**2.1.1 Historical abstract**

2 Will-be-set-by-IN-TECH

Sociology deals with the study of human groups and the formation of institutions (dos Santos França, 2010; Merton, 1968). Its origin came from Comte, Spencer and other 19*th* century researchers' need for a distinct perspective of the human behavior that derived from the individualistic studies that had been performed previously. For instance, Comte stood out that the human mind could only develop in a social environment. Thus, following this premise, Psychology was not enough to study the human' social behavior (Turner & Killian,

At first, Sociology was focused on culturally-oriented groups or social groups which behavior follows established rules. Because of such interpretation, some spontaneous and unorthodox social actions were perceived as abnormal and unstable or as exceptions that did not draw further attention. Sociology, as a science, attempted to "frame" reality into well-defined and established patterns. If a certain social action could not fit into any of such patterns, the action was considered a mistake or even a wrongdoing until society accepts the new behavior and

Taking a whole new approach, the field of Collective Behavior deals with human groups and collectivities that contradict or reinterpret society's norms and standards. These collectivities' behavior is not entirely detached from the socially accepted behavior discussed earlier. However, collective behavior deals with social groups that deny or reinterpret society norms and standards. Ralph Turner and Lewis Killian at (Turner & Killian, 1957) defined collective behavior as "*the set of social behaviors which the usual conventions stop driving the actions and the individuals transcend, exceed or collectively subvert the standards and the institutionalized structures*" (dos Santos França et al., 2009). This definition implies that the individuals engaged in a collective behavior are no longer bound to the rules and norms of society and they are free to act the way they intended even if such behavior is not socially accepted. At first, their actions are related to the institutionalized and established actions found in Society. But, as soon their need for socially unaccepted actions is reached, they start to bend and to overrule the norms

This sort of human group might happen due to many reasons, including by hazardous events, whether they are natural or human-induced. Also, their structure and formation follow a pattern that was mapped by some researchers. Finally, such mapped patterns could be used to understand disasters by a distinct perspective: how people react in a hazardous event and how this could be simulated in order to decrease material and human losses. The simulation

The understanding of the panic in crowds' phenomenon relies on the study of the collective behavior phenomenon. Thus, a historical overview is presented in the following sections, along with modern studies about panic and disasters, especially how people behave under such conditions. The following subsections show a historical overview of some studies of the collective behavior field and the theories that will be employed in Section 3 to build the

model presented in Section 3 deeply applies the information described in this section.

embraces it. Such acceptance could take decades or never happen.

that were built by society, creating their own.

**2.1 Crowd simulation: Theoretical elements**

simulation model.

**2. Sociology and collective behavior**

1957).

The collective behavior was studied in distinct ways through the ages. Initially researchers such as Tarde and Durkheim developed social theories in order to justify the actions performed by offenders or as a mean of explaining how an isolated individual could have a socially accepted behavior and the very same individual could be able to participate in criminal acts when he is in a collectivity.

Emile Durkheim claimed that the group was important to understand the individual's behavior. Culture would be formed by the combination of personal minds instead of a chain of imitations from one subject by the other members of the group. This was one of the early conceptions of the group mind, a supra-personal entity which has an autonomous existence from the composing members of the group (Durkheim, 1895). In other words, the individuals engaged in a collective behavior unconsciously help to form the group mind that guides their actions.

Following an opposite direction, Gabriel Tarde considered that the social behaviors happen due to man's natural inclination to mimic others. For Tarde, the interactions among individuals worked only to spread the mimic's individual results and the interactions were not responsible by their formation. According to Tarde's approach, collective behavior describes the person's socially anomalous behavior into a group and collective context and in situations not induced by criminal activities, such as the tulip mania (Mackay & Baruch, 1932) or the great social movements, such as the fall of the Bastille (Tarde, 1890; Turner & Killian, 1957).

#### **2.1.2 Collective behavior development**

After a criminal approach for the collective behavior, some researchers analyzed the collective behavior phenomenon in an individualized and superficial way, such as Sigmund Freud (Freud, 1955). However, some other researchers such as William McDougall and Gustave Le Bon developed the collective behavior studies further by creating an early classification of the phenomena, as well as a detailed profile of each member of the collectivity, but also taking into consideration that the collectivity itself has its own specific features. This second attempt to understand the collective behavior phenomenon followed a psychological standpoint (dos Santos França, 2010).

Le Bon is considered one of the founders of the collective behavior studies and he was one of the firsts to use the term crowd to describe the collectivities, developing the Crowd Psychology and treating the crowd as the prototype of all group behaviors. The focus of his studies was the social behavior by using the "the crowd mind" theory. For Le Bon, the main features of the crowds were:


other than criminal activities and psychological issues. Also, the individual engaged in collective behavior could belong to any social group, according to certain social-cultural

Simulating Collective Behavior in Natural Disaster Situations: A Multi-Agent Approach 439

Park also introduced the concept of "milling": a collective movement that represents fear or discomfort. The social unrest can amplify the fear which, in turn, leads the group to a tension state. Such unrest, even if it is merely mentioned, amplifies the fear. Thus, the milling and the social unrest make a vicious circle and their interaction becomes a circular reaction that increases the tension in the group and creates an expectation that mobilizes the group

