An unprotected human can survive approximately 90 seconds of space vacuum exposure without permanent injury, as long as they exhale to prevent lung rupture.
You Can Survive 90 Seconds in Space Without a Suit
Hollywood loves showing people exploding in space or freezing solid in seconds. The reality? Far less dramatic—and far more survivable than you'd think.
If you suddenly found yourself floating in the vacuum of space without a suit, you'd have roughly 90 seconds before suffering permanent damage. That's not a guess—it's backed by NASA research and one very unlucky (then lucky) test subject.
What Actually Happens to Your Body
The first thing to go isn't your life—it's your consciousness. Within 10-15 seconds, the lack of oxygen causes you to black out. But here's the crucial part: your blood doesn't boil, and you don't explode.
Your body experiences several things simultaneously:
- Ebullism—fluids in your tissues begin to vaporize, causing swelling (but your skin holds everything in)
- Hypoxia—oxygen deprivation leads to unconsciousness
- Temperature—you neither freeze instantly nor overheat; space is a poor conductor of heat
- Pressure drop—gases expand, which is why you must exhale or risk lung rupture
The Man Who Survived Space Exposure
In 1966, NASA technician Jim LeBlanc accidentally proved this science firsthand. During a spacesuit test in a vacuum chamber, his suit depressurized at an altitude equivalent to 120,000 feet.
The last thing he remembered was the saliva boiling off his tongue.
LeBlanc was unconscious within 14 seconds. The chamber was repressurized in about 30 seconds, and he recovered completely with no lasting effects. His accidental experiment remains one of the most valuable data points in understanding human vacuum exposure.
The 90-Second Window
Why 90 seconds specifically? That's roughly when oxygen deprivation causes irreversible brain damage. Your heart continues beating, your body stays intact, but your brain can only survive so long without oxygen.
Interestingly, animal studies from the 1960s showed that dogs and chimpanzees exposed to near-vacuum conditions for up to 90 seconds recovered fully once repressurized. Beyond that threshold, survival rates dropped dramatically.
The One Thing You Must Do
Exhale. That's the difference between survival and death. If you hold your breath, the air in your lungs expands rapidly as external pressure drops. This causes pulmonary barotrauma—essentially, your lungs rupture from the inside. Breathe out, and you buy yourself precious seconds.
So while space is absolutely lethal without protection, it's not the instant death sentence movies suggest. You'd have time to be rescued, if rescue was coming—and you'd wake up with one hell of a story to tell.