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

Mdemon · 28th January 2006, 21:57

I've been offered some O2 which ranges as low as 94% in the past. What is the lowest percentage you would be happy using?

Underwaterbear · 8th February 2006, 07:50

The highest I can get!

For me it's not a matter of what's the lowest I'd be happy with but whether the extra stress of dealing with the volume creep of the counterlung is worth the dive.

It all depends on circumstances but at some point your CCR becomes a SCR!

Cheers.

lizardland · 8th February 2006, 08:18

It would depend on what I'm paying for too. If it's a certified purity gas from a supplier then I wouldn't accept anything that strays from what I've paid for.

Also as most dive shops are hardly generous with their gas prices I'd be expecting an O2 bottle to be analysing pretty close to 100% or it goes back. Some shops I've been in got a tad over-excited that I analysed O2 fills in the shop before I took the gas away.

I think I'd be a bit worried about where the drift from the upper 90s% came from and what made up the shortfall.

***Beanie*** · 8th February 2006, 08:21

Given that you can get 100% in this country (UK) easily why use anything less

OK so in the red sea I was using O2 that came out at between 96% and 98% but thats all I had. At home I use 100% cause thats what I get its £0.01 a litre why do I need to save money using a lesser %? - I'm assuming this is a money saving venture?

**nigelh** · 8th February 2006, 10:18

I guess I'd use what I could get but unless I'm using air as a dil and the O2 is only cut with nitrogen I have little idea what the inerts are. With a trimix DIL you'd be using semi-closed predictions to get the helium percentage.

Duncan Price · 8th February 2006, 11:46

Quote: (Originally Posted by Mdemon)

I've been offered some O2 which ranges as low as 94% in the past. What is the lowest percentage you would be happy using?

I use 21% most of the time - lower (if cut with helium) when underwater.

Mdemon · 8th February 2006, 11:49

Quote: (Originally Posted by Beanie)

Given that you can get 100% in this country (UK) easily why use anything less

OK so in the red sea I was using O2 that came out at between 96% and 98% but thats all I had. At home I use 100% cause thats what I get its £0.01 a litre why do I need to save money using a lesser %? - I'm assuming this is a money saving venture?

No, this was in the Red Sea too. At home, even the welding O2 is 99.99!

Thanks for the responses - some interesting thoughts there.

I was also worried about inerts. 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...

In this instance the problem was tracked down to the mixing panel - air in the whips was being allowed into the cylinder. So the inerts were basically nitrogen which we have more experience with.

I wondered at which point the extra volume required and the danger of inert buildup during O2 Rebreather makes it more trouble than it's worth? There's also the issues of paying for 100% and not getting it...

jean-marc · 8th February 2006, 11:54

The problem is not having only 94% oxygen, but which gases are the 6% missing ?

ROB DAVIE · 8th February 2006, 13:29

Quote: (Originally Posted by Mdemon)

I was also worried about inerts. 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...

Joe Radomski was the one who pointed out that a lot of places in the world use Pressure Swing Adsorption methods for producing O2. Because of the way the method works, especially at higher efficiency settings (more flow, lower O2 percentage) the remainder tends to be a lot higher percentage of argon than we are used to. Over time during a dive without the occasional purge of your system, the argon level creeps up.

