How quickly does someone die in space?

The body doesn't explode or freeze instantly. The first danger is the lack of oxygen pressure: without opposing pressure, the lung can no longer pass gas into the blood — on the contrary, it draws oxygen out of it, and the brain shuts down within seconds. Anyone who holds their breath also risks a torn lung, because trapped gas expands. At the same time, body fluid begins to evaporate from tissues and mucous membranes, and tissue swells. Experience with low-pressure chambers shows that a person retains the ability to act for a few seconds — enough for a single well-trained action.

On June 30, 1971, Soyuz 11 was returning after the first stay aboard a space station. When the modules separated, a valve opened, the cabin lost pressure, and the crew — Georgy Dobrovolsky, Vladislav Volkov, and Viktor Patsayev — were not wearing pressure suits. The capsule landed with no technical faults; the three men were already dead when the rescue team opened the hatch. To this day, they remain the only known deaths beyond the atmosphere.

Since Soyuz 11, crews wear pressure suits during launch and landing, which in an emergency are automatically supplied with gas. Stations and capsules are designed for slow leaks, not sudden openings: multiple chambers, hatches that can be sealed, reserves of breathable gas, and procedures that isolate a leaking section. The same principle applies during spacewalks: the suit is a small cabin with its own pressure and oxygen supply, and in case of drifting away, the equipment includes a small propulsion device for returning.