6.1.1 Categories of Infrastructure6.2 Infrastructure Characteristics
6.2.1 Site Layout
6.2.1.1 Site Selection6.2.2 Interior Layout
6.2.1.2 Building Placement
6.2.1.3 Access Points to the Site
6.2.1.4 On-Site Vehicle Circulation
6.2.1.5 Particular Considerations for Mixed-Use and Intermodal Facilities
6.2.2.1 Asset Shielding6.2.3 Structural Engineering
6.2.2.2 Surveillance
6.2.2.3 Emergency Routes
6.2.3.1 Blast Management6.2.4 Architectural Features
6.2.3.2 Fire Management
6.2.4.1 Facade6.2.5 Systems and Services
6.2.4.2 Entrances
6.2.4.3 Fenestration
6.2.4.4 Small Architectural Features
6.2.4.5 Utility Openings
6.2.4.6 Signage
6.2.5.1 Public Utilities6.3 Security Approaches for Types of Transit Infrastructure
6.2.5.2 Electrical System
6.2.5.3 Functional Components
6.2.5.4 Heating, Ventilation and Air Conditioning (HVAC)
6.2.5.5 Lighting
6.2.5.6 Communications
6.2.5.7 Security Systems
6.2.5.8 Water and Sewer
6.2.5.9 Fire Protection
6.3.1 Transit Stations
6.3.1.1 Potential Threats6.3.2 Transit Stops
6.3.1.2 Site Analysis
6.3.1.3 Access Management
6.3.1.4 Protecting Critical Assets
6.3.1.5 Structural Engineering
6.3.1.6 Systems and Services
6.3.2.1 Potential Threats6.3.3 Administrative Buildings and Operations Control Centers
6.3.2.2 Site Analysis
6.3.2.3 Access Management
6.3.2.4 Protecting Critical Assets
6.3.2.5 Structural Engineering
6.3.2.6 Facility Services
6.3.3.1 Potential Threats6.3.4 Maintenance and Storage Facilities for Transit Vehicles
6.3.3.2 Site Analysis
6.3.3.3 Access Management
6.3.3.4 Emergency Response and Egress
6.3.3.5 Protecting Critical Assets
6.3.3.6 Structural Engineering
6.3.3.7 Facility Services
6.3.4.1 Potential Threats6.3.5 Elevated Structures
6.3.4.2 Site Analysis
6.3.4.3 Access Management
6.3.4.4 Emergency Response and Egress
6.3.4.5 Protecting Critical Assets
6.3.4.6 Structural Engineering
6.3.4.7 Facility Services
6.3.5.1 Potential Threats6.3.6 Tunnels
6.3.5.2 Site Analysis
6.3.5.3 Access Management
6.3.5.4 Emergency Response and Egress
6.3.5.5 Protecting Critical Assets
6.3.5.6 Structural Engineering
6.3.5.7 Systems and Services
6.3.6.1 Potential Threats6.3.7 Right-of-Way, Track, and Signals
6.3.6.2 Site Analysis
6.3.6.3 Access Management
6.3.6.4 Emergency Response and Egress
6.3.6.5 Protecting Critical Assets
6.3.6.6 Structural Engineering
6.3.6.7 Systems and Services
6.3.7.1 Potential Threats6.3.8 Remote Equipment and Unmanned Structures
6.3.7.2 Site Analysis
6.3.7.3 Access Management
6.3.7.4 Emergency Response
6.3.7.5 Protecting Critical Assets
6.3.8.1 Potential Threats
6.3.8.2 Site Analysis
6.3.8.3 Access Management
6.3.8.4 Emergency Response and Egress
6.3.8.5 Protecting Vulnerable Assets
Figure 6-1. Standoff Distance
Figure 6-2. Building Entrance Location
Figure 6-3. Variation of Explosive Pressure and Duration with Distance from Explosion
Figure 6-4. Isolation of Vulnerable Areas
Table 6-1. Bomb Size and Blast Rang
Table 6-2. Security-Oriented Design Strategies for Transit Stations
Table 6-3. Security-Oriented Design Strategies for Transit Stops
Table 6-4. Security-Oriented Design Strategies for Administrative Buildings and OCCs
Table 6-5. Security-Oriented Design Strategies for Maintenance and Storage Facilities
Table 6-6. Security-Oriented Design Strategies for Elevated Structures
Table 6-7. Security-Oriented Design Strategies for Tunnels
Table 6-8. Security-Oriented Design Strategies for Rights-of-way, Tracks, & Signals
Table 6-9. Security-Oriented Design Strategies for Unmanned Structures
How is this chapter useful? For transit administrators it is a resource for:
For operations or planning staff it is a resource for:
For engineers it is a resource for:
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Generally, infrastructure is the set of underlying structural or institutional elements that provide the framework in which a structure or facility operates and functions. The components of infrastructure are the elements that enable and facilitate carrying out certain activities. Transit infrastructure in particular refers to all the stationary assets in a system, such as real estate, buildings, tunnels, and rail tracks.
Infrastructure design is only one element of a larger security program. The process begins with a TVA, which identifies potential threats and their severity, and estimates how vulnerable each asset is to these threats. Scenario and Consequence Analyses then evaluate the maximum extent of damage or injury in the event of an attack. Based on these evaluations, transit agency officials can then prioritize their concerns and determine the appropriate level of protection through countermeasures.
Agencies adopting any of the infrastructure design security measures described in this chapter should consider coordinating them with other transit system components, such as vehicles and emergency procedures, to develop a comprehensive security strategy.
Overlaps between access management and infrastructure protection are extensive. Many of the threats facing infrastructure can be greatly reduced by instituting appropriate access management measures. Since no transit security program can be completely effective at eliminating risk while still providing convenient and high quality service, infrastructure design should also include measures to prevent attacks or reduce their effects in the event that perpetrators are able to gain access. Refer to Chapter 5: Access Management for additional information. Note also that this chapter is specific to infrastructure; design-related security measures for other transit assets are covered in Chapter 7: Vehicles and Chapter 8: Communications.
This chapter provides further details on the concept of CPTED 1 by showing how agencies can use the physical design of infrastructure components to help detect and prevent attempted terrorist attacks in their systems, and minimize the damage from attacks that do occur. This chapter begins with an overview of the various categories of transit infrastructure, then continues with a description of:
1CPTED is a branch of situational crime prevention based on the premise that the proper design and effective use of the built environment can lead to a reduction in crime and an improvement in the quality of life. CPTED differs from other crime prevention strategies by using environmental factors, such as site plan, building layout, and other physical characteristics, to bring about behavioral effects that reduce the fear and incidence of crime. Refer to www.cpted.com.au and www.cpted-watch.com and to the Security-Oriented Design Considerations for Transit Infrastructure" section of the 1998 FTA Transit Security Handbook at http://transit-safety.volpe.dot.gov/Publications/Default.asp for additional information.
6.1 Introduction to Security Design for Transitional Infrastructure
6.1.1 Categories of Infrastructure
Infrastructure categories relating to all of the fixed sites and facilities within a system are summarized below and described in more detail in Section 6.3.
- Transit Stations are facilities used for boarding and alighting of transit passengers, and fare collection; they can be below-grade, at-grade, or elevated. Their high profile, large volumes of pedestrian traffic, and central locations integrated with surrounding uses, make them likely targets for terrorist attack.
- Transit Stops are usually smaller and more open than transit stations. They are typically on public land, where passengers can board buses and light rail vehicles; these include everything from elaborate shelters to mere signposts. Transit agencies often lack control over these sites, which, combined with their high level of accessibility, makes them difficult to secure against attack.
- Administrative Facilities and Operations Control Centers (OCCs) are used for the operations and administration of the transit system and may be co-located on a site with non-transit uses. Although most administrative facilities are not open to the public and can therefore maintain stricter access control, they have a critical role in the transit system and have value as strategic targets.
- Vehicle Maintenance Facilities are used for the repair and storage of transit vehicles; they include vehicle garages, yards, and repair facilities. They often contain a large number of assets to be protected, including some high-risk elements such as fuel storage areas or containers. Maintenance facilities can be designed to allow transit vehicles and maintenance staff to enter and exit freely, while preventing access by unauthorized vehicles and people.
- Elevated Structures refer to all above-grade bridges and track structures, including pedestrian bridges and overpasses. Their high visibility and structural complexity present particular challenges to securing them against terrorist attack.
- Tunnels are used for the passage of transit vehicles underground and, in limited cases, underwater. They are more secure when designed to prevent unauthorized access from passenger platforms and at-grade entrances, while allowing transit vehicles to pass freely. Proper design can also facilitate evacuation in an emergency.
- Right-of-Way, Track, and Signals include all land and equipment dedicated to the movement of transit vehicles between stations. Like tunnels, a design goal is to allow transit vehicle movement while preventing access by unauthorized people or vehicles.
- Remote and Unmanned Structures capture all other physical assets. This category includes power substations and communications relays, and the like, which are not necessarily located on rights-of-way or in stations. These may be owned or controlled by other agencies or companies. Design features that take into account their remote locations and lack of consistent or continuous staff presence can improve their security.
