1. If the costs associated with mitigating man-made hazards is too high, there are three approaches: (1) reduce the design threat, (2) increase the building setback, or (3) accept the risk. In some cases, the owner may decide to prioritize enhancements, based on their effectiveness in saving lives and reducing injuries. For instance, measures against progressive collapse are perhaps the most effective actions that can be implemented to save lives and should be considered above any other upgrades.
Laminated glass is perhaps the single most effective measure to reduce extensive non-fatal injuries. If the cost is still considered too great, and the risk is high because of the location or the high-profile nature of the building, then the best option may be to consider building an unobtrusive facility in a lower-risk area instead. In some cases, for instance for financial institutions with trading floors, business interruption costs are so high they outweigh all other concerns. In such a case, the most cost-effective solution may be to provide a redundant facility.
3. This course addresses several types of terrorist threats, which are listed below: Explosive Threats:
Hand-delivered weapon Airborne Chemical, Biological, and Radiological Threats:
Large-scale, external, air-borne release
External release targeting building
4. Damage due to the air-blast shock wave may be divided into direct airblast effects and progressive collapse.
5. Direct air-blast effects are damage caused by the high-intensity pressures of the air blast close to the explosion. These may induce localized failure of exterior walls, windows, roof systems, floor systems, and columns.
6. Progressive collapse refers to the spread of an initial local failure from element to element, eventually resulting in a disproportionate extent of collapse relative to the zone of initial damage. Localized damage due to direct air-blast effects may or may not progress, depending on the design and construction of the building. To produce a progressive collapse, the weapon must be in close proximity to a critical load-bearing element.
7. Three types of building damage can lead to injuries and possible fatalities. The most severe building response is collapse. In past incidents, collapse has caused the most extensive fatalities. For the Oklahoma City bombing in 1995 (see Figure 4-3), nearly 90 percent of the building occupants who lost their lives were in the collapsed portion of the Alfred P. Murrah Federal Office Building. Many of the survivors in the collapsed region were on the lower floors and had been trapped in void spaces under concrete slabs.
8. In the Khobar Towers bombing in 1996 (see Figure 4-4), most of the 19 U.S. servicemen who loss their lives were impacted by high velocity projectiles created by the failed exterior cladding on the wall that faced the weapon. The building was an all-precast, reinforced concrete structure with robust connections between the slabs and walls. The numerous lines of vertical support along with the ample lateral stability provided by the "egg crate" configuration of the structural system prevented collapse.
9. figure 6-2 is:
An example of a stairway to a concrete shelter
An anti-ram knee wall
10. The following is a check list for site and layout design.
Provide a continuous line of defense around the site as far from the building as practical.
Place vehicular access points away from oncoming streets.
Limit the number of vehicular entrances through the secured perimeter line
Use a series of landscape features to create an obstacle course between the building and the perimeter. This approach is most effective if used in areas where there is ample setback.
Design planters for the design-level impact to displace the planter a distance less than the setback.
Use anti-ram barriers along curbs, particularly on sides of the building that have a small setback and in areas where high-velocity impact is possible.
Use operable anti-ram barriers at vehicular access points. Select barriers rated to provide the desired level of protection against the design impact.
11. Figure 6-4 is Schematics showing an example approach for improving the layout of adjacent unsecured and secured areas
The following is an Architectural check list.
Use simple geometries without sharp re-entrant corners.
Use lightweight nonstructural elements to reduce flying debris hazards.
Place the building on the site as far from the perimeter as practical.
Place unsecured areas exterior to the main structure or along the exterior of the building.
Separate unsecured and secured areas horizontally and vertically using buffer zones and/or hardening of walls and floors.
Provide sufficient queuing areas at lobby and delivery entrances.
Limit nonstructural elements such as false ceilings and metal blinds on the interior.
Mechanically fasten light fixtures to the floor system above.
Place desks and conference tables as far from exterior windows as practical.
Orient desks with computer monitors to face away from windows so the chair back faces the window, not the monitor.
13. The following is the Structural design checklist
Incorporate measures to prevent progressive collapse.
