76

I have taken several flights from Emirates, FlyDubai and Saudi Airlines. Why is it announced to put your own mask on before helping others with their mask. I wouldn't do it if I am travelling with my family. I would like to help them first. So what's the reason?

  • 1
    You can't help someone else if you're unconscious. – Chris Sep 1 '16 at 2:15
  • Comments are not for extended discussion; this conversation has been moved to chat. – Mark Mayo Sep 2 '16 at 3:08
  • 7
    An example of what happens with oxygen deprivation: youtube.com/watch?v=kUfF2MTnqAw – Francisco Presencia Sep 3 '16 at 2:50
  • 2
    I'm surprised this isn't a duplicate. I could've sworn I've seen this question asked before on the SE network. – Mast Sep 4 '16 at 15:17
  • 4
    You moved not only the "conversation" and "extended discussion", but also extremely important, safety-critical critique of the premise of the question. Good work. – Lightness Races in Orbit Sep 5 '16 at 13:56

11 Answers 11

141

It's actually quite simple. The reason they do this is to make sure you are able to help others. What do I mean by this? During an emergency where the air in the plane is thinning, it is important that you are able to breathe. You can become light headed and if you are trying to help someone put their mask on and you are becoming dizzy, it isn't as effective if you are able to think clearly in the situation.

Think about it this way, imagine you and a friend have been shot in the leg. If you are in agony and can't think clearly, how much do you think you can help your friend? Now imagine you have stopped the bleeding on your own leg and bandaged it. You are now much more capable of providing aid to your friend.

The same applies here. If you are sitting next to your family and becoming dizzy, disoriented, and fumbling with your child's mask, you are not just harming yourself to save the child, but also not giving the best aid possible. It is much better to put your own mask on, remain calm, think clearly, and provide aid to your family so that neither are hindered.

I'd like to add this (sourced from here: Flight Safety)

First of all you should know that in a commercial passenger flight the oxygen masks contain enough oxygen only for 12 minutes and after that everyone on board will go unconscious due to Hypoxia (oxygen deprivation). If the flight is at an higher altitude like 20,000 ft. or above, within 20 to 60 seconds one can get unconscious. This is the main reason flight attendants always advise you to put the oxygen masks first and then assist your children or other passengers – in case of an emergency.

  • 30
    I'd also highlight the fact that becoming unconscious != dieing, so even if all your family passes out after 10 seconds but you have your mask on you can take 1 minute to put the mask on all of them and save their lifes. If they aren't able to help you and you do the opposite the result is at least your death, maybe some other family member too. – Bakuriu Sep 1 '16 at 11:19
  • 30
    The last part of the answer suggests the same change I was about to suggest for the first part.... "Becoming light headed" or being "dizzy and disorientated" really isn't the issue here, unconsciousness is the thing you have to worry about. At 37,000-40,000 ft (a typical cruising altitude), "time of useful consciousness" is in the region of 10-15 seconds. Just about enough time to work out what's happening and to put your own mask on. Once your mask is on, you have several minutes to put masks on your children, regardless of whether they're conscious or not, before they come to any harm. – Jon Story Sep 1 '16 at 14:57
  • 11
    @Jon Story "being "dizzy and disorientated" really isn't the issue here" Well it's a matter of degrees. Yes, you basically have about 10 seconds to get your mask on, and after that your only hope is that someone else does it for you. However, you won't be unconscious after 10 seconds. You'll still be awake and "alert" for up to several minutes. It's just that you won't be able to think straight at all, to the point where if someone told you "hurry up and put your mask on before you die!" you won't understand what they mean, and/or couldn't figure out how to put the mask on anyway. – industry7 Sep 1 '16 at 20:16
  • 13
    Long before going unconscious (in 20-60 seconds), you'll lose enough brain function to become unable to put the mask on. It's demonstrated in this video. – Keith Sep 2 '16 at 1:10
  • 4
    In the better every day video that @Keith linked. Though they don't do rapid decompression, they show that after you lose oxygen 1. you can't do simple tasks like putting a square in a square hole and 2. you don't even realise that you're in danger/dying. – csiz Sep 2 '16 at 9:09
78

If you're travelling with someone who requires assistance, you need to remain conscious in order to assist them, especially if you have multiple people with you, say two children.

