Submarines are some of the most interesting machines created for sea exploration and naval warfare. Some submarines can spend up to 3 months under the surface at a time, but that raises one important question. How do humans breathe underwater for so long? The answer is what I am covering in this blog. The process of breathing underwater is split into two parts: the creation of oxygen and the removal of CO2 from the atmosphere. This blog will cover the creation of oxygen and another blog will cover the removal of CO2.

To begin, let’s talk about how the oxygen is created for the sailors to breathe. Humans need oxygen to survive and we use it in each and every breath. After some time on a submarine, the oxygen levels are depleted as humans use it all up. This creates the need for more oxygen to be made. This is done in two ways. The main way is through electrolysis. Electrolysis is the process by which electric current is passed through a substance to effect a chemical change. In the case of a submarine, electric current is passed through water to create hydrogen and oxygen. At first thought, it seems like there is water all around a submarine that can be used to create oxygen, but saltwater cannot be used. This is because saltwater consists of H2O and NaCl. When an electric current passes through saltwater, H2 gas and Cl2 gas are created. This causes a problem because chlorine gas is deadly for humans. To combat this problem, sailors use reverse osmosis filtration to remove the salt from the water.

This works the same way that desalination plants work. The product of the reverse osmosis filters is a salt brine and plain H2O. The brine is pumped back into the ocean and the pure water is used for electrolysis. When the pure H2O is charged, it breaks into hydrogen gas (H2) and oxygen gas (O2).

Both of these gasses are released into the atmosphere of the submarine for humans to breathe. This process is the preferred method of oxygen creation among sailors because it is automated and doesn’t need much attention. All of the energy required for the electrolysis is taken from the on-board nuclear reactors.
When the electrolysis machine fails, or is under maintenance, the crew does something that seems counterproductive. They literally burn candles. Most people figure that burning candles does not seem like a good idea. When fire is created, it removes oxygen from the atmosphere, but not with the candles the navy uses. The candles used on submarines are made of sodium chlorate, barium peroxide and iron powder. This combination of chemicals creates something called a self-oxidizing fire. This means that the fire creates its own supply of oxygen. When the candle is lit, the iron powder burns at an incredibly high temperature. This intense temperature starts a reaction inside the sodium chlorate. When it is heated to extreme temperatures, the reaction produces oxygen, sodium chloride (common salt) and iron oxide through a process known as thermal decomposition. The reaction in the candle ends up creating more oxygen than it is using, so the oxygen levels in the submarine ultimately rise.

Both of these methods are perfect examples of chemistry in the real world. It is super cool to see how these systems work. Oxygen creation systems like these can be found in space craft, mines, and other environments limited in oxygen. In the next passion blog, I will talk about how CO2 is removed from the atmosphere.