Herbert Blumer was a student of Robert Park and carried on his research. George Herbert Mead was also Blumer's teacher and developed the social act, a noticeable external behavior. With that theoretical basis, Blumer coined the Symbolic Interactionism, which society is built by the interaction among people that, when they are about to act, take into consideration the actions and features of the other individuals, a symbolic interaction driven by each individual

1. The persons interact by the meaning of their world's objects (tangible, abstract or social),

3. During the interaction, individuals use an interpretative process to change such meanings. The Emergent Norm theory was proposed by Lewis Killian and Ralph Turner and it was presented in (Turner & Killian, 1957). Based on Blumer's Symbolic Interactionism, it also considered that the collective behavior was the outcome of the interactions among persons able to assess the received information which leads to an interactive cognition. This approach analyzes the agents' features that aided in the formation of the social systems in a micro level,

Therefore, the emergent norm approach deals with the formation of the collective behavior by the micro level interactions of the collectivity members and the advent of patterns and norms triggered by these interactions. Although there is no emphasis in the definition of the social systems (as seen in (Luhmann, 1996)), the interactions and the complex behaviors formed by them allow the collective behavior to be seen as a complex system because from its micro-level interactions - simple by nature - complex behavioral patterns emerge, and such patterns cannot be noticed by just analyzing each individual alone (dos Santos França, 2010).

Due to the need of creating a symbol and meaning system, Blumer' symbolic interactionism

2. How the social relation comes from the orientation to the other in each attendant

meaning developed during the interaction process (Borgatta & Montgomery, 2000).

According to Blumer, Symbolic Interactionism is based on three premises:

2. The meaning of the objects is built from the interactions among individuals;

contexts (dos Santos França, 2010; Park, 1939).

members for the collective act (Park, 1939).

both individually and collectively;

as well as the behavioral patterns in a group level.

**2.1.4 Other approaches for collective behavior**

(Vanderstraeten, 2002).

has some unclear basic points related to social interaction:

1. How individuals relate to each other in spite of their differences;

A rough classification of the crowds was also proposed by Le Bon. Such classification was based on how the crowd was conceived and its main actions, and it can be summarized as follows:


The psychological approach for the collective behavior emphasizes the lost of personality, the liability being empowered by the collectivity and the fact that such collectivity is guided by some kind of collective mind (similar to Durkheim's). Le Bon's vision also had the collective (or mass) psychology and the phenomenon of contagion in a primitive form (Le Bon, 1896).

The mass psychology was important for the development of the collective behavior studies because it was the first attempt to establish, classify and broaden such studies. However, the followers of this particular approach still treated the members of the crowds as society outcasts due to gender, race or civilization level. That implies that the only the civilized western individuals were considered truly civilized. Women, children, the mentally impaired and the individuals that belonged to a race other than white were marginalized and the mass psychology theories were used to justify and amplify such condition, as tools to "domesticate" and to "civilize" such groups, so they could act under the control of a leader such as Napoleon or Alexander, the Great (dos Santos França, 2010).

#### **2.1.3 Symbolic interactionism and emergent norm theory**

The criminal and psychological approaches for collective behavior used the abnormal, the unusual, the uncommon to establish a line, a threshold between the socially accepted behavior and groups (studied by Sociology) and the socially unaccepted behavior and the human groups that engaged in such behavior. Some researchers at the University of Chicago developed a distinct way to see and understand the collective behavior.

Robert Park and Ernest Burgess wrote a whole chapter about collective behavior in their book *Introduction to the Science of Sociology*. In that chapter, the concept of social contagion was described as an element to spread a cultural matter, being compared to the fashion phenomenon and inducing people's feelings. Thanks to Park and Burgess' work (and similar works released almost at the same time) collective behavior was related to social phenomena 4 Will-be-set-by-IN-TECH

A rough classification of the crowds was also proposed by Le Bon. Such classification was based on how the crowd was conceived and its main actions, and it can be summarized as

**Active crowd** Crowds that act together with a strong sense of coordination. Examples include

**Casual crowd** A crowd formed with no specific goal and coordination, acting at the same time and place for a short period. For instance, a crowd watching a display window being

**Conventional crowd** When a group of people gather themselves for a specific goal, sharing feelings that drive the actions of the whole group, such as what happens in an audience

**Expressive crowd** A group of people gathered to move, make gestures together but for individual achievements, such as the dancing crowds at carnaval and some religious

**Panic crowd** A panic crowd is formed when people are exposed to a dangerous situation and that leads them to create the perception of need to stay away from danger in a social and shared way, such as earthquakes and fires (dos Santos França, 2010; dos Santos França

The psychological approach for the collective behavior emphasizes the lost of personality, the liability being empowered by the collectivity and the fact that such collectivity is guided by some kind of collective mind (similar to Durkheim's). Le Bon's vision also had the collective (or mass) psychology and the phenomenon of contagion in a primitive form (Le Bon, 1896). The mass psychology was important for the development of the collective behavior studies because it was the first attempt to establish, classify and broaden such studies. However, the followers of this particular approach still treated the members of the crowds as society outcasts due to gender, race or civilization level. That implies that the only the civilized western individuals were considered truly civilized. Women, children, the mentally impaired and the individuals that belonged to a race other than white were marginalized and the mass psychology theories were used to justify and amplify such condition, as tools to "domesticate" and to "civilize" such groups, so they could act under the control of a leader such as Napoleon

The criminal and psychological approaches for collective behavior used the abnormal, the unusual, the uncommon to establish a line, a threshold between the socially accepted behavior and groups (studied by Sociology) and the socially unaccepted behavior and the human groups that engaged in such behavior. Some researchers at the University of Chicago

Robert Park and Ernest Burgess wrote a whole chapter about collective behavior in their book *Introduction to the Science of Sociology*. In that chapter, the concept of social contagion was described as an element to spread a cultural matter, being compared to the fashion phenomenon and inducing people's feelings. Thanks to Park and Burgess' work (and similar works released almost at the same time) collective behavior was related to social phenomena

follows:

decorated;

groups;

et al., 2009).

mutinies, lynching mobs and rebellions;

for a soccer game or any other recreational activity;

or Alexander, the Great (dos Santos França, 2010).