6.2 Infrastructure Characteristics
This section describes transit property design elements that planners, designers, and administrators should consider when selecting a facility location and/or designing a new or renovating existing facilities to protect them against potential terrorist attacks. Characteristics include:
6.2.1 Site Layout
The physical characteristics of a site have a major impact on which security measures are possible and appropriate in safeguarding a facility. Some of these elements, such as building location, landscaping, and site circulation are under the control of the transit agency; while off-site features, such as topography and abutting uses, are not. Some on-site characteristics such as topography and vegetation are under limited control of the transit agency.
This section describes the factors a transit agency might consider when determining where to locate a facility and how to design the site. These include site selection, building placement, access points to the site, on-site vehicle circulation, and relevant factors to mixed-use facilities.
Site layout can be conducive to incorporating measures that protect personnel, riders, and other assets from attacks, and to limiting unauthorized access to the property. In addition, a facility's site design should enable security measures to be scaled and adapted in response to changing threat levels over time.
6.2.1.1 Site Selection
The unique characteristics of a site influence their appropriateness for different types of transit facilities, and have a direct effect on security. Relevant security issues for agencies include obstacles hindering outward surveillance, amount of available land, natural buffers, and the existence of nearby elevated vantage points.
Planners should consider the impact of the following site elements on site security when evaluating a property:
- Natural features (such as a stream or swamp)
- Manmade features (such as a pipeline or neighboring building)
- Existing easements
- General characteristics of abutting properties and access control
- Access to public roads
- Proximity to private roads
Natural Features
Natural elements, such as rolling hills and steep terrain, can provide hiding places for aggressors and hinder visual surveillance by security personnel. High points on the site elevate buildings where they are easily visible from off-site and therefore vulnerable to weapons fire from unsecured areas. Agencies should consider avoiding topography and vegetation that prevents clear lines of sight from the site to avoid making it easy for potential attackers to approach the site without notice.
Dense trees and shrubbery present similar challenges. Portions of sites (especially larger sites) are often left in their natural state, which can include steep terrain and dense vegetation. This occurs for a variety of reasons including unsuitable terrain, zoning or environmental regulations, and land banking for future use. Where these situations exist, agencies should consider perimeter protection to separate those areas from the developed portion of the site, to prevent them from being used for a covert approach to valuable assets. Refer to Section 6.2.1.2 for details on using unobstructed space as a strategy and Section 6.2.1.3 for access management strategies.
Some natural features benefit site security. For example a stream, especially one with a sunken bed, can be an effective barrier against vehicles trying to gain unauthorized access to the property. When incorporated strategically into site layout, these features can supplement access management strategies, however, agencies must be careful not to create security gaps where such features intersect with perimeter fences and other security measures (i.e., a person might use a streambed to crawl under a fence or wall where they intersect).
Manmade Features
Manmade features may present challenges to security. For example, storm drains and utility tunnels could enable someone to gain covert access to the property.
Existing Easements
Existing easements on the property might grant non-transit personnel the right to enter the property without prior approval from the transit agency. Agencies should make efforts to be familiar with the location of existing easements, especially in relationship to the location of critical assets.
Abutting Properties
While a transit agency may be able to design its property to meet agency security needs, it may have little or no control over neighboring properties. Site planners should therefore consider the characteristics of all nearby properties in the site selection process and layout of the transit property to avoid undermining even the best on-site security precautions.
Factors to take into account include topography, vegetation, buildings, and rooftops that can provide vantage points for aggressors. An additional consideration is what access controls, if any, exist on abutting properties. For example, if an adjacent building is a federal agency with tight security and access controls, this fact may mitigate concerns about the proximity of the building to the transit site. In contrast, an abutting public park, for instance, could be seen as a legitimate security concern-both for positive reasons (open areas provide clear views of approaching persons or vehicles) and negative reasons (open, public access is offered to a wide range of individuals). Agencies should consider these issues in addition to other non-security issues when acquiring property for transit agencies. Purchasing the abutting properties outright as a buffer or for less critical uses is also an option.
Access to Public Roads
Avoid siting critical facilities in such a way that vehicles may have direct routes between public roads and critical facilities. However, the site layout should neither preclude nor complicate access via public roads for emergency vehicles, nor should it inhibit emergency egress for passengers and/or employees.
Proximity to Private Roads
Agencies should be aware of any private roads close to the property that might introduce threats to the facility, the types of traffic attracted by adjacent uses and facilities, and traffic use of private roads near the facility.
6.2.1.2 Building Placement
Appropriate placement and orientation of buildings and other structures on the site is a major component of an effective security strategy to protect against damage from terrorist attacks. Agencies should consider the impact of the following building elements on site security: unobstructed space, standoff distances, and building orientation.
Unobstructed Space
Unobstructed space is an area around an asset, usually a building, which provides clear visibility around the asset.
Agencies should consider surrounding buildings and equipment by unobstructed space to facilitate surveillance of the property and prevent the concealment of explosives and other harmful devices next to structures. For buildings, federal standards for unobstructed space call for an area 10 meters (33 feet) wide adjacent to a building.2 This may not always be possible, particularly in dense urban areas, calling for alternate measures to accommodate existing conditions.
2UFC 4-101-01, Department of Defense, Minimum Antiterrorism Standards for Buildings, (31 July 2002)
Standoff Distances
Standoff distances are minimum distances between a building, or other asset, and a secured perimeter barrier established to protect the asset from blast damage. Standoff distances limit the proximity of a terrorist or explosive to the asset. The appropriate standoff distances are determined by the size of a potential explosive and the critical value of the asset. Standoff distances help minimize damage from an explosive attack.
Figure 6-1 illustrates the impact of standoff distances on building security.
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Standoff distances help minimize damage from an explosive attack Figure 6-1. Standoff Distance |
The area within the standoff distance, excluding unobstructed space, can be landscaped with trees, shrubbery and other features. If agencies use this area, wherever possible they should avoid inhibiting the security function of the space; activities such as parking should be avoided. If parking within the standoff distance is needed, agencies should consider parking access control measures. If threat levels increase, they should consider temporarily prohibiting parking. Agencies should also consider restricting bicycle parking within standoff distances as threat levels rise, especially where bicycle lockers are used since they might conceal bombs or weapons.
Building Orientation
Building orientation can be used to protect or shield external vulnerable features of a building from an attack. Vulnerable features include entrances, windows, lobby areas, drop-off areas, loading docks, and other miscellaneous openings.
Agencies should consider orienting buildings and other critical assets so that clear lines of sight between their vulnerabilities and uncontrolled areas or vantage points is avoided. On-site vantage points include publicly accessible areas such as lobbies and parking lots, which may have less stringent security measures. For example, entrances to critical buildings should not directly face a public street from which an aggressor could fire a weapon at the lobby. When orienting assets, the site planner should keep in mind that the aggressor does not have to be in the secured area to attack a person or asset within the secured area; likely origins of attacks from which a terrorist could fire a weapon or detonate an explosive include nearby buildings, hilltops, roadways, or other uncontrolled areas outside the transit property perimeter.
6.2.1.3 Access Points to the Site
Control over how and where vehicles and pedestrians approach and enter a transit property is a crucial factor in site security.
Key concerns include number and location of access points, dedicated entrances or areas, and speed-control approaches.
Number and Location of Access Points
Access points are the means by which people enter and exit a site. The quantity and location of access points depends on a number of factors, including directions from which people will be approaching the site, method of approach (car, on foot, etc.), and the volume and timing of people or vehicles the entrances must accommodate. The type of facility plays a role as well; a large transit station, for example, may need several entrances to function smoothly, while a maintenance yard may have only one entrance for vehicles and pedestrians.
A facility with fewer entrances is generally easier to secure. Agencies should consider designing a site with the minimum number of entrances needed to satisfy the requirements of its daily operations. In areas where local safety regulations require emergency entrances and exits, these points should be secured in a manner that prevents unauthorized everyday access while still meeting safety criteria; this often requires advanced coordination with emergency responders to ensure they will have access to the property through all entrances. As threat levels vary, some access points to sites or buildings can be closed off, to channel movement by less vulnerable assets.
Agencies should consider locating facility entrances at points that reflect their user population, while facilitating security. Facilities with heavy public use, such as transit stations, should have access points that maximize convenience and capacity, while facilities used less frequently by the public can have less convenient entrances without generating a significant negative impact on facility operations (see Figure 6 2).
Dedicated Entrances or Areas
At facilities with different types of users accessing the site, it may be appropriate to have specific entrances and areas within the site dedicated to particular users. The goal of this strategy is to segregate traffic that presents different security threats, and therefore requires different degrees of access management. Transit staff, for example, pose less of a threat than anonymous transit riders or delivery vehicles, and agencies should consider allowing their staff to access a site more easily and park their vehicles nearer to sensitive assets.
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Entrances should be oriented away from (right) rather than facing (left) uncontrolled areas such as roadways, provided that such orientation does not impinge on access by disabled persons and maintains safe, conventional pedestrian access. Figure 6-2. Building Entrance Location |
Delivery vehicles pose a particularly high threat to at-risk facilities, because of their large payload and authorization to enter sites. For these reasons, agencies should consider separate delivery entrances with a dedicated access road that admits vehicles directly to receiving areas or loading docks (and away from vulnerable assets) wherever possible. If a dedicated roadway is not practical, a designated route through the site could serve the same purpose. Any delivery vehicle parked inappropriately, or seen driving outside the designated route, would be noticed more easily and generate the appropriate response from security personnel.
