YD Scuba Diving Forums banner
1 - 20 of 24 Posts

· The Artist formerly known as 'Kirky'
Joined
·
2,138 Posts
Discussion Starter · #1 ·
Imported post

Me, daveJ and The Slicer went on our annual jaunt to Stoney yesterday - it was great, vis about 15m, water a tropical 11 degrees and not that busy.

Funny thing happened - Running a 32 mix at 30m in a 12 twinset I felt a little strange - could this be narcosis - even on the 32 mix
 

· Registered
Joined
·
12,115 Posts
Imported post

Kirky,

When you say 'strange', how do you mean? What feelings did you have and what was 'strange' about them? Care to share?
 

· A short fat well off crap cave diver. Likes wrecks
Joined
·
15,284 Posts
Imported post

There is a big debate on the narcotic level of 02 and the general consensus is that 02 is just as narcotic at Nitrogen. When calculating END's for trimix some divers include the percentage 02 in the depth calculation.

But just looking logically at your gas choice. 32% as apposed to air 21%. That’s only an 11% reduction in your Nitrogen level so it isn’t going to make a hell of a lot of difference. The minimum He I would plan for a dive would be 15% so on a 40m dive I would be running 28/15 which is a 21% reduction 15% of which is definitely a non narcotic gas.

I did a 46m dive on 23/20 as part of my Trimix course and I fluffed a shut down drill because I couldn’t find my slob knob. I was instantly narked. Not debilitating so but enough to here the banging of my hart beet in my head and take a deep breath.  

Loads of people think Nitrox doesn’t reduce Narcosis. Loads of people think it does and a few think it does but it’s just the placebo effect. I fall into the last category.
Check out Bret Gillinangm’s book Deep Diving for an interesting look at Narcosis and how it affects divers.

ATB

Mark Chase
 

· Moderator
Joined
·
3,278 Posts
Imported post

<font color='#000080'>Hi

When you look at how the narcotic effect of a gas is calculated through solubility O2 should be MORE narcotic than nitrogen although O2 differs in that a portion of it is metabolised.

GUE consider nitrox to be no less narcotic than air which is why helium is used anywhere below 30 ish metres and many times a 30/30 mix is preferred instead of 32%

Andy
 

· The Artist formerly known as 'Kirky'
Joined
·
2,138 Posts
Discussion Starter · #5 ·
Imported post

Bren - the usual stuff - narrowing of perception, heart beat raised etc - just like narc hits on air. the reason I went for a 32 mix was to stop this as I usually get some indications at around 20m ecspecially in cold water.

The only other info was that it was my first 30 this year so maybe I just need more exposure to this depth.

My point was - given the reduced N2 in the mix over air, I did not expect this and wondered if anyone had experience/info on this. My PPO2 was Ok (about 1.4 max) so I assume the effect was N2 induced
 

· Registered
Joined
·
1,751 Posts
Imported post

Hiya Phil

Yeah I suppose END is used more in Trimix calcs but  you could say that Equivalent Air Depth and Equivalent Narcotic Depth are fundamentally the same thing.

What I was trying to say (very poorly) is that Johns EAD on this 30m dive on 32% was approx 24m

Johns stated that he can get indications of narcosis at 20m on air, and so if his EAD was approx 24m on this dive then maybe he 'was' feeling the effects of nitrogen narcosis..

Did that make sense?? I'm terrible at explaining things....
 

· Registered
Joined
·
294 Posts
Imported post

This is a good place to put this post I just had my First  LARGE time tast of Narcosis I was diving at Vobster today enjoying a lights out ,silt city dive ,got down to 32M on the shotline then O WOW it all came at once , just like someone had  turned  on the spin dryer it went round and round .!!! just like the merry- go -round .assended about 5m and the spin dryer finally came to the end of its cycle .
Fiona.
 

· Registered
Joined
·
303 Posts
Imported post

<font color='#0000FF'>Guys, just to clarify somthing.

END is just as relevant with Nitrox as it is with Trimix.
Each mix has a ratio of Nitrogen that can be compared with an air dive to a similar depth.

Fair enough, this is one of the main aims of trimix (lowering END) but it applies to any gas mix in comparison to air.
IMO as long as a gas can be considered narcotic, it can have an Air END.

Stu.
 

· Registered
Joined
·
628 Posts
Imported post

<font color='#810541'>If you consider o2 to be as narcotic as nitrogen then surely the END doesnt come into it. Only when you add He do you lower the narcosis.

