Compressed gas cylinders can be found in many places, including manufacturing plants, laboratories, and hospitals. They can contain a variety of pressurized gases, such as nitrogen, oxygen, propane, and hydrogen. These vessels must be very durable and are constructed to resist corrosion and avoid explosions. Most facilities use a colour coding system to help quickly discern the gas within a cylinder. Although this coding system may vary from supplier to supplier, it provides users with a clear visual identification of the contents. As a precaution, every cylinder will also have a visible label to confirm the type of gas found inside.