Following four Continuous Duty Overnights (CDOs); a DHC-8 flight crew performed an emergency descent due to the failure of the cabin to pressurize. Once stable at a safe altitude they discovered the engine bleeds had never been opened despite the requirement that they be checked open during the performance of both the Before Takeoff and Climb checklists. The reporter stressed his belief that accumulated fatigue from the ragged rest schedule was a major contributor to the oversight.

Narrative

Level at 16;000 FT en route; we received a master warning 'CABIN PRESS' light. I checked cabin pressure it was at 10;000 FT. I called for memory items for emergency descent. We then did the QRC for an emergency descent. I notified ATC that we had pressurization problem and were immediately cleared to descend. At 10;000 FT we finished the checklist and then did QRH for 'CABIN PRESS.' We completed the checklist; which resolved the situation and continued to destination without further incident.This event occurred because we missed verifying the bleeds were on during both the 'Before Takeoff' and 'Climb Checklists.' During both checklists the packs were set correctly; but the bleeds were left in the off position. I feel that fatigue played a role in this incident as well as the dark conditions in the cockpit. This was our fourth night of CDOs (continuous duty overnights) and while I did sleep during the previous day and during the hotel stay I think that after four days of a choppy/disruptive sleep pattern; fatigue is inevitable. Prior to the flight I felt ok; certainly not what I would consider fatigued. When we got off the plane at our destination though I did feel tired; perhaps having to cope with the abnormal situation added to the feeling of fatigue. The dark conditions in the cockpit also contributed because of the difficulty in verifying the bleed switch position visually in the dark cockpit.I will certainly be more vigilant in the future regarding my observations during the before takeoff checklist; although this checklist is sometimes run during taxi; and during the climb checklist. I will also physically touch the bleed switches during my climb flow and make sure to visually verify the switch position and again when reading the checklist. I also feel that four CDOs in a row are too many. I feel two are acceptable and three should be the max. I will be avoiding CDOs in the future.