Hypoxia can hit in as little as 5-10 seconds and without special training, you can't fight it.

So, you need to keep yourself conscious first, then assist others. Even if someone passes out due to hypoxia, they will almost always regain consciousness once oxygen is restored.

  • 7
    Just out of curiosity: Considering that I can hold my breath for two or more minutes (ok I'm a diver, but any average person should easily manage at least 30 seconds) why would hypoxia set in after 5 to 10 seconds? What's the difference there? Partial pressure will be lower sure, but there must be some other factor to reduce times if that's accurate. – Voo Aug 31 '16 at 20:36
  • 21
    @Voo When you hold your breath for 2 minutes, you probably need advance warning. I bet you even take a deep breath beforehand. Try a different experiment. While breathing normally, exhale, and then stop breathing in. You'll make it for a bit, but nowhere near 2 minutes. To make it more realistic, right after you breathe out, cover your mouth and nose and try to breathe in. Somehow that makes it much worse for me. – Joel Aug 31 '16 at 21:08
  • 41
    @Voo The other difference between holding your breath and a rapid decompression at cruise altitude is that in the latter situation, oxygen will actually go "the wrong way" in your lungs, diffusing out of your bloodstream and into the air, due to the partial pressure gradient. – pericynthion Sep 1 '16 at 6:14
  • 5
    @Voo The pressure in your lungs would be higher then the pressure outside, which means when decompression happens the air in your lungs will go out of your lungs (which is quite different than holding your breathe and letting the air in your lungs to exchange oxygen...). Also: at those altitudes there is too few oxygen so even if you breath you actually lose oxygen as mentioned by others. So that's the difference. I'm pretty sure that someone trained in apnea that can handle 8-10minutes will probably last more than an average person, but surely not in the order of minutes. – Bakuriu Sep 1 '16 at 11:22
  • 18
    @Johns-305 world-class freedivers and alpinists are welcome to finish the chapter of their book and go to the bathroom before fitting their mask. The rest of us should probably do it promptly. – poolie Sep 1 '16 at 19:02
58

As others have already said, it's precisely to ensure you are best able to help your family. And one reason they have to instruct you explicitly not to do that is that every mother's or father's first response would be to do precisely that and they know it. But it might be interesting to understand exactly why the urge to help children first is wrong:

  • You are very unlikely to suffer from a few seconds of hypoxia (hypoxia at birth or long-term exposure are different matters). In case of depressurization (and if nothing else is wrong!), the crew will bring the aircraft down to an altitude where the air is breathable. Even if you fell unconscious in the meantime, you would almost certainly recover with little or no long-term sequel.

  • The main danger is completely different: Mood, perception and cognition are impaired. You quickly become unable to act coherently but you won't notice it. You simply become euphoric, can't control your movements precisely (e.g. during exercises in an hypobaric chamber, the participants' writing becomes gibberish) but do not even realize it.

Consequently, if you start by helping your children, you won't feel when the time to put your mask is coming and you might very well fail to put anyone's mask on. But if you put your mask first, your children are in no real danger and you will be best able to help them.

Incidentally and in line with what I wrote above, the oxygen masks are not there to save you from the hypoxia itself, it's to make sure everybody stays as calm as possible and prepares themselves for what's coming next (and possibly because many people would otherwise be afraid of the very idea of flying at an altitude where you cannot breathe). Passengers only have a few minutes of oxygen but pilots have a completely different system with at least 15 min of reserve. That's because it's a lot more important that they be able to stay conscious and alert and they could theoretically still save everybody's life even if you had no oxygen masks in the cabin.

