AN A300 FLT CREW REPORTS LOSS OF CABIN PRESSURE AT 30000 FT. THEY DECLARED AN EMERGENCY; DESCENDED; AND RETURNED TO DEPARTURE ARPT. FLT CREW REPORTS NO ECAM CABIN ALT ALERTS EVEN THOUGH THE CABIN ALT EXCEEDED 14500 FT.

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AFTER LEVELOFF AT FL300 WITH ALL PRESSURIZATION INDICATIONS NORMAL IN THE CLB; I SELECTED THE PRESSURE PAGE ON ECAM AND NOTICED THE CABIN ALT AT APPROX 8000 FT AND CLBING RAPIDLY. ASKED FOR A LOWER ALT AND BEGAN DSNDING TO 10000 FT. ADVISED ATC OF OUR PROB. DURING THE DSCNT; THE CABIN KEPT CLBING. WE DONNED THE OXYGEN MASKS AND INITIATED COMS VIA INTERPHONE. THE OUTFLOW VALVES INDICATED FULLY CLOSED THROUGHOUT THE ENTIRE EVENT. RAN THE EXCESSIVE CABIN ALT CHKLIST WHICH DID NOT ALLEVIATE THE PROB. SELECTED THE OTHER AUTO PRESSURE REGULATOR -- NO HELP. ATTEMPTED MANUAL PRESSURIZATION USING CHKLIST AND THE CABIN CONTINUED TO CLB ABOVE 14500 FT WHICH CAUSED AN OXYGEN MASK DEPLOYMENT. MADE THE APPROPRIATE PA'S TO THE PAX AND TO THE CREW TO USE THE OXYGEN AND RETURN TO SEATS UNTIL FURTHER NOTICE. AT NO TIME DID WE RECEIVE ECAM ALERTS OR WARNINGS FOR CABIN ALT. AT THE LOWER ALTS; THE CABIN BEGAN TO DSND TO THE ACFT ALT. DECISION WAS MADE TO RETURN TO ZZZ. ALERTED DISPATCH VIA ACARS. ADVISED ZZZ APCH OF OUR SITUATION AS AN EMER ACFT AND LANDED OVERWT. LNDG WAS SMOOTH AND TOUCHDOWN WAS APPROX 150 FPM. UPON ARR AT GATE; PERFORMED A POSTFLT WALKAROUND INSPECTION AND DISCOVERED 1 OF 2 PCA ACCESS DOORS AND THE CHK VALVE WAS BROKEN OFF ITS HINGES.