I was taught to consider o2 as narcotic as Nitrogen, PADI and IANTD.
 

· Registered
Joined
·
130 Posts
Imported post

[b said:
Quote[/b] (kirky @ Nov. 22 2003,21:27)]The only other info was that it was my first 30 this year so maybe I just need more exposure to this depth.

My point was - given the reduced N2 in the mix over air, I did not expect this and wondered if anyone had experience/info on this. My PPO2 was Ok (about 1.4 max) so I assume the effect was N2 induced
Kirky,

How was your descent for this dive?.

I find that if I do a rapid descent it usually causes a narked feeling for the first few minutes of a dive.

A nice slow descent seems to cure the problem or at least make it less noticable.
 

· Ginger, Irish, sometimes stroppy
Joined
·
5,898 Posts
Imported post

I'm not even Nitrox qualified, but I am interested in the gas laws being applied.

So would the following be right according to the tables ?

32% Oxygen => 68% Nitrogen, Pressure at 30M 4 ATM

ppN2 = 0.68x4 = 2.72

Surface Air 21% O2 => 79% N2

equivalent pressure on air => 2.72/0.79 = 3.44 ATM

So that means in terms of narcotic effects of Nitrogen at 30M of a 32% mix is equivalent to diving to 24.4 M (approx) on air.

So if a diver normally gets narked around 25 M the same diver could get narked at 30 on this mix, especially if he has some of the other risk factors (tiredness, cold, dehydration, stress etc).

Does this make any sense ?

Cheers

Conor
 

· PADI Internet Specialty Diver
Joined
·
10,655 Posts
Imported post

Conor - you are correct.

The calcs are correct - go do your EAN at once!!!

END and EAD are the same thing for nitrox - END for trimix refers to the PPN2 as a general rule and most of us do not bother with O2, which is wrong really as it is narcotic...

Cold water increases narcosis which may explain the event.

Chris
 

· Ginger, Irish, sometimes stroppy
Joined
·
5,898 Posts
Imported post

I do want to do the EANx course, mostly cos I am interested in the science.

On the subject of Narcotic effects of Oxygen, I found the following that states;
"In recreational divers, if oxygen has any narcotic effect at all, it is far less narcotic than nitrogen."
http://divermag.com/archives/dec96/divedoctor_Dec96.html

Hope this is of interest

Conor
 

· Ginger, Irish, sometimes stroppy
Joined
·
5,898 Posts
Imported post

Odd point....

The latter article states;
'What does this mean to us as divers? Oxygen is potentially twice as narcotic than Nitrogen. The upside being that at the partial pressures of oxygen within which we normally operate (0.21 to 1.6), oxygen narcosis is not a relevant issue'

The phrase 'Oxygen is potentially twice as narcotic than Nitrogen' strikes me as quite bizarre and possible in complete contradiction to the previous linked article.

Have to confess, I'll go with the Doctor on this one
 

· A short fat well off crap cave diver. Likes wrecks
Joined
·
15,284 Posts
Imported post

[b said:
Quote[/b] (camdiver @ Dec. 05 2003,13:14)]Odd point....

The latter article states;
'What does this mean to us as divers? Oxygen is potentially twice as narcotic than Nitrogen. The upside being that at the partial pressures of oxygen within which we normally operate (0.21 to 1.6), oxygen narcosis is not a relevant issue'

The phrase 'Oxygen is potentially twice as narcotic than Nitrogen' strikes me as quite bizarre and possible in complete contradiction to the previous linked article.

Have to confess, I'll go with the Doctor on this one
Funny I was told that 02 is AS narcotic as Nitrogen but not twice as?? But the science is based on weight of the gas or density of the gas and in those terms 02 is as narcotic as Nitrogen. However as 02 is metabolised by the body the effect is reduced so if 02 has twice the density of N2 then perhaps that explains the reduction.

Truth is if you think its better it will be. At Nitrox depths narcosis can be controlled by will power and confidence but it’s definitely still there waiting to bite you if things get a bit stressful.

I find it annoying that you have to spend more money on yet another course to do Helium Trimix diving. It’s far easier to learn than Nitrox as it has less affect on the dive. There should be a 50m cert for He, which is cheep (say £50) and allows people to dive a safe gas to recreational depths. 10 and 20% He fills are not that expensive and they make a massive difference in the 35 -50m range

ATB

Mark Chase
 
1 - 20 of 24 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top