Nitrogen Narcosis Tolerance?

[mgri]

This is a post by MHK which IMHO really exemplifies how people mistakenly think they can build up a tolerance for nitrogen narcosis


<Quote> I was at Duke University this past weekend doing a study for the US Navy and DAN. During a break from our study Gene Hobbs took me up to his lab and showed me a video from a study that was done a few years ago. In the chamber they had 2 guys from DAN [ Gene and Brian] and they had two other guys. The idea was that the four would do a series of tests at the surface and then do the same tests at 165' on air. Unfortunately they don't have releases from the other two so they can't release the video publicly, but the video was an incredible demonstration of narcosis.

Part of the test was that they would pick up small beads with tweezers and then put those beads into a tube in a 1 minute time frame. At the surface they did 24 and 22 respectively. At depth Gene did 22 slighty less whereas the other team did 6. But what was so surprising about this video was that one of the other team members was laughing uncontrollably, and Gene who did 22 at depth thought that he had *adapted* to narcosis because he only did 2 beads less then he did at the surface.. However what he realized after reviewing the video tape was that he had such tunnel vision, and was so focused on getting the beads into the tube that he had no idea that his buddy was laughing uncontrollably to the point that he couldn't even stand up..

The obvious point was that he thought he was adapting but any sense of division of attention, or multi tasking was lost upon him at depth. The other team was a complete disaster and upon reviewing the video tape didn't even remember half of the stuff that they were doing at depth.. So for those that think they can *adapt* to narcosis I say first off that narcosis is a small part of the issue and it can't be solved. C02 is much more of a concern breathing air at depth but it get's lost in the debate..<Quote>

 

[David Evans]

There's another point that is lost in this discussion.

Why on earth would you WANT to dive deep on air?

Really?

Even if you CAN acclimate yourself to narcosis, or even if the effects of narcosis are overstated (neither of which I believe, by the way), WHY DIVE DEEP AIR?

The point is this:

There's a BETTER GAS for that depth than air, and it's called trimix.

If I am going to go to that depth, and I have a choice of "acclimating" myself to narcosis, or eliminating it altogether by diving a different, PROVEN better mix, I'm going to select the latter.

Use the right tool for the job, whatever the job is.

If you need to dive to 180 feet, it doesn't matter if you could do it on air - the better tool for the job is trimix.

I think justification of deep air diving is unsound and terribly dangerous. There's no need for it whatsoever. Use the right tool for the job at hand.

 

[DA Aquamaster]

David Evans once bubbled...
There's a BETTER GAS for that depth than air, and it's called trimix.

If I am going to go to that depth, and I have a choice of "acclimating" myself to narcosis, or eliminating it altogether by diving a different, PROVEN better mix, I'm going to select the latter.

Use the right tool for the job, whatever the job is.

If you need to dive to 180 feet, it doesn't matter if you could do it on air - the better tool for the job is trimix.

I think justification of deep air diving is unsound and terribly dangerous. There's no need for it whatsoever. Use the right tool for the job at hand.

I agree, trimix is a good idea at 180 ft, but what about 150, or 120 or 100? Where do you draw the line? At present many peopel are drawing the line at 130 ft. or less. People take things a little far in both camps and the "I only dive trimix" crowd take this to extreme. Trimix at 120 ft is in my opinion a waste of helium. There is also the small problem that trimix is not available in many if not most places and it is not like you can go into any local dive shops and rent a tank of trimix.

There is some degree of validity to the "use the right tool for the job argument" but if trimix is not available for that 130 ft dive, the job won't get done as you will be sitting on the boat.

I will also concede trimix is a "better" gas for deep diving, but to do so you have to ignore its limited availability, extremely high cost of both the gas and the training, and the risks associated with mixing it> In the end you have to consider at what depth the benefits finally outweigh the costs for an individual diver.

mgri - As for the post by MHK, I'd love to see the study - the whole study. The unfortunate fact is most study results that are published or referenced outside of technical journals only include the good stuff and leave out the long boring methodogical descriptions. However, without being able to assess the research design, the methodolgy, and the statistical significance of the findings, the so called "results" can often be very misleading. Did our overly focused diver and his laughing buddy do this on dive one to 165 ft or dive 30? How was the deoth od this dive approached ? What were the descent rates used in the chamber? Could any diver ask for a 10 foot ascent before again decending deeper? How many subjects were tested? What was the experience level and training of the divers involved? Were there any intentional or unintentional demand characteristics to the study? Were any controls used for experimenter biases? subject biases? Was any thought given to doing a double blind study where the gas for individual divers was unknown by both the subject and the experimenter? etc, etc ,etc.

Most studies done to date on the topic have some serious flaws in them, but they end up being accepted as proof without any regard to the limitations they entail. In most reseach situations you can only say that the results are signifcant only in a certain situation or within narrow boundary conditions. More research is then needed to generalize these results to a broader range of conditions and hopefull someday to the real world.

