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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 ...


47

To add to Daniele's answer, from the final report: The forensic report concluded that the aircraft occupants had heart function during the impact. The report noted that this did not necessarily imply that they were alert. The report further estimated that they were in deep non-reversible coma due to their ...


37

Consciousness requires quite a bit more oxygen than merely being alive. Human beings can last remarkably long with very little oxygen, but not remain conscious. And lack of oxygen will soon enough cause permanent damage. The passengers may have been alive, even if they were not conscious, but they could have been anything from temporarily incapacitated to ...


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 ...


20

Let me start out by saying that Aviation Stack Exchange is not a substitute for medical advice. Most of us aren't doctors (though I have medical training I am certainly not a doctor), and even if we were doctors we are not your doctor and we don't know your medical history (or your child's medical history). If you're going to be flying with your kids in an ...


17

The question you're asking roughly translates to What is the time of useful consciousness at 39,000 feet?. The answer is "About 15-20 seconds, once the pressure bleeds off." The FAA has a handy table for this: From Chapter 16 of the Pilot Handbook of Aeronautical Knowledge. You can get a PDF of Chapter 16 here, or you can grab the whole thing from the FAA ...


16

Night vision is one of the first things affected by reduced oxygen levels, and that effect is masked in daylight, but can become consequential at night. But no, the O2 molecules are the same night or day. BTW, airline pilots in our 8000' cabins do not have different guidance for putting on the masks -- it's 10k, day & night both. Air Force was, IIRC, ...


13

The B307 may have been the first pressurized airliner, but it was usually flown at 12,000', and did not have a passenger supplemental oxygen system. Boeing 307 / C-75 Stratoliner 1938 "Captain Frank E. Adams, 23.02.2011 I flew the S-307 2 years for Pan American Airways (1943/1944) and today remain one of the few pilots in the world who is still rated for ...


13

While it would not significantly affect the O₂ percentage one thing that must be tabulated on a cargo aircraft is the amount of dry ice loaded. Dry ice is very common in packaging to keep perishable shipments cool during transport. Since dry ice sublimates into gaseous CO₂ as it warms there is a limit to how much can be loaded into an aircraft. If there is ...


13

Here is a list of those people who survived as stowaway in the unpressurized and extremely cold wheel well. On June 19, 2015 an unidentified male who was 24 years old survived 11(!!) hours in the wheel weel of British Airways Flight 54 from Johannesburg to London. As you also see, this is incredible because as you suggested most of the people simply die. ...


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, ...


10

The air in the lungs is in pressure equilibrium with the cabin, but not temperature equilibrium. It's always at body temperature. So the only variable that can affect how much oxygen is available to the body is the pressure of the outside air - thus pressure altitude, not density altitude, is physiologically relevant. That said, if the density altitude is ...


9

The air conditioning system on board airliners is an open system: it scoops up air from the atmosphere, compresses it, expels it through the cabin vents, and then outflows it through discharge valves. In modern airliners there is a certain amount of re-circulation: the expelled air was of such good quality that it seemed a waste to just dump it in the ...


9

Pressurized oxygen tanks have two big minus points: they are heavy, and they are essentially a small bomb. But they have two big plus points: they can be refilled easily and they don't generate any heat when you use them. Chemical oxygen generator plus points are they are lightweight, self-contained and more-or-less maintenance-free (they don't leak). Minus ...


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

There are always health implications at higher altitudes, even those approved by the FAA. Legally you are not prevented from flying at this altitude since the FAA does not stipulate an age for that particular FAR. You SHOULD consult a pediatrician on the specifics of you trip and its effects on children of the age you intend to carry. A 3 month old baby and ...


7

Assuming our lungs are like our engines They are not. Engine (at least spark-ignited reciprocating one) uses most oxygen in each charge and its RPM is limited, so it can't be run faster to compensate for the lower air density. However, our bodies only use small fraction of oxygen from each breath and we normally breathe much slower than we can if need be. ...


6

Long term, no, it is not. Any exposure to pressure altitudes over 26,000 ft will eventually cause death from hypoxia, even with acclimation to the higher altitudes. There is a period referred to as Time Of Useful Consciousness (ToC) associated with hypoxia. This is the approximate time that a healthy adult human with good lung capacity can maintain ...


6

The analogy that if someone can become acclimated to working at high altitudes and therefore should not need supplemental O2 in an airplane is flawed. While flying - at least straight and level - does not require strenuous exertion, it is very cognitively taxing. It's a constant process if taking in a deluge of incoming data, be it instrument read outs, ...


6

In General, Yes. As your image already shows, the same air is distributed throughout the cabin and the flight deck. For example, in the 737 NG FCOMv2 2.30.4 (Air Systems - Air Conditioning Description) it says: Since the flight deck requires only a fraction of the air supply provided by the left pack, most of the left pack air output is mixed with the ...


6

Source: Pilots Don MOPP Protective Gear - 25th Fighter Squadron, YouTube If the base is equipped, then yes. The ground/flight personnel don the specialized suits for chemical/biological warfare. And according to thedrive.com, a suit is also available for the F-35, though it took a decade to design. The delay was due to the F-35's complicated "enhanced man-...


5

An even more important question than how is how much oxygen to take, but there's no specific FAA guidance or regulation on either point. Different aircraft can carry different equipment, and people have different requirements depending on their age, lungs, blood chemistry, whether they smoke, day vs. night etc. The FAA's guide on oxygen equipment for GA use ...


5

There is no regulatory requirement for oxygen to be available for anyone on board an aircraft so long as it remains at altitudes of 12,500' MSL or less. And only the required minimum flight crew is required to have oxygen if they are flying above 12,500' up to and including 14,000 MSL' IF they will be at those altitudes for more than 30 minutes. CFR 91.211 ...


5

While researching for the question, I was only able to find the first liquid-based oxygen system, which is this answer: The Provisional International Civil Aviation Organization (PICAO) issued recommendations in May of 1946 that oxygen must be made available in commercial aircraft that fly above 10,000 feet (whether pressurized or not). (Source: Flight) A ...


5

Humans are diurnal. At night, we get sleepy. The effect is worse when we're extremely tired. As a result, we are more susceptible to things that affect cognitive processing during those times. Oxygen inadequacy or deprivation (meaning a reduction below the level we are physiologically accustomed to) is one of those things. It's nothing to do with the ...


5

The amount of oxygen in the air is the same day or night. The big difference - which isn't really explained in the part of the PHAK you quoted - is that at night your eyes work differently. Your eyes have two different types of photoreceptors: rods and cones. Cones work best with high light levels and rods work best at low light levels. So during the day, ...


5

Taking the B737 as an example, fresh air from the left pack flows directly into the cockpit (green airflow in the diagram), whereas the passenger cabin is served from the mix manifold only (yellow). Therefore pilots receive 100% fresh air while passengers receive a mix of 50% fresh air and 50% re-circulated cabin air on average, across all aircraft types ...


4

The cargo hold is indeed vacuumed, using a vacuum cleaner, regularly. It is however NOT drawn vacuum (so having all air removed). Some cargo holds may be pressurised, some are not. Depends on the aircraft and the requirements of the cargo (life animals want a pressurised cabin of course, just to give one example).


4

Very, very rare, probably in the range of sinlge digits per 100,000 flights (for major first-world airlines, perhaps higher elsewhere). I'll try to get you a more numeric answer tomorrow. Posting an answer now so that I can edit it, evem if the question gets closed between now and then. "Opinion based", horsefeathers!


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