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Home > Design Guidance > Design Objectives > Secure / Safe > Security for Building Occupants and Assets

Security for Building Occupants and Assets

by the WBDG Secure/Safe Committee

Last updated: 09-07-2012

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Overview

The 2001 terrorist attacks at New York City's World Trade Center and the Pentagon, the 1995 bombing of Oklahoma City's Alfred P. Murrah Federal Office Building, and the 1996 bombing at Atlanta's Centennial Park, shook the nation, and made Americans aware of the need for better ways to protect occupants, assets, and buildings from human aggressors (e.g. disgruntled employees, criminals, vandals, lone active shooter, and terrorists). The 2001 terrorist attacks demonstrated the country's vulnerability to a wider range of threats and heightened public concern for the safety of workers and occupants in all Building Types. Many federal agencies responding to these concerns have adopted an overarching philosophy to provide appropriate and cost-effective protection for building occupants.

the new Oklahoma City Federal Building

Security measures, such as setbacks, bollards, protective glazing, and structural hardening, are incorporated into the design of the new Oklahoma City Federal Building, located north of where the former Alfred P. Murrah Federal Building once stood.
(Designed by Ross Barney + Jankowski Architects and Atkins Benham)

The basic components of the physical security measures to address an explosive threat considers the establishment of a protected perimeter, the prevention of progressive collapse, the design of a debris mitigating façade, the isolation of internal explosive threats that may evade detection through the screening stations or may enter the public spaces prior to screening and the protection of the emergency evacuation, rescue and recovery systems. These protective measures are generally achieved through principles of structural dynamics, nonlinear material response and ductile detailing.

In addition to the FEMA risk reduction publications that provide background information for performing risk assessments and guidance for protective design approaches, different branches of the Federal Government developed design criteria for the protection of Federal facilities. The most prominent of these design criteria are the Interagency Security Committee (ISC), the Department of Defense Protective Design Center (DOD-PDC), the Veterans Administration (VA) and the Department of State (DOS). Each of these Government agencies considers the effects of terrorist explosive events on their facilities and the protection of their occupants.

Interagency Security Committee (ISC)

The most comprehensive of the documents was produced by the ISC. Membership in the ISC consists of over 100 senior level executives from 47 federal agencies and departments. In accordance with Executive Order 12977, modified by Executive Order 13286, the ISC's primary members represent 21 federal agencies and is chaired by the Department of Homeland Security (DHS). The ISC criteria underwent a major revision in April of 2010 and the current guidance supersedes the physical security standards provided in the 2004 documents "ISC Security Standards for Leased Space," "ISC Design Criteria for New Federal Office Buildings and Major Modernization Projects," and the 1995 DOJ Report.

The most recent revision of the ISC guidance is a risk-based approach that is split into multiple documents:

  • Facility Security Level Determinations for Federal Facilities (21 February 2008)
  • Physical Security Criteria for Federal Facilities (12 April 2010)
  • The Design-Basis Threat (routine updates, April 2012, 5th edition)
  • The Risk Management Process for Federal Facilities (21 March 2012) Draft
  • The Use of Physical Security Performance Measures (June 2009)
  • Facility Security Committees (est. Q4 2010)

Note: All of these documents are For Official Use Only (FOUO) and will only be distributed outside the Government on a need-to-know basis.

The Facility Security Level document provides the procedure for determining the Facility Security Level (FSL) based on the characteristics of the facility and the occupancies they house. Five factors (mission criticality, symbolism, facility population, facility size, and threat to tenant agencies) are quantified to determine the FSL. The FSL is determined by the Facility Security Committee (FSC), which consists of representatives of all Federal tenants in the facility, the security organization, and the owning or leasing department or agency. Once the FSL is established, the Design Basis Threat document provides the Design Basis Threat Scenario, Baseline Threat, Analytical Basis, Target Attractiveness and Outlook for twenty-nine "undesirable events" that range from Aircraft as a Weapon to Workplace Violence. This all-hazards approach provides a comprehensive review of the potential acts of violence the facility faces and provides guidance to assess the risk. The Physical Security Criteria document provides the overall basis for the threat and risk assessment. The Facility Security Committee is responsible for addressing the facility specific security issues and approving the implementation of security measures and practices. The implementation may be a combination of operational and physical security measures based on the FSL and the Level of Protection (LOP) that is deemed both appropriate and achievable. To facilitate the process, the document tabulates the requirements for all the individual security criteria categories relative to the desired LOP. The security criteria categories are further correlated to additional Appendix information and to the specific undesirable events that the protective measures are intended to address. This presentation of the protective design criteria helps illustrate the all-hazard risk based approach.

