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  Reply # 1834912 1-Aug-2017 13:27
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tripper1000:

 

Here you go, I got off my chuff and looked it up.

 

2 Hours per crew member is the required duration for certification by FAA/DOT.

 

Link

 

 

I saw that too. But where does it say it is 100% oxygen without entraining cabin air (potentially containing toxic gas)


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  Reply # 1834969 1-Aug-2017 14:06
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Batman:

 

tripper1000:

 

Here you go, I got off my chuff and looked it up.

 

2 Hours per crew member is the required duration for certification by FAA/DOT.

 

Link

 

 

I saw that too. But where does it say it is 100% oxygen without entraining cabin air (potentially containing toxic gas)

 

 

In fact, you wouldn't want 100% oxygen below about 25,000ft... that's poisonous, hence divers using helium. My guess is that aircraft systems would store 100% oxygen, and mix it with cabin air.

 

Generally speaking, the plan is to get below 10,000ft, where there's enough oxygen at atmospheric pressure for everyone to survive. If you could open a door/window, the poisoned air inside the aircraft would quickly be got rid of.

 

 


 
 
 
 


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  Reply # 1835017 1-Aug-2017 14:55
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frankv:

 

In fact, you wouldn't want 100% oxygen below about 25,000ft... that's poisonous, hence divers using helium. My guess is that aircraft systems would store 100% oxygen, and mix it with cabin air.

 

 

It is nitrogen that divers replace with helium, not oxygen - you'd die breathing helium instead of oxygen. It is also going deep, not high, that makes it poisonous to the body. Nitrogen narcosis.

 

The aircraft oxygen regulators have a selector switch which allows the pilot to choose between 100% oxygen and diluted - or mixed with cabin air. I believe most Air Lines default position for this switch is 100% as it is the safer of the two options. In a smoke/fumes/gas/hang-over saturation the pilot leaves it set to 100%. If cabin air is free from pollution they can select diluted and the regulator adds less oxygen with cabin air the lower the cabin altitude.

 

frankv:

 

Generally speaking, the plan is to get below 10,000ft, where there's enough oxygen at atmospheric pressure for everyone to survive. If you could open a door/window, the poisoned air inside the aircraft would quickly be got rid of.

 

 

Some models of aircraft have windows/doors/hatches etc that can be opened to duct ram air into the cabin specifically to clear smoke and fumes (and poison gas?) from the aircraft faster.

 

 

 

Edit: Spelling drivers vs divers.


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  Reply # 1835025 1-Aug-2017 15:04
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Batman:

 

tripper1000:

 

Here you go, I got off my chuff and looked it up.

 

2 Hours per crew member is the required duration for certification by FAA/DOT.

 

Link

 

 

I saw that too. But where does it say it is 100% oxygen without entraining cabin air (potentially containing toxic gas)

 

 

My speculation is as follows:

 

Given that passengers only have a few minutes oxygen and that supplementary oxygen is not required below 10,000ft, the only reason the regulations state flight crew need oxygen for 110 minutes at 10,000ft is if the flight deck is full of smoke/fumes/poison gas - that implies, but does not specifically state, 100% - ?

 

Getting back on topic, if the cabin air is replaced every 3-4 minutes, and the terrorist has a finite supply of gas, then the flight crew don't need 2 or 6 hours of oxygen, they only need to outlast the terrorist supply, plus 4 or 10 minutes-ish.

 

Doesn't help the passengers or cabin crew much though does it?


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  Reply # 1835071 1-Aug-2017 15:56
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tripper1000:

 

Batman:

 

tripper1000:

 

Here you go, I got off my chuff and looked it up.

 

2 Hours per crew member is the required duration for certification by FAA/DOT.

 

Link

 

 

I saw that too. But where does it say it is 100% oxygen without entraining cabin air (potentially containing toxic gas)

 

 

My speculation is as follows:

 

Given that passengers only have a few minutes oxygen and that supplementary oxygen is not required below 10,000ft, the only reason the regulations state flight crew need oxygen for 110 minutes at 10,000ft is if the flight deck is full of smoke/fumes/poison gas - that implies, but does not specifically state, 100% - ?