See also https://aviation.stackexchange.com/questions/2054/would-failure-to-put-on-an-oxygen-mask-during-loss-of-cabin-pressure-result-in-d

  • 2
    The second bullet point sounds terrifying... – Mehrdad Sep 2 '16 at 9:19
  • 5
    @Mehrdad And as you can clearly see from so many comments here, people have trouble understanding that holding your breath is in no way similar to hypoxia. They think they know what hypoxia feels like and does to your body, but they really don't have a clue. There's no easy and safe way to try it at home either, and hypobaric chambers are quite strict about your health before allowing you to enter - and even then, it's dangerous. – Luaan Sep 2 '16 at 11:39
  • 5
    @Mehrdad There's a really good video by SmarterEveryDay on youtube where you can see Destin (the guy running the channel) enter that euphoric state and when told to put his mask back on because he will die if he doesn't he just smile and says to the camera "I don't want to die" and continues to smile. They had to have the person in the chamber with him put the mask on for him because he just couldn't do it. (Link: youtube.com/watch?v=kUfF2MTnqAw) – d0nut Sep 2 '16 at 17:14
  • 1
    @iismathwizard: Yup, I saw that video! – Mehrdad Sep 2 '16 at 17:32
  • @Luaan: Actually, I'm not sure about that. I think what some people might have more trouble understanding (and which I did too) is not the danger of hypoxia itself, but rather the claim that you can experience hypoxia in 10 seconds, when they clearly know they can hold their breaths for half a minute or more. I did have a good idea of how dangerous hypoxia is, but what was terrifying about that bullet point was the idea that it occurs so easily and quickly in this scenario. It only finally made sense to me when I saw the explanation for the time reduction in another comment. – Mehrdad Sep 2 '16 at 17:42
48

Let's talk about lungs, baby, let's talk about you, and me, let's talk about all the good things and the bad things that can be...

But mostly, let's talk about those lungs.

The simple answer (that you put the mask on yourself so that you survive long enough to help your child) feels... really hard to swallow. Any parent can all hold their breath long enough to replace a diaper. A mask cannot take longer than that. The danger they claim seems just... improbable.

Well, no. And to show why, let's first talk about the volume of air in our lungs:

via http://image.slidesharecdn.com/lungvolumesandcapacities2013-140602134857-phpapp01/95/lung-volumes-and-capacities-17-638.jpg?cb=1401717035

Total lung capacity (TLC) in a healthy adult male is about six liters.

There's always 1.2 liters of air in his lungs - he physically cannot breathe out more than that. You cannot empty your lungs. If he could, the sticky wet tissues of his lungs would stick together and he may be unable to breathe in again. This is called the Residual Volume (RV).

There's a certain amount that he can force out if he must, below his normal "breathe in and out" cycle. This Expiratory Reserve Volume (ERV) is about 1.2 liters.

When breathing normally, he breathes in and out by about 0.5 liters each cycle. This is called the Tidal Volume (TV).

He can, if he must, breathe in an additional 3.1 liters on top of that.

There's also a little bit of air in his air passages, outside his lungs sealable inside by closing his mouth, which is about 0.2 liters or less when breathing normally.

  • 3.1 IRV Inspiratory reserve volume
  • 0.5 TV Tidal volume
  • 1.2 ERV Expiratory reserve volume
  • 1.2 RV Residual volume
  • 0.2 UV Unused volume

Now let's talk about pressure, the other half of Boyle's Law.

On the ground, around sea level, air pressure is around 15psi.

Say our average healthy man is sitting in a plane, with a pressurized cabin. While pressurized, the passenger cabin is typically only about 10psi. That's like normal air pressure at about 8,000ft.

However, the plane suffers an explosive decompression event at its legal flight ceiling of 45,000 feet, and air pressure in the cabin drops further to about 2 psi within the blink of an eye - he has no time to react. It's a couple of seconds before he's even realized what's happening, at which point he gets smacked on the head by his air mask.

