Abstract: A highly automated, fully-closed circuit rebreather and methods for operating the device by users with limited training and limited skill development are disclosed. Advanced sensors, electronics, software, assembly methods, and disposable cartridges dramatically reduce the skills required for assembly, operation, and maintenance of the unit. The use of the rebreather apparatus is primarily for recreational diving applications, but may be used for additional applications where the presence of breathable air may be absent or limited, such as hazardous duty applications, high altitude applications, no-atmosphere or low-atmosphere applications, and the like.