**2.1.3 Symbolic interactionism and emergent norm theory**

developed a distinct way to see and understand the collective behavior.

other than criminal activities and psychological issues. Also, the individual engaged in collective behavior could belong to any social group, according to certain social-cultural contexts (dos Santos França, 2010; Park, 1939).

Park also introduced the concept of "milling": a collective movement that represents fear or discomfort. The social unrest can amplify the fear which, in turn, leads the group to a tension state. Such unrest, even if it is merely mentioned, amplifies the fear. Thus, the milling and the social unrest make a vicious circle and their interaction becomes a circular reaction that increases the tension in the group and creates an expectation that mobilizes the group members for the collective act (Park, 1939).

Herbert Blumer was a student of Robert Park and carried on his research. George Herbert Mead was also Blumer's teacher and developed the social act, a noticeable external behavior.

With that theoretical basis, Blumer coined the Symbolic Interactionism, which society is built by the interaction among people that, when they are about to act, take into consideration the actions and features of the other individuals, a symbolic interaction driven by each individual meaning developed during the interaction process (Borgatta & Montgomery, 2000).

According to Blumer, Symbolic Interactionism is based on three premises:


The Emergent Norm theory was proposed by Lewis Killian and Ralph Turner and it was presented in (Turner & Killian, 1957). Based on Blumer's Symbolic Interactionism, it also considered that the collective behavior was the outcome of the interactions among persons able to assess the received information which leads to an interactive cognition. This approach analyzes the agents' features that aided in the formation of the social systems in a micro level, as well as the behavioral patterns in a group level.

Therefore, the emergent norm approach deals with the formation of the collective behavior by the micro level interactions of the collectivity members and the advent of patterns and norms triggered by these interactions. Although there is no emphasis in the definition of the social systems (as seen in (Luhmann, 1996)), the interactions and the complex behaviors formed by them allow the collective behavior to be seen as a complex system because from its micro-level interactions - simple by nature - complex behavioral patterns emerge, and such patterns cannot be noticed by just analyzing each individual alone (dos Santos França, 2010).

#### **2.1.4 Other approaches for collective behavior**

Due to the need of creating a symbol and meaning system, Blumer' symbolic interactionism has some unclear basic points related to social interaction:


in such behavior there is an attention strain. Thus, the individual does not think about the consequences of his acts in the same degree of his actions in ordinary conditions (Turner &

Simulating Collective Behavior in Natural Disaster Situations: A Multi-Agent Approach 441

The final kind of individual reaction found by Killian and Turner is the fear. A critical situation is known to pose as a threat to the individual's life or values. Thus, fear is the most common

Fear can be shown in many ways, from internal changes in the emotional and psychological state up to despair, whimper and foray, and it increases whenever the danger is unknown. Uncertainty leads to insecurity since the person does not have enough information to take the right decision in the new context. A person is less afraid of a dangerous situation than the lack

Panic in Crowds phenomenon has been studied by many researchers, mostly to understand its inner workings and specially to prevent the dangerous events to start it or to alleviate its effects if it is unpredictable. Enrico Quarantelli is a researcher that provided some essays

In (Quarantelli, 1975) Quarantelli identified a certain set of prejudgments related to how

• Thanks to media and films, panic is associated with despair, paralysis (shock) and an instinctive behavior caused by the panic itself, forcing a subtle mind changing similar to the one found in "Strange Case of Dr. Jekyll and Mr. Hyde" by Robert Louis Stevenson. These prejudgments are passed to the safety and damage control personnel, such as firefighters, police officers, public managers, among others. For example, the fear of inducing panic just by informing people about the hazardous event could be more dangerous than the life-threatening event itself. Even with relevant and crucial information for crowd control and to minimize material and human losses, the fear of generate more panic could block the right actions at the appropriate time, which in a panic situation could be disastrous. For Quarantelli, the mere mention of a dangerous situation does not trigger or amplify the crowd's panic state

In spite of what was proposed by the early researchers of collective behavior such as Gustave Le Bon, the human behavior during crisis is controlled instead of impulsive, it uses the right means to achieve its goals and it is organized and functional most of the time. However, that does not mean that an irrational behavior is avoided during the crisis; the incidence of such

Just like the other collective behavior and panic researchers, Quarantelli also provided the panic's main features, based on his studies and the analysis of other studies from Japan, France

• A person in a panic in crowds' situation deals with fear instead of anxiety;

• There is a trend to focus in a specific dangerous spot instead of a general threat;

• The future is more important in such situations than the past;

of information of the present condition and its uncertainty (Turner & Killian, 1957).

reaction in panic situations, even if such situation is not real.

about disasters and panic in crowds' phenomena.

people observe the crowds' behavior in panic situations: • People would behave "irrationally", out of control;

behavior is lower than what was intuitively observed.

and England, and they are the following:

Killian, 1957).