 

Getting back on topic, if the cabin air is replaced every 3-4 minutes, and the terrorist has a finite supply of gas, then the flight crew don't need 2 or 6 hours of oxygen, they only need to outlast the terrorist supply, plus 4 or 10 minutes-ish.

 

Doesn't help the passengers or cabin crew much though does it?

 

 

You can have an oxygen supply, that's easy.

 

But if you do not tape your mouth and nose to the oxygen tube/supply, you WILL entrain gas around you when you breathe. The human mouth cannot filter out the gas and only inhale the oxygen blown at you.


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  Reply # 1835089 1-Aug-2017 16:31
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tripper1000:

 

frankv:

 

In fact, you wouldn't want 100% oxygen below about 25,000ft... that's poisonous, hence divers using helium. My guess is that aircraft systems would store 100% oxygen, and mix it with cabin air.

 

 

It is nitrogen that divers replace with helium, not oxygen - you'd die breathing helium instead of oxygen. It is also going deep, not high, that makes it poisonous to the body. Nitrogen narcosis.

 

The aircraft oxygen regulators have a selector switch which allows the pilot to choose between 100% oxygen and diluted - or mixed with cabin air. I believe most Air Lines default position for this switch is 100% as it is the safer of the two options. In a smoke/fumes/gas/hang-over saturation the pilot leaves it set to 100%. If cabin air is free from pollution they can select diluted and the regulator adds less oxygen with cabin air the lower the cabin altitude.

 

 

 

 

Sorry for being unclear.

 

What divers breathe is heliox, a mixture of oxygen and helium. They don't want nitrogen because of nitrogen narcosis, as you say. But they don't want pure oxygen either, because it's poisonous at high partial pressures... i.e. anything exceeding 0.3bar, which is the standard air pressure  at 25,000ft as I said  (well, actually it's the pressure at 30,000ft, but that's my poor memory for ya). So *above* 30,000ft you can breathe pure oxygen, but below that it's poisonous.

 

Leaving the selector on 100% makes sense, since the most likely need for it would be due to depressurisation about 30,000ft, where 100% oxygen is safe.

 

 


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  Reply # 1835090 1-Aug-2017 16:34
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Maybe the Australian authorities could put the would be assassins in a sealed chamber with their device and let them see how good a chemists they really are. Possibly even rig up a couple of passenger oxygen masks for them to try.




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  Reply # 1835104 1-Aug-2017 17:03
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Dingbatt: Maybe the Australian authorities could put the would be assassins in a sealed chamber with their device and let them see how good a chemists they really are. Possibly even rig up a couple of passenger oxygen masks for them to try.

 

You need Donald Trump for that kind of stuff


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  Reply # 1835105 1-Aug-2017 17:04
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I find it quite strange that Air NZ regional flights (68 passengers) have no security checks at all, they won't know if someone has this (or a bomb). They only care if there are more passengers


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  Reply # 1835115 1-Aug-2017 17:32
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I find it quite strange that Air NZ regional flights (68 passengers) have no security checks at all, they won't know if someone has this (or a bomb). They only care if there are more passengers

 

 

 

Aviation Security screening is mostly for show, there are still checks that the airlines will do in the background when you buy a ticket. Anyway for regional flights its always a cost vs risk argument. If you want to install the expensive equipment, fencing and staff in a regional port like Timaru or Hokitika for the two or three flights a day; then that cost will be added to the ticket price. Last time I looked at the costing, the ticket price from regions would increase by $30 per passenger. The general public already believe they are being fleeced when flying from the regions already so to see a price increase will only feed fuel to the fire.

 

As far as the Oxygen systems in aircraft go for pilots we are required to have our oxygen masks selected to 100% at any time we use them, doesn't matter if its for smoke/fumes or depressurisation. We can take the masks off below 10,000 in the case of depressurisation, but if there is fire on board, its masks on 100% until we evacuate. That is written into our Standard Operating Procedures and based on industry knowledge and experimentation.