Many facilities may already have segregated entrances. Commercial and industrial facilities typically segregate entrances to satisfy a variety of needs such as maneuverability, aesthetics, and traffic flow. If existing facilities have segregated access routes, they should be evaluated and upgraded to address the concerns discussed in this chapter. When initiating or reconfiguring access points, planners and designers should also maintain safe, convenient access routes for pedestrians, persons with disabilities, and cyclists as well.
Speed-Control Approaches
Agencies should consider designing roadway alignments to impede high-speed vehicle approaches to site access points and assets such as buildings. This prevents an attacker from using a fast moving vehicle to ram through perimeter security or destroy an asset in a collision. Roadways approaching gates or assets can force a vehicle to pass through sharp curves that can only be negotiated at low speed. Staggered concrete or water-filled barriers or indirect roadway alignment lined with dense low shrubbery or other barriers are examples of obstacles to high-speed approaches. These methods limit the approach speed, while preserving clear views of the roadway from security checkpoints and building lobbies.
Approaches that allow a vehicle to approach a gate or checkpoint unseen can be avoided using speed bumps, speed tables, and similar traffic-calming techniques as speed controls, although they are less effective because they still allow a vehicle to accelerate. Similarly, agencies should consider avoiding clear straight approaches that allow high-speed acceleration toward lobby entrances, fuel storage, or other sensitive areas.
6.2.1.4 On-Site Vehicle Circulation
Controlling how vehicles and pedestrians move about within a transit property may also be a useful security measure. Designers might consider dedicated circulation routes for certain users and routes that limit high-speed approaches to assets on the site. The sophistication of a circulation plan depends on the size of the site, the diversity of activities, and the types of users at the site.3 This should include drivers, pedestrians, cyclists, etc. When selecting a facility site, an agency should consider how the property accommodates the circulation needs of both its everyday functions as well as its security concerns.
Key concerns include parking areas and drop-off areas.
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Vehicle barriers such as this and other access control measures assist in managing vehicles approaching a submerged access point. |
3For information about access control concerns such as perimeter vehicle inspection, access to parking, parking and traffic controls, vehicle registration, towage and access control systems, refer to Chapter 5: Access Management.
Parking Areas
Agencies should consider locating general parking in open lots or dedicated garages with access control systems. Vehicles should be parked beyond standoff distances that are sufficient to protect vital structures. Agencies should avoid locating parking under a transit building or on its rooftop. If this is unavoidable, agencies should consider stricter access controls, surveillance, or detection measures.
Depending on the type of facility, planners may segregate visitor or commuter parking from that of authorized personnel, especially at sites with substantial public activity. A separate visitor parking lot may be located near the visitors' entrance to buildings, but design measures (discussed above) can be used to protect the entrance from high-speed approaches or attacks from the parking lot.
Drop-Off Areas
Passenger drop-off areas should be located where vehicles pose a minimal threat to assets. If possible, they should be outside the required standoff distance, and should not provide clear lines of sight to openings, windows, lobbies, HVAC intakes, or other external building vulnerabilities. When it is impractical to have the drop-off area outside the standoff distance, designers may consider monitoring the drop-off area for suspicious activity or devices with additional surveillance.
Agencies should consider locating drop off areas away from areas of concern, such as a station platform, especially when the drop-off area is within the standoff distance. Depending on passenger volumes, the agency can also consider providing a shuttle bus to bring passengers or visitors from remote parking areas to a closer point. All drop-off areas should be in an open space, not under a covered entryway or building overhang, and they should not be in areas that would concentrate a blast toward a building or other sensitive assets.
6.2.1.5 Particular Considerations for Mixed-Use and Intermodal Facilities
Mixed-use facilities are buildings or parcels of land that incorporate more than one use. They are addressed in this chapter because mixed-use transit stations - those that combine transit facilities with residential, commercial or other space - are becoming a popular model in the United States. In addition, transit agencies' administrative offices are often located in buildings shared with other tenants.
Intermodal facilities are characterized by the multiple modes that meet at the location. They enable transfers or connections between bus, rail, or light rail and/or ferry lines. These facilities enable seamless transportation throughout one's journey by facilitating movement between the modes at the site.
Challenges
Securing mixed-use facilities presents unique problems because other uses will be in close proximity to transit facilities, and the transit agency's control over the entire site is typically limited. The result is that traditional access management techniques and security-oriented site design may not be possible. This is especially true for retail facilities and historic sites that integrate transit space, because of the abundance of non-secure public space surrounding the station.
Strategies
Options for addressing security concerns in mixed-use facilities vary depending on the included uses. When administrative offices share space with other tenants, security options are usually limited to access control and intrusion detection. Many office buildings have a security system for the entire building that incorporates access control, intrusion detection, and surveillance. Standoff distances for blast protection and vehicle barriers (other than for parking control) are not commonly found at commercial office properties.
Transit stations integrated into commercial, recreational, or historic facilities should focus on strategies for detection of attempted attacks. Security options for these sites include:
- CCTV and other surveillance methods
- Attack detection (fire, chemical release, explosion)
- Intrusion detections (intrusion into restricted areas such as mechanical rooms)
- Evacuation plans
A transit agency should work with the owners of the surrounding spaces to develop a security plan that meets all parties' needs. If such cooperation fails, and if the facility is judged to be at a high risk for attack, the transit agency may want to evaluate relocating to another facility.
Intermodal facilities can be somewhat easier to protect than mixed-use facilities because they are under the control of a transit agency or multiple transport agencies. The advantage is that all transit agencies have similar security concerns, making it easier to implement a comprehensive security plan. The high level of transient pedestrian traffic through intermodal stations, however, creates increased risk because it is easier for an attacker to access the site and the large amount of people make it an attractive target for an attack.
In order for the facility to work efficiently, agencies should consider balancing the need to accommodate the large numbers of people smoothly with the impositions created by security measures.
6.2.2 Interior Layout
The interior layouts of the buildings and other structures on the site may also support the detection and deterrence of harmful activity by establishing protective barriers around sensitive assets and by enabling effective surveillance within the structure. In addition, providing the necessary access routes and emergency equipment enables successful facility evacuation and emergency response.
This section describes the factors a transit agency might consider when designing the interior layout of the site. These include asset shielding, surveillance, and emergency routes.
6.2.2.1 Asset Shielding
A building's layout can be used to shield critical areas such as a central-control room, or vulnerable areas such as a station platform packed with people, from an attack at the outer edge of the site.
Agencies should consider using special reinforced materials between valuable features and easily accessible areas, such as lobbies, mailrooms, and loading docks, or locating these areas at a distance from each other. For example, designers may consider positioning a control room at the center of a building, behind layers of other non-public areas, and at a distance from a likely detonation point in case of an attack. Within a room, planners may be able to reduce the vulnerability of personnel and critical equipment by positioning them away from windows and doors. Critical assets might be dispersed so that they cannot be disabled by a single attack, and locate redundant or back-up systems in a different building, or even at a different site, if possible.
Agencies should consider using a facility's layout to help enforce zones for each type of activity taking place, to safeguard the nonpublic areas of a site. Public areas such as train platforms or lobbies can be separated from non-public spaces intended only for staff; and access management elements (such locked doors, checkpoints, etc.) may help prevent unauthorized movement between the zones. Agencies can insulate particularly sensitive non-public facilities from the public using other, less critical non-public spaces.
Agencies should also consider making pedestrian movement within the facility consistent with the access management tools in place. Signage and other pedestrian flow controls can direct public users away from non-public spaces. Separate entrances and routes can be used for the public and staff within the building wherever possible; this minimizes the opportunity for someone to gain unauthorized access to secure areas of the facility.
6.2.2.2 Surveillance
Public spaces can be designed to facilitate surveillance-a key CPTED principle-with large fields of vision and no blind spots or hiding spaces.
With clearly identified and understood zones of activity, staff and the public can more easily identify unauthorized people and suspicious behavior. Designers should try to avoid creating blind corners, isolated passageways, as well as columns and other sightline obstructions.
6.2.2.3 Emergency Routes
Emergency routes within, to, and from all areas of the building serve two purposes: evacuation of staff and the public, and access by responding agencies. Appropriate emergency routing is critical to safety and can vastly reduce the impact of an unexpected event.
Agencies should consider making emergency routes an integral element of a building's design and factor in the following principles:
- Locating corridors and stairways making up the routes away from likely areas of attack and reinforcing them to resist damage in an explosion or fire.
- Devising evacuation routes that are clearly marked, unobstructed, and adequately sized for the occupancy level of the building.
- Designing routes and protected "safe areas" to accommodate wheelchair users and other occupants with special needs.
- Providing multiple evacuation routes, in case the primary exit becomes damaged or blocked.
- Locating critical routes and systems that are logical and consistent with other buildings and the surrounding area, since during an emergency, authorities must be able to quickly access to the building and the on-site emergency equipment.
6.2.3 Structural Engineering
Structural engineering, or structural design, is the design of a building's internal support system. Structural design includes the selection of a framing method or structural system, as well as the selection and sizing of structural members, based on loading and architectural requirements. Structural members include beams, columns, the foundation, floor slabs, connections of these elements to each other, and other ancillary components.
