Abstract: An impact resistant external casing is provided to enclose a canister containing a multi-layered chemical bed, with by-passes in each layer to accommodate the flow across and through the bed of exhaled breath which reacts with potassium superoxide in tablet form, the casing being provided with a (top) lid section which contains a mouthpiece, breathing hoses, and neck straps, the opposite side of the casing being provided with a bottom cover which accommodates the storage of a folded breathing bag and chest straps. An air passageway constituting an annular section is provided to accommodate a chimney extending from the bag through the passageway section between the casing and the canister, which is open to ambient air for cooling purposes. The inside bottom portion of the canister is provided with a trammel to prevent escape of deliquesced KO.sub.