What's the lowest percentage "O2" you would use?

**JPJones** · 8th February 2006, 19:49

Quote: (Originally Posted by ScubaDadMiami)

So, what do you do about calibration when you know that your mix is low?

It would be close enough ie 1.2 would actually be 1.16

Andre · 8th February 2006, 20:10

Good point Jean-Marc!!!

E-man · 8th February 2006, 20:52

Quote: (Originally Posted by JPJones)

It would be close enough ie 1.2 would actually be 1.16

Can't you enter in a different percentage that your cal-ing to?

edster · 8th February 2006, 21:02

Quote: (Originally Posted by E-man)

Can't you enter in a different percentage that your cal-ing to?

if its an inspo you can

Mdemon · 8th February 2006, 21:45

Yes. On the Inspo I just set it to 94% and crossed my fingers...

E-man · 8th February 2006, 23:38

Quote: (Originally Posted by edster)

if its an inspo you can

Well that sucks...id think all electronics would allow this...

I guess you would have to just pressurize the loop to make it 100% which I think is something that Joe has said before...

for 94% youd pressurize it to 25.964840719 inches of water

abowie · 9th February 2006, 01:16

Quote: (Originally Posted by Mdemon)

.

I think someone mentioned on Rebreather World that for some O2 extraction methods the difference could be made up in a large part with argon. This clearly is very scarey - very narcotic at depth and guess where I was playing...

Yup and that's the nub of the issue.

tdvanniekerk · 27th February 2006, 00:16

The problem is not 92 or 94% O2, the problem is what is in the remaining 6 or 8%.

If you go to the gas supply companies you will find that they have many grades of O2, all classified as "Medical" grade. You should also check for the CO content and then decide if it is going to be a factor in the depth you are going to dive. I have no idea at what percentage CO will have negative physcological affect, but if you are going to drop standards, then at least do it with knowledge. Remember at a 90m dive the pressure is 10 ata. If you have 2% CO in the mix it will be ppCO 20 at 90m, with a setpoint of 1.2 you will be breathing the equivalent of 2% CO. (Not sure if my calcs are correct, need to check it for yourself). Maybe some expert out there will know if 2% CO will be bad for you.

A lower O2% will also be a factor when calibrating the O2 cells in rebreathers. If you think you have 100% O2 but only have 92% it can affect your actual setpoint. Off course if you know you only have 94% O2 you can set the rebreather to calibrate on 94% (at least you can on the Inspiration).

TD

decoweenie · 27th February 2006, 00:48

Quote: (Originally Posted by tdvanniekerk)

...If you have 2% CO in the mix it will be ppCO 20 at 90m, with a setpoint of 1.2 you will be breathing the equivalent of 2% CO. (Not sure if my calcs are correct, need to check it for yourself)...

I dunno, at first glance, looks about right...

***jradomski*** · 27th February 2006, 05:35

a quick summary of what I go over with my students..

Oxygen in Many parts of the world is created by PSA systems (yes even in first world countries - Home oxygen generation systems for the sick are scaled down PSA systems) , one that the flow is tuned in dead on will produce 95.4% oxygen, 4.5% argon and .1% trace gases (from the atmosphere)..

if they raise the flow rate, the oxygen percentage drops slightly and is replaced by nitrogen.. Most units end up putting out between 92-93% oxygen, it still has about 4.5% argon and ~1% trace gases, but now contains nitrogen as a "contaminate".

This small change in Oxygen purity actually produces a much higher volume of "oxygen" than you would expect. This is why most systems operate around this purity..

For a rebreather diver, The effect is cumulative, so periodic flushes are needed.. The contaminate percentage caused by oxygen is a greater percentage when shallower, than when you go deeper (a simple matter a physics - more of the "volume" is made up of diluent gas which has a lower percentage of argon), the addition of "oxygen" simply replaces the metaboliozed oxygen with Oxygen + argon

addited:

The approximate compositions of a perfectly working system can be found by multiplying normal atmospheric concentrations by 4.78

for example Argon is .934% x 4.78 = 4.46%

You can do the same for other trace gases like CO and CO2 (these numbers will vary by location, but can also be filtered out before or after the sieve)
Even without filtration CO should be below 10ppm even at breathing air at the limits.