Building design (structural and architectural) can contribute to infrastructure security by minimizing the extent and depth of damage in an attack. Structural integrity can help mitigate blast and fire damage to the building; protect inhabitants; protect equipment, property, and records; allow critical operations to function immediately after an attack; and allow rescue operations in and around the building preserved after an attack.
This section focuses on blasts and fires, describing engineering concepts for structural integrity and strategies for minimizing damage. The concepts discussed include:
- Blast loads
- Blast damage
- Progressive collapse
- Blast mitigation
- Fire damage
The sections of most building codes relating to structural components address service loads and methods to determine the proper size of structural members and their connections. Service loads specified in building codes are based on the location and intended use of the proposed structure, and include:
- Minimum dead load: the weight of the structure
- Live load: variable loads such as people, cars, furniture, etc.
- Earth load: earth pressure on buried structures, retaining walls, foundations, etc.
- Wind load: pressure applied to the structure by wind
- Snow load: the weight of snow on a building
- Seismic load: loads induced on structural members during an earthquake
Building codes do not usually address "blast loads"; the force exerted on a building from the detonation of an explosive device.
Blast loads are different from the usual types of service loads considered by a structural engineer when designing a building. Service loads are relatively predictable in their magnitude and placement on the structure. In contrast, blast loads are much greater in magnitude, are unpredictable in size and placement. However, there are certain engineering strategies that agencies can use to enable a building to maintain its structural integrity after some of its components have been compromised or completely destroyed in a blast.
6.2.3.1 Blast Management
Blast Loads
A bomb exploding at ground level produces a hemispherical shock wave. As with other waves, such as sound waves, the shock wave can reflect off objects, concentrate in confined areas such as tunnels, or change direction. This is important to understand because once the skin of a building is breached, the shock wave can travel or ripple through a building's corridors as the energy in the wave dissipates.
| Type of Explosive | Explosive Capacity in TNT Equivalents |
Lethal Air Blast Range |
|---|---|---|
| Pipe Bomb | 5 lbs. (2.3 kg) |
|
| Breifcase, Backpack, or Suitcase Bomb |
50 lbs. (23 kg) |
|
| Compact Sedan | 500 lbs. (227 kg) |
100 ft. (30 m) |
| Full Size Sedan | 1,000 lbs. (454 kg) |
125 ft. (38 m) |
| Passenger or Cargo Van |
4,000 lbs. (1,814 kg) |
200 ft. (61 m) |
| Small Box Van 14 ft box |
10,000 lbs. (4,536 kg) |
300 ft. (91 m) |
| Box Van or Water/Fuel Truck |
30,000 lbs. (13,608 kg) |
450 ft. (137 m) |
| Semi-trailer | 60,000 lbs. (27,216 kg) |
600 ft. (183 m) |
Source: Transportation Security Working Group, "Terrorist Bomb Threat Standoff (Card)," Government Printing Office (1999).
A bomb or other explosive device produces a blast that creates a blast load. Explosions cause damage by the generation and propagation of heat, pressure, and flying debris (shrapnel). An explosion is a rapid, often violent, release of energy that produces a rapid release of gases and heat. The rapid release of gases compresses the air immediately around the bomb, creating a shock wave. This shock wave, or pressure wave, propagates through the air outwards from the explosion. When this shock wave encounters an object, such as a building or a trash receptacle, it exerts a force on that object. The magnitude of these forces can be tremendous: a 74 mph wind (threshold hurricane wind speed) produces a pressure of approximately 21 psf (0.1480 psi); in contrast, according to Tod Rittenhouse, "the blast pressures exerted on the building façade in the Oklahoma City bombing were on the order of 4,000 psi." 4 Ranges for various types of explosives are further described in Table 6 1.
4"Designing Terrorist-Resistant Buildings," Tod Rittenhouse, Fire Engineering (November 1995).
The blast load striking a building or other object depends on the amount and quality of explosive detonated and the distance of the explosion from the building. Maximizing standoff distances is important; the farther away an explosion, the weaker its effects. As the shockwave radiates away from the explosion, the magnitude of the shockwave decreases and the duration of the shockwave increases. (See Figure 6 3.)
The peak magnitude of the shockwave increases by a reflection factor as it encounters the face of a building. This increase in magnitude is analogous to ocean waves rising as they strike a sea wall and the water "piles up" against the wall. The reflection factor varies with the incident angle (the angle at which the shockwave hits the building). The increase is maximized when the direction of wave travel is perpendicular to the building. This can increase the pressures by an order of magnitude.
Explosive materials vary in their efficiency (energy released per pound of material). In calculating blast loads, current practice expresses all explosives in terms of an equivalent weight of TNT, regardless of the actual explosive material used. Information for determining blast load magnitudes in relation to building hardening design is available through the Department of Defense, General Services Administration, and in other security-related publications.
Damage from Blasts
The main threat to the structural integrity of a building is blast force, regardless of whether the explosion occurs inside or outside the building. The primary vulnerability is the overloading of the structural system by blast loads that cause the system to fail and the building to collapse.
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Figure 6-3. Variation of Explosive Pressure and Duration with Distance from Explosion |
Blast damages are classified as either direct (those that occur in the explosion) or indirect (those that occur as a subsequent consequence of direct damage).
- Direct Damage
- A hole in the ground or foundation.
- Localized damage to the building's façade (bricks, windows, signs, etc.).
- Damage or removal of a structural member or members (a beam, column or other structural element) directly caused by the blast.
- Indirect Damage
- Flying shards of glass: Glass shards thrown from a window can cause serious injury to people, even if they are several feet from the window that shattered.
- Flying debris: If the force of the explosion breaches the building's façade (building skin, curtain wall), the energy not absorbed by the façade can hurl furniture and other light objects. These "missiles" can cause injury, damage property, and rupture service systems such a gas, water, electric and communications.
- Progressive collapse: If a blast directly destroys a column or beam locally, other structural members may fail. This can start a chain reaction of failures that results in damage disproportionate to the blast and collapse of the entire building.
Progressive Collapse
The worst-case consequence of blast damage related to structural engineering is progressive collapse. This is the disproportionately large collapse of a building or structure from an explosion, caused by the loss of one or more structural members, resulting in only localized damage. Progressive collapse occurs because most buildings are designed to carry the required loads, based on the assumption that all structural members are in place.
Two types of progressive collapse are possible:
- Pancaking is the stacking of floors on top of each other. It occurs when an explosion destroys a structural member or members, causing the floor directly above the destroyed members to collapse, which causes the next floor above it to collapse, and so on.
- Cascading is the collapsing of a series of bays (the section of a building between two rows of columns) from the destruction of one or a few bays. Cascading occurs when an explosion destroys a bay, or bays, causing the adjacent bay or bays to collapse in succession.
Progressive collapse occurs in stages, as summarized below. A complete discussion of progressive collapse is beyond the scope of this report; for more details refer to the latest edition of ASCE Standard ANSI/ASCE 7, Minimum Design Loads for Building Structures.
Beams (Including Girders)
Beams are horizontal structural members that support the floor slab. They carry gravity loads and are typically supported by columns or girders. Transfer beams or girders can support floor slabs, other beams and other columns. Beams and girders also provide lateral support to columns to prevent the columns from buckling.
When an explosion destroys a column, the supported beams lose their support at the destroyed column and become cantilever beams. If the beams are connected to the remaining columns with non-rigid connections (connections unable to transfer bending loads from a beam to a column), all beams previously supported by the destroyed column will collapse along with the floor slabs those beams support. This can extend through several stories. The loss of these beams can also reduce the lateral stability of the adjacent columns not damaged by the initial blast, causing those columns to fail, followed by more beams, and so on.
Floor Slabs
Floor slabs are typically designed to carry gravity loads. Sometimes the slabs are designed as diaphragms and are part of the lateral support system.
When the shockwave enters the building through an open window or breached curtain wall, it can exert an upward load on the bottom of the slab, causing the slab to fail. The loss of the slab can increase the unbraced length of the adjacent columns, potentially causing the columns to buckle. Failed columns can result in collapsed beams and the other consequences discussed above.
Columns
Columns typically carry axial gravity loads and are usually not designed to bend. When columns are part of the lateral resisting system, bending is taken into account. The strength of a column is limited by its length and by the size and shape of its cross section. If the unbraced length of a column (the distance along the column between horizontal members) increases due to the loss of a beam or slab, the strength of the column is reduced.
If an explosion destroys a perimeter column or columns, the girders and beams supported by those columns lose their support. This may increase the unbraced length of the adjacent columns due to the failures described above.
Blast Mitigation
The best methods of protecting a building from blast damage are effective access management techniques and appropriate standoff distances. Since no security system is foolproof; however structural engineers need to anticipate that buildings may be subjected to blast forces. Structures designed to resist catastrophic effects from blast forces are referred to as "hardened" buildings; these use a combination of structural design, architectural design, and mechanical design to minimize the consequences of a blast.
Constructing hardened structures can be expensive and time consuming, particularly when retrofitting an existing building. One possible alternative is to add redundant structural components to a building, although this approach can be just as expensive. Before hardening a structure, a transit agency should consider whether such an approach is necessary.
