I’ll do that!!
Is it OK to turn off O2 in Rebreather Training?
- Thread starter doctormike
- Start date
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I contend that a LOT of people diving CCR don’t really understand what’s happening on the dive or how CCR really works. And the last few posts just showed it.
njdiverjoe
Contributor
Care to elaborate?
I probably won’t publicly.
Kay Dee
Contributor
Given you previous slightly snarky (but totally 'assumptious') remark about me (yeah, I make them too, and can be rude at times too, although many Ozzies would oft just call that being 'blunt' or 'straightforward') seems like you don't have the decency to actually ID yourself save behind your 'superlyte27' moniker, given that I ID'd myself immediately in response to your 'assumption' and asked you for your name (and, more to the point, if you knew me personally?), what 3 or 4 pages ago?
Or did I just miss your response to my question? Or, is it just go'na be another "I probably won't publicly"?
Kevin Denlay
At a given setpoint, for the same loop volume, the ambient pressure doesn’t make a difference, the surface is a special case because not all set points are possible. The setpoint is a partial pressure, not a fractional pressure. So at 3m depth to maintain a ppo2 of 1.3 you need 100% o2. Say the loop is 5l, that is 6.5l of oxygen. At 90m you need 13% o2 as 10 bar (ambient) times 13% is 1.3bar. So the free gas equivalent in that 5l loop at 90m is 50l. 13% of 50l is 6.5l
So, for all depths (where a setpoint may be maintained) the quantity of o2 in the loop is the same. So the rate of change of ppo2 with a fixed consumption is the same. The time to pass out is the same at all these depths.
So Superlyte27’s point is that this is blindingly obvious information that any rebreather diver ought to know. I think I mentioned the poor maths of some posters in a previous post of mine when admitting to my own incompetence. That was months back and the same mistake is being made over and over on this thread. So he is drawing attention to an apparent lack of understanding of the gas laws and how they apply to a rebreather which ought to have been covered in the initial training and follows from regular OC nitrox diving.
I have to say I have some sympathy. The presentation of the gas laws on my course materials was so stupid (in an attempt to avoid showing the proper equations I suppose) that I didn’t even bother trying to reverse them into something sane.
What he said.
Jack Hammer
Contributor
@Kay Dee , @Superlyte27 is just as abrasive in person as he is online.
Only to the people I don’t like. 
Some people call it abrasive, I call it an intolerance and impatience with stupidity.
But I wasn’t trying to be abrasive here. I didn’t post the reason publicly because potential students come from this board, and I didn’t want him to look bad to a potential student.
I have had conversations through PM with him and a few others that didn’t understand. Seriously, it’s not your fault as a new rebreather diver if you don’t know this. I think it’s your instructors fault. It’s simple concepts that aren’t being explained or understood.
I’ll give you another that I hear ALL THE TIME.
If you’re in the ocean and run completely out of DIL, what do you have to do? The instructor’s answer all the time is BAIL OUT. That’s the wrong answer.
The purpose of DIL is make up gas. It’s gas to get you to the bottom. You can’t breathe pure oxygen, so you need something to get you there. But, you’re on the bottom in 200’ of water and your DIL is gone. Do you need to bailout? NO! You have to abort the dive, but as you start ascending your loop volume is increasing and your PPO2 is plummeting. So you add oxygen.
I’ve co-taught with half dozen instructors who overlook this, and when I lay it out just like that they go, “oh yeah, that’s right”. I’d much rather be on the loop than on open circuit if it can be helped. Especially in a cave.
Some people call it abrasive, I call it an intolerance and impatience with stupidity.
But I wasn’t trying to be abrasive here. I didn’t post the reason publicly because potential students come from this board, and I didn’t want him to look bad to a potential student.
I have had conversations through PM with him and a few others that didn’t understand. Seriously, it’s not your fault as a new rebreather diver if you don’t know this. I think it’s your instructors fault. It’s simple concepts that aren’t being explained or understood.
I’ll give you another that I hear ALL THE TIME.
If you’re in the ocean and run completely out of DIL, what do you have to do? The instructor’s answer all the time is BAIL OUT. That’s the wrong answer.
The purpose of DIL is make up gas. It’s gas to get you to the bottom. You can’t breathe pure oxygen, so you need something to get you there. But, you’re on the bottom in 200’ of water and your DIL is gone. Do you need to bailout? NO! You have to abort the dive, but as you start ascending your loop volume is increasing and your PPO2 is plummeting. So you add oxygen.
I’ve co-taught with half dozen instructors who overlook this, and when I lay it out just like that they go, “oh yeah, that’s right”. I’d much rather be on the loop than on open circuit if it can be helped. Especially in a cave.
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