The General Services Administration (GSA) has developed the "General Services Administration Facility Security Requirements for Explosive Devices Applicable to Facility Security Levels III and IV, GSA's Interpretation of the Interagency Security Committee (ISC) Physical Security Criteria" (2 August 2011) (SBU) for GSA facilities.

Although the ISC Physical Security Criteria for Federal Facilities were not changed, a new Physical Security Criteria Interpretation document was developed by the GSA. This document provides the specific facility security requirements for explosive devices for Facility Security Levels (FSL) III and IV. Whereas the ISC document is risk based and open to the interpretation of the protective design consultant, the interpretation of these criteria for use on GSA projects are more prescriptive. Tables 1 for FSL III and Table 2 for FSL IV identify the design requirements and prescriptive measures associated with specific threats and standoff distances at various locations surrounding and within protected facilities. The guidance includes the calculation of blast loads, material strength factors, flexure and shear response criteria, and glazed system response criteria. The Interpretation document recognizes the use of advanced analytical methods, such as finite element analyses, that may produce more efficient protective systems; however, the guidelines specify the documentation that must accompany the use of advanced analytical methods.

Similar to the changes to the UFC criteria (see below), the structure and façade are to be designed relative to the available standoff distances with few mandatory minimum distances. Design criteria for protected structural systems encourage ductile detailing and the criteria for debris mitigating façade address acceptable glass types, minimum bite requirements, and design of frame members and connections. Although FSL III facilities must only provide a debris mitigating facade, 90% of the glazing of FSL IV facilities must satisfy the specified performance criteria in response to the actual blast load intensity resulting from the design basis threat at the actual standoff distances. Furthermore, the frames and connections of FSL IV facilities must satisfy balanced design requirements. Additional guidance is provided to prevent the likelihood of progressive collapse due to an exterior vehicle borne explosive event and specific hardening measures are specified to address internal explosive events.

Department of Defense (DoD)

A revised version of the UFC 4-010-01 was issued on 9 February 2012 that contained several significant changes in procedure for the protective design of DoD facilities. In addition to expanding the applicability of the minimum Antiterrorism standards to the purchase of existing buildings, visitor centers, museums and visitor control centers, the revised UFC expanded the requirements for design submittals, calculations, test reports, and narratives. However, the most significant change involved the redefinition of conventional construction standoff distance that is based on the type of construction materials and structural systems. As a result, more robust materials and construction types were assigned shorter conventional construction standoff distances than less robust materials and construction types. Furthermore, the criteria relaxed the minimum standoff distance requirements so long as the designer hardens the structure and façade based on the actual standoff distances for the vehicle borne and placed explosive weights. These changes allow the project team to balance the resistance and robustness of the structure with the standoff distances available at a given site. Additional modifications to the UFC changed the requirements for unobstructed spaces, which now either extent to parking and roadways standoff distances or the actual standoff distance to the unobstructed space is used for explosive weight II. The revised criteria also identify the required access control at building entrances for interior load bearing structural elements to be exempt from protective measures that address vulnerabilities for progressive collapse.

Major modifications were also made to the Standard 10 static design procedure using ASTM F2248 and ASTM E1300 methods. Designers must now check the glazing for the 3-second duration equivalent design load and all glazed elements must be designed to resist the applicable threats based on the available standoff distances. The framing for the static analysis approach must resist twice the glazing capacity and the connections must develop the reaction forces determined in the frame analysis. However, the greatest change involves the design of the structural elements supporting the glass framing members. Under this approach, the structure supporting the window is designed to develop the shear and moment capacity of a conventionally designed wall system without any fenestration that is amplified by a tributary area increase factor at the window opening. The new criteria rely on PDC-TR-10-02 for response limits for dynamic analyses. Further changes adopted ASTM F2247 for the design of doors and provided guidance for the design of exterior stairwells, covered/enclosed walkways and bridges.

