Contrary to the spectacular portrayals conveyed by cinema, exposure of the human body to outer space does not result in an explosion or instant freezing. Films like Total Recall and 2001: A Space Odyssey have contributed to the idea that the absence of atmospheric pressure would literally cause the human body to burst. However, the reality is quite different, as evidenced by NASA’s observations and scientific studies.
“All tissues containing water would immediately begin to expand. As you can imagine, given that 60% of the human body is made up of water, this is a serious problem”, explains Dr. Kris Lehnhardt from NASA’s Human Research Program to Live Science.
This phenomenon, called ebullism , occurs when the water present in cells turns to vapor due to depressurization, causing rapid and painful swelling of muscles and blood vessels. A complex chain of physiological reactions ensues.
Ten Seconds Before Loss of Consciousness
Loss of consciousness typically happens in less than ten seconds . As noted in NASA’s Bioastronautics Data Book, the amount of oxygen dissolved in the blood is insufficient to maintain consciousness for more than a few seconds after the air in the lungs has been expelled due to pressure drop. The Federal Aviation Administration (FAA) estimates the “useful consciousness time” ranges between 9 to 12 seconds .
At this stage, ebullism escalates: tiny capillaries burst, and vapor bubbles form in tissues, particularly around the heart and brain, gradually hindering blood circulation. Death usually occurs within two minutes , as noted by Kris Lehnhardt, although rapid repressurization can, in rare cases, prevent permanent damage.
Hypoxia, but Not Freezing
Myths regarding the body’s freezing in space are also exaggerated. “The body does not freeze instantly,” stresses astronaut Chris Hadfield in an interview with Vanity Fair. In the absence of an atmosphere, heat loss through radiation is slow. The vacuum of space does not suck away heat because it simply has no mechanism for transferring it. Moist areas like the eyes, nose, or mouth may cool off faster due to evaporation, but the rest of the body experiences a gradual thermal decline.
Astrophysicist Paul Sutter points out in Forbes that the temperature in outer space depends on molecular movement, and there are very few molecules in space to facilitate this transfer.
Survivors of Exposure to Outer Space
Documented cases confirm the brutality of pressure variations. In 1983 , the Byford Dolphin accident resulted in the instantaneous death of several divers subjected to a rapid decompression from 130 psi to 15 psi. Conversely, in 1971 , the three cosmonauts of Soyuz 11 lost their lives after a slow but fatal depressurization that caused internal hemorrhaging and gas bubbles in their circulatory system.
Other cases, like that of Jim LeBlanc during a test at the Johnson Space Center, confirm survival is possible if repressurization occurs within seconds. “As I was falling backward, I felt the saliva on my tongue begin to bubble just before I lost consciousness, and that’s about the last thing I remember,” the survivor recounted in the episode The Space Suit from the documentary series Moon Machines, aired in 2008 .
In summary, the human body can tolerate very brief exposure to the vacuum of space, but beyond one to two minutes , the damage becomes irreversible, and death awaits.