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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making 3 Components of Building Protection: Building Design, Technologies, and Operational Responses To achieve the specific goals for building protection from a variety of biological and chemical threat types and to meet the requirements set by building administrators, designers, and security experts, many components can be selected. Selection of components requires an evaluation of many facility-specific details. Buildings have to be evaluated largely on a case-by-case basis because buildings vary in their “tightness”: that is, their resistance to infiltration of outside air, leakiness of their air transport systems, location, degree of physical security and access to outsiders, training of the occupants, options for personal protection, and ability of surrounding resources to respond to an incident. (Figure 3-1 illustrates the complexity of planning for protection.) The relative importance of different possible outcomes of a biological or chemical attack is determined by the activities (operations or missions) in the facility. The activities also determine the required response time of the building protection to certain threats—for example, if continuity of operations in the facility is necessary, then a rapid response to fast-acting threat types is required to ensure continuous operation. To facilitate later discussions, this chapter first discusses passive and active building protection and introduces the committee’s definitions of levels of protection. Second, it reviews the options that could be used in building protection. Finally, it discusses how to integrate various protective measures to provide different levels of protection to buildings of different types and designs and considers the limitations of each level of protection.
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making FIGURE 3-1 Illustration of the complexity of building protection (adapted from the Defense Advanced Research Projects Agency). This figure, which is not intended to be comprehensive, illustrates some of the activities and resources necessary for building protection. The flowchart does not show the different groups of threat agents and building activities that would determine the response and outcome.
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making BUILDING PROTECTION Active and Passive Strategies for Protection Incidents of terrorism that involve biological and chemical threat agents have raised awareness that buildings could be better protected from such attacks. The technologies and operational response plans currently used for building protection in most federal buildings (including military and nonmilitary structures within and outside the United States) and nonfederal buildings involve primarily “passive” approaches. Passive protection refers to systems that do not involve detectors or sensors of threat agents to influence an operational response. Passive protection utilizes the following: The integrity of the building as a whole to protect occupants from external threats; Compartmentalized spaces within the building that offer better protection from indoor releases through enhanced physical integrity of the space or from continuous local cleansing of the airstream; and Visual recognition of threats and their effects—directly via video monitoring or indirectly from clinical signs of the occupants—to initiate protective response actions such as evacuation, sheltering in place, mass drug administration, or donning personal protective equipment. Automated video analysis can also be used to transition visual recognition from a passive to an active system. Although passive systems can provide protection from a variety of threat agents and scenarios, they have gaps in protection that result in vulnerabilities. These vulnerabilities fall into two categories. First, occupants could be exposed to an unidentifiable threat that goes untreated and for which therapeutic options decrease with time. An example would be an indoor release of a biological threat agent with an incubation period of days. Second, occupants could be exposed to an unidentifiable threat that is fast-acting, such as a chemical threat agent, released inside the building space. (Note that passive measures could be used to protect occupants from outside release, but only some occupants could be protected from inside release through passive compartmentalization methods.) These vulnerabilities and their variations could be addressed by an “active approach” to protection that uses detectors to recognize the presence of a threat agent. Once detected, the threat agent could then be identified and an operational response initiated to limit the threat and allow treatment of exposed occupants. Active building protection based on sensors and detectors is not currently in wide use within the Department of Defense (DOD, 2005) because of the high initial and maintenance costs and because the risk of biological or chemical attack is low in most buildings. Test beds and current deployments such as Nord Hall of the Immune Building Program and the Pentagon will provide a basis for considering the use of sensor-based active protection (see also Chapter 5).
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making Levels of Protection Nearly all buildings offer some protection from an outside release by virtue of being enclosed by walls, roofs, and openings protected by doors and windows, which limit the transport of contaminated outdoor air indoors. Buildings are typically not designed or constructed to resist infiltration of outside air entirely. In fact, some leakage or infiltration is commonly assumed to provide “fresh air” in some buildings. (For example, no ducted fresh air from an air intake louver might be provided in some simple commercial buildings or single-family residences.) Similarly, buildings are not typically built with airtight interior construction or filtration effective against the kinds of particulates and chemicals of concern in this study. All buildings are subject to widely varying quality of design and construction and to varying quality of maintenance and repair over their lifetimes. Buildings are also subject to many changes over time from aging of materials, wear and tear from ordinary use, and renovations to accommodate evolving needs and new technology. The protective performance of most buildings, therefore, is not planned, monitored, or verified. Unless the building is carefully monitored and maintained, it is unlikely to provide the protection it did when it was new, and this is a major limitation of passive protection options. The required level of building protection from biological and chemical attacks is determined by the use of the building and the possible threats (Chapter 2). The type of building protection that can be implemented depends on many factors including the life-cycle cost of the protection system, building type, and ease of access. The committee developed the concept of four levels of protection—low-level passive, high-level passive, low-level active, and high-level active—to facilitate discussion. The level of protection is based on vulnerabilities and risks to threat agents, and a system could provide different levels of protection for different agents; a given protection system could offer active and passive protection from some biological or chemical threat agents and only passive protection from others. Like the biosafety levels (BSL-1 to BSL-4) for microbiological and biomedical laboratories (DHHS, 2007), the four levels of protection are qualitative. The science and application of building protection from biological and chemical threat agents is not nearly as mature as biosafety in laboratories. Even for biosafety in microbiological and biomedical laboratories, the guidelines promulgated by the Centers for Disease Control and Prevention in 1984 (DHHS, 1984) are still qualitative (DHHS, 2007). Because of the variability in threat, risk, building design, and operational use of the wide array of buildings in the DOD inventory, the committee could not suggest measurable and quantitative criteria for either design or function at the time this report was written. The four levels of protection represent a plan for considering building protection. Although most buildings are designed to decrease the impact of natural disasters and fire hazards and to provide some level of indoor air quality control, they are not designed to decrease the impact of biological and chemical attacks. Therefore, some buildings have no or little
