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How long can a naked human survive at the surface of the Mars planet?

For instance, let's say a worker's base takes fire while he sleeps, and he has to run to the emergency building 200 meters away without any respiratory equipment, pressure suit, UV protections or anything.

Maybe a human could survive for a rather long time, and apnea time is the real limiting factor?

Climate:

  • Temperature: 27 °C to −50 °C (base is at a rather warm location, on Equator)
  • Pressure: 600 Pa (Earth: 101,000 Pa)
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I think two things might be the issue: 1) lack of atmospheric oxygen and 2) the dust. –  dd3 May 9 '13 at 6:39
    
@dd3: Don't hesitate to propose an answer around this :-) –  nic May 9 '13 at 7:14
    
Frost Burns are likely to be the real killer here. Lack of blood flow due to constricting vessels means that cells and tissue could freeze solid from the dramatic temperatures –  RhysW May 9 '13 at 11:22
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"You should only ask practical, answerable questions based on actual problems that you face" - I'd take care if you're planning to test this ;-) –  Rory M May 9 '13 at 19:10
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I did wonder if it was related to Mars One :L –  Rory M May 10 '13 at 12:41

4 Answers 4

up vote 6 down vote accepted

Long story short, the astronaut probably wouldn't make it, and would first loose consciousness then suffocate.

There is a lot of myth and hollywood dramatization regarding this kind of thing. Here are some:

  1. You will explode. This is just ridiculous. The skin is air tight (relatively speaking). It is also very elastic and can pull and bend quite a great deal before tearing. Through quite a few, equally durable, tissues, it is connected to the bones, which are unaffected by negative air pressure.
  2. Your blood will boil. The circulatory system is also a closed system. It is not directly exposed to the environment. Also, the blood pressure in a healthy person is averaged around 100 mmHg and Earth's atmosphere at sea level is 700 mmHg. There is already a massive disparity, yet Earth's atmosphere doesn't go pouring into our veins at random. Likewise, the blood in a person's veins won't go pouring out into the atmosphere simply because the pressure is extremely low.
  3. Any air in your lungs will be forcibly sucked out of you. Again, this is a closed system, if you hold your breath. As long as you don't try to breathe there is nothing forcing the air from your lungs.
  4. Your eyes will be sucked from their sockets. Thank you Total Recall (the original) for this myth. The eyes are very firmly in place. You might feel a pull on them, but they aren't going anywhere.

Absolutely none of these would happen in the vacuum of space and certainly not on the Martian surface.

Here's what will happen:

Any liquid material on the surface of your body will vaporize. All sweat, saliva (if you open your mouth), water in the mucous, and tears on the eyes, will nearly instantly vaporize. It would be quite uncomfortable, especially the eyes, but very survivable. Long term exposure to a vacuum might damage the eyes eventually, but in this scenario there are far more pressing matters.

The negative pressure may also cause your eardrums to rupture. Try to imagine the feeling your ears get on the plane at 30 thousand feet times about 100. Since you can't close your ears, plugging them with your fingers may help, but likely just postpone the inevitable pressure disparity, which will lead to at least great discomfort and possible drum rupture.

If you had the chance, you should take a deep breath before jumping out and avoid trying to breathe at all costs. Opening your lungs for a breath would very quickly draw whatever breath you had in them out into the atmosphere and also vaporize any fluid that was in them. Considering the rapid pace of this event, you would surely have permanent damage from this and begin suffocating and will die in a minute or two unless you get medical attention. There seems to be conflict in the procedure for this, with some sources suggesting that emptying your lungs would be better to avoid this. Considering the astronaut in your example is about to do a 200 meter dash he is going to need all the O2 he can get.

The cold is also a treacherous factor. At -50C the heat from your body would dissipate so rapidly that it would likely be very debilitating, perhaps causing you to seize up and clutch your extremities to your chest. It would also be excruciatingly painful. It might cause you to fall into shock. In a total vacuum however, this does not exist. A vacuum is actually very insulating, but on Mars' what little atmosphere is there is enough for you to feel the chill.

The lack of oxygen and high CO2 would be what would eventually kill you. You would eventually try to breathe and loose consciousness within a breath or two (or you might loose consciousness first then your body would try to breathe naturally). Your body would try to keep you alive as long as possible by pumping your heart faster and increasing your blood pressure, but your heart would eventually fail and you would die within seconds after that.

Evaluating your particular scenario

There are first a few things about the scenario that seem unlikely.

  1. The astronaut would not be naked. They remain in some of their protective gear in case of emergencies like this. He would have some protection against the cold if he had to run out without it.
  2. Certain things like extinguishers are always nearby. The idea that one was unreachable is a little silly.
  3. Space vehicles, shuttles, and buildings all are compartmentalized like a submarine. They could simply close off the affected areas.
  4. Fire only burns in the presence of oxygen (with few exceptions). After being closed off, compartments can be decompressed, halting the fire immediately. They can then begin refilling them with breathable atmosphere. This poses the same vacuum problem if the astronaut is in the affected area, but he won't be trying to run across the surface naked. People have survived rapid decompressions before without a single injury, as listed in my second source, however, others have never regained consciousness.
  5. Assuming you made it to the other building, they usually only open from the inside. So unless someone saw you coming and opened the door for you, your last minutes would be better spent desperately fighting the fire until it consumed you rather than banging on the neighbor's door.

But let's say all of this breaks down and poor Astronaut Joe finds himself making a mad, streaker's dash across the Martian surface.