Design floor systems for uplift in unsecured areas and in exterior bays that may pose a hazard to occupants.
Limit column spacing.
Avoid transfer girders.
Use two-way floor and roof systems.
Use fully grouted, heavily reinforced CMU block walls that are properly anchored in order to separate unsecured areas from critical functions and occupied secured areas.
Use dynamic nonlinear analysis methods for design of critical structural components.
The following is the Building Envelope check list.
Use the thinnest panel thickness that is acceptable for conventional loads.
Design cladding supports and the supporting structure to resist the ultimate lateral resistance of the panel.
Design cladding connections to have as direct a load transmission path into the main structure as practical. A good transmission path minimizes shear and torsional response.
Avoid framing cladding into columns and other primary vertical load-carrying members. Instead frame into floor diaphragms.
Use the thinnest glass section that is acceptable for conventional loads.
Design window systems so that the frame anchorage and the supporting wall are capable of resisting the breaking pressure of the window glass.
Use laminated annealed glass (for insulated panels, only the interior panel needs to be laminated).
Design window frames with a minimum of a ½-inch bite.
Use a minimum of a ¼-inch silicone sealant around the inside glass perimeter, with a minimum tensile strength of 20 psi.
15. The following is the Mechanical and Electrical checklist.
Place all emergency functions away from high-risk areas in protected locations with restricted access.
Provide redundant and separated emergency functions.
Harden and/or provide physical buffer zones for the enclosures around emergency equipment, controls, and wiring.
For egress routes, provide battery packs for exit signs, use non-slip phosphorescent treads, and double doors for mass evacuation.
Avoid using glass along primary egress routes or stairwells.
Place emergency functions away from structurally vulnerable areas such as transfer girders.
Place a transformer interior to building, if possible.
Provide access to the fire control center from the building exterior.
16. The following is the chemical, biological & radiological protective measures checklist.
Place air intakes servicing occupied areas as high as practically possible (minimum 12 feet above ground). GSA may require locating at fourth floor or above when applicable.
Restrict access to critical equipment.
Isolate separate HVAC zones and return air systems.
Isolate HVAC supply and return systems in unsecured areas.
Physically isolate unsecured areas from secured areas.
Use positive pressurization of primary egress routes, safe havens, and/or other critical areas.
Commission building throughout construction and prior to taking ownership.
Provide redundant, easily accessible shutdown capabilities.
For higher levels of protection, consider using contaminant-specific filtration and detection systems.
Incorporate fast-acting, low-leaking dampers.
Filter both return air and outdoor air for publicly accessible buildings.
Select filter efficiencies based upon contaminant size. Use reputable filter media installed into tight-fitting, gasketed, and secure filter racks.
For higher threat areas (mail room, receiving, reception/screening lobby):
Preferably locate these areas outside the main building footprint.
Provide separate HVAC, with isolated returns capable of 100% exhaust.
Operate these areas at negative pressure relative to secure portion of the building.
Use air-tight construction, vestibules, and air locks if there is high traffic flow.
Consider installation of an emergency exhaust fan to be activated upon suspected internal CBR release.
Lock, secure, access-log, and control mechanical rooms.
In public access areas, use air diffusers and return air grills that are secure or under security observation.
Zone the building communication system so that it is capable of delivering explicit instructions, and has back-up power.
Create safe zones using enhanced filtration, tight construction, emergency power, dedicated communication systems, and appropriate supplies (food, water, first aide, and personal-protective equipment).
Ultimately, the willingness to pay the additional cost for protection against man-made hazards is a function of the "probability of regrets" in the event a sizable incident occurs.
18. In some situations, the small probability of an incident may not be compelling enough to institute these design enhancements. Using this type of logic, it is easy to see why it is unlikely that they will be instituted in any but the highest-risk buildings unless there is a mandated building code or insurance that requires these types of enhancements. This scenario is likely to lead to a selection process in which buildings stratify into two groups: those that incorporate no measures at all or only the most minimal provisions and those that incorporate high levels of protection. It also leads to the conclusion that it may not be appropriate to consider any but the most minimal measures for most buildings.