Veterans Administration (VA)

The Veterans Administration conducted a detailed survey of representative hospitals and administrative buildings in both urban and rural areas and identified the vulnerabilities that are common to most facilities. Based on this detailed survey, the VA developed two different Physical Security Design Manuals, one for "Life Safety Protected" and the other for "Mission Critical Facilities." These documents outline the most practical and cost effective protective measures that address the most common hazards to which occupants may be exposed. Both design manuals address site conditions, building entrances and exits, functional areas, building envelope, building structure, utilities and building services, building systems and security systems. The VA Security Design requirements are generally less restrictive than either the UFC or the ISC Criteria.

Department of State (DoS)

The Department of State (DoS) criteria are generally documented in the OBO-ICS 2009 Overseas Building Operations—International Code Supplement. Although the DOS requirements are controlled information, their approach is to enforce both an anti-ram and anti-personnel standoff distance, provide a debris mitigating and forced entry ballistic resistant (FEBR) façade, provide a regular moment resisting frame that is inherently resistant to progressive collapse and to design the structure to resist the blast induced base shears. Both the magnitudes of the design basis threats (DBT) and the performance criteria for the DoS Buildings are generally much more arduous than the corresponding requirements imposed by either the ISC or UFC Criteria.

Guidance for Commercial Buildings

Despite the various Government Criteria and Protective Design guidance, there are no comparable documents for commercial buildings. The American Society of Civil Engineers (ASCE) therefore undertook the task to develop a consensus based Blast Standard that identifies the minimum planning, design, construction, and assessment requirements for new and existing buildings subject to the effects of accidental or malicious explosions, including principles for establishing appropriate threat parameters, levels of protection, loadings, analysis methodologies, materials, detailing, and test procedures. The document does not prescribe requirements or guidelines for the mitigation of progressive collapse or other potential post-blast behavior. Unlike the Government Guidelines and Criteria, the ASCE Standards are written for structural engineers with specific information pertaining to the design and detailing of blast resistant structure and façade systems.

Application of Standards to Buildings

As is evident in the overview of the different existing standards above, there are currently no universal codes or standards that apply to all public and private sector buildings. However, most designers agree that security issues must be addressed with other design objectives and integrated into the building design throughout the process. This will ensure a quality building with effective security. This concept is known as an all-hazard design.

Depending on the building type, acceptable levels of risk, and decisions made based on recommendations from a comprehensive threat assessment, vulnerability assessment, and risk analysis, appropriate countermeasures should be implemented to protect people, assets, and mission.

Some types of attack and threats to consider include:

  • Unauthorized entry/trespass (forced and covert)
  • Insider threats
  • Explosive threats: Stationary and moving vehicle-delivered, mail bombs, package bombs
  • Ballistic threats: Small arms, high-powered rifles, drive-by shootings, etc.
  • Weapons of mass destruction (chemical, biological, and radiological)
  • Disruptive threats (hoaxes, false reports, malicious attempts to disrupt operations)
  • Cyber and information security threats
  • Supervisory Control and Acquisition Data (SCADA) system threats (relevant as they relate to HVAC, mechanical/electrical systems control and other utility systems that are required to operate many functions within building)

Protective design is the design of structures to mitigate blast effects. This will require the involvement of protective design and security consultants at the onset of the programming phase. Early and ongoing coordination between the protective design consultant, the structural engineer, and the entire planning team is critical to providing an optimal design that is both open and inviting to the public and compliant with updated security requirements.

Crime Prevention Through Environmental Design (CPTED)

Crime Prevention Through Environmental Design (CPTED) is a proven methodology that not only enhances the performance of these security and safety measures, but also provides aesthetics and value engineering. CPTED utilizes four (4) primary, overlapping principles: Natural Surveillance, Natural Access Control, Territoriality, and Maintenance. Natural surveillance follows the premise that criminals do not wish to be observed; placing legitimate 'eyes' on the street, such as providing window views and lighting, increases the perceived risk to offenders, reduces fear for bona fide occupants and visitors, as well as lessening reliance on only camera surveillance. Natural Access Control supplements physical security and operational measures with walls, fences, ravines, or even hedges to define site boundaries, to channel legitimate occupants and visitors to designated entrances, and to reduce access points and escape routes. Territoriality involves strategies to project a sense of ownership to spaces such that it becomes easier to identify intruders because they don't seem to belong. Clear differentiation between public, semi-public, and private spaces by using signage, fences, pavement treatment, art, and flowers are examples of ways to express ownership. Maintenance is a key element to preserve lines of sights for surveillance, to retain the defensiveness of physical elements, and to project a sense of care and ownership. Together, the principles of CPTED increase the effectiveness of operational, technical, and physical safety methods, thereby lessening equipment and operating costs.

