Starting from the established and common principles of the terrorism threat in the cities, this chapter presents the results of the phenomenological analysis in Europe and reorganizes the main literature and international experiences in the prevention, mitigation, and management of the threat in the built environment in order to delineate the factors that influence the risk of outdoor Open Areas (OAs) as “soft targets”. In fact, if several previous experiences have already investigated the effects of events on people involved, the strategies used by perpetrators and tested mitigative strategies in detailed case studies following an “a posteriori” approach, a unique approach to describe and discuss the risk of OAs seems to be still unexplored. The aim is thus reached by merging two levels of details. I) The assessment of events during the last 20 years in Western Europe allows to understand how (the attack type) and why (which uses affect the likelihood of events) OAs are emergent “soft targets”. On the other hand, II) the critical categorization of Risk Mitigation and Reduction Strategies already experimented and regulated in the international panorama helps in highlighting how such soft targets can be physically improved towards resilient parts of the cities.
2.1 Terrorist Threat in the European Urban Built Environment: Understanding Levels of Riskiness in Outdoor Open Areas Using Risk Matrix
In the extensive range of risks to which the urban built environment (BE) is exposed, terrorism is classified as a Sudden Onset Disaster (SUOD), caused by human will. Unlike those generated by natural processes, terrorism is driven by the ideology of a political or religious movement and aims to instil fear and destabilize a community through hostile and violent actions carried out on symbolic targets with high media impact. However, while radicalism constitutes the driving force behind the goals of violent actions, recent studies on terrorism have highlighted the high variability in the modus operandi of terrorist acts, requiring specific analyses at a macro-territorial scale for understanding events [1]. This variability is not only influenced by pre-existing political, social, and/or cultural relations between the attacking nations and the radicalist matrix but also considers the possibilities of weapons procurement and the feasibility of the attack in relation to specific protection and security measures in place. It is not coincidental that counterterrorism actions operate at the national level with evident variability even on an international scale [2].
On the other hand, as suggested by the latest events in Europe, outdoor Open Areas (OAs) are commonly described as “soft targets” as a consequence of the lower levels of protection usually present in such places [3]. However, when the focus is on the OAs as a system of infrastructures, buildings, un-built areas, and users, it is necessary to understand how their uses can influence the global riskiness of the OAs themselves and as a whole.
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Due to these points of discussion and coherently with the common strategies for understanding complex issues, an analysis of previous historical events is required to describe the threat quantitively. In detail, to support this aim a phenomenological analysis of the violent events is carried out aiming at solv-ing the following goals:
Determine the most frequent and riskiness scenarios in the urban BE considering homogeneous classes of uses of places and buildings and the weapon types to provide if some uses can alter the inherent level of proneness of OAs (Goal 1—G1)
Identify the most relevant (in frequency and efficaciousness) weapon types in increasing the global riskiness of places considering the uses of buildings facing the OAs, in order to delineate dominant traces to focus on for OAs (Goal 2—G2)
The analysis of the phenomenon is focused on Western European countries, in view of the significant relevance of the phenomenon and to the recent development of guidelines on the matter [3]. Specifically, the analysis starts from a discretization process of the urban BE and the weapon types applied to recent violent acts in the European territory.
2.1.1 The Discretization of the Terroristic Phenomenon in the Outdoor Open Areas Within the GTD Database
Coherently with the goals of the analysis, the terroristic phenomenon in Western Europe is pursued by means of the analysis of the recorded traumatic occurrences catalogued in the Global Terrorism Database (GTD)™. It is the most complete and extended database for terroristic events worldwide thanks to the interpolation of research actions, taxonomy, and cataloguing activities of the National Center for the Study of Terrorism and Responses to Terrorism (START), established in the University of Maryland. The START activities aim at merging previous databases and enriching them coupling external data (articles, legal documents, etc.) in order to obtain a coherent and structured collection of details. The first attacks that appear in the GTD refer to the period between 1970 and 1997 and were collected by a private security agency, the Pinkerton Global Intelligence Service (PGIS). The digitization process of information, collected by START, continued with the collaboration of the Center for Terrorism and Intelligence Studies (CETIS). It expanded the quantity of information of each attack, beyond 1997. From 2008 to 2011, the data and information search were carried out by the Institute for the Study of Violent Groups (ISVG). The University of Maryland continued the research until 2020, structuring the database coherently with a rigid set of criteria, which involves geographical data (e.g., coordinates, country, city), the date of the terrorist event and details about the cruel events (attack type, type of weapon and numbers, target type, information on perpetrators, causalities). In that sense, the parametrization of criteria and data are the basic conditions to explore the phenomenological analysis of the terroristic events in Europe—and specifically in its western part—adapting them coherently with the goals of the analysis. In fact, the focal point involves the systematic correlation of data pertaining to event frequency and their ensuing consequences, deriving information and details about OAs, in terms of matrices of risk.
