In article ,
Michael Ash wrote:

At the risk of turning this thread into something useful,

Heaven forfend!

does anyone have
any recommendations as to when it's a good idea to give oxygen to
passengers? I'm not talking about the legal requirements, but just when
it's the smart thing to do. For example, as the pilot I like to start my
oxygen at about 10,000ft even though it's not required until quite a bit
higher. But then again, it doesn't really matter too much if my passengers
have mildly impaired judgement during the flight, even though I'd really
want to avoid that myself.

This is really an academic question since I don't plan to take anybody
that high to begin with, but I'm curious.

Depends on the person, really.

I have a friend who begins to exhibit severe headaches and some cyanosis
(his lips and fingernails start to go purple) above about 8000'. He's
been warned to be very cautious about higher elevations, as he's
probably a prime candidate for mountain sickness. So much for his dreams
of trekking the Himalayas.

That's a bit extreme, but it's worth watching for if you have a
passenger who's never been at altitude before.

Heavy smokers, or anyone with compromised cardiopulmonary function
should be cautious, probably.

There are affordable blood oxygenation meters, typically used by
clipping on a finger, to determine blood O2 levels if you spend much
time at higher elevations without supplementary oxygen.