Flying with oxygen : recommended also for 20.000 plus feet?

[aviatoreb]

33 minutes ago, Austintatious said:

This is a good thread... I have a few pennies to toss in.

 

First off, If you are going high and using oxygen, you are really missing out if you don't have a pulse demand system such as Mountain High.  Not only does it conserve oxygen to a degree you will not believe if I tell you, but it adds what I consider a large margin of safety. The unit will sound an alarm if you are not breathing oxygen.  

I have had my O2 system fail on me at FL210... well, fail may be a bit harsh, but what happened was that my elbow knocked my scott connector (before I had the MH system)  loose and I stopped receiving oxygen.  I noticed pretty quickly,  hypoxia for me feels miserable so there is no going off into a euphoric la la land for me.  This is obviously different for different people.  This is why I feel the MH system adds so much safety, you miss ONE breath and an alarm will go off, you cannot ask for better awareness of your O2 intake.   

As far as how high is safe:  That probably varies for everyone.  I am comfortable with FL210 and I will explain why.  Having been in an altitude chamber, I know what it is like at FL250 and it is MUCH more rapid onset of symptoms and you will find yourself in bigger trouble a lot faster than at 210. 

Looking at the TUC chart

So, by staying at FL210 or lower I have 10 min.... go to FL250 and you drop to 3-5min.  And believe me, the 5 min is for the youngsters.  More than likely if you are 30 or older it will be closer to 3 min.

Now, keep in mind, if you found yourself at FL250 with a failed O2 system and symptoms of hypoxia (which you will feel IMMEDIATELY) , you dont need to get down to only FL 180, you are ALREADY hypoxic, you need to get much lower, probably 12,500 or less.  So you have 12,500 feet to lose and you need to do it pretty quickly. 

I can pop speed brakes and reduce power a few inches and come down at about 1500 FPM at the yellow arc.  That will take 8.3 min to get down to breathable air.... IMHO this is simply not fast enough.  So, from FL250 if I have an 02 failure I need to be making a large reduction in power and getting that rate to more like 3000 FPM which will get me to 12.5 in 4 min.   This is certainly achievable, however I now put my engine at risk of shock cooling.  Or at the very least subject it to large rapid changes in CHT which is also not good. 

I don't want a failure of my 02 system to be a major event.  If I limit myself to FL210, I start with 10 min of Useful consciousness,  which in itself is plenty of time to 1: see if the problem can be solved, say by plugging the scott connector back in!  and  2.  begin a much more normal descent down to breathable air.

You give up about 8 knots staying at 21 vs 25.     Over A full tank of fuel that gives 5 hours of cruise flight, this is less than 15 extra min of flying.

 

 

I've always been confused by tables like that.  9 seconds to not conscious at FL43?  I understand its very unhospitable up there, but most of us can simply hold our breath right now sitting where we sit, for maybe a minute.  We can go underwater for a minute.  Some people can hold their breath for five minutes, and more.  How can it be that thin air causes us to go unconscious within 9 seconds?  I am not doubting - I know that table is carefully researched - I am declaring this is a point of confusion I would appreciate if someone can explain to me the seemingly contradictory things here.

[Austintatious]

1 hour ago, aviatoreb said:

I've always been confused by tables like that.  9 seconds to not conscious at FL43?  I understand its very unhospitable up there, but most of us can simply hold our breath right now sitting where we sit, for maybe a minute.  We can go underwater for a minute.  Some people can hold their breath for five minutes, and more.  How can it be that thin air causes us to go unconscious within 9 seconds?  I am not doubting - I know that table is carefully researched - I am declaring this is a point of confusion I would appreciate if someone can explain to me the seemingly contradictory things here.

Yea, seems strange I know.   it sort of just pulls the oxygen right out of you.  remember, when you are holding your breath, there is air in there... when you decompress, that air is either coming out of you or exploding your lungs if you try to hold it. 

At our breathable altitudes, even if you exhale completely, there is still more air in your lungs than at those extreme altitudes.

On top of that, the  partial pressure is very low and thus you cannot as easily absorb the tiny amount of O2 that is present.

 

 

Edited April 23, 2023 by Austintatious

[aviatoreb]

7 minutes ago, Austintatious said:

Yea, seems strange I know.   it sort of just pulls the oxygen right out of you.  remember, when you are holding your breath, there is air in there... when you decompress, that air is either coming out of you or exploding your lungs if you try to hold it. 

At our breathable altitudes, even if you exhale completely, there is still more air in your lungs than at those extreme altitudes.

On top of that, the  partial pressure is very low and thus you cannot as easily absorb the tiny amount of O2 that is present.

