Some Comments after Nitrox Certification

[MikeFerrara]

How to dive nitrox for recreational divers.

1. Get the guy in the dive shop to analyse the gas with the shop's analyser.
2. Look up the MOD on your slate.
3. Set your computer to the O2 percentage.
4. Go dive. Do not exceed the MOD

Now which bit did you say wasn't covered in your course?

Chris

I don't have a computer. Could you explain that again?

or...This rental computer is different than the others I've used. I'm pretty sure that I set the mix right but I'm at 70 ft and I'm not sure the PPO2 display is right. I know I'm above my MOD but can I trust the NDL display? Isn't there a way that I can at least estimate PPO2 to do a logic check on the computer? I could just end the dive and go through all the screens on the surface to make sure that it's set up right but shouldn't I be able to get an idea what's going on right here without trashing the dive?

Aside from all that...check your own gas. Better yet, every one diving together should check their gas on site and sign off on each others gas.

Something that really happened. A trained, certified and bonified gas blender had to mix some nitrox for a customer. The blender, not being real great with math uses PC software. ok, gas is mixed, analyzed and the happy customer leaves to go do their dive. I walk by and see the blending software output still on the screen and ask about it. I'm told that it's John's gas. I say no way, what would he be using that for. There were two tanks mixed and one was still there. I check the calibration of the analyzer and check the tank and it comes out ok. I suggest that the blender may have mixed correctly dispite the wrong software output and I'm ready to let it go. The blender swears they mixed per the software output. Something isn't adding up. Both can't be true. I swap out the fuel cell and check the gas again and things are not ok. the Blender spends the next hour on the phone trying to reach some one who can stop poor John from getting in the water with that tank. Fortunately John and his buddies checked his has again like they had been taught and caught the problem even before any one caught up with them.

It was a really freak thing where a data entry error resulted in the wrong output in the blending software and just the right failure in the analyzer caused the gas to test exactly as expected. What are the chances? Multiple failures that wouldn't have been caught without multiple checks. Me, being a math sort of guy who usually doesn't use blending software caught the mistake at a glance but no one else did. The divers were vigilant enough to check gas on site, even though it had already been checked and had some one looking for them to make sure that they did. It turned out ok. The diver got his mix fixed before the dive and the other mixed tank in the shop was fixed before anyone picked it up but it was close. If John had dived to his planned depth with that mix there is a very good chance that he wouldn't have survived. If John and every one else involved would heve used your simple outline, he'd probably be dead. The blender and I would be worse than dead. The diver who picked up the other tank might not have checked it and they too could have been in real trouble.

ok the universe may never align itself in such a way for the exact same thing to happen again but I wouldn't count on it. If it does though, lets hope that the interested parties catch it when computers spit out numbers that are out of wack.

 

[stardiver]

I want to start by saying that, in case anybody doesn't know it, I'm in the same camp as the OP. I want to know the WHY, and drove my OW instructors crazy with it.

That said, I've done PADI classes through Rescue, and NAUI Nitrox, and one of the comments I immediately made about the NAUI class was how much better, and better written, I thought the Nitrox teaching materials were than anything I had gotten from PADI. Although not written at the level that would excite me (but I majored in math), it was still thorough enough, and had enough theoretical underpinning, to make me feel as though it was a very legitimate class.

There's a fairly current thread from someone who took ADVANCED Nitrox and felt the same way. The problem is that there doesn't appear to be any class that teaches what I (and I suspect the OP) want to know about this stuff, or if there is, it's so far up the technical diving ladder that our actual DIVING skills won't let us take it. Thus my burgeoning library of books and downloaded documents . . .

I know what you mean, TSandM.

When I began to teach nitrox, it was the NAUI nitrox program in its infancy. You would have liked the course even more than current one. Information on physiology of O2 in the body was rich at least for the non-medical person. Your dives were done noting your depth and tank pressure every few minutes so that during the debriefing, you could calculate your gas consumption and your O2 load. You hand-graphed your profile and it was my experience that students liked doing this. It was easy to see that oxtox is unlikely using mixes of less than 40% for recreational profiles for repetitive dives. Of course this is not done again, but students enjoyed doing it once. I think it gave students a real feeling of empowerment to know the things in that course that are being phased out now. But then, I see most every incidence of dumbing down as an insult to the student, no matter the topic.

Perhaps in your course you were fortunate and your instructor still taught some of these "older" methods.

