It’s yet another boring day at the space station. You check your holographic wrist-watch, and you finally get excited: in 10 minutes you’re supposed to have a delicious lunch of turkey in a toothpaste tube, with a side of telomere-enhancing pills. You get too excited though, and accidentally open the hatch to the airlock. Seconds later you find yourself floating through space with no spacesuit, wearing just the typical astronaut pajamas. Boy, did you mess up big time!

Although you’ve seen all the Sci-Fi movies, as a trained astronaut, you actually know better. No, you won’t explode and your blood won’t boil. But that doesn’t mean it’s pretty. Far from it! If you’re lucky maybe if you have a good 15 seconds to do something before you lose consciousness.

As you’re drifting through space, the flow of time grinds to a crawl. You begin to remember your training and what those NASA nerds explained would happen in the unlikely event that one ends up hurled in space without a spacesuit.

Rapid depressurization is horrible, but it won’t kill you on the spot

When on Earth, the weight of the air around us pushes against the body. In turn, the pressure inside our body pushes back against the weight of the air pressing the skin. The result is a state of perfect balance.

However, space is virtually vacuum, which means that any person unfortunate enough to find their self unshielded in such an environment will experience rapid internal decompression. They won’t explode, though — and you have our skin to thank.

The largest organ in the human body, the skin, is extremely flexible and tough. Therefore, it is able to expand without “spilling its contents”.

Yet, this doesn’t mean that the experience is pleasant. The body will expand to roughly twice its volume because the water in the tissue will rapidly turn into water vapour. This action will also push against internal organs. For instance, air expansion in the gut will push against the diaphragm and heart. As air is rapidly expelled out of the lungs, there might be some damage to the delicate tissue the lines the lungs and the airways.

The sudden loss of pressure will also cause decompression sickness due to bubbles of nitrogen in the muscles and bones, as well as the lack of oxygen, known as ‘hypoxia’. In fact, it is the loss of oxygen that will kill you first.

Oxygen starvation

The worst thing one could do in a situation when you’re flung into space is to hold their breath. If you do this, bubbles of air will be forced into the bloodstream, eventually arriving in the brain where they will cause a stroke. Holding your breath will also expose the lungs to the force of atmospheric-pressure air against pure vacuum, likely rupturing quickly. This can happen to scuba divers if they descend too quickly into deep waters.

Even if you breathe normally, you won’t have time for much else, though. Starved of oxygen, the brain will enter ‘safe mode’ to conserve energy about 15 seconds after being exposed to the vacuum of space. But even though the unfortunate astronaut might be unconscious, they’re not dead yet. That happens around the two-minute mark when all the other organs fail from oxygen deprivation.

There are quite a few instances of vacuum-induced hypoxia that we know of. In 1982, a technician who was running tests on a vacuum chamber was accidentally exposed to extremely low pressure, equivalent to 3.6% of sea-level atmospheric pressure. He spent a full minute in these conditions until he was pulled out. His skin turned blue, the lips were frothing, and there was bleeding from the lungs. The man recovered fully not long after, but others who suffered accidents in vacuum chambers weren’t so lucky and died due to prolonged exposure.

The chilling touch of space

When the International Space Station faces the sun, the external temperature is around 121 °C (250 °F). When the sun is blocked by Earth, the temperature around the space station hovers around -157 °C (-250 °F).

At face value, any of these temperatures sound horrific. A spacesuit-less human just outside the space station would surely either boil alive or get turned into a popsicle in under a minute, right? However, you’re thinking of heat transfer on Earth.

In space, there is no air, so heat can’t be transferred through conduction (direct contact between two objects) or convection (energy transfer through a fluid like water or air). The only viable means of heat transfer between two objects — in this case the human body and space — that you’re left with is radiation.

Humans radiate heat at a rate of only 100 Watts, much like an incandescent light bulb. Given the sheer mass of the human body, it will take a long time before you freeze. Other things would have killed you long before this happens.

No one can hear you scream in space

It’s been a full second since you stupidly flung yourself outside the space station, basically bare naked in space. During this time, your mind went into overdrive. You remember from your training that you shouldn’t hold your breath, nor that your body will explode, boil, or instantly turn into a popsicle as you see in the movies. The thought of missing turkey also creeps to mind.

Now, you have approximately 14 seconds left before you’ll get knocked out. You decide to put this little time to good use and immediately make quick taps on your wristwatch’s holographic display and alert the rest of the crew on the space station. Black out.

You slowly open your eyes — which hurt badly due to the evaporation of water inside the ocular tissue — and are greeted by the familiar face of the captain of the mission crew. “Another 5 seconds and you would’ve been done for,” she retorts. “Good thing we got your message and used the station’s telescopic arm to pull you back in right on time.”

Lesson learned. Always wear protection!