Argon Hazard

**Paul Haynes** · July 13th, 2012, 05:29 PM

Hi All,

reading the thread on calibration using less than 100% and seeing where it was heading, I thought I would start a new one on oxygen generation and argon. Having only dived where 100% oxygen was available, it is something I have no practical experience of and therefore unsure whether in practice excess argon has proven to have a detrimental impact to rebreather safety. However I have heard of it triggering a CCR fatality, although the source of this data is up for question and so do not intend to discuss the incident further.

Anyway as for the production of oxygen in remote locations and the potential hazard of argon, here goes:

Dry air contains 20.947% oxygen, 0.934% argon and the remainder nitrogen (ignore trace gases for this discussion). If you remove only the nitrogen by either molecular sieve, membrane separation or cryogenic distillation, the ratios of the oxygen and argon remains the same. So if you sieve air to produce 96% oxygen, you will end up with approximately 4% argon.

As ‘oxygen’ injected into the ‘loop’ is metabolised, the argon remains and gradually continues to build up as ‘oxygen’ is injected. In effect you’re breathing an oxygen, nitrogen, argon trimix if using an air diluent or a quad mix of oxygen, nitrogen, helium, argon if using a trimix diluent.

Whilst the actual percentage of argon within the loop may not be be that great depending upon the duration of the dive and the amount of 'oxygen' injected, argon I understand to be over twice as narcotic as nitrogen and the narcosis itself has a more psychotic effect. What then is the potential impact to decompression and / or narcosis levels? Is a periodic loop diluent flush good practice in such a scenario? Thoughts please guys and girls.

***nickb*** · July 13th, 2012, 06:09 PM

That's pretty much the discussion I had with a number of the other divers on the trip. I didn't do any flushing and, as far as I know, neither did anyone else.

I did feel slightly more narc'd than I would have expected at those depths with that mix and that's what prompted the discussion. I didn't notice this getting worse as the dives progressed and the longest I spent at 50m+ was just under 50 minutes. The longest run time was 140 minutes, but we were doing north of 4 hours every day.

I assumed the premixed dil was blended using the same generated O2, but never asked.

Empirical evidence, albeit based on a small population, would suggest that it's not much of a problem, if at all.

Interesting topic though.

SimonK · July 13th, 2012, 07:11 PM

I did think the other thread was missing some dodgy maths so here goes.

If you assume:
4% Argon in your 'oxygen',
O2 injected at 1 litre/min,
18L loop volume (from DTs post)
Dive to 6 Bar for 50min

Then over the 50 min you will add 2l of Argon to the loop (50l/m x 0.04). The loop will contain 108L (18L x 6Bar) of gas, call it 100L to keep the sums simple. So you have added 2% argon. If we assume that Argon is twice as narcotic as Nitrogen then after 50min at 50m it would be equivalent to an 4% increase in the fraction of Nitrogen in the mix.

S

***nickb*** · July 13th, 2012, 08:15 PM

So, no biggy then? Which would seem to explain why it wasn't much of an issue for us.

Nice 'dodgy maths'

matt · July 13th, 2012, 09:01 PM

Here's a bit of info about Ar and rats:http://www.biomed.cas.cz/physiolres/...201/56_S39.pdf

**Paul Haynes** · July 13th, 2012, 10:36 PM

Quote: (Originally Posted by matthewoutram)

Here's a bit of info about Ar and rats:http://www.biomed.cas.cz/physiolres/...201/56_S39.pdf

Cheers, some bed time reading ;-)

