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

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    Question 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?
    Last edited by Mdemon; 29th January 2006 at 14:25.

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    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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    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.

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    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?



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    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.

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    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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    Thumbs up 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 RBW 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 RB makes it more trouble than it's worth? There's also the issues of paying for 100% and not getting it...

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    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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    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 RBW 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

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    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?

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