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Protecting buildings against bioterrorism--review of guidance and tools.


Ever since the September 11, 2001, terrorist attacks and the subsequent anthrax incidents in the US, attempts have been made to thwart further attacks and other forms of terrorism. Attacks involving chemical and/or biological agents (CBA) are among the most dreaded because of the ease with which they can be produced and disseminated as well as their fatal potency.

Protecting buildings and built-in environments against bioterrorism or CBA attacks are key issues in homeland security. Unfortunately, the threat posed by chemical and/or biological agents is so complex that building professionals should be educated about what they are, possible scenarios of their release, how they may be detected, how buildings may be "immunized" against such threats, etc. Terrorists will try to cause as many casualties as possible, with high-occupancy structures such as commercial buildings being at elevated risk in any such CBA release. Building owners and building professionals should, therefore, have some level of understanding and appreciation of the dangers that such an attack poses. This paper reviews some of the necessary guidance and tools that are available for educating building professionals on protecting building occupants against CBA attacks.


The 9/11 terrorist attacks and the subsequent anthrax incidents in the US suggest that much more effort is needed to protect buildings against attacks by chemical and/or biological agents (CBA). Buildings are attractive targets because of the high density of people in them at any given time and the fact that most people in the United States are known to spend about 90% of their time indoors in homes, schools, offices, etc. (EPA 1997).

In response to the fear, chaos, and destruction that followed the September 11 attacks, federal, state, and local authorities have issued safety and other protective measures to safeguard high profile buildings and facilities against CBA attacks. These include the use of concrete barriers, shatterproof windows and reinforced steel plates, and HVAC systems that are designed to prevent the circulation of contaminated air in the event of CBA attacks. Some private building owners and operators have also taken steps to increase security. In fact, building owners and building designers have abandoned the illusion that their buildings are "immune" against terrorist attacks and instead accepted the reality that these buildings are indeed vulnerable.

Unfortunately, not all buildings are well protected, and, hence, designers and owners may have to worry about more than mere moral culpability for the loss of life that ensues. They also face potential civil lawsuits, since September 11-style attacks against buildings are now foreseeable under the "Totality of the Circumstances" test (Pharr and Menzel 2005). Building owners and designers can no longer circumvent legal liability by arguing that a release of chemical or biological agents in a building's HVAC system was unforeseeable.

The Terrorist Risk Insurance Act (TRIA) has been enacted to insure, among others, commercial buildings against terrorist attacks. The Act is, however, restricted to the use of conventional weapons and attacks by foreign terrorists (RAND 2005). TRIA has an exclusion clause for domestic terrorist activities and attacks involving chemical, biological, radiological, and nuclear weapons. It is, therefore, incumbent upon every commercial building owner to find ways of preventing CBA incidents from occurring or reducing the impact of CBA incidents should they occur.

Several tools are available that can be used to help mitigate or reduce the impact of CBA attack. This paper reviews some of the guidance and tools that are available to educate building professionals on how best buildings may be operated or designed to protect them from CBA attack or to reduce the impact from such attacks. A discussion of some of the guidance that can be used during an outdoor or indoor CBA release will be made. This will be followed by an assessment of certain guidelines that are available for safe building design. Two main filter rating systems are very prevalent in the US--the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standards 52.1-1992 and 52.2-1999 (FEMA 2003). These are also briefly discussed. Finally, we also discuss the tools that are available for modeling the dispersion and transportation of CBA, with focus on zonal and computational fluid dynamic models.


Indoor and Outdoor Release of CBA

US Army Regulation AR 50-6, Nuclear and Chemical Weapons and Material--Chemical Surety, prescribes procedures, policies, and responsibilities for the Army Chemical Surety Program (DOA 2001). AR 50-6 stipulates that when evidence of a chemical leakage is established, the source should be located, isolated, and contained as soon as practicable. If the source cannot be located immediately, the facility should be closed, then continuously filtered and periodically monitored until the source is isolated or until low level monitoring indicates the source no longer exists (DOA 2001).

Implementing this guidance in buildings will be difficult in that once a sign of a CBA incident has been established, a decision has to be made immediately on whether to evacuate the building or take shelter in place. Most buildings will not have detectors, or most detectors may not be functional. Therefore, waiting to locate the source, isolating the area, and containing the area will be virtually difficult to achieve, if not impossible. A list of some of the guidance and standards for protecting buildings against CBA attacks are given in the appendix.

The ASHRAE Presidential Ad Hoc Committee on Homeland Security has issued numerous recommendations on how to protect buildings against CBA that can be implemented almost immediately (ASHRAE 2003; Persily 2004).The recommendations may be summarized as follows:

1. Make sure that the ventilation system is working as designed by evaluating its operation relative to its design intent, i.e., it should operate in accordance with ASHRAE Standard 62. If it is not performing as intended, address the deficiencies immediately.

2. Secure mechanical rooms and outdoor air intakes to prevent tampering. Air intakes should be located as high as possible above ground. Where relocating the intakes is not possible, monitoring systems, such as surveillance cameras or alarms, can be used.