(Quarantelli, 1975).

These points were addressed by Talcott Parsons in his studies about social groups, which led to the Structuralism Approach for the collective behavior phenomenon.

The Structuralism Approach turns over the concept described in the previous section by highlighting the social structures' studies and their impact on the individuals. The focus lies on the social structures that triggered the phenomenon and the structures affected by the members of the collectivity, using the macro level elements to think about the micro level elements and behavior. Therefore, the social structure is analyzed as deep as possible. Any behavior that subverts the established social order is reviewed by observing how the social structure and the collectivity respond to that (dos Santos França, 2010).

Neil Smelser was a researcher at the Oxford University, and he was Talcott Parsons' student at the time. Enhancing Parsons' collective behavior studies (Parsons, 1937), Smelser pointed out that, although rumors, panic or lunatic conditions, commotion and revolution are unexpected and surprising, they happen regularly (Smelser, 1963). He also stated that as much institutionalized the behavior is, it will become less distinguishable in a social point of view. The purpose of collective behavior, according to Smelser, is the resettlement of the social order that was shook by a tension on the elements that make the social structure. The resettlement induces people to act in a collective and rational way. After that, social norms and institutions are crystallized due to the comeback of the social order or by the formation of a new one. This shows Smelser's top-down approach for the collective behavior phenomenon (Smelser, 1963).

#### **2.1.5 Panic in crowds**

Panic in crowds can be triggered by various factors, such as natural threats (floods, earthquakes, volcanic eruptions), threats induced by man (terrorist attacks, lost of the social control by State), among others. In a panic situation there is always an imminent risk and the urge to act by the individuals (dos Santos França et al., 2009).

Killian and Turner also studied the behavior of individuals during crisis. In (Turner & Killian, 1957) the micro interactions are the key elements for the changes in the society. The same would happen with culture that changes thanks to each person, even if that happens in an unusual and unconscious way. According to Killian and Turner, it is in the reaction of the individuals in critical and unstructured situations that the basis of the collective behavior can be found. Such personal responses should be accepted as a required background for the study of the development of new norms and social structures.

Three kinds of individual reactions were found by Killian and Turner. The first kind of reaction is Defense: people act in a limited fashion, unable to comprehend what happened and to deal with new situations, and some of them will be in shock, even with no physical damage. On the other hand, there will be others that become more suggestible and readily accept commands from somebody else (Turner & Killian, 1957).

The second kind of reaction that usually happens after the shock from a violent accident is an impulsive and apparently irrational action. The individual acts apart from the environment and the other individuals, with actions entirely out of his normal self, in some kind of "super focus". Even though that individual is aware of what happens in the environment, his actions are directed towards a specific spot inside the event, acting in a conscious way. It seems that 6 Will-be-set-by-IN-TECH

These points were addressed by Talcott Parsons in his studies about social groups, which led

The Structuralism Approach turns over the concept described in the previous section by highlighting the social structures' studies and their impact on the individuals. The focus lies on the social structures that triggered the phenomenon and the structures affected by the members of the collectivity, using the macro level elements to think about the micro level elements and behavior. Therefore, the social structure is analyzed as deep as possible. Any behavior that subverts the established social order is reviewed by observing how the social

Neil Smelser was a researcher at the Oxford University, and he was Talcott Parsons' student at the time. Enhancing Parsons' collective behavior studies (Parsons, 1937), Smelser pointed out that, although rumors, panic or lunatic conditions, commotion and revolution are unexpected and surprising, they happen regularly (Smelser, 1963). He also stated that as much institutionalized the behavior is, it will become less distinguishable in a social point of view. The purpose of collective behavior, according to Smelser, is the resettlement of the social order that was shook by a tension on the elements that make the social structure. The resettlement induces people to act in a collective and rational way. After that, social norms and institutions are crystallized due to the comeback of the social order or by the formation of a new one. This shows Smelser's top-down approach for the collective behavior phenomenon

Panic in crowds can be triggered by various factors, such as natural threats (floods, earthquakes, volcanic eruptions), threats induced by man (terrorist attacks, lost of the social control by State), among others. In a panic situation there is always an imminent risk and the

Killian and Turner also studied the behavior of individuals during crisis. In (Turner & Killian, 1957) the micro interactions are the key elements for the changes in the society. The same would happen with culture that changes thanks to each person, even if that happens in an unusual and unconscious way. According to Killian and Turner, it is in the reaction of the individuals in critical and unstructured situations that the basis of the collective behavior can be found. Such personal responses should be accepted as a required background for the study

Three kinds of individual reactions were found by Killian and Turner. The first kind of reaction is Defense: people act in a limited fashion, unable to comprehend what happened and to deal with new situations, and some of them will be in shock, even with no physical damage. On the other hand, there will be others that become more suggestible and readily accept commands

The second kind of reaction that usually happens after the shock from a violent accident is an impulsive and apparently irrational action. The individual acts apart from the environment and the other individuals, with actions entirely out of his normal self, in some kind of "super focus". Even though that individual is aware of what happens in the environment, his actions are directed towards a specific spot inside the event, acting in a conscious way. It seems that

to the Structuralism Approach for the collective behavior phenomenon.

structure and the collectivity respond to that (dos Santos França, 2010).

urge to act by the individuals (dos Santos França et al., 2009).

of the development of new norms and social structures.

from somebody else (Turner & Killian, 1957).

