Effect of removing helmet in space?

[Molydood]

Hi guys,

we got into a discussion over lunch today about the effects of removing a spacemans helmet while in space.

Assumptions:
Space is colder than earth
Space is lower pressure than earth
Others?

Opinions:
Human expands/explodes
Human freezes
Human freezes then explodes

Any help is appreciated.
I'm also curious why space is perceived as cold when there isn't any air.. it receives the same amount of sunlight (if similar distance away from Sun) so why do spaceship cabins get cod, if there is no air surrounding it to conduct the heat away? surely it would be perfectly insulated against conduction. Does it radiate away?

thanks
Martin

 

[quddusaliquddus]

We'd explode then freeze!

 

[KingNothing]

I think it would take a while after we freeze to decompress...that's a more applicable term than explode.

 

[Artman]

The loss of pressure would cause the astronaut's body fluids to boil. The side of the astronaut facing the sun would fry at about 250 degrees F while the side away from the sun would freeze at as low as -250 degrees F. There is also the risk of tiny meteors striking the astronaut and radiation burns from unfiltered sunlight. If the event was extremely short, the astronaut would probably at least suffer a case of the bends.

 

[enigma]

In space you have a hard vacuum. With the vacuum, there is no material to conductively take heat away.

What'll happen first is any saliva in the mouth will boil. If the astronaut had a full breath drawn, the air will do severe throat and lung damage as it gets ripped through his throat and into the void. Seconds later, the astronaut will lose consciousness due to lack of oxygen to the brain. It will take a long time for the body to freeze. Radiation of heat at body temperatures is slow. The side facing the sun will burn fairly quickly though.

 

[Chi Meson]

Have you seen the movie "Outland"? (Early 80's Sci-fi with Sean Connery, it's in the top 5 of the Best SF movies ever IMOHO). There are several scenes of what happens without your helmet. They are of course exaggerated for cinematic effect.

To continue the previous descriptions, if you try to hold in a breath of air through a tube (a long snorkle) when you are merely at 5 feet of water depth, you will see what one ten thousandth of the pressure difference of total vacuum will do. (EDIT: Oops, I meant one tenth, the pressure difference at 5 feet is about 10,000 pascals)

 

[LURCH]

You've also got to remember that a cosmonaut is decompressed to only about 7# psi before going EVA, (or something like that, I forget the exact amount, but it's less than 10#), 'cause a spacesuit at the normal pressuers of around 14# psi would be as stiff as a car tire. So the rapid loss of air (explosive decompression) would nto be enuogh to pop the individual like tick, as so aften happens in the movies, btu the blood would indeed boil ratgher quickly, causing the subject to bleed from the nose, ears, and probably eyes.

In a previous thread, someone who had read A. C. Clark's "2001; A Space Odyssey " asked a similar question, and we discovered that a person could survive exposure to the vacuum for up to ten seconds without permanent damage!

 

[KingNothing]

I forget, why does your blood boil? I remember being told it once, I don't think it was the pressure or heat...what was it?

 

[cookiemonster]

It's pressure. Pressure changes the boiling point of substances. That's why water at higher altitudes (Denver?) boils at a lower temperature than at sea-level.

Higher pressure holds the molecules together more strongly, so it requires more energy (temperature) to break them apart.

cookiemonster

 

[Janitor]

The great writer of science fiction and science fact, Arthur C. Clarke, wrote an essay in which he made the claim that Hollywood's idea of what happens to a human when all pressure is lost is an exaggeration. Clarke thinks that the astronaut would remain in one piece, and could even maintain consciousness for several seconds. I wish I could remember where I read this...

On the other hand, I know a retired Air Force fellow, and he says that in the altitude chamber test he lost his wits very quickly when they took him down to some low pressure.

 

[KingNothing]

It's pressure. Pressure changes the boiling point of substances. That's why water at higher altitudes (Denver?) boils at a lower temperature than at sea-level.

Higher pressure holds the molecules together more strongly, so it requires more energy (temperature) to break them apart.

cookiemonster

Wow, I just got the sickest feeling when I read that...I feel horrible now. All this time I thought boiling point never changed, and all this time I have been carrying around false knowledge. It's like not knowing you've been carrying an armed bomb. Inadequacy sucks.

 

[Molydood]

Thanks, that confirms (and unconfirms) all of the theories we came up with over lunch.
For the record; none of us were completely correct, but as a collective we had all the possibilities covered, other than the boiling point variance :-)
Martin

 

[Molydood]

regarding the second half of my original question, can anybody explain why the cabins are cold on spacecraft ?

thanks,
Martin

 

[Cheman]

Many of you have said that a decrease in pressure causes liquids to boil. Why is this the case?

 

[Adrian Baker]

A simple way of thinking of it is to imagine all the air molecules above the liquid battering into the liquid surface. These interactions would prevent many liquid molecules from escaping. Remove some of these air molecules (ie lower the pressure), and the liquid molecules find it easier to escape.. ie the boiling point becomes lower.

 

[HallsofIvy]

Just about any packaged cake mix will have "high altitude" instructions (referring to baking in mountains, not on airplanes!). Since water will boil of at a slightly lower temperature, both heat and time have to be adjusted so that the cake will not be too dry.

 

[UltraPi1]

In space you have a hard vacuum. With the vacuum, there is no material to conductively take heat away.

This is just dead wrong. In the vacuum of space there nothing there to reradiate heat back to you. It will be colder than a witches tit if you're not facing the sun. You might as well put your head in a vat of liquid nitrogen. You will lose heat as fast as your flesh can pass it.

 

[krab]

This is just dead wrong. In the vacuum of space there nothing there to reradiate heat back to you. It will be colder than a witches tit if you're not facing the sun. You might as well put your head in a vat of liquid nitrogen. You will lose heat as fast as your flesh can pass it.

No. Enigma is right; he was commenting about conductance. You are commenting about radiation. Radiation is a far slower heat loss under normal conditions (standard Earth pressure) than conduction. So you will not "lose heat as fast as you flesh can pass it". You will lose heat more slowly than standing naked at the north pole. "Putting your head in a vat of liquid nitrogen" is far far worse than vacuum. Since we are talking about what happens in the space of seconds or minutes, getting cold is not the first concern.

 

[chroot]

According to the basic Stephan-Boltzmann law, a one-foot diameter blackbody at 300K would be radiating 134 watts to space. A real head might only be half-efficient, so let's just say 75 watts or so.

Assuming your head is just a one foot diameter ball of water, it'll take more than four hours for that water to freeze.

- Warren