Nitrox vs. Regular Air?

[espenskogen]

Nitrox? Why the heck would anyone want to dive Nitrox for? Trimix is where it's at. All the advantages of Nitrox without all the narcosis.

I'd like to see the schedule for the poor sod trying to deco on a 18/40 mix.. Would be spending some time on the 3 meter stop...

EDIT: And here's the schedule for that dive done with 18/40, 55 and 100, and lost gas scenarios to illustrate


-- lost gas -->

OK 55 100 Both

78 (12) (12) (12) (12)
48 0 (16)
42 1 (17) 1 (17)
36 1 (17) 1 (18) 1 (17) 1 (18)
33 1 (18) 1 (19) 1 (18) 1 (19)
30 1 (19) 1 (20) 1 (19) 1 (20)
27 1 (20) 1 (21) 2 (21) 2 (22)
24 2 (22) 2 (23) 1 (22) 2 (24)
21 2 (24) 2 (25) 3 (25) 2 (26)
18 4 (28) 3 (28) 4 (29) 3 (29)
15 4 (32) 4 (33)
12 1 (30) 5 (37) 1 (31) 6 (39)
9 3 (33) 8 (45) 3 (34) 8 (47)
6 4 (37) 5 (50) 6 (40) 12 (59)
3 7 (44) 8 (58) 9 (49) 24 (83)

E

 

[Age]

All the NAUI books are metric-enabled. In fact, they usually write things like, "...still for actual depths from 21 meters (70 feet) to 33 meters (110 feet),..." (p. 55). Examples may be in "U.S./Imperial", but they are usually accompanied by metric examples (or "The procedure is identical in an S.I./metric calculation." for some that are trivial). All the charts are either multi-system (dive tables) or in pairs (figure 4-1a in fsw, with figure 4-1b in msw right below).

(They're called "NAUI Worldwide", so it'd be a crying shame if we couldn't work in meters and bars. On second thought, forget the meters. )
Well, I seem to be flat out of firstborn, for one.

Quite frankly, I don't know how you guys manage with feet and inches. Happily my instructor has advised that he has metric tables. Let's hope the exam is too, because I signed up for it today. Thanks to all for your time and advice.

 

[ACR]

Quite frankly, I don't know how you guys manage with feet and inches. Happily my instructor has advised that he has metric tables. Let's hope the exam is too, because I signed up for it today. Thanks to all for your time and advice.

The NAUI exam that I took had both.

It's way easier to divide by 10 msw than by 33 fsw... of course that all goes out the window if you're talking fresh water (and want to be accurate)...

 

[mempilot]

Why would someone deco out on 18/40???? That would be absurd.

I'd like to see the schedule for the poor sod trying to deco on a 18/40 mix.. Would be spending some time on the 3 meter stop...

 

[Blackwood]

Why would someone deco out on 18/40???? That would be absurd.

Loss of deco gas.



They wouldn't. He wrote that in response to your post which, read literally, could imply that Nitrox is pointless.

 

[mempilot]

Loss of deco gas.



They wouldn't. He wrote that in response to your post which, read literally, could imply that Nitrox is pointless.

LOL. Take it easy champ. No one stated Nitrox is pointless. My post was to imply that putting one more gas in the mix gets rid of the last effect that Nitrox can't.

His post about deco'ing out on 18/40 with a lost deco gas scenario is a poor attempt to make trimix look invaluable since the TTS would be impossible. On a dive requiring 18/40, you'd be looking at a MOD of 260 fsw and a TOD of around say 220 fsw if one was looking for a max 1.4 PPO2. Deco'ing out on back gas is impossible for this dive, and I'll let you do your math to figure that one out. I would carry multiple decompression gasses for this dive, both of which would contain enough gas in themselves to deco out on. My back gas would be 18/45; and, I'd probably carry an AL80 of 30/10 and an AL40 of O2. On a planned 20 minute bottom time, the RT would be 67 minutes. Lose the AL80, and the RT would be 95 minutes with the majority of deco at 30 and 20 fsw. Lose the AL40, and the RT would be 92 minutes.

The only way, and it would be catastrophic unless there were contigencies in place, that one would use 18/45 to deco out on would be to lose multiple deco gasses and not have a buddy to pass you either his deep trimix deco gas or shallow O2 bottle. BTW, with a loss of O2, there is no reserve in the AL80. With a loss of 30/10, there is still a significant reserve of O2.

Anyway, my original post was just to point out the next logically step from Nitrox, even for recreational dives, which is what this thread was about anyway until he brought up 18/40, is to move on with Recreational Trimix. Diving NDL tables with a squirt of He in the bottle makes for an excellent dive, narcosis free.

Anything else is absurd!!!!

 

[Blackwood]

LOL. Take it easy champ. No one stated Nitrox is pointless.

? I am taking it easy. I understood your post. I just think he replied interpreting it differently.

Maybe I should stop trying to interpret/explain other people's posts





FWIW, I agree that a dive on 18/40-45 is a two bottle dive at least (a 120-bottle and even a 190-bottle may be advisable depending on reserve gas requirements). But that's beside the point, and a topic for a different thread.

 

[String]

If lower nitrogen loading reduces the likelihood of DCS for any given dive (with respect to doing an identical profile in identical conditions, environmental and physiological), then it follows that using nitrox instead of air must have that benefit.

What follows on paper isnt always what actually happens in the real world. The change if any at all was found to be statistically insignificant on the only large scale study into determining if diving nitrox on air tables reduced the risk of DCS. Real world tissues may not obey tissues and just because something seems "obvious" on paper doesn't mean it is in reality.

 

[String]

No empirical proof is necessary, it's true by definition (assuming the IF statements are true).

No its not. You're assuming that tissues react in a simplistic way. The benefit if any maybe a lot lower than logic would dictate. Real life effects can be so small as to be insignificant or masked by many other factors.

 

[ClayJar]

Real life effects can be so small as to be insignificant or masked by many other factors.

I would assume, given the sample to which I have been exposed, that the vast majority of divers do not pay careful attention to their (momentary) ascent rates. That in itself should easily be a confounding factor of sufficient magnitude to render nitrox vs. air statistics meaningless. That does not mean that there are no benefits, only that there are plenty of people who don't dive with as much consideration as I. (Sadly, studies have not generally filtered their subject membership nearly as much as I have filtered my diving.)