An ERJ-170 crew was rushed between flights and during preflight failed to see that maintenance positioned the pressurization switch in manual. The crew took off unpressurized. The oxygen masks dropped requiring a return to land.

Narrative

During climbout from ZZZ through 10;000 FT; 'Cabin Altitude High' appeared on the EICAS with the associated visual and aural warnings. The Captain ordered oxygen masks on; performed the Quick Reference Handbook checklist; and ordered the declaration of an emergency with a return to ZZZ. After having performed the checklist; the Captain found the cabin pressurization switch to be in manual mode; but continued to ZZZ since passenger oxygen masks were deployed. Landing and taxi were normal. Factors that led up to the event included: the cabin pressurization knob being placed in a nonstandard position by Maintenance; a quick turn on a late flight with a plane change; ACARS weight and balance not working with a full flight (including jumpseater) and an aircraft that was overfueled creating additional weight and balance issues and requiring additional communication with Dispatch. All of these issues contributed to a rush situation that facilitated the failure to recognize the switch out of position. This event could have been avoided by recognition that the pressurization panel was not properly set during the originating/receiving flow and by not allowing additional tasks or time pressures to compromise checklist adherence.