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making protection—particularly the ones that are poorly maintained or highly porous to the outside environment. These buildings do not even reach the lowest level of protection described below. Level of Protection 1 (LP-1)—Low-Level Passive Protection. Passive protection refers to protection without the capability of actively sensing the environment for the presence of threat agents. Low-level passive building protection is based on the demonstrated protection provided by a well-constructed, well-maintained building that provides a healthy environment for occupants and operations. A building designed to provide a high-quality environment during normal operation also provides some protection from external and internal threats (Hitchcock et al., 2006). In general, an LP-1 building meets or exceeds all requirements of consensus indoor air quality standards, such as the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62.1, in terms of its design, construction, and operation (ASHRAE, 2004a). An LP-1 building has a well-sealed envelope to limit infiltration of outdoor air and any contaminants it might contain and to provide for minimal leakage of heating, ventilating, and air-conditioning (HVAC) air distribution to reduce unintended airflows inside the building. HVAC system types that inherently limit the spread of indoor contaminants are also LP-1 options. A sufficient supply of outside air to dilute contaminants and a moderate level of particulate filtration are also found in LP-1 buildings. Although most HVAC systems offer some degree of particle filtration, not all buildings have the high degree of filtration required for consideration as LP-1. Buildings usually do not contain adsorbents (for example, activated carbon) and absorbent filters (for example, air washers) as part of typical HVAC installations except in special circumstances. An LP-1 building has to be well maintained to ensure that protection is available when needed. The LP-1 options align with a recent study (Hitchcock et al., 2006) that recommends the above options as realistic protection of public buildings, eschewing more complex alternatives. Most DOD buildings and many public buildings have security and operational activities that are not intended for, but offer some protection from, biological and chemical airborne threats. These measures have dual-use advantages and are also part of the LP-1 options. An LP-1 building also contributes to the performance of protection systems that include sensors (that is, active protection as described below). Detectors have higher reliability and fewer false positives (a wrong indication that a threat agent is present) when operated in a clean environment provided by the LP-1 option. Level of Protection 2 (LP-2)—High-Level Passive Protection. LP-2 provides protection by further limiting exposure to intentionally released threat agents, and it is similar to MilStd Class 1 collective protection (USACE, 1999). This level of protection involves options for reducing the vulnerability to threat agents that are not part of a “standard” building system. The protective measures in LP-2 are passive because they do not actively detect the presence of threat
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making agents (although the operational response plans could change from passive options to active response in some situations). LP-2 options include adding gas filtration and upgrading aerosol filters and other control technologies specific to biological and chemical threats, zoning the building interior with differential pressures, relocating outside air intakes and filtering outside air, and providing local air-washes (areas that are provided with isolated, enhanced laminar airflow with local filtration at the returns). Many protection options in LP-2 serve dual purposes because they improve the working environment and the building security. Level of Protection 3 (LP-3)—Low-Level Active Protection. Active protection refers to protection with the capability of actively sensing the environment for the presence of threat agents. LP-3 offers low-level active protection and directly addresses one of the main vulnerabilities of passive systems (LP-1 and LP-2)—exposure of the building’s occupants to a threat agent that is not detected and identified in time to execute therapeutic responses. LP-3 is a “detect-to-treat” option that would allow identification of a threat agent in time for treatment. LP-3 requires a broad-spectrum detection and identification system that could determine the presence of a variety of known threats within the time period necessary for an operational response. The time for detection varies by threat agent; the threat requiring the longest detection time typically involves a biological agent. Because the LP-3 option detects and identifies the threat in time only to treat the people exposed, it might not be an appropriate option for facilities that require continuous operations. Some threat agents that escape detection could have a quick impact on facility operations. Level of Protection 4 (LP-4)—High-Level Active Protection. LP-4 is a high-level active protection that addresses the second major vulnerability of the LP-1 to LP-3 approaches to building protection—the inability to mitigate an attack through timely detection. LP-4 would allow detection and identification early enough to treat the exposed victims and to make operational responses that might minimize the impact of the threat agent by preventing or limiting exposure. These operational responses might include high-regret options. (In this context, “regrets” are negative consequences of actions, as discussed in detail later in this chapter; see section titled “Operational Procedures for Protecting Buildings.”) The LP-4 option is considered to be at the edge of current detection and identification technology and ability to operationally deploy. Because of current limitations in detection and identification technologies, a successful LP-4 option requires tiered levels of detection and response and uses combinations of low-regret response options with fast, nonspecific detection systems. Box 3-1 summarizes the levels of protection and the options each level comprises. LP-2 generally has all the virtues of LP-1 and some additional passive protection. LP-1 and LP-2 are usually part of active protection so that LP-3 and LP-4 generally have all the virtues of LP-1 and LP-2. However, LP-3 and LP-4 could
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making BOX 3-1 Levels of Building Protection from Biological and Chemical Airborne Releasesa LP-1: Low-Level Passive Protection Select systems to minimize normal exposure. Dilute indoor air and reduce recirculation. Minimize leakage in HVAC system and in building (external and internal). Add filtering as needed for healthy workplace. Protect air intakes to reduce air contaminants. Use construction methods and materials that reduce chemical exposure. Consider security, site selection, and operational activities that have dual-use advantages for building protection. LP-2: High-Level Passive Protection (LP-1 + options specific to protection from biological and chemical threat agents) Use upgraded protection from biological and chemical threat agents compared to LP-1. Upgrade filters (particulate and adsorption) specific for biological and chemical threat agents. Use zoning with graded pressurization (compartmentalized). Provide local air-washing vestibules. Protect air intakes specifically to reduce biological and chemical threats. be implemented without some of the basic options in LP-1 and LP-2. In general, active protection has fewer vulnerabilities, higher life-cycle costs, more complex operation, and higher risk of failure as a result of technological and operational complexity. In addition, the use of sensors also introduces the possibility of false positives and false negatives (no indication despite the presence of a threat) from the sensors. False positives are disruptive to operations and cannot be tolerated in many operational situations, so it is important to minimize false positive responses. False negatives when sensors are present could also provide an undesired sense of complacency compared to when sensors are not present (and there is also no indication of a threat). The four levels of protection address different types of vulnerabilities. Figure 3-2 shows a cross-comparison of the levels of protection and the threat groups (selected on the basis of the ability to detect and treat the threat) they could address. The “cannot detect, cannot treat” group (Group D) of threat agents poses the greatest challenge because of the inability to detect the threat. Including sensors