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Hardening vulnerable areas, such as a lobby, can protect other parts of the building from an attack. Figure 6-4. Isolation of Vulnerable Areas |
Avoiding Progressive Collapse
Agencies should consider designing buildings to sustain localized damage, including the total loss of multiple structural members, and still remain standing. Designs should take into account the stability of a structure if the structure loses a column or columns, a bearing wall, a beam or a combination of structural elements. Design techniques that help prevent progressive collapse include:
- Stiffening the perimeter frame by designing it as a rigid frame.
- Strengthening floor slab systems to distribute and sustain a load by catenary action to account for the loss of a column.
- Designing floor slabs to span in a direction in other than normal conditions (a lower factor of safety may be used for the secondary span condition).
- Designing load-bearing partitions to accept loading when slab spans change direction.
- Increasing the load capacity and ductility (ability to deform without breaking) of beam-to-column connections.
- Building returns (an angled section of wall at the free-standing end of a wall) on walls to increase their stability under suddenly increased loads.
- Reinforcing and tying walls and slabs together, allowing them to act respectively as the web and flanges of a beam to compensate for the loss of other structural members.
Underground parking presents an opportunity for a car bomb or other similar device to be placed under a building, and agencies should consider avoiding this design feature. When underground parking facilities are warranted, agencies can use structural design modifications. For example, columns in the garage can be designed for a greater unbraced length: double the unbraced length for one level of parking, triple it for two levels of parking, and so on.
Agencies should consider structurally isolating sections of the building from each other, to prevent substantial damage in one area from causing a progressive collapse in other areas (see Figure 6 4). This compartmentalization serves two purposes. It can buffer high-risk areas (mailrooms, public lobbies, chemical storage areas, or other areas where an explosion is more likely to occur), from the rest of the building, so the destruction of such an area does not result in the total collapse of the building. It can also provide extra protection for critical rooms and equipment, such as control rooms, communications rooms, and staffed areas, so these remain structurally sound if a blast occurs elsewhere in the building.
6.2.3.2 Fire Management
While accidental fires may occur, fires resulting from an attack may have a different kind of impact. For example, an accidental fire usually starts at one location and often, but not always, spreads relatively slowly. On the other hand, a fire from arson is often strategically set in multiple locations to maximize the rate of spread and damage. An arsonist may also sabotage the fire protection system. An incendiary bomb that produces a fireball or intense heat (as opposed to a bomb that produces only a shock wave) ignites a large area and can cause substantial damage, including local damage to the fire suppression system.
Well-established design and construction practices for protecting structural members from fire are particularly important in case of an attack. Although not all structural materials will "burn," all structural members, regardless of their material composition, will lose a percentage of their original strength when subjected to intense heat. Excessive heat is the principal cause of a fire's detrimental effects on a structure. Therefore, upgrading or hardening the automatic sprinkler system is of tremendous benefit in mitigating the effects of fire on a structure. Additionally, many of the mitigation measures for blast impacts apply to fire management as well, such as isolating vulnerable areas to prevent the spread of fire and avoiding progressive collapse (see Figure 6 4).
This section discusses the effects of fire on four major structural construction materials: steel (structural steel), reinforced concrete, pre-stressed concrete, and timber.
Steel
At high temperatures, unprotected steel looses its strength. For this reason structural steel members used in building construction are protected (fireproofed). Fireproofing methods to protect steel members from heat insulate the steel from the fire. This increases the time required for heat to transfer from the fire to the steel.
There are several insulating methods for steel members:
- Concrete encasement. Encasing steel members in concrete provides excellent insulation to the steel. Lightweight concrete (see the About Concrete illustration on the next page) provides better insulation than standard concrete. The selection of concrete type depends on several design factors that are beyond the scope of this document. This method is well suited to insulating columns. It may also be used to insulate floor beams supporting a concrete floor slab. However this can be expensive due to complicated forming and increased dead load.
- Sprayed on mineral fiber coatings. Mineral fiber coatings are easy to apply, and they provide excellent protection when applied correctly. However, these coatings are easy to scrape off, and explosive blasts may damage portions of the insulation. Protection of the insulation is discussed at the end of this section.
- Cementitious material coatings. Cementitious coatings form a continuous coating around the steel. However, during a fire, they can spall (chip or flake on the surface), and there is a history of problems with lack of adhesion to the steel.
- Intumescent paints and coatings. Intumescent coatings swell when heated, thereby insulating the steel and retarding the effects of the flames and high temperatures. These coatings work well to protect the steel from heat. Exposure to flames can damage or destroy this type of coating and therefore should only be applied to components unlikely to be directly exposed to flames.
About Concrete...
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There are several concerns when selecting a method to fireproof steel, including method of building construction, and installation and maintenance costs. During a blast, it is likely that the fire proofing on the steel in the immediate vicinity of the blast will be damaged. However, the fire that may result (and spread) will have an effect similar to conventional fires. Assuming the progressive collapse considerations were used in design, protection of the remaining steel members will be effective.
Reinforced Concrete
Concrete is often used as an insulating material. Although concrete structures rarely collapse from fire damage, the strength of concrete and reinforced concrete members is reduced by exposure to high temperatures. Type of aggregate and moisture content are the principal factors that determine concrete's sensitivity to heat.
Type of aggregate is the most significant factor. Lightweight aggregates such as vermiculite and perlite are used in lightweight concrete. Lightweight concrete, in addition to having better insulating characteristics, has better strength retention when exposed to intense heat.
The amount of moisture in a concrete affects the member's resistance to heat. The moisture is trapped in the small capillaries within the concrete. As heat energy is absorbed, the water in the concrete vaporizes, which locally helps maintain the concrete's strength until the moisture is burned off. However, voids left by the vaporized moisture weakens the area. Structural engineers should consider this when fire is a concern for concrete members.
Pre-Stressed Concrete
The relevance of aggregates and moisture content for pre-stressed concrete are similar to those for reinforced concrete. The concrete used for pre-stressed concrete members is usually stronger than the concrete used for reinforced concrete members and has better fire resistance, but tends to spall and expose the reinforcement.
Pre-stressing steel is the principal concern when exposing pre-stressed members to intense heat. High carbon-cold drawn steel used in pre-stressing is more sensitive to intense heat than low carbon, hot rolled steel used in reinforced concrete. Also, the loss of strength in pre-stressing steel is permanent and not regained upon cooling. For example, the pre-stressing steel is initially under great tension. Over time this tension decreases, as the steel tends to creep (continually deform or lengthen). This is taken into account during the design process; however exposure to high temperatures, exacerbated by the spalling concrete, accelerates this "creeping" process. Engineers should consider this when considering fire effects on building hardening.
Timber
Unlike steel and concrete, wood will burn. The principal factors that determine how timber responds during a fire are the size of the timber member and its moisture content.
As wood burns, a charcoal layer forms on the wood's exterior. This char layer is an insulator and as the layer thickens, it slows down the rate of burning. The unburned interior wood retains its strength. Buildings constructed with large timber members can maintain their integrity for a long time during a fire, providing an opportunity for the fire to be extinguished before structural failure occurs. As is in all cases, but especially for timber construction, a hardened sprinkler system is important. Fire retardants can slow combustion and delay ignition of wooden members.
6.2.4 Architectural Features
The design of architectural features on a site can aid in surveillance, help deny an opportunity for an attack, and reduce injuries and property damage in case of an event.
This section describes the factors a transit agency might consider when designing security features into a site. These include:
- Façade
- Entrances
- Fenestration
- Small architectural features
- Utility openings
- Signage
6.2.4.1 Façade
A façade is the outside face of a building or wall. It can refer to just the outer surface, or more generally to all construction between the exposed surface and the structural frame. In some instances, the structural frame is visible as an integral part of the façade.
Materials
Façade design affects a building's resilience to terrorist attacks and other incidents. Designers can construct a building façade with materials that resist fire and produce little or no toxic fumes or minimal debris in an attack. Materials that ignite and spread fire quickly or produce toxic fumes, such as plastics, paints, and other finishes can trap building occupants and cause suffocation or other consequences.
Façade materials can be attached in a manner that will reduce the amount of secondary debris. Masonry or pre-cast concrete panels can be reinforced and securely fastened to the building frame. Bricks or other face materials that come loose in a blast may become projectiles and cause secondary damage. As with progressive structural collapse (refer to the subsection on progressive collapse in Section 6.2.3.1), façade design should prevent indirect damage that destroys the entire facade. On sides of the building that face likely directions of attack (such as public streets or nearby buildings), agencies should consider minimizing the use of weaker materials and/or openings. Overhanging design features should also be avoided where they could receive a blast load from underneath.
Façade features can also impact visibility; elements such as light color schemes, translucent canopy materials, and skylights provide more light in interior spaces. Transparent materials like glass may provide added opportunities for surveillance, allowing transit employees and passengers to see from one zone of a facility to another and to share light from one area to the next. Conversely, solid materials such as concrete block walls may prevent potential attackers from observing facility activity patterns at non-public locations such as maintenance facilities, compared to chain link fences, which allow unhindered observation.
Decontamination
Incident recovery may also be relevant to consider when choosing materials. Weapons of mass destruction, such as chemical or radiological agents, can be absorbed into materials such as concrete and plastics. Non-porous coatings may be able to minimize absorption of chemical contaminants when applied to porous materials like concrete or brick. Agencies should consider decontamination efforts-whether cleaning or removal-when choosing façade materials, and perhaps even consider comparing the extent of the decontamination effort required for the material options before settling on a selection.
