Ar, did not konw that those O2 masks in passenger jets were ‘chemical’, while crew for good reasons have trditional tanks of O2.
In ours the pilot dons a quick donning mask and O2 flows automatically if the O2 was turned on at the start of the flight. The chemical generators must be pulled in order to activate (same as in your 767). They are under the seats.
My retired BA Captain friend (747-400) when I told him I was way over 10k over Alps to Mali Losinj with no O2 was not a bit shocked. He said a health person should be OK at 14k and that was their ‘get down to’ height in a decompress emergency.
I feel a lot better for hearing that. I didn’t have a terrain problem (Eastern Alps) but wanted at all cost to stay above the cloud – ice.
I instigated the long climb well in advance and was eventually down to less than 200fpm.
Subsequently found out at the following 100 hours that the engine was down on power – low compression on two cylinders and worn cams!!
Ah, IF the O2 was ‘ON’ at start of the flight and I guess sufficent for the flight.
In reality much of this stuff “depends”.
Plenty of airliners have had gaseous oxygen for the cabin. They had a load of the large cylinders screwed to the cargo hold walls. I recall reading one accident report where the top of one of these blew off and the thing went at some supersonic speed in the opposite direction, making a hold (about 25cm diameter) which was so clean it might have been drilled. So one can see why the chemical generators are popular.
On the TBM, Socata were (last time I looked, a long time ago) offering “gaseous oxygen” as an option, so presumably they moved from chemical to gaseous at some stage. The cylinder is a composite one and is mounted externally, inside one of the wing root fairings. Where I am hangared they work on them all the time.
The ability to fly at 14k is highly dependent. As I have written before, I have flown with a “short and round” chap who could not read the altimeter (or anything else) at 12k. He said he doesn’t need oxygen… I think that flight with me (he is an instructor) was a useful lesson because he would have probably killed himself. Sure one can appear and feel OK at 14k (I have walked up Mt Kinabalu, 16k) but you won’t be in a fit state to do much when you land after some time up there 
An airliner cabin at 14k is a total emergency, not least because some passengers are going to die.
So I would not play with this stuff, because somebody tells you you will be fine at 14k. That airline pilot may well have been blind at 14k… that job doesn’t encourage fitness, except a certain kind of “fitness” and long haul flights and attractive cabin crew are needed for that 
Ah, IF the O2 was ‘ON’ at start of the flight and I guess sufficent for the flight.
It doesn’t have to be sufficient for the flight. Just for the time you need to get to a lower level. You have it on but it doesn’t flow until you pull out the mask.
Yes, after posting, I realised I hadn’t really said what I meant. I understood all at #47. The O2 is only required/used in an emergency (pressurized aircraft).
Where is the on/off tap/switch ? flight deck or behind some hatch on the side of the fuselage.
I’m trying to workout in my head why it didn’t save that TMB900 !!
Do people get blasé in pressurized aircraft about the O2 back-up system, that in most cases will never get used?– bit like an injector seat in the fast jets or airbags in cars.
Does the O2 in the tank have to be changed at intervals – serviced
Where is the on/off tap/switch ? flight deck or behind some hatch on the side of the fuselage.
Behind copilot’s seat. Reachable from pilots seat while strapped in.
Do people get blasé in pressurized aircraft about the O2 back-up system, that in most cases will never get used?
I don’t. Can’t speak for others.
Does the O2 in the tank have to be changed at intervals – serviced
Yes. It is naturally part of the normal aircraft maintenance programme.
