HF Issues: If in swinging open, a gate (or door) passes over an abrupt change in elevation, does that increase the likelihood that the change will not be seen in time for the person to avoid harm? Expectancy, visual performance, familiarity with the setting, and distractions were additional considerations.

HF Investigation: Information collected included, but was not limited to: AA's physical and sensory characteristics and limitations; the illumination levels incident on the steps and the contrast between the step's nosings and treads; stairway geometry and stairway proximity to gate; the time available to preview changes in elevation.

HF Analysis: A scale 3D computer model of the exterior stairway, the fence, and of the person who fell was created. The model was used to determine at what point visual cues were present that could have alerted AA to the change in elevation. Consideration was given to the conspicuity of the step under the ambient lighting conditions that likely existed at the time of the accident.