3. Understand the consequences of any HVAC changes that are considered in response to CBA incidents. Changes made to the building operation with the intention of reducing building vulnerability should not degrade indoor air quality or comfort under normal operation.

Ventilation systems are used in buildings mainly to provide heating, cooling, and humidity control for the comfort of the building occupants. They are designed and operated to bring in sufficient outdoor air to remove indoor air contaminants as well as to create pressure differences to limit the movement of undesirable contaminants (Persily 2004).

Ventilation and air distribution are critical with respect to such issues as CBAs entering buildings, their movement within buildings, and their subsequent removal. Ventilation can impact buildings both negatively and positively (Persily 2004). Ventilation can reduce the amount of CBA in the indoor environment through dilution with outdoor air. It can also direct airflow to filters and air-cleaning devices that can remove contaminants. Furthermore, the ventilation systems can be used to create pressure differences between zones, thereby isolating potentially contaminated harmful areas from other spaces. However, the ventilation system can also bring in contaminated air from the outdoors into the building through the outdoor air intake or via the building envelope leakage induced by negative pressure in the building. In addition, CBA can effectively and quickly be disseminated throughout the building by the ventilation system. The impact of ventilation is strongly dependent on the layout of a building and the design and performance of its ventilation system. Therefore, before any CBA response plans involving the ventilation system can be developed, it is important to understand what the system is supposed to do and what it is actually doing (Persily 2004).

The consensus among building professionals is that it is easier to keep certain areas at negative pressures if they are served by their own air-handling units. Building pressurization has often been touted as a means of protecting buildings against outdoor release of CBA. This requires the supply of sufficient outdoor air to a building such that the indoor pressure increases above the outdoor pressure at all air leakage sites. This strategy, together with outdoor air filtration and cleaning, can be an effective tool to protect against outdoor CBA release (Persily 2004). Can one, therefore, continue operating the HVAC system even during an external CBA releases? Unfortunately, positive pressurization of a building means bringing in more outdoor air than is being exhausted. A successful application of pressurization to combat external CBA release will depend upon a knowledge of the CBA release and a level of building envelope airtightness that unfortunately does not always exist in typical buildings. Protection can only be given against those agents that the filtration system can remove, e.g., particle filters cannot remove chemical agents (Persily 2004).

The Centers for Disease Control (CDC) guidelines for preventing the transmission of mycobacterium tuberculosis in health care facilities stipulates that a minimum differential pressure of 0.249 Pa (0.001 in. w.c.) is needed to achieve a directional airflow into or out of a room (Wiseman 2003). This value is deemed too small, since it can be adversely affected by thermal stratification in a room, room supply air diffusion, and door swings (Wiseman 2003). The American Institute of Architects' Guidelines for the Design and Construction of Hospitals and Health Care Facilities also recommends a minimum differential pressure of 2.49 Pa (0.01 in. w.c.). The American Conference of Governmental Industrial Hygienists' (ACGIH) Industrial Ventilation, a Manual of Recommended Practice notes that the proper flow differential will depend on the physical conditions of the area, but a general guideline would be to set a 5% flow difference but no less than 24 L/s (50 cfm) (Wiseman 2003). When designing an HVAC system to obtain the desired room pressurization or directional airflow, one should make sure that the room has a minimum negative or positive pressure of 2.49 Pa (0.01 in. w.c.), with values greater than 12.5 Pa (0.05 in. w.c.) being more preferable (Wiseman 2003). FEMA's Reference Manual to Mitigate Potential Terrorist Attacks Against Buildings also suggests that building environments should have a positive pressurization of about 5 Pa to 12 Pa (0.02-0.048 in. w.c.). NFPA Standard 92A and NFPA Standard 101 (refer to appendix) stipulate a minimum pressure differential of 12.5 Pa (0.05 in. w.c.) in sprinkler systems and 25 Pa (0.1 in. w.c.) in non-sprinkler systems. Care should be taken, however, when designing to the minimum standard, to ensure that the effectiveness of the pressurization is not eroded by stack effect and wind.

Understanding the consequences of the HVAC changes that are considered in response to CBA incidents, as recommended by the ASHRAE Presidential ad hoc Committee on Homeland Security, will be very helpful. One may implement changes in the HVAC system operation based on CBA detection to achieve isolation of contaminated areas and safe egress paths or safe refuges for building occupants. This is similar to smoke control systems where smoke detectors are used to trigger damper and fan operation to isolate the fire zone and provide a safe exit route for the building occupants (Persily 2004). However, unlike smoke detectors, which are available on the market at reasonable costs, CBA detectors are still being developed and economics will always limit the extent of their implementation. Beside, there are currently no detectors that can detect all the potential chemical agents or biological agents, let alone both chemical and biological agents simultaneously. The appropriate response depends on the particular building, its ventilation system configuration, and the location and type of release. In many situations, the relevant HVAC system changes may not be obvious. Therefore, any changes in the implementation of the HVAC system operation should be done only when one understands the system performance as it exists and how the changes will impact the airflow patterns in the building (Persily 2004). That is to say, designers should have a thorough understanding of all airflow patterns in all operational modes.