In response to the anthrax attacks at the Hart Senate Office Building and Brentwood Post Office, gaseous chlorine dioxide gas was pumped through the buildings' heating and ventilation systems and kept inside the buildings for 9 to 12 hours to ensure that all spores were killed. Liquid chlorine dioxide and other antibacterial gels were also used and potentially contaminated mail was irradiated before being sent to its destination. The Hart building was closed for three months while cleanup and testing was completed. The estimated costs for cleaning the 700,000 square foot Brentwood postal facility were $22 million.
6.2.4.2 Entrances
Agencies should consider locating entrances to the building, including main lobbies, service entrances, and loading docks, away from uncontrolled public spaces whenever possible. This reduces the opportunity for a direct attack on an entrance. Agencies should also consider locating exterior entrances where there is no direct access to key assets (such as OCCs) within a building.
The sizes of doorways and lobbies should be appropriate for the access management techniques used on-site. For example, at security checkpoints that span entryways it is extremely difficult to bypass them without detection, and in larger lobbies additional security staff may be required.
6.2.4.3 Fenestration
Fenestration is the design and arrangement of windows and other glass features on a building, including glass façade panels and openings. The location and construction of windows will likely vary, based on the location and contents of a building.
Designers may reduce the number of windows around sensitive or valuable assets, to make those assets less visible to the public and to minimize damage in the event of an attack. For facilities with large fenestrated areas, designers may compensate by incorporating standoff distances and orienting the windows away from unsecured areas. Where possible, agencies should consider locating windows out of convenient reach and use security screens or wire mesh to prevent unauthorized access through the opening.
Agencies should consider using windows and frames constructed of materials that resist tampering and easy destruction, and that prevent flying glass shards in an explosion. For example, tempered glass or polycarbonate composites that shatter cleanly (such as those found in automobile windows) may prove safer than conventional annealed glass that breaks into dangerous shards. Planners might also consider window treatments, including adhesive films, coatings, and blast curtains that limit the depth of in-room damage from shattering window glass.
6.2.4.4 Small Architectural Features
Agencies should incorporate small architectural features or amenities, such as planters, benches, and trashcans, in the facility design in such a way as to prevent them from causing damage in a blast. Anchoring objects made of blast resistant, reinforced materials to the ground will make them less likely to act as projectiles and cause secondary damage.
Agencies can also incorporate these design elements into access management techniques, such as barriers for vehicles, but should also be cognizant of not placing them in a location that could provide hiding spaces or shielding for potential attackers, especially near entrances or critical assets.
6.2.4.5 Utility Openings
Many buildings require numerous functional openings, such as utility tunnels, sewers, and HVAC vents, which provide the potential for unauthorized access or the introduction of harmful substances into a structure or tunnel.
Agencies should consider locating openings in inaccessible locations or where any suspicious activity would be easily observed to protect the openings. Security doors, hatches and grilles should resist tampering or damage and can be sized to prevent entry by a person or the introduction of harmful substances. In some cases, additional monitoring or surveillance equipment may be justified.
6.2.4.6 Signage
Signs are effective tools for access management and for assisting people unfamiliar with the building. They can direct public users to proper areas of the building, warn against unauthorized entry into nonpublic spaces, and indicate emergency evacuation routes.
Signs can also inform and instruct visitors on proper and improper activities within the building or facility. In some cases, transit agencies may consider reducing or eliminating signage for key assets, to hinder their discovery by potential aggressors. All signs should be legible and easily discernable to all passengers, including those with disabilities. 5 Emergency exit signs can also be designed with lighting elements, to make them visible in the dark. Agencies should consider designing signs in public areas to resist tampering or destruction, and, when placing signs on walls or other surfaces, should avoid adhering them in a way that allows items to be hidden on, in, or between the sign and the surface.
5All signs, emergeny facilities, and any security measures should be compliant with the American with Disabilities Act (ADA).
6.2.5 Systems and Services
Building services create a safe and comfortable environment for occupants and enhance a building's functionality. Individual systems have many similarities and may rely on shared or auxiliary systems for part of all of their service. In addition to having similar attributes, they also have many parallel vulnerabilities and countermeasures.
This section describes the principal systems and services in a transit building. These include:
- Public utilities
- Electrical system
- Functional components 6
- Heating, ventilation and air conditioning (HVAC)
- Lighting
- Communications
- Security systems
- Water and sewer
- Fire protection
6Building services use functional components such as wiring, mechanical equipment, switchgears and alarms that manipulate system inputs to produce the desired outputs. The only human interaction with functional components should be by maintenance or operational staff as these components are not part of the public interface.
Many of these services are vital to emergency response and may be targets of terrorism themselves. Consequences of building service disruptions can range from inconveniences to the public and the transit agency to a total shutdown of the system and potentially dangerous conditions. If the building services and utilities are required for emergency response, then willful disruption of these services may supplement the primary attack.
6.2.5.1 Public Utilities
Most transit systems receive electric power from public/private utility companies through the normal public transmission system. Transit agencies also rely on public gas and water supplies. The location of these utilities is public information that can be easily obtained by anyone.
Damage to power and gas lines can cause major disruptions at transit facilities. External utility lines for all services and systems need to be protected and monitored to prevent tampering. Natural gas lines are of particular concern because of the explosive nature of their contents.
Utility lines within transit buildings may also be targets of terrorists and agencies should consider their placement as part of the building design. Perimeters and parking garages are vulnerable to large explosions and vehicle ramming. Keeping utilities away from these areas reduces the risk of additional destruction or loss of critical emergency systems. Agencies should consider concealing and protecting all utilities to the greatest extent possible.
6.2.5.2 Electrical System
Agencies should consider facility backup power sources in case of a local or regional power failure, and identify those systems requiring emergency power in the event there is an outage.
Backup power can consist of a generator that uses fuel to create electricity or a battery that can store enough power to act as a supply in an emergency. Agencies should consider regular maintenance checks to ensure backup power is operational. It is important to locate backup systems far away from the primary systems so that they are not damaged by incidents affecting the primary systems.
6.2.5.3 Functional Components
Control systems include electrical and mechanical equipment such as switchgears, alarms, sensors, meters, and other associated equipment used to coordinate other systems' functions and monitor their performance. Tampering with these controls can halt operations and compromise emergency response and evacuation.
Distributed control systems (DCS) are used to monitor whether the system is working properly, make system adjustments when necessary, and shut down the system if problems are identified. DCS can be integrated into ventilation, communication, and security systems, and located adjacent to other control components. They can be connected to an integrated facility communications system as an alarm system to notify system monitors of malfunctions or unusual activity.
Access to the control components is needed for maintenance but agencies should consider using appropriate access management controls to protect these components, and not leave them out in the open. They should also consider locating mechanical rooms away from the building perimeter, loading docks, and parking garages that are vulnerable to attack.
6.2.5.4 Heating, Ventilation and Air Conditioning (HVAC)
HVAC systems create a climactically comfortable environment and ensure air quality is adequate by regulating temperature and humidity, and filtering and replacing stale inside air with fresh outside air.
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Miscellaneous Openings - refer to Section 5.3.9 |
While some buildings provide sufficient natural ventilation to remove carbon dioxide and other pollutants generated indoors, many buildings require mechanical ventilation systems to provide conditioned air by filtering, exchanging with outside air, and temperature and humidity control. Air vents collect air from outside; fans and ducts distribute it throughout the building and vent the "used" air out of the building.
Ventilation
Heating and cooling systems may be used in conjunction with ventilation systems to keep indoor temperatures comfortable. Transit buildings, such as open garages and above-grade stations, may not have mechanical HVAC systems since they have sufficient natural air transfer, while ventilation systems are a key component of tunnels and underground facilities.
Air vents may be used to gain access to the building if not properly located and secured. A terrorist could enter a facility through the vent shaft or use the opening to disperse weapons of mass destruction throughout the facility.
Agencies should consider designing HVAC systems to reduce the potential for break-in. Some techniques that can be used include:
- Designing vent shafts to have minimally sized openings.
- Securing doors and grates on ventilation systems accessed for maintenance.
- Locating vents away from areas with public access, such as sidewalks or medians, wherever possible. It is especially important they are not located on roadway gutters or other low spots, where oil spills or floodwaters could enter.
- Locating vent openings high up where they are out of reach.
- Installing actuated louvers over vent openings that open only while the fans are running.
- Monitoring vent openings with alarms and intrusion/tamper detectors to alert officials of the presence of humans or chemical substances.
- Installing sensors in vents to detect foreign substances in the ventilation systems.
Smoke and Fume Control
In addition to the vulnerabilities the HVAC system creates, it can also play an important role in smoke and toxic fume removal, especially for large or underground facilities. Agencies may use separate or auxiliary ventilation systems for smoke and fume control.
HVAC systems can create "safe zones" in buildings for occupants who cannot leave via emergency routes. Safe zones work by creating areas of higher pressure to keep fumes and smoke out until properly equipped rescue workers can assist the trapped occupants. It is important that these systems have backup power supply and can be manually controlled safely during emergency situations.
Fuel Oil/Propane
Some facilities, generally smaller ones and those in the northeastern United States, use fuel oil or propane for heating. Agencies should take into account that fuel storage locations and methods at these sites may cause security vulnerabilities.
