Does Blood Boil in Space?

No, blood does not boil in space despite popular belief, although liquids do boil rapidly in a vacuum.

Understanding Boiling in a Vacuum

The referenced video shows a beaker of room-temperature water rapidly boiling when exposed to the vacuum of space. This demonstrates a core principle of physics: the boiling point of a liquid is heavily dependent on pressure. In the near-vacuum of space, where pressure is close to zero, liquids boil at much lower temperatures than they do at sea level, where there is substantial air pressure.

The Boiling Point of Water

• At Sea Level: Water boils at 100°C (212°F) at standard atmospheric pressure.
• In a Vacuum: Water can boil at much lower temperatures because there is very little pressure counteracting the water molecules becoming gas.

Why Human Blood Doesn’t Boil in Space

Although a beaker of water will boil in a vacuum, human blood does not. Here's why:

• Internal Pressure: The human body maintains an internal pressure higher than the near-vacuum of space. The circulatory system keeps the blood under pressure within the blood vessels and prevents it from reaching its boiling point.
• Body Tissues and Organs: The tissues and organs surrounding blood vessels provide an additional barrier. They also contain fluids, which means blood does not directly contact a vacuum.
• Evaporation: If a human was exposed to the vacuum of space, blood would not boil. Instead, water in the blood and bodily fluids could evaporate rapidly (sublimate), leading to swelling. This effect can cause tissues to dehydrate and potentially cause harm.

Astronauts and Space Suits

Astronauts are never exposed directly to the vacuum of space. Space suits are pressurized to ensure that the astronaut's blood doesn't boil, the blood pressure can be maintained, and the body is protected from rapid sublimation.

Key Takeaways