However, in order to take adherent information about terroristic events in Western Europe related to the OAs, the target information within the GTD database has been re-elaborated highlighting the events users and space targeted. Specifically, six macro-classes of uses of the built environment (CBE) are derived from the classification within the events recorded in the database, while all the attacks oriented to people are excluded. The process of classification of the BE results in the detailed classes summarized in Table 2.1, where similar uses of buildings can be recognized. In addition, the criterion of the attack type in the database has been preserved in order to discuss the weapon types. In this case, eight typologies are identified and summarized in Table 2.2.
Table 2.1
Details of the classes of built environment (CBE) considered in the parametrization
Code of CBE
Class of built environment
A
Transportation infrastructure (airport, docks, metro, and rail stations)
B
Public buildings with entertainment uses (theatres, museums, bars, restaurants, hotels, shopping centres)
C
Hospitals, schools, universities
D
Representative (symbolic) or strategic buildings
E
Residential buildings and industries
F
Public un-built areas, squares, and streets
Table 2.2
Codification of the attack types coherently with the “attack information” of the GTD
Code
Description
T1
Assassination
T2
Armed assault
T3
Bombing/Explosion
T4
Hijacking
T5
Barricade incident
T6
Kidnapping
T7
Facility/Infrastructure attack
T8
Unarmed assault
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On the other hand, the consequences related to the effects of the violent acts are obtained considering the number of injured persons and victims.
2.1.2 The Frequentistic Analysis of the Terroristic Phenomenon in Western Europe: From the Built Environment to the Outdoor Open Area Scale
The applied method for the comprehension of the terrorism phenomenon in Western Europe is underpinned by the construction of risk matrices derived from the combination of:
The frequentistic probability (PF), representing the outcomes of event observation (the ratio between the number of occurrences of a specific event type and the total number of events).
The consequences (C) in terms of damage, evaluated as the cumulative sum of injured individuals and victims, excluding the details about building damages.1
Then, PF and C values are translated into homogeneous classes of “likelihood” and “consequences” considering the medium value of data as central descriptors of the phenomenon and distributing minimum and maximum values within the five classes. Finally, the resulting matrices summarize the levels of likelihood and consequences within defined ranges of PF and C, offering a rapid reading of common recurrences in the phenomenon. It is in line with an “a posteriori analysis” of a general phenomenon usually used for risk assessment [4, 5].
The phenomenon is thus focused on a representative sample of events. The period of attention is referred to 2001–2020, in order to consider the Twin Tower attack (11th September 2001) as a breaking event towards the current concept of terroristic threat in a significant extension of the period (20 years). The selection of events for the phenomenological analysis is summarized in Fig. 2.1, where the number of events is details, too. Moreover, due to the goals of the phenomenon reading (G1 and G2), the analysis has been specified following two levels of detail:
A flow diagram. G T D whole sample of terrorist attacks from 2001 through 2020 in Western Europe is 3530. The absorted events are 855. The success events include targets referred to B E of 1655 and specific targets of 1020. The targets referred to O As are 794.
Fig. 2.1
Process of selection of events for the samples, detailed for GTDBE2001–2020 and GTDOutBE2001–2020
The first focuses on the whole set of events that occurred in Western Europe BEs during the selected period (GTDBE2001–2020).
The second concerns the events that occurred outside the buildings, to relate the inherent proneness of squares and streets to the uses of buildings (GTDOutBE2001–2020), which counts approximately 50% of the whole one.
×
The results of the phenomenon analysis of the BE controlled by attack types and CBEs have shown two main data:
An attack type is mainly pursued every week in the BE of Western Europe.
The main value of the consequences for the whole set of violent events counts three people (victims and injured).
Thus, by combining the main values for the identification of the levels of likelihood and consequence (Tables 2.3 and 2.4), the risk matrix has been set up to discuss the terroristic phenomenon in the BE of Western Europe, assuming values from 1 to 5 to each level of likelihood and consequence and calculating the final classes of risks (PF x C) in coherence with Fig. 2.2.