 

 

So its the rapid decompression? If you were at FL43 but in stasis it would be different.  If in an unpressurized hull wearing oxygen if you stop using the oxygen then would useful time of consciousness be more like a minute or more if you took a big breath before removing the mask?  Again in absence of no rapid depressurization.

[802flyer]

7 hours ago, Will.iam said:

Right about the time your lungs are screaming for air about a minute and 30 seconds my oxygen level starts diving through the 80’s but what is really interesting is when i take the first breath, i start to feel better but the oxygen reading actually continues to drop about 5 more points lower (my personal record is 77) but then jumps back up 15 points and on the next breath goes back to 98 or 99. S

A good illustration of the lag of the SpO2 sensor for sure.

The lungs-screaming sensation is from CO2 building up rather than oxygen dropping down. So you feel better once you start blowing off the CO2 by breathing again.

[Austintatious]

13 minutes ago, aviatoreb said:

So its the rapid decompression? If you were at FL43 but in stasis it would be different.  If in an unpressurized hull wearing oxygen if you stop using the oxygen then would useful time of consciousness be more like a minute or more if you took a big breath before removing the mask?  Again in absence of no rapid depressurization.

The rapid decompression does have an effect, but I do not know how much.   That being said, in the alt chamber that is precisely what I did... took the O2 mask off at FL250.  And I only made it 3 min.  So I suspect we are talking mere seconds of difference, not minutes

 

Edited April 23, 2023 by Austintatious

[aviatoreb]

6 minutes ago, Austintatious said:

The rapid decompression does have an effect, but I do not know how much.   That being said, in the alt chamber that is precisely what I did... took the O2 mask off at FL250.  And I only made it 3 min.  So I suspect we are talking mere seconds of difference, not minutes

 

What happened after 3 min - did you pass out or did you become useless?  I am interested since I bet you became useless before that.

I've been up to FL25 on a one time been there done that situation but I dont plan on going back in large part because of this discussion.

But I do go to FL19 as sort of my last stop reasonable place and pretty much FL21 is my personal limit.  17,000 frequently.  I am curious how to read the 20-30 min at FL18.  I bet that is before passing out - and one is useless well before then.

I've hiked several times to 14,000 in Colorado and I can say - yeah oh yeah you feel it - and its in the head too.

[802flyer]

The lungs are very good at gas exchange, i.e. equalizing the concentration of gasses between our blood and the environment. If we suddenly find ourselves in an atmosphere with a low partial pressure of oxygen, there's no gatekeeper standing in our alveoli making sure that the oxygen doesn't diffuse out of our blood into the exhaled air instead of the other way round. So if we take the mask off, our lungs start scrubbing O2 out of the blood.

The freshly de-oxygenated blood also has a very short trip through the pulmonary veins, though the left side of the heart, and then straight up the neck to the brain. So it only takes a few breaths for the brain to start receiving blood that has been scrubbed of oxygen by us breathing in an oxygen-deplete atmosphere.

If you are breathing through a functional mask at FL430 and hold your breath with the mask still on your face, of course you'll get the full minute-ish before wanting to breath again. So if you were to take your mask off your face 9 seconds after beginning to hold your breath, you won't suddenly pass out by virtue of the mask being removed from your face. However if you start breathing again, your brain will soon be bathed in useless blood and you'll become useless in short order.

[Austintatious]

13 minutes ago, aviatoreb said:

What happened after 3 min - did you pass out or did you become useless?  I am interested since I bet you became useless before that.

I've been up to FL25 on a one time been there done that situation but I dont plan on going back in large part because of this discussion.

But I do go to FL19 as sort of my last stop reasonable place and pretty much FL21 is my personal limit.  17,000 frequently.  I am curious how to read the 20-30 min at FL18.  I bet that is before passing out - and one is useless well before then.

I've hiked several times to 14,000 in Colorado and I can say - yeah oh yeah you feel it - and its in the head too.

Keep in mind, everyone is different...

I became useless long before the 3 min mark.... At the 3 min mark the instructor had to put the mask on my face as I was unable to do it.  My heart rate was 195 bpm and my O2 had dropped to 57.   At ~60 is where consciousness can be expected to be lost.

[wombat]

I'm no medical expert.     Here is what I think is going on...

I think it takes more than 9 seconds for the oxygenated blood in your lungs to reach your brain, so there has to be something going on that acts on your entire circulatory system at the same time.    

So if we consider the pressures and partial pressures, and pressure differentials, how about this as a theory....