We should assume that our astronaut is both quite athletic and knowledgeable about the environment outside of his shelter, knowing that he should take a deep breath before heading out, but literally has no time to grab a shirt, goggles, breathing mask, or anything. Just him and Mars.

If he's lucky, it's not too cold and he doesn't seize up and fall into the fetal position within a few steps. Let's say it's -20C, which is pretty darn cold, but tolerable for a minute or two. I next see him flailing across the surface, trying to run in Mars' low gravity (no easy task). He begins to loose vision as a cloud of steam of what should be tears pours from his dry eyes. His eyelids then begin to stick to his eyeballs because there is no longer any lubrication. He is desperate to reach the other building, and his movements get more and more erratic, as his body is rapidly using all of the available oxygen. All the while, he is still holding his breath, knowing that if he attempts to breathe he will likely collapse within seconds and perish. But the more he struggles to make it, the more his innate urge to breathe overpowers his conscious thought to prevent it. Eventually, against his own willpower, he gasps and attempts to inhale deeply. He takes two or three dying breaths, if they can be called that, then falls to the ground unconscious. He dies shortly after when his heart stops and his brain tissues die.

The whole ordeal lasts under 30 seconds and he is 100 meters at most away from his shelter. If he did get lucky and actually made it to the other building, he would likely have frostbite over much of his body, permanent damage to his eyes and ears, and possibly deadly exposure to cosmic rays.

The event would be very similar to being drug by a fishing line to the bottom of the sea and drowning.

Sources:

A fun questionnaire to see how long you would last in space
What really happens in a vacuum

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One other important event that can kill the person is that the atmospheric pressure on Mars surface is less than one percent that of earth at ground level. Suddden exposure to extremely low atmospheric pressure will immediately release dissloved gases within blood and and other body fluids as bubbles and the individual is likely to get a very severe form of Decompression sickness as in divers coming up too fast. The person is likely to lose conciousness and die within a couple of meters after leaving the shelter.

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That sounds like the fastest factor so far, thanks! Is there any reference or research on the topic? Accepting this answer. –  nic Aug 25 '13 at 2:28
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The pressure difference human normal atmosphere - near vaccuum is about 1bar or the same as 10m of water. Are you sure this is enough to cause divers sickness? –  mart Aug 26 '13 at 13:17

Less then a minute breathing in the atmosphere (and a very painful death). Mars' atmosphere is >95% CO2 with only trivial O2. These are atmospheric conditions similar to those used to euthanize laboratory animals. He probably wouldn't even make it 200 meters before suffocating.

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i havent done the math but you can hold your breath longer than a minute, i think you would die of freezing to death long before you suffocated though –  RhysW May 9 '13 at 12:36
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Certainly humans can hold their breath longer than a minute, but can they run 200 m while holding their breath given the elevated heart rate and blood pressure resulting from general sympathetic response resulting from their sleeping quarters being on fire? They won't freeze at 27 C. –  kmm May 9 '13 at 14:05
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27 degrees is the highest recorded temperature on mars, the average temperature of the surface is -55 degrees C –  RhysW May 9 '13 at 14:11
    
the time to death after being submerged in ice water is not that short. I'd say asphyxiation (< 5 minutes) would do it first. This is kinda a bar-bet conversation... but still interesting. –  shigeta May 9 '13 at 18:05
    
@kmm: "These are atmospheric conditions similar to those used to euthanize laboratory animals" ← Very interesting! That should give us a pretty good idea of the time, right? Has this euthanisia method ever been used on a big monkey for instance? How long is usually necessary? –  nic May 10 '13 at 2:11

Coming up with the exact number is likely to be very difficult but i would put it in the range of 1-2 minutes to impossible.

Let's ignore the lack of oxygen and assume you could hold your breath long enough to reach the safe haven.

The extreme cold would easily drop your core temperature to the realm of severe hypothermia within minutes.

If that doesn't kill you first then the extreme cold has already caused your blood vessels to shrink before you can even take more than a few steps. On top of this the extreme cold is enough to freeze solid any muscles and other tissue, making movement painful / difficult / impossible.

Now lets assume that through some miracle none of that kills you and you make it to the safe haven. The distinct lack of a magnetic field around the planet exposes you to high levels of UV radiation. Being completely naked and having your entire body exposed to this level of UV is likely to cause lots of mutations throughout your cells. Which in itself will kill you.

So your chances aren't looking good for anything beyond a minute!

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good point - big difference between sunlight and day/night conditions, but there is a limit to how quickly the body can lose heat.... –  shigeta May 9 '13 at 18:06
    
Interesting! At sciencebuddies.org/science-fair-projects/project_ideas/… I see that UV kill bacteria in 6 days, I guess it Mars UV are more violent but would UV alone really result in such a sudden death? –  nic May 10 '13 at 1:52
    
@NicolasRaoul i will find the link, the UV exposure levels on mars are something like 10 thousand times greater than what we are exposed to on earth –  RhysW May 10 '13 at 7:55
    
You have a point RhysW, it sort of depends on whether you are talking about the most extreme conditions, average , or what. –  shigeta May 10 '13 at 18:17
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U.S. standards limit an astronaut’s lifetime radiation exposure to 1 Sievert and news.discovery.com/space/… says "even the shortest roundtrips to Mars would get radiation doses of about 662 millisieverts". While the number is impressive, it also means that UV-death won't occur before a few days, which means long after suffocation. –  nic Jun 3 '13 at 8:07

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