Table 2.3
Likelihood levels determined for classes of values of PF referred to the period (7300 days) and extended description
Likelihood levels
PF range
Description
Very likely
x > 50%
Until 1 event per day
Likely
14.25% < x ≤ 50%
Until 1 event per 2 days
Possible
3.3% < x ≤ 14.25%
Until 1 event per week
Unlikely
0.3% < x ≤ 3.3%
Until 1 event per month
Remote
x ≤ 0.3%
Until 1 event per year
Table 2.4
Consequence (C) levels determined for classes of values of people involved in the violent acts, considering the sum of injured people and victims
Consequence levels
n. of people involved (injured and victims)
Extreme (Ex)
x > 3 × 103
Major (Ma)
3 × 102 < x < 3 × 103
Medium (Me)
3 × 101 < x < 3 × 102
Moderate (Mo)
0 < x ≤ 3 × 101
Minor (Mi)
x = 0
A table depicts risk levels and their range of risk values. The risk levels are very high, high, medium, and low. Very high has a range of greater than 15 and less than 25.
Fig. 2.2
Classes of risk levels identified for the BE in Western Europe
×
The resulting risk matrix (Fig. 2.3) highlights four conditions of particular interest. Regarding public open spaces, and thus OAs (CBE F), a medium to high-risk exposure for T2 (armed assault) and T3 (bombing/explosion) attacks is evident, driven by the elevated probability of occurrence (T3) and the generated impact (T2 and T3). Compared to the CBE B, events in this context exhibit high hazard due to prevalent recurrence and effect in combination with T2 and T3 attack types. This is attributed to the intrinsic nature of all public buildings (pubs, museums, etc.) falling under this environmental class, typically characterized by low control levels.
A table depicts consequence levels including minor, moderate, medium, major, and extreme in the columns, and likelihood levels including remote, unlikely, possible, likely, and very likely in the rows.
Fig. 2.3
Matrix risk of the terroristic phenomenon in BE of Western Europe (reference sample GTDBE2001–2020). Cells combine the CBE and attack type classification according to Tables 2.1 and 2.2 (void cells imply that no specific combination is present), respectively, while colours refer to Fig. 2.2
×
Events occurring in the CBE D (representative or strategic buildings) constitute an intermediate condition with significance in combination with T3 attacks. However, this highlights the greater feasibility of events occurring outside these buildings.
Lastly, airports and railways constitute the CBE A intrinsically more critical due to the potential crowd density, resulting in a high-risk value due to a combination of the number of involved users and the low frequency of events.
However, this corresponds to the highlighting of two fundamental aspects. The first is related to the high susceptibility of open and public spaces characterized by low strategic relevance to undergo an attack. This is in line with the intrinsic definition of soft targets, where confined and non-confined spaces are not easily predisposed to violent acts due to the absence of control and protection systems, regardless of the number of users.
Therefore, CBE A can be excluded from the evaluation, considering the high crowding levels of users and the presence of protection and control systems, which configure it as a hard target. The second aspect is instead related to the specificities of the identified attack locations for CBE D. The use of vehicles as a tool for perpetrating violent acts highlights that the relevance of such events should not only be assessed as acts of high symbolism towards the building and the users within that confined space but also extends to the external environment. In fact, this confirms the necessity of analysing the OAs as a complex system of buildings, infrastructure, open space, and users.
Based on these considerations, the second level of analysis of the phenomenon was led on the reduced sample (GTDOutBE2001–2020), following the same frequentistic details (Tables 2.3, 2.4, Fig. 2.3) to determine the matrix of risk for OAs. However, only events that occurred outside of CBEs D and B are considered, being part of OutBE classes, since they are correlated to events that occurred outside the buildings to relate the inherent proneness of squares and streets to intended uses of buildings.
Due to their connection with OAs (CBE F in Table 2.1), these classes are herein considered in a systemic way with F one (FB, FD, F). Therefore, the matrix of risk for OAs, summarized in Fig. 2.4, is based on the significance of these three OutBE classes, combined with two main attack types. Specifically, T2 and T3 result in all combinations being classified as high (FB/T2, FD/T2, FB/T3, FD/T3, F/T3) or very high (F/T2) risk levels. The reason for their heightened risk lies in the higher consequence levels, which are directly influenced by the likelihood of these areas being crowded.
A table depicts consequence levels including minor, moderate, medium, major, and extreme in the columns, and likelihood levels including remote, unlikely, possible, likely, and very likely in the rows.
