There are many myths surrounding human exposure to vacuum, not helped by science fiction continuing to perpetuate them. Make no mistake, space is hostile, and exposure to hard vacuum is not something I will be queuing up to try. But notions of blood boiling, bodies exploding, and instant freezing are all incorrect. Humans can survive brief exposure to vacuum – the shorter, the better. The longer, the higher the risk of injuries developing and, inevitably, death.

The truth is, you could probably survive for a minute or two, and you’d stay conscious for roughly fifteen seconds, at which point the blood would have no oxygen to carry to the brain. However, the time limits are not fully understood. Our current understanding of human exposure to vacuum to date has developed from both theory and real-life examples of human and animal exposure.

In the 1960s, there was a ground incident at NASA where a subject was accidentally exposed to near vacuum due to a hole in his spacesuit. After approximately 14 seconds of exposure, the subject lost consciousness. The altitude chamber was quickly repressurized and the subject survived unharmed. The subject was aware of the leak and also recalls feeling the moisture on his tongue boiling.

The lungs wouldn’t explode and the blood wouldn’t boil because they are well protected within the human body. However, if you’re ever exposed to the vacuum of space, I’d suggest you let all the air out of your lungs. This is because the pressure differences will cause the air to be forced out (and fast!) so there is a risk of damage. NASA’s Imagine the Universe site also points out that blocked Eustachian tubes in the ears could result in eardrum problems.

The film Sunshine had a scene where a human was exposed to vacuum and froze very quickly. In space, heat would radiate away from your body but this idea that it would happen instantaneously is unsound. It would probably take hours, not seconds, for you to freeze. But your skin, if not protected, could also burn if in proximity to a star such as the Sun (Earth orbit is near enough). Bad burns could occur in a matter of minutes.

What would a human exposed to vacuum look like? The film Event Horizon would have us believe that blood sprays from our eyes dramatically. It doesn’t, that’s just in Hollywood. After around 10 seconds, your skin (and underlying tissue) will undergo some mild swelling, but you wouldn’t instantly look like a zombie. If you managed to return to a normal atmosphere, the swelling would go down.

In his Bad Astronomy site, Philip Plait points that it takes time (hours) for the body’s cells to freeze and break. But when they do, yes, it would not be a pretty sight. The moral of the story is this: don’t take off your helmet.

Sources

Human Body in a Vacuum, Ask an Astrophysicist, NASA’s Imagine the Universe website, accessed: 23rd November 2008, no author specified.

Review of Mission to Mars, Phil Plait’s Bad Astronomy website, accessed: 23rd November 2008, author: Plait, P.