Disrupt emergency exits to boost evacuation rates

Obstructing the exit could save lives (Image: Scott Craig/cancerbot/StockXchng)

Need to evacuate people quickly through a narrow opening? Put something in their way.

Physicists timed a crowd of 50 women as they exited as fast as possible through a door, and then repeated the experiment with a 20-centimetre-wide pillar placed 65 centimetres in front of the exit to the left-hand side.

The obstacle improved the exit rate by an extra seven people per minute – from 2.8 people to 2.92 people per second.

Daichi Yanagisawa at the University of Tokyo, Japan, who led the research team, explains that the pillar creates a relatively uncrowded area where it's needed most – just in front of the exit.

Usually, the exit becomes clogged by people competing for the small space, and the crowd is slowed. The pillar blocks pedestrians arriving at the exit from the left so effectively that the number of people attempting to occupy the space just in front of the exit is reduced, says Yanagisawa. With reduced crowding there are fewer conflicts and the outflow rate increases.

But the positioning of the pillar is crucial, says Yanagisawa. When the researchers moved the pillar so that it stood directly in front of the exit's centre, rather than to the left, the outflow rate dropped to 2.78.

That's because there's a second factor influencing outflow rate, dubbed the turning function. As pedestrians approach the busy doorway they weave and duck to squeeze through the crowd. With every turn they lose momentum and their walking speed decreases, which reduces the rate of outflow through the exit

With the pillar offset to the left, the turning function of pedestrians approaching the exit from the left increases. Although they take longer to reach the exit, the total effect is an increase in outflow rate since those approaching from the centre or the right have a comparatively free and empty route to the exit.

But if the pillar is central, it affects the turning function of most pedestrians approaching the exit. Because more pedestrians are slowed down by the obstacle, the total outflow rate drops.