A submarine is a ship that operates completely under water for days together. It is a watercraft capable of independent operation underwater. It mainly indicates a warship with a streamlined hull designed to operate completely submerged in the sea for long periods. They are cylindrical in shape and completely enclosed on all sides as they remain under the surface of water. Many types of equipment are present inside a submarine including a periscope that is used to watch what is happening on the surface of water.
There is no abundant supply of air inside the submarine. An oxygen generator is used for the supply of oxygen. There is a computerized system which measures the percentage of oxygen inside the submarine. If it falls below a certain level, suitable amount of oxygen is released to make sure the levels are appropriate for the survival of the people on board.
The carbon dioxide that gets exhaled by the people inside is removed from the air chemically using soda lime (which is calcium hydroxide and sodium hydroxide). The moisture that is given out along with carbon dioxide is removed by a dehumidifier. This prevents condensation of moisture on the walls and the equipments inside.