Nitrogen Narcosis

[DCBC]

At the very least, the "correct" answer on the ACUC test is the most conservative one...and cannot be faulted for urging students to dive more safely, eh?

That's my take on it as well. My youngest son stopped me on his AOW "deep water dive" and gave me a thumbs-up because he didn't like the feeling at 80'. I think that if a diver knows that it will affect him, they will be more inclined to be cautious when it comes to depth.

If I'd taught my son's class that nitrogen narcosis started at 100', he may well have continued, shrugging it off as an impossibility. It took him a couple of dives before he felt comfortable in deep water. Its been my experience that small steps are far better than giant steps when it comes to diving.

 

[SDAnderson]

For what it's worth, I've been on quite a few chamber rides in a multi-man chamber packed with 10 - 15 divers at a time. In all of those dry dives, it has been my observation that everyone is showing signs of narcosis by the time we hit 3 ATA. Some folks a little shallower but nobody holds out past 70 feet. This doesn't mean that everyone is falling down stupid at 70 feet - they aren't - but their emotions and motor control are noticeably affected.

Sensible divers will assume they are narked long before they feel any signs of it.

 

[Diver0001]

There were measurable differences in most divers at 33 FSW (some at 10'). These same divers did not usually recognize the first symptoms of narcosis until 100 FSW. Clearly they were affected by it long before they recognized that they were being affected.

That's my experience too but it doesn't strike me as particularly relevant if it starts at the surface or not. Performance being "measureably" affected isn't the same as being "significantly" affected. I'd probably be measureably affected with one sip of wine but I"m not significantly affected until I've had a lot more. I'm significantly affected on most days at about 30 metres.

On another note, the narcosis seems to get worse a lot faster from 30 meters and deeper. The difference between 0 and 20 metres is a lot less significant than the difference between 30 and 50 metres.

Was there anything in the study that seemed to indicate that the effect gets exponentially worse? That's what it seems like.

R..

 

[knotical]

Is it possible that having a lower level of inert gas dissolved in one's tissues might result in measurably improved cognitive/psychomotor testing? Sure, why not? Anything's possible. Likely? Not sure about that.

Right on ! I know I got smarter when I moved to Colorado.

 

[DCBC]

That's my experience too but it doesn't strike me as particularly relevant if it starts at the surface or not. Performance being "measureably" affected isn't the same as being "significantly" affected. I'd probably be measureably affected with one sip of wine but I"m not significantly affected until I've had a lot more. I'm significantly affected on most days at about 30 metres.

To put this into context, a person's performance is dependent upon the situation. Keep in-mind that if you are diving with a buddy and if s/he requires your assistance, the affects of narcosis are compounded. Your buddy will react more slowly (even if this is only "measurably") AND you will react more slowly (than normal) as well.

How long in seconds is too long? Again this depends upon the nature of the problem. In some cases the extra seconds may be too long.

Was there anything in the study that seemed to indicate that the effect gets exponentially worse? That's what it seems like.

Performance decreases with depth. In one test we compared two sets of 3rd year medical students from the University of Toronto. We ran the first test in a similar way as the one previously described, to a depth of 150'.

The second group had foreknowledge of the fact that the nitrogen would lower their performance. They were asked to be serious, concentrate and be deliberate in their thought process from the moment of their descent. The overall results showed the second group to have a marked increase in performance (almost 20%).

We compared these results with 6 experienced Navy divers. The 150' results of these divers showed a performance increase of approx 50% over the second group, and almost 80% better than the first group.

We later joked about the fact that we would all be considered geniuses if the earth's atmospheric pressure ever increased. Experience dealing with narcosis and familiarity with the environment were credited with the increased results.

Again these results are of limited value, in-that the numbers of those tested were small (26). It does demonstrate however why I feel that divers going deep should prepare themselves mentally and first gain several hundred hours of diving experience.

 

[MXGratefulDiver]

To put this into context, a person's performance is dependent upon the situation. Keep in-mind that if you are diving with a buddy and if s/he requires your assistance, the affects of narcosis are compounded. Your buddy will react more slowly (even if this is only "measurably") AND you will react more slowly (than normal) as well.

How long in seconds is too long? Again this depends upon the nature of the problem. In some cases the extra seconds may be too long.

