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FAR 91.211 tells us when supplemental oxygen is required, but it's not very specific as to how that oxygen is to be provided. FAR 23.1447 gives some information about installed systems, but I can't find much on FAA requirements if you're using a portable system (cylinder, regulator, and cannula/mask like a Mountain High system).

Are there specific requirements/recommendations regarding portable oxygen equipment for Part 91 General Aviation, or can you just pick up a a medical or welding tank, stick a regulator on it, and pass out masks to your passengers?

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    $\begingroup$ I don't think a welding tank is fit for human respiration, though it seems a heavy debate on the internet $\endgroup$ – ratchet freak Oct 26 '14 at 9:35
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    $\begingroup$ I don't have references right now so I'll save an answer for later, but you should have aviators oxygen because it has the water removed. The others actually have enough water in them that they could freeze during a rapid decompression, which is just when you would need it the most. $\endgroup$ – Lnafziger Oct 26 '14 at 15:44
  • $\begingroup$ @Lnafziger I was more thinking about the sort of equipment you'd carry on an unpressurized plane, but as far as the fill yes: it's important that the oxygen used in pressurized aircraft is "dry" - around here everything I can get my hands on (ABO, welding oxygen, and diving oxygen) is dry condensed O2 - they fill it all from the same LOX truck). I think medical oxygen is the same these days (at least in hospitals and local EMS the standard is to use an external water chamber to humidify it). Still not a big price difference to get ABO at the airport :) $\endgroup$ – voretaq7 Oct 26 '14 at 22:25
  • $\begingroup$ @ratchetfreak the big incompatibility is often the regulator fitting (if you can't hook up your masks to the tank it's not gonna be too useful) $\endgroup$ – voretaq7 Oct 26 '14 at 22:28
  • $\begingroup$ O2 in the US is normally sourced from the same fractional distillation plant. The difference between ABO, medical and welding that the purity requirement of O2 is greatest for welding. The practical difference is that ABO and medical tanks are sampled after filling to assure contents. $\endgroup$ – mongo May 4 '17 at 9:59
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An even more important question than how is how much oxygen to take, but there's no specific FAA guidance or regulation on either point. Different aircraft can carry different equipment, and people have different requirements depending on their age, lungs, blood chemistry, whether they smoke, day vs. night etc. The FAA's guide on oxygen equipment for GA use is extremely limited and although it describes a range of equipment types it doesn't mention any specific requirements.

Having said that, the 'usual' approach seems to be to use a pulse oximeter to measure your oxygen saturation and if it's too low then go on oxygen immediately, regardless of altitude or other considerations. The moderator of AOPA's medical forum is an AME and he recommends oxygen use any time your saturation level drops below 90%, which is apparently also the required level in hospitals for a patient to make an "informed" - i.e. clearheaded - decision.

But returning to the question of equipment, there aren't any regulations on this at all, so provided that the equipment is safe to use in the aircraft (including not obstructing exits and so on) and not illegal under any other law that might apply (carriage of dangerous goods or whatever) then you can go for it. But the usual 'always act as if you'll have to justify your decisions to the FAA tomorrow' advice applies here, IMO, and personally I would always go with an aviation-specific setup if I needed one.

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  • $\begingroup$ I thought the FAA had something in an advisory circular on flow rates (LPM) at various altitudes for mask/cannula use - that would probably make another interesting question. Everyone I know just uses a pulse oximeter though - better than guesswork with flow rates and differing lung conditions/capacities. $\endgroup$ – voretaq7 Oct 26 '14 at 22:28
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    $\begingroup$ It would also be important to SECURE the oxygen bottle so that it doesn't become a missile in an accident/turbulence, and to protect it so that the regulator isn't broken off. $\endgroup$ – Lnafziger Oct 27 '14 at 5:16
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If your aircraft is certified under Part 23 as opposed to CAR3, it would be obligated to abide by the following:

§23.1441 Oxygen equipment and supply.

(a) If certification with supplemental oxygen equipment is requested, or the airplane is approved for operations at or above altitudes where oxygen is required to be used by the operating rules, oxygen equipment must be provided that meets the requirements of this section and §§23.1443 through 23.1449. Portable oxygen equipment may be used to meet the requirements of this part if the portable equipment is shown to comply with the applicable requirements, is identified in the airplane type design, and its stowage provisions are found to be in compliance with the requirements of §23.561

I added the boldness to the text.

So, what portable oxygen is identified in an aircraft's type design? What is a "type design" anyway?

One source says Type design is this:

(1) The drawings and specifications, and a listing of those drawings and specifications, necessary to define the configuration and the design features of the product shown to comply with the requirements applicable to the product;

(2) Information on dimensions, materials, and processes necessary to define the structural strength of the product; and

(3) The Airworthiness Limitations section of the ICA as required by Parts 23, 25, 27, 29, 33, and 35, or as otherwise required by the Administrator

So how do you get from needing it to be identified in the type design to its ok to use it? Unless you find where it is identified... you can't connect them.

But CAR3 was more lenient on this and portable oxygen systems do not violate it. I find no mention of Oxygen requirements in CAR3.

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