Fig. 2.4
Matrix risk of the terroristic phenomenon in OAs of Western Europe (reference sample GTDOutBE2001–2020). Cells include attack type classification according to Tables 2.1 and 2.2, respectively, while colours refer to Fig. 2.2
×
In addition, five main results can be summarized for OAs, merging the quantitative results with the principles of the phenomenon (TP—Chap. 1, Sect. 1.1), as follows:
1.
F and FB are found to be more vulnerable than FD (strategic and symbolic ones) due to their distinct “protection and security systems” that serve as a lesser deterrent (Inter-dependence and replacement of targets, TP.3).
2.
The significance of T7 in strategic and symbolic areas reflects the symbolic importance of FD, where attacks target the environment itself (“Publicity Impact is Key to Targeting” TP.2).
3.
T2 and T3, being the most frequent attack types, align with the principle that guides the choice of weaponry by terrorists (weaponry characterization TP.4).
4.
T2 and T3 represent the most utilized attack types combining the lower level of resistance in perpetrating the violence (TP.1—micro-terror), and consequently, they generate the most significant impacts.
5.
The amplification of impact is particularly pronounced in the FB OutBE Class. In contrast to FD, which has a higher level of openness due to the need for visibility, the presence of obstacles in FB can impede escape and decrease overall resilience (TP.3—soft targets).
2.2 Secure Urban Built Environment Prone to the Terrorism Threat: The Risk Mitigation and Reduction Strategies
As introduced in the previous sections, the focus of terrorist risk lies in the will of those planning and executing the event to commit a violent act towards crowds and significant locations. However, considering the complexity of urban BEs, it is evident that all the events impact the crowd that experiences the event.
If the phenomenological analysis supports the comprehension of the violent acts in the pre-event phase, the reading and systematization of the international experiences and regulation framework support the knowledge about the relationship between urban users and the physical place and its elements for their risk reduction, mitigation, and management. Specifically, the analysis and assessment of the so-called Risk Mitigation and Reduction Strategies (RMRS) allow the comprehension of (i) interferences of the physical space and all its elements with the choice phases (mode and location of the attack), (ii) risk reduction, and (iii) emergency management processes.
2.2.1 Classification of Risk Mitigation and Reduction Strategies in the Built Environment: An International Overview
Starting from the analysis of the main national guidelines and American and European regulations for increased sensitivity to the topic, it is possible to classify RMRS according to five specific criteria:
The type of target (target-oriented strategies) [6, 7], taking into account the classification already introduced between hard and soft targets. Moreover, this criterion distinguishes RMRS based on the varying level of public area accessibility, restricting the perpetrator's proximity to the sensitive target (human-to-event). A secondary division pertains to potential interactions with users, distinguishing between active actions (generating a bi-univocal relation between overarching governance and urban users in prevention processes such as intelligence, active user education, and security surveillance) and passive actions (application of predefined instructions, e.g. regulatory norms, risk communication, urban space redesign).
The types of attack (attack-oriented) [8, 9], where the definition, selection, and organization of RMRSs may involve simple or complex control and management systems for public space or sensitive buildings, depending on the possible or anticipated modus operandi, as well as their effectiveness concerning space configuration and predisposition to attack.
The event timings (time-dependent classification) [10, 11], where, coherently with the times of risk, RMRSs are classified with a focus on prevention (pre-event) or management (post-disaster) capabilities, also in relation to potential attack modalities. The perpetrator's operational approach can significantly impact the choice of RMRSs and predict possible human-to-event and event-to-user interactions (e.g. intervention times for video surveillance activities or first responder actions).
The morphology and nature of the BE [12, 13], consistently with principles outlined in Chap. 1, Sect. 1.1, a terrorist act may target a specific part of public space, necessitating diverse distribution of RMRSs throughout the entire built sector in which the target is situated (e.g., a car bomb attack in areas characterized by varying vehicular accessibility). This includes design strategies for “zones” or “defence areas”, recognizing the boundary (a) externally locating all physical barriers and control systems for entire areas characterized by high vulnerability; (b) intermediate, aiming to limit and protect areas or objects within the physical boundary of OAs; (c) internal, referring to the envelope of the vulnerable, sensitive, or strategic building, or areas within them (core) when identified as primary targets of the attack.
