O2 clean regs for back mount doubles?

[geoff w]

@geoff w you don't need extra filter stacks between whips and what not. Personal filters don't really do anything as the fill rates are far too fast and there isn't a back pressure regulator on them. Dwell time is woefully inadequate to really do anything but if it makes you feel better, then go for it.

MOST all compressors come with filters that are capable of spitting out O2 clean air from a capacity and it's then up to the owner of said compressor to put filter cartridges in that will give OCA which really is ridiculous
So OCA vs CGA Grade E vs EN12021 *divers
CO is <2 vs <10 vs<15 -this has no bearing on oxygen compatibility
OCA does not have a dewpoint spec, but CGA is -65F and again has no bearing on O2 compatibility
Oil is <0.1 vs <5 vs <0.5 mg/m3

So the oil is obviously the most important part of this since it is what actually matters for oxygen compatibility. Now, pretty much all modern compressors if properly maintained and using synthetic oil can meet the <5mg/m3 without any filtration at all. No water knock out, no filters, literally at the outlet of the final stage. The moisture separator will take quite a bit of oil out with it as the water condenses and that's why in Europe especially the effluent from the traps has to be captured. @iain/hsm knows a lot more about this, but it's one of the perks of having a Rix where it's just distilled water. The rest of the oil is taken out by activated carbon in the filter stacks. So long as the AC bed is big enough and replaced at the right time *calculated based on volume pumped through* and the PMV is set properly, the air coming out will have essentially non detectable oil levels. This is also why it's important to get your air checked at the END of the filter life to make sure that your PM frequency is sorted out.
The math for the AC bed life is basically assuming 5mg/m3 incoming to the filter, the mass of the AC bed so for easy math say 100g, and the AC beds can absorb somewhere around 8% of its weight in oil IIRC but call it 5% for easy math and conservatism. So the filter can absorb 5g of oil. 5/.005=1000m3=35k cf. Say the dive shop has a 10cfm pump, so every 3500mins/60hrs the filters have to be changed. Obviously adjust for the actual mass of AC in your specific filter and your compressors fill rate and I would double check the % absorption of the AC if you're running your own compressor, but that's how the calculation works.

So, all this to say that if you are getting gas from a compressor that has an adequately sized filtration stack, that has an AC bed in it, and it is changed at the right frequency, you should be receiving what we call "OCA" from the pump. Ask the dive shop to look at their last analysis and if they don't show it to you run away very quickly. If the oil level is <0.5mg/m3, then I wouldn't worry about it. Of note fresh analysis is usually <0.05mg/m3 so it's not something you have to worry about...

Wow!! Thanks for the detailed explanation. I'll check with the dive shop I get my nitrox fills to see what their filtering specs are and latest test results. I have 8 tanks in there now from the past two weeks; they're not doing fills at the moment because of all the crap in the air from the west coast fires. They figure they would be going through filters like crazy if they were filling tanks right now. They have a Bauer Vertecon, so from that I can look up the specs and work out the math, then see how that compares to their actual practice

 

[tbone1004]

@geoff w the vertecons have more than adequate filtration capacity so whether it is OCA or not will depend on their replacement schedule as the filters should have an AC bed in there.

 

[rsingler]

I did some reserarch a long while back and what I found is that there is a hazzard with titanium in an O2 rich environment. However that environment was 14,000 psi and above. What that means I do not know. the obvious says it is not an issue...

Take your Atomic T2x or T3 into a dark room with the lights out. Put a 5/32" hex key in one of the titanium port plugs. Unscrew and re-screw the port plug into place. Little tiny red sparks. In air, not oxygen. Now imagine with EAN and some hydrocarbon from sloppy cleaning...

Blew my mind the first time I saw it.

 

[rjack321]

@geoff w you don't need extra filter stacks between whips and what not. Personal filters don't really do anything as the fill rates are far too fast and there isn't a back pressure regulator on them. Dwell time is woefully inadequate to really do anything but if it makes you feel better, then go for it.

