A B747-400 CABIN ATTENDANT RPTS HVY CONDENSATION MIST IN FIRST CLASS CABIN WHILE ON THE GND. EXPLANATION OF CAUSE WAS HIGH HUMIDITY AT DEP ARPT.

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WHILE PARKED AT GATE; AIR CONDITIONING IN FIRST AND BUSINESS PRODUCED CONDENSATION MIST IN CABIN. FROM BOARDING DOOR 1L; BEHIND ROW 5; WAS UNABLE TO SEE FORWARD FROM ROW 4 TO ROW 1. UNABLE TO SEE PAX; UNABLE TO SEE FLOOR. FROM DOOR 1L UNABLE TO SEE FLT ATTENDANT AT DOOR 2L. UNABLE TO SEE PAX IN CABIN. WAS UNABLE TO SEE IF OVERHEAD BINS CLOSED BEFORE DOOR CLOSURE. HAD TO WALK UP AND DOWN AND CALL FLT ATTENDANTS. UNABLE TO SEE IF PAX DOWN FOR PUSHBACK. HAD TO WALK UP AND DOWN AND CALL DIFFERENT CABINS. MIST SUBSIDED AFTER PUSHBACK THEN RETURNED IN THE MIDDLE OF SAFETY DEMO. PAX IN 'B' ZONE WERE UNABLE TO SEE FLT ATTENDANTS PERFORMING DEMO. CAPT HAD INFORMED FLT ATTENDANTS TO REMAIN SEATED AFTER TKOF DUE TO POSSIBLE WX. AFTER TKOF; CONDENSATION DRIPPED HEAVILY ON PAX IN BUSINESS AND ECONOMY. PAX STARTED GETTING UP WITH SEATBELT SIGN OFF TO ESCAPE WATER. FLT ATTENDANTS IN THE BACK COULD NOT REMAIN IN SEATS. TOO MANY PAX UP. WAS TOLD THIS WAS DUE TO HUMIDITY LEVEL IN ZZZZ; BUT I HAVE FLOWN THERE MANY TIMES. THIS IS THE ONLY SUCH INCIDENT I HAVE WITNESSED. OTHER FLT ATTENDANTS TOLD ME THAT ACFT X WAS KNOWN TO HAVE THIS CONDENSATION AND MIST PROB.