(Smelser, 1963).

**2.1.5 Panic in crowds**

in such behavior there is an attention strain. Thus, the individual does not think about the consequences of his acts in the same degree of his actions in ordinary conditions (Turner & Killian, 1957).

The final kind of individual reaction found by Killian and Turner is the fear. A critical situation is known to pose as a threat to the individual's life or values. Thus, fear is the most common reaction in panic situations, even if such situation is not real.

Fear can be shown in many ways, from internal changes in the emotional and psychological state up to despair, whimper and foray, and it increases whenever the danger is unknown. Uncertainty leads to insecurity since the person does not have enough information to take the right decision in the new context. A person is less afraid of a dangerous situation than the lack of information of the present condition and its uncertainty (Turner & Killian, 1957).

Panic in Crowds phenomenon has been studied by many researchers, mostly to understand its inner workings and specially to prevent the dangerous events to start it or to alleviate its effects if it is unpredictable. Enrico Quarantelli is a researcher that provided some essays about disasters and panic in crowds' phenomena.

In (Quarantelli, 1975) Quarantelli identified a certain set of prejudgments related to how people observe the crowds' behavior in panic situations:


These prejudgments are passed to the safety and damage control personnel, such as firefighters, police officers, public managers, among others. For example, the fear of inducing panic just by informing people about the hazardous event could be more dangerous than the life-threatening event itself. Even with relevant and crucial information for crowd control and to minimize material and human losses, the fear of generate more panic could block the right actions at the appropriate time, which in a panic situation could be disastrous. For Quarantelli, the mere mention of a dangerous situation does not trigger or amplify the crowd's panic state (Quarantelli, 1975).

In spite of what was proposed by the early researchers of collective behavior such as Gustave Le Bon, the human behavior during crisis is controlled instead of impulsive, it uses the right means to achieve its goals and it is organized and functional most of the time. However, that does not mean that an irrational behavior is avoided during the crisis; the incidence of such behavior is lower than what was intuitively observed.

Just like the other collective behavior and panic researchers, Quarantelli also provided the panic's main features, based on his studies and the analysis of other studies from Japan, France and England, and they are the following:



 

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patterns, as in the induction process.

**2.2.1 How a simulation is designed**

be impossible, impractical or hazardous.

section.

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Fig. 1. Blumer's Collective Behavior Stages (McPhail, 1989).

 

 

Simulating Collective Behavior in Natural Disaster Situations: A Multi-Agent Approach 443

 


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on-the-fly modifications, everything must be tested and checked beforehand.

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mission was performed. Since the mission posed a great risk and there was no much room for

In Ruas et al. (2011) simulation (especially multi-agent based simulation) is regarded as a third way of doing science. While induction studies the whole by a sample, deduction does the opposite. Simulations get the best of induction and deduction at the same time: the general and macro-level of a process provides the framework, while the interactions among simulation elements show the micro-to-macro transition and the emergence of behavioral

Throughout this section, the simulation process is described. The focus will be on the multi-agent based simulation, which will be applied in the model presented in the next

The design of a simulation is the building of a model that will be able to mimic the operational and dynamic features of a real system. This model allows a deeper study of the system in a controlled and isolated context Zeigler et al. (2000). This usually poses as a requirement for some systems since the analysis and observation of certain phenomena and their activities can

There are two major approaches for computer simulations. The first approach uses differential equations and other mathematical formulas to build the simulation model. The simulation execution becomes the evaluation of such formulas and the iterative resolution of the

 

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• The members of the collectivity define the situation as dangerous and identify a direct threat for their survival (Quarantelli, 1975).

Quarantelli stressed that individuals keep their rationality and sociability during their escape from hazardous places: they avoid obstacles and other people as much as possible. The individual still can force his way over the others, but that will happen only in extreme conditions (Quarantelli, 1975).

This chapter will present a simulation model for panic in crowds phenomena based on the symbolic interactionism approach. The panic phenomenon works as follows.

Initially, people are in an **ordinary condition**. In that condition, social structures and norms are lined up to what is accepted by society. At the moment disarray in the established social structure is noticed, individuals start feeling uneasy and apprehensive, trying to understand the ambiguous situation that occurred. A disturb is an event that shows itself as an imminent threat to the individual's life, such as a fire alarm, a smoke cloud or objects falling from the shelves, and such event calls up the person and compels him to act, leading to a **social unrest**.

After that, the persons search information that could help them in redefining the present context. They become more likely to rumors because of the feeling of uncertain and insecurity. The conventional behavior starts to break down. The need to comprehend the situation increases, so they engage in a **milling** process, watching the other individuals' reactions and comparing those reactions with your own set of expectations. Also, a need for a sanctioned and socially-built meaning arises into a relatively non-structured situation (Turner & Killian, 1957). Milling is substantial since it makes the individual focused to the situation and the actions performed by the collectivity, removing the focus out of him. Due to the fact that the focus now lies on them, the individuals reply faster and directly to each other, setting up the environment for the shaping of a shared knowledge of what is happening. From that point, the collective enters the **collective excitement** stage, when the group blends and synthesizes the personal representations, helping in the formation of a collective representation/image of the situation. The individual's susceptibility is enhanced by this shared representation, which also decreases his capability of making distinct impressions from the collectivity.

