FIGURE 7-3 Personal, indoor, and outdoor PM5 estimated mass concentration (µg m−3) time series. SOURCE: Ferro et al., 2004.


Although HVAC systems are primarily designed for general ventilation, they can be considered part of the control strategy that might be adopted in the event of an act of bioterrorism. The proper use of HVAC systems for those cases will require a detailed understanding of the infectious or toxicological properties of biological agents, air distribution patterns, air-cleaning or extraction techniques, and the requirements for ongoing operation and maintenance (Ludwig, 2001). But even a properly designed and maintained HVAC system can actually exacerbate exposure by distributing the agent throughout a building during direct recirculation or transfer through poor pressure control. In most cases, it is unrealistic to plan for a risk reduction strategy that relies on reducing the concentration of the contaminant in the air supply. Although outside air dampers could be opened, supply fans generally are not large enough to provide the volume of air that would be effective. A typical HVAC system provides one complete air change every 8-15 minutes. An exhaust system also could be necessary to remove excess outside air from the building. Additional research by structural engineers

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