MOST all compressors come with filters that are capable of spitting out O2 clean air from a capacity and it's then up to the owner of said compressor to put filter cartridges in that will give OCA which really is ridiculous
So OCA vs CGA Grade E vs EN12021 *divers
CO is <2 vs <10 vs<15 -this has no bearing on oxygen compatibility
OCA does not have a dewpoint spec, but CGA is -65F and again has no bearing on O2 compatibility
Oil is <0.1 vs <5 vs <0.5 mg/m3

So the oil is obviously the most important part of this since it is what actually matters for oxygen compatibility. Now, pretty much all modern compressors if properly maintained and using synthetic oil can meet the <5mg/m3 without any filtration at all. No water knock out, no filters, literally at the outlet of the final stage. The moisture separator will take quite a bit of oil out with it as the water condenses and that's why in Europe especially the effluent from the traps has to be captured. @iain/hsm knows a lot more about this, but it's one of the perks of having a Rix where it's just distilled water. The rest of the oil is taken out by activated carbon in the filter stacks. So long as the AC bed is big enough and replaced at the right time *calculated based on volume pumped through* and the PMV is set properly, the air coming out will have essentially non detectable oil levels. This is also why it's important to get your air checked at the END of the filter life to make sure that your PM frequency is sorted out.
The math for the AC bed life is basically assuming 5mg/m3 incoming to the filter, the mass of the AC bed so for easy math say 100g, and the AC beds can absorb somewhere around 8% of its weight in oil IIRC but call it 5% for easy math and conservatism. So the filter can absorb 5g of oil. 5/.005=1000m3=35k cf. Say the dive shop has a 10cfm pump, so every 3500mins/60hrs the filters have to be changed. Obviously adjust for the actual mass of AC in your specific filter and your compressors fill rate and I would double check the % absorption of the AC if you're running your own compressor, but that's how the calculation works.

So, all this to say that if you are getting gas from a compressor that has an adequately sized filtration stack, that has an AC bed in it, and it is changed at the right frequency, you should be receiving what we call "OCA" from the pump. Ask the dive shop to look at their last analysis and if they don't show it to you run away very quickly. If the oil level is <0.5mg/m3, then I wouldn't worry about it. Of note fresh analysis is usually <0.05mg/m3 so it's not something you have to worry about...

This is pretty close but the vast majority of oil is actually found as a mist and removed by the filter pads before it even gets to the 13x or AC. More is removed by the 13x and the last tiny fraction which is not actually combustible is the volatized fraction which is removed by AC. Its not combustible because the concentrations of gaseous hydrocarbons are way way lower than the flash point by default. The oil mist is the critical fraction.

 

[rjack321]

Wow!! Thanks for the detailed explanation. I'll check with the dive shop I get my nitrox fills to see what their filtering specs are and latest test results. I have 8 tanks in there now from the past two weeks; they're not doing fills at the moment because of all the crap in the air from the west coast fires. They figure they would be going through filters like crazy if they were filling tanks right now. They have a Bauer Vertecon, so from that I can look up the specs and work out the math, then see how that compares to their actual practice

It's fine for them to not fill right now. But smoke particulate is not going to make it into anyone's tanks anyway. It's pretty effectively removed by inlet filters. And what does get past that is in 100+% humidity air so ends up in the liquid fraction. And that's before it even gets to the multiple filter pads in the stack.

Better safe than sorry by not bothering to fill at the moment, but its not a high risk pathway in any case

 

[tbone1004]

This is pretty close but the vast majority of oil is actually found as a mist and removed by the filter pads before it even gets to the 13x or AC. More is removed by the 13x and the last tiny fraction which is not actually combustible is the volatized fraction which is removed by AC. Its not combustible because the concentrations of gaseous hydrocarbons are way way lower than the flash point by default. The oil mist is the critical fraction.