Thus, the individual could follow a socially forbidden line of conduct that he could not conceive and perform, such as pushing and running over people. **Social contagion** starts as an intense form of collective excitement, it starts fomenting a fast propagation of the collectively formed representation, strengthens the social cohesion and prepares the crowd for a collective action. Finally, after a collective representation of the situation is built by the individuals, it is possible to pick an action and execute it. Up to this moment, the collective crisis started by a struggle for survival comes to an apex, and the **collective panic** is installed. Considering that the crowd members do not share conventional expectations about how they are supposed to behave, the outcomes are uncertain. Figure 1 shows an overview of these stages.

#### **2.2 Multi-agent based simulation: Usage and features**

A simulation is the representation of a contextualized system into another context. This description applies to any kind of simulation, not just computer simulations. The Apollo space mission had applied simulations to evaluate techniques and devices before the real 8 Will-be-set-by-IN-TECH

• The members of the collectivity define the situation as dangerous and identify a direct

Quarantelli stressed that individuals keep their rationality and sociability during their escape from hazardous places: they avoid obstacles and other people as much as possible. The individual still can force his way over the others, but that will happen only in extreme

This chapter will present a simulation model for panic in crowds phenomena based on the

Initially, people are in an **ordinary condition**. In that condition, social structures and norms are lined up to what is accepted by society. At the moment disarray in the established social structure is noticed, individuals start feeling uneasy and apprehensive, trying to understand the ambiguous situation that occurred. A disturb is an event that shows itself as an imminent threat to the individual's life, such as a fire alarm, a smoke cloud or objects falling from the shelves, and such event calls up the person and compels him to act, leading to a **social unrest**. After that, the persons search information that could help them in redefining the present context. They become more likely to rumors because of the feeling of uncertain and insecurity. The conventional behavior starts to break down. The need to comprehend the situation increases, so they engage in a **milling** process, watching the other individuals' reactions and comparing those reactions with your own set of expectations. Also, a need for a sanctioned and socially-built meaning arises into a relatively non-structured situation (Turner & Killian, 1957). Milling is substantial since it makes the individual focused to the situation and the actions performed by the collectivity, removing the focus out of him. Due to the fact that the focus now lies on them, the individuals reply faster and directly to each other, setting up the environment for the shaping of a shared knowledge of what is happening. From that point, the collective enters the **collective excitement** stage, when the group blends and synthesizes the personal representations, helping in the formation of a collective representation/image of the situation. The individual's susceptibility is enhanced by this shared representation, which

symbolic interactionism approach. The panic phenomenon works as follows.

also decreases his capability of making distinct impressions from the collectivity.

behave, the outcomes are uncertain. Figure 1 shows an overview of these stages.

**2.2 Multi-agent based simulation: Usage and features**

Thus, the individual could follow a socially forbidden line of conduct that he could not conceive and perform, such as pushing and running over people. **Social contagion** starts as an intense form of collective excitement, it starts fomenting a fast propagation of the collectively formed representation, strengthens the social cohesion and prepares the crowd for a collective action. Finally, after a collective representation of the situation is built by the individuals, it is possible to pick an action and execute it. Up to this moment, the collective crisis started by a struggle for survival comes to an apex, and the **collective panic** is installed. Considering that the crowd members do not share conventional expectations about how they are supposed to

A simulation is the representation of a contextualized system into another context. This description applies to any kind of simulation, not just computer simulations. The Apollo space mission had applied simulations to evaluate techniques and devices before the real

threat for their survival (Quarantelli, 1975).

conditions (Quarantelli, 1975).

Fig. 1. Blumer's Collective Behavior Stages (McPhail, 1989).

mission was performed. Since the mission posed a great risk and there was no much room for on-the-fly modifications, everything must be tested and checked beforehand.

In Ruas et al. (2011) simulation (especially multi-agent based simulation) is regarded as a third way of doing science. While induction studies the whole by a sample, deduction does the opposite. Simulations get the best of induction and deduction at the same time: the general and macro-level of a process provides the framework, while the interactions among simulation elements show the micro-to-macro transition and the emergence of behavioral patterns, as in the induction process.

Throughout this section, the simulation process is described. The focus will be on the multi-agent based simulation, which will be applied in the model presented in the next section.

#### **2.2.1 How a simulation is designed**

The design of a simulation is the building of a model that will be able to mimic the operational and dynamic features of a real system. This model allows a deeper study of the system in a controlled and isolated context Zeigler et al. (2000). This usually poses as a requirement for some systems since the analysis and observation of certain phenomena and their activities can be impossible, impractical or hazardous.