To put that in different terms, depending on circumstances it may take you longer to recognize that there's a problem, it may take you longer to decide what to do about it, and it may take you longer to implement the solution you decide on. It's also possible that in an impaired condition you will decide on a course of action that may not be the one you would have chosen had you not been impaired. And, as noted, because your buddy is also narc'ed you may not be getting helpful responses from him or her to deal with the situation.

Most scuba accidents are not the result of one thing going wrong, but rather a series of cascading failures that were not recognized or handled at a point where the accident could have been avoided. Narcosis significantly increases the risks of that cascading series of events taking place.

Performance decreases with depth. In one test we compared two sets of 3rd year medical students from the University of Toronto. We ran the first test in a similar way as the one previously described, to a depth of 150'.

The second group had foreknowledge of the fact that the nitrogen would lower their performance. They were asked to be serious, concentrate and be deliberate in their thought process from the moment of their descent. The overall results showed the second group to have a marked increase in performance (almost 20%).

We compared these results with 6 experienced Navy divers. The 150' results of these divers showed a performance increase of approx 50% over the second group, and almost 80% better than the first group.

We later joked about the fact that we would all be considered geniuses if the earth's atmospheric pressure ever increased. Experience dealing with narcosis and familiarity with the environment were credited with the increased results.

Again these results are of limited value, in-that the numbers of those tested were small (26). It does demonstrate however why I feel that divers going deep should prepare themselves mentally and first gain several hundred hours of diving experience.

While we don't truly understand the mechanics of narcosis, we do know that psychology plays a significant role in how effectively it's dealt with ... people who are insecure in their skills or lacking the experience to have adapted to dealing with it typically won't handle it well, regardless of the severity of physical effects. The majority of casual or recreational divers would fall into this category.

... Bob (Grateful Diver)

 

[Brian Sharpe]

For what it's worth, I've been on quite a few chamber rides in a multi-man chamber packed with 10 - 15 divers at a time. In all of those dry dives, it has been my observation that everyone is showing signs of narcosis by the time we hit 3 ATA. Some folks a little shallower but nobody holds out past 70 feet. This doesn't mean that everyone is falling down stupid at 70 feet - they aren't - but their emotions and motor control are noticeably affected.

Sensible divers will assume they are narked long before they feel any signs of it.

A little OT but a compelling argument in favour of using nitrox.:acid:

 

[Bubbletrubble]

That's my experience too but it doesn't strike me as particularly relevant if it starts at the surface or not. Performance being "measureably" affected isn't the same as being "significantly" affected. I'd probably be measureably affected with one sip of wine but I"m not significantly affected until I've had a lot more. I'm significantly affected on most days at about 30 metres.

@Diver0001: The issue of whether narcosis starts at shallow depths is relevant to the question posed by the OP. The question was: "When does narcosis begin?" I interpreted the question to be: "At what depth (or ambient pressure), do the effects of narcosis manifest?" I think others approached the question similarly. I agree, however, that the distinction between mild/barely detectable effect and severe/significant impairment is of great practical importance.

For what it's worth, I've been on quite a few chamber rides in a multi-man chamber packed with 10 - 15 divers at a time. In all of those dry dives, it has been my observation that everyone is showing signs of narcosis by the time we hit 3 ATA. Some folks a little shallower but nobody holds out past 70 feet. This doesn't mean that everyone is falling down stupid at 70 feet - they aren't - but their emotions and motor control are noticeably affected.

Sensible divers will assume they are narked long before they feel any signs of it.

A little OT but a compelling argument in favour of using nitrox.:acid:

@Brian Sharpe: Are you sure about that? Please explain what you mean by this. It is, in fact, quite relevant to the topic. (This should spark more good discussion. )

 

[DennisW]

A little OT but a compelling argument in favour of using nitrox.:acid:

Nitrox does not decrease the effects of Nitrogen Narcosis. Many people think that it does, but in reality it does not. People that say they have never been under the effects of Nitrogen Narcosis either don't understand the physiological effects of diving, or they have never dived. Brian, go back to your Nitrox manual and re-read that section.

 

[MXGratefulDiver]

A little OT but a compelling argument in favour of using nitrox.:acid:

I have not, personally, experienced any noticeable difference in the degree of narcosis I feel on nitrox, as compared to just breathing air at the same depth. Both air and EAN30 will typically put me at a "whoa!" point at around 120 ... how much of that is due to the expectation of it happening I can't really say ...

... Bob (Grateful Diver)