Experimental Study on Descent Speed on Stairs of Individuals and Small Groups Under Different Visibility Conditions

Staircases play an essential role in multi-story buildings during emergencies, such as fire. Fires and the resulting smoke cause low visibility, which could affect the movement speed of the occupants. This must be taken into consideration during evacuation experimental design. This paper aims to study the stairwell evacuation performance of individuals and small groups under normal and impaired visibility conditions. The evacuation experiment was conducted in a five-story office building, with 75 subjects. The descent speed, the evacuation behavior, and the characteristic of small groups were analyzed and discussed. The descent speed of individuals decreased sharply when the visibility was reduced. The descent speed of small groups showed a relatively small downward trend. Group behavior had a negative effect on the evacuation performance during normal visibility. The group speed converged to the speed of the slowest group member. The group behavior contributed to a quicker movement speed in the low visibility condition. This was due to the stress of occupants being relieved. The group speed tended to be as fast as the fastest member of the group.