There are two major approaches for computer simulations. The first approach uses differential equations and other mathematical formulas to build the simulation model. The simulation execution becomes the evaluation of such formulas and the iterative resolution of the

affect the group and, likewise, how the group itself affect these components. The analysis of the situation implies the analysis of the environment where the agents are located, the decisions taken by those agents, how such decisions affect the environment and the other agents and how the groups of agents can affect the agents' internal attributes dos

Simulating Collective Behavior in Natural Disaster Situations: A Multi-Agent Approach 445

The multi-agent model for the panic in crowds phenomenon described in Section 3 belongs to the social-cognitive model class David et al. (2004) because such models have their focus on formalization and testing of theories, models and hypothesis related to theoretical-structural aspects of social systems. The main concern in this class of simulation models is the dynamic behavior of the simulation instead of an exact and perfect outcome analysis. For this class, the straight comparison of the simulation outcome and some empirical data could render pointless because the target system cannot be fully represented in any form, especially if the system is complex. Therefore, the subject of study of the panic model described in Section 3

1. To propose new structures or replacements for social systems, checking their viability and

2. To get a better understanding of the social, psychological and anthropological bases which sustain and direct the panic collective behavior dos Santos França (2010); dos Santos França

The multi-agent based simulation models share some common features. The model has autonomous and heterogeneous, they are not under a central authority's orders because they

The agents are in an environment that encourages the interaction among agents so that the model can fulfill its main goal: to be open to the emergency of phenomena due to the interaction among agents and the environment, which makes the multi-agent based simulations work as complex systems. A system is said to be "complex" if its overall behavior cannot be described by just looking at its inner elements' behaviors. In order to understand a complex system's behavior, the observation of the emerging patterns created by the agents'

The following list has some situations which the agent-based models are more suitable for

1. When there is a substantial need to design heterogeneous agents populations, and such heterogeneity enables the modeling of agents with rationality and clear and distinct

2. Every time the agents' interactions are discontinuous, non-linear such as the individuals'

3. Whether the agents' interactions' topology presents itself as heterogeneous and complex, such as the social processes, in specific the inherent complexity of the physical and social

complex behavior, which make the process harder for classical analytic ways;

matches the structural logic of the target system and it works in two dimensions:

are built to be self-organized and with local interaction rules.

watching the emergent behavior da Silva et al. (2008):

Santos França (2010).

working;

et al. (2009).

**2.2.3 Conceptual model**

interactions is required.

behaviors;

networks.

differential equations. Such approach is named analytic and it has its value and it is quite practical and useful for certain applications. However, it usually lacks a detailed vision of what happened, working as a "black box". For some simulations, this is not an issue because the only thing that matters is the final result and not the mid-steps required to achieve it. Also, this sort of simulation usually deals with a continuous stream of time. Since there is no need to observe the simulation's inner steps, a continuous approach is more logical.

On the other hand, a second approach for simulations uses a set of autonomous modules (programs) called agents. The resemblance of agent based technologies and a realistic social system model has created a new scientific field with a strong emphasis on the interdisciplinary called Multi-Agent Based Simulation (MABS) Cohen & Felson (1979). It is a collective effort to integrate scientific areas and the usage of computational technologies that were previously applied to other tasks, such as networking. The main purpose of MABS researchers is to create and study computational models for simulation taking the technical and theoretical infrastructure of the Distributed Artificial Intelligence into consideration.

Based on such approach, the simulation model represents a specific target system that allows (i)the observation and study of the global behavior of the modeled system under certain criteria and (ii) the analysis of the consequences of the changes in the system's internal components Gilbert & Terna (2000), which implies that MABS can be used to detect emergent patterns and how changes interfere on the agents' behavior. Ruas et al. (2011).

#### **2.2.2 Agent and multi-agent based simulations**

A specific definition of Agent describes it as a discreet entity with its own goals and behaviors, and also internal states and behavior rules that allow the interaction with the other agents and with the environment. Another definition can be found in Russell & Norvig (2004), and states that "*An agent is anything able to perceive the environment through sensors and to act upon the environment by actuators*". Once more, the emphasis lies on the agent, the environment and the relationship between them. Whatever entity that needs to be considered in the simulation by its autonomy, by its independence in the decision making and by its ability to interact in the environment can be seen as a simulation agent dos Santos França (2010).

Agents must have autonomous actions, and such actions must happen synchronously with an event-based time scheduler, that will serve as an observer and a time and step manager along with the agents.

The main concept behind a Multi-agent simulation model is to simulate an artificial world which is made of computational interactive entities. Simulation is then created by the transposition of entities (or sets of entities) and the interaction among such entities from the target system to the artificial world Dimitrov & Eriksen (2006).

The multi-agent based simulations have an adequate infrastructure for modeling, studying and understanding the process related to complex social interactions such as coordination, collaboration, group formation, conflict solving, among others. Thanks to the relationship between local and global behaviors and the analysis of the agents' influence over themselves and the environment, it is possible to analyze the social interactions, which leads to cause-effect relations of how agents' components affect their behavior, how such behavior affect the group and, likewise, how the group itself affect these components. The analysis of the situation implies the analysis of the environment where the agents are located, the decisions taken by those agents, how such decisions affect the environment and the other agents and how the groups of agents can affect the agents' internal attributes dos Santos França (2010).

