Why not 30%?

[BobK]

Maybe it's "perfectly sane", but wouldn't 30% be even more so? For me the extra risk is not worth a few extra minutes of hang time.

I have stated my reasons for the 30%, I am curious what yours are for the 32%.

Well then, I suppose 21% is even more sane then 30%. Probably could push it to 18%, then I bet your risk of Ox Tox would be virtually zero.

OTOH, Given the number of dives in Ginnies over the years (10s of thousands ?) and the number of Ox Tox incidents with diver's using 32% or greater (I don't know of any, I suppose there has to be at least a few), I don't see what the issue is.

As others have said, it's really a personal choice on balancing deco time with "risk of Ox Tox". I don't personally see any significant risk at PPO's of 1.4 and below for the amount of dive time I do at Ginnie. If you're going for all day dives lowering your PPO is probably a good idea. It's all part of planning the dive.

[FW]

...OTOH, Given the number of dives in Ginnies over the years (10s of thousands ?) and the number of Ox Tox incidents with diver's using 32% or greater (I don't know of any, I suppose there has to be at least a few), I don't see what the issue is.....

There was at least one, 3/9/02. It is on the IUCRR website.

[Jim Wyatt]

Of course 32% is the most common but it seems 30% should be for the many systems in the 100 ft range, keeping the 02pp below the 1.4 or 1.5 range.

I have a fill station at home. I fill for myself, a few friends and students. I have banked and dive EAN30 for a long time now in order to keep the PPO2 lower.

[Jim Wyatt]

If you're going for all day dives lowering your PPO is probably a good idea. It's all part of planning the dive.

How about for dives where you work very hard? Would you consider reducing PPO2 in that event?

Is swimming against relatively high flow in a cave considered "work" to you? It is to me....

[Jim Wyatt]

Navy divers in water recompression treatment includes O2 exposures to just shy of 3ATA (I beleive 60 FSW is the switch but it's been a long time sense I've looked at the tables it could be deeper). Chamber rides can also hit a 2 during their runs depending on what they are treating. OTU/CNS is just like any other dive/deco table and very conservative for 99% of the population on 99% of the days they dive.

Speaking as a former US Navy Diving/Salvage officer....I have done chamber rides & surface supplied working dives with PPO2's exceeding 2.0. The difference is we were on a mask in the chamber or in a hard hat where the convulsions from a tox event does not cause us to drown.....just gets bruises on your noggin'

[BillBowden]

Well, I keep my setpoint to 1.0 for most dives and only up it on deco, does that count?

Dive safe,

Celia

I use 1.3 which gives me @ 1.25 in the loop. How long are your dives running? In my old age I don't do dives much over 3 hours.
Bill

[crawford]

I usually show in Cave Country with air in my doubles from local diving, do a short shake down dive to check gear with the 21%, then top off on 32% for next several dives. This usually gives me 27-30% 02 for several dives, then I'll top off on air to keep it down around 28-30%...or do some short or shallow dives toward the end.

I also tend to keep air in my buddy bottle when solo so I have something lower to go to if I start to experience symptoms of ox tox.

[Marc Bryan]

Marc,

There is one shop (really close to you) where the analyzer almost always says 31 percent on my tanks when I check it, which I think is good.

That's because sometimes I get to fill the banks...

[Howard]

Okay I’m going to preface this by saying Ox Tox underwater is a really really bad thing and would be worse than DCS on any day. That said…

... I personally like higher PPO2 and lower PPN whenever possible for narcosis and deco (I don’t mind deco but if something comes up I’d rather be able to get out sooner). I’m even known to throw some HE in there even on shallow stuff just to make work of breathing easier among other things.

You may want to look into getting tri-mix training. It will change you outlook on reducing PPN by adding O2.
Right Idea.... wrong gas

[OneBrightGator]

Maybe it's "perfectly sane", but wouldn't 30% be even more so? For me the extra risk is not worth a few extra minutes of hang time.

I have stated my reasons for the 30%, I am curious what yours are for the 32%.

It may not be hang time, if you have to get out of the water early it could be the difference between a deco obligation or none. You'd have to run the numbers to find out how much though.

For me, I don't see much of a difference and you have to draw the line somewhere, there is no way to remove all the risk from this sport/activity. Most places pump 32% and it's within the ppO2 for all the major cert. agencies... good enough for me.