I don't know what the current common specifications are for oxygen you'd get for the welding shop, but do know that for medical uses (breathing) your medical advisor will send you to different sources who provide "medical oxygen."

For portable or temporary "emergency" use, a backup bottle of compressed oxygen will usually be provided, but even at lowest common "dosages" the most common size (portable) bottle provides only about 4 hours use, down to an hour or two per bottle for people who need the maximum common rate of O₂.

Not long ago, it was common for long term home use, to have liquid O₂ delivered and stored in fairly large cryogenic dewars. Obviously, this requires a rather substantial installation and some rather complex controls, filters, and temperature conditioners. Liquid oxygen (LOX) supplies may still be in use at some hospitals where they pipe O₂ to all the rooms, but I haven't asked anyone what local facilities are doing.

Most long term individual users now will use a "concentrator" that extracts oxygen directly from the air. The (US Medicare) spec for these devices is that they provide at least 98% pure O₂ output.

Full-face masks are almost never used if the treatment is just to supply supplemental O₂, with just a small "nose piece" inserted about a quarter inch into each nostril, so you still mix a significant amount of ambient air with what you breathe. Common concentrator "doses" start at about 2 Lpm and the most commonly used machines top out at about 5 Lpm.

The concentrator blows air through a "diatomaceous earth" filter that absorbs the nitrogen, with pure oxygen as the remaining output. Back-flushed at a different pressure and flow, the nitrogen is swept out for the next cycle. Most machines use two filters and switch them between filter and flush cycles for constant O₂ delivery, resulting in a mildly annoying characteristic noise - sort of a "Grrrrrrr-poof" in 3 to 5 second cycles.

The filters appear quite durable, with manufacturers recommending replacement at about 5 year intervals. Some people have reported using "salvaged" concentrators for generating welding O₂. The capacity of most machines would be too low for useful "shop welding" but might be good for jewelry work. Concentrators with a supplemental compressor to charge "bottles" are available, but are about double the (retail) price of the more common kind. Portable units are also available, and are quite compact, but I don't have any reliable reports on battery life between charges.

Full-face masks are used for treatment of apnea, but the machines used for this typically use just compressed air, to provide "forced positive pressure breathing" during sleep. Systems that provide "oxygen enrichment" may be availabe, but I haven't seen one with that feature.

Anyone actually needing 100% O₂ for medical treatment would have to be using a full-face mask, and would probably be in a hospital or otherwise under very stringent medical supervision. Even in this use, most "medical grade" masks retain some exhaled air and mix it with the incoming O₂, so that "less than 100%" effective mixtures can be provided (and so that CO₂ levels needed to regulate voluntary breathing aren't depleted).

So when does Little Hawk's Oxygen Bar open? And has the market analysis shown that the critters in the back yard can afford to spend enough there to support a profitable business?

John