The multi-agent model for the panic in crowds phenomenon described in Section 3 belongs to the social-cognitive model class David et al. (2004) because such models have their focus on formalization and testing of theories, models and hypothesis related to theoretical-structural aspects of social systems. The main concern in this class of simulation models is the dynamic behavior of the simulation instead of an exact and perfect outcome analysis. For this class, the straight comparison of the simulation outcome and some empirical data could render pointless because the target system cannot be fully represented in any form, especially if the system is complex. Therefore, the subject of study of the panic model described in Section 3 matches the structural logic of the target system and it works in two dimensions:


#### **2.2.3 Conceptual model**

10 Will-be-set-by-IN-TECH

differential equations. Such approach is named analytic and it has its value and it is quite practical and useful for certain applications. However, it usually lacks a detailed vision of what happened, working as a "black box". For some simulations, this is not an issue because the only thing that matters is the final result and not the mid-steps required to achieve it. Also, this sort of simulation usually deals with a continuous stream of time. Since there is no need

On the other hand, a second approach for simulations uses a set of autonomous modules (programs) called agents. The resemblance of agent based technologies and a realistic social system model has created a new scientific field with a strong emphasis on the interdisciplinary called Multi-Agent Based Simulation (MABS) Cohen & Felson (1979). It is a collective effort to integrate scientific areas and the usage of computational technologies that were previously applied to other tasks, such as networking. The main purpose of MABS researchers is to create and study computational models for simulation taking the technical and theoretical

Based on such approach, the simulation model represents a specific target system that allows (i)the observation and study of the global behavior of the modeled system under certain criteria and (ii) the analysis of the consequences of the changes in the system's internal components Gilbert & Terna (2000), which implies that MABS can be used to detect emergent

A specific definition of Agent describes it as a discreet entity with its own goals and behaviors, and also internal states and behavior rules that allow the interaction with the other agents and with the environment. Another definition can be found in Russell & Norvig (2004), and states that "*An agent is anything able to perceive the environment through sensors and to act upon the environment by actuators*". Once more, the emphasis lies on the agent, the environment and the relationship between them. Whatever entity that needs to be considered in the simulation by its autonomy, by its independence in the decision making and by its ability to interact in the

Agents must have autonomous actions, and such actions must happen synchronously with an event-based time scheduler, that will serve as an observer and a time and step manager along

The main concept behind a Multi-agent simulation model is to simulate an artificial world which is made of computational interactive entities. Simulation is then created by the transposition of entities (or sets of entities) and the interaction among such entities from the

The multi-agent based simulations have an adequate infrastructure for modeling, studying and understanding the process related to complex social interactions such as coordination, collaboration, group formation, conflict solving, among others. Thanks to the relationship between local and global behaviors and the analysis of the agents' influence over themselves and the environment, it is possible to analyze the social interactions, which leads to cause-effect relations of how agents' components affect their behavior, how such behavior

to observe the simulation's inner steps, a continuous approach is more logical.

infrastructure of the Distributed Artificial Intelligence into consideration.

patterns and how changes interfere on the agents' behavior. Ruas et al. (2011).

environment can be seen as a simulation agent dos Santos França (2010).

target system to the artificial world Dimitrov & Eriksen (2006).

**2.2.2 Agent and multi-agent based simulations**

with the agents.

The multi-agent based simulation models share some common features. The model has autonomous and heterogeneous, they are not under a central authority's orders because they are built to be self-organized and with local interaction rules.

The agents are in an environment that encourages the interaction among agents so that the model can fulfill its main goal: to be open to the emergency of phenomena due to the interaction among agents and the environment, which makes the multi-agent based simulations work as complex systems. A system is said to be "complex" if its overall behavior cannot be described by just looking at its inner elements' behaviors. In order to understand a complex system's behavior, the observation of the emerging patterns created by the agents' interactions is required.

The following list has some situations which the agent-based models are more suitable for watching the emergent behavior da Silva et al. (2008):


The validation process aims to certify that the conceptual model represents the target system in an acceptable degree of adherence. Thus, the validation processes fundamentally addresses a specific question: Does the simulation outcomes correspond to those from the target system? On the other hand, the verification process' main purpose is to assure that the conceptual model was correctly translated to the computational environment. Specifically, a multi-agent simulation model is based on the concept that it is feasible to simulate an artificial world inhabited by interactive computational entities. Such simulation can be achieved by transposing the population from a target system to its artificial counterpart. In that sense, an agent is similar to an entity or a group of entities of the target system. Moreover, agents can be of distinct natures and granularities, such as human beings, robots, computer algorithms,

Simulating Collective Behavior in Natural Disaster Situations: A Multi-Agent Approach 447

In order to build a conceptual model for the panic in crowds' phenomenon the following

2. Three environments (General, Physical, Communication) where the interactions' main

3. A socially built system - Collective Mind - that describes how individual representations are transformed and synthesized by the group so they form a shared context (dos

This model proposes the interactionism approach presented by authors such as Blumer (Section 2.1.3). A generalized flow based on that theory is shown in Figure 2. It is worth noticing that the exhibition of the steps is in a sequential order for didactical purposes. However, it is possible that a person follows a distinct order, not performing some steps or

This element represents a general overview of the environment where all the interactions among agents will happen, and it has the Physical Environment, the Communication Environment and the Collective Mind. Its purpose is defining the boundaries of the other environments and their linking points. Figure 3 shows the proposed diagram for the

The Physical Environment describes the space where the physical interactions among agents occur, as well as the interactions between the agents and the other objects such as obstacles and walls. There are specific spots for the threat and the exits. Figure 4 shows this environment

1. The architecture of the agent that represents a person in a panic situation;

inanimate objects and organizations. (Ruas et al., 2011)

**3.1 From theory to practice: Conceptual model**

elements will be discussed:

Santos França et al., 2009).

aspects happen;

repeating others.

**3.1.1 Model's environments** 3.1.1.1 General environment

relationship of these elements. 3.1.1.2 Physical environment

**3. A simulation model for panic in crowds phenomenon**
