QUESTION:  
Have you ever had to actually wear the weird looking oxygen 
masks during a flight?  If so, why?  What happened?

ANSWER from Juan Rivera on October 10, 1995
Those masks are pretty weird looking aren't they?  They're not too 
comfortable to wear either!

Well the answer is yes.  We have never had a real emergency which 
required us to wear the masks but when we fly above 41,000 feet we get 
extremely serious about safety and actually have a check list we go 
through before climbing up to our highest cruise altitude of 45,000 
feet.  (The Air Force considers the edge of outer space to be at 50,000 
feet so you can see that we are very high indeed when we are cruising 
less than a mile below the edge of space!)

One third of us pre-breath oxygen for twenty minutes to purge all 
the nitrogen from our systems before we are ready to climb past 41,000 
feet.  This is so that we will not suffer from the "bends" if there is a 
rapid decompression that depressurizes the cabin.  And even the people 
who are not on oxygen can not leave their seats.  That way they are very 
close to their masks and one of the folks who is already on oxygen can 
help them is there is a problem.

But I may be getting too technical so let me back up a minute and 
explain why the masks are there at all...  Humans evolved for millions of 
years living on the surface of the earth where there is plenty of oxygen 
to breath.  That's what our bodies are used to, and that is what they 
need.  But at the altitudes we fly at the air is so thin that there is not 
enough oxygen up there to keep you alive.  As a matter of fact most 
healthy people would be incapacitated and unable to even save their own 
lives in as little as four seconds if they had to breath the air at that 
altitude.  To make it as comfortable as possible for the folks inside, 
jet airplanes are pressurized.  So even when we are flying at extremely 
high altitudes the air inside the cabin is the same density as it would 
be on an 8000 foot mountain.  But there is always a very small chance 
that the cabin might spring a leak of some kind and the air would leak 
out till it was as thin as it is on the outside.  Once that happens then 
we need the oxygen masks just to stay alive.

I hope that answers your question and thanks for writing!
Juan Rivera - Telescope Operator