Protective Architectural and Mechanical Building Design Features

Elevating fresh-air intakes
Most easily applied in new construction, elevating the fresh-air intakes has two main benefits. It provides passive security against malicious acts by making it more difficult for a container of hazardous material to be inserted directly into the building's HVAC system and transported throughout the building. It also makes it less likely that high concentrations of hazardous material will occur at the intakes if there is a ground level release near the building.

Air intakes should be placed at the highest practical level on the building. For protection from malicious acts, screens should also cover the intakes and external air filtration systems, such as Hunter FFA Series units, so that objects cannot be tossed into them. Protective screens should also be sloped to allow thrown objects to roll or slide away from the intakes.

Separation of HVAC zones
Large buildings usually have multiple HVAC zones and each zone is served by its own dedicated air handling unit and duct system. In practice, these zones are not completely separated if they are on the same floor. Air flows between separate zones through hallways, and doorways that are normally left open.

Isolating the separate HVAC zones minimizes the potential spread of an airborne hazard within a building, reducing the number of people potentially exposed if there is an internal release. Zone separation also provides limited protection against an external release, as it increases internal resistance to airflow produced by wind forces and the chimney effect, thereby reducing the rate of infiltration. In essence, isolating zones divides the building into separate more manageable environments, limiting effects of a single release to an isolated portion of the building.

Securing exterior windows
Secured windows can prevent certain types of intentional or malicious acts involving grenades or thrown dissemination devices. Securing windows includes locking against forced opening, screening and grating and specifying window material (glass and plastic) resistant to being broken by thrown objects.

Unsealed windows that can be opened and/or left open are also potential contamination inlets, which can compromise sheltering-in-place. Also, large windows may not be able to sustain the additional load created by positive pressurization. In such cases, metal or solid shutters can be installed on unsealed and/or large doors and windows to prevent contaminant intake.

Even more important is the fact that a nearby explosion or sonic boom can shatter windows and compromise the entire building's integrity for sheltering-in -place. In such an event, evacuation and protective masks are the only viable protective actions.