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making Include all human-in-the-loop detection options and responses, such as visual or clinical detection and the corresponding responses. Consider site selection, protective access control, and operational responses specific to biological and chemical threats. LP-3: Low-Level Active Protection Ensure that a hidden threat agent is detected and identified in time to treat any exposed persons, essentially detect to treat. Provide protection for latent-acting threat agents with possible treatment. Include all human-in-the-loop detection options and responses in LP-2. Consider site selection, protective access control, and operational responses specific to biological and chemical threats. LP-4: High-Level Active Protection Detect to protect (warn and mitigate). Include automated detection and response systems for faster reaction times. Use a tiered detection-response system in most cases with currently available sensor technology. Typically, low-accuracy sensors trigger low-regret responses if a threat is detected, and sensors with confirmation and identification capability are used for higher-regret responses. Consider site selection, protective access control, and operational responses specific to biological and chemical threats. aThe levels of protection could be different for different threats; for example, a system might offer LP-4 for certain chemical threat agents, but LP-3 for biological threat agents. (LP-3 and LP-4) does not enhance protection from these threat agents because the systems cannot detect them. Hence, LP-1 and LP-2—filtration without sensors— could enhance protection from the most challenging threat types. Although detection and identification technologies will improve in breadth, specificity, and response time and expand the opportunities for the LP-4 option, passive options will continue to play an important role in building protection. STRATEGIES AND TOOLS FOR PROTECTION Building Design and Planning Strategies When the built environment is to be tasked to provide protection against airborne threat agents, generalized solutions must be considered with caution because no two buildings are exactly alike, even when they have been “standardized.” Unlike mass-produced appliances or automobiles, every building is custom built. Therefore, every building must be studied individually for ways to
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making FIGURE 3-2 Illustration of how the four levels of protection (LP-1: low-level passive protection; LP-2: high-level passive protection; LP-3: low-level active protection; LP-4: high-level active protection) can be applied to the four groups of threat (A: can detect, can treat; B: cannot detect, can treat; C: can detect, cannot treat; D: cannot detect, cannot treat). In general, passive protection offers some protection from threat agents but might not be effective for all. Active protection aims to detect the threat agent in time to treat exposed victims (LP-3) or to limit exposure (LP-4). mitigate airborne releases of threat agents. The design of a building is a product of response to functional program, climate, topography, geology, and aesthetic or iconic objectives. In DOD facilities, the functions are classified in the Unified Facilities Criteria as billeting, primary gathering, or other DOD inhabited. In fact, these classifications might embrace everything from dwellings to offices to large armories, and more than one function could be housed within a single structure. The design responses will result in the spatial layout and selection of the structural system, HVAC, and other systems, including physical security. Although test beds and laboratory-built spaces can be carefully controlled and ideal conditions can be achieved, field conditions for most buildings constructed for DOD and other clients vary widely from one project to another. Such variables as worker skills, false alarms due to background material, temperature and humidity conditions during construction, and materials from different manufacturers and lots can result in departures from the strict design intent and different performance characteristics for the building. If, for example, one of the mitigation strategies includes creating pressurized zones or compartments, great care must be taken to ensure that the field conditions result in airtight construction
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making because most building assemblies are quite porous. Even different contracting methods (design-bid-build, design-build, or multiple contracts) can affect the final building results. Buildings also change over time: they are dynamic, not static, and respond to temperature, humidity, wear and tear of use, quality of maintenance, and impacts of renovations. Modern buildings with increasingly sophisticated technologies are more than ever subjected to changes as new technologies become available. Constant rewiring or re-piping of systems can compromise the integrity, for instance, of an originally airtight partition. Therefore, it is important that designers of threat mitigation methodologies for new or existing buildings consider the field conditions that can affect construction and the likely impact of time on the original design. From its beginnings, the built environment has had shelter and protection of its inhabitants and their possessions from natural and human-made threats among its primary objectives. It is, then, within the tradition of building design to include some element of physical security. Design strategies of an architectural nature that could be useful in mitigating the effects of airborne contaminants, including biological or chemical threat agents, are passive and belong in the LP-1 and LP-2 categories. Furthermore, the passive strategies complement the active strategies in the LP-3 and LP-4 categories. New Building Design New buildings can be designed for physical security—including mitigation of airborne hazards—more readily and economically than retrofits to existing buildings, especially if the security needs are anticipated early in the pre-design and design phases and are identified in a threat and risk assessment. The physical security needs, including mitigation of any biological and chemical threat agents released, become part of the functional program, budget, and design brief. Site Selection Considerations Design for physical security begins with the selection of the building site. A well-chosen site with access control and adequate standoffs from uncontrolled neighboring sites and rights-of-way can save costs of mitigation. However, the cost of the land could offset the savings in construction in some markets. Site selection is, of course, limited to new projects. In deciding to construct a building, the following should be taken into account to the extent feasible to achieve LP-1 and LP-2: Ideally, the site should be away from coastal regions subject to hurricanes and flooding, in order to minimize potential damage to the exterior envelope from winds. A damaged building envelope could affect the airtightness of the building and hence the protection from external airborne threats.
