O2 clean for mixed gas?

[cdennyb]

OK, would someone please settle this disagreement between myself and a fellow diver buddy.
He says the tanks, reg, etc. need to be O2 cleaned when we run mixed gas like He/Ox/N2 even if the O2 is down below 21%. I said the only tank & reg, etc. that needs to be cleaned is the 100% O2 tank for deco coming up.
We never mix the regulators 'cause the O2 reg will only fit the O2 bottle. Am I just an accident waiting to happen or what?

I agree that it probably wouldn't hurt to clean everything but sometimes we switch between mixed gas and plain air on casual dives. If we cleaned the main gas stuff wouldn't it just become contaminated again when we run air through them that was filled at a dive shop?

thanks

 

[Karl_in_Calif]

It depends on how you local dive store mixes.

If they partial pressure blend with pure oxygen, then you need O2 cleaned tanks and O2 cleaned tank valves.

 

[OneBrightGator]

IMO, any tank you plan on using for anything other than air should be clean, even if your LDS doesn't use PP blending. Most shops do use PP, so if you ever plan on traveling with your tanks or even using another shop they would need to be clean.

If you're using your tanks with just air then tell the dive shop your tanks are clean and you need hyper-filtered air.

Ben

 

[padiscubapro]

cdennyb once bubbled...
OK, would someone please settle this disagreement between myself and a fellow diver buddy.
He says the tanks, reg, etc. need to be O2 cleaned when we run mixed gas like He/Ox/N2 even if the O2 is down below 21%. I said the only tank & reg, etc. that needs to be cleaned is the 100% O2 tank for deco coming up.
We never mix the regulators 'cause the O2 reg will only fit the O2 bottle. Am I just an accident waiting to happen or what?

I agree that it probably wouldn't hurt to clean everything but sometimes we switch between mixed gas and plain air on casual dives. If we cleaned the main gas stuff wouldn't it just become contaminated again when we run air through them that was filled at a dive shop?

thanks

Your friend is right..

most places mix trimix by partial pressure blending although continuous blending is becoming more common..

If you are not diving Heliar (trimix made from strictly blending air and helium) the blender must put oxygen into the tank to raise the oxygen content... for example if you wanted a mix like 18/50 or even 16/50 oxygen has to be added, if you use 50% helium and top with air you get approximately a 10/50 mix...

yes only use oxygen compatible gas..

 

[pt40fathoms]

Tanks and valve MUST be O2 clean if you are partial pressure blending the gas. In the vast majority of the times, this is the case. End of story, no further discussion needed. If you are not partial blending the gas, I would still O2 clean them. It's cheap and good insurance.

Now for your reg.

Only if you are planning to use gas blends that contain 40% or more O2. If not, than O2 cleaning of the reg is not required. That is not to say that you can pick up any old dirty seldom serviced piece of Ebay bargin special and use it. It should be clean and serviced, but O2 clean is not a requirment. BEWARE of some regs that have "exotic" metals. Titanium WILL react in an O2 enriched environment, causing it to start on fire. This would make for a very short dive,,,and life.

 

[100days-a-year]

Guess we bettter ground all those fighter planes with titanium components in them as they operate in an enriched 02 environment in the cockpit.Yes aluminium,magnesium and titanium will combust and burn so hot they will self-generate 02 from water.Aluminum in fact is an ingredient in napalm.But spontaneous combustion is a myth.Fire requires fuel,oxygen and a source of ignition and the abdiatic heat generated in a reg seems hardly sufficient to provide the spark.Product liability lawyers have got everyone sceaming "the sky is falling".02 cleaning is better than not but viton and halocarbon lubes are combustible.There's no harm in it, so I 02 clean every piece of equipment I own that may come into contact with enriched air.

 

[padiscubapro]

100days-a-year once bubbled...
Guess we bettter ground all those fighter planes with titanium components in them as they operate in an enriched 02 environment in the cockpit.Yes aluminium,magnesium and titanium will combust and burn so hot they will self-generate 02 from water.Aluminum in fact is an ingredient in napalm.But spontaneous combustion is a myth.Fire requires fuel,oxygen and a source of ignition and the abdiatic heat generated in a reg seems hardly sufficient to provide the spark.Product liability lawyers have got everyone sceaming "the sky is falling".02 cleaning is better than not but viton and halocarbon lubes are combustible.There's no harm in it, so I 02 clean every piece of equipment I own that may come into contact with enriched air.