 

As for Oxygen poisoning below 25,000ft, the time taken to descend my aircraft below 10,000 will be less than 2 minutes. If there is fire on board I'm planning to be landing somewhere in under 10 minutes - it won't necessarily be an airport, any flat land or water will do. In the past most aircraft break up in flight if there has been a fire on board in about 12 minutes, if they are uncontrolled. The chances of an uncontrolled fire on an aircraft becoming controlled is extremely slim. Fire would be my biggest fear when it comes to emergencies on board.

 

 


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  Reply # 1835139 1-Aug-2017 18:28
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Not sure this business of pure oxygen being toxic below 30,000

Sea level is 1 bar and plenty of people have exposure to near pure oxygen everyday in most Nz cities. Ie operating theatres.

Hyperbaric oxygen therapy usually involves breathing 100% at 2 or 3 times atmospheric pressure.




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  Reply # 1835142 1-Aug-2017 18:44
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Oxygen normally moves from Alveoli in lungs into the bloodd stream.

At sea level inspired partial pressure oxygen is 150mmHg (.21x716).

As you ascend, the atmospheric pressure drops and so does the inspired partial pressure oxygen, we can compensate by increasing the oxygen concentration to maintain the inspired partial pressure and ultimately driving force into the Alveoli and blood stream.

The passenger oxygen supplies are to supplement this to maintain an inspired partial pressure. But there are limits to when 100% oxygen can no longer maintain usable partial pressures.

In any case the oxygen supplies are only there to last long enough that the planes can decend to lower altitude where atmospheric pressure will rise and so a normal oxygen partial will be produced.

Put oxygen on adults first so you don't pass out putting the mask on the kids.

I've ignored the alveolar gas equation and effects of co2 depletion.


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  Reply # 1835163 1-Aug-2017 19:08
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While 100% oxygen might preserve consciousness to altitude of 12000m or 40,000feet if slow.

Rapid decompression exposure to altitude greater than 6000m or 20,000 feet can result in unconsciousness in 15s which corresponds by lung to brain circulation time and capacity of high energy phosphate stores.

Commercial cabin pressures corresponds to hypoxia similar to breathing 15% oxygen at sea level.

Patients who's sea level oxygen saturation are less than 92% shouldn't fly without hypoxia challenge. Ie check they are still OK breathing 15% oxygen at sea level.

Physiology nerd.

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  Reply # 1835212 1-Aug-2017 20:15
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empacher48:

 

 

 

Aviation Security screening is mostly for show, there are still checks that the airlines will do in the background when you buy a ticket....

 

...Fire would be my biggest fear when it comes to emergencies on board.

 

 

 

 

Hello, this is your pilot.  We're ascending at the moment heading for our final cruising altitude of 38,000 ft, expecting weather to be pretty good en route, possibly a bit of minor turbulence as we fly over the mountains, we've got a good tailwind, so at this point we're expecting to pulling up at the terminal a few minutes ahead of time.  Hope you enjoy your flight.

 

Sorry we left a bit late - all those security scans, checks, pat-downs at the airport that held us up were a waste of time. As for the crew safety instructions, just to let you know in the unlikely event of my biggest fear - that we catch fire at 38,000 feet  - the life-jacket under your seat isn't fireproof, and there's probably still a hell of a drop even if you do make it to the nearest emergency exit. 


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  Reply # 1835278 1-Aug-2017 21:31
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Batman:

 

 

 

You can have an oxygen supply, that's easy.

 

But if you do not tape your mouth and nose to the oxygen tube/supply, you WILL entrain gas around you when you breathe. The human mouth cannot filter out the gas and only inhale the oxygen blown at you.

 

 

@Batman why capitalise the word will? you assertion is highly off the mark

 

google Boeing flight crew mask, it covers the mouth and nose, if not the whole face

 

then there is the fact that its coming out at a higher than the surrounding atmospheres pressure, and it likely creates a seal on your face, this prevents the ingress of any fumes from outside the mask.

 

no real difference to what a firefighter wears or how a hospital operating theater works, higher pressure in the mask/room to keep bad things out

 

i wear one of these on a regular basis
http://www.keison.co.uk/sabre_centurion.shtml


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