No Technical Training for Me.

[Rick Murchison]

I'm a 100% guy, this is why

1. Cave diving and lakes, I don't have to worry about not being able to hold a 20 foot stop

2. warm fuzzy factor for me, 100% o2 at 20 cleans N2 faster than 80% at 30, (80 is slightly faster get you out of the water gas as you get on higher ppo2 sooner) this is not an absolute statment that 80% is a better deco gas, or that 100% is a better deco gas, in the end as long as you do your crap right you get out clean, 80 or 100, I just want to make sure my warm fuzzy factor is understood that my statement of 100% is faster is in the context of the amount of gas removed AT THAT STOP not over the entire deco.

3. I dont' have to mix 100%

4. I don't mind an extra couple minutes of deco to keep from mixing 80%

5. I don't mind a couple clicks on the o2 clock to keep from mixing 80%

Now there's a good sound case for 100%

I can't help but think if Gi3 had never existed, this thread wouldn't have either.

Truer words would be hard to find.
Rick

 

[wedivebc]

2. warm fuzzy factor for me, 100% o2 at 20 cleans N2 faster than 80% at 30, (80 is slightly faster get you out of the water gas as you get on higher ppo2 sooner)

Good post, just want to clear something up; if 80% gets you out of the water sooner why does O2 give you a cleaner deco? How do you know it is a cleaner deco? Isn't the whole point of deco to reduce the supersaturation of inert gas to a level where it is safe to surface? So why is one gas "cleaner" than another?

 

[FIXXERVI6]

Good post, just want to clear something up; if 80% gets you out of the water sooner why does O2 give you a cleaner deco? How do you know it is a cleaner deco? Isn't the whole point of deco to reduce the supersaturation of inert gas to a level where it is safe to surface? So why is one gas "cleaner" than another?

Not cleaner deco, I'm saying at a given stop, 100% will pull N2 out faster than 80%, but thats at a given stop, overall 80% is faster as you get on it sooner, as far as cleaner goes if you do all your stuff right you come out clean on 80% or 100%, only way 100% would get out out cleaner is if you rushed the 80% or if you hung on 100% long enough to clean out all your N2, but I suspect you'd have some oxygen issues before that happened

Same as 50%, if you do a dive to 130 feet and use 50% as your deco gas you'll get out a little faster than just using 100%, but the 100% stop you will pull nitrogen out faster (more nitrogen in a given amount of time offgased) but for the overall deco the 50% is faster as you start cleaning up sooner.

Not sure I'm explaining it right

 

[loosebits]

We're misunderstanding him, he means that O2 will remove N2 from your system faster but since you can get on a leaner mix ealier, a leaner mix may get you out of the water faster since you are on it longer.

 

[FIXXERVI6]

The warm fuzzy factor point 2. was just that, a "warm fuzzy factor" for my personal factor, doesn't matter if it TRUELY is better or not, it gives me warm fuzzies, so point 2 is just a personal perspective, not really a valid point in if 80 is better than 100 or vise versa

Just explaing why I"m a 100% guy not making an argument that 100% is better than 80

 

[wedivebc]

The warm fuzzy factor point 2. was just that, a "warm fuzzy factor" for my personal factor, doesn't matter if it TRUELY is better or not, it gives me warm fuzzies, so point 2 is just a personal perspective, not really a valid point in if 80 is better than 100 or vise versa

Just explaing why I"m a 100% guy not making an argument that 100% is better than 80

Never underestimate the placebo effect
You made some good points. It is refreshing to hear solid arguments as opposed to Irvinisms spouted by the flock.

 

[ClayJar]

Okay, although perhaps I ought to think twice before posting here, physics beckons...

I guess I don't understand the situation or something. Your reason for not wanting 100% is because you can get shoved down 10' or so during a down current. I get that, but 80% doesn't change anything.

Actually, 80% *does* change things. As the fraction of oxygen is lower, obviously the partial pressure of oxygen is lower, and the increase of partial pressure with depth is also reduced.

100% oxygen at 20' gives you a partial pressure of oxygen of 1.606 atm. To reach a partial pressure of 2 atm, you would have to descend (say, in a downcurrent) to 33'. The difference is, obviously, 13 feet.

80% oxygen at 30' gives you a partial pressure of oxygen of 1.527 atm. To reach a partial pressure of 2 atm, you would have to descend to 49.5'. The difference there is, also obviously, 19.5 feet.

Perhaps the 6.5-foot difference isn't significant in actual diving, perhaps it is. I don't know enough to say. I will say that it's 50% more margin on 80% (as apparently used according to the information I've read) than on 100%, however, so it would seem to be not entirely correct to say it is nothing. (That said, I haven't run any deco numbers or anything like that, so *all* I'm commenting on is the depth cushion.)

 

[Rick Murchison]

Yea, I know. But...I doubt it has much effect on PPO2.

Now ye're talkin' 'bout some "pretty" math! The variables are wave height, period, and how much your body moves up and down as the waves pass... It is sufficient to say that if you can feel the up & down then there's probably enough affect to make your stop somewhat less exact and more prone to unpleasant fizzies than you'd like - and we can definitely say that "deeper is better" from that perspective alone, so choosing a leaner deco mix (up to a point) can make good sense if you want to complete your deco at, say, 30 or 40 FSW.
FWIW, and just for fun, for N₂ offgassing, using the EAD principle, here's a little table you could use (could use... I do not recommend it!) that "bottoms out" at either 1.6 PPO₂ or an EAD of 10', whichever's shallower. I've chosen 10FSW as the limiting EAD because I have reliable tables that finish on air at that depth...
80% - 33' - limit 1.6 PPO₂
70% - 42' - limit 1.6 PPO₂
60% - 52' - limit 10' EAD
50% - 35' - limit 10' EAD
So it looks like if you really wanted to finish deco as deep as is feasible, you could get 50' on EAN60.
Are we havin' fun yet???
Rick

 

[Rick Murchison]

It is refreshing to hear solid arguments as opposed to Irvinisms spouted by the flock.

Hear hear! On that note I think I'll have a wee spot o' Añejo
Rick

 

[*Floater*]

I'm not an advocate of 80% nitrox for deco gas (nor against it), but if someone wanted the ppO2 of 1.6 with it, then they could just do their 30' stop at 33' instead.