Why would the ground make any difference to oxygen content?
IIRC, the percentage of oxygen is the same. The pressure is less.
The presumption here is that the aircraft has taken off from a very low altitude, and climbed to a very high altitude (say, 30,000 feet) in a relatively short amount of time. That’s the problem with all these mountain comparisons. People typically spend six to eight weeks slowly acclimatizing their bodies to the higher altitudes when mounting Himalyan expeditions. During this process, the number of red blood cells in the body doubles, allowing it to carry more oxygen, so people like Ed Viesturs can climb all the way to 29,035 feet without bottled oxygen. So, while it’s true that many people can survive (in the short term) at 30,000 feet, absolutely nobody could come out unscathed if they were carried to that same elevation in a matter of minutes.
I was gonna chime in earlier with my own “I was on Denver in business and hiked Mt. Audubon (13,221 ft) in a spare afternoon without passing out” story, but then I realized that Denver was already at around 5k feet and I’d been there a week, I may have been somewhat acclimated.
Do you think that may play a role? When you go on your 14,000 foot hikes, are you going from sea level to 14,000 in a day?
The air is certainly thinner at 14,000 feet. Climbing and hiking at Pike’s Peak (14,000 ft) and in the mountains around New Mexico (around 13,000 ft) has shown me that. I had arrived from a modest New England elevation of about 200 feet above sea level, and while I was hardly gasping for breath, things got decidedly easier on the lungs as the weeks went on.
Most passenger aircraft are designed to fly with a maximum normal cabin altitude of 8000 ft so you were on a flight that was operating at the max. level. Usually it’s set a little less and there are safety devices present to ensure the max. cabin altitude is not exceeded.
One of these devices can automatically deploy the oxygen masks at a preset cabin altitude.
FWIW, Boeing is designing the 787 for a cabin altitude of 6000 feet, not the usual 8000, for the sake of passenger comfort.
Sorry for this hijack but seeing as how there is someone who I can finally ask this question of it needs doing…
What is the point of the bag on passenger oxygen masks that they tell you won’t inflate? Seems superfluous just hanging there doing (seemingly) nothing but doubtless there is an actual reason for the things…I just never figured out what it was.
Won’t this increase the stress on the airframe at altitude?
It’s not just aircraft that need to be pressurised:
According to other Chinese articles I googled, the rail line is as high as 5072 metres (more than 16,600 feet) above sea level.
Another pilot-type checking in, I thought I’d post the actual text from the (USA) regulations…
91.211 Supplemental Oxygen
(a) General. No person may operate a civil aircraft of
U.S. registry —
(1) At cabin pressure altitudes above 12,500 feet (MSL) up to
and including 14,000 feet (MSL) unless the required minimum
flight crew is provided with and uses supplemental oxygen for
that part of the flight at those altitudes that is of more
than 30 minutes duration;
(2) At cabin pressure altitudes above 14,000 feet (MSL) unless
the required minimum flight crew is provided with and uses
supplemental oxygen during the entire flight time at those
altitudes; and
(3) At cabin pressure altitudes above 15,000 feet (MSL) unless
each occupant of the aircraft is provided with supplemental
oxygen.Yeah, but they’re making the fuselage out of composites anyway, so it’s still a much-lighter plane than it would have been. They’ve just traded a small amount of fuel burn for increased market acceptance and sales volume.
AFAIK, passenger oxygen supplies are constant-flow, not constant-pressure, so they don’t require a tight seal to work. Even if the bags look like they’re just hanging limply, they are still putting out enough O2 to keep you alive.
The Air Force took me to 25,000 feet in the altitude chamber and told me to take my mask off. I lasted 4 minutes before I started to black out. As soon as I put the mask back on I was fine. It was virtually instantaneous.
With a whole boatload of warm clothes and supplemental oxygen going at all times (which would deplete very rapidly at altitude) you could go without pressurizing an aircraft. But why would you want to?
It’s the pressurisation cycles that govern the life of an airframe. Have it always unpressurised and it will last longer.
Why not have the passengers sitting there with blankets and oxygen masks.
Please don’t take my last sentence seriously 
For people who think Southwest and JetBlue are too expensive, huh? 
Aeroflot.
olpeculiar, thanks for the bale out. I have repacked thousands of the oxygen masks but never really knew the answer to Whack’s question. During our testing, only drop the oxygen doors against the safety stops on most psu’s, only 3 or 5 are actually fully dropped, that number depends on the passenger capacity of the aircraft. And during our testing safety pins are in all the oxygen cannisters to prevent activation of the cannister. I do know that the cannisters release oxygen at .3 to .35 inch pounds of pressure and are designed to operate at least 8 minutes. Next month Boeing is building it’s first civilian 737 designed for high altitude take offs and landing. Instead of oxygen cannisters, it will be hard plumbed and the auto deploy system will be deactivated when the landing gear is lowered. I have a meeting with engineering and functional test planning tomorrow about the system.
It wouldn’t really. Some parts of the fuselage will have slightly higher than ambient pressure; others have lower. On balance, the average outside pressure is essentially equal to ambient.
Unless you postulate some sort of oxygen-emitting ground, there is no reason for this to be true.
It’s because deterioration in night vision is often the first symptom of slight hypoxia.
You might be trying to set an altitude record in a glider, which now stands at over 49,000’. (But note that this is generally considered higher than is safe without pressurization, so current attempts at this record include the use of pressure suits.)