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making The site should be as remote as possible from major thoroughfares such as interstate highways, main railroad lines, or navigable waterways where hazardous agents (including toxic industrial chemicals and materials) could be transported and where accidental or deliberate releases could affect the site. The site should be outside the landing and takeoff patterns of an airport to minimize exposure to aircraft accidents. The site should be located away from a neighbor or community that is potentially a target of terrorism, such as an iconic federal installation or monument. If the site is in a dense urban area, access to and from the site should be via streets that are not so congested that emergency responders cannot access the site quickly and evacuation cannot be effected promptly. Access from more than one street and from more than a single side of the site permits an alternative should the main access be blocked in an emergency. The site should be remote from and upwind of hazardous manufacturing, processing, or storage of potential airborne contaminants and far enough from combustibles so that it would not be affected by fire or explosions on the neighboring property. Site Planning Considerations Once a site has been selected, the designer and owner have to consider the ease with which the building can be protected from threats by the site’s design. To achieve LP-2, the site perimeter can be controlled by topography such as steep slopes, berms, or ditches, or physical barriers such as walls or fences to prevent or impede access to the buildings from outside the site by unauthorized pedestrians or vehicles. Sufficient distance between buildings and uncontrolled areas outside the perimeter might be required to allow time for detection and interdiction of a threat—for example, a person approaching the building with intent to break and enter, explode a device, or introduce toxic chemicals into the building’s environment. The distance from an event at the perimeter, such as an accidental or deliberate release of a toxic substance into the air or an explosion, can mitigate the effect of the event on the occupants. At least two alternative places on the site perimeter should be provided for access and evacuation, where possible. Because entrances are inherently attractive targets, if one entrance is the site of an event, emergency response and evacuation require an alternative. For similar reasons, there should be redundancy of utility services to the site. Water, power, communications, and other utilities should serve the site from more than one point. These points of service should be protected from illicit access and potential tampering. Another protection option is to select a site large enough to allow adequate distances between uncontrolled and unscreened vehicles and the building(s). Adequate space will be needed at the site perimeter entrances for vehicle inspection, including queuing, turnaround, and screening. On-site, keeping screened vehicles
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making cases, biological threat agents must be lysed and their proteins or nucleic acids extracted before analysis. One exception is identification that is based on the molecular recognition of proteins or other molecules on the bioagent surface using antibodies or other molecular recognition elements. For sensitive identification, the analysis of nucleic acids requires additional time for their amplification. Molecular methods for biodetection require multiple reagents, some of which must be stored at cold temperatures to prevent degradation. Consequently, molecular methods require time and laboratory-based instrumentation. Progress is being made to miniaturize and automate most of these processes using “lab-on-a-chip” methods involving integrated microfluidic systems. Even when the systems become available, they will require a collector, will not provide continuous detection, and will take time to carry out the analysis. Consequently, they cannot be considered monitors but offer near-real-time identification. Function-based sensing is a detection scheme using materials that exhibit a response to the agent type based on some biological function in contrast to a typical binding or physical-based method. For example, living cells or tissues can be engineered to express a fluorescent protein or exhibit bioluminescence when exposed to an agent. This response is often based on an intrinsic biological function, such as apoptosis or a signal cascade. Unlike simple binding assays, function-based assays show biological relevance because they provide information about bioavailability, binding, and effect of the agent. Function-based sensing approaches can be designed to detect either biological or chemical threat agents. The gold standard for detecting and identifying biological agents is to use culture-based assays. In this approach, a sample is used to inoculate a culture medium enabling any living organisms to multiply and grow. Culture techniques typically require 24 to 48 hours and can take up to weeks for some viruses and bacteria, such as Mycobacterium tuberculosis, or if the strain is unknown (which might occur for engineered or emerging organisms). In addition, culture techniques have to be conducted in a laboratory environment, so they can be used only for post-event identification (LP-3) rather than for warning or treatment modalities that require immediate action (LP-4). Culture techniques cannot be used for all biological threat agents because of the inability to culture some agents. Detection and Identification of Chemical Threat Agents Each chemical agent possesses a unique chemical structure with unique chemical and physical properties that enables it to be detected and identified by different detection methods. The traditional way to detect chemical agents in a vapor state is to first pre-concentrate on an adsorbent by passing several liters of air through an adsorbent column. Thermal desorption causes all of the vapors to be released from the column. A variety of methods exist for detecting these vapors. The most common commercial off-the-shelf and government off-the-shelf systems use ion mobility spectrometry (IMS). In IMS, molecules are first ionized. The gas-phase ions then migrate through a drift tube exposed to an