For total design efficiently and cost effectiveness, security, safety, and CPTED measures are best applied at the beginning of a project. Security programming is a useful practice to identify security design requirements necessary to satisfy stakeholder concerns.

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Recommendations

Essential to the security plan and design of a high quality building is the implementation of appropriate countermeasures to deter, delay, detect, and deny attacks. Often the countermeasures work on the layered defense concept or "Onion Philosophy." This concept provides for increasing levels of security from the outer areas of the site or facility towards the inner, more protected areas. Some or all of the issues outlined below need consideration for effective security design and building operations.

Unauthorized Entry (Forced and Covert)

Protecting the facility and assets from unauthorized persons is an important part of any security system. Some items to consider include:

  • Compound or facility access control
    • Control perimeter: Fences, bollards, anti-ram barriers
    • Traffic control, remote controlled gates, anti-ram hydraulic drop arms, hydraulic barriers, parking control systems
    • Forced-Entry-Ballistic Resistant (FE-BR) doors, windows, walls and roofs
    • Barrier protection for man-passable openings (greater than 96 square inches) such as air vents, utility openings and culverts
    • Mechanical locking systems
    • Elimination of hiding places
    • Multiple layer protection processes
  • Perimeter intrusion detection systems
    • Clear zone
    • Video and CCTV surveillance technology
    • Alarms
    • Detection devices (motion, acoustic, infrared)
  • Personnel identification systems
    • Access control, fingerprints, biometrics, ID cards
    • Credential management
    • Tailgating policies
    • Primary and secondary credential systems
  • Protection of information and data
    • Acoustic shielding
    • Shielding of electronic security devices from hostile electronic environments
    • Computer screen shields
    • Secure access to equipment, networks, and hardware, e.g. satellites and telephone systems

Insider Threats

One of the most serious threats may come from persons who have authorized access to a facility. These may include disgruntled employees or persons who have gained access through normal means (e.g., contractors, support personnel, etc). To mitigate this threat some items to consider include:

  • Implement personnel reliability programs and background checks
  • Limit and control access to sensitive areas of the facility
  • Compartmentalization within the building/campus
  • Two-man rule for access to restricted areas

Explosive Threats: Stationary and Moving Vehicle-Delivered, Mail Bombs, Package Bombs

Explosive threats tend to be the terrorist weapon of choice. Devices may include large amounts of explosives that require delivery by a vehicle. However, smaller amounts may be introduced into a facility through mail, packages, or simply hand carried in an unsecured area. Normally the best defense is to provide defended distance between the threat location and the asset to be protected. This is typically called standoff distance. If standoff is not available or is insufficient to prevent direct contact or reduce the blast forces reaching the protected asset, structural hardening may be required. If introduced early in the design process, this may be done in an efficient and cost-effective manner. If introduced late in a design, or if retrofitting an existing facility, such a measure may prove to be economically difficult to justify. Some items to consider include:

  • Including qualified security and blast consulting professionals from programming forward.
  • Providing defended standoff for vehicle-borne weapons using rated or certified barriers such as anti-ram fencing or bollards, by using reinforced street furniture such as planters, plinth walls or lighting standards, by using natural and man-made elements such as storm water elements, berms, ditches, tree masses, etc., by site layout strategies for parking areas, roadways, loading docks and other locations accessible by vehicles, by critical asset location strategies, and/or by security protocol through policy and procedures (e.g. vehicle inspections, etc.)
  • Consider structural hardening and hazard mitigation designs such as ductile framing that is capable of withstanding abnormal loads and preventing progressive collapse, protective glazing, strengthening of walls, roofs, and other facility components.
  • Provide redundancy and physical separation of critical infrastructure (HVAC), utility systems (water, electricity, fuel, communications and ventilation)
  • Provide for refuge and evacuation.
  • Consider plans for suicide bombers. Confer with authorities who have had previous experience.
  • Provide defended standoff for hand-carried weapons with anti-climb fencing, barrier (thorny) plants, natural surveillance of routine occupants and unobstructed spaces, electronic surveillance, intrusion detection, territoriality using defined spaces, natural access control suing exterior and interior pedestrian layout strategies, security protocol through policy and procedures (visitor management, personnel and package screening, etc.)
  • Consider handling mail at alternate or remote locations not attached to the building or in a wing of the building with a dedicated HVAC system to limit contamination and damage to the main building.
  • Consider loading docks in structures unattached to the main building with a dedicated HVAC system to limit contamination and damage to the main building.

