MD82 CREW LOST CABIN PRESSURIZATION IN ZDC CLASS A AIRSPACE.

Narrative

WHILE CRUISING AT FL280; THE 'FLOW' LIGHT ILLUMINATED ON THE PRESSURIZATION CTL PANEL. THE CABIN WAS CLBING AT OVER 2000 FPM. THE CAPT ASSUMED PF DUTIES; OXYGEN MASKS WERE DONNED; AND EMER CHKLIST ITEMS WERE COMPLETED. WE WERE CLRED TO FL260 (ATC DID NOT YET KNOW OF THE PROB); AND A DSCNT WAS INITIATED. THE CABIN WAS STILL CLBING RAPIDLY THROUGH 10000 FT; SO THE PAX OXYGEN MASKS WERE DEPLOYED AND AN EMER DSCNT WAS INITIATED. THE CAPT INFORMED ATC THAT A LOWER ALT WAS NEEDED; AT WHICH TIME ATC ISSUED A CLRNC TO FL240. THE CAPT EMPHASIZED THAT AN IMMEDIATE DSCNT TO 10000 FT WAS NEEDED AND RESPONDED 'AFFIRMATIVE' WHEN ATC ASKED IF AN EMER WAS BEING DECLARED. ATC ISSUED A CLRNC TO DSND TO 10000 FT AND NO PREVIOUS ALT CLRNCS WERE VIOLATED. AT NO TIME DID THE 'CABIN ALT' AURAL WARNING SOUND. THE 'MASTER WARNING' AND 'CABIN ALT' LIGHTS ILLUMINATED APPROPRIATELY. AT 10000 FT THE CAPT TERMINATED THE EMER AND THE FLT CONTINUED TO PIT; 85 NM AWAY; WHERE MEDICAL PERSONNEL EVACED SEVERAL PAX WITH EAR COMPLAINTS.