The question, therefore, is how should a building's HVAC system be operated during a CBA releases Should it be turned off, run at diminished capacity, or 100% outdoor air, or 100% exhausts It is extremely difficult to generalize on the best response to a CBA release because it depends on the building configuration, the HVAC system design, and the type and location of the release. For an outdoor CBA release, the focus is to limit the entry into the building through pressurization strategies or by reducing the outdoor air intake by closing dampers or shutting down the HVAC system (Persily 2004). The Lawrence Berkeley National Laboratory (LBNL) guidelines, Protecting Buildings from a Biological or Chemical Attack: Actions to Take Before or During a Release, also suggest that under this circumstance (i.e., during an external release of CBA) the HVAC and all dampers should be shut down. NFPA Standard 730, Guide for Premises Security, also recommends turning off all HVAC systems during a chemical or biological attack.

Closing all outdoor dampers, for instance, could damage the ductwork. As such, one must be careful to ensure that the pressures in the HVAC system are well managed to avoid damaging the ductwork. Another consequence of shutting down the HVAC or closing all outdoor dampers can be loss of building pressurization, and, hence, the building's ability to control infiltration of contaminated air will be impaired. In addition, dilution and removal of the contaminants will be difficult to achieve.

Experts in the field are of the view that if the release is indoors, the objective will be to limit the transportation of contaminants beyond the point of release and if possible to remove them from the occupied space by filtration or exhaust. If the HVAC system has been properly designed and tested, one can close the exhaust dampers and intake dampers, but let the HVAC system operate so as to recirculate air through the filters. Otherwise, the system should be shut down and outdoor air dampers closed (Price et al. 2003).

Shutting down the HVAC will result in loss of pressurization control and exhaust of the contaminants from the building. Operating in full recirculation mode means high-efficiency filters should be available. Consequently, one should be careful to make sure that the right filters are installed to deal with the agents in question.

The lack of federal regulation on indoor air quality (IAQ) in buildings should not be seen by building designers and owners as a reason to circumvent IAQ requirements because an unhealthy building will not attract tenants into the building. In addition, designers and builders can be held accountable under certain circumstances should the health or life of the building occupants be compromised due to poor IAQ. In fact, it is in their interests and those of the building occupants to make sure that the appropriate IAQ is met. The measures taken to protect buildings against CBA release should not degrade the IAQ or thermal comfort under any circumstance (ASHRAE 2003). ASHRAE Standard 62, Ventilation for Acceptable Indoor Air Quality, provides a guideline for establishing IAQ that will be acceptable to human occupants and is intended to minimize the potential for adverse health effects (ASHRAE 2001, 2005). The minimum ventilation requirements set in building codes of most states are directly or indirectly linked to the standard.

The purpose of ASHRAE Standard 62 is to specify minimum ventilation rates as well as IAQ that will be acceptable to building occupants and will also minimize the potential for adverse health effects (ASHRAE 2001; Dougan and Damiano 2003). It applies to all indoor or enclosed spaces occupied by people, except where other applicable standards and requirements demand larger amounts of ventilation. Chemical, biological, as well as physical contaminants affecting air quality are regulated by Standard 62 (ASHRAE 2001).

An acceptable IAQ can mostly be achieved through proper ventilation. Standard 62 specifies two main procedures for achieving acceptable IAQ. These are the ventilation rate procedure and the IAQ procedure (ASHRAE 2001, 2005). Using the ventilation rate procedure, a building or space is said to have acceptable IAQ if it is ventilated at the specified airflow rate. Standard 62 assumes that the air in the occupied space is well mixed and that the concentration of the contaminant is relatively uniform throughout the space (ASHRAE 2005).

In recent years, ASHRAE Standard 62 has been incorporated into several building codes (Dougan and Damiano 2003). Where the Standard has been made part of building codes, it has been realized that the interpretation of the Standard has always proved to be difficult for code enforcement agencies. In fact, the main motivation for designing to the Standard has been to avoid or reduce liability and risk management concerns (Dougan and Damiano 2003). In today's changing environment, especially after 9/11 when concern about the use of CBA is on everyone's mind, building owners and building occupants have become more and more inclined to increase productivity and protect human health by improving IAQ in occupied spaces.