Ballistic Threats

These threats may range from random drive-by shootings to high-powered rifle attacks directed at specific targets within the facility (assassinations). It is important to quantify the potential risk and to establish the appropriate level of protection. The most common ballistic protection rating systems include: Underwriters Laboratories (UL), National Institute of Justice (NIJ), H.P. White Laboratory, and ASTM International. Materials are rated based on their ability to stop specific ammunition (e.g., projectile size and velocity). Some items to consider include:

  • Obscuration or concealment screening using trees and hedges, berms, solid fencing, walls, and less critical buildings
  • Ballistic resistant rated materials and products
  • Locating critical assets away from direct lines of sight through windows and doors
  • Minimize number and size of windows
  • Physical energy absorption screens such as solid fences, walls, earthen parapets
  • Provide opaque windows or window treatments such as reflective coatings, shades or drapes to decrease sight lines.
  • Avoid sight lines to assets through vents, skylights, or other building openings
  • Use foyers or other door shielding techniques to block observation through a doorway from an outside location.
  • Avoid main entrances to buildings or critical assets that face the perimeter or an uncontrolled vantage point

Weapons of Mass Destruction: Chemical, Biological, and Radiological (CBR)

Commonly referred to as WMD, these threats generally have a low probability of occurrence but the consequences of an attack may be severe. While fully protecting a facility against such threats may not be feasible with few exceptions, there are several common sense and low cost measures that can improve resistance and reduce the risks. Some items to consider include:

  • Protect ventilation pathways into the building
    • Control access to air inlets and water systems
    • Provide detection and filtration systems for HVAC systems, air intakes and water systems
    • Provide for emergency HVAC shutoff and control
    • Segregate portions of building spaces (i.e., provide separate HVAC for the lobby, loading docks, and the core of the building)
    • Consider positive pressurization to keep contaminates outside of the facility
  • Provide an emergency notification system to facilitate orderly response and evacuation
  • Avoid building locations in depressions where air could stagnate
  • Provide access control to mechanical rooms
  • Provide CBR monitoring apparatus

Cyber and Information Security Threats

Businesses rely heavily on the transmission, storage, and access to a wide range of electronic data and communication systems. Protecting these systems from attack is critical. Some items to consider include:

  • Understand and identify the information assets you are trying to protect. These may include personal information, business information such as proprietary designs or processes, national security information, or simply the ability of your organization to communicate via email and other LAN/WAN and wireless functions.
  • Protect the physical infrastructure that supports information systems. If the computer system is electronically secure but vulnerable to physical destruction it may need more protection.
  • Provide software and hardware devices to detect, monitor, and prevent unauthorized access to or the destruction of sensitive information.

Development and Training on Occupant Emergency Plans

Occupant Emergency Plans should be developed for all buildings Operations staff and occupants to be able to respond to all forms of credible attacks and threats. The Emergency Plan needs to include clearly defined lines of communication, responsibilities, and operational procedures parts of Emergency Plans. These plans are an essential element of protecting life and property from attacks and threats by preparing for and carrying out activities to prevent or minimize personal injury and physical damage.

Safety will be accomplished by pre-emergency planning; establishing specific functions for Operational staff and occupants; training Organization personnel in appropriate functions; instructing occupants of appropriate responses to emergency situations and evacuation procedures; and conducting actual drills to ensure everyone is aware of policies and procedures.

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Related Issues

Integrating Security and Sustainability

Providing for sustainable design that meet all facility requirements is often a challenge. With limited resources, it is not always feasible to provide for the most secure facility, architecturally expressive design, or energy efficient building envelope. From the planning and concept stages through the development of construction documents, it is important that all project or design stakeholders work cooperatively to ensure a balanced design. Successful designs must consider all competing design objectives and make the best selections. This applies as well to the site, as well as the building. Ensure sustainable site design and CPTED are considered in concert with each other.

Designing for Fire Protection and Physical Security

Care should be taken to implement physical security measures that allow Fire Protection forces access to sites, buildings and building occupants with adequate means of emergency egress. GSA has conducted a study and developed recommendations on design strategies that achieve both secure and fire safe designs. Specifically, the issue of emergency ingress and egress through blast resistant window systems was studied. Training was developed based on this information and is available at the GSA Firefighter forcible entry tutorial.

