Getting narced.

[Hobbs]

Originally posted by simon66
[B
What i refer to is the equivalent air depths
i.e a dive to a max depth of 40 metres on a Ean 32 mix at a ppo2 of 1.6 for a max time of 45 minutes would give you an equivalent air depth of 33 metres .

simon . [/B]

I do understand that you are talking about the equivalent airdeapth, but there is a problem when you max out the values like you have in your example.
45 minutes on a pp02 1.6 ? do you realy like that ? I am not going to start a holywar on anything and calculate things,
but as I remember it 1,4 is the recomended (and some even recomend lower values than that) pp02 value where 1,6 is the absolute maximum value. Add the absolute maximum time at that deapth and you will understand that it migh not be so smart to risk CNS toxicity or burnt out lungs. shure it shouldnt happen you are within the limits, but still same thing happens with DCS. you shouldnt get it you are within the limits but oups you got it anyhow.

We where talking about the nitrogen narcosis and as I stated, I would be able to make an educated guess why ppl are less narked (se my last posting) when diving nitrox. But I also stated that there are other things that increase the risks with that dive.

I might be out of bounds here but it feels that you choose between getting nitrogen narked or getting nitrogen narked AND CNS toxicity and/or burntout lungs

The choice is whether you will get drunk and do something stupid that might kost you your life (deep on air ) or you will get less drunk and tie a shotgun to your head then risk shooting it off (same real depth on nitrox)

Hope you understand what I am trying to tell you

if you now have nitrox and wants to go down deep, then why not make heliox out of it instead ? (of course get the right training first)

point stands you dont get down deep on nitrox, you buy time with nitrox but not depth.

 

[Hobbs]

Originally posted by devjr
I'm fairly certain that there is a level of variability in nitrogen narcosis not represented by the information in Hobb's post above. In the course of deep diving(below 130')

No single rule for everybody.

The notion that one may not be aware of danger while under narcosis is possibly true. However, it is not true in my case. Under no circumstances have I ever been less than acutely aware of the progression of effects. A lack of awareness does appear to subvert the minds of some deep divers. In one of the ironies of my diving career, I was a witness to an appalling event; a narced SCUBA diver unexpectedly swam over the wall straight down to 300 feet and beyond despite efforts by others to catch up and turn him around. He never returned. The diver, who perished at Cay Sal Bank in 1976, was a dentist.

I agree totally with the statemnt that no diver reacts the same!
I dont even think the same diver reacts the same on different dives.
The text I was refering to is just a smal part of the link.

dive safe

 

[Uncle Pug]

Originally posted by devjr
The notion that one may not be aware of danger while under narcosis is possibly true. However, it is not true in my case. Under no circumstances have I ever been less than acutely aware of the progression of effects.

You might want to re-examine the logic in the above...

 

[Uncle Pug]

Originally posted by simon66
uncle pug ,
do you use nitrox

It ain't air in thair...

Uncle doesn't just use it...
He brews it.....

 

[Divesherpa]

Originally posted by Uncle Pug


You might want to re-examine the logic in the above...

I agree with Uncle Pug. Video yourself the next time you cross 200feet. Perform a few basic feats for the camera. If you are anything like me, you won't do it again.
The video isn't narced. That was a hard lesson for me to learn, as I thoroughly believed in the goodness of deep air.


Cheers

 

[simon66]

Originally posted by Hobbs


if you now have nitrox and wants to go down deep, then why not make heliox out of it instead ? (of course get the right training first)

point stands you dont get down deep on nitrox, you buy time with nitrox but not depth.

Of course you would use tri mix or heliox for diving depths over 165 ft .
Since my normal max depths are up 40 m (132 ft) i use a nitrox mix of 28% which is a ppo2 of 1.4 bar and my computer is set with a warning at 1.5 .
The example i stated was max values worked out from the tdi advanced nitrox training manual and yes there is a warning that to dive with a ppo2 of 1.6 could cause oxy toxy .
These are published by NOAA O2 partial pressure and exposure time limits:
po2 single exposure limit
1.6 45 mins
1.5 120 mins
1.4 150 mins
1.3 180 mins
1.2 210 mins
and so on . this is only part of the table .

And back to the narc thing i do not dive very often past 35 metres (115 ft) as the dive sites around here do not normaly exceed that depth so the use of tri mix or heliox would mean an expensive hobbie and not an enjoyable dive due to all the kit and everything involved with mixed gas diving.
The amount of narcosis i get varies on the depth and temp and how i feel on the day and the viz , sometimes i don`t feel anything much at all , i have a clear head and yes sometimes i feel abit light headed , if i`m not happy at that depth then i`ll ascend a bit , as from all the other replies everybody here has gone down to 200 ft or close to it for some reason and i suspect to know their max limit that they are happy to dive to on air . None of us are angels !
we `ve all been there and did`nt like it that much thats why everyone is replied with warnings against it .
I don`t dive too get narced , thats one of the reasons i did the tdi advanced nitrox and decompression courses was too use a mix at depths around 20 m (66 ft) to40 m (132 ft) to reduce the amount of narcosis and cut down on deco time or lenghten bottom time .


