A Review of Building Evacuation Models - NIST Virtual Library

developers of the model. The local level (selection of a detour route) determines the occupant’s
response to the current or local situation and the global (which is specified by the user but can be
overridden by the local level) level keeps track of the overall strategy of the occupant (such as to
use the most familiar exit to leave the building). After the behavioral model has made a
decision, it passes this information onto the movement submodel to move the occupant.
Occupant behavior: Rule-based or conditional behavior.
Occupant movement: The movement submodel controls the physical movement of the
occupant from the current position to the next. Or, if a delay time was initiated by the user, the
model holds the occupant in position. The movement model can also incorporate overtaking,
side stepping, and other actions. The movement submodel determines the speed at which the
occupant will move, and checks with the occupant submodel to make sure the occupant has the
capability of performing specific maneuvers during evacuation (i.e., jumping over obstacles).
The user can set one of six levels of walking speed for each individual occupant, randomly
generated for the population, or group-defined. Those six levels are:
• Fast walk – default speed of 1.5 m/s
• Walk – 90 % of fast walk
• Leap – 80 % of fast walk
• Crawl – 20 % of fast walk
• Stairs-up (based on Fruin data 60 and dependent upon age and gender)
• Stairs-down (based on Fruin data and dependent upon age and gender)
The occupant “slows” due to other occupants occupying the grid cells in front of him/her. When
moving to a grid cell that another occupant also wishes to occupy, the conflict resolution input
assigns a certain delay time to each occupant in “conflict.” Also, the drive variable also affects
which occupant will actually occupy the grid cell. If one of the occupants is assigned a higher
drive value than the other, that occupant will obtain the next grid cell. However, if both
occupants are assigned the same drive value, the decision is random. In short, the evacuation
time of movement from grid cell to grid cell is made up of actual movement at unimpeded speed
plus any conflict delays that occur along the way.
At the global level of the occupants’ view of the building, the evacuation strategy is defined by
the user. The default route is determined by the potential map (marking 0 as the exit and all
other nodes as higher number the further away the node is from the exit), which leads people to
the nearest available exit. If an exit is labeled as familiar or more attractive, this default potential
map and route changes. The occupants always move onto a node with a lower potential than the
one they are presently occupying. If an exit is more attractive, the potential for that exit is
lowered. As mentioned earlier, the global level information is followed until an event occurs on
the local level. At the local level, two behavioral options are available to the user, normal and
extreme behavior. In normal behavior, the occupants’ movements are determined by the
potential map, and they strive to lower their potential. If the option to lower potential is not
there, the occupant will move onto a node with equivalent potential. If this option is not
available, the occupant will wait. In extreme conditions, occupants may act in a more extreme
manner by taking a more indirect route. In this case, the occupants do not mind accepting a
A-41