Breathing Vacuum
Published on Apr 10, 2006 at 6:57 pm.
10 Comments.
Filed under Uncategorized, space exploration.
Several movies have scenes where the key figures are exposed to a vacuum for some period of time with apparently no ill effects. 2001, A Space Odyssey has our hero doing several seconds of unprotected space walking. The Hitchhiker’s Guide to the Galaxy has our heroes tossed into space without spacesuits, only to be rescued seconds later. And, the lead character in Sudden Recall is suddenly exposed to the Martian atmosphere, which is nearly a vacuum. All survived. How realistic is this? How would we know how the human body really reacts in space?
Well, it turns out that we do have a pretty good idea what happens to a human body in a vacuum. We can get a pretty good estimate of what would occur from looking at divers who suddenly depressurize from depth to one atmosphere. All sorts of bad things can happen. But, we have an even better model. Animals, and humans, actually have been exposed to vacuum conditions, so we have first hand data.
In the earliest days of spaceflight, the space agencies considered the possibility of a breach in the integrity of a spacecraft to be a very real possibility. It still is, but is now thought to be much less likely than it was then. Naturally, there was concern about what would happen to the astronaut. Everyone knew that you’d die without air, but the question was whether or not a human could live long enough to put on a spacesuit’s helmet, or to close the visor if the helmet were already in place. If a spacesuit were punctured on a spacewalk, how long would an astronaut’s companion have to get him to the safety of a pressurized spacecraft? These were questions that animals helped to answer. Personally, while I agree that the answers to the question are important, I don’t think that I could ever purposefully do that to an animal. Nor, would I want to be anywhere around before, during, or after the experiment.
In addition to animal tests, there have been human tests for exposure to very low pressures, such as those experienced by the sudden decompression in a high altitude aircraft. Extrapolation of these test results lets us figure what may happen with no pressure rather than low pressure. And, there have been accidents. Humans have accidentally been exposed to vacuum, or to pressures so low as to be effectively vacuum as far as human physical responses go.
An actual human exposure accident occurred during the early tests for Apollo at the Johnson Space Center in Houston. JSC has several vacuum chambers, with at least two large enough for humans to work and move about in while in a vacuum. These chambers not only operate at a vacuum, but they also have lights, heat lamps, and chilling coils to simulate both thermal and radiation conditions experienced in space. In one space simulation in 1966, a technician at the Manned Spacecraft Center in Houston (later it was renamed the Johnson Space Center) was testing a spacesuit in such a vacuum chamber. The suit tore and rapidly depressurized. An emergency repressurization procedure was initiated and the subject was rescued by medical personnel standing by for just such an emergency. The technician was exposed to vacuum and low pressure conditions for under a minute, and though he has severe problems at the time and shortly after, he eventually fully recovered. Other accidents also occurred, not all of which resulted in survival of the victim. Still other incidents involved ruptures in pressure suits resulting in partial body decompression. And, in 1971, Soyuz 11 had a failure resulting in sudden decompression during reentry. The cosmonauts onboard did not survive. Animal studies coupled with medical accounts (for the accident survivors) or autopsy reports (for those that did not survive) give us a pretty good idea of how the human body responds to vacuum exposure. These incidents, though, were accidental, and were not carefully controlled experiments, so the data is a bit incomplete in places. Needless to say, there are few volunteers for controlled experiments detailing vacuum exposure!
So what does happen? There has been all sorts of speculation by laymen and science fiction writers. Many suggest that the victim will simply explode (after all it is called explosive decompression!). Well, obviously this can’t be right, since some people survive! There is also speculation that the victim’s blood would boil. This, too, did not happen with the technician in Houston, nor with many of the animals. Why would this speculation even occur, though? Doesn’t water boil at 100C? Yes, and no. As pressure drops, the boiling point of water drops. At sufficiently low pressure, the boiling point drops all the way to freezing, and water exists only as a solid or a gas. The atmospheric pressure on Mars is this low! However, remember that you are a fairly sealed system. So, unless something bad happens (which I’ll mention later), even if the pressure outside your body drops, then the pressure inside your body should remain high enough (at least on the arterial side of the circulatory system) to just avoid your blood boiling.
But what does happen? Well, it isn’t really pretty, but here is a synopsis of what I gather is likely to occur, based on studies human and animal vacuum exposure. First, it depends upon how quickly the lungs empty. If the victim is smart enough to quickly exhale, then massive internal injuries can be prevented. On the other hand, if the victim tries to hold his breath, or has some sort of airway obstruction, then the lung tissues can rupture, spilling air into the body cavities. This causes massive system failure, and the victim, if holding his breath, can no longer hold his breath. The rapid reduction in pressure in the lungs now results in reduction of pressure within the body, and bodily fluids do begin to boil. Such an event is always fatal, even if pressure is rapidly returned to normal.
If the victim exhales, though, then several things happen. First to occur is that there is no air for the blood to exchange oxygen and carbon dioxide with. In fact, worse than no air, the blood flow through the lungs can even lose oxygen to space! This can occur only for about 10 to 15 seconds with a human before loss of consciousness. Hypoxia and impaired judgment begin to occur within about 7 or 8 seconds, though. So, anything the victim must do to save himself must be instinctive, and drilled and trained to the point of being nearly automatic, without much thought. Given the surprise factor likely in a sudden accident, there may be only five seconds or so to react. If exposed to sudden explosive decompression, the victim must remember to exhale at once. This must be automatic and drilled into the subject. There are only a couple of seconds before serious, and often irreversible, damage to the lungs occurs. The 1966 accident victim at the Manned Spaceflight Center remembered to exhale. He did report the rather strange feeling that occurred as water in the saliva on his tongue began to boil. A more serious problem is that water on the surface of the eye also begins to boil, drying the eye, resulting in severe pain almost immediately. Hypoxia results in loss of vision after 10 seconds or so. This loss of vision often remains for a while after the victim is returned to atmospheric pressure.