Photo of an integrated security system

Integrated security systems can offer more efficient access and control.
(Courtesy of Integrated Security Systems, LTD)

Integrated Systems

There has been a general trend towards integrating various stand-alone security systems, integrating systems across remote locations, and integrating security systems with other systems such as communications, and fire and emergency management. Some CCTV, fire, and burglar alarm systems have been integrated to form the foundation for access control. The emerging trend is to integrate security systems with facility and personnel operational procedures. By involving facility stakeholders from the programming stage throughout the life of the project, the behavioral-based policies can be successfully integrated with security systems and forces.

This provides for a seamless and flexible mode of operation for the facility and its occupants. First and Second Generation Crime Prevention Through Environmental Design (CPTED) are time and results proven crime prevention practices. The primary guiding principles of CPTED include natural access control, natural surveillance and territoriality. These principles are augmented strongly by the second generation (behavioral based) CPTED strategies. The best practice is for first and second generation CPTED to merge with the integrated systems concept which results in an integrated security process.

Blast Design vs. Seismic Design

Seismic and blast resistant design share some common analytical methodologies and a performance based design philosophy that accepts varying levels of damage in response to varying levels of dynamic excitation. Both design approaches recognize that it is cost prohibitive to provide comprehensive protection against all conceivable events and an appropriate level of protection that lessens the risk of mass casualties can be provided at a reasonable cost. Both seismic design and blast resistant design approaches benefit from a risk assessment that evaluates the functionality, criticality, occupancy, site conditions and design features of a building.

While there may be more predictability with natural hazards, this is not the case with man-made hazards. Also the explosive threats of the future are very likely to be very different from the explosive threats of the past. Another fundamental difference between seismic and blast events are the acceptable design limits. Since earthquakes are more predictable and affect more structures than are affected by blast events, owners may be willing to accept different levels of risk relative to these different events, and this may translate into differences in acceptable design limits, as defined by allowable deformation, ductility and other functions.

Both seismic design and blast resistant design approaches consider the time-varying nature of the loading function. The response of a building to earthquake loads is global in nature, with the base motions typically applied uniformly over the foundations of the buildings. These seismic motions induce forces that are proportional to the building mass. Blast loading is not uniformly applied to all portions of the building. Parts of the structure and components closest to and facing the point of detonation will experience higher loading than components at a greater distance and/or not facing the point of detonation. The structure's mass also contributes to its inertial resistance. Due to the local versus global nature of blast loading, seismic loading analogies, including the concept of blast-induced base shears, must be applied with great care or they may be misconstrued to provide a false sense of protection.

Building configuration characteristics, such as size, shape and location of structural elements, are important issues for both seismic and blast resistant design. The manner in which forces are distributed throughout the building is strongly affected by its configuration. While seismic forces are proportional to the mass of the building and increase the demand, inertial resistance plays a significant role in the design of structures to reduce the response to blast loading. Structures that are designed to resist seismic forces benefit from low height-to-base ratios, balanced resistance, symmetrical plans, uniform sections and elevations, the placement of shear walls and lateral bracing to maximize torsional resistance, short spans, direct load paths and uniform floor heights.

While blast resistant structures share many of these same attributes, the reasons for doing so may differ. For example, seismic excitations may induce torsional response modes in structures with re-entrant corners. These conditions provide pockets where blast pressures may reflect off of adjacent walls and amplify the blast effects. Similarly, first floor arcades that produce overhangs or reentrant corners create localized concentrations of blast pressure and expose areas of the floor slab that may be uplifted. In seismic design, adjacent structures may suffer from the effects of pounding in which the two buildings may hit one another as they respond to the base motions. Adjacent structures in dense urban environments may be vulnerable to amplification of blast effects due to the multiple reflections of blast waves as they propagate from the source of the detonation. While the geology of the site has a significant influence on the seismic motions that load the structure, the surrounding geology of the site will influence the size of the blast crater and the reflectivity of the blast waves off the ground surface.

On an element level, the plastic deformation demands for both seismically loaded structures and blast-loaded structures require attention to details. Many similar detailing approaches can be used to achieve the ductile performance of structural elements when subjected to both blast and seismic loading phenomenon. Concrete columns require lateral reinforcement to provide confinement to the core and prevent premature buckling of the rebar. Closely spaced ties and spiral reinforcement are particularly effective in increasing the ductility of a concrete compression element. Carbon fiber wraps and steel jacket retrofits provide comparable confinement to existing structures. Steel column splices must be located away from regions of plastic hinging or must be detailed to develop the full moment capacity of the section. Local flange buckling must be avoided by using closely spaced stiffeners or, in the case of blast resistant design, the concrete encasement of the steel section.