The IAQ of a building can be affected by HVAC design and contaminant sources as well as the efficiency of the air-cleaning systems. All these factors acting together make achieving acceptable IAQ in buildings more complicated. ASHRAE Standard 62 addresses this complexity by establishing guidance for the design, construction, start-up, operation, and maintenance of HVAC systems (ASHRAE 2005). The standard also includes provisions for managing sources of contamination, controlling indoor humidity, and air filtration (ASHRAE 2005). Standard 62 requires that the contaminants from stationary local sources within the space should be controlled by collection and removal as close to the source as practicable. But local exhaust can be difficult to achieve or may not always be possible. Under this circumstance, the most practical and cost-effective approach would be the use of outdoor air to dilute the contaminants. Outdoor air contaminants can enter a building, either through outdoor air intake or by infiltration (ASHRAE 2005; Persily 2004). The standard states that, "Makeup air inlets and exhaust air outlets shall be located to avoid contamination of the makeup air." Built-up HVAC systems can meet this stipulation by carefully locating the outdoor air intakes relative to contaminant sources. However, this can be difficult in the case of packaged roof-mounted unitary systems because once they have been mounted it will not be easy to relocate them relative to contaminant release (ASHRAE 2005). The question then becomes, where is the appropriate location for the outdoor air intakes According to FEMA 426 Guidelines (refer to Appendix), air intake should be located as high as possible (at least 12 ft above ground).

Outdoor air requirement may be reduced by recirculating air that has been cleaned of contaminants. The amount of outdoor air required depends on the concentration of the contaminants in the indoor and outdoor air, the filter location, the filter efficiency, supply air circulation rate, as well as the fraction of recirculated air (ASHRAE 2001). Standard 62 prescribes that outdoor air for air ventilation purposes should be introduced at the lowest volume necessary to maintain acceptable IAQ. For economic reasons, therefore, most building operators may size their HVAC systems to comply with this minimum requirement and thereby risk making it difficult to increase the rate of outdoor air when need be.

Indoor air dilution as defined by Standard 62 is the process of bringing outdoor air into the occupied space to reduce the concentration of contaminants. In this definition, the outdoor air is assumed to be less contaminated. Dilution can be 100% outdoor air or a mixture of outdoor air and recirculation air that has been filtered. Ventilation rate is defined as the number of complete air changes per unit time. It may also be defined as the cubic feet per minute (cfm) of outdoor air needed to meet the minimum IAQ requirements. Standard 62-2001 specifies that a minimum of 15 cfm per person should be observed in nonsmoking areas, while 60 cfm per person is required in smoking areas, irrespective of how much air is used by each person in the space. It also recommends that the concentration of [CO.sub.2] should not exceed 1000 ppm in conditioned space.

Standard 62 demands that ventilation air be supplied throughout the occupied space and that whenever there is a reduction of supply air, as can occur in variable air volume (VAV) systems, then provision should be made to ensure acceptable IAQ throughout the occupied space (ASHRAE 2001). It also requires particulate air filters with a MERV rating of not less than 6 to be provided upstream of all cooling coils or other devices with wetted surface through which air is supplied to the required space, whereas appropriate gas cleaning technologies may be used to control gaseous contaminants. It also suggests that the relative humidity of habitable spaces should not be less than 30% or greater than 60% to minimize the growth of allergenic or pathogenic organisms (ASHRAE 2001).

Standard 62 defines acceptable IAQ as "air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction." Most HVAC systems today do not meet the minimum ventilation requirements prescribed by the standard during operation. In practice, more building occupants show dissatisfaction toward the quality of ventilation and indoor air. Furthermore, there are no guidelines to effectively overcome the effect of changing system dynamics on ventilation rates and distribution for modern HVAC systems, resulting in numerous design deficiencies (Dougan and Damiano 2003).

Another limitation of Standard 62 lies in the fact that there are only two main procedures that are used to attain acceptable indoor air quality. Building designers are to choose one of these procedures just to be in compliance. They do not need to use a combination of the two procedures. One can be in compliance by merely providing ventilation air of a specified quality and quantity to the space or by controlling known and specifiable contaminants. However, the ventilation rates as prescribed by the ventilation rate procedure of the standard are derived from physiological considerations, subjective evaluations, and professional judgments, while the IAQ procedure specifies acceptable IAQ based on certain guidelines, without prescribing ventilation rates or air treatment methods. In addition, the standard is limited in its ability by the fact that different buildings meeting the same requirements of the standard may not achieve the same acceptable IAQ.

Building Design and Cleanroom Standards

Today, terrorist attacks can impact anyone, at any time, at any location, and can take several forms (DOD 2003). Most existing Department of Defense (DOD) buildings do not offer adequate protection against terrorist attacks. As such, DOD issued minimum antiterrorism standards for buildings to protect occupants in its facilities. The objective of the standards is to minimize the possibility of mass casualties in DOD buildings or facilities. The standards are not based on any known threat but are meant rather to provide the easiest and most economical method to minimize injuries and fatalities should a terrorist attack take place. Under these standards, therefore, buildings are designed, inter alia, to maximize standoff distance, to prevent collapse, to reduce hazards from flying debris, and to limit airborne contamination. The standards set a minimum effective standoff distance of 10 m (33 ft) for new buildings, although this may be reduced for existing buildings (DOD 2003).