Sorry, but you just can't quote a third hand summary of a study of unknown methodolgy that may or may not have met the requirements of a true experiment or even a quasi experiment and then conclude that that adaptation does not occur.

I am also not advocating air as the ultimate mix for deep diving, but I am suggesting that it is useful to greater depths than many people would propose at present, that it is a reasonable option for many divers.

I would also suggest that there is a cetain amount of hysteria about the effects of narcosis at relatively shallow depths (100-130') that is being hyped by training agencies and that may have an undesireable and potentially dangerous effect on divers who find themselves below 100ft.

I'd also have to state that agencies doing trimix mix training are capitalizing on this often, ironically, at the same time they require a deep air course prior to a trimix course.

 

[World Champion]

Thanks to all for a very interesting discussion.

 

[padiscubapro]

David Evans once bubbled...
There's another point that is lost in this discussion.

Why on earth would you WANT to dive deep on air?

Really?

Even if you CAN acclimate yourself to narcosis, or even if the effects of narcosis are overstated (neither of which I believe, by the way), WHY DIVE DEEP AIR?

The point is this:

There's a BETTER GAS for that depth than air, and it's called trimix.

If I am going to go to that depth, and I have a choice of "acclimating" myself to narcosis, or eliminating it altogether by diving a different, PROVEN better mix, I'm going to select the latter.

Use the right tool for the job, whatever the job is.

If you need to dive to 180 feet, it doesn't matter if you could do it on air - the better tool for the job is trimix.

I think justification of deep air diving is unsound and terribly dangerous. There's no need for it whatsoever. Use the right tool for the job at hand.

trimix is the better gas but many times it unavailable.. Most divers who take this higher than holy attitude when confronted with you cant get helium but we are doing this dive, do it on air or don't do it.. in most cases they do it.. the problem is that many of theses people have no experience at this and are totally unprepared..

Go to truk He is usually impossible to get, youll miss some of the best wrecks. go to bikini, forget about trimix.. so you wount dive at all..

when there is a choice TRIMIX or Heliox is the obvious solution, but its not always a choice.

 

[MechDiver]

padiscubapro once bubbled...


when there is a choice TRIMIX or Heliox is the obvious solution, but its not always a choice.

Famous last words of the Rouses. The decision to call a dive is always a choice. Making a dive that is stupid because you don't have the correct equipment...is just that.

 

[David Evans]

I agree Mech.

If there's a dive I want to go do, but I don't have the equipment to do it, I don't do the dive. I call it. As simple as that.

As an instructor in Seattle, I wouldn't allow my students to dive in a 5 mil wetsuit in the Puget Sound. Sure, they could do it, but it doesn't mean it would be safe. That's not the right equipment.

When I dive in a wreck, I view my reel as a mandatory piece of equipment. If I don't have my reel, I don't go in the wreck. The dive would be unsafe otherwise.

Well - I view the gas I dive as the MOST important piece of "equipment" I carry.

And if the "equipment" isn't right, then I don't do the dive - or I modify the dive plan to suit the equipment on hand.

 

[padiscubapro]

MechDiver once bubbled...


Famous last words of the Rouses. The decision to call a dive is always a choice. Making a dive that is stupid because you don't have the correct equipment...is just that.

they chose not to use He when it was available.. There is a BIG difference doing a 200ft dive in warm clear water, little or no current vs doing a dark, cold, limited viz 240+ fsw dive with all kind of entanglement hazards, strong currents PLUS entering an overhead enviroment...

In the latter case its just stupid....

I personally don't have a problem doing "deep air" dives when the conditions permit, but with a real overhead enviroment 130ish is the usually the limit before I dive with mix these days..

Truk has been my only real exception since chances of siltout are unlikely, there are lots of ways in and out, and with a CCR running out of gas isn't a concern..

 

[MikeFerrara]

MechDiver once bubbled...


Famous last words of the Rouses. The decision to call a dive is always a choice. Making a dive that is stupid because you don't have the correct equipment...is just that.

Few would argue the value of mix at those depths but there's more to the story. Even IF you were going to do a deepish dive on air would you plan it and attempt to conduct it the same as you would if you were on mix? In OW I don't ever leave my gas. These guys did.

If I were to get drunk on a friday night I could still get to and in my front door. I might move a little slower and be a little more careful stepping over the mole holes in the yard but I'd get there.

PS, I'm just trying to make a point. I am not advocating diving deep without the best gas or equipment for the dive.

 

[David Evans]

PadiScubaPro:

Wanted to clarify that I'm not trying to be argumentative with you. Just stating my opinion.

Regarding Truk and Bikini:

I *sincerely* thank you for letting me know that He is impossible to get there. Both are dream destinations for me. If the conditions there require He to get to do the cool dives, and it's not available, I guess I won't get to go.



-d