The design objectives are to protect life safety for the occupants while accepting a significant degree of damage to the assets and structure. However, physical security alone does not assure a safe structure. A comprehensive security plan requires a balance between operational, technical, and physical security measures. The four basic features of physical protection for buildings involve the establishment of a secure perimeter; the prevention of progressive collapse; the isolation of internal threats from occupied spaces; and the mitigation of debris resulting from the damaged façade. Other considerations, such as tethering of non-structural components and the protection of emergency services, are also key design objectives that require special attention. The size of the explosive threat will determine the effectiveness of each of these protective features and the extent of resources needed to protect the occupants. The selection of the appropriate threat is fundamental to the design process and therefore requires careful consideration. The definition of the design threat is based on history and expectation. However, it is limited by the size of the means of delivery. The building’s exterior is its first real defense against the effects of a bomb. Hardening of the façade is typically the single most costly and controversial component of blast protection. Equally important to the design of the glass is the design of the window frames. The requirement that the glass be capable of resisting a specified overpressure typically produces a cascade of costly upgrades to the façade. A curtain wall is a nonbearing exterior enclosure that is supported by a building’s structural steel or concrete frame that can hold either glass, metal, stone or precast concrete panels.