# Max altitude without pressurization but with supplemental oxygen?

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#### Floydr92

##### Well-Known Member
Hi, just a curiosity more than anything.

How high can one fly without cabin pressurization but with an oxygen mask on?

There must be a point at which ear drums explode and blood boils.

#### FWSwe

##### Member
The Armstrong limit, about 19 km, where the boiling point is 37 degrees Celcius, ie: body temp.

#### Floydr92

##### Well-Known Member
Thanks, severe discomfort must come before that point though?
So how high could a pilot physically remain concentrated on flying without major discomfort, for an hour or so before dropping in altitute.

#### Rockiedog2

##### Well-Known Member
HBA Supporter
IIRC the airlines and military don't go above 250. somebody correct me if wrong. but that's just an FAR. I don't think our blood boiled.. Believe I would remember that for sure.

#### Hot Wings

##### Grumpy Cynic
HBA Supporter
Log Member
With supplemental O2 the limiting factor is going to be the oxygen partial pressure*. At some point to much O2 is just as bad as too little. The limit will also depend on the conditioning of the individual. This article is geared to diving but the physics is all the same:

https://www.quora.com/What-is-the-minimum-oxygen-content-in-air-that-we-need

*Partial pressure is not = to the relative concentrations of the gasses in the mixture.

#### rv6ejguy

##### Well-Known Member
You need a pressure mask above about 35,000 feet to maintain maximum blood saturation- which is very uncomfortable and tiring. You need to forcefully breath out against pressure and simply relax to let it fill your lungs. Pressurization is a wonderful thing...

#### TFF

##### Well-Known Member
If you are physically fit you can go pretty high, maybe 19,000. I have been to 14,000 without for short times and 11,000 for about 4 hours a couple of times. I have known people who zone at 9000. First Everest climbers did not have O2. My friends dream is to be able to fly his 2 seat Grumman at 20,000 sucking on O2; he thinks he can if he gets his 0-320 conversion.

#### Marc Zeitlin

##### Exalted Grand Poobah
How high can one fly without cabin pressurization but with an oxygen mask on?
~35K ft. with a regular, well fitting non-pressure mask - about 38K - 39K ft. with a pressure mask. As rv6ejguy pointed out, pressure masks are very uncomfortable. Jim Price flew his Long-EZ to 35,027 ft. with a standard mask (and obviously unpressurized aircraft). He said the main issue was icing of the canopy due to exhalation, and the freaking extreme cold. No real issues with breathing, though. And it took a LONG time to come down - you're pretty much in the coffin corner at that altitude - can't go faster without exceeding Vne and can't go slower without stalling. He said he wouldn't do it again .

Above ~39K ft., even a pressure mask can't maintain required partial pressure of O2, and time of useful consciousness decreases. When training for flying in Proteus at 52K ft., we used both regular and pressure masks. But TUC at 52K ft., even with a pressure mask, is shorter than the time it takes to descend to <39K ft., so we relied on the pressure vessel not to break, and didn't worry about it (much).

There must be a point at which ear drums explode and blood boils.
You can't get that high in an aircraft you can afford to buy. There are guys that fly EZ's in the low to mid 20's on a regular basis, with non-pressure masks. The cannulas you get with normal O2 tanks are good to 18K ft. - if you want a mask that's good to 35K ft, you've got to pay some \$.

#### psween

##### Well-Known Member
Not sure what gear he used, but Bruce Bohannen set the piston altitude record of level flight above 40k. I assume he was using a military pressure mask, pretty sure not a pressure suit though. He wasn't up there long of course, and an awful lot of training and testing lead up to the record. I have worn a pressure breathing mask though and can attest to how purely uncomfortable they are. Maybe they get better with practice, but I didn't ever get there!

