88

The key point here is that your body does not measure blood oxygen levels. Instead, the urge to breathe is caused by a surplus of carbon dioxide in your blood. At sea level, this is fine: the only way to get so much carbon dioxide in your blood is if you used up all the oxygen. At higher altitudes, the pressure is lower, and consequently the oxygen partial ...


61

When you are breathing, oxygen ($\mathrm{O}_2$) and carbon dioxide ($\mathrm{CO}_2$) are exchanged between the alveoli in your lungs and the environment. This gas exchange is based on diffusion, which means the partial pressures of each gas involved will move towards equalization: Henry’s law states that the amount of a specific gas that dissolves in a ...


57

The other answers are good, but don't touch on one key method... Prevention. Small aircraft like a Cessna 172 have a limited cruise time, about 4 hours maximum. They are small enough that they get relatively uncomfortable after 2-3 hours, and if flying in turbulence or challenging conditions, flights can be relatively short. The best way I've found to ...


44

What happens during a flight cycle is the humidity is high during departure, from ambient air and the moisture from the pax, but over time the air dries out because the bleed being supplied to keep the pressure hull "inflated" is coming from the engine compressors, which at 35000 ft has almost no humidity, and what humidity there is is being extracted by the ...


30

I have had success with these things. They are basically a little baggy that has the same stuff they put in a diaper. You can always wear adult diapers (and I have heard of it being done) Some small planes can be fitted with a pilot relief tube. This is effectively a tube connected to a small venturi outside the plane. The venturi creates a low pressure ...


27

No, lack of oxygen, in an of itself does not trigger negative physiological responses; quite the opposite. Most people who are affected by hypoxia have a general feeling of elation or euphoria and think everything is fine. The body will, however, respond strongly to high levels of carbon dioxide in the blood and lungs but not low levels of oxygen; this is ...


24

The situation in a high altitude depressurization is different because: The air in your lungs is now "FL500 air" - i.e. the pressure is about 0.1 atmosphere. This means that the partial pressure of O2 (ppO2) is about 0.021 atm, instead of 0.21 atm. Oxygen will rapidly diffuse out of your blood and into your lungs, and your brain will very soon not have ...


23

According to: Time of useful consciousness: Altitude (measured barometrically) - TUC FL150 (15,000 ft; 4,550 m) - 30 minutes or more FL180 (18,000 ft; 5,500 m) - 20 to 30 minutes FL220 (22,000 ft; 6,700 m) - 5-10 minutes FL250 (25,000 ft; 7,600 m) - 3 to 6 minutes FL280 (28,000 ft; 8,550 m) - 2.5 to 3 minutes FL300 (30,000 ft; 9,150 m) - 1 ...


18

Why is the air so dry Its in part by design and in part a constraint of the system. All aircraft are at risk of corrosion not just big airliners. So keeping them dry is a good way to cut down on that risk. Even though they use fancy anti corrosive paints these days internal corrosion presents a serious risk as some areas may only be exposed during a ...


12

As someone who has experienced hypoxia numerous times, the simple answer is that as you climb at 500-1000fpm into thinner air, the effects are very subtle, and, having compared them with other people, very personal. For me, at about 86% O2 saturation, measured on a pulse oximeter, the first thing I start to feel is a very slight decline of mental function, ...


11

As mentioned prevention is generally best. Part of my job involves aerial survey work in a P.68, with flights regularly going over 5 hours. My personal record is a 7.5 hour flight. This is my method to keep bodily functions at bay: The day before a long flight drink plenty of water to stay as hydrated as possible. On the day of the flight get your fluids in ...


9

200 humans exhaling persistently in an enclosed, relatively warm, high pressure atmosphere creates large quantities of condensation on the cold interior surfaces & structure of the aircraft hull, creating a serious corrosion liability. Like computer mainframe facilities being carefully air conditioned & temperature controlled, de-humidifying the air ...


