  To investigate the evacuation behaviors of pedestrians considering action of
the guard and develop an effective evacuation strategy in the artificial
attack, an extended floor field model was proposed. In this model, the assault
on pedestrians, the death of pedestrians and the capture of the guard were
involved simultaneously. An alternative evacuation strategy which can largely
reduce the number of death was developed and effects of several key parameters
such as the deterrence radius and capture distance on evacuation dynamics were
studied. Results show that congestion near the exit has dual effects. More
specially, the guard could catch all attackers in a short time because the
attackers would have more concentrated distribution, but more casualties would
happen because pedestrians are hard to escape the attack due to congestion. In
contrast, when pedestrians have more preference of approaching the guard,
although the guard would take more time to capture the attackers result from
the dispersion of attackers, the death toll would decrease. One of the reason
is the dispersal of the crowd and the decrease in congestion would be
beneficial for escape. Another is the attackers would be killed before
launching the attack to the people those are around the guard, in other words,
the guard would protect a large number of pedestrians from being killed.
Moreover, increasing capture distance of the guard can effectively reduce the
casualties and the catch time. As the deterrence radius reflecting the tendency
of escaping from the guard for attackers rises, it would become more difficult
for the guard to catch the attackers and more casualties are caused. However,
when the deterrence radius reaches a certain level, the number of deaths would
be reduced because the attackers would prefer to stay as far away as possible
from instead of the position where they could attack more people.
