A self contained breathing apparatus, or SCBA, sometimes referred to as a compressed air breathing apparatus (CABA), air pack, or simply breathing apparatus (BA), is a device worn by rescue workers, firefighters, and others to provide breathable air in an IDLH (Immediate Danger to Life and Health) Atmosphere. When not used underwater, they are sometimes called industrial breathing sets. The term "self-contained" means that the breathing set is not dependent on a remote supply (e. g. , through a long hose). If designed for use under water, it is called SCUBA (self-contained underwater breathing apparatus). An SCBA typically has three main components: a high-pressure tank (e. g. , 2,216 to 4,500 psi(15,280 to 31,000 kPa)), a pressure regulator, and an inhalation connection (mouthpiece, mouth mask or face mask), connected together and mounted to a carrying frame. A self-contained breathing apparatus may fall into two different categories. These are open circuit and closed circuit