This study provides an investigation into the fundamental assumptions made in many current egress models and serves as a case-control investigation regarding stairwell evacuations. The evacuation of a six-story office building was filmed and observed. The introduction of two-directional travel within the same stairwell was considered: the upward direction of firefighters trying to get into the building, and the downward direction of occupants trying to get out. This provided conditions outside the assumptions generally made. Also an investigation into human behavioral patterns has been considered. The effects of these conditions have been analyzed both qualitatively and quantitatively. Results demonstrate that the higher a person entered the stairwell the more significant the effects of counterflow became. The wing with counterflow maintained more dense conditions throughout the duration of the evacuation. Behavioral patterns such as carrying objects, socializing, nonadaptive behaviors, and interaction with the firefighters were determined to have a significant influence on the population's performance.