Lesson 1 - Pressure

While there are many conditions in space that make it hard for the human body to survive, the most difficult of them all is pressure. Pressure is defined by Merriam-Webster dictionary as:

"the force or thrust exerted over a surface divided by its area"

On Earth, the weight of our atmosphere pushes down on everything below it, causing a force that is spread out over the entire surface of the Earth. This is known as atmospheric pressure. Every living being on Earth has evolved to exist under pressure.

As you move higher up in altitude through the atmosphere, the amount of atmosphere above you gets less. Therefore, the weight of the atmosphere above you is less, and there is less atmospheric pressure. Pressure (which is measured as 101.3 kilopascals at sea-level) continues to decrease until you reach space, where the pressure is so low that it is usually defined as 0 kilopascals.

The moon also has basically no pressure, as it has no atmosphere. Mars has a very thin atmosphere that provides 0.1 kilopascals of pressure.

There are two main reasons why very low or no pressure is bad for the human body.

Keeping Bodily Liquids Inside

The human body needs pressure to push down on the skin and stop our body from swelling. Pressure keeps the liquids inside our body from turning into gas and bubbling away.

There is an activity on Earth that is a great example of how pressure affects the liquids in the human body - scuba diving! The atmosphere isn't the only object that can apply pressure to the human body. The weight of water (such as from oceans or even a swimming pool) can also push on the human body. As a diver goes deeper down into the water, there is more weight of water above them, and therefore more pressure on their body.

If a diver has been deep underwater for some time, their body has been experiencing increased pressure compared to when the diver was at sea-level. This causes the air they are breathing to dissolve into the liquids inside their body, such as blood. Once the scuba diver decides to swim back up to the surface, the pressure begins to decrease and the air that was trapped inside their bodily liquids turns back into gas. If the diver ascends slowly, the dissolved air forms tiny bubbles and leaves the body safety. However, if the diver ascends fast, the dissolved air turns back into gas very quickly, forming big bubbles of gas inside the diver's blood vessels and bodily tissues. This is called 'decompression sickness' or 'the bends' and is extremely painful and life threatening.

A human body exposed to space without any protection will also experience decompression sickness due to the lack of pressure in space. However, unlike a scuba diver, ALL the liquids inside of the human body begin to turn to gas and bubbles in space. In fact, the attitude at which liquid water begins to turn into gas inside a human body is about 20 km, which is equivalent to around 6.3 kilopascals of pressure. 

I think this would be a very painful experience!

Oxygen

The second reason why very low or no pressure is bad for the human body is oxygen - or the lack of it. Oxygen makes up 21% of our atmosphere. As you rise higher in the atmosphere, such as when you climb a mountain, the air gets 'thinner', or harder to breathe, because there is less oxygen. One way to help visualize this is to think of the atmosphere like a cake. The higher up in the atmosphere we go, the smaller the cake becomes. If I give you a slice that is 21% of the cake, you will have a much smaller slice high in the sky rather than on the ground.

Another example of how pressure affects oxygen is airplanes. You may have heard air crew talking about the cabin being 'pressurized'. Airplanes fly so high that the amount of oxygen in the air would make it very hard to breathe. The airplane pumps more air into the cabin to increase the pressure so that there is about the same amount of oxygen in the air as at sea-level. This is also why airplanes carry oxygen masks in the rare case that the cabin loses pressure.

A human body exposed to space without any protection will not have any oxygen to breathe!

Surviving Pressure in Space

Muggles have overcome the difficultly of low pressure in space by simply adding air into their spacecraft to reach a safe level of pressure. They have even created very tiny spacecraft that they call 'spacesuits' which are about the size and shape of a human body.

International Space Station

The largest human spacecraft operating today is the International Space Station. It has a livable area the size of a 5-bedroom house and have a crew of up to 6 humans. The International Space Station is pressurized to 101.3 kilopascals, with 21% oxygen and 79% nitrogen.

Spacesuits

In order for muggles to build and repair their spacecraft, they invented spacesuits which can be worn to protect the human body from the dangers of space. One type of spacesuit, called the Extravehicular Mobility Unit (or EMU) was built by muggles from the U.S.A. It is made up of a helmet, torso, legs, boots, arms and glove sections. The EMU is pressurized to just 30 kPa but uses 100% oxygen.

Resources:

https://www.merriam-webster.com/dictionary/pressure
https://en.wikipedia.org/wiki/Armstrong_limit
https://www.liveabout.com/sponge-analogy-nitrogen-absorption-scuba-diving-2962818
https://www.iflscience.com/space/what-would-happen-your-body-space-without-spacesuit/