Patrick

#### D Hillberg

##### Well-Known Member
some folks need supplemental O2 at sea level..........

#### Pops

##### Well-Known Member
HBA Supporter
Log Member
If you are physically fit you can go pretty high, maybe 19,000. I have been to 14,000 without for short times and 11,000 for about 4 hours a couple of times. I have known people who zone at 9000. First Everest climbers did not have O2. My friends dream is to be able to fly his 2 seat Grumman at 20,000 sucking on O2; he thinks he can if he gets his 0-320 conversion.
I used to routinely fly at 11k for 8-10 hours a day without O2. Maybe a total of 1500-2000 hrs.

Dan

#### Rackman

##### Member
Back in the day we flew the T-37 at FL250 almost every day. The plane was unpressurized, but a pressure demand regular would give you the correct amount of O2 at any altitude. The best I remember I think at FL250 you were on almost 100 % oxygen. If you flew that high for two or three hours (three sorties) the oxygen would form gas bubbles in your ears as you slept. Again just from memory, I think it was somewhere in the mid 60,000 ft range that your blood would boil if you lost pressurization.

#### Marc Zeitlin

##### Exalted Grand Poobah
Bob Harris did, to 49k and change. With only a pressure demand regulator.
49K doesn't burst your eardrums and boil you blood, which is what the OP asked, and was what I was referring to. It's freaking high, though . To get to the Armstrong limit, you've got to be somewhere around 60K ft. Close, but no cigar.

But I'll take back the "can't afford to buy" - at some point, someone will get over 60K ft. in a glider in a wave . But 60K ft. is a lot harder than 35K, or 40K, or 49K.

#### davidb

##### Well-Known Member
There must be a point at which ear drums explode and blood boils.
Your eustachian tubes prevent the eardrums from exploding. Imploding (on the descent) is more the problem if you have a head cold. As others have stated, your blood will "boil" at about 60K. But, evolved gasses (small bubbles in your blood and joints) could become a problem well before 60K. Prolonged flight at 25K is considered safe with suitable oxygen mask.

#### Toobuilder

##### Well-Known Member
HBA Supporter
Log Member
The blood pressure in your veins and arteries prevents boiling even in space. Just like a radiator cap on every car made in the last 80 years or so. Any blood in an open wound will likely foam, but not the whole system.

#### harrisonaero

##### Well-Known Member
some folks need supplemental O2 at sea level..........
Sidenote... when I was doing certified seat testing at FAA Civil Aerospace Medical Institute (CAMI) in OK City quite a few years ago we got to see their altitude chamber. The staff told us a story of a good looking blonde Air Force woman officer that showed zero signs of altitude exposure. No hypoxia effects whatsoever no matter the altitude. The guys in the chamber were loopy as everything and she was doing math, talking, etc like it was nothing. Of course many blonde jokes ensued.

Another sidenote... once when our company was doing flight testing at altitude one of the new engineers, a *very* straight laced tetotaller <and great guy>, all of a sudden couldn't keep his speech straight or seem to use his calculator. Of course his oxygen had quit working without him knowing. He got ribbed a bit for getting drunk at work

#### Kevin N

##### Well-Known Member
Just because you can do it, should you do it ? If you have reason to sit at altitude wearing o2 then go for it but to do it on purpose in my opinion you need a legitimate reason.

#### PW_Plack

##### Well-Known Member
You need a pressure mask above about 35,000 feet to maintain maximum blood saturation- which is very uncomfortable and tiring. You need to forcefully breath out against pressure and simply relax to let it fill your lungs...
...a phenomenon familiar to any user of a CPAP machine. Some people adjust quickly, others feel a sense of panic that they are "suffocating." Most people are somewhere in the middle, so practice may help.

Come to think of it, I wonder if a CPAP pressure mask would work for this application? If you repurposed the whole machine, you could also make use of the hose heater and maybe even the humidifier. The thing would even record your performance on an SD card. Hmmm...

#### Floydr92

##### Well-Known Member
Thanks for the responses guys, im pondering an electric aircraft. Being electric, the higher it can cruise the better...for the 'proof of concept' (if i ever get round to building it), FL250 unpressurized for one speed run is plenty...should do 383kts at that altitude on full power.
Just dreaming at the moment though.