Building air intakes to HVAC systems located at ground level provide opportunity for terrorists to place contaminants that could be introduced into the building (DOD 2003). Unified Facilities Criteria (UFC)--DOD Minimum Antiterrorism Standards for Buildings (DOD 2003) prescribes for new buildings that air intakes should be located at least 3 m (10 ft) above ground, while this is a recommendation for existing buildings. Mailrooms are also to be provided with separate dedicated air ventilation systems and should be maintained at negative pressures (DOD 2003). FEMA 426 Guidelines (see appendix), recommend positioning air intakes at least 12 ft above ground.

USDA 242.1M-ARS Standards (refer to the appendix) suggest that the first step in developing a containment facility program is to perform a risk assessment for the agent involved (Frasier and Talka 2005). The information obtained from the risk assessment studies can then be used to determine the facility features (which include directional airflow, HEPA filtration, system redundancy, robust control system, and emergency power) that can mitigate risk (Frasier and Talka 2005). Even before the events of September 11, 2001, the federal government initiated steps to protect the occupants of federal buildings by establishing a mandate to develop construction standards for new federal office buildings. This culminated in the establishment of the interagency security committee (ISC) security design criteria. After the 9/11 attacks, the National Institute of Health (NIH) developed guidelines for these facilities to supplement the ISC criteria. The underlying premise for determining the security requirements for a facility is the threat and risk assessment, which establishes the main factors that may lead to a specific threat to a facility by certain groups and the risk of harm and the resulting consequences of the attack. Setbacks, charge weights, and hardening may be incorporated in building designs to improve protection (Frasier and Talka 2005). UFC 4-010-01 Standards recommend a minimum effective standoff distance of 10 m (33 ft). In addition, they stress that other security systems, such as closed circuit television (CCTV) systems around the perimeter and within the building, zoned security access, and perimeter access and enclosure, can also be incorporated into the design. The American Institute of Architects (AIA) Guideline, Security Planning and Design--a Guide for Architects and Building Design Professionals, suggests the standoff distance be about 15.24 m (50 ft) for government buildings. It should, however, be emphasized that defining the appropriate standoff for any building to protect against explosive blast is difficult because this will require an advance knowledge of the explosive weight of the weapon likely to be used. In fact, there is no ideal standoff distance. The distance will be determined by the type of threat, the type of construction, and the desired level of protection (FEMA 2003). Therefore, the guideline, as issued by AIA, will most likely be underestimated, especially for explosive blast, and, hence, should be used with care.

The major concern in using excessive security systems in a building is that it may be seen as a high target facility, thereby increasing the threat of an attack, since terrorists will normally choose high profile or iconic targets or structures likely to cause significant emotional or economic damage (FEMA 2003).

USDA 242.1M-ARS Standards mandate that dedicated, single pass, directional, and pressure gradient ventilation systems be used for a research facility involved with the use of certain biological agents. These systems, according to 242.1M-ARS, are operated to provide directional airflow as well as a negative pressure within the containment area, with airflow moving from areas of least hazard potential toward areas of greatest hazard potential. The standards further recommend the use of an alarm system, to warn of any changes in the set pressure differential, and prescribe that the air supply and the exhaust systems be interlocked to prevent positive pressurization within the containment area should the exhaust system fail. The good thing with such a design is the fact that zones can be isolated from each other to prevent air from moving from contaminated to uncontaminated areas. Such systems are, however, in a very disadvantageous position to protect buildings from outdoor CBA release. In addition, recirculation of ventilation air is not possible.

USDA 242.1M-ARS Standards also suggest that the supply and exhaust air be HEPA filtered, with the air-handling unit (AHU) providing 100% outdoor air. But circulating 100% outdoor air can sometimes be economically insurmountable due to the fact that an enormous amount of energy may be required to condition the outside air.

The standards also stipulate that HVAC systems be selected for long-term durability, energy and cost efficiency, flexibility, and ease of operation and maintenance. It is suggested that the system be located in a less vulnerable area and that access to the mechanical systems should be limited. In addition, it is recommended that a provision should be made for a reasonable amount of redundancy. The standards emphasize that the mechanical system should continue the operation of key life safety components following an incident. It is further recommended that air intakes be located as high as possible. Ventilation equipment should be protected and located away from high risk areas. The designer should consider having separate HVAC systems in lobbies, loading docks, and other locations where significant risk of an internal event exists (USDA 2002). In addition, stairways and the emergency egress route should be maintained at positive pressure. A stairway pressurization system should maintain positive pressure in stairways and the emergency egress route for occupant refuge, safe evacuation, and access by firefighters. USDA 242.1M-ARS Standards further suggest that effort should be made to minimize the entry of smoke and hazardous gases, and they stress that space where exhaust systems are used to remove contaminated or hot air be maintained at a negative pressure to prevent exfiltration to other areas. Furthermore, the standards maintain that negative pressure should be created by exhausting 5% to 15% more air than the supply air. According to USDA 242.1M-ARS Standards, filters should be provided where particulate matter must be removed from the supply or exhaust air.


