AN ACR FLC FLYING AN EMB120 EXPERIENCED A LOSS OF PRESSURIZATION AT FL220 NEAR BHI AND PERFORMED AN EMER DSCNT.

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OCCURRENCE 20 NM E OF BISHOP VOR AT FL220. CABIN BEGAN TO CLB AT 2500 FPM. WE FIRST SUSPECTED A PACK OR BLEED PROB BUT CABIN BROKE 10000 FT MSL QUICKLY. WE HAD ALREADY REQUESTED FL200 AS SOON AS THE PROB MANIFESTED ITSELF. AFTER RED 'CABIN ALT' LIGHT ILLUMINATED; CAPT WENT ON OXYGEN FIRST THEN; WITH THE EXCHANGE OF CTLS TO CAPT; FO WENT ON OXYGEN. COM WAS ESTABLISHED. FO THEN CALLED BACK TO FLT ATTENDANT TO TELL HER OF SIT. CAPT DECLARED EMER TO ZOA. A FULL EMER DSCNT WAS NOT COMMENCED DUE TO THE VICINITY OF TERRAIN. CAPT DSNDED ACFT TO APPROX 14000 FT MSL. FO COMPLETED 'CABIN ALT' EMER CHKLIST; NO CHANGE IN SIT OCCURRED. THE DECISION TO CONTINUE TO FRESNO AT 16000 FT MSL WAS DISCUSSED BY FLC. CAPT CLBED AND STAYED AT 16000 FT MSL TO CROSS MOUNTAINOUS AREA FOR A DURATION OF 18 MINS. AT THAT POINT CLOUD COVERAGE DISSIPATED AND CAPT ADVISED ATC THAT SEPARATION FROM TERRAIN COULD BE MAINTAINED AND ACFT WAS DSNDED TO 10000 FT MSL. AT THAT POINT CREW REMOVED OXYGEN MASKS AND FO RESUMED CTL OF ACFT. FLT CONTINUED WITHOUT INCIDENT TO THE LNDG AT FRESNO. EMER EQUIP WAS STANDING BY BUT NOT USED.