to provide protective effects. For example, HVAC filters and the isolation of internal air circulation zones are important passive elements in facility defenses. In an attack, these systems will reduce agent concentration and slow the movement of contamination throughout the facility. Physical security, including denial of access to the most threatening release points, is another important passive defense element. Some passive defenses can also enhance the capability of active response systems. For example, high-quality filters in a facility may reduce the biological aerosol backgrounds (including particle shedding transients caused by movement of building occupants), permitting nonspecific bioaerosol detectors to employ lower alarm thresholds. The effective isolation capabilities of well-zoned air handling systems also allow longer active defense time lines for the protection of occupants.

Effective detect-to-warn systems will also require a broad range of ancillary systems in support of the detectors. Video and other surveillance systems can provide information on unusual events in the alarm areas and on the status of occupants throughout the facility. Communication and decision support systems can provide situation assessment for the automatic controls and human decision makers who must confirm the alarms and responses. Enhanced HVAC options and perhaps controllable barriers can enable tailored airflow strategies that adapt to specific attack conditions. Communication and control systems can expedite other operational responses such as movement of personnel away from the threat cloud (evacuation or shelter-in-place) or employment of personal protective measures.

Much more systems analysis and process development are needed to define criteria for design of cost-effective defensive systems. Several general guidelines for reducing vulnerability for facility owners currently exist.1 This general guidance is useful as an orientation to first operational steps for facility protection but does not specify the more detailed process steps that would allow facility owners to complete credible assessments and response plans. Detector-based architectures, even the more straightforward detect-to-treat options, are also beyond the scope of current guidance documents. Because so many of the factors affecting detect-to-warn performance are site specific, effective ways of characterizing the potential for passive defenses and response options for active systems are essential. Criteria for considering and balancing investment in near-term upgrades of passive defenses with more advanced detect-to-treat and detect-to-warn capabilities are needed. These criteria will certainly depend on the function and importance of the protected site. For example, critical military facilities may demand a higher level of both passive and active defense than most civilian infrastructure facilities.

KEY PRINCIPLES FOR DETECTION SYSTEM DESIGN

A number of useful design principles have emerged from the consideration of nominal attack scenarios in light of current and anticipated biodetection capabilities. These have influenced the committee's recommendations on detector development pathways and on strategies for national implementation of detect-to-warn capabilities. These principles are outlined below and are illustrated in the examples discussed in this chapter.

Nonspecific, rapid (less than 1 minute response time) bioaerosol detectors can initiate significant responses for some scenarios.

Some release scenarios create potential detection sites at which agent concentration is much higher than background biological aerosol levels. For example, to attack a large facility, a rapid interior release in one of the rooms of that facility will result in very high local agent concentrations immediately following the release. Under these circumstances, nonspecific bioaerosol or standoff detectors will be able to generate a high-confidence alarm based on the abnormally elevated bioaerosol loading that could be used to initiate medium- to high-regret responses. A thorough assessment of the bioaerosol backgrounds for the defended facility is essential to the development of such a system.

1  

See, for example: Department of Health and Human Services, National Institute for Occupational Safety and Health (NIOSH). 2002. Guidance for protecting building environments from airborne chemical, biological, or radiological attacks. Publication Number 2002-139. May.

W. Blewett. 2001. Protecting buildings and their occupants from airborne hazards. U.S. Army Corps of Engineers Technical Instruction. Avaliable at http://securebuildings.lbl.gov. Accessed August 2003.



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