Oxygen @ Night?

pilatus028

New Member
Hello pilots and persons alike ;-)

I'm almost done with my ground training for my commercial liscense and I just quench for airplane knowledge. Anyways, I'm probably going to post a bunch of questions on this forum prior to taking my written so I can have a better understanding of what is going on. This one isn't so much for the written and probably too detailed for the checkride, but I'm curious. Why does the FAA recommend to use oxygen above 5000 MSL @ night? I realize the oxygen in the air is less, but why? I'm guessing it has to do with the trees and the sun? lol Thanks in advance, look forwarding to posting more questions.

Best Regards,
Clement "Clem" Quinones
Tamiami-Executive (TMB)
 

EatSleepFly

Well-Known Member
[ QUOTE ]
Why does the FAA recommend to use oxygen above 5000 MSL @ night? I realize the oxygen in the air is less, but why? I'm guessing it has to do with the trees and the sun?

[/ QUOTE ]

Actually, it has nothing to do with that. In fact, by volume, there is just as much oxygen in the air at sea level as there is at even 18,000 feet no matter what time of day or night. It is the lack of oxygen pressure that creates the issues.

But I digress...

Oxygen is recommended above 5000 ft. MSL at night because the first thing that is affected because of lack of oxygen pressure is your night vision.

Hope that helps!
 

cimepilot

Well-Known Member
At night, you use the rods in your eyes to see rather than the cones like during the day. The rods in your eyes require more oxygen than the cones to see colors and decipher images and objects. Your night vision can deteriorate above 5,000 at night without oxygen because the oxygen content is less up there. Honestly, I've never noticed a change.
 

aviator

New Member
[ QUOTE ]
I realize the oxygen in the air is less, but why? I'm guessing it has to do with the trees and the sun?

[/ QUOTE ]

Uhhh no. The oxygen level content is the same at night as during the day. The recomendation is due to the fact that your vision is one of the first body functions that becomes impared due to hypoxia. Your night vision is particularly sensitive.

seems like everyone answered at the same time...
 

JJOB757

New Member
Uhhh,no.It is not hypoxia, I dont believe the factors change day or night.The rods feed on oxygen, and although the oxygen content is the same as altitude increases, there is less pressure acting on it.I could be wrong, but why is hypoxia changing at night?
 

EatSleepFly

Well-Known Member
It is the "beginning stages" of hypoxia...which you don't notice during the day, because its light out.
 

rausda27

Well-Known Member
Its because the Rods (night vision) are more oxygen dependent than the cones (color), thus to preserve your visual acuity at night they recommend the altitude restriction...
 

stuckingfk

Well-Known Member
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Your night vision can deteriorate above 5,000 at night without oxygen because the oxygen content is less up there.

[/ QUOTE ]

Actually, like EatSleepFly said, the oxygen content, which is 21%, is the same percentage throughout all altitudes whether it be 5000 ft or 50000 ft. But the pressure changes very predictably as you ascend.

Partial Pressure = (total pressure) x (% of gas)

sea level 760 mm HG x .21 = 159 mm HG of O2 (each breath)

FL180 380 mm HG x .21 = 80 mm HG of 02

This shows that every time you breathe at 18,000 ft, your body absorbs half of the oxygen that it is used to at sea level.

If you decide to breathe supplemental O2 by nasal canula or mask, and take in 40% O2, your body will absorb the same amount of 02 at 18000 ft as it would at sea level.
 

pilatus028

New Member
go figure, my instructor told me that, but then a friend of mine @ riddle told me otherwise...o well, thanks gents.
 

chunk75

Well-Known Member
Also, the "liquid purple" required for night vision also requires a steady flow of O2 to fight off bleaching.
 

E_Dawg

Moderator
Read this:
When Humans Fly High: What Pilots Should Know About High-Altitude Physiology, Hypoxia, and Rapid Decompression' by Linda D. Pendleton.
-www.avweb.com

It will answer ALL of your questions. Probably.
 
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