gas mixtures that have very different fractions of nitrogen and helium can result in "fast" tissues (those tissues that have a good blood supply) actually increasing their total inert gas loading. This is often found to provoke inner ear decompression sickness, as the ear seems particularly sensitive to this effect.
Because Isobaric Counterdiffusion is usually only a problem at signficant depths(greater than 300ft and usually closer to 400ft). We switch from trimix to nitrox all the time at 100-120 coming back up on deco. On long deco dives, it can save quite abit in deco time/
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