I figured I'd try to keep it high level, but yeah very little of it ever ends up in the AC beds, but I've always seen the AC beds as the calculation for filter replacement which is why I left it at the final stage vs the intermediate stages since the AC can do it all on its own

 

[nadwidny]

@geoff w yo
So, all this to say that if you are getting gas from a compressor that has an adequately sized filtration stack, that has an AC bed in it, and it is changed at the right frequency, you should be receiving what we call "OCA" from the pump. Ask the dive shop to look at their last analysis and if they don't show it to you run away very quickly. If the oil level is <0.5mg/m3, then I wouldn't worry about it. Of note fresh analysis is usually <0.05mg/m3 so it's not something you have to worry about...

This. I have done thousands of analyses on air samples from high pressure compressors (as defined as above 2216psi as per CSA standards). I have only had 2 or 3 fail on OPC (Oil Particulate, Condensate) at the CSA limit of 1.0 mg/m3. Pretty much all the rest are at 0.1 mg/m3 or less.

As suggested, ask for the LDS for their latest test.Hell even ask for their last 3 or 4. They should be on file. If they balk or run away, then run away.

FWIW, OCA is a made up standard from a couple of agencies. It isn't a real thing. And pretty much every compressor with filtration meets this fake standard.

 

[nadwidny]

It's fine for them to not fill right now. But smoke particulate is not going to make it into anyone's tanks anyway. It's pretty effectively removed by inlet filters. And what does get past that is in 100+% humidity air so ends up in the liquid fraction. And that's before it even gets to the multiple filter pads in the stack.

Better safe than sorry by not bothering to fill at the moment, but its not a high risk pathway in any case

When I was working at the air testing lab we had a request to test from the hospital in Ft McMurray, Alberta when the whole town was evacuated because the city was burning down.Needless to say it was very smoky there. The hospital had to keep their low pressure breathing air supply compressors going through out the event. I don't know why. i'm not a hospital guy. So we analyzed some samples and despite the extreme conditions the air produced by those compressors met the standard. i expected elevated CO or CO2 but nope. Even some of the weird **** wasn't there.

However personally I wouldn't run my compressor during a big smoke event, like i'm having now at Kootenay Lake. Just because.

 

[sabbe]

I'm planning to start tech training some time in the near future, depending on scheduling everything with the pandemic. From talking to several people, they all use Atomic M1s for their back mount double regs because they're O2 clean and rated for higher percentage O2 right out of the box. After thinking about this for a little bit, it didn't make sense, because you'd need O2 clean for a deco bottle, not back gas. I asked one friend who has his set up this way, he didn't know the reason, and said it's because that's what an instructor recommended to him

Is there any reason to use something like an Atomic M1 for back gas, or is a properly configured Atomic ST1 or similar fine for doubles, and use an M1 for higher percentage O2 stage bottle?

I wouldn’t necessarily replace an ST1 but the M1 offers more options as a backup To mix match with deco regs. I normally use 80% deco do any reg should be able to handle it. Currently have 3 M1s and 2 of the Hollis O2 regs. They’ve been performing like champs. Options helped while loaning wife regs while she was building her kit.

I also wanted their cold water performance after have several lesser Atomic and Hollis freeze during ice diving. Haven’t been back to 31 degree water but they worked flawlessly in 40 degree many times.

 

[geoff w]

I wouldn’t necessarily replace an ST1 but the M1 offers more options as a backup To mix match with deco regs. I normally use 80% deco do any reg should be able to handle it. Currently have 3 M1s and 2 of the Hollis O2 regs. They’ve been performing like champs. Options helped while loaning wife regs while she was building her kit.

I also wanted their cold water performance after have several lesser Atomic and Hollis freeze during ice diving. Haven’t been back to 31 degree water but they worked flawlessly in 40 degree many times.

I have an M1 (still in the box) slated for a high O2 stage bottle, and based on all the great advice here I'll plan to use my ST1s for back mount doubles.

I think the environmental seal for the M1 and ST1 (and T2/T3) are the same. Some friends and I did an ice diving class early this year (back when it was safe to go outside and be around other people). I borrowed a Poseidon reg and didn't have any problems, but a buddy did have his Scubapro MK25 start to freeflow once or twice, even though it was environmentally sealed. I figure for the rare times I'm going in water close to freezing I'll just borrow a Poseidon and enjoy my ST1 for pretty much everything else