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making electric field at different rates depending on their size, shape, and mass. Another detection method is gas chromatography (GC), in which the vapors are separated on a chromatography column and identified by their retention times. A thorough discussion of the characteristics of IMS, GC-flame photometric detectors, and GC-mass selective detectors as utilized in the Army’s chemical weapons storage and disposal programs can be found in the National Research Council (NRC) report titled Monitoring at Chemical Agent Disposal Facilities (NRC,2005c). If more definitive speciation is required, the separated vapors are introduced into a mass spectrometry system for molecular identification. These systems all take air samples at discrete intervals so that sampling is not continuous. They also are power intensive and relatively large, so they are consequently relegated to a remote laboratory or central analysis center. Such systems can be used in an autonomous fashion but can require frequent technical intervention. In addition, because of their size and maintenance requirements, they cannot be deployed in a distributed fashion throughout a building. For new construction, however, sample ports could be introduced throughout a building in which air could be pumped continuously through inert tubing to a central laboratory, where a suite of gas chromatographs would be located. If continuous monitoring is required, vapor sensors can be used. The most common type of vapor sensor is the metal oxide sensor (MOS). In general, a MOS responds to virtually all organic vapors and provides information that a vapor release has occurred with little or no identification capability. These types of sensors have the requisite sensitivity to detect vapors at parts per million to parts per billion levels and do not require pre-concentration. Some chemical warfare agents are resistant to oxidation so they are undetectable at low concentrations by metal oxide sensors, unless the sensors are operated at elevated temperatures. A newer technology involves sensor arrays. For vapor identification, these types of arrays are sometimes referred to as “electronic” or “artificial” noses. Sensor arrays operate on principles loosely based on the mammalian olfactory system. Multiple different sensors in the array provide differential responses to a particular vapor, and a pattern recognition algorithm can identify the agent on the basis of the collective responses. The approach relies on the use of sensor array materials with different abilities to partition vapors of interest and a transduction mechanism to measure the amount of vapor partitioned into the sensor array material. The most common array-based sensing system is the surface acoustic wave device, which uses different sensor coatings on an array of piezoelectric crystals. When the array encounters a chemical vapor, the vapor adsorbs to the sensing layers differentially and produces a characteristic pattern that is used to identify the compound. Such sensors have limited specificity. Array-based sensor systems exist in a number of research and industrial laboratories, and systems with limited functionality have been used in an operational environment. Future improvements in array-based sensors are expected to improve their sensitivity and specificity (NRC, 2005c). Chemical identification systems could, but usually
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making do not, rely on a triggering mechanism. Systems either operate in a continuous mode or they have a pre-concentration step followed by analysis. Deployment Considerations In deploying detection and identification systems for building protection applications, it is important to consider the performance and life-cycle costs of the complete system rather than individual detectors or identifiers. Performance of a complete system needs to be evaluated on the basis of sampling, processing (if needed), detection, analysis, and response. The first step in designing an effective detection and identification system is determining the types of situations and scenarios for which the system will provide protection. (See Chapter 6 for a detailed discussion.) The analysis will provide response time, detection limit, and selectivity requirements for biological and chemical agent detectors as a function of placement of the detectors. The type of detectors needed will be influenced by the backgrounds within the building, so it is also necessary to understand facility backgrounds as measured by the biological and chemical agent detectors being considered for deployment. For example, particle counters could be very effective triggers for biological agents within facilities with relatively stable, low backgrounds but would not be effective triggers in facilities with high background particle counts. Ideally, detectors and identification systems will be placed close enough to one another to be able to detect an agent with spatial and temporal resolution high enough to prevent its dissemination over a large area or redistribution throughout the facility. For example, release of a nerve agent would provide a locally high concentration that would not require the most sensitive chemical agent detector as long as the detector was in reasonable proximity to the point of release. Deployment and distribution strategies can therefore be used for effective containment of a release. Distributed sensors also provide the ability to pinpoint the release location with higher precision and might enable dispersion modeling throughout the facility to optimize response options. However, the deployment of distributed biological or chemical agent detectors and sensors is limited by currently available technologies and their cost. Because of the limited availability and high cost of biological and most chemical agent detectors, a tiered approach could be useful in some facilities. In this case, lower-cost triggers are used to initiate low-regret responses to contain the potential release and trigger confirmation using more expensive but typically slower detectors. Clearly, the concept of operations of the system needs to be considered when designing the detection system architecture. What action will be taken when a detector (or set of detectors) gives a warning? If a detector alarm results in no action (either automated or manual), then the detector provides no benefit and funds should not be spent for its deployment.
