Nitrox on boat with air refill

[rx7diver]

rx7diver, PPO2=1.6 may have been "recreational" in 1993 when you first learned about Nitrox, but it is not anymore.
You need to recognize that we have gotten smarter since 1993.

tursiops,

I don't think I personally would ever choose to do the working part of a recreational dive at PO2 = 1.6 ata. However, I would certainly use PO2 = 1.6 ata for dive planning—as I've done in the two examples I posted above. (In those two examples, using the next deeper depth pushed the PO2 from 1.5 ata to 1.6 ata.)

Safe Diving,

rx7diver

 

[Centrals]

You did your calculations wrong.


Even if you did a 30 minute dive at a PO2 of 1.6, your single dive exposure is only 67%. At 40 minutes, 89%. When you consider 90 minute half time (why wouldn't you?) you're still starting your second 30 minute dive at 34%, your 40 minute dive at 45%. In fact, the only way to actually exceed 100% CNS loading is to specifically make 2 dives for 40 minutes at a PO2 of 1.6, both of which are beyond your NDL in the first place, and thus not subject for discussion.

You've gotta use the right math to get the right numbers. You can't arbitrarily choose conditions just to try and make it work in your favor. Remember, we're not talking random hypotheticals, we're talking an actual planned dive that goes to plan. Your planned dive in fact.

Making up rules to suit your internet argument is SUPER lame.

He has to kicks out the 90mins half time to suit his calculation!!

---------- Post added November 15th, 2015 at 12:23 PM ----------

PPO2=1.6 may have been "recreational" in 1993 when you first learned about Nitrox, but it is not anymore.
You need to recognize that we have gotten smarter since 1993.

The whole exercise was to plan two consecutive recreational dives to see if one can exceed the CNS%permitted.

 

[JohnnyC]

JohnnyC,

I used the NOAA CNS oxygen exposure table seen in the linked article (by Doppler). This is the table I committed to memory a very long time ago, before my hair and beard turned completely grey, in fact.

Safe Diving,

Ronald

And you are still dead wrong. I proved it to you with the same data that's on that table.

You manipulated the dive profiles using incorrect information and some wild assumptions to shoehorn it into your argument. You're obfuscating the issue by trying to add in EAD's and SAC rates and such, but none of that matters.

You clearly didn't read any of the glaring proof that I posted, because it totally kills your argument. You. Are. Wrong.

Look, I can keep trying to explain it to you, but I can't understand it for you.

That you choose to ignore even the most glaring of information simply means that you are unwilling to admit that you are wrong. That doesn't change the fact that you are wrong.

 

[NAM001]

The problems with higher PPO2 is pretty linier to about 1.65 i think and then it increases almost in a log function. 1.6 is as good as ever was. We have just backed off of using 1.6 for the dive and went to 1.4 for the continuous limit. 1.6 is still ok for a dip such as to pick up a tool ect. We still use for deco limit although there are considerations that make that safe compared to 1.6 through out the dive. Ill have to find that chart also to add to the post.

 

[JohnnyC]

It doesn't matter. He's picking and choosing rules to follow in order to make his calculations work, and then contradicting his own made up rules to suit. Nobody dives at even 1.5, let alone 1.6 for a half hour. Hell, they'll run you at 2.0 in a chamber ride. The point is, he's using dive parameters that are outside the realm of a reasonable recreational dive, while ignoring other factors just to try and prove his point. Which, coincidentally, has been so thoroughly disproven I don't even know why he would continue posting here.

 

[KenGordon]

... and nitrogen was something like 45 in half life and that runs the bar graphs on the computer ...

Dissolved gas models have more than one half time for nitrogen to simulate different kinds of body tissue. Which of those limits the dive depends on the profile.

If the books you are going to pull out are agency manuals I'd recommend an upto date specialist text instead.

 

[NAM001]

I was not trying to suggest all tissues were the same time. The slow tissues don't even come into play in the rec world its the fast tissues that count. I did some looking on the net and ti is the out calculations that are pretty linear till about PPO2 pf 1.65 and they skyrocket. You can see the effect between 1.5 and 1.6 going from 120 min to 45 min per dive. I believe the first tissue is the controlling for rec diving ideally. I know its too complex to break it down this simple of statements. Im trying to speek form the NDL arena.

Dissolved gas models have more than one half time for nitrogen to simulate different kinds of body tissue. Which of those limits the dive depends on the profile.

If the books you are going to pull out are agency manuals I'd recommend an upto date specialist text instead.

 

[KenGordon]

I was not trying to suggest all tissues were the same time. The slow tissues don't even come into play in the rec world its the fast tissues that count. I did some looking on the net and ti is the out calculations that are pretty linear till about PPO2 pf 1.65 and they skyrocket. You can see the effect between 1.5 and 1.6 going from 120 min to 45 min per dive. I believe the first tissue is the controlling for rec diving ideally. I know its too complex to break it down this simple of statements. Im trying to speek form the NDL arena.

It depends on the profile, if you go deep first and then hang about in the shallows the fast compartments will have caught up and a slower one may become the limit. Similarly over a number of dives. During the surface interval the fast compartments get rid of their nitrogen but you get back into the water still loaded up in the slower ones.

Here fast means 5 minutes or so.

 

[Centrals]

I finally found the time to hand-calculate an example that demonstrates (to some degree) that a diver should be concerned with CNS oxygen exposure even when diving only recreational profiles--when subsequent (i.e., repetitive) dives are done using an EAN cylinder that has been topped up with air (from the dive boat's compressor). The example in detail winds on for several hand-written pages. To simplify the presentation, I will first post a simple example. Then I will post the full example. The simple example actually suggests the critical elements that make the full example "work."

9. For dive planning re CNS oxygen exposure, do NOT give credit for oxygen half-life.

This is the critical element to make your calculation work!!!!
You cannot arbitrary remove a known constant from your calculation in order to serve your purpose.

 

[NAM001]

I don't see that happening. Remember I am referring to NDL and you cant get a slower compartment to fill before a faster one. Of course you can fill say 3 compartments and then do a SI and have the slowest not full and the slower ones still full,,,, but you have left the NDL criteria presumed to be associated with rec diving. full means you are no longer diving NDL and the slowest fills first. No way around it.

It depends on the profile, if you go deep first and then hang about in the shallows the fast compartments will have caught up and a slower one may become the limit. Similarly over a number of dives. During the surface interval the fast compartments get rid of their nitrogen but you get back into the water still loaded up in the slower ones.

Here fast means 5 minutes or so.