Emergency evacuation for supertall buildings with heights over 200 m require a very long time for occupants to travel down the buildings. Occupants might jam into protected lobbies and staircases, extending the waiting time. There is not yet any code requirement specifically for emergency evacuation in supertall buildings, which are criticized for using the same codes for buildings with normal heights. Further, the evacuation design for several existing supertall buildings does not even follow prescriptive fire-safety codes. The underlying problems have not yet been addressed by thorough studies. Evacuation in such tall buildings in Hong Kong will be studied in this paper. The assumptions made in the local prescriptive codes for safe egress will be justified. Three buildings with evacuation design complying with the local codes are considered as examples. A commercial building, a hotel, and a residential block in Hong Kong are taken as examples. The key design parameters in the local codes are for 40 people evacuating with a flow rate of 1.1 person/s through the staircase between typical floors. The evacuation time from each floor to the protected lobby is assumed to be within 5 min. The evacuation times in different scenarios with these assumptions are calculated. Such assumptions do not hold under a high occupant load. The total evacuation time would be extended significantly when the travelling flows of occupants are blocked in any of the evacuation routes. Different fire-safety management schemes with staged evacuation, such as assigning higher priorities to evacuate lower or upper floors first, are evaluated. The results observed for safe egress are then discussed.