Reinforced concrete beam sections require resistance to positive and negative bending moments. In addition to the effects of load reversals and rebound, doubly reinforced sections possess greater ductility than singly reinforced counterparts. Steel beams may be constructed composite with the concrete deck in order to increase the ultimate capacity of the section; however, this increase is not equally effective for both positive and negative moments. While the composite slab may brace the top flange of the steel section, the bottom flange is vulnerable to buckling.

Addressing blast and seismic design goals may be achieved through the consideration of many of the same building attributes and utilizing similar design and detailing solutions. An understanding of the differences between these two loading phenomenon, the effects on the structure, and the performance requirements are essential in order to select and implement the appropriate choices for achieving the project's goals.

Building Design to Mitigate the Potential for a Progressive Collapse

Progressive collapse is loosely defined as a situation where a localized failure of a primary structural element leads to the collapse of adjacent structural elements, which propagates to disproportionate collapse of the structure. ASCE 7 states "Progressive collapse is defined as the spread of an initial local failure from element to element, eventually resulting in the collapse of an entire structure or disproportionately large part of it." The initial failure or damage could be from a number of different causes, which might include natural or man-made hazards. The phenomenon is applicable to structure of any appreciable size and type of construction. Concern is greatest for taller structures, as the propagation mechanism is typically vertical.

Design guidelines for the prevention of progressive collapse typically take a threat-independent approach that, regardless of initial cause, is intended to develop inherent robustness and continuity in the structure to resist and arrest propagation of failure. For example, design of a structural frame to resist propagation of damage after loss of a primary vertical-load-carrying element (such as a load-bearing wall or column) is a typical threat-independent approach to providing this resistance. This approach assumes complete damage of the structural element being considered and enhances the structure to prevent disproportionate spread of damage. By assuming loss of single vertical-load-carrying elements at key locations in the structure, the designer can reduce the potential for progressive collapse, should an initiating event occur. Design approaches and requirements are presented by the Department of Defense (UFC 4-023-03 Design of Buildings to Resist Progressive Collapse) and the General Services Administration (Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects). Each of these guidelines provides methods for analysis and measures of acceptability to meet each specific criterion. These Progressive Collapse Guidelines (GSA and UFC) are currently the most complete sets of criteria in terms of providing usable guidance to the designer.

For buildings that are designed to incorporate physical security hardening measures to protect occupants against explosive or other intentional threats, progressive collapse mitigation measures are typically also applied and work in concert with the hardening measures to achieve the necessary protection of the building occupants and assets. Although the physical hardening measures include design features that protect against the specific identified threats, the progressive collapse mitigation measures provide a level of redundancy and continuity that will enhance the building performance, regardless of the actual threat size or weapon. When considered in the selection and design of the building structural system, progressive collapse design methodologies often lead to the utilization of inherently redundant and ductile systems, which are capable of more easily achieving the performance requirements. Additional discussion of the role of Progressive Collapse mitigation measures in securing buildings can be found in the resource pages for Blast Safety of the Building Envelope and Designing Buildings to Resist Explosive Threats.

Security for Historic Buildings

Securing historic buildings is particularly challenging with having to conserve exterior architectural features and interior finishes and amenities. Windows pose a unique challenge in that they often must retain the look of the original windows, while being upgraded for security reasons and further, must be more energy efficient to meet current sustainable design requirements. The GSA has developed guidelines to assist in meeting these challenges in their Technical Preservation Guidelines the guidelines include fire safety retrofit, interior signage, perimeter security, and upgrading historic building windows among the topics covered.

Blast Resistant Design

Weather related (hurricane and tornado) protection benefits from blast resistant design. Blast resistant façade systems requires the glass to satisfy the debris hazard conditions in response to the specified blast loading, while the mullions and anchors are required to resist the collected forces within the specified deflection and ductility limits. In addition to resisting the specified blast loads, the criteria often require the designer to consider the damages resulting from a more extreme blast loading. The criteria therefore require a balanced design for which the mullions must develop the capacity of the selected glass within allowable deformation limits and the anchors must develop the capacity of the selected mullions.

