Nitrox on boat with air refill

[Freewillow]

The unbelievable comments and the stubbornness of the so called "tek divers" is unreal.

That reminds me of a statement from a french decaesed comics: Coluche.

Here is the statement in it's original version : "Quand on est mort, on ne sait pas qu'on est mort, c'est pour les autres que c'est difficile....... quand on est CON c'est pareil !!!"

Here is the rough translation: " when one is dead, one does not know ( realise) that he is dead. It's for the others that it is painful.......well for an idiot, it is sadly the same phenomenon"

Happy discussion, I am going out of this threat. I have heard enough from self acclaimed "scientists". Fed up

Freewillow, Ph.D in sciences ( gained in a University, not on a forum .

 

[IVC]

IVC - The point is that in recreational diving, it is highly unlikely CNS or OTU will be a factor in single day diving. Even at the richest of mixes, you would need significant amount of dives to go over either.
...
Oh and NDL is not about O2 exposure.

Thanks - the point is that the calculation and estimates you show are why it's not a factor. There is no magic "you'll be fine because only tech divers worry about CNS or OTU." My concern was that I was in position where I both: (1) didn't/couldn't do the calculation, and (2) couldn't use my computer to get an answer. This left me with blind faith that it would all be good, which is the position I wouldn't like to be in while diving.

And for the O2/NDL, I messed it up rushing to respond and, in a way, I'm glad I'm catching heat for it since we have to be accurate and precise in diving. (Incidentally, that's why I was seeking answer in the first place.)

 

[packrat12]

It can be fun at first. Run a number of scenarios and you will see that you will be well clear even in the most extreme recreational dives that you plan to dive. You must really work to get beyond CNS or OTU. The bigger issue is pushing your NDLs while believing you have a richer mix when you actually are more lean. That could lead to an interesting chamber ride. This is why everyone is saying that they would set it to air. With the mix being richer then set, you will just have a better safety margin for NDL. My rec computer will reset itself back to air as a safety factor if you do not dive before it shuts down. I hate the feature but the manufacturer thought it was better to do it. The idea again is that at worst case you come up with more time away from NDL.

I have had a tech dive where I did unexpectedly hit 100% once. Really was surprised because I expected about around 80 something. Found out that my computer penalizes you at 1% per 4 seconds for all time spent with a PPO2 above 1.61 (I think). I did spend time to figure out why I had the difference. Nothing wrong with curiosity.

I would recommend getting an analyzer. It does have a peace of mind factor. I carry mine on the boat and will analyze all of my gas, even air. I also lend it out as necessary.

 

[IVC]

I would recommend getting an analyzer.

Already have, even before I started this thread.

Between analyzer, keeping better track of initial/final pressure (before they start filling up my tank,) and doing some calculations to get good estimates, I think I'm ready for worry free dives with "mystery mixes."

 

[Centrals]

Here is my thinking:

1. First of all, for these *recreational* dives, I would be completely comfortable using a P02 of 1.5 ata. So, I would be completely comfortable using NOAA Nitrox II at 100 fsw. (Moreover, this is completely consistent with what was taught in the IANTD Nitrox course I took in 1993 or so.)

2. For *planning* these 100 fsw recreational dives, I would compute using a max depth of 110 fsw (rather than 100 fsw), for which EAN36 has a corresponding PO2 of 1.6 ata, which has a NOAA CNS oxygen limit of 45 min.

Keep in mind, I am assuming you have only someone's (US Navy in my case) standard air tables, an oxygen analyzer, and a pencil and slate (and, maybe, a calculator).

Freewillow, Centrals, et al, does this additional detail help? If I can find some extra free time, I'll actually run through the hand calculations. It will be a fun exercise, and, besides, I'll get a chance to use the new iPhone HP 15C calculator app (reverse Polish notation) I recently purchased from Hewlett Packard!

Safe Diving,

rx7diver

I can't wait to see your result!!!! It won't take more than 5 mins for the calculation so please do not drag your feet.
I learnt how to calculate the CNS% and OTU without any App back in 1998(IANTD Adv Nitrox). It is just simple arithmatic not any complex calculus.

A quick glance at NOAA CNS Exposure Chart
A dive of 30mins at PPO2 of 1.6 will accumulate 66%. The half life is 90mins.

 

[1978davidw]

fill the tank and dive as air.. dont pay attention to all the scientific , lets calculate each and every percent of 02.. I say BS.. its not needed your not going to be anywhere near your maximum exposure for oxygen and setting your computer for air on the subsequent dives just gives you a bit of a safety factor..So dive and have fun.

 

[rx7diver]

I can't wait to see your result!!!! It won't take more than 5 mins for the calculation so please do not drag your feet.
I learnt how to calculate the CNS% and OTU without any App back in 1998(IANTD Adv Nitrox). It is just simple arithmatic not any complex calculus.

Centrals,

Please don't wait on my account! Have at it, if you wish. And, if you wish, show your result here. When I have time, I'll do likewise. Then we can compare our two results. And we'll get to see if my suspicions bear out. Now, won't that be fun??!!

Safe Diving,

rx7diver

 

[packrat12]

Centrals,

Please don't wait on my account! Have at it, if you wish. And, if you wish, show your result here. When I have time, I'll do likewise. Then we can compare our two results. And we'll get to see if my suspicions bear out. Now, won't that be fun??!!

Safe Diving,

rx7diver

Centrals did provide a solution on post #58 although I do not think Centrals accounted for 2hr SI (he used 1hr), air refill and for subsequent NDL as this is a recreational dive. Even with that in mind, he still did not limit out.. We are waiting on your example of how your proposed dive actually exceeds CNS and/or OTU limits. Remember that you stated that this easily exceeds the limits. I would require that any solution be to the proposed dive and not using next depth or next time rounding as you indicated the proposed dive will exceed the limits. I did mine quickly and it indicates that when ready for the 3rd dive, I would only be at 1/3 OTU and around 11% CNS - Far from exceeding any limit, which is what we are saying here. This was in spite of using a higher PPO2 then any agency recommends for the work portion of the dive.

 

[Freewillow]

s. And we'll get to see if my suspicions bear out. Now, won't that be fun??!!

Safe Diving,

rx7diver

Not a chance in a million Dr rx7diver.

Like Packrat and many others have told you already. I am impatiently waiting for your calculation. It's a bit late for the Nobel prize this year, but who knows, 2016 ? :cheerleader:

 

[Centrals]

Centrals,

Please don't wait on my account! Have at it, if you wish. And, if you wish, show your result here. When I have time, I'll do likewise. Then we can compare our two results. And we'll get to see if my suspicions bear out. Now, won't that be fun??!!

Safe Diving,

rx7diver

I have been trying very hard to plan two consecutive recreational dives that will exceed 100% CNS but without any luck. Therefore I got nothing to show.
I hope you can enlighten me on this.

---------- Post added November 11th, 2015 at 09:18 AM ----------

Not a chance in a million Dr rx7diver.

People do win the lottery.
I wonder how long we have to wait for his calculation/plan?