6.2.5.5 Lighting
Lighting is an essential facility requirement, especially where buildings do not have adequate natural light or are used at night.
Surveillance
In addition to making buildings functional, lighting has a pivotal role in helping a facility prevent and recover from a terrorist attack. Appropriate lighting also creates a sense of security for people in the building. Without adequate light, surveillance, either human or mechanical, is limited in scope. Security and other personnel require light to clearly see what is going on around them and, more importantly, beyond their immediate area. CCTV and motion detectors also require adequate levels of illumination in order to detect suspicious activity.
Lighting should provide illumination of pedestrian walkways and eliminate shadowed areas where attackers could hide. The selected type of exterior lighting should cast consistent color throughout the site, so the video surveillance quality is clear. The lighting intensity (foot-candles/square foot) should be greater around critical assets. 7 Lighting should be compatible with the particular camera systems in use, and should be designed to provide a bright, even distribution of light to eliminates hiding spots.
Lighting can also be faced outward away from a building entrance, to produce "glare" that reduces the visibility of anyone approaching a site or building checkpoint at night and providing an advantage to security personnel on duty. However, when selecting and positioning fixtures agencies should consider the possibility of concealed injurious devices within fixtures or between fixtures and the surface to which they are attached.
Evacuation
Lighting also plays a key role in the evacuation of a facility when an emergency occurs. Building occupants need sufficient light to safely exit the building without tripping or falling into others. Backup power is important for ensuring a safe evacuation if the main power source has been affected.
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Security lighting installation - refer to Section 5.3.2 |
7Sight lighting levels must satisfy the established minimum recommended levels outlined by the Illuminating Engineering Society of North America (IESNA) and other applicable codes.
6.2.5.6 Communications
Communications systems interconnect various areas of transit facilities, connect to other transit facilities, and link to outside connections, such as emergency responders and the local phone network. In addition to facility and passenger communications systems, security systems and DCS should be connected to a central location to quickly identify and set in motion the response to emergency situations. Agencies should consider backups of vital communications systems, preferably through a secondary type of network. Wire-based communications should be backed up by radio or cellular systems and vice versa.
Agencies should consider all of the following communications systems when building a new facility or when updating existing communications systems.
Pubic Address Systems
Public address systems play a vital role in providing information to facility occupants in the event of an emergency, especially when on-going emergency egress training is impossible, such as at public facilities like transit stations. Where feasible, agencies should provide clear audio and visual directions in an emergency situation to direct patrons to safe locations. Agencies can also connect fire alarms to public address systems to alert all building occupants of an emergency situation.
Call Boxes
Call boxes provide a direct communication, linking isolated parts of a facility to either on-site personnel or a remote security service. They are commonly sited where they can be easily found at stations and stops on the platform, outside the station building and/or in parking lots. These systems allow citizens to report incidents quickly without leaving the site.
Agencies should keep public call boxes in working order, even if they are rarely used, and should design and locate call boxes that are accessible to persons with disabilities. They should also consider providing training for all staff responding to these calls so that emergency calls are responded to promptly and helpfully. It is important that the public is aware there are public call boxes available for reporting incidents and that they feel confident they will receive an appropriate response from the agency.
Emergency Response
Communications systems not only provide on-site communications, but also connect facilities to transit administrators and emergency response teams. Agencies should consider providing field employees with direct lines of communication between supervisors, control centers and/or emergency response personnel. Customer service booths and building reception desks can also be outfitted with silent emergency alarm buttons to inconspicuously activate an emergency response if required.
Agencies can also network monitors and alarms connected to building services, operations and surveillance equipment into the security system. Streamlining the communications networks can ensure they are all being monitored so that a response can be implemented rapidly when an incident occurs.
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Communications technology overview - refer to Section 8.3 |
6.2.5.7 Security Systems
Security systems include CCTV, remote surveillance devices, video recorders, intrusion and motion detectors, tamper detectors, smoke or chemical detectors, and alarms.
Since constant surveillance by on-site personnel is often infeasible for most agencies, the practice must be supplement with other measures that can expand the ability of security staff to monitor large facilities. Surveillance equipment may be particularly appropriate in high-traffic and high-value areas since these systems can be integrated with other monitoring and communications systems to create a coordinated oversight and response center.
While remote surveillance and detection systems are important for identifying suspicious activity, an agency response plan should consider what actions to take once these activities have been identified. If possible, the systems should be designed so that a response team can prevent the threat from being carried out. In order for this to occur, there needs to be contact between those monitoring the alarms and local responders so that action can be taken quickly. Where possible, additional mechanisms, such as secondary locks or barriers, high-pitched alarms or pepper spray, should be used to thwart an attacker, to provide time for a response team to arrive and intercede.
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Surveillance systems overview - refer to Section 5.2.5 Intrusion detection overview - refer to Section 5.2.6 |
Cameras can be either stationary or remotely/locally adjustable (pan/tilt/zoom) to make sure that they provide surveillance to the entire target area. A surveillance system that feeds video to a monitor for real-time observations is generally considered better for security, but is labor-intensive and requires constant diligence. As such, theses systems should be tempered with other measures: operationally, technically or both. Real-time observations can be supplemented if the surveillance system has integrated sensors and alarms. This "exception detection" method alerts security personnel when something abnormal occurs. Recorded feeds to be used for investigation are another option.
Sending feeds to a central, off-site location is preferable to on-site monitors. While some agencies prefer cameras and monitors to be available to on-site staff, remote monitoring can be more effective in the event of an evacuation. Agencies should consider how emergency responders can plug in locally to video feeds for on-site cameras.
When designing a remote surveillance system, it is important agencies consider potential obstacles to full surveillance, such as structural columns and sharp corners, when positioning cameras. Where a single camera cannot capture the entire area, multiple cameras can be set up to provide overlapping coverage areas. Agencies should consider motion detectors and other alarm systems as part of the security system design, to provide maximum coverage with a minimum of false alarm opportunities. These systems can be used in combination with other access management tools to provide an efficient and dependable security system.
Agencies can use these security measures as deterrents if they are designed to be obvious. Conspicuous surveillance measures provide a heightened sense of security, but they are also more vulnerable to vandalism. Vandal-proofing these systems is key to their proper functioning. Agencies should consider placing cameras, detection devices, and wiring beyond reach in secure enclosures. Surveillance cameras and other security technology can also be used to monitor an area covertly.
6.2.5.8 Water and Sewer
Transit facilities typically receive their water supply from the public network. This water supply is critical for fire suppression, but localized sections of the fire sprinkler system may be damaged in a blast or other violent event. Agencies should consider designing the on-site water distribution system with reinforcements and redundancies, to ensure there is a continuous supply of water throughout a facility and that damage to one section does not incapacitate the entire system. Agencies should consider providing access to water gates, manholes, and control valves only within a secured perimeter, to prevent someone from cutting off the water supply to the facility. Likewise, storm water culverts and other drainage facilities should be within a secure perimeter, to prevent them from being used to access the site.
6.2.5.9 Fire Protection
Fire protection systems are designed to minimize harm to people and the structure in the event of a fire. Fire detection systems include smoke detectors and alarms. Sprinkler systems, standpipes, and chemical fire extinguishers are used to minimize fire damage while emergency ventilation systems and emergency exit routes allow inhabitants to exit the building. Flammability of construction materials, furnishings, and other materials stored on-site are also regulated to minimize the risk of a major fire. A compartmentalized structure that allows fire or contaminants to be isolated can also minimize risk. Such compartmentalization might be accomplished through various measures, including movable barriers or partition walls, fire doors, etc.
This information is intended to supplement existing codes and considerations on fire protection, rather than to replace such information. States and municipalities regulate minimum fire protection for different types of structures and facilities. Many of these regulations are based on National Fire Protection Agency codes and standards, which can be viewed in NFPA 130, Standard for Fixed Guideway Transit and Passenger Rail System.
6.3 Security Approaches for Types of Transit Infrastructure
This section describes different types of transit infrastructure and facilities that agencies maintain and operate as part of the normal functions of a transit system, from the most obvious and visible to the most remote. They include:
- Transit stations
- Transit stops
- Administrative buildings and OCCs
- Maintenance and storage facilities for transit vehicles
- Elevated structures
- Tunnels
- Right of way, track, and signals
- Remote equipment and unmanned structures
For each type of transit infrastructure, where applicable there are subsections that describe: potential threats, site analysis, access management, emergency response and egress, protecting critical assets, protecting vulnerable assets, structural engineering, facility services, and systems and services.
6.3.1 Transit Stations
Transit stations are facilities where passengers board and alight from transit vehicles. They vary greatly in size and design, both across systems and within a given system.
This section focuses on the more elaborate stations that typically include enclosed structures, full-time personnel, and separate paid waiting area, such as underground subway stations and off-street bus terminals. Since transit stations are prone to a different set of threats than less elaborate "transit stops," the two facility types are discussed separately. (See Section 6.3.2 for security approaches for transit stops.)
A major security challenge at stations lies in balancing the need for openness and conveniences with the need to control the environment in order to protect its users and systems operations |
Stations may serve one or more modes of transit and differ in their levels of design complexity. All transit stations have some component that is at-grade, to connect with the surrounding pedestrian landscape. They may also have components that are underground or elevated, depending on the system. Since stations are designed for optimum passenger convenience and efficient traffic flow, they must be fully accessible and open as well as centrally located, often tightly integrated within a complex urban landscape.
