Oxygen M20K

[aviatoreb]

This is sad - and timely.

 

Pilot lost at sea Hypoxia may have been a factor

http://www.aopa.org/News-and-Video/All-News/2014/September/02/Pilot-lost-at-sea

[jlunseth]

Well, that table you are thinking about would not go to 50k because without a pressure suit of some kind we can't go to 50k. The lack of total pressure becomes a bigger factor than the loss of O2 partial pressure. The existing tables are fairly accurate for the " lower" altitudes because the primary effect there would be the loss of oxygen. I was trying to get across why you would pass out quickly at 50k - because other mechanisms besides just O2 loss are at play.

A table that assumes tapering off of the O2 in the lower altitudes would not be very useful because if your O2 starts dying how do you know you are tapering at the rate assumed in the table and not a faster or slower rate? The tables assume a "worst case" which is instant loss of O2.

[aviatoreb]

Well, that table you are thinking about would not go to 50k because without a pressure suit of some kind we can't go to 50k. The lack of total pressure becomes a anger factor than the loss of O2 partial pressure. The existing tables are fairly accurate for the " lower" altitudes because the primary effect there would be the loss of oxygen. I was trying to get across why you would pass out quickly at 50k - because other mechanisms besides just O2 loss are at play.

A table that assumes tapering off of the O2 in the lower altitudes would not be very useful because if your O2 starts dying how do you know you are tapering at the rate assumed in the table and not a faster or slower rate? The tables assume a "worst case" which is instant loss of O2.

 

I bet you are right - that the tables are already accurate at non decompression altitudes.

 

Reading:

FL 220 5-10 min 

FL 250 3 to 6 min

 

Which seems as if 22000 to 25000 seems to be the cross over from breathing a little bit possible to nothing much to breath since 5-10 minutes is suggesting you are getting a little but 3-6 to passed out is almost what I would expect underwater.  

 

Whereas above that then as you say the decompression effects and vacuum like effects become important.

 

Another paradox for those in the know please - 30 minutes at 15000 seems inaccurate as far as I can tell though.  From my own experience having hiked to the top of several "14ers" in Colorado in years past, I can, and I saw a lot of other people not only not passing out at 14k but even staying very physically active.  Yes it was harder, and yes I wouldn't claim to have the higher cognitive abilities required to fly at that altitude, but passing out, no.

[jlunseth]

I basically agree, except that decompression sickness or lack of total pressure are not significant to us, flying at 22 or 25 in a nonpressurized aircraft. For example, decompression sickness (the bends) is caused by breathing air (actually the nitrogen which is 79% of of air), and then relatively quickly finding yourself at a significantly lower ambient pressure. It is the same mechanism that causes pop to fizz when you open the top. If we are flying along at 25k and our O2 flow stops, the ambient pressure does not change, so no DCS, what gets us is lack of O2. On the other hand, if you were breathing air at a cabin altitude of 8,000 (standard) but an absolute altitude of 50 k, and the cabin were to suddenly decompress, DCS would be an issue (among other problems).

What I consider important for us is the short time of useful consciousness above 22 because of lack of O2.. It drops off fairly fast. And when you consider that in all likelihood you will not detect the lack of O2 flow immediately, that delay will cost you part of the 3-5 minutes you had to begin with, so you have very little time left to get down to denser air. My personal rule is to stay at or under FL220 unless there is a good reason to go higher.

[AZ231]

 

An O2 system can be expensive if the tank needs to be replaced.  And some tanks need to be retired after a certain number of years.

 

This is worth looking into while you are shopping for your plane.  I purchased my M20K earlier this year (with factory O2) and found out that the O2 tank was original and had to be replaced.  The service life was 24 years and the tanks cannot be overhauled.  Budget $1,500-1,800 plus any labor costs.