Even though he reads Quora, and has read this thread, clamping his mouth and nose shut will not have been his first instincts in those valuable first moments. Instead, it's natural and instinctive for him to gasp, to pull in that additional three liters of air, nearly doubling the air volume in his lungs. Normally, this would help him survive.

But, when he was breathing normally, idly perusing the safety card, the air in his lungs was fluctuating between 2.5 and 3 liters. By opening his mouth at 2 psi, and doubling the air in his lungs, he reduced his available oxygen. Air rushed out.

He went from three liters at 10psi, to six liters at 2 psi.

Six liters at 2psi is the same as 1.2 liters at 10psi: that's only 40% of the air he had before breathing in! Put another way, if he'd breathed out as much as he possibly could before the decompression, then closed his mouth and relied just on the RV air he'd been unable to breathe out, he'd be no worse off.

But it's worse than that, really. Because that's same as 0.8 liters at sea level. That's less air than he has ever had in his lungs in his life.

EXCEPT... it's even worse than that. Because, he won't do that. He won't grab that lungful of air. Because there's no CO2 shortage telling him he needs to get more air. He's breathing normally. His lungs aren't extended to six liters. They're only extended to the normal 3 liters (equivalent to 0.4 liters). He's breathing normally, so only half a liter per breath (equivalent to about 70 ml).

And remember, he's an average fit, healthy adult male. Unhealthy or unfit? Female? Young, Old? Smaller than average? Your lungs will be smaller. Maybe much smaller.


Now let's change tack completely, and instead talk about freediving.

@Johns-305 pointed out that the world freediving record was eleven minutes, which is totally plenty of time to help everyone around you, and still have a quick coffee break.

This is true, but freediving requires:

  • many years of training, granting...
    • enlarged lungs (increased IRV), and
    • reduced metabolic rate,
    • hypoxia resistance,
    • muscles that can operate on lower oxygen;
  • a lengthy prep period of hyperventillation, breath packing and other exercises, to maximize the oxygen and minimize the CO2 in both the blood and the lungs;
  • cool water, giving body cooling,
  • cool water to the face to trigger the diving reflex, granting...
    • blood shift to vital organs,
    • reflex brachycardia (slowed heart rate),
    • body and brain cooling,
    • splenic contraction increasing red blood cell circulation;
  • and a big lungful of air taken at about 15psi.

Ignoring all factors but the last, consider that freediver Herbert Nitsch is reported to have a lung capacity of 14 liters (not sure if this is with or without packing).

A trained, prepared professional with 14 liters of air in his lungs and plenty more hyperoxygenated into in his blood, can last 11 minutes, max, before blacking out.

What does this mean for our healthy but untrained and unprepared adult male, with his equivalent of 0.4 liters, plus 0.07 every breath?

He blacks out in less than 20 seconds.

33

Smarter Everyday did a video on the subject. It doesn't add much to the other answers, but it's fun to see what actually happens when you lack oxygen.

Why You Should Put YOUR MASK On First (My Brain Without Oxygen) - Smarter Every Day 157 (YouTube)

  • 8
    I came here to post the same link. It really highlights the details given in other answers with a good visualization of what happens. It is compelling to see what happens when the presenter is told to put his mask on or he's going to die. He just can't piece it together. This is a smart guy in decent physical shape too. No one is immune to oxygen deprivation! – Freiheit Sep 1 '16 at 15:01
  • I came here to post the same link too... – Ryan Weaver Sep 1 '16 at 17:15
  • 2
    Totally this. Seeing is believing. – piers7 Sep 2 '16 at 8:02
29

The key concept here is time of useful consciousness: how long you can take meaningful actions in a low-oxygen environment. At 35,000 feet (the typical altitude for a long-distance flight), that's about 30 seconds. If you help someone else put on their mask first, you probably won't have enough time left to put on your own.

This question on Aviation.SE and the linked video of training in a hypobaric chamber cover what happens in a hypoxic situation.

