Abstract: A respirator canister provided with openings for flow of air therethrough is filled with a chemical that removes water vapor and carbon dioxide from the air and liberates oxygen into it. A breathing tube communicates with one of the canister openings, and an expandable breathing bag or equivalent has an opening communicating with the other canister opening. A spring or the like resists expansion of the bag during exhalation through the breathing tube and canister in order to maintain the air in the respirator under positive pressure to prevent toxic air from leaking into the respirator.