Modeling Tools

There are two main types of models that may be used in modeling CBA dispersal and transport in buildings. These are zonal and computational fluid dynamics (CFD) models. Most multi-zone modeling programs are designed so as to rely on simplifying assumptions. These assumptions thus restrict their ability to implement several important models, such as certain types of dynamic behavior, detailed duct systems, pollutants that do not satisfy the well-mixed assumption, and mixed natural and forced convection across horizontal partitions (Lorenzetti 2002). Without any additional modification, these software programs cannot model ventilation control systems, duct system design, and natural or hybrid ventilation (Lorenzetti 2002). The multi-zone modeling tools such as CONTAMW normally assume that the air in each zone is well mixed with uniform temperature, pressure, and contaminant concentrations (Walton 1995, 1997; Dols 2001). The models also assume instantaneous air mixing of contaminant introduced into a zone. Another assumption underlying these models is that the concentrations of contaminants are such that they do not affect the density of the air within a zone and that pressure differences within each zone are negligible. Heat transfer phenomena cannot be handled by the model, since it assumes a constant temperature within the zones. The applications of the program are, however, numerous. It can be used to determine building air change rates, analyze ventilation strategies and contaminant transport, design indoor air quality (IAQ), isolate the source of a contaminant, and design smoke management systems (Dols 2001). The models allow a macroscopic analysis of airflow and contaminant in a zone, unlike a CFD model that uses a microscopic technique for detailed analysis of airflow, temperature, and contaminants in a zone. Multi-zone modeling is, therefore, only suitable for applications that require knowledge on a whole building scale (Dols et al. 2000; Dols 2001; Dols and Walton 2002).

Computational fluid dynamics (CFD) can be used to model room airflows and contaminant transport prediction (Baker et al. 1997). CFD can be used to predict fluid level and pressure differences to very insignificant levels, which are experimentally difficult to measure. The model, however, relies on numerous assumptions and approximations that lead to inaccurate results (Baker et al. 1997). In fact, the CFD method for analyzing fluids uses the Navier-Stokes (NS) equations, which are partial differential equations, whose primary dependent variables are velocity, pressure, temperature, and some scalar, with space directions and time as the independent variables (Baker et al. 1997; Ladeinde and Nearon 1997; Gadgil et al. 2003). The NS equations require initial and boundary conditions to be specified before they can be solved. The NS equations are also mathematically manipulated, using Reynolds averaging (RA), so as to make them computationally tractable (Baker et al. 1997; Gadgil et al. 2003). These equations are highly nonlinear and, hence, cannot be solved explicitly by closed-form analytical methods. Therefore, numerical approximation methods, such as finite difference, finite element, and finite volume methods, must be used to solve these equations (Ladeinde and Nearon 1997).

The use of CFD in HVAC design has bright prospects, especially in its ability to predict very low level velocity fields and small pressure variations when doing experiments is almost impossible (Baker et al. 1997). The Reynolds-averaged Navier-Stokes (RANS) CFD model has also been found to be adequate for predicting the isothermal pollutant transport in large rooms with simple geometry (Finlayson et al. 2003).

Some of the advantages of CFD lie in its ability to simulate realistic systems inexpensively, compared to the high cost of doing experiments. The cheaper cost of computing today is also an advantage of the method because of its huge computational requirements (Ladeinde and Nearon 1997). On the other hand, it is sometimes very difficult to set the initial and boundary conditions for certain problems using CFD (Ladeinde and Nearon 1997). It can also be very challenging building a CFD model for turbulence, chemical reaction, radiation, and two-phase systems, such as boiling, condensation, and multiphase flow through a pipe. CFD can be used in boundary layer and turbulence developments in heat exchanger systems and, hence, pressure drop and heat transfer coefficients. CFD can also be used to produce high accuracy and detailed results for the distribution of flow and temperature inside buildings (Ladeinde and Nearon 1997). The acquisition cost of a CFD software package such as FLUENT can be financially very demanding (Martin 1999). By comparison, the latest version of CONTAMW can be downloaded for free from the National Institute of Standards and Technology (NIST) Web site. The multi-zonal models are excellent tools for predicting thermal comfort in rooms, while CFD models are suitable tools for estimating airflow details (e.g., pollutant transport modeling) in rooms (Mora et al. 2002, 2003).

The United Technologies Research Center has also developed a software tool that can be used to help designers add building security to protect against chemical and biological agents, the so-called Chemical-Biological Tool (CBT) (Kirschner 2004). CBT is a Windows-based program that uses holistic techniques to add security to buildings by assessing the interrelationship among the building design variables such as energy, comfort, and IAQ (Kirschner 2004). The program assesses the vulnerability of buildings and cost-effective protective measures to determine optimum measures that will be required to protect the building against chemical or biological attacks (Kirschner 2004).

