PRM1 CLIMBS TO FL270 UNPRESSURIZED ACCOUNT BLEED AIR NOT TURNED ON. HYPOXIA FOR ALL ABOARD IS ABATED WHEN FO REALIZES THE SITUATION AND INITIATES AN EMERGENCY DESCENT.

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PART OF THE 'TAXI' CHKLIST WAS MISSED DUE TO THE CAPT TRYING TO HELP ME WITH A RTE CHANGE IN THE FMS. THERE WERE SEVERAL INTERRUPTIONS DURING THE TAXIING TO THE ACTIVE RWY. THE FLT WAS PLANNED AT A CRUISING ALT OF FL270. THE MISSED ITEM ON THE CHKLIST WAS THE BLEED AIR SWITCH NOT PLACED IN THE 'BOTH' OR 'ON' POS; HENCE UNPRESSURIZED. CABIN ALT CLBED TO A POINT THAT HYPOXIA BEGAN TO SET IN. I WAS THE PNF AND SITTING IN THE R SEAT SINCE I HAD NOT BEEN TO TRAINING ON THE ACFT. SOMEWHERE DURING THE FLT AT FL270; I KEPT HEARING CTR CALLING AND ASKING IF WE COULD MAKE OUR XING RESTR THAT I HAD ACKNOWLEDGED. AT THIS POINT (DUE TO HYPOXIA) I WAS UNABLE TO REACH THE YOKE MIKE BUTTON TO RESPOND. SOMEHOW I REALIZED THAT WE WERE NOT DSNDING TO OUR ASSIGNED ALT AND MY FLYING PARTNER AND ALL PAX WERE NOT RESPONSIVE. I DISCONNECTED THE AUTOPLT AND DEPLOYED THE SPD BRAKES AND STARTED AN EMER DSCNT. AT ABOUT FL180; I GOT THE CAPT ON OXYGEN AND CONTINUED DSCNT TO BELOW 10000 FT. I MADE A SAFE LNDG AT ZZZ. 1) CREW DISTR WAS THE PRIMARY FACTOR CAUSING THIS EVENT; 2) THERE WAS NO CABIN 'ALT HIGH' MASTER CAUTION; AND 3) THE CABIN OXYGEN MASK DID NOT PRESENT (DROP). 4) THE USE OF ELECTRONIC CHKLIST SHOULD BE USED SINCE AN ITEM WOULD NOT BE MISSED AS IT WAS USING A PAPER CHKLIST. 5) THE CAPT HAD FLOWN SEVERAL TRIPS THE 3 PREVIOUS DAYS -- ALL STARTING VERY EARLY AND ENDING VERY LATE AT NIGHT. FATIGUE WAS A HUGE FACTOR. THERE IS NO STATUS LIGHT ON THE ANNUNCIATOR PANEL INDICATING THAT THE BLEED AIR SWITCH IS IN THE 'OFF' POS AS THERE IS ON ALL PRESSURIZED ACFT THAT I HAVE FLOWN. SUPPLEMENTAL INFO FROM ACN 778901: DURING PREFLT CHKS; ATTN WAS DIVERTED FROM QUICK TURN CHKLIST TO ASSIST NEW CREW MEMBER IN PROGRAMMING RTE CHANGE INTO FMS. THIS TOOK 3-4 MINS TO ACCOMPLISH. RETURNING TO CHKLIST; BLEED AIR SWITCH WAS MISSED AND NOT TURNED ON. AFTER TKOF AND CLB TO ASSIGNED ALT OF FL270; CABIN ALT CLBED TO THE POINT THAT HYPOXIA BEGAN TO SET IN. NEW CREW MEMBER RECOGNIZED THE PROB AND STARTED DSCNT WHILE CALLING FOR CREW TO GO ON OXYGEN. 1) CREW DISTR AND BREAKING THE FLOW OF PREFLT CHKLIST WAS PRIMARY CAUSE OF THIS EVENT. 2) CABIN 'ALT HIGH' WARNING LIGHT FAILED TO ILLUMINATE WHEN CABIN ALT PASSED 10000 FT. 3) CABIN OXYGEN MASKS FAILED TO DROP AFTER CABIN ALT CLBED ABOVE 10000 FT EVEN THOUGH THE SYS WAS ARMED AND SUFFICIENT OXYGEN PRESSURE WAS PRESENT. 4) USE OF ELECTRONIC CHKLIST WILL HELP PREVENT THIS IN THE FUTURE. THIS FEATURE DOES NOT FORGET WHERE IT LEFT OFF. 5) SUGGEST THAT A STATUS LIGHT INDICATING THAT THE BLEED AIR SWITCH IS IN THE OFF POS BE ADDED TO THE ANNUNCIATOR PANEL. MOST PRESSURIZED ACFT HAVE THIS FEATURE. 6) NO INJURIES OCCURRED DURING THIS EVENT. 7) THIS WAS THE THIRD LEG OF THE DAY AND IS WHY QUICK TURN CHKLIST WAS USED.