The drill covered a 32-storey office building with around 1,400 people taking part.

The plan set a target of eight minutes to clear the building. The drill took about fifteen. The gap opened where flows merged in the stairwell on the middle floors.

Where the bottleneck was

In the debrief, fire officers pointed out that the problem was not stairwell width but timing: floors entered the stairwell simultaneously rather than in sequence, creating local congestion.