 

Your cells need a oxygen pressure differential in order to oxygenate themselves that is an absolute differential.  Let's call it 0.5 PSI (I'm sure anyone with medical training is screaming in their heads on on their keyboard at me right now!  Just be glad I didn't measure it in cars per football field).    So without a 1 PSI difference in the partial pressure of the oxygen in the blood and the partial pressure of oxygen in the cells, the cells will not absorb the oxygen in the blood.

 

So when the atmospheric pressure is 3 PSI (21% of 14 PSI)  your blood has maybe 2.5 PSI, and then your brain cells have 2 PSI.   Life is good.

When the atmospheric pressure drops 7 PSI (18,000'), the air has 1.5 PSI, blood now has 1 PSI and your brain cells have 0.5 PSI.  Not good but not instantly deadly.

When the atmospheric pressure drops to 3.5 PSI, the air has about 0.75 PSI, blood has 0.25 PSI, and the brain... Has nothing.  

 

 

This is just a half-baked theory.   I did have a cup of earl grey tea this morning, but I did not stay at a Holiday Inn Express.

[donkaye]

3 hours ago, Austintatious said:

This is a good thread... I have a few pennies to toss in.

 

First off, If you are going high and using oxygen, you are really missing out if you don't have a pulse demand system such as Mountain High.  Not only does it conserve oxygen to a degree you will not believe if I tell you, but it adds what I consider a large margin of safety. The unit will sound an alarm if you are not breathing oxygen.  

I have had my O2 system fail on me at FL210... well, fail may be a bit harsh, but what happened was that my elbow knocked my scott connector (before I had the MH system)  loose and I stopped receiving oxygen.  I noticed pretty quickly,  hypoxia for me feels miserable so there is no going off into a euphoric la la land for me.  This is obviously different for different people.  This is why I feel the MH system adds so much safety, you miss ONE breath and an alarm will go off, you cannot ask for better awareness of your O2 intake.   

As far as how high is safe:  That probably varies for everyone.  I am comfortable with FL210 and I will explain why.  Having been in an altitude chamber, I know what it is like at FL250 and it is MUCH more rapid onset of symptoms and you will find yourself in bigger trouble a lot faster than at 210. 

Looking at the TUC chart

So, by staying at FL210 or lower I have 10 min.... go to FL250 and you drop to 3-5min.  And believe me, the 5 min is for the youngsters.  More than likely if you are 30 or older it will be closer to 3 min.

Now, keep in mind, if you found yourself at FL250 with a failed O2 system and symptoms of hypoxia (which you will feel IMMEDIATELY) , you dont need to get down to only FL 180, you are ALREADY hypoxic, you need to get much lower, probably 12,500 or less.  So you have 12,500 feet to lose and you need to do it pretty quickly. 

I can pop speed brakes and reduce power a few inches and come down at about 1500 FPM at the yellow arc.  That will take 8.3 min to get down to breathable air.... IMHO this is simply not fast enough.  So, from FL250 if I have an 02 failure I need to be making a large reduction in power and getting that rate to more like 3000 FPM which will get me to 12.5 in 4 min.   This is certainly achievable, however I now put my engine at risk of shock cooling.  Or at the very least subject it to large rapid changes in CHT which is also not good. 

I don't want a failure of my 02 system to be a major event.  If I limit myself to FL210, I start with 10 min of Useful consciousness,  which in itself is plenty of time to 1: see if the problem can be solved, say by plugging the scott connector back in!  and  2.  begin a much more normal descent down to breathable air.

You give up about 8 knots staying at 21 vs 25.     Over A full tank of fuel that gives 5 hours of cruise flight, this is less than 15 extra min of flying.

 

 

The Mountain High System was a complete failure in my airplane, possibly as a result of the built in altitude compensating regulator (I did buy the adapter; didn't work).  I sent the unit back.  Even on the highest level I couldn't get a saturation level above 93 and I demand at least 96.  I, also, didn't like hearing breathing constantly over the headset.  Compared to other airplane costs, buying O2 along the way is relatively cheap.

[Fly Boomer]

5 hours ago, Austintatious said:

So, from FL250 if I have an 02 failure I need to be making a large reduction in power and getting that rate to more like 3000 FPM which will get me to 12.5 in 4 min.  

From FL250, if I have an O2 failure, I need to grab one of my two oxygen backups.

[Austintatious]

2 hours ago, donkaye said:

The Mountain High System was a complete failure in my airplane, possibly as a result of the built in altitude compensating regulator (I did buy the adapter; didn't work).  I sent the unit back.  Even on the highest level I couldn't get a saturation level above 93 and I demand at least 96.  I, also, didn't like hearing breathing constantly over the headset.  Compared to other airplane costs, buying O2 along the way is relatively cheap.

