A lightweight compressed oxygen rescue breathing apparatus (rba) for rescue and recovery missions in mine rescue work was developed for the Bureau of Mines. The rba is a positive-pressure, closed-circuit system that lasts 4 hours. The weight of the complete rba, including an optional cooler, is slightly over 30 pounds. Weight reduction over currently available rba's is achieved by using lithium hydroxide for scrubbing co2 instead of conventional chemicals and using a composite glass fiber-aluminum shell cylinder for oxygen storage instead of a steel cylinder. Positive pressure is maintained in the breathing circuit at all times by applying a constant spring force to the breathing bag. The harness was designed to reduce the work of the wearer by redistributing the weight of the rba to the wearer's hips.