HK high-rise fire shows how difficult it is to evacuate in an emergency

Human behaviour is one of the biggest sources of delay in high-rise evacuations.

- Milad Haghani, Erica Kuligowski and Ruggiero Lovreglio

The Hong Kong high-rise fire, which spread across multiple buildings in a large residential complex, has killed dozens, with hundreds reported missing.

The death toll at the time of writing was over 40, with close to 300 people still unaccounted for and dozens in hospital with serious injuries.

This makes it one of Hong Kong's deadliest building fires in living memory, and already the worst since the Garley Building fire in 1996.

Although more than 900 people had been reportedly evacuated from Wang Fuk Court, it was not clear how many residents remain trapped.

This catastrophic fire - which is thought to have spread from building to building via burning bamboo scaffolding and fanned by strong winds - highlights how difficult it is to evacuate high-rise buildings in an emergency.

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.

We've seen this in the biggest modern examples, from the World Trade Center in the United States to Grenfell Tower in the United Kingdom.

The patterns repeat: once a fire takes hold, getting thousands of people safely down dozens of storeys becomes a race against time.

But what actually makes evacuating a high-rise building so challenging?

It isn't just a matter of "getting people out". It's a collision between the physical limits of the building and the realities of human behaviour under stress.

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.