Can one breathe industrial oxygen

Hey, this is a cool group. Just found it. I'm definitely a novice metalworker, though I have an ancient lathe and make stuff on it from time to time. I hope someday to own a better one, and a vertical mill to go with it (grin).

Around here, at least (mid-state NY), the price difference between welding O2 and USP (medical) O2 is negligible for the large (200cf-ish) cylinders. It's only a few dollars more for USP O2, though I don't recall exactly how much. Aviation O2 isn't available at my local gas supply company (I asked), so I never got a price on it.

As to whether one can breathe welding/industrial O2 safely, what follows is my opinion: It depends. For scuba diving, Technical Diving International gas mixing standards call for USP or Aviation O2 to be used for mixed-gas (Nitrox and Trimix) blending because the partial pressures of any contaminating gases rise as a function of depth, exacerbating their effects. Clearly, this also applies to using pure O2 under water.

At sea level or above, depending on whatever else was in there, you're still taking a chance. For example, consider a tank that contained 100% acetylene at atmospheric pressure before being filled with O2. The usual fill pressure of 2400 PSI would yield one part in 163 (2400/14.7), or ~6,100 ppm at sea level. The OSHA exposure limit for acetylene is

1,000 ppm. Oops. (Do your own math and research the exposure limits before you breathe anything!)

For CO, 50 ppm is a problem and 70 ppm is a real problem. 6,100 ppm is obviously Right Out. Even at 10,000 feet, where if I recall correctly flight crew must use O2 after 20 minutes, that's still 70% or so of

6,100 ppm (~4,300 ppm), so aviation use would not be safe either in this case. There could be other contaminating gases I haven't thought about that might be worse than CO. And if the fill pressure is 2105 PSI, the percentages are even worse.

Now, how an O2 cylinder would wind up *full* of a bad gas, or even with a high percentage of it, before being filled with O2 is not at all clear to me. Someone would almost have to work at it! Nonetheless, safe definitely beats sorry hands down in this case, and "probably OK" means that sometimes it won't be OK. Since "not OK" can translate to "dead," I'm going to continue to buy USP O2 for breathing.

My understanding is that USP and aviation grade O2 are put in cylinders that have been purged with O2 before final filling, so the maximum levels of contaminants are quite low no matter what's in the tanks before they are purged. This is a very "practical difference" to me when the O2 will be a breathing gas, even though the source of the O2 used to fill any tank (industrial, USP, or aviation grade) is very likely to be exactly the same.

JRE wrote in sci.engr.joining.welding on Fri, 28 Jan 2011 19:10:53 -0500:

If you like it here, you might like rec.crafts.metalworking. More noise, but nothing good filters can't fix.

Acetylene cylinders are purpose-built and can't be filled with anything other than acetylene.

It's 12,500 feet and 30 minutes. At least in the US. And the chances of finding a large C0 cylinder at a welding shop is just about zero.

If the tank was full of acelelene at atmospheric pressure before filling with oxygen the ppm od acelelene in the breathing gasses would be the absolute least of your problems, as pure acetelene in it's free form is extremely unstable at anything over about 16psi. Combine that characteristic of acetelene with 100% oxygen environment and you won't have a TANK, much-less an unbreathable mixture.

Also, putting CO into a highly pressurized pure oxygen atmosphere for any time would LIKELY end up with an exothermic reaction producing CO2.

Why is acetylene even in this discussion, it is kept in a special bottle in suspension in acetone.How would you get acetylene contamination in an oxy bottle?

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MT O2 cyl @ 0 psi connected to a torch with a blocked tip and no (or non functioning) anti flashback check valves could result in acet moving into the O2 side of the system, perhaps all the way to the O2 tank. More often results in flashback and destroyed hoses (and regulators), but there is always the potential for something worse. The difference in normal working pressures will more often result in O2 travelling up the acet side but as always YMMV. This is a good reason not to try to get the very last bit of gas from any cylinder and to keep your torch tip out of the mud. Usually when used for cutting the O2 cyl will be changed while it still contains greater than the max acet operating pressure, but the acet side usually is operating well below the pressure of the O2 side. When welding or heating, the pressures are more likely to be similar and a large rosebud heating tip will often demand more acet delivery than a small or low acet cylinder can deliver, which is why acet manifolding of multiple cylinders is often recommended. Cold can also reduce the delivery rate of acet.

Acetylene is a very unstable high energy gas and oxygen supports rapid and vigorous combustion (of almost anything). In isolation or even more so in combination (or proximity) they both require respect and careful handling.

Good luck, YMMV

Anything that goes boom, causes shards of glass and metal to fly, and leaves you dazed, bleeding, blackened, and saying, "huh?", is generally serious.

Steve