Oxygen?

[oxyhacker]

Most of the distinctions we hear about between grades of oxygen exist only on paper. The distillation of air produces one very clean base grade that the supplier uses for just about everything, testing it and certifying it as necessary to meet the standards for each grade as it is bottled. For example, while medical O2, if as dirty as the USP and CGA specs allow, would be a very scruffy gas, and too dirty for good welding, it has been (in the US at least) just about impossible to find any medical oxygen that is actually as bad as the standards permit. And while the specs for aviator's O2 show it as being drier, several suppliers have told me that they bottle it exactly as the same way as they do all the other grades, and that only occasionally does a bottle fail to meet the dryness standard, and when it does it is just about always a tank which is fresh back from hydro.
The catch is, this may be changing. Using membrane separation technology it is possible to build a very small, self contained, oxygen plant that will produce fairly but not super pure O2, and these are starting to turn up all over as hospitals find it is cheaper to make their own. These plants can produce up to 99% O2 but are used mostly to produce lower UPS 93% (though the non-O2 is these mixes is almost exclusively nitrogen, which could be compensated for in your calculations if no other source existed) which is plenty good for most medical purposes but, obviously, questionable for diving or welding. So if one had to generalize it would be safe to say the welding O2 is probably a safer bet than medical O2. However, it is always dangerous to generalize about such things, so the best advice remains, as always - talk to the lab man at your gas supplier's plant and find out how they are doing things since that is the gas you will actually be breathing.

BS

Medical Oxygen is one of the lower grades of oxygen vailable, its just certified at the grade you are buying.. and in SOME juristrictions requires a prescription.

There are varying grades of medical o2.. the lowest alllows oxygen purity to be as low as 90%..

Avaiators grade is specified as 99.9%+ with a specifcic dew point (although 99%+ is not always availabel in all countries)


In several countries there is a DIVING grade, which is specified as 99.9% plus it has a very low dew point.. (very dry)

Industrial non graded is just that... This being said Industrial is usually 99% plus becaue its important to not have any contaminates when welding..

 

[jeffkruse2000]

I thought the non-O2 part was primarily Argon? That would be true if they used PSA to produce the O2.

 

[webediving]

Also have in mind that the welding O2 is not analyzed for contents. Hospital grade O2 is. Another big problem is that that some places when they re-fill the welding O2 botles, the botles are not put under vaccum before re-filling them. If the previous owner of the botle had it hooked up to another gas and contaminated the botle you will never know. O2 for medical & aviation are subjected to a vaccum before re-fills! I had problems before with Helium specially when botles are used in HPLC machines in Labs. So I rather have a gas that has been analyzed.

I stress you read the O2 Hacker book it will give you plenty of info on O2 and also take a Blender course. I can not believe that they did not cover O2 gas in your Nitrox class.BTW there is another source for O2 that is LOX (liquid O2).

T

 

[pescador775]

I use welding O2 and it tests 99+ percent, totally odorless & tasteless. The statement that some suppliers refill welding 02 storage cylinders without vacuuming is questionable. Good luck on their insurance and liability. I doubt that any major supplier would be that callous. Also, it is hard to believe that any distributor of cryogenic gas would use membrane technology.

I should mention that gas distributors typically take delivery of cryogenic oxygen which by its nature is bone dry. Therefore, I am confused about statements saying that some grades of oxygen decanted to storage cylinders are dryer than other grades or batches. I am interested in the explanation, from a technical standpoint.

 

[captain]

I use welding O2 and it tests 99+ percent, totally odorless & tasteless. The statement that some suppliers refill welding 02 storage cylinders without vacuuming is questionable. Good luck on their insurance and liability. I doubt that any major supplier would be that callous. Also, it is hard to believe that any distributor of cryogenic gas would use membrane technology.

I should mention that gas distributors typically take delivery of cryogenic oxygen which by its nature is bone dry. Therefore, I am confused about statements saying that some grades of oxygen decanted to storage cylinders are dryer than other grades or batches. I am interested in the explanation, from a technical standpoint.

I operated a cryogenic gas plant for several years. The process produces gases with no moisture. All mosture is frozen out of the air long before it is distilled into oxygen, nitrogen and argon.

 

[cool_hardware52]

Also have in mind that the welding O2 is not analyzed for contents. Hospital grade O2 is. Another big problem is that that some places when they re-fill the welding O2 botles, the botles are not put under vaccum before re-filling them. If the previous owner of the botle had it hooked up to another gas and contaminated the botle you will never know.T

Perhaps this is possible, but that's not how my supplier does it. The guy filling the O2 bottle has a vested interest in filling a clean bottle. If your thoretical contaminated bottle has "fuel" in it everybody in the surrounding area might know.

