  People often help others who are in trouble, especially in emergency
evacuation situations. For instance, during the 2005 London bombings, it was
reported that evacuees helped injured persons to escape the place of danger. In
terms of game theory, it can be understood that such helping behavior provides
a collective good while it is a costly behavior because the volunteers spend
extra time to assist the injured persons in case of emergency evacuations. In
order to study the collective effects of helping behavior in emergency
evacuations, we have performed numerical simulations of helping behavior among
evacuees in a room evacuation scenario. Our simulation model is based on the
volunteer's dilemma game reflecting volunteering cost. The game theoretic model
is coupled with a social force model to understand the relationship between the
spatial and social dynamics of evacuation scenarios. By systematically changing
the cost parameter of helping behavior, we observed different patterns of
collective helping behaviors and these collective patterns are summarized with
a phase diagram.
