IT’S A LONG WAY DOWN TO SAFETY
The biggest barrier is simply vertical distance. Stairwells are the only reliable escape route in most buildings.
Stair descent in real evacuations is far slower than most people expect. Under controlled or drill conditions people move down at around 0.4 to 0.7m per second. But in an actual emergency, especially in high-rise fires, this can drop sharply.
During 9/11, documented speeds at which survivors went down stairs were often slower than 0.3m/s. These slowdowns accumulate dramatically over long vertical distances.
Fatigue is a major factor. Prolonged walking significantly reduces the speed of descent. Surveys conducted after incidents confirm that a large majority of high-rise evacuees stop at least once. During the 2010 fire of a high-rise in Shanghai, nearly half of older survivors reported slowing down significantly.
Long stairwells, landings, and the geometry of high-rise stairs all contribute to congestion, especially when flows from multiple floors merge into a single shaft.
Slower movers include older adults, people with physical or mobility issues and groups evacuating together. These reduce the overall pace of descent compared with the speeds typically assumed for able-bodied individuals. This can create bottlenecks. Slow movers are especially relevant in residential buildings, where diverse occupants mean movement speeds vary widely.
Visibility matters too. Experimental studies show that reduced lighting significantly slows down people going down stairs. This suggests that when smoke reduces visibility in real events, movement can slow even further as people hesitate, misjudge steps, or adjust their speed.
https://www.channelnewsasia.com/commentary/hong-kong-fire-wang-fuk-court-high-rise-building-evacuate-5493676
