EMER DECLARED AND REQUEST MADE FOR EMER DSCNT WHEN THE CABIN PRESSURE SYS FAILS ON A CPR C750 AFTER START OF DSCNT ON FREQ WITH ZZZ CTR.

Narrative

DURING CRUISE THE BAGGAGE DOOR SEAL CAS MESSAGE ILLUMINATED. FOLLOWED CHKLIST AND SIT WAS NORMAL PER MESSAGE. (CABIN ALT MAINTAINED; OK.) WE WERE EXPERIENCING SOME TURB AND ASKED ATC FOR LOWER TO FL370. IT WAS RPTED AS SMOOTH. WE WERE APPROX 100 MI FROM TOP OF DSCNT. ANYWAYS; AS SOON AS I REDUCED PWR FOR DSCNT; THE CABIN BEGAN TO CLB AT A RATE OF APPROX 2000 FPM. SOON FOLLOWED THE BAGGAGE; ALT CAS MESSAGE. WE ISOLATED THE BAGGAGE COMPARTMENT IMMEDIATELY PER CHKLIST. HOWEVER; THE CABIN CONTINUED TO CLB AND WE CONTINUED TO DSND; ASKING FOR LOWER. I BELIEVE ATC CLRED US TO FL330. SHORTLY; THE CABIN ALT 'AMBER CAS' MESSAGE ILLUMINATED. WE BOTH PUT ON OUR OXYGEN MASKS. WE LET ATC KNOW OF OUR PRESSURIZATION PROB AND ASKED FOR LOWER. ATC CLRED US FL240. SINCE THE CABIN CONTINUED TO CLB; I HAD THE FO BRIEF THE PAX ON OUR SIT AND TO KEEP THEM CALM. IT WASN'T LONG AND THE CABIN ALT 'RED CAS' MESSAGE ILLUMINATED. WE WERE APPROX AROUND FL310. I INITIATED A MORE AGGRESSIVE DSCNT PER EMER DSCNT PROFILE. ATC WAS NOT ACCOMMODATING OUR LOWER ALT REQUEST (DUE TO MIL AIRSPACE). SO WE IMMEDIATELY DECLARED AN EMER. WE BRIEFLY PAUSED OUR DSCNT AT FL240 AND THEN WERE CLRED TO 13000 FT. AS I FLEW THE DSCNT PROFILE; THE FO KEPT THE PAX INFORMED AND RAN THE APPROPRIATE CHKLISTS. ONCE WE GOT TO APPROX 14500 FT (CABIN MAX ALT) THE CABIN ALT DSNDED AS WE DSNDED. SINCE WE WERE CLRED TO 13000 FT WE LEVELED OFF THERE MOMENTARILY AND THEN STEPPED DOWN SLOWLY TO 10000 FT. WE INFORMED ATC THAT THINGS WERE UNDER CTL AND COULD CONTINUE TO OUR DEST OF ZZZ. PLEASE NOTE: THE ACFT SAT OUTSIDE IN ZZZ1 THE EVENING BEFORE IN EXTREMELY HVY RAIN.