Oxygen masks on planes

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hansov

Registered User
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A question I have always wanted to ask, and need I say, I didn't want to find out the answer from experience .

Before take-off cabin crew always tell you that "in the event of a sudden drop in cabin pressure, an oxygen mask like this will fall from overhead". Say you are sitting in a row of three seats - how many masks fall? Three or four? And I ask this as they always say "attend to your own mask first before...." If there are only three, if all seats are occupied by adults and if one of those adults has a baby in their arms.......????
 
Was watching Air Crash Investigation one night on Discovery. Apparently there is only 15 minutes oxygen available anyways!
 
Well I suppose the pilot should be able to correct things in 15 minutes by coming to a lower altitude or indeed landing.
 
There are 4 O2 masks for 3 seats.
Asked the question when my wife and I each with a child were not seated in the same side of the aisle.
This was the reason given.
 
hansov said:
Well I suppose the pilot should be able to correct things in 15 minutes by coming to a lower altitude or indeed landing.
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Is this an airline euphemism for falling screaming from the sky as bits are stripped of the plane from the velocity of the descent and crashing into a deserted mountain and perishing in a ball of flame?

No?
 
correct... 4 oxygen masks per three seats. Chemically generated oxygen lasts for 15 minutes. Once the cabin altitude reaches 10,000 ft or rises at a significant rate due rapid or slow decompression we initiate an emergency decent. From a cruising altitude of 39,000 ft at a descent rate of 5,000 ft per minute (with speed brake out) it will take approximately 6 minutes to reach 10,000 ft where the air becomes breathable again.
 

....and then they just open the window?
 
heard that the cause of a crash in greece last year was because ground crew didn't connect the air cylinders up to the system before take off. so when the aircraft decompressed and the masks fell down there was nothing in them. greek air force was sent up to see if they could find out what was happening but afaik they reported that the pilots etc were slumped over the controls. frightening scenario. especially for someone enjoys getting away a few times a year and doesn't mind flying.
on the same subject -only different - has anyone every survived a plane crash over the sea?
 
EvilDoctorK said:
- You can breath normally at a cabin altitude of 10,000ft - there's sufficient oxygen at that level so no oxygen masks required
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But how does it get in to a sealed cabin? It has to be sealed, remember, to pressurise and hold air as the aircraft climbs.
 
Miles said:
Was watching Air Crash Investigation one night on Discovery. Apparently there is only 15 minutes oxygen available anyways!
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This greek aircrash was probably the one that Miles was referring to. It wasn't that the ground crew didn't hook up the air cylinders - some maintenance work the previous day had required the cabin pressurisation system to be set to manual rather than auto and it wasn't switched back - and the captain didn't notice this in his pre-flight checks. So, the aircraft didn't pressurise at all and when it reached 10,000ft, warnings went off which the captain misinterpreted - and he wasn't aware that the oxygen masks had dropped in the passenger cabin. By the time ground engineers asked the captain to check the pressurisation switch was set to auto, he was a bit zonked from lack of oxygen and didn't understand what they were saying. So, everyone drifted off into unconsciousness (they were all technically still alive when the plane hit the ground) after their 12/15 mins of oxygen was used up and the plane eventually crashed when it ran out of fuel - probably all very peaceful for them really. Except for one poor cabin steward (deep sea diver so probably used to using less oxygen) - he managed to stay alive by using 4 portable oxygen tanks on board - and was seen by the greek air force pilots at the controls (he was also a trainee pilot) just before it crashed after circling for 2-3 hours - he couldn't communicate with the ground as the radio frequency was still set to the take-off airport and he couldn't/didn't know how to change it. Can't have been much fun for him particularly as his fiancee was also a stewardess on board.
 
AlastairSC said:
But how does it get in to a sealed cabin? It has to be sealed, remember, to pressurise and hold air as the aircraft climbs.
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The cabin isnt quite sealed in the way you might think. Actually atmospheric air is allowed into the cabin, by air inlets where it passes through air conditioning units and then out through an outflow valve. By adjusting the rate of flow of the exiting air you can control the pressure of the aircraft. Closing this valve means air entering the cabin has no where to go and so pressure increases and vice versa. As the aircraft climbs the valve closes and this pressurises the aircraft to a similar pressure to that at ground level.
In an emergency decent when you reach 10,000 ft the air entering the aircraft through the air inlets is already at a sufficient pressure for the passengers to breathe normally. Hope that explains it.......
 
orka said:
some maintenance work the previous day had required the cabin pressurisation system to be set to manual rather than auto and it wasn't switched back - and the captain didn't notice this in his pre-flight checks.
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Or the co-pilot? Sounds like a gross pilot error to me? Was there ever any investigation?
Yeah - they were better off. Didn't know about the other poor chap!
 
AlastairSC said:
But how does it get in to a sealed cabin? It has to be sealed, remember, to pressurise and hold air as the aircraft climbs.
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It's not sealed - as far as I know the pressure is maintained through the forwards motion / engine power of the aircraft compressing the outside air and putting into the cabin and it's vented out at a controlled rate to maintain the pressure at the desired level in the cabin
 
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