8th February 2006, 19:49	#11 (permalink)
JPJones O2ptima Test Dummy Current Rebreather/s: Inspiration Classic Megalodon Sport Kiss Classic Kiss Optima Titan Other Rebreather/s: Join Date: Sep 2005 Location: Florida Posts: 367	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by ScubaDadMiami) So, what do you do about calibration when you know that your mix is low? It would be close enough ie 1.2 would actually be 1.16 __________________ NSS/CDS Training Chairman www.jpjscuba.com
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8th February 2006, 20:10	#12 (permalink)
Andre New Member Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Jun 2005 Location: Switzerland, Aarau Posts: 137	Re: What's the lowest percentage "O2" you would use? Good point Jean-Marc!!!
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8th February 2006, 20:52	#13 (permalink)
E-man On the loop! Current Rebreather/s: Inspiration Classic Optima Other Rebreather/s: Titan Join Date: Sep 2005 Location: Eastern Coast ;) Posts: 212	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by JPJones) It would be close enough ie 1.2 would actually be 1.16 Can't you enter in a different percentage that your cal-ing to?
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8th February 2006, 21:02	#14 (permalink)
edster Mr Cheesebox Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Apr 2005 Location: Avening UK Posts: 149	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by E-man) Can't you enter in a different percentage that your cal-ing to? if its an inspo you can __________________
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8th February 2006, 21:45	#15 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,926	Re: What's the lowest percentage "O2" you would use? Yes. On the Inspo I just set it to 94% and crossed my fingers... __________________ www.southwestmafia.com "small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!" The WRONG Attitude will get you killed. "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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8th February 2006, 23:38	#16 (permalink)
E-man On the loop! Current Rebreather/s: Inspiration Classic Optima Other Rebreather/s: Titan Join Date: Sep 2005 Location: Eastern Coast ;) Posts: 212	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by edster) if its an inspo you can Well that sucks...id think all electronics would allow this... I guess you would have to just pressurize the loop to make it 100% which I think is something that Joe has said before... for 94% youd pressurize it to 25.964840719 inches of water Last edited by E-man : 9th February 2006 at 02:20.
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9th February 2006, 01:16	#17 (permalink)
abowie Fighting Girl Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: May 2005 Location: Land of Oz Posts: 574	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by Mdemon) . I think someone mentioned on Rebreather World that for some O2 extraction methods the difference could be made up in a large part with argon. This clearly is very scarey - very narcotic at depth and guess where I was playing... Yup and that's the nub of the issue. __________________ Andrew Bowie Rebreather-friendly Buddy
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27th February 2006, 00:16	#18 (permalink)
tdvanniekerk New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Classic Inspiration Vision Evolution Join Date: Feb 2006 Location: Hong Kong Posts: 13	Re: What's the lowest percentage "O2" you would use? The problem is not 92 or 94% O2, the problem is what is in the remaining 6 or 8%. If you go to the gas supply companies you will find that they have many grades of O2, all classified as "Medical" grade. You should also check for the CO content and then decide if it is going to be a factor in the depth you are going to dive. I have no idea at what percentage CO will have negative physcological affect, but if you are going to drop standards, then at least do it with knowledge. Remember at a 90m dive the pressure is 10 ata. If you have 2% CO in the mix it will be ppCO 20 at 90m, with a setpoint of 1.2 you will be breathing the equivalent of 2% CO. (Not sure if my calcs are correct, need to check it for yourself). Maybe some expert out there will know if 2% CO will be bad for you. A lower O2% will also be a factor when calibrating the O2 cells in rebreathers. If you think you have 100% O2 but only have 92% it can affect your actual setpoint. Off course if you know you only have 94% O2 you can set the rebreather to calibrate on 94% (at least you can on the Inspiration). TD
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27th February 2006, 00:48	#19 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,487	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by tdvanniekerk) ...If you have 2% CO in the mix it will be ppCO 20 at 90m, with a setpoint of 1.2 you will be breathing the equivalent of 2% CO. (Not sure if my calcs are correct, need to check it for yourself)... I dunno, at first glance, looks about right... __________________ "...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..." - Rebreather World PM
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27th February 2006, 05:35	#20 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 3,001	Re: What's the lowest percentage "O2" you would use? a quick summary of what I go over with my students.. Oxygen in Many parts of the world is created by PSA systems (yes even in first world countries - Home oxygen generation systems for the sick are scaled down PSA systems) , one that the flow is tuned in dead on will produce 95.4% oxygen, 4.5% argon and .1% trace gases (from the atmosphere).. if they raise the flow rate, the oxygen percentage drops slightly and is replaced by nitrogen.. Most units end up putting out between 92-93% oxygen, it still has about 4.5% argon and ~1% trace gases, but now contains nitrogen as a "contaminate". This small change in Oxygen purity actually produces a much higher volume of "oxygen" than you would expect. This is why most systems operate around this purity.. For a rebreather diver, The effect is cumulative, so periodic flushes are needed.. The contaminate percentage caused by oxygen is a greater percentage when shallower, than when you go deeper (a simple matter a physics - more of the "volume" is made up of diluent gas which has a lower percentage of argon), the addition of "oxygen" simply replaces the metaboliozed oxygen with Oxygen + argon addited: The approximate compositions of a perfectly working system can be found by multiplying normal atmospheric concentrations by 4.78 for example Argon is .934% x 4.78 = 4.46% You can do the same for other trace gases like CO and CO2 (these numbers will vary by location, but can also be filtered out before or after the sieve) Even without filtration CO should be below 10ppm even at breathing air at the limits. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated. Last edited by jradomski : 27th February 2006 at 09:45.
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