Oxygen masks failed when pressure lost on commercial flight

Aero

Sat Jul 26 19:54:44 -0700 2008

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While I believe that the cockpit crew has actual pressurized oxygen tanks (like SCUBA), the passenger oxygen supply is actually chemical generator based, not tanks.

Not that they are any safer, but that pretty much moots most of your post, especially the Apollo 13 non sequitur.

Oxygen masks failed when pressure lost on commercial flight

Michael Smith

Sat Jul 26 22:10:29 -0700 2008

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Not that they are any safer, but that pretty much moots most of your post, especially the Apollo 13 non sequitur.

The media are reporting that a exploding oxygen tank most likely damaged the skin of the aircraft.

When an oxygen tank explodes you can get a very hot fire because high density oxygen can cause normally safe materials like thermal insulation and aluminum to burn. The insulation fire on Apollo 13 contributed to damage in the command module.  A fire resulting from a talk letting go in this aircraft could have damaged the airframe near the wing root.

But my main point is that you can't just install safety gear and expect it to work decades later without inspection. One passenger I heard on the radio today had to tie a knot in the elastic band which is supposed to hold the mask to the face.

Oxygen masks failed when pressure lost on commercial flight

AB3A

Sat Jul 26 21:30:12 -0700 2008

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Apollo 13's oxygen tank exploded because of a neglected heater thermostat which wasn't updated for 65 volt service from the 28 volt service which had been in the specification earlier.  It held the heater on, causing the explosion. There was also latent damage in the tank caused by dropping.  Nobody made a full validation of that tank.  It was only pressure tested.  

Also, the phenomenon of passengers acting as if nothing is wrong, or ignoring the danger is well known to the psychiactric profession.  People often deny the emergency because they simply can't shift mental gears to deal with it.  It's outside their experience, so they do whatever they have done before...

As for safety gear on aircraft, this is an issue the FAA is dealing with right now.  Until recently, there was very little critical analysis of the quality of foreign shops. Some are excellent.  Apparently, however, there are a few that shouldn't be in business. 

You also need to understand that at cruising altitudes of 35,000 ft, No amount of oxygen will fill your lungs with enough oxygen to survive for long.  Even pure oxygen at that air pressure will not give you enough to survive with for long.  

The only survival for the passengers is a rapid decent to something below 25,000 ft.  To breath air without oxygen, the aircraft should descend to 15,000 or below. 

Just a few background facts...

Oxygen masks failed when pressure lost on commercial flight

Beryllium Sphere(r)

Sat Jul 26 23:05:09 -0700 2008

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Are you sure? The first place I looked says 3.47 psi at 35,000 feet, and the partial pressure of oxygen at sea level is 2.94.

Oxygen masks failed when pressure lost on commercial flight

wowbagger

Sun Jul 27 05:56:10 -0700 2008

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You need a bit more than 2.94psiO₂ due to the partial pressure of water vapor in the lungs, the partial pressure of CO₂, and so on. NASA runs 3.5psi IIRC on suits and the old Apollo capsules.

A person in good shape, doing no physical activity, who understands the "grunt-and-hold" method of increasing the pressure in the lungs could be OK on 2.94psi, but considering how many overweight, asthmatic, and/or smoker passengers are on your average plane....

Oxygen masks failed when pressure lost on commercial flight

chinakow

Sat Jul 26 23:34:02 -0700 2008

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IIRC one of the symptoms of hypoxia is euphoria so organizing passports doesn't seem all that out of the ordinary to me. Glad they made it down without any fatalities.

Personal experience with O2 Masks

wowbagger

Mon Jul 28 08:03:32 -0700 2008

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I was flying back from Washington DC one time, and the pilot gets on the PA:

Ladies and gentlemen, this is your pilot speaking. Ahhhh, we are having some minor problems with maintaining cabin pressure, nothing to be worried about, but it is possible that we might not keep the pressure below 10000ft equivalent - and if that happens the oxygen masks might deploy. If so, we will have to descend, but it's nothing to worry about.

Of course, a few minutes later, guess what happens. I think "Well, kiss good-bye landing in Wichita at a reasonable time." (the flight had already been delayed by weather).

Now, in the pre-flight briefing, they always tell you "pull on the mask to start the air flow". So, I pull on the mask - and the tube comes off the fitting. Silly me, I actually followed the directions. It turns our that what you need to pull on is a string that connects to a pin that gets pulled out, NOT the mask itself. No biggie - I just pushed the hose back on, and pulled the pin.

I did consider just ignoring it - I know I can take 14000+ feet with no real problems, and I know the aircraft is already descending, so the odds of passing out are minimal, but I'd feel really stupid if I DID pass out, so I got it working and put it on.

Of course, we had to descend to below 10000ft, and that put us right into the dirty air from the storms, so now the plane is constantly getting buffeted around. We land at KCI, and since it's about 2AM, the airport is closed. That bites, because at KCI there is no "sterile zone" outside the gates themselves, and there is no one to run the security station, so we cannot leave the gate area. Guess where the bathrooms and water fountains AREN'T.

We end up waiting about 3 hours for a plane to land (in which time, had they just put us on a freaking BUS they could have gotten us to Wichita), and I get in to the airport about 5AM, only to find my car battery is dead, and I have to wait for the airport parking person to get everybody else out of the lot before she can give me a jump start (with a jump start kit she never thought to just HAND TO ME).