Protecting Building Occupants and Operations from Biological and Chemical Airborne Threats A Framework for Decision Making (2007) / Chapter Skim
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3 Components of Building Protection
3 Components of Building Protection
Pages 26-68
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From page 26... ...
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.)
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From page 27... ...
The flowchart 27 does not show the different groups of threat agents and building activities that would determine the response and outcome.
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From page 28... ...
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.
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From page 29... ...
The committee developed the concept of four levels of protection -- lowlevel 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.
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-- 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)
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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)
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U • onsider security, site selection, and operational activities that have dual-use C advantages for building protection. LP-2: High-Level Passive Protection (LP-1 + options specific to protection from biological and chemical threat agents)
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From page 33... ...
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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From page 34... ...
. In general, passive protection offers some protection from threat agents but might not be effective for all.
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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.
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Another protection option is to select a site large enough to allow adequate distances between uncontrolled and unscreened vehicles and the building(s)
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From page 37... ...
or the U.S. Department of Agriculture and non-overlap select agents of DHHS • Utility tunnels and meter rooms • Rooftops and penthouses • Areaways -- especially if used for air intakes • Storage for bottled gases, liquids, flammables, pressurized containers, fuel tanks, and other hazardous products • Food storage • Pharmacies and pharmaceuticals storage Air intake louvers are best located out of reach or access from the ground or other uncontrolled areas.
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From page 38... ...
Threat agents can also be introduced surreptitiously anywhere in the building by someone (such as an employee) who has not been screened at the entrance.
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From page 39... ...
Although site selection is not an option for an existing building, site organization and access design could improve protection of an existing building. Relocating fresh air intakes might be possible, or existing intakes might be protected with barriers that permit the intake of air but protect against the introduction of threat agents directly into the air system.
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From page 40... ...
UFAD systems have the potential to produce better indoor air quality in buildings during normal operation (Bauman, 2003) , but they could be more vulnerable to indoor biological and chemical attacks than conventional ducted air distribution systems.
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From page 41... ...
Design to eliminate supply plenums is typically an LP-1 measure. Outside Air Supply Systems Most large buildings are required by code to take in and distribute outside air to dilute indoor contaminants for the purpose of maintaining acceptable indoor air quality (an LP-1 option)
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From page 42... ...
Although proper location of air intakes can provide a certain level of protection, it contributes little to mitigating the consequences of a large-scale release, such as the rupture of a railroad tank car containing a toxic chemical or a release from an aircraft. To protect against such possibilities, outside air supply protection in the form of tight shutoff dampers -- and, possibly, alternative outside air supplies or filtered outside air supplies -- might be needed.
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The efficiency of this mechanism increases with decreasing particle size and velocities. Microorganisms generally are net negatively charged and are attracted to positively charged filter media.
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However, neither an arrestance nor a dust-spot efficiency rating specifies performance for specific particle sizes. The newer minimum efficiency reporting value (MERV)
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Polydispersed aerosols are used for the efficiency-by-particle size method. Upstream and downstream measurements are made using optical particle counting devices at a variety of flow rates.
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. To a lesser extent, such filters also remove particles in the size range associated with biological threat agents.
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Instrumentation and Controls HVAC system controls are an important part of any building protection system. Controls range from global enable or disable functions to outside air (ventilation)
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(The typical all-air system circulates a volume equal to the building volume roughly every 10 minutes, and the time for contaminated air to return to the AHU and begin reaching other spaces is much shorter.) At the other extreme, every space within a building could be served by its own independent system, in which case a localized threat agent release might have little global effect on a building or its occupants.
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From page 49... ...
The consequences of a threat agent release and the actions needed to mitigate those consequence depend on the extent to which airflows actually occur within a building and the extent to which its HVAC system differs from the system intended by the designer. For particulate air contaminants, a primary failure mode is improper installation of filters in their filter banks.
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. Although there are no background concentrations of chemical threat agents, there could be low levels of certain toxic industrial chemicals (TICs)
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Particulates in indoor air can increase greatly with foot traffic on carpets and during cleaning activities using buffers and other high-energy appliances. Outdoor bioaerosol concentrations will strongly affect the indoor air if the building includes outdoor and indoor ventilation (for example, open windows)
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. Consequently, considerations of the complete detection and identification system, of the uncertainty of preparation of a threat agent, and of the backgrounds might result in an optimum range of particle sizes for sampling beyond the standard 1- to 10-μm range.
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Detection systems for LP-3 do not require as rapid a response time for most threat agents and can use slower, but more specific and accurate identification methods. There are two strategies for detecting and identifying agents: periodic and continuous.
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From page 54... ...
Sensors and sensor systems that detect and identify chemical agents currently exist; however, they differ in levels of specificity and could have problems distinguishing between the threat agent and the background measured by the sensor at the location of interest. The background signal can arise from scattered photons (in optical detectors)
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From page 55... ...
Operationally, remote sensing in a protected building could be used for both biological and chemical threat agents indoors and outdoors. Remote sensing includes active methods, where a remote stimulus is introduced and the response is recorded by the sensor, and passive methods that use only an ambient stimulus.
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From page 56... ...
However, specificity is difficult to achieve because of the complexity of the absorption spectrum and because the important differences in biological threat agents are contained in the nucleus and are not responsive to absorption. Furthermore, the wavelengths required for identification of particular agents are in the ultraviolet region of the spectrum and pose a safety hazard.
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From page 57... ...
Detection and Identification of Biological Threat Agents Biological identification systems frequently include a triggering mechanism prior to initiation of the identification system, because the identification system is expensive and it takes time to collect enough material (toxin or organism) for the system to generate a reliable and accurate identification.
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From page 58... ...
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.
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report titled Monitoring at Chemical Agent Disposal Facilities (NRC,2005c)
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From page 60... ...
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.
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. 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)
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. 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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. A facility manager can prepare a CONOPS for a given threat scenario from a set of specific operational response options.
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From page 64... ...
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.
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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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From page 66... ...
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.
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Although LP-3 provides protection for latent-acting threat agents with possible treatment, it
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From page 68... ...
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.
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