Filter Performance Testing Standards

ASHRAE Standards 52.1-1992 and 52.2-1999 are the two main standards that can be used to measure the efficiency of particle air filters (FEMA 2003). Standard 52.1-1992 (ASHRAE 1992) measures arrestance, dust spot efficiency, and dust-holding capacity. Arrestance is the ability of a filter to collect a mass fraction of coarse test dust and may be used to describe the efficiency of low- and medium-efficiency filters. Dust spot efficiency measures the ability of a filter to remove large particles, especially those that tend to soil the building interior. Dust-holding capacity is a measure of the total amount of dust a filter is able to hold during a dust-loading test.

ASHRAE Standard 52.2-1999 (ASHRAE 1999) is the standard method for evaluating and rating HVAC filters. The purpose of Standard 52.2 is to establish a test procedure for evaluating the performance of air-cleaning devices as a function of particle size (ASHRAE 1999). The method of test measures the performance of air-cleaning devices in removing particles of specific diameters as the devices become loaded by standardized loading dust fed at intervals to simulate accumulation of particles during service life (ASHRAE 1999). The procedures for generating the aerosols used in the test are defined by the standard. In addition, it also provides a method for counting airborne particles of 0.3 to 10 [micro]m in diameter upstream and downstream of the air-cleaning device in order to calculate removal efficiency by particle size (ASHRAE 1999).

Standard 52.2 (ASHRAE 1999) quantifies filtration efficiency in different particle size ranges for a clean and incrementally loaded filter to provide a composite efficiency value. It gives a better determination of the effectiveness of a filter to capture solid particulate rather than liquid aerosols. Particle-size efficiency results are rated as a MERV between 1 and 20, with a lower MERV indicating a filter of lower efficiency and higher MERV indicating a more efficient filter. Filters with MERV rating of less than 5 must be tested in accordance with ASHRAE Standard 52.1-1992 in order to determine their performance (Hofacre et al. 2005). Although four MERV categories are added to the lists of definitions of the various MERV ratings to demonstrate the approximate rating of HEPA/ULPA performance, the standard is not meant to be used to evaluate HEPA filter performance. Different standards will be required for these types of filters (Hofacre et al. 2005).

The National Air Filtration Association (NAFA) Position Statement on Bioterrorism--Using ASHRAE Standard 52.2 in Preparedness for Bioterrorism suggests that most buildings use filter systems that only provide protection for the HVAC system. According to NAFA, this level of protection does not even address particles in the size range of spores (0.5-2 [micro]m) let alone viruses (less than 0.005 to 0.05 [micro]m). It asserts that HEPA filtration having minimum particle removal efficiency of 99.97% on 0.3 [micro]m particles can be very useful as cleaning agents in this size range but cautions that most HVAC systems do not have the fan capacity or the framing systems necessary to use these filters. NAFA maintains that ASHRAE Standard 52.2 test report is an excellent tool for selecting filters to remove specific contaminants, once the size is known.

There are currently no standards for testing gas-phase filters. Manufacturers normally provide their own performance measure. In view of this, effort should be made to develop a standardized performance measure since manufacturers may overestimate the performance efficiency of their products.


Due to the changing environment in which we find ourselves today, especially after September 11, 2001, building owners and building designers should take all the necessary precautions to make sure that they do not end up in the courts of law should chemical or biological agents be used to attack their buildings. After 9/11, the legal community can always use the "totality of the circumstance" test to argue cases pertaining to lawsuits involving victims of CBA attacks in buildings. Currently, several high-profile buildings and buildings of high vulnerability are taking the necessary measures to prevent CBA attacks. There are still a substantial number of buildings without sufficient or any protective measures against CBA attacks.

This study reviewed some of the guidance and tools that are available for building owners, operators, and designers to protect buildings against CBA attacks. In our quest to protect buildings against CBA, the IAQ and thermal comfort should not be compromised. ASHRAE Standard 62 (ASHRAE 2001) provides guidance that can be used to make sure that adequate IAQ is maintained. It provides reasonable guidelines on basic equipment and system design requirements, minimum ventilation rates, and construction, operation, and maintenance procedures to minimize the health risk of building occupants through the proper provision of acceptable IAQ. It is a minimum requirement on which HVAC system design can be based. At the end of the day, the standard is a guideline, and it is proper HVAC system design and selection and proper building operation and maintenance that will dictate the provision of acceptable IAQ.

Computer programs are currently available for modeling the transport and dispersion of CBA in buildings. These include multi-zone models (e.g., CONTAMW) and CFD models (e.g., FLUENT). These tools can be used to assess the vulnerability and methods of protecting buildings against CBA.

The question is not if an attack involving CBA will take place but rather, unfortunately, when. Preparing in advance can help prevent or reduce the number of casualties should such an attack take place.


ASHRAE. 1992. ANSI/ASHRAE Standard 52.1, Gravimetric and Dust Spot Procedures for Testing Air-Cleaning Devices Used in General Ventilation for Removing Particulate Matter. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

ASHRAE. 1999. ANSI/ASHRAE Standard 52.2, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. Atlanta: American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE).

