Oxygen System is a set of tools protecting the crew and passengers from hypoxia caused by low partial pressure of oxygen in the air as a result of low pressure inside the cabin, as well as from the exposure to combustion products in case of fire. Oxygen systems can be built-in, portable and life-saving, may cover the nose and mouth (oral nasal mask) or the entire face (full-face mask). They may be made of plastic, silicone, or rubber.