Rob

***ScubaDadMiami*** · 8th February 2006, 14:36

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

28th January 2006, 21:57	#1 (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: 1,927	What's the lowest percentage "O2" you would use? I've been offered some O2 which ranges as low as 94% in the past. What is the lowest percentage you would be happy using? __________________ 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?" Last edited by Mdemon : 29th January 2006 at 13:25.
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8th February 2006, 07:50	#2 (permalink)
Underwaterbear A Prismer in Megland Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: May 2005 Location: Seattle, WA Posts: 192	Re: What's the lowest percentage "O2" you would use? The highest I can get! For me it's not a matter of what's the lowest I'd be happy with but whether the extra stress of dealing with the volume creep of the counterlung is worth the dive. It all depends on circumstances but at some point your CCR becomes a SCR! Cheers.
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8th February 2006, 08:18	#3 (permalink)
lizardland Yak Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Classic Kiss Home Build Join Date: Mar 2005 Location: North... Posts: 1,304	Re: What's the lowest percentage "O2" you would use? It would depend on what I'm paying for too. If it's a certified purity gas from a supplier then I wouldn't accept anything that strays from what I've paid for. Also as most dive shops are hardly generous with their gas prices I'd be expecting an O2 bottle to be analysing pretty close to 100% or it goes back. Some shops I've been in got a tad over-excited that I analysed O2 fills in the shop before I took the gas away. I think I'd be a bit worried about where the drift from the upper 90s% came from and what made up the shortfall. __________________ Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you? www.westons-cider.co.uk Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler
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8th February 2006, 08:21	#4 (permalink)
*Beanie* give a man an inch....... Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Vision Join Date: Jan 2005 Location: In da house! yeah baby! Posts: 3,175	Re: What's the lowest percentage "O2" you would use? Given that you can get 100% in this country (UK) easily why use anything less OK so in the red sea I was using O2 that came out at between 96% and 98% but thats all I had. At home I use 100% cause thats what I get its £0.01 a litre why do I need to save money using a lesser %? - I'm assuming this is a money saving venture? __________________ Beanie Gallery Admin & Library Assistant. www.outlawdivers.org.uk www.beandiving.co.uk www.beanengineering.co.uk
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8th February 2006, 10:18	#5 (permalink)
nigelh New Member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 839	Re: What's the lowest percentage "O2" you would use? I guess I'd use what I could get but unless I'm using air as a dil and the O2 is only cut with nitrogen I have little idea what the inerts are. With a trimix DIL you'd be using semi-closed predictions to get the helium percentage. __________________ nigelh
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8th February 2006, 11:46	#6 (permalink)
Duncan Price Sump Monster Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Feb 2005 Location: Wells, Somerset, UK Posts: 335	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by Mdemon) I've been offered some O2 which ranges as low as 94% in the past. What is the lowest percentage you would be happy using? I use 21% most of the time - lower (if cut with helium) when underwater.
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8th February 2006, 11:49	#7 (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: 1,927	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by Beanie) Given that you can get 100% in this country (UK) easily why use anything less OK so in the red sea I was using O2 that came out at between 96% and 98% but thats all I had. At home I use 100% cause thats what I get its £0.01 a litre why do I need to save money using a lesser %? - I'm assuming this is a money saving venture? No, this was in the Red Sea too. At home, even the welding O2 is 99.99! Thanks for the responses - some interesting thoughts there. I was also worried about inerts. 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... In this instance the problem was tracked down to the mixing panel - air in the whips was being allowed into the cylinder. So the inerts were basically nitrogen which we have more experience with. I wondered at which point the extra volume required and the danger of inert buildup during O2 Rebreather makes it more trouble than it's worth? There's also the issues of paying for 100% and not getting it... __________________ 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, 11:54	#8 (permalink)
jean-marc New Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Inspiration Classic Inspiration Vision Join Date: Jan 2006 Location: Montpellier - France Posts: 60	Re: What's the lowest percentage "O2" you would use? The problem is not having only 94% oxygen, but which gases are the 6% missing ?
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8th February 2006, 13:29	#9 (permalink)
ROB DAVIE Administrator Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: HOUSTON, REPUBLIC OF TEJAS Posts: 1,120	Re: What's the lowest percentage "O2" you would use? Quote: (Originally Posted by Mdemon) I was also worried about inerts. 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... Joe Radomski was the one who pointed out that a lot of places in the world use Pressure Swing Adsorption methods for producing O2. Because of the way the method works, especially at higher efficiency settings (more flow, lower O2 percentage) the remainder tends to be a lot higher percentage of argon than we are used to. Over time during a dive without the occasional purge of your system, the argon level creeps up. Rob __________________ [SIZE=2]"CC Rebreathers will become a viable part of tech diving [U]WHEN PIGS FLY[/U]!!"--GI3[/SIZE]
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8th February 2006, 14:36	#10 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 2,132	Re: What's the lowest percentage "O2" you would use? So, what do you do about calibration when you know that your mix is low? __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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