If you have a chance and would PM me, I'd love to know who your instructor was. I'm relatively new to the Puget Sound area.

 

[Web Monkey]

The blender swears they mixed per the software output. Something isn't adding up. Both can't be true. I swap out the fuel cell and check the gas again and things are not ok. the Blender spends the next hour on the phone trying to reach some one who can stop poor John from getting in the water with that tank. Fortunately John and his buddies checked his has again like they had been taught and caught the problem even before any one caught up with them.

I picked up a couple of Nitrox fills at a shop in Tobermory (I won't say which one, but it has a good view of the docks )

The girl behind the counter was "analyzing" tanks by hooking them up to the analyzer and cranking the adjust knob until it said "32%".

Now I bring my own analyzer.

Terry

 

[theatis]

I didn't notice any comments on the EAD explaination that I gave in answer to the original post. Did it answer the question? Were there any parts that weren't clear?

Hi Mike, that was just an example to illustrate the problem, I actually kind of figured out the logic behind all the formulas on my own (MOD and COD would obviously be more readily apparent under the Metric system but we can't ask for everything ). However, your explanation was exactly the type that I wish was in the text. I agree with everyone's point that the instructor is a great resource, but my main complaint is with the text to begin with.

 

[theatis]

How to dive nitrox for recreational divers.

1. Get the guy in the dive shop to analyse the gas with the shop's analyser.
2. Look up the MOD on your slate.
3. Set your computer to the O2 percentage.
4. Go dive. Do not exceed the MOD

Now which bit did you say wasn't covered in your course?

Chris

If this was a response to my opening post, there is really no way to respond to it, since all it does is completely circumvent my argument. What you state was definitely covered in my course but I'm sure you agree that this is only a practical application with no theory whatsoever. So, your answer to NetDoc's supposition 'theory vs. practical application' is no theory at all? And, going by the above, your answer to me is 'you don't need any more theory?'

 

[Rick Inman]

As far as the theory presentation for a nitrox class, I always liked the way the IANTD texts presented it about the best. The use the circle devided into three parts with "gas pressure" above and "pressure" and gas "fraction" below. If you haven't seen it, it might be hard to picture from my descroption but it's a nice graphical representation that clearly shows the relation ship and how to rearange the equation to solve for any quantity you need.

__PPO2
___________
FO2 | ATA

 

[cerich]

I picked up a couple of Nitrox fills at a shop in Tobermory (I won't say which one, but it has a good view of the docks )

The girl behind the counter was "analyzing" tanks by hooking them up to the analyzer and cranking the adjust knob until it said "32%".

Now I bring my own analyzer.

Terry

I hope you also said something to the shop.

 

[DivesWithTurtles]

If this was a response to my opening post, there is really no way to respond to it, since all it does is completely circumvent my argument. What you state was definitely covered in my course but I'm sure you agree that this is only a practical application with no theory whatsoever. So, your answer to NetDoc's supposition 'theory vs. practical application' is no theory at all? And, going by the above, your answer to me is 'you don't need any more theory?'

My answer would be, "That's correct, you don't need any more theory". (You may need a little more practical application than stated, but I believe that was a bit of humor there.)

If you, like me, want more theory (I have studied well beyond just practical application), it would be no problem shopping around a bit to find an instructor willing to cover anything you want to cover, including providing an advanced nitrox education and cert along with the basic nitrox cert. Of course, you'll have to spend more time and money. Or, study on your own from the readily available resources. But don't mandate that level of knowledge for everyone. It's just not necessary for safe use of nitrox, and would be a waste of time and money for many.

 

[H2Andy]

__PPO2
___________
FO2 | ATA

peepeetwo effohtwo ayteeay to you too, pal

(i speak spanish and i have no clue what that means, so it must be italian)

 

[The Chairman]

All the non-engineers in the room now understood the principles of partial pressures and variation with depth.

I tried using colored marshmallows. What a pain! They were the miniature size and I bought two of the multicolored types. I have a graduated cylinder and several baggies with 8 green and 2 blue marshmallows in them. Every baggie represented an atmosphere and they soon got the concept.

Finding these colored marshmallows is a royal pain. However, I found that once they visualised it the equations were easier to comprehend.

Last night I tuaght yet another easy NitrOx class. SDI's material had already gotten them past the pain zone for the concept and so we spent most of the time filling in gaps for being a safe diver (both off and on NitrOx).