The external pressure on the body is suddenly released, and this causes pressure in the soft tissues to fall, resulting in some water vapor forming in those tissues. This water vapor then presses on the veins, increasing pressure. The water vapor also causes the tissues to distend, swelling to nearly double their normal size. The body appears bloated. Some capillaries can rupture, causing bruising. In an incident on a high altitude balloon flight, a glove lost pressure. The pilot’s hand became bloated and he experienced great pain. After several seconds, the hand became useless. In another incident, a potentially fatal accident occurred during a spacewalk on STS-37. During this mission, the astronaut punched a tiny hole in the hand of his spacesuit. However, the pressure in is spacesuit pressed his hand against the hole. The vacuum at this hole caused tiny ruptures below the skin, and his blood actually clotted to seal the edges of the hole to his flesh. Upon returning to the shuttle, he had a small, very red, and very painful lesion on his hand. He was quite fortunate.
As a response to loss of oxygen in the blood, the heart begins to beat very rapidly, as if the victim were doing heavy exercise. However, there is no oxygen to get. Eventually, the heart beat slows, and with the slowing heart, the blood pressure drops. When the blood pressure on the arterial side of the circulatory system drops to equal that on the venous side, then blood no longer will flow. After about 45 seconds or so, effective circulation stops, even though the heart continues to pump. The body goes into convulsions shortly after cessation of consciousness, then paralysis sets in. Starved for oxygen the heart itself stops after 60 to 90 seconds, though some reports report fibrillation beginning prior to the time that it stops beating, sometimes even during the first minute of exposure. A second set of convulsions hits at the end, then the heart stops. To my knowledge, no subject has ever survived this point, even if oxygen is immediately restored. In some animal studies, sometimes, distension of the stomach can press on the diaphragm, compressing the thoracic cavity, causing heart fibrillation or cardiac arrest prematurely. None survived this event, either.
So, if you are ever in a spacecraft or a spacesuit, and you suddenly experience explosive decompression, then you need to remember at once to exhale, then you need to position yourself for assistance. You’ve only got seconds before you are helpless. Then, you just have to hope and pray that someone gets you back into pressure within a minute or so. Subjects who manage to avoid some of the more unpleasant events above seem to achieve a complete recovery if they get oxygen again within 45 to 60 seconds.
So, that is what happens to a human body in a vacuum.
-Astroprof
Pluto on March 26, 2007 at 6:03 pm: 1
The divers in the Byford Dolphin accident were exposed to the a pressure drop similar to what would happen if you were flung out of an airlock and into space, right? They exploded into tiny pieces.. Why?
Astroprof on March 26, 2007 at 6:18 pm: 2
Actually, that was much higher difference in pressure. The divers were at 9 atm, and they explosively decompressed to 1 atm. A space accident at most goes from 1 atm to 0, and normally it is even less of a difference because spacesuits operate at lower pressure than 1 atm.
trapper on August 8, 2007 at 8:30 am: 3
That doesn’t sound right to me. Gas expansion is proportional to the percentage pressure change not the absolute pressure change.
So a 9atm to 1atm change would increase gas volume 9/1 = 9 times, but a 1atm to 0atm would increase volume 1/0 = infinitely. (or for arguments sake 1 / 0.01 = 100 times)
Astroprof on August 8, 2007 at 8:55 am: 4
You are thinking of percentage change. I was referring to the actual force, which is pressure times area. So, the people had the same surface area, and that means that nine times the pressure is nine times the force.
mark schwarz on August 18, 2007 at 5:04 am: 5
ok, what if a man is in rapid decompression from 1 ATM - 0 ATM and he has an elastic suit on, such a wet suit, to prevent tissue swelling and he exhales while decompressing and then once it’s over, he firmly holds a handheld oxygen tank with a special mask that covers his eyes, nose and mouth (like a big scuba mask)up to his face, how long will he then live????
Astroprof on August 18, 2007 at 2:19 pm: 6
Good question. I’m an astrophysicist. You’d need a biophysicist or a doctor to answer that one. Are any out there reading this?
mark schwarz on August 19, 2007 at 12:28 am: 7
you’d think it was a good question, but i cant seem to find an answer for it. seems to me that a person should be good for hours. i would say indefinitly, but i’m pretty sure that eventually the vacuum would have some kind of negative effect on the body and/or mind.
Rebecca Farrier on May 22, 2008 at 6:45 pm: 8
i really want to knnow what effect a vacuum actually has on BREATHING itself. so, say the rapid decompression didn’t require the subject to exhale, then what, in theory, would happen to the lungs/airways?
I guess you’d just suffocate?
Justin on November 14, 2008 at 5:25 pm: 9
Very well written this article. I highly recommend Mr/Ms Astroprof to put this on Wikipedia. Very informative.
Steve on June 16, 2009 at 1:55 pm: 10
A rather technical abstract on exposure to vacuum is at http://www.geoffreylandis.com/ebullism.html
Also of interest, http://en.wikipedia.org/wiki/Space_suit#Skintight_suits
Talks about, what basically, is a super spandex type of suit that tested well. NASA went with the bladder system and rigid suits though.