In some instances, the selected glass exceeds the strength requirements for blast resistant design. This may occur when the blast resistant glass must also provide forced entry and/or ballistic resistance (FE/BR) or when the façade must also satisfy the large missile impact requirements specified by the most severe hurricane design codes. For these cases, the selection of the glass make-up may far exceed the blast requirements and produce deeper mullions and more robust anchors. These different requirements often lead to a façade design that increases blast load reactions on supporting elements. In order to resolve this dilemma, one may either allow larger deformations, since the façade will resist the specified blast loads or the glass may act as a diffuser by disengaging for blast loading that significantly exceeds the specified intensity. Since current Government Standards and Criteria do not currently provide guidance regarding these conditions, the designer needs to create a solution that satisfies all the governing protective criteria.

Bollard spacing for accessibility is related to access for fire vehicles and personnel. The Americans with Disabilities (ADA) Act calls for spacing bollards no closer than 36 inches to meet clear opening requirements. Site security designers need to balance their security needs with access, considering bollard location and spacing respective to vehicular traffic, bus stops, hardened street furniture, and pedestrian traffic. Access requirements can usually be met by providing innovative bollard positioning.

Anti-Ram Barriers Test Standard

Effective February 1, 2009, the United States Department of State (DOS) stopped certifying anti-ram barriers under its Anti-ram barrier standard, STD-02.01 Revision A dated March 2003. Beginning February 1, 2009, DOS evaluates only new anti-ram barriers tested under ASTM F2656-07 Standard Test Method for Vehicle Crash Testing of Perimeter Barriers for the selection and approval for use at DOS facilities. The only barriers considered will be those with an ASTM F2656-07 rating of M30 P1, M40 P1, and M50 P1. Furthermore, DOS will only consider barriers in which the impact point has been chosen or agreed to by the DOS. As stated in ASTM F2656-07, failure to consult with DOS regarding the impact point may jeopardize the eligibility of the barrier to be installed at DOS facilities.

DOS no longer issues anti-ram barrier certification letters for tests performed after January 31, 2009. Any tests successfully performed on or before January 31, 2009 will be considered eligible for the issuance of a DOS certification letter. Upon issuance of the last certification letter, DOS published the last List of DOS Certified Anti-Ram barriers in 2009.

DOS is currently transitioning to an internal approved barrier list. This list will be a subset of all current and future barriers that meet the ASTM F2656-07 and/or STD-02.01 Revision A dated March 2003 test criteria. Barriers placed on this new list will be selected specifically for DOS facilities based on newly developed in-house criteria. Barriers will be added and removed from this new internal approved list as facility needs warrant.

Pandemic Illness is another factor to consider. Many facilities e.g., medical facilities, must stand and operate during an epidemic. Consideration needs to be given to HVAC, water supply and waste disposal systems under threat.

Green Walls and CPTED: designers are beginning to incorporate vertical gardens, called "Vegitecture" into their projects. These green walls could block sight lines and provide hiding places which counter the CPTED strategies. When considering vertical gardens, ensure they are designed with CPTED principles in mind.

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Relevant Codes and Standards

Highly complex security system design is still neither codified nor regulated, and no universal codes or standards apply to all public and private sector buildings. However, in many cases, government agencies, including the military services, and private sector organizations have developed specific security design criteria. These standards must be flexible and change in response to emerging threats.

Mandates

Federal Guidelines

Others

Private Sector Guidelines

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Major Resources

WBDG

Building Envelope Design Guide

Fenestration Systems—Exterior Doors

Resource Pages

Blast Safety of the Building Envelope, Chemical/Biological/Radiation (CBR) Safety of the Building Envelope, The Site Security Design Process, Landscape Architecture and the Site Security Design Process, Effective Site Security Design, Cost Impact of the ISC Security Design Criteria, The Bollard

Tools

Security Information and Technologies Exchange (SITE)—SITE is a website for accessing and providing information on best practices and existing and emerging products, systems and technologies that can provide protection for federal facilities. The project is supported by the Technology Best Practices Subcommittee of the U.S. Department of Homeland Security (DHS) Interagency Security Committee. SITE was developed by DHS Science and Technology Directorate, Infrastructure Protections and Disaster Management division and is managed by the National Institute of Building Sciences.

Websites

Security Centers

Organizations and Associations

Trade Journals / Magazines

Training Courses

Tools

Others

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