Physical or managerial purposes [14, 15] according to which, RMRSs can be geared towards risk reduction or emergency event management, focusing on physical interventions in the urban BE and its sub-parts. Additionally, in relation to the first, attention is directed to coordination and management with strategies related to planning, regulation, as well as user education and risk preparedness to maximize effectiveness.
A second level of categorization relates the elements constituting the BE and RMRSs, focusing on the design by users responsible for urban security. Literature and supporting regulations allow the recognition of four macro-classes of RMRS design (S1, S2, S3, S4), comprising specific physical elements in the BE and its layout. These are appropriately integrated with systems for access control, surveillance, and the management of safety and user protection within it. Specifically, these are referred to:
S1.The design of the physical elements. Perimeter design [S1.1] and secure envelope [S1.2] [12, 15, 16] are addressed for open spaces requiring heightened levels of security and well-being for users; perimeter design incorporates effective mitigative systems evaluated for impact resistance, geometric efficacy concerning accessibility (for T3 attacks), and compatibility with emergency evacuation flows; when the target is confined to a specific element of the built space, the discussion revolves around the building envelope, particularly concerning explosion dynamics.
S2.The design of BE layout, combining physical elements [S2.1] and layout geometries [S2.2] [15, 16], aims at identifying and creating secure external (standoff) or internal (sheltering) spaces during emergency events by combining physical elements with risk management tools, such as the design of emergency plans [S2.3] [17, 18].
S3.Pursuing the access control [S3.1] and surveillance [S3.2] [12, 15, 19, 20]; these are predominantly used in managing large events, often combined with perimeter control systems [S1.1], supported by personnel or advanced technologies (body scanners, optical people counting devices, facial recognition in video surveillance). Effective lighting systems [S3.3] [12] are also recognized as necessary to improve visibility and support during emergency evacuations.
S4. Ensure safety and security management [15, 21‐25] by means of several layers of strategies; the use of security personnel [S4.1] as a preventive strategy to deter attacks, support recognition of aggressors, and provide initial aid during and after an attack. This strategy requires broader support, including emergency plan design [S2.3], and, in this context, should be aimed at developing specific issues related to the planning of first aid interventions [S4.2], and their coordination [S4.3]. Finally, the users’ involvement [S4.4] through content sharing on various devices has shown significant benefits in public security management, especially after recent traumatic events in Belgium, France, and Germany.2
2.2.2 The Sustainability of Risk Mitigation and Reduction Strategies in the Built Environment
As it is clear, the multiplicity of guidelines and experiences show the complexity of the design of RMRSs in the BE, which have to ensure preventive actions, facilitate the emergency phases, and guarantee good acceptability by urban users. On the other hand, the design of RMRSs has to face multiple levels of sustainability, including the efficacy towards several attack types and the expected ones, the promotion of redundancy in supporting the risk reduction in all the phases of risk (prevention, mitigation, emergency) [6, 20, 26‐29].
With these purposes, the following Table 2.5 summarizes the critical evaluation in promoting the sustainable design of RMRSs in the BE, focusing on the relations between strategies and the BE. Specifically, starting from the analysis of the efficacy of RMRSs (S1–S4, see Sect. 2.2.1) with the classification of attack types (T1 to T8, see Table 2.2), and the possible levels of coordination among S-classes of strategies, Table 2.5 shows the levels of applicability (for indoor and outdoor places, for their possible conditions of use) and the features which influence costs.
