The breathing bag has an upper region； a lower region； a conduit for delivering exhaled air to the lower region and a conduit for withdrawing breathable air from the upper region. The device also has a baffle mounted therein for entrapping exhaled air in the lower region and for causing the exhaled air to remain in a low turbulence mode, for promoting a separation of oxygen and carbon dioxide from the exhaust air by stratification and for causing carbon dioxide to accumulate in the lower region of the bag. Consequently, the breathable air rising from the lower region of the bag has a higher oxygen content. In another aspect of the invention, a method for separating carbon dioxide and oxygen by stratification from exhaled air is also described.