Anyway all in all my first post was a reply to the very first question asked " getting narced " what depths etc .
Hope we`re starting to understand each other .
Simon

 

[The Iceni]

Originally posted by Hobbs

"Personally when in a highten state of awareness I have been feeling the effects of narcosis at a depth at around 18 meters. not much but it was there."


I am conviced that Nitrogen behaves exactly like all inhalational anaesthetics although the parallel with alcohol is also valid. In all cases there is an initial, short-lived, period of excitability before the depressive effects of all these agents predominate but I fear a diver rarely experiences the direct effects of narcosis until the demands of an essential task bring the reduced cerebral fuction to the diver's attention and various degrees of panic occur. I believe this distress/disquiet is what most divers REPORT as narcosis and possibly explains why it is worse in poor visibility, where there is added stress.

Regardless of the analogy you like to use, I agree that narcosis is present on ALL dives and it is related to the partical pressure of Nitrogen. Even the hardened alcoholic, who never appears to be drunk, does suffer from the depressing effects of alcohol, whether it is reaction time or some other psychometric measurement. So it is with narcosis.:madelf:

Nitrox has been suggested, above, as being safer that air on shallowish dives. Oxygen is theoretically even more narcotic than Nitrogen but it is not at all narcotic in practice, which is very confusing. Some possible reasons for this were discussed at http://www.scubaboard.com/t4425/s.html

It is a shame Helium is so expensive (and requires longer and more strict adherance to planned decompression) since diluting the Nitrogen with non-narcotic Helium seems to be such a good idea.

Simon aluded to Heliar. I consider this to be a very dirty gas because it is just as narcotic as air for the same Oxygen partial pressure. For what it's worth I consider (enriched) trimix to be the better gas for open circuit deeper diving with the Oxygen partial pressure set to give 1.4 bar at the target depth, the proportions of Nitrogen and Helium being adjusted pro rata for the required clear headedness, deco requirements and cost!

Rebreathers do have their problems but one great advantage they have is that the ppO2 can be set to a constant 1.3 bar (or even 1.4 bar) throughout the dive so that there is even less exposure to Nitrogen.

(I always thought the Brits spelt it as "narked". I would read narced as narsed!!!

 

[devjr]

Rhymes with "naked".

All I know on the subject of the alcohol/nitrogen analogy is what I have inferred from observation of actual tests of response times, from personal experience and from reading some articles published in lay scientific magazines. Addressing this board, I have not and will not refer to "second sources" such as dive magazines or industry lecturers, and by this I'm not implying anything, just leveling.

To start, one would have to define the effects of nitrogen gas and those of alcohol. That might be difficult. I mentioned variability of both among individuals. I have experienced this personally and observed it in others. Another factor is variability between races. It was common knowledge for centuries that American Indians became dangerously "mental" when drinking booze. Hence, sale of alcohol, even beer, was made a serious crime. Back in the seventies, an article appeared in Scientific American which verified this bit of folk wisdom and gave an explanation. It turned out that alcohol is metabolized differently by Asians, including American Indians. Toxic chemicals appear in the blood and cause mental instability. The toxity of alcohol to Asians was said to explain why, historically, the intoxicant of choice was weed--poppy and hemp being examples. This toxic effect does not usually occur among most Caucasions. Yet, even among these, the only generality that I have observed in actual tests is that one to two ounces of spirits appear to increase focus and awareness but beyond this level of consumption there is a depressive effect with varying specific responses including euphoria, reduction of response time and reduced motor skill.

I have never personally experienced "excitability" due to nitrogen although reactions of some divers might be interpreted as such. Among me and my buds this seems to be rare to nonexistant. I'm not sure about putative "excitability" with intitial alcohol intake. Semantics which I would describe as reduction of inhibition? Again, effects would probably vary.

Before declaring that alcohol and nitrogen are similar, one has to define the effects of both. However, remarks above indicate the difficulty in assigning the effects of even one of these in any broad way. As discussed, differences exist between individuals as well as whole races. Furthermore, there is the general issue of linear effects. As I explained in an earlier post, nitrogen appears to be linear but alcohol is apparently not, at least not among those participating in the aforementioned driving proficiency test, and not with me. Thus, direct evidence suggests that progression of effects from the two intoxicants does not follow the same path.

Portraying the depressive effects of nitrogen as a "Martini" effect may be trivializing the whole issue and undermining the 130 feet rule for recreational air divers.

Instructors should admit that some divers are going to dive below this depth anyway. While on the subject, he should say that narcosis has varying effects in individuals and can not be predicted. Furthermore, narcosis should be viewed as extremely dangerous and individual tolerance should only be tested under controlled conditions. At the very least, such a dive would include an experienced buddy diver.