Table 2.5
Analysis of levels of sustainability for RMRS classes to consider in their design
RMRS
Redundancy with attack typologies
Coordination with other RMRS classes
Adaptable for existing BE
Main application context (intended use; overcrowding)
Factors influencing costs
Design of the physical elements of the BE [S1]
Safe
perimeter [S1.1]
T3
S2.1, S3.1
Adaptable, if punctual installations are used
For hard targets, because of their complexity level
Adopted technologies, BE perimeter length
Secure
envelope [S1.2]
T1, T2, T3
S2.2
Usually, they consider new facades, while interventions on openings are more sustainable
For public buildings featuring high crowding levels
Reinforcement typologies for existing openings
technology and extension of facades for new constructions
BE layout [S2]
Standoff [S2.1]
T3
S1.1, S1.2, S3.1
Massive impact is expected when combined with S1.1. Otherwise, adaptable to the existing layout using management actions
Specific for strategic buildings but extendable to soft targets when hosting a high number of visitors
land use costs in guaranteeing the distances, for new constructions
In existing BEs, costs concern the space use management
Sheltering [S2.2]
T2, T3, T8
S2.3, S4.2
Adaptable if limited to shelter areas; not compatible when interventions are applied to facades and structures
Single and strategic buildings with something/
someone to protect
Costs are limited only if intervention is applied to existing shelter areas
Emergency layout [S2.3]
all
S1.1, S2.1, S2.2, S3.1, S4.1, S4.2, S4.3
Adaptable for each situation
Adaptable in each event typology
Width of the emergency area and use of BE
Access control and surveillance in the BE [S3]
Access
control [S3.1]
T1 to T6
S1.1, S2.1, S2.3, S4.1, S4.3
Adaptable due to the possibility to limit areas (i.e. square perimeter)
Useful for events with significant crowding conditions
Number of installed control points
number employed
Security service [S3.2]
T1 to T6
S1.1, S3.1, S3.3, S4.1, S4.2
Adaptable for all the existing BE (including historical) because not invasive installations
Adaptable to all conditions and uses
Width to monitor
Adopted technologies
Illumination [S3.3]
T1, T2, T3, T7
S1.1, S3.1
Adaptable for existing (including historical) BEs with possible restrictions at the technological level (e.g. systems integration/installation)
Adaptable to all conditions and uses
Number of devices
operational and maintenance issues
Safety and security management in the BE [S4]
Security personnel [S4.1]
T1, T2, T3, T4, T5, T6
S1.1, S2.2, S2.3, S3.1, S4.2, S4.3
Adaptable in each condition
Adaptable to all conditions and uses
Building dimensions and floors
In mass gatherings, event area extension and number of participants
First aid [S4.2]
all
S.2.2, S2.3, S4.1, S4.3
Adaptable in each condition
Mandatory for mass gatherings and in hard targets of the BE
Low costs by considering the direct possibility of saving lives
Coordination [S4.3]
all
S2.2, S3.1, S4.1, S4.2
Not dependent on the BE typology
Always necessary in each case
special consideration for hard targets or mass gathering events
employed technology
Users’ involvement [S4.4]
all
S1.2, S2.2, S2.3, S4.1, S4.2,
S4.3
Not dependent on the BE typology
Users should be trained to face disaster in all conditions
Financing informative campaign
Types of guiding tools (e.g.: apps)
Another level of assessment and qualification of RMRSs (for classes and sub-classes) can be related to their interrelations with users in the evacuation processes. The human-centred focus is required to define a set of qualitative screening of potentialities and criticalities of RMRS classes useful in simulation analyses. These should consider, near to the human-to-human interactions (both perpetrator to BE users and among BE users), the interference RMRSs-to-human. As it is clear, two levels of details are discussed for RMRS classes [18, 29‐31]:
The potential interference with behavioural issues;
Their representability in modelling evacuation processes in simulators.
With that aim, Table 2.6 summarizes the critical behavioural design-based analysis of RMRS classes.
Table 2.6
Analysis of behavioural design factors for RMRS classes to consider in their design and evacuation simulation (N.A.: not assessed)
RMRS [code]
Interactions with behavioural issues
Possibility to be represented in crowd evacuation simulators
Design of the physical elements of the BE
Safe perimeter [S1.1]
Barriers ought to be crafted with a thoughtful consideration of users’ perceptions and behaviours during emergencies, such as evacuation, while maintaining a correlation with emergency layout and strategic planning
Geometry and obstacles can be represented in a virtual environment, studying the influence on the perpetrator and pedestrian evacuation dynamic
Secure envelope [S1.2]
N.A
Attack effects on the BE elements
BE layout
Standoff [S2.1]
N.A
BE planimetric geometry
Sheltering [S2.2]
Their design should ensure the safety of users, addressing their essential needs in an emergency
Safe places are attractive for refuging
Emergency layout [S2.3]
Its design should consider the number of users and typologies to support the behaviour (literature or in simulation)
It constitutes input data for the setup of final conditions in simulation, influencing the evacuation paths to reach the defined safe areas
Access control and surveillance in the BE
Access control [S3.1]
Aiming to discourage the perpetrators
It is an element/a set of elements influencing the pedestrian presence in the environment, representing input data in simulations
Security service [S3.2]
Aiming to discourage the perpetrators
Their incorporation into emergency scenarios enables the simulation of “intelligent” solutions, utilizing input data for the detection of emergencies and the management of evacuation
Illumination [S3.3]
Aiming to discourage the perpetrators
The degree of illumination affects the movement of individuals and influences the selection of specific paths, both in regular circumstances and during emergency evacuations
Safety and security management in the BE
Security personnel [S4.1]
Aiming to discourage the perpetrators
It can be modelled as a source which modifies the pedestrian’s evacuation
First aid [S4.2]
Adequate to users’ typologies and number
It can be expressed as a decrease in the number of victims and a directed movement of rescuers towards specific areas
Coordination [S4.3]
N.A
Simultaneous and coordinated employment of different countermeasures
Users’ involvement [S4.4]
Instructions provided to users should align with their instinctive responses in hazardous situations
Capabilities of the users to perform proper safety behaviours
As a final remark, the normative and physical sustainability levels of such systems of RMRS require to be merged with the potential exposure levels that affect the emergency and evacuation process, extending the dimension of the matter towards a holistic approach (compare with Chaps. 3 and 4).
