Functionaing with only 92% O2

jradomski

yes and no..
if you are using a dil that is either Air, or a trimix dil that has no oxygen added you will start with NO argon in the loop.. ARgon will only be added by o2 injections.. If you are using an Air dil and a setpoint of 1.3 then shallower than 51 meters (47m for 1.2, 42m for 1.1 and so on) you will have some argon added to the loop to get up to the 1.3po2, deeper than 51 meters you will truely start at no argon (with a flush)..

Argon is about 2.4 times more narcotic than nitrogen so if you want to calculate you approximate narcosis level you first need to know the %of N2 in the loop, then you can calculate how much ar was added over time figure this % out then multipley it by 2.4 and add it to the nitrogen (use this sum as the nitrogen number) and you can use your "normal" END formula (don't worry that the % goes over 100% your just figuring out an equivalency), at depth it does add on but its not that bad with regular flushes..

figuring out how much Ar is added is trivial.. if you need 1.0 lpm of o2 that means you have to inject 1.08lpm of gas (lets assume 92% o2) , so your adding .08lpm of Argon..

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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.

Mixaddict

On CCR I will typically use some helium starting at about 145' depending on the conditions of course. Most of the time on OC, I am good to 180' or so, again depending on conditions. In Truk, the conditions are pretty favorable, so the San Fransisco Maru at 195 is not particularly difficult for me on OC on air. On CCR, I can notice a substantial difference while on air.

As far as set points go, I have started playing around with 1.1 or 1.2 on the bottom, especially when I am past 200 feet, but I am using helium of course at those depths.

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Randy Thornton (MixAddict)
Inspiration, Evolution,Hammerhead & Sentinel
CCR Instructor

Sutty

Oops, sorry, I forgot to account for the O2 in the dil in my calculations!
(It was late)

Minimum partial pressure argon assuming 5% Argon and 95% O2 in "O2" supply and assuming air dil and 1.3 set point would be:

(1.3-0.21)/0.95 x 0.05 = 0.057bar

As you say argon is about 2.4 as narcotic as nitrogen, I must admit I was thinking it was more. So I don't think it will make a huge difference to overall narcosis levels assuming regular flushing.

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Never forget that life is a finite resource.

jradomski

yes but it is still depth and time dependent.. the closer you are to the po2 that the diluent can supply the lower the minimum partial pressure of argon will be.. if you are at the po2 the dil can supply, the lowerst pp of argon is 0..

the deeper you go the less o2 thats needed to reach the sp so the less argon thats initially injected..

__________________
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.

AD_ward9

The argon will increase in your loop, as you metabolise the O2. One thing about argon narcosis, is it interferes with short term memroy resulting in lapses in time. That is, 20 minutes can pass and you think it is a few seconds. So relying on flushing frequently is probably not a good plan.

I would rather plumb in 60% nitrox than 92% O2 where I do not know what the other 8% is. At least with nitrox I am running a SCR and have a guaranteed flush.

Alex

iain-hsm

Hi Joe.
Your posts on this is a much better post thanks, I regret I was still thinking military LAR V and pure oxygen breathing units, I should have disclosed that point.
To “make up” so to speak and shed light on the problem as we see it is the way gas for breathing purposes is certified in Europe as we do this at the point of dispensation. In UK at present the Argon maximum limit is in BS8478: 2006 (enclosed PDF file below) and is set at less than 0.5%. So with the PSA generating systems producing 10 times that allowed amount between 4.5 to 5% were stuffed.
Granted we can engineer out of this but our UK cost for the production plant and filter system is doubled against the single pass units popular with the liveaboards who get to ignore the 10 times Argon loading. Were also stuffed.


Another problem (see Alex post above on nitrox) is with these membrane systems for nitrox, granted few people have them in UK as with them now the C02 is also greater than the maximum allowed in the standards with either standard you wish to use. BS8478:2006 for the Breathing Gas or the BS EN12021 for the Divers Breathing Air. In fact the permeate C02 content from the membrane is over double the maximum allowed, hence why we only see “Italian” versions of these products. Iain Middlebrook

Attached Images

Air-__Nitrox_Specs[1].pdf (30.0 KB, 10 views)