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The Question

(Submitted June 03, 1997)

How would the unprotected human body react to the vacuum of outer space? Would it inflate to bursting? or would it not? or would just the interior gases hyperinflate? We are also relating this to short-term exposure only. This question primarily relates to the pressure differential problems. Temperature or radiation considerations would be interesting as well.

The question arose out of a discussion of the movie 2001. When Dave "blew" himself into the airlock from the pod without a helmet, should he have "blown up" or is there "no difference" as shown in the movie correct?

The Answer

From the now extinct page http://medlib/jsc.nasa.gov/intro/vacuum.html:

How long can a human live unprotected in space?

If you don't try to hold your breath, exposure to space for half a minute or so is unlikely to produce permanent injury. Holding your breath is likely to damage your lungs, something scuba divers have to watch out for when ascending, and you'll have eardrum trouble if your Eustachian tubes are badly plugged up, but theory predicts -- and animal experiments confirm -- that otherwise, exposure to vacuum causes no immediate injury. You do not explode. Your blood does not boil. You do not freeze. You do not instantly lose consciousness.

Various minor problems (sunburn, possibly "the bends", certainly some [mild, reversible, painless] swelling of skin and underlying tissue) start after ten seconds or so. At some point you lose consciousness from lack of oxygen. Injuries accumulate. After perhaps one or two minutes, you're dying. The limits are not really known.

You do not explode and your blood does not boil because of the containing effect of your skin and circulatory system. You do not instantly freeze because, although the space environment is typically very cold, heat does not transfer away from a body quickly. Loss of consciousness occurs only after the body has depleted the supply of oxygen in the blood. If your skin is exposed to direct sunlight without any protection from its intense ultraviolet radiation, you can get a very bad sunburn.

At NASA's Manned Spacecraft Center (now renamed Johnson Space Center) we had a test subject accidentally exposed to a near vacuum (less than 1 psi) in an incident involving a leaking space suit in a vacuum chamber back in '65. He remained conscious for about 14 seconds, which is about the time it takes for O2 deprived blood to go from the lungs to the brain. The suit probably did not reach a hard vacuum, and we began repressurizing the chamber within 15 seconds. The subject regained consciousness at around 15,000 feet equivalent altitude. The subject later reported that he could feel and hear the air leaking out, and his last conscious memory was of the water on his tongue beginning to boil.

Aviation Week and Space Technology (02/13/95) printed a letter by Leonard Gordon which reported another vacuum-packed anecdote:

"The experiment of exposing an unpressurized hand to near vacuum for a significant time while the pilot went about his business occurred in real life on Aug. 16, 1960. Joe Kittinger, during his ascent to 102,800 ft (19.5 miles) in an open gondola, lost pressurization of his right hand. He decided to continue the mission, and the hand became painful and useless as you would expect. However, once back to lower altitudes following his record-breaking parachute jump, the hand returned to normal."

References:

Frequently Asked Questions on sci.space.*/sci.astro

The Effect on the Chimpanzee of Rapid Decompression to a Near Vacuum, Alfred G. Koestler ed., NASA CR-329 (Nov 1965).

Experimental Animal Decompression to a Near Vacuum Environment, R.W. Bancroft, J.E. Dunn, eds, Report SAM-TR-65-48 (June 1965), USAF School of Aerospace Medicine, Brooks AFB, Texas.

Survival Under Near-Vacuum Conditions in the article "Barometric Pressure," by C.E. Billings, Chapter 1 of Bioastronautics Data Book, Second edition, NASA SP-3006, edited by James F. Parker Jr. and Vita R. West, 1973.

Personal communication, James Skipper, NASA/JSC Crew Systems Division, December 14, 1994.


Henry Spencer wrote the following for the sci.space FAQ:

How Long Can a Human Live Unprotected in Space?

If you *don't* try to hold your breath, exposure to space for half a minute of so is unlikely to produce permanent injury. Holding your breath is likely to damage your lungs, something scuba divers have to watch out for when ascending, and you'll have eardrum trouble if your Eustachian tubes are badly plugged up, but theory predicts -- and animal experiments confirm -- that otherwise, exposure to vacuum causes no immediate injury. You do not explode. Your blood does not boil. You do not freeze. You do not instantly lose consciousness.

Various minor problems (sunburn, possibly "the bends", certainly some [mild, reversible, painless] swelling of skin and underlying tissue) start after 10 seconds or so. At some point you lose consciousness from lack of oxygen. Injuries accumulate. After perhaps one or two minutes you're dying. The limits are not really known.

References:

The Effect on the Chimpanzee of Rapid Decompression to a Near Vacuum, Alfred G. Koestler ed., NASA CR-329 (Nov. 1965)

Experimental Animal Decompression to a Near Vacuum Environment, R.W. Bancroft, J.E. Dunn, eds, Report SAM-TR-65-48 (June 1965), USAF School of Aerospace Medicine, Brooks AFB, Texas.


You would probably pass out in around 15 seconds because your lungs are now exchanging oxygen out of the blood. The reason that a human does not burst is that our skin has some strength. For instance compressed oxygen in a steel tank may be at several hundreds times the pressure of the air outside and the strength of the steel keeps the cylinder from breaking. Although our skin is not steel, it still is strong enough to keep our bodies from bursting in space.

Also, the vapor pressure of water at 37 C is 47 mm Hg. As long as you keep your blood-pressure above that (which you will unless you go deep into shock) your blood will not boil. My guess is that the body seems to regulate blood pressure as a gauge, rather than absolute pressure (e.g. your blood vessels don't collapse when you dive 10 feet into a pool).

The saliva on your tongue might boil, however.

For more information and references, see http://www.sff.net/people/geoffrey.landis/vacuum.html

Hope this helps!
The Ask an Astrophysicist Team

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