There are those who care about papers and pay through the nose (if they can, availability is poor), and those who don’t and happily fly on welding Oxygen.
Airborne_Again wrote:
I could well be for administrative reasons. Different certifications/standards are involved and even though the same O2 could meet both standard, it may not come with “double papers”.
That may well be the case. I’m new to the O2 game and queried it with these Medevac guys (who were very helpful – they just filled up our bottle FOC from their supply. There was no commercial option at that airfield) and the answer was ‘because of the humidity and risk of freezing at low temps’, a bit along the lines of what @kwlf mentions in an earlier post.
But it seems to me that if the furred up ice was on the outside of the regulator, it must have been from the atmosphere rather than the tank.
This website states that medical oxygen can contain up to 60ppm of water
[ links fixed; note that links must not contain spaces within the URL, etc. ]
I have just read that story. Very entertaining and nicely written!
However I see no evidence of anything freezing up due to moisture. He mentions a mask; unless otherwise rigged, a mask is going to be delivering 100% oxygen. He doesn’t mention a demand regulator or an baro-controlled regulator of any sort. And you can get a lot of exhaled moisture in a mask which at -35C would freeze up.
However I don’t see evidence that his oxygen flow was ever interrupted; if it was constant flow then at 21.5k whatever would be ok on the ground would not be enough up there.
It’s a nice story but he makes it really clear that he didn’t have a clue about a lot of it.
Yes; 60ppm is in the right order of magnitude for commercial cryogenic distillation. It is 0.006%. If you take say a 10 litre cylinder that would be 0.6 of a cubic centimetre which is a few drops. It certainly won’t freeze up in the pipes unless the cylinder is upside down and it runs out into the fitting (it will be liquid at the relevant pressure in the cylinder) and it will not do anything for the human body water vapour requirements (whatever they are).
An old article, but still relevant:
https://apps.dtic.mil/dtic/tr/fulltext/u2/a041245.pdf local copy
At risk of putting silly mistakes in the public domain:
For aviation grade oxygen the max figure is 6.7ppm so there does seem to be a difference. I think the figure must pertain to decompressed gas, so if you imagine a 10L cylinder at 100 ATM with 60ppm of H2O vapour, that might be 60mls of water vapour (when decompressed). Air weighs 1.2kg/M^3 and water vapour will be about 18/29th the mass of air. So 60/1000,000*1.2*1000 (mass of rtp air in grams per cubic metre) = 0.072g of ice which is 0.09mls. On the face of it, this is not a lot, but I can imagine that it might be enough to block a needle valve in a regulator if it flash freezes as it decompresses. I know this can be a problem. This page suggests that scuba air should contain less than 24ppm of H2O. and this document discusses the risks of scuba regulators freezing up.
Quote
The essential phrase in Bob Grimstead’s story is further down the page:
Although I say in the article it was nearly empty, it actually wasn’t. It was still half full, but the bottle’s neck, valve etc were all white with furry ice when I looked over my shoulder after starting the descent.
The difference between a Turbulent and a hospital is that the hospital will be at 15 or 25 degrees (it is a law that every room in a hospital is either too hot or too cold) but the Turbulent at 20k feet will be really cold. ‘2 degrees per thousand feet’ really means something when you’re in a Turbulent. The gas will be even colder in the regulator as the oxygen decompresses.
For the sake of argument, if we accept that 0.09mls of ice might block a regulator (but 1/10 of this won’t), then if you are in a hospital environment that keeps the regulator warm enough to melt it as it forms, then you will not have a problem. If you are in an enclosed aircraft with decent cabin heating, you will not have a problem. If you have aircraft oxygen you will not have a problem. If you have medical oxygen which happens to have 6ppm rather than 60ppm of H20 vapour you won’t have a problem. But if you are in a cold environment and use medical oxygen which happens to have 60ppm of H2O vapour then just maybe you will get unlucky.
Perhaps Bob Grimstead is the only person ever to have suffered from using medical rather than aviation grade oxygen.
I phoned up British Oxygen a few years ago and they told me it is the same gas for all end uses; just the paperwork differs.
I suppose it is possible that, around the world, they have different specs for different end uses. But I bet you the gas will be the same, because the same process is used and quite possibly the machines come from the same company.
Regarding that high altitude flight, he reports visible ice, and you would get that forming simply due to gas expansion. The first stage reg on my MH kit gets very cold in use, and if the ambient was really low (like he had, but a TB20 is heated) then you would get ice forming on it. But this doesn’t mean ice is forming internally.
Also his story was written a while ago when processes may have been different.
If there was ice on the outside then I agree this is nothing other than a marker that the apparatus was cold enough to freeze water on the inside, if there was any.
Would there be any reason to economise when making different grades of oxygen even if you were using the same machines? For example, the scuba article talks about the need to refresh the drying agent, and that it may work less well in warm weather.
Would there be any reason to economise when making different grades of oxygen even if you were using the same machines?
Yes ! Happens anytime that someone sees an opportunity to charge more for a niche group.
As we know from misc hardware, a piece od f paper works wonders for profits.
Happens similarly in boating vs caravaning.
A German industrial gases supplier also confirmed that it is all the same, but for administrative process control.
When someone brings an aviation-marked container, he will het aviation oxygen – unless he requests something else explicitly.
I think you misunderstand me. I know marking up identical products to make money is a ‘thing’, but on the other hand you sometimes do get what you pay for.
My guess is that it’s probably generally going to be cheaper for a big company like BOC to make one type of high quality oxygen and give everybody the same, but if there were a company making dedicated medical oxygen (as an example) it might be worth their while using the same Oxygen-o-matic as BOC but perhaps changing the settings.
Is anybody else following this thread seeing lots of adverts for standalone liquid nitrogen generators? They seem to be about the size of a fridge, and if the adverts are to believed you plug them in and they take air in at one end and have a tap for liquid nitrogen at the other. I find myself tempted.
