QUESTION WHETHER ACR LGT LEGAL TO OPERATE WITH ONE INOPERATIVE WATER FIRE EXTINGUISHER.

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DURING PREFLT INSPECTION FOR THE FIRST FLT OF THE DAY; ONE OF THE F/A FOUND A BROKEN SEAL ON AN H20 FIRE EXTINGUISHER IN THE PAX CABIN. I VERIFIED THAT THE CO2 CARTRIDGE (PROPELLANT/PRESSURE SOURCE) HAD BEEN PUNCTURED. A DESCRIPTION OF THE DEFICIENT FIRE EXTINGUISHER WAS ENTERED IN THE ACFT LOGBOOK. WE CONTACTED THE CONTRACT MAINT PERSONNEL TO TAKE CARE OF THE EXTINGUISHER. WHEN THE MECH CALLED TECHNICAL SVCS FOR INFO ON SERVICING THE EXTINGUISHER HE WAS TOLD THAT WE DID NOT NEED THE EXTINGUISHER TO MEET THE REQUIREMENTS OF THE MEL. THE LOG BOOK ITEM WAS CLRED WITH A NOTE TO THAT EFFECT. WHILE ENRTE TO THE FIRST STOP WE IN THE COCKPIT BEGAN DISCUSSING THE MATTER OF THE FIRE EXTINGUISHER; UPON REVIEWING THE EMER EQUIP LISTING IN THE AIRPLANE FLT MANUAL; DISCOVERED A CONFLICT BETWEEN THE FLT MANUAL AND THE MEL; I.E. THE FLT MANUAL WAS MORE STRINGENT THAN THE MEL. AFTER LNDG IN ABQ I CALLED THE FLT DISPATCHER AND TOLD HIM OF THE CONFLICT BTWN THE AFM AND MEL. THE RESOLUTION OF THE SITUATION WAS THAT THE FLT MANUAL PREVAILED. AFTER A 34 MINUTE DELAY THE MISSING EXTINGUISHER WAS REPLACED AND WE CONTINUED THE FLT. IN A LATER PHONE CONVERSATION I WAS ADVISED THE MEL WILL BE UPDATED TO AGREE WITH THE AIRPLANE FLT MANUAL. HUMAN PERFORMANCE CONSIDERATIONS: THERE WAS PROBABLY A TENDENCY ON MY PART AS CAPT TO ACCEPT THE INFO FROM TECHNICAL SVCS SINCE WE HAVE A NOTICE IN OUR FLT DEP PAPERS REFERRING TO THE REVISED MEL THAT TECHNICAL SVC HAS AND THAT THE REVISED LIST MAY BE DIFFERENT FROM THE MEL WE HAVE IN THE AIRPLANE. FOR SOME REASON I DID NOT INITIALLY RESPOND TO A 'GUT FEELING' THAT SOMETHING WAS WRONG WITH THE INFO FROM TECHNICAL SVC; EVEN THOUGH IT WAS NOT LOGICAL THAT THE MEL WE HAVE IN THE AIRPLANE SHOWS 4 EXTINGUISHERS INSTALLED/ 4 REQUIRED AND THE AIRPLANE ACTUALLY HAS 5 EXTINGUISHERS INSTALLED (IN AGREEMENT WITH FLT MANUAL). WOULDN'T 5 BE REQUIRED?