First dive at 40 meters - Newbies recreational

[Storker]

Now you are just giving me the trouble of going to google translate

Schiller.

 

[KenGordon]

We've all been there. Problem is, the OP has resorted to snark instead of learning from what has been said by very competent divers and instructors (me not included)

Yes, well, maybe you should come and argue in the pub if you want to make an impact?

 

[Dody]

We've all been there. Problem is, the OP has resorted to snark instead of learning from what has been said by very competent divers and instructors (me not included)

I took me 35 pages to get there. I won't go as far as saying that I should be sanctified but it can be hard to exchange with GOD divers.

 

[Storker]

maybe you should come and argue in the pub

I'm there already. Can't remember having seen you there.

 

[Edward3c]

This one for example. But you should read the full study not the summary. There are many more if this too old.
Memory and metacognition in dangerous situations: investigating cognitive impairment from gas narcosis in undersea divers
Malcolm Hobbs et al. Hum Factors. 2014 Jun.

The problem with scientific papers is that there are plenty of views, for example:
P.J. Mumby, et al, (1995), A Critical Assessment of Data Derived From Coral Cay Conservation Volunteers, Bulletin of Marine Science, Vol 56, No 3, p.p. 737-751.
This study, which I was part of, confirmed NN effected the accuracy of observations which deteriorated progressively from 15m to the max survey depth of 30m.

 

[Dody]

The problem with scientific papers is that there are plenty of views, for example:
P.J. Mumby, et al, (1995), A Critical Assessment of Data Derived From Coral Cay Conservation Volunteers, Bulletin of Marine Science, Vol 56, No 3, p.p. 737-751.
This study, which I was part of, confirmed NN effected the accuracy of observations which deteriorated progressively from 15m to the max survey depth of 30m.

That was exactly my point. Science is not yet 100% on a few subjects. Then, we say maybe, maybe not. I don't know. I am not sure. I got crucified because of that.

 

[David Novo]

That was exactly my point. Science is not yet 100% on a few subjects. Then, we say maybe, maybe not. I don't know. I am not sure. I got crucified because of that.

I do not think that it was anyone's goal to "crucify" you.
Narcosis sneaks on you, sometimes without you realizing and, from your description, it seemed to be the case.

 

[Storker]

I got crucified because of that.

Don't play the victim. Several very competent divers have tried to point out to you where you messed up. And have tried to show you how to avoid making those mistakes again. Because we've all been there and realize what kind of stupid unnecessary risks we took. "But for the grace of God..."

If you choose to take that as a personal attack, that's totally on you. But I'd rather see that you learned from those who already did those mistakes and got away with them. Because I'd hate to read about you in A&I.

 

[KenGordon]

That was exactly my point. Science is not yet 100% on a few subjects. Then, we say maybe, maybe not. I don't know. I am not sure. I got crucified because of that.

The thing is, everyone on this thread will have had some personal experience of nitrogen narcosis. Claiming the science might not support nitrogen narcosis being a thing at 40m is like saying alcohol has no influence. People have personal experience.

Your experience is much narrower and you ought to realise that reading a paper, or indeed a forum, is no substitute for personal experience. If you take one thing away from this thread I would hope it would be to gain more experience shallow before going deep.

 

[Celt]

The purpose for rule of thirds is to get yourself and your buddy safely out of an overhead environment to open water. A third of the gas to go in, a third to come out, and a third left in reserve. As @Storker quoted above it's use is rather restrictive for open water except for one condition: where you descend, swim out, and must return to the entry point (i.e. descent or anchor line). Some plausible scenarios might be situations where one could pop up in heavy boat traffic, or on a night dive in heavy seas, or in high surface currents.

The rationale for the rule of thirds is based on a worst-case scenario where one of the divers has a catastrophic gas loss at the furthest point in the overhead, and both divers must share gas to exit safely. For those of you who are unfamiliar with how to calculate rule of thirds, here is an example:

Diver 1 uses an AL80. Tank factor = 3000 psi / 80 ft3 = 37.5 psi/ft3.
Diver 2 uses a steel 95. Tank factor = 2400 psi / 95 ft3 = 25.3 psi/ft3.

Tank factor is rated pressure divided by rated volume. Base the turn pressures on the lowest volume of the two divers which is Diver 1. To surface with a reserve pressure of 400 psi the turn pressure of Diver 1 is 3000 - ((3000 - 400) / 3) = 3000 - 867 = 2133 psi. The volume of this gas is 867 / Diver 1's tank factor = 867 / 37.5 ~ 23 ft3.

To calculate Diver 2's turn pressure multiply Diver 1's usable 1/3 volume with Diver 2's tank factor and subtract from full pressure which equals 2400 - 23 x 25.3 = 1818 psi.

Whichever diver hits their turn pressure first, turns the dive and both divers head back to the starting point.

Is there some way to save some posts like this? I’m on a mobile phone. Great info.