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making Relative Risk of Degradation and Activities Just as is true with the relationship between the LP-1 options and general building maintenance, the performance of all sensing and monitoring systems depends on maintenance and adherence to operational protocols. Degradation of sensor performance often occurs as the active sensing components lose sensitivity and calibration over time. Loss either of sensitivity or calibration can result in missed detection (false negative) of an agent release. Understanding and specifying the degradation characteristics of a system prior to installation are important so that replacement of components and maintenance can be performed and built into the concept of operations (CONOPS). Replaceable components need to be accessible for easy maintenance. The context in which detection systems will operate is as important as proper maintenance. Activities that generate high concentrations of dust or high levels of vapors can compromise sensor performance. For example, particle counters used as triggers can be activated because of construction dust. The use of high concentrations of some chemicals in buildings could cause chemical sensors to give false alarms or to become saturated and lead to a false negative if simultaneous release of an agent occurs. Chemicals that have molecular structures similar to nerve agents, such as pesticides, could lead to false positives. Such agents should not be used in the proximity of detector systems. Operations such as construction, pesticide application, and cleaning activities involving solvents must be cleared beforehand to allow adequate preparations to be made to avoid false alarms or compromised sensor performance. Physical operations also can affect sensor performance. For example, if doors are left ajar, they create unpredictable airflows or cause dilution of air that could prevent material from reaching the sensor properly. Lack of funding to support the maintenance and proper operation of detection and identification systems would rapidly lead to a loss of performance. Assuming ongoing and reliable funding is essential when contemplating system installation because the initial capital costs have to be supported by ongoing operating cost commitments. In summary, proper resources and procedures are critical to ensure that the performance of detection and identification systems remains within the necessary range to detect agents at the requisite levels. Technological Readiness The NRC published a report titled Sensor Systems for Biological Agent Attacks: Protecting Buildings and Military Bases (NRC, 2005b). That report concluded that detection and identification technologies available at that time were insufficient for providing real-time “detect-to-warn” notification of building occupants (LP-4 option). Notional detection and identification systems were postulated that provided notification of biological organisms within a few minutes (NRC, 2005b, Box 6-1). The committee is unaware of recent technological ad-
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making vances that provide significant improvements to technologies since the release of that report. The committee agrees with the findings and recommendations of the earlier report, which includes a detailed analysis of specific sensor technologies (NRC, 2005b). Risk of Obsolescence of Technologies Technologies are changing fast. A tremendous amount of research and development is taking place, and the sensor area receives particular attention. Smaller, more sensitive, and more functional detection systems are being developed in research laboratories and commercially. It is essential that installed systems have the flexibility to incorporate innovations in detection and identification without requiring massive building renovations and changes in procedures. For sensor systems to remain flexible, standardization of their implementation is necessary so that when new technologies become available, they can readily be incorporated into a building to replace obsolete systems. For example, sensors and triggers are modular. By designing a building so that sensors can readily be replaced with improved and validated sensors as they become available—without major building disruption—the protection level can be improved periodically as technology advances. In the most optimistic scenario, highly functional miniature sensing systems with onboard processors and wireless communication capabilities will become available. Because such systems require power, access to power for sensors should be built into the building design. Even with the most advanced sensors, planning for future technology changes is required in the building design phase to anticipate such developments. In addition to new identification technology, capabilities exist to synthesize new chemical agents and to engineer new organisms. Consequently, identification systems have to be adaptable to anticipate new agents rather than limited to detecting existing threats only. In this regard, sensor arrays that enable multiple, user-defined agents to be identified are superior to single-agent identification platforms. Multiplexed arrays that have the capacity to detect additional analytes as they are identified are particularly attractive. Having sensors or arrays that detect specific classes of chemical agents is likely to be the most practical solution. For example, knowledge of the exact identity of a chemical warfare agent is not necessary for a trigger event. However, given that all G-agents effectively have similar reactivity, a functional sensor for all of those agents would be sufficient to trigger countermeasures and a confirmatory sensing (by a mass spectrometer, for example). OPERATIONAL PROCEDURES FOR PROTECTING BUILDINGS The protection of existing buildings and their occupants from a biological or chemical threat requires the integration of operational procedures with specific building and detection or identification system attributes and response options.
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making Operational protective measures span actions prior to the event (for example, maintenance of the building; security procedures that reduce the likelihood of an event; and the vulnerability of the facility) to operational procedures in response to an event that mitigate the hazard to the building’s occupants or contents (for example, changing the operation of the HVAC system; evacuation of occupants). A facility manager can prepare a CONOPS for a given threat scenario from a set of specific operational response options. The operational responses should be reviewed and practiced periodically. However, uncertainties in an actual event make the operational response a complex balance of developing situational awareness and responses to protect the building and occupants. Furthermore, each of the response options affects the operation of a facility or its occupants to some extent. Some options could lead to secondary consequences, such as the possibility of deaths. The threshold below which these undesirable consequences are acceptable often determines when “low-regret” response options (for example, shelter in place in the event of an external release) are used before “high-regret” response options (for example, donning personal protection). The CONOPS needs to balance the effectiveness and potential regrets of the options and to address the uncertainties in the threat situation (type and extent of the threat). Because the development of protective action plans is presented in detail elsewhere (DOD, 2005, Appendix E), this section focuses on CONOPS when active protection (LP-3 or LP-4) is in use. An update of detailed planning guidelines for operational responses is beyond the scope of this report. Development of an Operational Response Plan The development of an operational response is essential because each building has its own protection system designed on the basis of its mission, location, type, protection options, and so on. Therefore, instead of developing a general plan for all buildings, an operational response plan that incorporates risk assessment and risk management approaches needs to be developed for each building to be protected (see Chapter 6). Following are the steps of a general guideline to use in developing a building-specific operational response plan in the absence of detectors (DOD, 2005, Appendix E). Conduct a building survey. Write specific procedures for Hazard determination (threat-vulnerability analysis), Decision-making process based on conditions and events, Communication of emergency instructions to building occupants, Evacuation, sheltering in place, ventilation and purging, and use of protective masks, and Special situations. Designate and train protective action coordinators. Train building occupants on response procedures.
