WHY STAIRS AREN’T ENOUGH​

WHEN THE STAKES ARE HIGHEST

Evacuations of high-rises don’t happen every day, but occur often enough. And when they do, the consequences are almost always severe. The stakes are highest in the buildings that are full at predictable times: residential towers at night, office towers in the day.

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.


 

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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.