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by chipotle on February 17th, 2007

chipotle

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What really does happen to the human body if exposed to the vacuum of outer space?. I have seen Sci-Fi movies that show different things happening, ie Veins popping, intantly freezing etc.

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  • by canadianhelper on February 17th, 2007

    canadianhelper

    Need more room than comments allow:

    According to the 1966 edition of the McGraw/Hill Encyclopedia of Space, when animals are subjected to explosive decompression to a vacuum-like state, they do not suddenly balloon-up or have their eyes pop out of their heads. It is, in fact, virtually impossible to compress or expand organic tissues in this way. Instead, death arises from the response of the free gasses trapped within the tissues.

    If decompression takes 1/2 second or longer, even lung tissue remains intact. When the ambient pressure falls below 47 mm of mercury (similar to the pressure at the surface of Mars), the water inside all tissues passes into a vapor state beginning at the skin surface. This causes the collapse of surface cells and the loss of huge amounts of body heat via evaporation. After six seconds, the process of cell collapse involves the heart and lungs causing circulatory interruption, followed by acute anoxia, convulsions and the relaxation of the bowel muscles. After 15 seconds, mental confusion sets-in, and after 20 seconds you become unconscious. You can survive this for about 80 seconds if a pressure higher than about 47 mm mercury is then reestablished, otherwise, you turn into freeze-dried dead meat on a stick.

    http://www.gsfc.nasa.gov/scienceques2004/20041105.htm

    Also:

    What does all this mean for an unprotected person in space? The vapor pressure of water at body temperature, 98.6 F or 37 C, is about 0.93 pounds per square inch (PSI), or 48 mm of mercury (Hg). For comparison, the pressure of the atmosphere is 14.7 PSI or 760 mm Hg. Since the surrounding pressure is zero in space, water in the body might be expected to start boiling furiously, except for one important thing: the water in the body is very significantly contained by skin, blood vessels, etc. If the vapor pressure at body temperature were 1 atmosphere, the results would be immediately disastrous, as the skin and blood vessels cannot contain such a high pressure. The result might well be something like an explosion, certainly severe rupture and hemorrhaging from many points. But since the actual pressure is only about 50 mm, we have to ask how much pressure can the skin and blood vessels really contain? Well, the normal blood pressure in the arteries is 70-150 mm Hg, so there is no way the blood is going to boil in the arterial side of the circulatory system, so long as one has a working heart and normal blood pressure. Furthermore, the arteries can contain at least 200 mm for short periods without rupture. Even the veins have to withstand the pressure differences caused by gravity between head and feet when we stand up, and these must be of the order of 75-150 mm, well above 50 mm.

    It appears to me that the main source of water loss will be through the lungs. As soon as one is exposed to the vacuum, almost all of the air in the lungs will escape, since one cannot effectively contain more than a fairly low pressure, much less than 1 atmosphere, by closing the mouth and nose. So taking a deep breath in advance won't help much. After that, the lungs should fill with water vapor at about 50 mm pressure, mixed with some gases that are dissolved in the blood, oxygen and carbon dioxide certainly, and some nitrogen. Because 50 mm is such a low pressure, I believe that a trained person could significantly slow the loss of water vapor and gases from the lungs by simply trying to keep the mouth and nose closed as much as possible. Then unconsciousness and death would come when the amount of oxygen in the blood was sufficiently depleted. The time for this to occur would probably depend on the oxygen content of the blood immediately prior to the depressurization; it could range from a few seconds if you were caught in the midst of strenuous exercise, to possibly as long as a minute or more if one had some warning and were to hyperventilate in advance.

    After death, water and gases would continue to escape slowly, and the interior of the body would cool off. The cooling would cause the vapor pressure to drop even more; at freezing temperatures it is less than 5 mm Hg. Thus the escape of water vapor (along with gases and other volatile substances) would be progressively slower and slower. This process is known as "outgassing", and happens whenever anything with a significant content of volatile substances is placed in a high vacuum or in space. In the end, the body would be entirely dried out, dessicated, and reduced to a small fraction of its original mass.

    http://www.madsci.org/posts/archives/may98/891504185.Bp.r.html

    And this:

    When the human body is suddenly exposed to the vacuum of space, a number of injuries begin to occur immediately. Though they are relatively minor at first, they accumulate rapidly into a life-threatening combination. The first effect is the expansion of gases within the lungs and digestive tract due to the reduction of external pressure. A victim of explosive decompression greatly increases their chances of survival simply by exhaling within the first few seconds, otherwise death is likely to occur once the lungs rupture and spill bubbles of air into the circulatory system. Such a life-saving exhalation might be due to a shout of surprise, though it would naturally go unheard where there is no air to carry it.

    In the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim's mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments. This bloating may result in some superficial bruising due to broken capillaries, but it would not be sufficient to break the skin.

    A NASA vacuum chamberA NASA altitude chamberWithin seconds the reduced pressure would cause the nitrogen which is dissolved in the blood to form gaseous bubbles, a painful condition known to divers as "the bends." Direct exposure to the sun's ultraviolet radiation would also cause a severe sunburn to any unprotected skin. Heat does not transfer out of the body very rapidly in the absence of a medium such as air or water, so freezing to death is not an immediate risk in outer space despite the extreme cold.

    For about ten full seconds– a long time to be loitering in space without protection– an average human would be rather uncomfortable, but they would still have their wits about them. Depending on the nature of the decompression, this may give a victim sufficient time to take measures to save their own life. But this period of "useful consciousness" would wane as the effects of brain asphyxiation begin to set in. In the absence of air pressure the gas exchange of the lungs works in reverse, dumping oxygen out of the blood and accelerating the oxygen-starved state known as hypoxia. After about ten seconds a victim will experience loss of vision and impaired judgement, and the cooling effect of evaporation will lower the temperature in the victim's mouth and nose to near-freezing. Unconsciousness and convulsions would follow several seconds later, and a blue discoloration of the skin called cyanosis would become evident.

    At this point the victim would be floating in a blue, bloated, unresponsive stupor, but their brain would remain undamaged and their heart would continue to beat. If pressurized oxygen is administered within about one and a half minutes, a person in such a state is likely make a complete recovery with only minor injuries, though the hypoxia-induced blindness may not pass for some time. Without intervention in those first ninety seconds, the blood pressure would fall sufficiently that the blood itself would begin to boil, and the heart would stop beating. There are no recorded instances of successful resuscitation beyond that threshold.

    Though an unprotected human would not long survive in the clutches of outer space, it is remarkable that survival times can be measured in minutes rather than seconds, and that one could endure such an inhospitable environment for almost two minutes without suffering any irreversible damage. The human body is indeed a resilient machine.

    http://www.damninteresting.com/?p=741

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