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making Once a building survey is completed, the process generally requires prioritization of a list of hazards—threats and their signatures (the ability to observe a threat)—usually presented in the form of credible scenarios. The signature of a threat can be the observation of the agent itself (such as a visible chemical agent or munitions) or the clinical signs caused by the agent. A signature, or its absence, largely determines the timing and ability to respond to an event. A major response bifurcation is the determination of whether the hazard is external or internal because of the different operational response options. Response to external hazards typically involves stopping the entry of outside air into the building and shelter in place, whereas response to internal hazards usually involves purging the air within the building and ultimately evacuating. Operational response plans can be constructed and executed on the basis of likelihood of threats, their entry into the facilities, response options, and their cost and benefits including possible regrets of actions. A detailed summary of the above process is found in the report Security Engineering: Procedures for Designing Airborne Chemical, Biological, and Radiological Protection for Buildings (DOD, 2005). In this study, two levels of response options are added to traditional building protection plans: detect to treat after an event (LP-3) and detect to protect during an event (LP-4). It is beyond the scope of this report to develop guidelines for the implementation of response plans for new protection technologies, but some observations can be made. For LP-3 (detect to treat), because of the inherent delays in obtaining actionable information, the immediate response plans do not change; any responsive actions will be based on the previously defined signatures above. The fundamental change is the moderate- to long-term response that determines therapeutic care for occupants, situation stabilization once the threat is known, and decontamination. The addition of LP-3 to building protection is similar to what has been developed for the BioWatch program within the Department of Homeland Security (DHS), a detect-to-treat program for cities with a 12- to 36-hour response time for a specific set of biological agents (DHS, 2006). Detailed planning and response documents were developed by the cities that are using the BioWatch technologies based on the guidance provided by DHS. Similar guidance documents likely have been developed for equivalent detect-to-treat implementations in DOD (for example, the Guardian Program of the Joint Program Executive Office for the Chemical and Biological Defense). Because of the many possible response options for LP-4 (detect to protect), the operational plan can be complex, and the plan usually involves low-regret options initiated by higher-uncertainty detection and higher-regret actions initiated based on confirmatory detection. This type of tiered response requires commensurate operational plans, which can include triggering the capture of additional information (for example, visual confirmation of symptoms or triggering of detectors with higher operating expense) and assessment of the evolving situation. Examination of multiple scenarios is critical to ensure that the operational plan is complete for the hazard assessment. Consideration of different scenarios is likely to lead to more complex response plans. Although automation of response
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making options, such as detection triggers shutting down HVAC systems, can reduce the complexity of human response activities and provide rapid and effective response, automated components or systems cannot be realized in most facilities in the near future. Consequently, response plans with humans in the loop are still required, and continuous updating of plans and training of personnel are necessary. Because inappropriate response actions (for example, evacuation through a contaminated part of a building or into contaminated air outside) can increase the hazard to occupants or compromise the mission of the building, resources and occupant protection require appropriate operational procedures to be developed and practiced. Even passive protection systems (LP-1 and LP-2) are more effective with some degree of operational procedures. Furthermore, developing operational plans for LP-3 or LP-4 technologies is critical to the overall performance of the system, and guidelines for developing such plans would be useful. Personal Protective Equipment Personal protective equipment (PPE) includes clothing and equipment used to protect individuals in their working environment from contact with infectious or toxic chemicals or physical hazards. A basic tenet of health and safety management is that collective options such as the passive and active building design elements described above are preferred to reliance on protective equipment. This concept applies also to the protection of building occupants from a biological or chemical weapons attack. Nevertheless, where collective options are themselves inadequate to protect building occupants for all scenarios of interest, protective equipment can play an important role. This section focuses on respiratory protection only because that is the primary focus of most PPE programs for building occupants. The appropriate PPE for occupants of a facility depends on the operations conducted in the facility and the potential hazards associated with the activity. In a laboratory, factory, or research environment where hazardous materials are routinely used, PPE typically serves only as a secondary barrier for protection. In a typically nonhazardous setting, respiratory protection may be required to provide additional protection for unforeseen events, such as a toxic industrial agent spill or a terrorist attack. Proper PPE must be carefully chosen to mitigate the hazards presented by the risk of attack and the class of threat agent of concern. In a biocontainment laboratory setting, workers would consult agent summary statements on biosafety and worker protection (Richmond and McKinney, 1999; DHHS, 2007), agent manuals (Heyman, 2005), material safety data sheets (for hazardous or potentially hazardous chemicals), facility standard operating procedures, and people (such as facility safety personnel) knowledgeable about the associated hazards to assist in the selection of appropriate PPE. In a typically nonhazardous setting, the nature of the threat agents of concern, the potential concentrations of the agents, the level of training of PPE users, and the purchase and maintenance costs of PPE are
