[TexasCajun]

And did you catch this from the guy on FoxNews?

Those air bags/mask that drop down during lost of pressure will not work properly above 30,000 ft. A little inside info the guy said.

[F-117A]

Nope!

Guess I better carry my own Oxygen supply and stay at a Holiday Inn Express.

[leadpenny]

Those . . . mask that drop down during lost of pressure will not work properly above 30,000 ft.

That can't be right.

[Mr. Jeeves]

He probably meant they wouldn't work if the cabin pressure was lowered far enough to be equivalent to the air pressure at 30,000 feet - but depressurization is usually gradual, not instantaneous, unless there is a big hole in the plane.

[Turbopilot]

The problem with oxygen masks at very high altitudes is the result of the so-called "partial pressure" of oxygen. Your body needs a certain number of molecules (mass) of O2 to function, but your lungs hold a given volume, so the amount of O2 in your lungs is based on the pressure times the fraction of oxygen in the air. At sea level, regular air with about 21% O2 has a high enough partial pressure of oxygen for normal breathing. Above about 10,000 feet, there's not enough O2 pressure in the air to supply your body adequately, and so that's about the altitude above which people in unpressurized aircraft tend to wear oxygen masks or cannulas (though it's not required until 12,500 feet).

But once you get above about 30,000 feet, the partial pressure of oxygen even in 100% O2 isn't sufficient - in other words, there aren't enough O2 molecules in a lung volume of 100% O2 to supply your body. Above that altitude, you need to breathe pressurized oxygen to force more O2 molecules into a given volume, which isn't available from the cabin oxygen masks (don't know about the pilots' system), or be in a pressurized aircraft.

In any event, the standard procedure for decompression would be to expedite a descent to an altitude at which oxygen masks wouldn't be needed. I'll be curious to find out exactly why that didn't happen before everyone on board lost consciousness.