That is strange, there was definitely something strange going on.  Also, I cannot hear my breathing over my headset, not sure how this was even an issue for you.  I have no issues with low O2 even using a cannula at FL210.

O2 refills range in cost... at my home base it was about 80 bucks to get someone to come fill it.  I have had issue on the road with not being able to find someone to do it... now with the MH system, I need a refill  about every 1.5 years.

A really long and high flight with myself and my wife will use up maybe 80psi from the bottle.

Edited April 23, 2023 by Austintatious

[Austintatious]

34 minutes ago, Fly Boomer said:

From FL250, if I have an O2 failure, I need to grab one of my two oxygen backups.

Sure, if you carry a backup and keep it accessible... Me personally, I'd  rather not have it to bother with for hardly any benefit.  I can operate safely at FL210 without the need for it... I have enough stuff in the plane as it is.  But that is just me.

[Will.iam]

I remember reading or maybe it was an interview but i remember the test pilot was up at altitude and all of a sudden he had hypoxic symptoms and recognized he needed to get down fast and immediately lowered the gear popped the speed brakes and dropped down very quickly. At the time i was like wasn’t flying at cruise speed be too fast to lower the gear? but my experiences up to that point was flying down low where IAS was much higher than when up in the FL’s where even though true airspeed is very high the IAS is actually below gear extension speed and once down and locked can go up to 165kias in my M20K so if it means the difference between staying conscious or not, I’m lowering the gear before my IAS starts climbing from the emergency descent to help me expedite down. 

[Fly Boomer]

53 minutes ago, Will.iam said:

I remember reading or maybe it was an interview but i remember the test pilot was up at altitude and all of a sudden he had hypoxic symptoms and recognized he needed to get down fast and immediately lowered the gear popped the speed brakes and dropped down very quickly. At the time i was like wasn’t flying at cruise speed be too fast to lower the gear? but my experiences up to that point was flying down low where IAS was much higher than when up in the FL’s where even though true airspeed is very high the IAS is actually below gear extension speed and once down and locked can go up to 165kias in my M20K so if it means the difference between staying conscious or not, I’m lowering the gear before my IAS starts climbing from the emergency descent to help me expedite down. 

As @Austintatious points out above, based on his experience at FL250, you probably have seconds, not minutes, to do whatever you are going to do.  While  you may not be unconscious in the first few seconds, you might as well be.  I have read lots of strategies for getting down fast, but none will get you down in seconds.  In those few precious seconds, I'm reaching for my oxygen backup.

[Schllc]

Anyone who is planning to fly in the flight levels should do the hypoxia training to see how their body reacts. It will be very edifying, just seeing the diversity of the effect it has on people. 

[Pinecone]

THIS ^^^^

YOUR symptoms and TOC is not the same as mine or other people here online.

Again, when I was about 27 years old in USAF UPT, I went probably close to 10 minutes, functioning (sign name, do simple math problems, etc), until they finally gave up on me.  Others in my class were gone in a minute or two.

And the problem is, explosive decompression, you KNOW you have a problem.  System issues, you don't realize you have a problem until it is too late and you are not functional.

[Austintatious]

Good post @Pinecone

The effects on me where an almost complete inability to do even basic calculations.  Or at least to write it down, I remember being able to think but translating those thoughts to actions was difficult.  I know that sounds strange, but that is the best way I can describe it.  Hamsters running really fast, but the chain was off the sprocket.

 

 

[A64Pilot]

20 hours ago, wombat said:

I'm no medical expert.     Here is what I think is going on...

I think it takes more than 9 seconds for the oxygenated blood in your lungs to reach your brain, so there has to be something going on that acts on your entire circulatory system at the same time.    

So if we consider the pressures and partial pressures, and pressure differentials, how about this as a theory....

 

Your cells need a oxygen pressure differential in order to oxygenate themselves that is an absolute differential.  Let's call it 0.5 PSI (I'm sure anyone with medical training is screaming in their heads on on their keyboard at me right now!  Just be glad I didn't measure it in cars per football field).    So without a 1 PSI difference in the partial pressure of the oxygen in the blood and the partial pressure of oxygen in the cells, the cells will not absorb the oxygen in the blood.

 

So when the atmospheric pressure is 3 PSI (21% of 14 PSI)  your blood has maybe 2.5 PSI, and then your brain cells have 2 PSI.   Life is good.

When the atmospheric pressure drops 7 PSI (18,000'), the air has 1.5 PSI, blood now has 1 PSI and your brain cells have 0.5 PSI.  Not good but not instantly deadly.

When the atmospheric pressure drops to 3.5 PSI, the air has about 0.75 PSI, blood has 0.25 PSI, and the brain... Has nothing.  