I know of at least 1 incident that a titaium reg spontaneously combusted.. it happened in california a few years back. The reg ignited when the gas was turned on (the person was severly injured).. his mix was just over 70%, in fact the diver used an 80% mix more than once with the same reg...

in fact, going from ambient to 3500 psi 100% oxygen can generate temperatures over 2000f at the compression point!!! This definately meets the requirements for an ignition source!

Viton definate can burn but the flash point is very high, EPDM (used in APeks regs sold in the US) has even a higher flash point but is not as durable.. cristolube is extremely inert.. try this.. get a spoon, put a dab of cristolube on the spoon now heat it with a torch, the cristolube protects the covered portion while the unprotected turns color...

 

[jviehe]

The basic rule is that anything that will touch more than 40% oxygen, whether when filling or breathing, needs to be 02 clean. So, if they are PP filling -any- tank, it needs to be 02 clean. If you are breathign pure 02, the tank, reg needs to be clean.

 

[100days-a-year]

Where does 02 go from ambient to 3500 psi? Why don't Al tanks blow up when PP filling where it is possible to see the pressure actually go from 3500 to ambient?In a reg the air is at no time ever greater than 150~ more or less over ambient as the 1st stage steps down the pressue .The 1st stage orifice allows only a small volume of air by at lo pressures.Also what does a reg do when it freeflows.....? it gets cold or freezes up due to the expansion of whatever gas is coming out.I beleive there's a lot of legal hype and internet folklore here.Magnesium,Aluminum and to some extent titanium are used in inlet plenums for a variety of engines as well in a hot environment lots of fuel and in many cases increased PP02 due to turbo or superchargers.In a supposedly 02 clean environment,with deltaPs of less than 200 psi limiting abdiatic heat generation I'd have to see it happen in a lab repeatedly to believe it could happen.

 

[padiscubapro]

100days-a-year once bubbled...
Where does 02 go from ambient to 3500 psi? Why don't Al tanks blow up when PP filling where it is possible to see the pressure actually go from 3500 to ambient?In a reg the air is at no time ever greater than 150~ more or less over ambient as the 1st stage steps down the pressue .The 1st stage orifice allows only a small volume of air by at lo pressures.Also what does a reg do when it freeflows.....? it gets cold or freezes up due to the expansion of whatever gas is coming out.I beleive there's a lot of legal hype and internet folklore here.Magnesium,Aluminum and to some extent titanium are used in inlet plenums for a variety of engines as well in a hot environment lots of fuel and in many cases increased PP02 due to turbo or superchargers.In a supposedly 02 clean environment,with deltaPs of less than 200 psi limiting abdiatic heat generation I'd have to see it happen in a lab repeatedly to believe it could happen.

AMBIENT TO 3500- try the spg and the initial pressurization of a regulator first stage or did you forget it is connected to the tank... an oxygen fill at 3000 is more likely but the temp is still around that point.. I have a picture of an SPG that the boot melted from an oxygen ignition, it happened underwater so there was no catastrophic fire but lots of heat was generated. Even with the "restricted" orifice of the HP hose the gas gets heated quite rapidly, a free flow is a different issue you are getting cooling because there is a pressure drop (and expansion)not a rise... raising pressure of any gas generates heat, dropping the pressure loses heat... once the reg is pressurized the risk due to a small delta p is minimal (cant say zero), all problems are on the initial pressurization, there is very little retriction on the HP side, another source of ignition on initial pressurization is particle impingement, that is small rust particles hitting the screen on the first stage..

Al tanks don't burn for 2 reasons first the alloy is a combination of metals not just al, secondary the tank is a HUGH heat sink.. rapid heat buld up is only going to occur in a place where there is not sufficient material to sink the heat away.. in Russia they used to use TITANIUM cylinders with oxygen and they don't get ignition, why same reason - its one big heat sink....

there are plenty of studies about adiabatic compression with regards to oxygen and more patents to help solve the issue..