The classification used in this section highlights the complexities of relations among the physical and management-related elements within the BE, encompassing both outdoor and indoor spaces. This accomplishment stems from a meticulous consideration of robust regulatory frameworks and guidelines. The findings underscore the critical perspective that the BE and its occupants should not be construed merely as a backdrop for potential attacks but rather as integral components of the RMRSs themselves. Safety planners are advised to strategically coordinate two pivotal aspects: firstly, the design of the BE layout to facilitate spatial organization in regular usage, incorporating considerations such as standoff distances, and ensuring controlled areas and access under the purview of stakeholders; and secondly, BE-oriented interventions aimed at establishing secure perimeters and implementing constructive measures to safeguard building components, façades, and structures during emergency conditions, thereby mitigating the effects of terrorist acts [14, 23, 24, 32‐34].
2.3 Factors Affecting the Terroristic Risk in the Outdoor Open Areas for the Most Recurrent Attack Typologies
As introduced in previous sections, the terroristic threat is a human-induced phenomenon, and its comprehension should consider three levels of elements:
The perpetrator’s will and decision capability.
The BE features and uses.
The user behaviour in evacuation and emergency processes.
These can be combined into two main issues which concern the main goals of the section in a BE-centred view, focusing on the assessment of its relations with both perpetrators and users.
In that sense, the discussion of the anthropic phenomenon and the current regulation and experiences framework at the international scale can support the interpretation and the parametrization of main features and properties related to the BE that should be considered in a risk assessment procedure.
Coherently with other risks, i.e. fire and earthquake, the risk assessment of a disaster usually considers tangible and intangible features related to the analysed elements (buildings, sub-components) in order to translate them into a final performance value towards a homogeneous system of elements to be compared, while users’ behaviour has to be considered to understand and test mitigative strategies and solutions overcoming the risk dimensions towards resilient scenarios.
In this framework and in consequence of previous analyses presented in Sects. 2.1 and 2.2, a systematization of properties and elements affecting the risk assessment is discussed, in order to provide a limited set of elements to consider for a reduced and fast formulation of risk assessment.
Specifically, the attention is related to the OAs and the main attack types identified as efficient ones in Sect. 2.1, merging major results from the international experiences in mitigating the terroristic risks for mass gathering events and special/strategic targets. In the details of the summary presented in Table 2.7, nine recurrent keywords are identified to describe the terroristic risk which are discussed as follows, detailing the associated features:
Table 2.7
Summary of recurrent keywords identified in the analysis of the collected background about the issues, including references and correlation with terrorism principles in Chap. 1, Sect. 1.1], classified by risk determinant type
Risk determ
Keyword
Terrorism principle
Contents
Refs.
HAZARD
TARGET
TP.3; TP.3.2
Inter-dependence and replacement of targets; soft target
“TARGET” describes the type and inherent proneness of the place to be attacked. It is demonstrated by the phenomenological analysis of events in the BE and in OAs, highlighting the higher relevance in likelihood for CBEs B and D, consequently extending to FB, FD, and F for the events that occurred in relation to the outdoors (compare with Table 2.1). Specifically for OAs, the environmental significance of a location is contingent upon its inherent likelihood of being attacked, influenced by the notion of “soft target”. Moreover, the size of the target does not preclude the symbolic importance of OAs. Even though the prior assessment of the terrorism phenomenon adopts a geographically independent analysis, the selection of an OA (one among other soft targets) should be tied to their symbolic relevance (i.e. religious, political, economic), which depends also on the presence of representative and symbolic buildings.
