AirWillie6475 From United States of America, joined Jan 2005, 2448 posts, RR: 1 Posted (10 years 9 months 2 weeks 4 days 12 hours ago) and read 2302 times:
Some publications recommend that you fly with oxygen aid above 10k feet during the day and above 5k feet during the night. Why is it that the oxygen requriement is at a lower altitude during the night? Isn't it true that when we experience loss of oxygen at high altitudes its because of the decreasing pressures not because of absence of oxygen? What does night and day have to do with it?
TWAMD-80 From United States of America, joined Oct 2001, 1006 posts, RR: 3
Reply 2, posted (10 years 9 months 2 weeks 4 days 8 hours ago) and read 2128 times:
Your eyes use two basic types of detectors - Rods and Cones. Rods are used when light is scarce (ex. at night). Cones are used when there is a significant amount of light; cones also detect color in your surroundings. If I have explained this correctly (I think I have) you will need extra O2 up at altitude at night because you will lose you visual acuity much easier than you would in daylight.
Two A-4's, left ten o'clock level continue left turn!
MrChips From Canada, joined Mar 2005, 984 posts, RR: 0
Reply 3, posted (10 years 9 months 2 weeks 4 days 6 hours ago) and read 2120 times:
It's not law that you are on oxygen above 5000 feet at night...merely a recommendation. If you are above 10000 feet for 30 minutes or longer, or above 13,000 feet for any time (here in Canada, at least), day or night, you are required to use supplemental oxygen in an unpressurized aircraft.
Is it a good recommendation? Hard to say...field elevations here can be 3600 feet or more, so its a bit of a hassle for us here...I think it applies to people who live at or near sea level, and thus aren't as acclimatized to higher altitudes. Myself, I judge it on how I feel...at night, I might put the oxy on as low as 8000 feet just because I'm not feeling 100%.
As mentioned above, vision is one thing, but there are a lot more stressors out there at night that cause the body to need a bit more. Vision is a big one. Not only does it function differently, but you are straining it to identify things in the dark both inside and outside the cockpit. Another is the body's natural sleep cycle. Unless you are a professional who regularly flies at night time you proably would normally be asleep in the dark. A bit of O2 can help keep you more alert.
Undehoulli From , joined Dec 1969, posts, RR:
Reply 5, posted (10 years 9 months 2 weeks 3 days 6 hours ago) and read 2071 times:
I can speak for the effect of oxygen on night vision. At school we're fortunate enough to have an altitude chamber. After experiencing hypoxia at 25,000 feet we don our oxygen masks and descend (not sure exactly to what altitude, I think around 18,000 feet). The lights are dimmed and we look at a picture trying to determine the colors, off of oxygen. When you put the mask back on, it's amazing how quickly the colors become clearer and the image sharpens.
Even after being hypoxic for around 5 minutes at 25,000 feet, putting oxygen on brings you back very quickly, within 2 or 3 breaths. I had to be assisted back on oxygen my first time as I had lost muscle control and coordination.