8

The 'breathe faster and harder' is a cinema trope. One of the first things to go with hypoxia is judgement. Do you feel good? You cannot trust your assessment. As an impecunious glider pilot (not able to afford oxygen gear), the drill my syndicate stick to is this. You don't go above 13000ft. If you're above 10000ft, and you yawn, that's it, you descend to ...


8

Apart from the points raised in other answers about breathing response being triggered by carbon dioxide in the blood, and the feeling of euphoria when hypoxic, there is also the fact that low blood oxygen impairs brain function. So not only do you feel giddy, but your ability to perform mental tasks degrades - you don't just feel fine, but you can't think ...


7

On small GA aircraft, you are limited to urination as there is no reasonable way to defecate in such an aircraft. The problem can be handled similar to what the military provides for combat aircraft ie 'Piddle Packs' - basically a Ziploc bag with strip of dry sponge to absorb liquid waste. There are also specialized bottles and liquid waste containers sold ...


6

Though almost any wide-mouthed bottle will serve for a male, there are also relief bottles, such as the Little John, which offer an adapter for females (the Lady J). There are also the pouch-type, such as the Travel John, which work for both genders and contain chemicals that turns the urine into gel and masks its odor. The major pilot supply stores, ...


6

I was on an EMB-145. The longest flight we usually had were 3.5 hours so my experience doesn't compare to Trans Pacific routes. As a crew-member I could get up to use the restroom, but there wasn't enough room to stand on the flight deck. You learn to sit different ways (one leg under you) to makes adjustments. Then the other leg under you later and so one. ...


5

Time of useful consciousness tables are useful as a first order approximation. The reality is that there is a great degree of difference between individuals, and also their conditioning. In one chamber ride, nearly an hour after explosive decompression (which can be very disorienting, even when anticipating it), I was still performing the cognitive ...


4

It's also the starting gun. When you hold your breath, you choose when to start. That is known. In a hypoxia incident, you rarely discover the pressurization problem at the very start of the event. It may be well along before you notice it. So you don't know when you actually started "holding your breath". It would be more of a fair comparison if ...


2

Hang glider pilots normally fly in a prone position in a sleeping-bag-like harness that may be unzipped from the toes to the waist. So, you might imagine, it's quite possible to drop liquid ballast in flight. Look out below! Many sailplanes have pee-tubes installed-- a funnel-like cup attached to a rubber tube leading to the outside. Other times a condom ...


2

I used to fly on occasion on only USAF aircraft. Ones from the 50s and 60s. Their solution to the pee problem? There was a vertical pee tree, with multiple "cups" you could stick your johnson in and let go. For EVERYONE in the plane to enjoy. For women? Who knows!


2

I can second Ron's answer (you don't) and add a personal anecdote; back in the mid 80s I was invited to join some skydivers taking a High Altitude Indoctrination Course at the Defense and Civil Institute of Environmental Medicine in Toronto when they had an open spot. A jumper had to have taken the course to be able to jump from altitudes above 12000 feet ...


2

The simple answer is "they don't". Training will dictate that at altitude, they need to be able to don masks within a few seconds, regardless of an individuals tolerance to altitude. The problem isn't that you have X seconds of full-cognition and then you pass-out, your brain function degrades during that period. It's best to get your mask on and oxygen ...


1

The humidity inside the plane has three constraints: at what point does the humidity become a corrosion risk for the plane? The 787 and presumably other future planes are now mostly "plastic" (composites) and can't corrode, so this limit is just in the process of increasing rapidly. what the hardware can in theory deliver: air at altitude is cold, and ...


1

I piloted 4 hour flights without much physical issue. There was noticable mental fatigue as they were single pilot operations with a complex flight plan, having a copilot will help a lot with that part. Pilot seats are much better than passenger seats, both in basic shape and adjustment. Pilots also have rudder pedals and many hand controls so there is ...


1

A simple explanation is that, if you reach the point when the Oxygen in blood is not high enough, then your alertness is reduced, and you may faint, and even die. This is why warnings are to put the oxygen mask yourself, before helping the one in the seat next to yours. There are devices at a very low price, that measure Oxygen in Blood and Pulse Rate just ...


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