SR251 Emergency egress - merging flows at floor stairway interfaces (2011)

This is a report prepared from a literature search of merging behaviour observed in trial evacuations and studies following the World Trade Center evacuations. Validated merging behaviour and occupant behaviour in general is incorporated into egress models to demonstrate that delays in the merge process do not adversely affect egress times in the current building regulation environment.

Overall building evacuation time has shown to be relatively independent of the merging flows at stairway entrances. However, the clearance rates of individual floors are greatly influenced by the respective egress flow or merge ratio from each floor.

In ideal conditions, the total evacuation time of a building was shown to be primarily dependent on a critical flow through a single most restrictive point, such as a final exit of a stairwell or an exit of the building. Deference behaviour, whereby persons in merging streams offer the other the opportunity to go first, also ensures relatively even distribution between floors and stairs where people merge like a zip. As a result, the default scenario is that buildings tend to clear from the bottom up.