Human behavior in evacuation : Decision making

Human behavior in evacuation : Decision making

During the decision making phase (Kuligowski, 2008) or the cognition stage (Galea et al., 2010) occupants can decide between different options. One of these is to evacuate the building. 

According to Gershon and colleagues (2007), who have conducted an analysis on the World Trade Center 9/11 evacuation, the evacuation decision-making is composed by the decision to initiate the evacuation and to go on with the evacuation until reaching the area outside the building.

The decision to initiate the evacuation depends on several factors that can be grouped in three levels of analysis: individual, organizational and environmental. At the individual level there are some conditions that will facilitate the decision to leave and other that will impede this kind of action.

In the specific case of the WTC 9/11 evacuation the first were: emergent perception of risk formed by sensory cues, intuition, prior experience in WTC in 1993 (a previous terroristic attack), thought of a terrorist event, knowledge about how to exit and the communication with significant to leave the building.

On the other hand, the barriers were: a low knowledge level about the building layout or the emergency procedures, delaying behaviors (such as calling others or gathering personal belongings), fear of physical capabilities and the fact of being new to the job with a subsequent hesitation for fear of consequence of leaving. Similarly, at an organizational level the authors founded that an occupant instructed by a person in authority or by a colleague to leave were more likely to decide to evacuate.

Also a person with an authoritative voice shouting the directions to egress the building was a facilitator.

On the contrary, no guidance or ambivalent or contradictory messages played an important role on the occupants’ decision to not evacuate.

Taking into account the environmental level, important factors were: hearing, seeing or feeling the explosion or a flash of light or the plane hitting the first building or smelling smoke; while factors that have prevent the decision were communication failures and the fact of no receiving environmental cues.

Also the decision to progress with the egress can be analyzed using the 3 different levels.

Considering the individual, the decision to keep on leaving was more likely in case of: high degree of fire safety knowledge, prior experience, building knowledge, good footwear, the presence of a leader or a crowd to follow and the heeded encouragement by others to keep moving.

At the organizational level of analysis, it was found that management behaviors (executive used bullhorn to order evacuation, people left and kept going) but also first responders in the lobby assisting with directions out of the building and encouraging evacuees to keep going were facilitator to the decision of proceeding with the evacuation.

Regarding the environment, clearly, strong environmental cues, supportive social milieu on staircase and good condition of the stairwell were crucial factors in the progress of the evacuation process