Smooth move, Dave. You've done pissed off the ship's nav-com enough to warrant bailing out of an airlock. Now, find yourself in the cold embrace of interstellar space sans helmet. Here's what you have to look forward to during your last few moments alive.
Death by vacuum has become a hallmark of modern space cinema. 2001, Total Recall, Outland, Armageddon, every one of the Aliens series — no movie set outside Earth's atmosphere is complete without somebody getting sucked out of an airlock, tearing their suit, or otherwise being subjected to the vacuous extremes of space. However, every film seems to find new and inventive ways for people to expire. Some go by explosive decompression — Quaid had his eyes nearly burst in Total Recall, and the construction worker from Outland had his head explode outright. Still, others simply flash freeze into meat Popsicles (a la Event Horizon). So which is it? Well, a bit of both, actually.
Thankfully, the effects depicted in films are exaggerated in both magnitude and speed. You do not, in fact, instantly freeze or explode — heat transfers too slowly for that. Nor does your blood immediately boil, thanks to the resilience of your cutaneous system. You do not immediately fry to a crisp by unadulterated solar radiation, though you will get one hell of a sunburn. No, no, you have good 10 to 15 seconds with which to freak the fuck out before you begin to black out, and a solid two minutes or so before you fully expire.
You only get fifteen seconds, because that is roughly how long it takes deoxygenated blood to circulate from your lungs to your brain. See, when you're placed in a vacuum, the gas exchange process works in reverse — your lungs actually pull oxygen out of the body and dump it back into the lungs where it's exhaled, which only serves to hasten the onset of hypoxia. Holding your breath doesn't help either. The pressure differences in and outside of the body cause a severe form of the bends, similar to what divers experience when ascending too quickly. This will likely cause your lungs to rupture. In fact, you will remain conscious for up to a half minute if you exhale within the first few seconds.
In addition to your body actively expelling the one thing it needs most, various other maladies begin to onset at the 10 second mark. Exposed skin begins to burn (sunburn, not catch on fire), and your dermal tissues begin to swell due to water in your muscles spontaneously evaporating, causing minor bruising. Moisture in the nose, eyes, and mouth evaporates, causing localised frostbite. The onset of hypoxia has its own set of issues, including loss of vision (and wits), followed by convulsions, loss of consciousness, and cyanosis (when your skin turns blue). At this point, you're not "dead" dead, just "mostly" dead — your brain is still functional and your heart is still going. You can still be revived, surprisingly with minimal permanent injury, if you are immediately returned to an atmosphere. However, this saviour window only lasts 90 seconds. After that, your blood pressure drops low enough that it does begin to boil, which damages your heart and nixes any chance of resuscitation. According to the Bioastronautics Data Book, your demise will occur something like this:
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.
Science is generally certain of the intricacies of death by vacuum, largely due to a number of close calls and mishaps that have occurred since the start of the Space Race. For example, in 1965, an astronaut was exposed to a near vacuum (less than one psi) for 14 seconds due to a leaky space suit. In just that small amount time, he lost consciousness and suffered cyanosis, later reporting that just before he blacked out, he could feel the water on his tongue begin to boil. In another incident at JSC, a flight technician was trapped in a malfunctioning altitude chamber for nearly four minutes before a a quick-thinking manager kicked in one of the test chamber's glass gauges to immediately begin repressurising the room.
The Almanac of Soviet Manned Space Flight also describes the effects of vacuum exposure as experienced by three cosmonauts aboard a Soyuz prototype in 1971:
…the orbital module was normally separated by 12 pyrotechnic devices which were supposed to fire sequentially, but they incorrectly fired simultaneously, and this caused a ball joint in the capsule's pressure equalization valve to unseat, allowing air to escape. The valve normally opens at low altitude to equalise cabin air pressure to the outside air pressure. This caused the cabin to lose all its atmosphere in about 30 seconds while still at a height of 168 km. In seconds, Patsayev realised the problem and unstrapped from his seat to try and cover the valve inlet and shut off the valve but there was little time left. It would take 60 seconds to shut off the valve manually and Patsayev managed to half close it before passing out. Dobrovolsky and Volkov were virtually powerless to help since they were strapped in their seats, with little room to move in the small capsule and no real way to assist Patsayev. The men died shortly after passing out. [...] The rest of the descent was normal and the capsule landed at 2:17 AM. The recovery forces located the capsule and opened the hatch only to find the cosmonauts motionless in their seats. On first glance they appeared to be asleep, but closer examination showed why there was no normal communication from the capsule during descent.
So, while the end of your life in space may not be nearly as dramatic as Hollywood would have you believe, exposure to its vacuous expans is still going to suck and and you're more than likely going to die. Sorry. Just remember to breathe out first. [NASA - Geoffrey Landis - Damn Interesting]