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making factors to be considered when selecting the appropriate PPE. Resources are available to guide the selection of appropriate respiratory protection devices (OSHA, 1999; DHHS, 2000; NFPA, 2001; NIOSH, 2004). Irrespective of the specific devices that are selected, the implementation of an active program is essential to ensure that PPE is properly selected, inspected, and maintained periodically and that users of the devices are trained. The most likely personal emergency equipment to be used in conjunction with other modes of building protection is “escape hoods” and other respirators. Escape hoods are typically single-use transparent “bags” that fit over the entire head and contain HEPA and activated charcoal filters. Although HEPA filters used in respirators are not certified by the National Institute of Occupational Safety and Health (NIOSH) for use in a biological environment (IOM, 1999), they have been used successfully to protect personnel for many years. However, implementing a program for use of disposable airways protection equipment in a building protection system is difficult—especially in the case of a biological attack—for the following four reasons: (1) occupants have to be warned in a timely manner to don the equipment; (2) the equipment has to be tested periodically for performance; (3) there is a small chance of injury and death from use of the equipment; and (4) the equipment cost per device could be $100 or more. SYSTEMS INTEGRATION TO ACHIEVE PROTECTION As Figure 3-1 illustrates, the effectiveness of building protection depends on the complex interaction of multiple factors. Selection of strategies and tools for protection requires careful consideration of the threats and vulnerabilities against which to protect, the goals and objectives of protection, the procurement and type of the building to be protected, and the desired level of protection. Although technology-based sensors and detection and identification systems define active protection, their presence does not infer that LP-3 or LP-4 is achieved. Active detection systems do not enhance protection unless they are complemented by an operational response plan and operate in an environment with high air quality to maximize performance of the sensors. LP-4 protection from some biological and chemical threats, particularly the category of “cannot-detect, cannot-treat” (Chapter 2 and Figure 5-2), is not possible at this time because of the fast-acting nature of the threat agents or the technological limitations of identification technologies. Given the complexity of building protection, a tool that assists in the selection of protection options for building specifications under different scenarios would be helpful (see Chapter 6). LIMITATIONS AND RISKS OF EACH LEVEL OF PROTECTION Different levels of protection can be achieved using a combination of building design, detection and identification technologies, and operational responses.
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making However, retrofitting LP-1 and LP-2 systems into existing buildings that are poorly constructed or have marginal HVAC systems might not be possible. For example, the extent to which filtration systems can be upgraded is limited by the characteristics of such air distribution components as fans and space constraints in mechanical equipment rooms. Buildings served by a small number of large-volume recirculating systems could be difficult to compartmentalize effectively. To implement protection in buildings, an LP-3 or LP-4 system might be considered, but as noted earlier, these options work optimally in clean (LP-1) facilities and might perform poorly in other circumstances. LP-1, a low-level passive protection option, relies on site selection, access control, construction of the building to reduce exposure, and selection of systems to minimize normal exposure. Site selection and construction are practical when the planning and construction of a new building is considered, but they are not an option for existing building stock unless surrounding areas can be altered and construction materials can be retrofitted. Access control can be retrofitted in most buildings, with a range of options from gating and guards to sophisticated screening procedures. Routine building systems provide for dilution of indoor air and reduce recirculation of building indoor air. There are minimal external (from outdoors to indoors) and internal (between compartments within the building) leakages in the HVAC system and in the building envelope. However, as stated earlier, the envelope becomes more susceptible to leakage as buildings age, and this parameter is rarely assessed in routine maintenance practices. LP-1 also incorporates particle filtering as needed for a healthy workplace, but filtration systems require maintenance and changing of filters by qualified individuals. LP-1 does not include a monitoring option and, as such, cannot provide information to document that airborne contaminants are present for possible public health response or for forensics. LP-2, a high-level passive protection option, builds on the features of LP-1 and provides an upgraded protection from biological and chemical attacks. Upgrading of filters (particulate and adsorption) can be efficacious, but it requires monetary resources and technical personnel to routinely change the filter matrix and ensure that there is no filter bypass following filter change-out. The use of current sorption-based chemical filters often requires significant upgrades to the HVAC system because of the large pressure drop across the filter bed. The size and weight of these systems is also an important consideration. In addition, the methods to ensure adequate filter bed capacity (lifetime) are difficult, especially when chemical agents are considered. Zoning with graded pressurization, local air-washing vestibules, and protected air intakes are necessary retrofits for existing buildings and important considerations in the design of new buildings. None of the features of LP-2 buildings provides a monitoring capability. LP-3 is a low-level active protection option that ensures that a hidden threat agent is detected and identified. LP-3 is a detect-to-treat option. Although LP-3 provides protection for latent-acting threat agents with possible treatment, it
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Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats: A Framework for Decision Making might not capture information quickly enough for fast-acting threat agents. LP-3 can be a fully automated detect-to-treat system and can also include human-in-the-loop decisions and actions to activate systems—that is, the sensor system notifies a person of a potential biological or chemical attack and the person takes action to minimize impact of the release. Thus, LP-3 might require training and sophisticated operational procedures to minimize human error. Another limitation of LP-3 and LP-4 is that active detection has the potential of falsely indicating the presence or absence of a threat. LP-4 is a high-level active protection that can “detect to treat,” “detect to mitigate,” or “detect to warn and protect.” LP-4 includes rapid, automated systems. LP-4 eliminates the human decision factor, but the complex and sophisticated automated systems require routine maintenance to ensure their proper operation. The relative risks of different levels of protection in the event of a biological or chemical attack depend on multiple factors. The fundamental risk underlying all levels of protection is the risk of exposing occupants to harm and disrupting building operations. One factor that influences this fundamental risk is the environment in which the protection system operates. If an active detection system (LP-3 or LP-4) operates in an environment with high background that causes either high false positives or negatives, an LP-3 or LP-4 system might not offer additional protection compared to an LP-2 system. The relative risks of different levels of protection can be assessed only in the context of the building in which the protection system operates.
Representative terms from entire chapter: