Abstract: Apparatuses and methods are disclosed for improving the Weight/Duration ratio of Self Contained Breathing Apparatuses (SCBAs) by decreasing the amount of fresh breathing gas required from the system by saving exhaled air that is low in carbon dioxide in a reservoir and reusing it at the subsequent inhalation. Electronic control units (“ECUs”) including conventional oxygen sensors and special types of carbon dioxide sensors are used to monitor and predictably regulate the consumption of breathing gas, further contributing to a significantly lower overall system weight for any given duration of the SCBA.