Stations are typically divided into three types of areas, each of which has different security concerns and mitigation measures.
- Unpaid public areas are those locations within the site that passengers occupy before paying their fares (including entryways, lobbies, fare vending space, and concessions).
- Paid public areas are those locations that passengers occupy after paying their fares but before entering a vehicle (including additional passageways, platforms, and waiting areas).
- Non-public areas are intended only for authorized transit staff (including administrative offices, electrical and mechanical rooms, HVAC and maintenance areas, and vendor stalls).
Subsections describe:
- Potential threats
- Site analysis
- Access management
- Protecting critical assets
- Structural engineering
- Systems and services
6.3.1.1 Potential Threats
Stations are likely targets because they are high-profile facilities that serve large numbers of people in enclosed, relatively small spaces, are easily accessible, and are centrally located.
Arson
While stations are designed to be fire resistant, they are still vulnerable to an arson attack ignited either from an accelerant (flammable substance used to increase the spread of fire) brought to the station or from incidental materials such as garbage, vendor goods, and passenger baggage within the station. Any fire that does occur may damage the station and other property, as well as injure passengers and employees. Fires may be particularly dangerous in those stations that are enclosed or underground, where people may become trapped and exposed to fumes and heavy smoke.
Explosives
A vehicle carrying explosives that approaches the outside of a station or enters the station could generate a large explosion. The closer the detonation is to the station and its key components, the greater the potential for damage.
Stations are also vulnerable to people hand-carrying explosives into the facility. While the amount of explosives a person can carry produces a smaller blast, human carriers can penetrate deep within a station without detection and can choose a detonation point with the maximum destructive impact on people or structures. Explosives may be detonated on the carrier (a suicide attack) or be hidden in the station for future detonation.
Explosions can cause injuries and fatalities to the passengers and employees in a station, property damage or structural collapse of the station itself, and cause subsequent fire.
Weapons of Mass Destruction
Stations that are enclosed or underground may be particularly vulnerable to a WMD attack, and may serve as an access point for an attack on an entire underground network. As with explosives, someone could carry a WMD device into a station without detection and position it in a location for maximum destructive effect.
Substances may be released by hand or hidden for future dispersion, and may cause property damage as well as irritation, injuries, and fatalities among the patrons and employees exposed. Riders moving through the transit system can inadvertently spread a harmful substance to which they have been exposed, greatly increasing the consequences of such an attack.
Hostage or Violent Event
Stations may be seen as prime targets for a violent event because they are easily accessible, heavily populated by the public, and generally enclosed.
6.3.1.2 Site Analysis
Since stations are situated in areas where large numbers of people live, work, and travel, they are often adjacent to public space, dense development, and other facilities that might not otherwise be considered security threats. However, site planners may be able to make some choices that improve security without compromising nearby facilities.
Facilities located above, below, or adjacent to the station deserve special attention, especially roadways, loading areas, vehicle-service areas, offices, and parking lots, all of which may serve as access points for explosive-laden vehicles or as vantage points. Surveillance by transit personnel and the general public and the ability to identify and respond to an emergency situation are key components of safety within the station setting; open layouts with wide fields of vision support this goal.
6.3.1.3 Access Management
Transit stations are designed for convenient access, typically by large numbers of riders and agency staff. Stations may include access for a single, discrete transit line, or may feature transfers to other lines or services. For safety and security reasons, there are areas that must be inaccessible to the public and still other areas that must be inaccessible by vehicle.
The following sub-sections present an overview of access management at transit stations for perimeter security, vehicle access, and human access. Cross-references are provided to more specific details in Chapter 5: Access Management.
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Admissions Control overview - refer to Section 5.3.3 |
Perimeter Security
It is impractical to establish a strong perimeter around a transit station, even though it is often necessary to pay and pass through admissions-control barriers to enter the platform. Stations must be as accessible as possible to potential patrons arriving both by foot and in vehicles.
A transit station may have a range of other entrance types depending on the modes served, including tunnel portals for rail service or on-the-road throughways for buses to approach docking areas. Some of these entrance types may warrant additional security measures to prevent inappropriate vehicle access, which need not compromise passenger mobility. In addition, selecting a site where it is possible to maintain unobstructed sightlines around key access points or critical areas may also improve security without compromising the station's accessibility.
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Perimeter Protection and Barriers overview - refer to Section 5.2.2 |
Vehicle Access
Agencies should consider how to minimize the potential for unauthorized vehicles to gain proximity to the station, crash into the station at a high speed, or enter the station through one of its entrances. Barriers to vehicle access need not be brick or concrete structures; natural elements such as trees and shrubs may also be appropriate depending on the location and configuration of the area.
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Both passenger access and vehicular security are easier to manage when vehicle loading areas are segregated from passenger drop-off areas. |
Planners should consider locating key load-bearing structural components, as well as densely populated passenger waiting areas, away from areas that unauthorized vehicles can access. Design choices (the depth or height of the station, the dimensions of passageways between the street and the core of the station, and shielding passenger-waiting areas behind other structural elements) can mitigate the risk of a successful attack.
Transit vehicle entrances to the station can be limited to a small number of controllable access points. These entrances should be separate and clearly distinguishable from any public right-of-way or entrances, through the use of signs and/or channeling circulation. In addition, designers can use access controls, such as bollards, to limit the type of vehicle that may easily enter. Pedestrian entrances should be constructed in a manner that bars vehicles altogether or prevents access by vehicles other than maintenance or emergency responders.
In vehicle areas that must be close to the station, such as passenger drop-off areas, agencies should consider using traffic circulation tools to slow traffic, such as S-route curves, to minimize the opportunity for ramming (refer to Section 6.2.1).
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Vehicle Access Control and Parking overview - refer to Section 5.3.4 |
Human Access
While transit stations are generally designed to make human access as easy as possible, agencies should consider preventing after-hours access and access to non-public parts of the facility. When the facility is closed, the facility should be secured at its outermost perimeter, with locked gates or doors. Outdoor lighting can be used to illuminate station access points. Intrusion alarms and surveillance may also be helpful.
Since the non-public parts of a transit station may be located in publicly accessible spaces, a combination of access management measures may be necessary to consider. Locks, surveillance, credentialing technology, and highly visible locations may help secure the equipment from tampering. Designs can also cultivate an atmosphere of exposure, which is useful in both discouraging and detecting any unwanted activity. The combination of staff, surveillance technology, and unobstructed sightlines can help both transit personnel and the public to serve as watchdogs, helping to deny the opportunity for covert endeavors, and making any unusual activity easily detectable. In any areas of the station where direct surveillance by staff is difficult or impractical, call boxes can help connect patrons with authorities.
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Credentialing overview - refer to Section 5.2.4 Surveillance Systems overview - refer to Section 5.2.5 |
Emergency Response and Egress
A station's emergency response plan should consider the capacity of the station and the fact that many users will not be familiar with the layout of the station and its emergency exits. Emergency systems can direct occupants to safe exit locations, especially if there are additional exits that are not commonly used for station access.
Agencies should consider including emergency communications systems, including blue-light phones and public address systems, in the plan, to allow rapid communications between remote areas of the station. Stations should be equipped with emergency lighting, sprinkler systems and safe rooms, especially if there are subway or elevated platforms.
6.3.1.4 Protecting Critical Assets
Agencies should consider locating critical assets in transit stations, such as building systems and operations equipment, in secure locations with adequate surveillance. For example, mechanical rooms should be within a secure perimeter, and, where feasible within sight of station attendants or monitored by surveillance systems. Agencies should also protect the assets from attack by explosives by locating them away from the site perimeter, where explosions are more likely to occur, and should protect station platforms against access by non-transit vehicles, using different types of barriers.
The location of entrance controls and station attendants is important in protecting the facility. Locating controls and attendants at the outer edge of a building may enhance security of the entire site if these attendants have views of the surroundings. This may mean there are other areas within the station that do not have constant surveillance. If the station attendant is located at platform level, they can observe activity in this area, although this may leave stairways and corridors leading to the platform vulnerable.
If bicycle lockers are on-site, agencies should try to locate them away from critical structures and dense areas, or designed so that the interiors are visible. While bicycle racks are less problematic, bicycle lockers may provide hiding spaces for bombs, weapons, etc. unless constructed of transparent or translucent materials. Building materials are critical in minimizing the impact of an attack. Qualities such as fire resistance and resistance to absorption of toxic materials can greatly reduce the work needed to recover from an attack. For more information on building materials, see Section 6.2.3.
6.3.1.5 Structural Engineering
Structural considerations for the station depend on the station design: elevated stations will have very different concerns than underground stations. The primary consideration for agencies should be to protect the lives of staff and riders during an attack. A design that has redundant structural elements to prevent progressive collapse in the event of an explosive blast, vehicle ramming, or fire can greatly improve the security of people in the building. (See Section 6.2.3)
| Design Feature | Goal (Detect/Deter/Minimize) | Able to Retrofit |
|---|---|---|
| Site Layout | ||
| Structures set back from roads and parking areas, if applicable | Deter/Minimize | |