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.