 

 

This is just a half-baked theory.   I did have a cup of earl grey tea this morning, but I did not stay at a Holiday Inn Express.

PPO2 or partial pressure has a LOT to do with it, I think in fact it has everything to do with it I believe.

Going just from memory a cannula is good to 18K, where you have to wear a mask, which is good to 25K, above that you have to wear a pressure / diluter mask, that not only supplies O2 but does so under pressure.

I’ve never worn one but it’s my understanding that they are particularly obnoxious to wear.

As PPO2 is the issue, just plain air and a pressure mask would allow some higher altitude than 12,000 I have no idea how much higher, but I believe we breathe O2 because the pressure mask is so obnoxious.

Interesting to me is that at a water depth greater than 20 ft, the PPO2 of O2 rises to a level that’s toxic, breathing pure O2 deeper than 20’ can kill you.

My chamber ride I didn’t do well at all, at the time I was worried it might wash me out, I don’t remember the numbers, but when they took the mask off I didn’t like the feeling and asked for it back.

 

[Pinecone]

Yes, it is ALL about PPO2.

Yes, you could use some pressure with standard air to raise your critical altitude.  There are some people online experimenting with CPAP to see how that works to raise pulse ox readings.

Pressure demand breathing is tiring.  Normally we relax to exhale and use muscles to inhale.  With pressure demand, when you relax, the system pushes air into the lungs.  So you have to forcibly exhale.  Backwards from normal.  And using your muscles in ways they are not used to.

The basic O2 requirements in the regs are no based on science, but based to the altitude requirements in the mountains to no require O2 to fly almost anywhere.

And, as has been mentioned many times, each person is different. And things change over time with age, weight, conditioning.  This is why a chamber ride and a pulse oximeter are so important.

Many people really should be on O2 at much lower than 12,500 feet.

[Schllc]

43 minutes ago, Pinecone said:

 

Many people really should be on O2 at much lower than 12,500 feet.

especially at night

[Pinecone]

The night demo in the altitude chamber was eye opening, literally.

They took us "up" to about 5,000, maybe 8,000.  Dim lights.  And we sat there for maybe 20 - 30 minutes.

They handed out these cards about 18" square and told to leave them face down on our laps.

After the waiting period, they told us to turn over the cards.  There was like a pie chart with lots of "slices" in shades of gray.

Then they had us put our masks one.  ONE inhalation and the chart BRUST in color.  It was so dramatic, every one of us recoiled back away from it, the colors were so vivid.

[wombat]

Further thoughts on the cannulas....

While there is nothing prohibiting us from flying with a non-certified piece of equipment, there are rules in place prohibiting us from using equipment in a way that is prohibited, like flying above Vne.  So while nothing in the plane says you can't use a cannula up to 25,000' (Again, ignoring the actual real-life safety issue here!!!), I suspect all of the cannulas we have have been certified, and their certification and operating limitations include not using it above 18,000'.   If you were to find an uncertified cannula, you'd be legal.  Although you'd be no safer.

 

As far as the oxysaver cannulas and why they are only useful up to 15,000' from @jaylw314and @Schllc...   They have very small reservoirs in them that are supposed to fill with oxygen during your exhale and then when you inhale, they provide a flow rate that is higher than the nominal flow rate from the bottle.   But as the required flow rate increases, the capacity of the reservoirs is exceeded.   If you breathe out quickly and inhale slowly, they'll conserve oxygen the whole time.  But relying on a specific breathing pattern to maintain awareness sounds like a recipe for failure.

[Yooper Rocketman]

On 4/23/2023 at 7:44 AM, Austintatious said:

First off, If you are going high and using oxygen, you are really missing out if you don't have a pulse demand system such as Mountain High.  Not only does it conserve oxygen to a degree you will not believe if I tell you, but it adds what I consider a large margin of safety. The unit will sound an alarm if you are not breathing oxygen.  

I have Oxygen saving canula's I bought back around 2001.  I think what you are talking about is a much better system.  Can you point me out to the exact link on Mountain High's website that you recommend for the Mooney Rocket built in O2 system?  I can't make a trip to Florida and back on one tank of O2.  Maybe I could with the system you are using.

Tom

[ilovecornfields]

15 minutes ago, Yooper Rocketman said:

I have Oxygen saving canula's I bought back around 2001.  I think what you are talking about is a much better system.  Can you point me out to the exact link on Mountain High's website that you recommend for the Mooney Rocket built in O2 system?  I can't make a trip to Florida and back on one tank of O2.  Maybe I could with the system you are using.

Tom

https://www.mhoxygen.com/product/o2d2-x-str/