FEMA 453 Design Guidance for Shelters and Safe Rooms

Three methods are followed for the evacuation of buildings. One
method consists of evacuating all occupants simultaneously.
Alternatively, occupants may be evacuated in phases, where the
floor levels closest to the event are evacuated first and then other
floor levels are evacuated on an as needed basis. Phased evacuation
is instituted to permit people on the floor levels closest to the
threatening hazard to enter the stairway unobstructed by queues
formed by people from all other floors also being in the stairway.
Those who are below the emergency usually are encouraged to
stay in place until the endangered people from above are already
below this floor level.
The concept of occupant relocation to other floors is usually the
best course of action for many types of building emergencies. This
method normally involves movement of occupants, from the fire
floor, the floor above, and floor below to a lower level until the
danger passes.
Evacuation involves providing people with the means to exit the
building. The egress system involves the following considerations:
Capacity. A sufficient number of exits of adequate width to accommodate
the building population need to be provided to allow
occupants to evacuate safely.
Access. Occupants need to be able to access an exit from wherever
the fire is, and in sufficient time prior to the onset of untenable
conditions. Alternative exits should be remotely located so that all
exits are not simultaneously blocked by a single incident.
Exit Design. Exits need to be separated from all other portions of
the building in order to provide a protected way of travel to the
exit discharge. This involves designing to preclude fire and smoke
from entering the exit and will usually involve structural stability.
In general, the means of egress system is designed so that occupants
travel from the office space along access paths such as
corridors or aisles until they reach the exit or a safer place. An
1-46 design considerations