Not accelerating decompression?

[Red Sea Shadow]

Some old tech divers say that for extended range dives, having deco stages (especially for the rich mix) lower than 50% O2 is not accelerating decompression and the whole schedule should be calculated on air.

Personally I believe it's just another myth. What do you guys think?

 

[Kevrumbo]

Well if that's their practice and belief . . .I hope they have enough Air mix for the longer deco, and that they feel as well or better post-dive than those tech divers using Oxygen at 6meters, and eanx50 at 21m. . .

 

[Red Sea Shadow]

They still use their deco stages but plan the dive as if they were using air.

For instance, one might order a 50% stage but on analysis finds out that it's only 48%. He still uses the tank but re-plans his dive as if he's compressing on air!

 

[TSandM]

Well, gas kinetics are what they are . . . if the nitrogen in what you are breathing is less than what's in your body, you're going to offgas, and if the nitrogen in one gas is less than in another, you'll offgas faster on it. But how MUCH of a difference it makes to be on, say, 32% as opposed to air, you'd have to do the math. I personally suspect the results would be such that it's probably not worth carrying extra bottles with that little O2 in them, unless you just plain need the gas.

 

[Blackwood]

I have no problems with someone using deco gases and treating it like backgas deco. They'll get out of the water very clean that way, but

For instance, one might order a 50% stage but on analysis finds out that it's only 48%. He still uses the tank but re-plans his dive as if he's decompressing on air!

Wow. That's totally missing the forest for the trees.

 

[Diver0001]

I have no problems with someone using deco gases and treating it like backgas deco. They'll get out of the water very clean that way, but



Wow. That's totally missing the forest for the trees.

Maybe. They're probably using tables to plan the deco and don't know what else to do if they get a lean mix. The IANTD for one teaches that 50% is the minimum for accelerated deco. Could be that they're jsut following their training.

R..

 

[Rhone Man]

Well, gas kinetics are what they are . . . if the nitrogen in what you are breathing is less than what's in your body, you're going to offgas, and if the nitrogen in one gas is less than in another, you'll offgas faster on it. But how MUCH of a difference it makes to be on, say, 32% as opposed to air, you'd have to do the math. I personally suspect the results would be such that it's probably not worth carrying extra bottles with that little O2 in them, unless you just plain need the gas.

What Lynne said.

Personally, I don't run very aggressive deco schedules, so I tend not to carry stages and just deco on air (plus any kind of nitrox is hard to get ahold of here, much less super rich nitrox). The benefit of trimming my 10 minute deco to 7 minutes is just not worth humping a side bottle around.

If I was doing 30+ minutes deco, I might reconsider...

 

[liuk3]

What is extended range?

 

[Blackwood]

Maybe. They're probably using tables to plan the deco and don't know what else to do if they get a lean mix. The IANTD for one teaches that 50% is the minimum for accelerated deco. Could be that they're jsut following their training.

R..

You're probably right.

That said, while their training likely says +/- 1% is the FO₂ tolerance, to me 2% is within giggle room.

 

[Rhone Man]

What is extended range?

What used to be called "deep air" in less politically correct days:

International Training :: Get Certified :: Extended Range Diver :: English