July 13th, 2012, 05:29 PM	#1
Paul Haynes CCRX Supporter Join Date: Mar 2012 Location: Scotland Posts: 195 Thanks: 61 Thanked 143 Times in 27 Posts	Argon Hazard Hi All, reading the thread on calibration using less than 100% and seeing where it was heading, I thought I would start a new one on oxygen generation and argon. Having only dived where 100% oxygen was available, it is something I have no practical experience of and therefore unsure whether in practice excess argon has proven to have a detrimental impact to rebreather safety. However I have heard of it triggering a CCR fatality, although the source of this data is up for question and so do not intend to discuss the incident further. Anyway as for the production of oxygen in remote locations and the potential hazard of argon, here goes: Dry air contains 20.947% oxygen, 0.934% argon and the remainder nitrogen (ignore trace gases for this discussion). If you remove only the nitrogen by either molecular sieve, membrane separation or cryogenic distillation, the ratios of the oxygen and argon remains the same. So if you sieve air to produce 96% oxygen, you will end up with approximately 4% argon. As ‘oxygen’ injected into the ‘loop’ is metabolised, the argon remains and gradually continues to build up as ‘oxygen’ is injected. In effect you’re breathing an oxygen, nitrogen, argon trimix if using an air diluent or a quad mix of oxygen, nitrogen, helium, argon if using a trimix diluent. Whilst the actual percentage of argon within the loop may not be be that great depending upon the duration of the dive and the amount of 'oxygen' injected, argon I understand to be over twice as narcotic as nitrogen and the narcosis itself has a more psychotic effect. What then is the potential impact to decompression and / or narcosis levels? Is a periodic loop diluent flush good practice in such a scenario? Thoughts please guys and girls. __________________ When you dive you enter an alien world, death is evolution's default state; at some point your life support will fail to function correctly, plan on it.
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July 13th, 2012, 06:09 PM	#2 (permalink)
*nickb* The JJ Kid Join Date: Mar 2012 Location: Cardiff, UK Posts: 513 Thanks: 75 Thanked 87 Times in 60 Posts	That's pretty much the discussion I had with a number of the other divers on the trip. I didn't do any flushing and, as far as I know, neither did anyone else. I did feel slightly more narc'd than I would have expected at those depths with that mix and that's what prompted the discussion. I didn't notice this getting worse as the dives progressed and the longest I spent at 50m+ was just under 50 minutes. The longest run time was 140 minutes, but we were doing north of 4 hours every day. I assumed the premixed dil was blended using the same generated O2, but never asked. Empirical evidence, albeit based on a small population, would suggest that it's not much of a problem, if at all. Interesting topic though.
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July 13th, 2012, 07:11 PM	#3 (permalink)
SimonK New Member Join Date: Mar 2012 Location: Cumbria Posts: 44 Thanks: 0 Thanked 2 Times in 2 Posts	I did think the other thread was missing some dodgy maths so here goes. If you assume: 4% Argon in your 'oxygen', O2 injected at 1 litre/min, 18L loop volume (from DTs post) Dive to 6 Bar for 50min Then over the 50 min you will add 2l of Argon to the loop (50l/m x 0.04). The loop will contain 108L (18L x 6Bar) of gas, call it 100L to keep the sums simple. So you have added 2% argon. If we assume that Argon is twice as narcotic as Nitrogen then after 50min at 50m it would be equivalent to an 4% increase in the fraction of Nitrogen in the mix. S
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July 13th, 2012, 08:15 PM	#4 (permalink)
*nickb* The JJ Kid Join Date: Mar 2012 Location: Cardiff, UK Posts: 513 Thanks: 75 Thanked 87 Times in 60 Posts	So, no biggy then? Which would seem to explain why it wasn't much of an issue for us. Nice 'dodgy maths'
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July 13th, 2012, 09:01 PM	#5 (permalink)
matt New Member Join Date: Apr 2012 Location: London Posts: 1,541 Thanks: 168 Thanked 72 Times in 59 Posts	Here's a bit of info about Ar and rats:http://www.biomed.cas.cz/physiolres/...201/56_S39.pdf
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July 13th, 2012, 10:36 PM	#6 (permalink)
Paul Haynes CCRX Supporter Join Date: Mar 2012 Location: Scotland Posts: 195 Thanks: 61 Thanked 143 Times in 27 Posts	Quote: (Originally Posted by matthewoutram) Here's a bit of info about Ar and rats:http://www.biomed.cas.cz/physiolres/...201/56_S39.pdf Cheers, some bed time reading ;-) __________________ When you dive you enter an alien world, death is evolution's default state; at some point your life support will fail to function correctly, plan on it.
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