They do view bottles returned with less than ~200 psi with suspicion.

They have one Big LOX tank from which they fill everything, ABO, Medical, welding....


Tobin

 

[gcg]

MAN, did i open a can o' worms. ok i think ive had my question answered, and im going to pursue using my welding 02. aftet 1 getting more info from my gas supplier about where and how they're aquireing the gas 2. after mreading the oxyhacker book. i could probubly fill scuba tanks with water at my dive shop and the guys wouldnt notice nor care to look at what im doing.
thanks for all your post and by all means
DEBATE ON....

 

[PaulChristenson]

Oxygen is available in 3 grades.

Industrial (i.e.: for welding)

Aviators (low moisture content)

Medical (requires prescription in some areas and by quantity)

The main significant difference in these cylinders is not the gas it the handling of the cylinder. A welding O2 cylinder since it is ASSUMED that it will not be for breathing can be refilled ON TOP of what is in it. There is a chance, albeit small that some acetylene MAY have back flowed into that cylinder due to a bad check valve on the welding rig. It has no affect on welding but could if you breathed it at depth.

Medical and Aviators Grade Oxygen are handled more meticulously. When a cylinder is returned for recharging the cylinder is emptied REGARDLESS of how much is in it and is further emptied to a vacuum. There by eliminating the possibility of ANY gas being in the cylinder at time of refilling. These cylinders are then labeled and tagged, serial marked and if you like a purity report will be provided to you as to the exact percentage of oxygen (usually 99.??).

These procedures are not arbitrary they are set by the CGA compressed gas association.

http://www.fda.gov/cder/dmpq/freshair.htm

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=FEDERAL_REGISTER&p_id=18073

 

[cool_hardware52]

Oxygen is available in 3 grades.

Industrial (i.e.: for welding)

Aviators (low moisture content)

Medical (requires prescription in some areas and by quantity)

The main significant difference in these cylinders is not the gas it the handling of the cylinder. A welding O2 cylinder since it is ASSUMED that it will not be for breathing can be refilled ON TOP of what is in it. There is a chance, albeit small that some acetylene MAY have back flowed into that cylinder due to a bad check valve on the welding rig. It has no affect on welding but could if you breathed it at depth.

Medical and Aviators Grade Oxygen are handled more meticulously. When a cylinder is returned for recharging the cylinder is emptied REGARDLESS of how much is in it and is further emptied to a vacuum. There by eliminating the possibility of ANY gas being in the cylinder at time of refilling. These cylinders are then labeled and tagged, serial marked and if you like a purity report will be provided to you as to the exact percentage of oxygen (usually 99.??).

These procedures are not arbitrary they are set by the CGA compressed gas association.

http://www.fda.gov/cder/dmpq/freshair.htm

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=FEDERAL_REGISTER&p_id=18073

Acetylene tank are full of acetone, and the acetylene is a dissolved in the liquid acetone. A "full" acetylene tank is usually under 400 psi. Output to the torch is almost always under 15 psi

Welding O2 is furnished in bottles are full at ~2500 psi, and "empty" at 200-300 psi.

It would require very unique set of multiple failures to get Acetylene to backup into the Oxygen bottle. Lets see, first you need the acetylene reg to suffer "IP" creep so the Acetylene pressure rises to ~300 psi. Then you need both torch valves open and the torch tip plugged, just when the O2 bottle is down below 300 psi.

Acetylene is very unstable. A mixture of acetylene and air will Detonate, not just burn, but detonate, when ignited at 1 ATA. This is the classic fill a bag with Acetylene and light it. (Don't do this at home, please)

I wouldn't want to mess with 300 psi Acetylene mixed with air, much less mixed with 200-300 psi O2. If this was a real risk welding shops would be in ashes routinely.

You might be able to make a case for other contaminates in welding O2 bottles, but if acetylene is your concern I think it unlikely.

Tobin

 

[duckster3d]

i buy my gases from Praxair, as tobin said they pull a vac on all bottles before refilling. I talked to the lab tech and she took me on a tour of the plant and the filling station. I was quite impressed on how carefully they handled all the bottles. also a bottle is a bottle. till they put the sticker on they are all the same. i went in once to pick up some helium and they were out of the welding grade, so they just pulled off the med sticker and replaced it with a welding sticker. enough said.