“USES” is related to the impact “maximization” of violent acts, because the use of OAs and their structures assumes varying degrees of importance in terms of likelihood. Near the common uses of places, the “attractiveness” of squares/streets or buildings facing OAs increases the potential proneness to perpetrators’ choice, increasing locally the touristic flows [35]. Similarly, the presence of public buildings influences the use of the OAs, even if these are dependent on the opening times.
“PREVENTION” considers the current significance of terrorism in urban environments, due to the fact that the extensive deployment of countermeasures or mitigative solutions can impact the potential likelihood of threats in OAs. This stems from the distinction between hard and soft targets (TP.3). Likewise, preventive strategies may vary based on weaponry and attack types aimed at achieving violent objectives (TP.4). In this context, the prevention encompasses both the existence of preventive measures in the urban BE (e.g., access control, robust barriers) and their efficacy against specific attack types (e.g., vehicular or armed assaults) [11, 35‐38]. Thus, all mitigative urban physical elements, including geometric features of accesses, both within OAs and along their boundaries, participate in the discussion.
“FORM/SHAPE” which discusses the morphological feature of the OAs and their relations with the assaults. This is strongly clear focusing on the attack typologies: for T2, mainly executed with cold arms or with guns, the perpetrator's violent act is “centralized” covering a circular area of interest; while for T3 the prevalent elongated features of places allow vehicles to reach higher speeds to pursue the act [12, 22, 36, 38, 39].
“ACCESSIBILITY” related to the geometric dimensions of OAs while discussing their perimeter. The concept of accessibility is clearly stated in terms of the physical permeability of OAs as the ratio of physical geometries of accesses and the overall perimeter but also related to the urban regulations about vehicular accessibility (for the T3) [22, 36] or the topographic/human-induced conditions along the accesses (e.g., stairs, squatting) [40].
“OBSTACLES” recurs to describe all the OAs elements (within the area and along the frontier) that constitute temporal rendezvous for people. It’s the case of bar-covered terraces, staircases, or greening that may increase locally the vulnerability of a place in terms of meeting points [37].
“ATTACK TYPE” describes the relationships between the potential severity of the attack and the type of the attack itself. As demonstrated in previous sections, most of the mitigative strategies are classified coherently to the weapons or the means of the attack. On the other hand, the attack type itself constitutes the way to describe the severity of events when related to the OAs uses, as highlighted in the phenomenological analysis [35, 37].
“CROWDING” is mostly related to the quantification of severity. In this case, the keyword is related to the maximum number of people to be involved in the events, considering the density of OAs and the associated facing buildings for their uses [37].
“REACTION/OBSTACLE” describes the quality of OAs and its part in enhancing the responsiveness of users in the moment of the attack. Specifically, a first level of quality can be discussed focusing on the relationship between the physical objects/obstruction within the OAs and users. Here, their “protective” or “obstructive” potentialities can be considered [37, 41‐43], following the main suggestions shared by some national guidelines to users: “hide” or “run”.3 The second level of discussion about the “reaction” refers to detailed countermeasures present within the OAs, assessed as effective for the attack types.
The discussed keywords and their association with the risk determinants (hazard, vulnerability and exposure) offer the opportunity to parameterize the phenomenon in the OAs, combining specific boundary conditions. In fact, the recognized influence of the building uses in increasing or altering the proneness of events in squares and streets (CBEs F, B, D) and the attack types (T2 armed assault and T3 car bombing/car ramming) in Sect. 2.1 allow to limit the threat analysis towards a risk assessment of the phenomenological scenarios. As it is clear and fully argued in the literature and theory of risk assessment and management, the determination of simplified formulations for the analysis of scenarios can take advantage of collaborative methods, trying to overcome the limited knowledge about the issues while enhancing the single skills of other expert judgement.
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These European countries have already experimented “educative” initiatives with urban users by means of smartphone applications to communicate real-time the location of events, as well as guidelines for the suggestion for correct behaviours during the violent event. Two main examples are the Belgian virtual platform info-risques.be (available at: https://centredecrise.be/fr/risques-en-belgique), the German KATWARN mobile application (available at: https://www.katwarn.de/en/system.php) and the French guidelines Gérer la Sureté et la Sécurité Des Événements et Sites Culturels [35] (last website access: 26/02/2024).
The plans “Vigipirate” and “ACT—Action Counters Terrorism” [42, 43] summarize briefly the suggestion in the related French and English suggestions “s’échapper, se cacher, alerter et resister” and “hide, run and tell”, promoted as smart guidelines for urban users involved in a terroristic acts.
