A Review of Building Evacuation Models - NIST Virtual Library

Occupant movement: Cellular automata model.
The movement speed of the occupants is dependent upon the surrounding density. The
movement speed, according to the references for the model, is also affected by the level of
hazard of the environment, personal characteristics (gender, age) and building configuration.
The model allows the user to input speed adjustment for each individual, but also provides
default values. Ultimately, the speed of the individual is dependent upon the crowd density, the
number of nodes representing the building, the number of people in the building, and the
processing time.
As crowds increase, the model determines the number of people around each individual in a predetermined
area. If there are no other occupants in a 1.12 m 2 area around the simulated
occupants, an individual’s speed is regarded as unimpeded 87 . However, when occupants come in
contact or “conflict” with another occupant, they have three options: turn 45° to the left, turn
45° to the right or stay in their cell. The model records the number of occupants in the 1 m
region around the occupant (3 cells in the forward and lateral direction forming a 1.2 x 1.2 m
area).
Through exits, the model moves occupants at the front of the crowd through an exit at an
unimpeded speed depending upon the exit type (revolving door, turnstile, swinging door, etc).
However, the other people adjacent to these occupants near the exit move at controlled flow rates
through the exit. When moving occupants from one zone to another zone through an internal
exit, the model uses a balance between the number of occupants entering into a zone and
occupants escaping from the previous zone.
Formula for walking speed:
To establish the crowd flow function for the SGEM model, the gas-lattice model (cellular
automata model) was used to simulate movement of crowds through a corridor with 100 x 20
cells under the “periodic boundary condition.” Each “walker” moves in a “preferential”
direction (forward, downward, or upward) with no back stepping or overlapping of a single cell.
“A non-dimensional drift is applied to the preferential direction for random walkers to represent
the tendency of moving towards an exit.” People are randomly distributed along the corridor for
a specific density and for an average of 3000 runs, the mean velocity was calculated for all
occupants. For movement of the occupant by the gas-lattice model, probabilities are calculated
to move into certain adjacent cells, with a higher tendency for occupants to move toward the
exit. For more information on how the gas-lattice model compares with other researchers in the
field, the following reference should be consulted 85 .
From a curve fit of the gas-lattice model, the following is the crowd density versus velocity
equation:
V = (1.4 d≤0.75,
0.0412d 2 - 0.59d + 1.867 0.754.2),
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