Scientists have worked hard to describe what is happening to people who were in space without a protective spacesuit. Some believe that the unfortunate person will instantly turn into a piece of ice. Others believe that his veins or eyeballs must explode first. And still others argue that it will simply begin to inflate, like a balloon, due to excessive internal pressure. However, reality is much less spectacular and, most importantly, it leaves a person with some chance of survival.
The first effect that a person who finds himself in outer space will feel is the expansion of air in the lungs and digestive tract, caused by a drop in external pressure. A victim of sudden decompression can dramatically increase their chances of survival by simply exhaling. If the air is not released from the lungs within the first seconds, they can simply burst, large air bubbles will enter the bloodstream - and both lead to inevitable death. Most likely, the salutary exhalation will turn out to be a cry issued by an astronaut who has realized his position. However, this cry is unlikely or will be heard by anyone - as you know, sounds do not propagate in airless space.
In the absence of atmospheric pressure, the water will begin to evaporate quickly, so all moisture will evaporate from the surface of the victim's eyes and mouth. Water will begin to boil in the muscles and soft tissues, due to which some parts of the body will approximately double their normal volume. The enlargement will cause multiple capillary ruptures, although not enough to tear the skin. After a few seconds, the dissolved nitrogen in the blood will also begin to form gas bubbles, causing the "decompression sickness" from which divers suffer: these bubbles clog small vessels, making it difficult for blood to circulate through the body and thereby causing oxygen starvation of tissues. All exposed areas of the body exposed to direct sunlight will develop ultraviolet burns. Despite the terrible cold, instant freezing does not threaten the victim,because in the absence of an atmosphere, heat will be removed from the body very slowly.
For ten whole seconds, a person will maintain a sober mind and the ability to take action. In principle, this may be enough to take urgent rescue measures. Otherwise, after a couple of moments, the brain will begin to experience an acute lack of oxygen, loss of vision and orientation will occur. In the absence of an atmosphere, the gas exchange process in the lungs will go in the opposite direction: oxygen is removed from the blood and thrown into space, which, together with the caisson effects, accelerates the onset of deep hypoxia - oxygen starvation of tissues. Complete loss of consciousness will occur a few seconds later, and by this time the victim's skin will take on a distinctly bluish tint.
Despite the deep collapse, the victim's brain will still remain intact and the heart will still beat. If, within a minute and a half, the victim is placed in a chamber with an oxygen atmosphere, he will most likely come to his senses rather quickly, having escaped with only minor injuries to the body (although blindness caused by hypoxia may persist for some time). After 90 seconds, the pressure in the circulatory system will drop so much that the blood begins to boil, and the heart stops. After that, returning to life is no longer possible.
Thus, the survival time of an unprotected person in outer space is measured not in seconds, but rather in minutes. This amazing fact once again testifies to how resilient the human body is.