And if you're worried about your kids, notice that the test subject in that video recovers almost instantly once his mask is back on.

23

A short answer to tell others (not 100% accurate, but right in principle): It takes 30 seconds until you pass out without mask. It takes two minutes until you die without mask. If you try to put a mask on your children first, you pass out and two minutes later you all die. If you put your own mask on first, your children will pass out, but you have plenty of time to put their masks on and no real harm is done.

It is better for your children to put your own mask on first.

  • 2
    This is the key point that some of the highest-voted answers fail to point out. – Peter Cordes Sep 1 '16 at 10:59
  • This answer is the one that will make all the mothers out there put on their own mask first. The highest voted answers are the ones that make the fathers put their own mask on first... – awe Sep 2 '16 at 9:04
  • Where does the 30 second number come from? (especially given that shorter timeframes are claimed in other answers) – Christian Sep 7 '16 at 11:10
15

It is easier to help someone else while conscious.

5

It's just a simple medical fact: if you lack of oxygen and you have a fast pressure decrease around you - you will loose some air from your lungs to equal the pressure. And you will fall unconcious very quickly - even in about of a tens of seconds. So - to be "online" - you need to put your mask on and provide some oxygen to yourself very first hand. No, it's not a selfish act even if you need to help someone near: helping means physical and brain activity that will drain your oxygen level even faster, you won't be able to help them if you won't put your mask on. Even if they will fall unconcious - there still some minutes for you to put their masks on their faces.

That's it!

3

The reason is that you need to be safe and as healthy as possible in order to help others. If there is a real danger of getting out of air und you begin to lose consciousness, you won't be able to help your family either.

-2

There is a general principal in medicine -- first of all, do no harm. This extends to lifesaving practice in that you should, while attempting to help others, not put anyone else at risk including yourself.

It simplifies a lot of discussion to say that by first helping yourself you are best able to help your family. The reason is that you will be clearheaded and able for a longer time. This has been proven many times for lifesaving:

  • running into a burning building that may be about to collapse
  • moving someone who has been in a car wreck and may have spinal damage (when there is no imminent danger)
  • attempting to separate a biting animal from a person who is being bitten
  • grabbing a live electrical wire without proper equipment
  • swimming out to try rescuing a person caught in a rip current without equipment (like a float), excellent swimming skills, training

All of these items and more can put the potential rescuer and others into danger. When you are given directions for lifesaving procedures by authorized personnel, it is pretty safe to assume that they are providing expert advice, though it is sometimes calculated to be the best advice for the least strong, capable or experienced person likely to be in the situation that it covers, it is likely to be the best advice for you.

In a plane, follow the directions of the trained personnel to exit the craft, pay attention to the marked emergency exits, use your seat as a flotation device, take your high heels off before jumping into the emergency exit ramp, and put your mask on first before assisting others! It makes sense when you think about it long enough, but you won't have the time to think about such things in the event!

  • Not sure why the down vote? I added new information and answered the original question – Old Uncle Ho Sep 4 '16 at 2:50
  • 1
    Most parents put the safety of their children above their own safety. This answer does nothing to correct the notion that helping yourself first is trading off your child's safety against your own. The key point is that there's a large time window between time of useful consciousness and any permanent injury. So it's not like running in front of a car to push your child out of the way, which many parents would do no matter how many people told them not to. – Peter Cordes Sep 4 '16 at 13:36
  • Putting more people at risk through a type of action that is not recommended is not reasonable, even if, arguably, some people would take that unreasonable action against expert advice. If you do not follow instructions you may be barred from flying -- it's not just an inept choice, failing to observe stated safety protocol always puts a greater number at 'risk'. The risk is the created uncertainty or additional uncertainty of safety. While it's not a certainty, as risk never is, there is a certain basis for requiring people temporarily under their care follow best safety procedures. – Old Uncle Ho Sep 6 '16 at 16:02

protected by JonathanReez Sep 2 '16 at 12:53

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.