A portable breathing apparatus for oxygen enrichment of breathable air comprises: an adsorption vessel； an air compressor for pumping air into the adsorption vessel； a valve for purging pressure from the adsorption vessel； an adsorbent disposed within the adsorption vessel adsorbing a non-oxygen constituent of air when the vessel is pressurized, thereby producing oxygen-enriched air, and desorbing the non-oxygen constituent when the pressure is purged.
