# Tag Info

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 ...

58

I did high altitude training about three months ago, up to 30,000 feet simulated altitude. Here's the timeline: Within 30 seconds (oximeter 100-95): noticed physical symptoms beginning. I could tell that something was wrong, but felt functional. Within 60 seconds (oximeter ~90): mild headache. Still able to write my name. Not feeling good, but ...

42

In short: acclimatization, both chronic and acute. During your Tibet-trip, you had probably spent days at high altitudes, allowing your body to acclimatize to the lower oxygen partial pressure (similar to how some elite endurance athletes prepare themselves for competition), by increasing your hemoglobin count (and other mechanisms), making you better ...

34

First, let's be crystal clear on something: A person experiencing symptoms of acute hypoxia is an emergency which requires immediate action to ensure the safety of that person. In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule … to the extent required to meet that emergency. (FAR 91.3 (b)). So if you're ...

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 ...

22

At lower altitudes, "useful" consciousness doesn't end when you are unable to act. Rather, what happens is that your ability to make sound decisions and carry them out effectively degrades: for example, instead of responding to an alarm buzzer by figuring out what's causing it, you might simply hit the "silence" button, or you might be so fixated on keeping ...

21

The answer depends on what kind of aircraft you're talking about, and how much control the crew has over the pressurization systems. For example, in theory you could very well reduce or completely shut off the air to the cabin on a 777. This could also be done by a single crew member alone. The pilots have full control of this system should say the one of ...

20

You don't have to divert, in fact it may be a bad option depending on conditions (I would recommend you don't go if conditions will make diverting dicey though). You can treat the hypoxia with low cost bottled oxygen supplies specifically made for this situation. At 11,000ft it's unlikely lack of oxygen will make your mother really ill, a top of oxygen is ...

18

The simple answer is to rent or buy a supplemental O2 system for Mom. Don't fake this one. As Voretaq7 said in the first answer, "A person experiencing symptoms of acute hypoxia" Focus on the word "acute". Just having your Mom feeling a little light-headed is probably not going to hold up as a valid reason to divert lower in any faa action. And if ...

14

Short answer? It's entirely possible that not putting on a mask could result in death. Long answer: The classic example of hypoxia is the Payne Stewart Learjet crash that happened in 1999; the jet lost cabin pressure (and the crew lost consciousness) sometime in the 6 minutes between 23,000 feet and 36,500 feet. All 6 aboard perished in the crash. From ...

13

Yes, I think it would be very easy for the pilot in command of a 777 to do this — here's one scenario: Ask the copilot to get a glass of water and lock the cockpit door behind him Don and activate the oxygen mask Close the engine bleed air valves that supply cabin pressure Open the controlled outflow valves to equalize cabin pressure to altitude ...

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

That would depend on at least the following: how high the cabin got during the process how long it stayed high the physical condition of the passenger perhaps to some degree how much oxygen was coming out of the masks of adjacent passengers I went through NASA's altitude chamber program at the Johnson Spaceflight Center back in the early 80s. They wouldn't ...

9

The other answers focus on the physiology of failing to put a mask on, but I am going to offer another take on this. Whether you die from not putting on a mask depends on one thing: Did the pilots get their masks on before useful consciousness ran out? If they did, you live. If they didn't, you die. It is as simple as that. In the case the pilots get ...

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 ...

8

Yes, all pressurized aircraft have cabin altitude (= altitude at which the same pressure as currently in the cabin normally occurs) indicator with alert when it exceeds safe value. On Helios 522 that alarm did sound. The crew however mistook it for configuration alarm which only makes sense during take-off roll and thus considered it spurious. When the ...

7

A good amount of information can be found in the Operator's Guide to Human Factors in Aviation: Hypoxia can be recognized from both objective (i.e., capable of being perceived by an observer) and subjective (i.e., perceived by the pilot only) symptoms. Objective signs include increased rate and depth of breathing, tachycardia, cyanosis (blue-colored lips ...

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

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 ...

5

In principle at least, you can begin to experience hypoxia at 5000ft. By 10,000ft, it's affecting your eyesight, and probably starting to affect your judgement a little. At 15,000ft, your judgement can be measurably impaired, and you'll often experience euphoria, so you can't TRUST your judgement even if you think everything is okay. Your personal experience ...

5

Very simple operation and you don't need to be at 41,000 feet to do it. Anything above about 21,000 feet and you die in a few minutes; you just fall asleep. If you are really paying attention, you would first notice your fingernails (under them) will turn blue due to a lack of oxygen first. A few giggles perhaps, then you'd pass out and DIE. Quite ...

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

Most people can function at 12,000 ft. Pilots do as well and don't need oxygen there. Above that altitude, however, it gets worse very quickly. By 14,000 ft (where oxygen is always required for crew) most people will be noticeably short of breath and between 16,000 – 17,000 ft they may pass out. I was once that high in the mountains. We were hiking, so ...

4

The passengers on Helios 522 were incapacitated or died due to hypoxia. Those masks in the aircraft only have enough oxygen to sustain the passengers while the plane descends to a safer altitude, or about 12 minutes. Helios 522 was on autopilot at 34,000 feet for 2 and a half hours. The autopsy showed that the passengers were alive at the time of the crash, ...

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 ...

3

Yes, people have died due to depressurization of commercial aircraft, as well as military. There was a famous case of a Learjet where everyone became unconscious from a depressurization and the plane kept flying until it ran out of fuel. A more recent incident, a couple of years ago in a TBM 900 where the plane flew on with the crew and passengers ...

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