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 or any environment that is unknown or has unknown levels of contaminants.. When not used underwater, they are sometimes called industrial breathing sets.