No Technical Training for Me.

[MXGratefulDiver]

Ok, what happens when you go from 30 ft to 40 ft quickly? My point is that 80% doesn't change the situation. Or are you suggesting using 80% at 20' to compensate? If you are, why not use 100% at 15' where you still have the same offgasing rate (because there is no N2)?

All the time. How does 80% fix this?

Gets you on the gas a bit sooner ... and a bit deeper where the surge isn't quite as bad.

Not a question of "fix" ... it's a question of "trade-offs" ...

... Bob (Grateful Diver)

 

[Soggy]

Gets you on the gas a bit sooner ... and a bit deeper where the surge isn't quite as bad.

Why half-*** it at 30'. If you want to start deeper, start deeper and bring 50%. 10 ft isn't going to change much.

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. Being on the gas sooner doesn't change anything. You still have the same toxing problems.

Aww, crap, I said I was done...

 

[MXGratefulDiver]

Why half-*** it at 30'. If you want to start deeper, start deeper and bring 50%. 10 ft isn't going to change much.

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. Being on the gas sooner doesn't change anything. You still have the same toxing problems.

Aww, crap, I said I was done...

Don't be "done" ... this is a mental exercise for me. I'm not advocating the use, per se ... just want to see the rationale (as opposed to the rhetoric) for doing so or not ...

... Bob (Grateful Diver)

 

[MikeFerrara]

Gets you on the gas a bit sooner ... and a bit deeper where the surge isn't quite as bad.

Not a question of "fix" ... it's a question of "trade-offs" ...

... Bob (Grateful Diver)

Now, I don't get in a bunch of ocean diving because we just don't have any of those in the county where I live.LOL but the last time I was in any surge worth mentioning was at about 65 ft and we saw everything about a half a dozen times. It didn't effect depth though.

We have some waves in the Grat Lakes though and once in a while you might do a little up and down but I don't think the depth guage notices because the surface is going up and down too.

I don't think rough water has much to do with it.

 

[Soggy]

We have some waves in the Grat Lakes though and once in a while you might do a little up and down but I don't think the depth guage notices because the surface is going up and down too.

At least in my neck of the woods, we deco on a fixed line attached to the boat, which is attached to the bottom. Topside waves move the line that you are usually holding onto up and down. There are techniques to mitigate this, but in really rough seas, it can be a pain (literally).

 

[deignor]

There are a number of reasons why 80% is a lousy choice. The biggest being that 80% is used "like" O2, except that it has N2 in it. N2 is what you are trying to get rid of. Additionally, it is used starting at 30 ft, which isn't even a PO2 of 1.6, so you aren't getting full benefit from the O2 window. At the 20ft and 10 ft stops on 80%, which is the most critical phase of the dive, the PO2 is roughly useless for decompression (1.2 and 1.0). On O2, the O2 window is always wide open regardless of depth since there is no inert gas.

You seem to be confusing the term "Oxygen Window" with the gradient of inerts. The Oxygen Window is the difference between arterial and venous PO2. By your reasoning, breathing oxygen at the surface would be "roughly useless" for treating DCS, because the PO2 is only 1.0.

Mike
mwpowell

Edit: Inadvertently posted on my wife's account.

 

[Rick Murchison]

One minute of advantage over a 90 minute period of time? Compare that to the added labor of mixing, the surface usefulness of O2, the fact that N2 does nothing positive for you....seems obvious to me.

One at the time... personally, I usually find that last minute of deco to be the most distasteful, especially if I'm getting a little cold. "The fact that N₂ does nothing positive for you"... have you figured out why you can shave a minute off your deco by using 80%? It is because you can offgas more of the dreaded N₂ quicker than waiting for 20' and 100%. So why not use it? All your arguments for using 50% apply to 80%.
Labor of mixing - huh? Pick a final pressure. Whatever it is, I have to do less boosting of oxygen by topping with EAN32 to get to 80% than to end up with 100%, and I'm all for that. Indeed, for the first bottle off a new supply bottle I can get my full 3000psi of 80% without any oxygen boosting. And I don't like to boost O₂ whenever I can avoid it... the bugger's in the boosting.
O₂ is definitely a better surface deco gas than anything else you can use. No doubt about it. But even that doesn't make 80% "silly." Or "antiquated" or "useless" or any of the other adjectives you've applied.
And if you really want people to think then you'll quit implying they're silly (or worse) for thinking differently than you do. You'll notice no one's characterizing the use of 100% as a single deco gas as "silly" - even if it isn't as good - from a staged decompression point of view - as 80%.
Rick

 

[loosebits]

I prefer O2 to EAN80 just because there's not much of a difference between the two in most profiles (one will usually only shave a few minutes off the other) so if I'm doing a profile that benefits from a rich deco gas, I'll use O2. Now the difference between 50 and O2 is significant enough that profiles benefiting from using 50 over O2 can do so enough to be quite significant so the pain of mixing is well justified.

Now, saying using EAN80 as a deco gas is silly is just nonsense. If someone doesn't mind mixing it and has an O2 kit on the surface for emergencies, why would anyone care?

Every dive has an optimal set of n deco mixes. For many profiles, 80 will be included in that set and O2 won't be.

 

[FIXXERVI6]

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%

I could see using 80% if I needed the volume but could not boost pure o2, I'd use 80%

I could see using 80% if for some reason a 20 foot stop wasn't doable, rough water, downcurrents whatever the case may be.

I find people that will only use 80% at any time for any reason under any condition are silly.

I find that people that will only use 100% at any time for any reason under any condition are silly.

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

 

[MikeFerrara]

At least in my neck of the woods, we deco on a fixed line attached to the boat, which is attached to the bottom. Topside waves move the line that you are usually holding onto up and down. There are techniques to mitigate this, but in really rough seas, it can be a pain (literally).

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