From: "Geoffrey A. Landis" 
Subject: Vacuum exposure

Here is suggested text for a FAQ page about vacuum exposure.

A frequently asked question is, is the scene in 2001: A Space Odyssey where Bowman makes a space-walk without a helmet realistic? How long could a human survive if exposed to vacuum? Would you explode? How long would you remain conscious?

The quick answers to these questions are: Clarke got it about right in 2001. You would survive about a ninety seconds, you wouldn't explode, you would remain conscious for about ten seconds.

The best data I have comes from _Bioastronautics Data Book_, Second edition, NASA SP-3006, edited by James F. Parker and Vita R. West, 1973, in the article "Chapter 1: Barometric Pressure," by Charles E. Billings. This chapter discusses animal studies of decompression to vacuum.

page 5, (following a general discussion of low pressures and ebullism): "Some degree of consciousness will probably be retained for 9 to 11 seconds (see chapter 2 under Hypoxia). In rapid sequence thereafter, paralysis will be followed by generalized convulsions and paralysis once again. During this time, water vapor will form rapidly in the soft tissues and somewhat less rapidly in the venous blood. This evolution of water vapor will cause marked swelling of the body to perhaps twice its normal volume unless it is restrained by a pressure suit. (It has been demonstrated that a properly fitted elastic garment can entirely prevent ebullism at pressures as low as 15 mm Hg absolute [Webb, 1969, 1970].) Heart rate may rise initially, but will fall rapidly thereafter. Arterial blood pressure will also fall over a period of 30 to 60 seconds, while venous pressure rises due to distention of the venous system by gas and vapor. Venous pressure will meet or exceed arterial pressure within one minute. There will be virtually no effective circulation of blood. After an initial rush of gas from the lungs during decompression, gas and water vapor will continue to flow outward through the airways. This continual evaporation of water will cool the mouth and nose to near-freezing temperatures; the remainder of the body will also become cooled, but more slowly. "Cook and Bancroft (1966) reported occasional deaths of animals due to fibrillation of the heart during the first minute of exposure to near vacuum conditions. Ordinarily, however, survival was the rule if recompression occurred within about 90 seconds. ... Once heart action ceased, death was inevitable, despite attempts at resuscitation.... [on recompression] Breathing usually began spontaneously... Neurological problems, including blindness and other defects in vision, were common after exposures (see problems due to evolved gas), but usually disappeared fairly rapidly.

"It is very unlikely that a human suddenly exposed to a vacuum would have more than 5 to 10 seconds to help himself. If immediate help is at hand, although one"s appearance and condition will be grave, it is reasonable to assume that recompression to a tolerable pressure (200 mm Hg, 3.8 psia) within 60 to 90 seconds could result in survival, and possibly in rather rapid recovery."

Henry Spencer suggests Arnauld E. Nicogossian, Carolyn L. Huntoon and Sam L. Pool, _Space Physiology and Medicine_, 2nd Edition, Lea and Febiger, Philadelphia 1989.

Another useful reference is "Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects", by Emanuel M. Roth, NASA CR-1223, circa 1968. Its focus is on decompression, rather than vacuum exposure per se, but it still has a lot of good info.

There are three cases of human exposure to vacuum worth noting. In 1966 a technician at NASA Houston was decompressed to vacuum in a space-suit test accident. This case is discussed by Roth in the reference above. He lost consciousness in 12-15 seconds. When pressure was restored after about 30 seconds of exposure, he regained consciousness, with no apparent injury sustained.

In 1960, in a balloon-jump, another vacuum exposure for longer term but not for a whole-body exposure occurred:

"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." [quoting from Leonard Gordon, _Aviation Week_, February 13th 1996.

Finally, posting to sci.space, Gregory Bennett discussed an actual space incident:

"Incidentally, we have had one experience with a suit puncture on the Shuttle flights. On STS-37, during one of my flight experiments, the palm restraint in one of the astronaut's gloves came loose and migrated until it punched a hole in the pressure bladder between his thumb and forefinger. It was not explosive decompression, just a little 1/8 inch hole, but it was exciting down here in the swamp because it was the first injury we've ever head from a suit incident. Amazingly, the astronaut in question didn't even know the puncture had occured; he was so hopped on adrenalin it wasn't until after he got back in that he even noticed there was a painful red mark on his hand. He figured his glove was chafing and didn't worry about it.... What happened: when the metal bar punctured the glove, the skin of the astronaut's hand partially sealed the opening. He bled into space, and at the same time his coagulating blood sealed the opening enough that the bar was retained inside the hole."
More details can be found in the sci.space FAQ:

http://www.cis.ohio-state.edu/hypertext/faq/usenet/space/top.html
or at:

http://medlib.jsc.nasa.gov/intro/vacuum.html