ASHRAE. 2001. ANSI/ASHRAE Standard 62-2001, Ventilation for Acceptable Indoor Air Quality. Atlanta: American Society of Heating, Refrigerating and Air-conditioning Engineers, Inc.

ASHRAE. 2003. Report of Presidential ad hoc Committee for Building Health and Safety Under Extraordinary Incidents on Risk Management Guidance for Health, Safety, and Environmental Security Under Extraordinary Incidents. Atlanta: American Society of Heating, Refrigerating and Air-conditioning Engineers, Inc.

ASHRAE. 2005. 62.1 User's Manual. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Baker, A.J., R.M. Kelso, E. Gordon, S. Roy, and E. Schaub. 1997. Computational fluid dynamics: A two-edged sword. ASHRAE Journal 39(8):51-58.

DOA. 2001. Nuclear and chemical weapons and material--Chemical surety. Washington, DC: Department of the Army (DOA), report AR 50-6.

DOD. 2003. Unified Facilities Criteria (UFC)--DoD Minimum Antiterrorism Standard for Buildings. Washington, DC: US Department of Defense.

Dols, W.S. 2001. A tool for modeling airflow and contaminant transport. ASHRAE Journal 43(3):35-42.

Dols, W.S., and G.N. Walton. 2002. CONTAMW 2.0 User Manual. US Department of Commerce, National Institute of Standards and Technology, Washington, DC.

Dols, W.S., G.N. Walton, and K.R. Denton. 2000. CONTAMW 1.0 User Manual. US Department of Commerce, National Institute of Standards and Technology, Washington, DC.

Dougan, D.S., and L.A. Damiano. 2003. ASHRAE Standard 62: Ventilation for acceptable indoor air quality--Analysis and recommendations. Article.

EPA. 1997. An Office Building Occupant's Guide to Indoor Air Quality. US Environmental Protection Agency (EPA).

FEMA. 2003. Reference Manual to Mitigate Potential Terrorist Attacks Against Buildings. Washington, D.C.: Federal Emergency Management Agency (FEMA).

Finlayson, E.U., A.J. Gadgil, T.L. Thatcher, and R.G. Sextro. 2003. Pollutant dispersion in a large indoor space: Part 2-Computational fluid dynamics (CFD) predictions and comparison with a scale model experiment for isothermal flow. Submitted to Indoor Air.

Frasier, D., and J. Talka. 2005. Facility design considerations for select agent animal research. ILAR Journal 46(1):23-33.

Gadgil, A.J., C. Lobscheid, M.O. Abadie, and E.U. Finlayson. 2003. Indoor pollutant mixing time in an isothermal closed room: An investigation using CFD. Atmospheric Environment.

Hofacre, K.C., R.T. Hecker, A. Wang, M.C. Shell, and S.J. Lawhon. 2005. Critical assessment of air cleaner technologies--A draft report. Columbus, OH: Battelle Columbus Operations.

Kirschner, P. 2004. Building Protection Improvement Design Protocol--Chem/Bio: User's Guide. Hartford, CT: United Technologies Research Center (UTRC).

Ladeinde, F., and M.D. Nearon. 1997. CFD applications in the HVAC & R industry. ASHRAE Journal 39(1):44-48.

Lorenzetti, D. 2002. Assessing multizone airflow simulation software. Presented at Indoor Air 2002 Conference.

Martin, P. 1999. CFD in the real world. ASHRAE Journal 41(1):20-25.

Mora, L., A.J. Gadgil, and E. Wurtz. 2003. Comparing zonal and CFD predictions of isothermal indoor airflows to experimental data. Indoor Air 13(2): 77-85.

Mora, L., A.J. Gadgil, E. Wurtz, and C. Inard. 2002. Comparing zonal and CFD model predictions of indoor airflows under mixed convection conditions to experimental data. Third European Conference on Energy Performance and Indoor Climate (EPIC) in Buildings, Lyon, France, October 23-26, 2002.

Persily, A. 2004. Building ventilation and pressurization as a security tool. ASHRAE Journal 46(9):18-24.

Pharr, S.M., and K.E. Menzel. 2005. Thinking about the Unthinkable: Landowner and Design Professional Liability for September 11-Style Attacks. Winston Salem, NC: Pharr & Boynton.

Price, P., M.D. Sohn, A.J. Gadgil, W.W. Delp, D.M. Loren-zetti, E.U. Finlayson, T.L. Thatcher, R.G. Sextro, E.A. Derby, and S.A. Jarvis. 2003. Protecting buildings from a biological or chemical attack: Actions to take before or during a release. Lawrence Berkeley National Laboratory.

RAND. 2005. Terrorism Insurance and the Evolving Terrorist Threat. Santa Monica, CA, RAND Center for Terrorism Risk Management Policy.

USDA 2002. ARS Facilities Design Standards. US Department of Agriculture (USDA).

Walton, G. N. 1995. CONTAM94--A multizone airflow and contaminant dispersal model with a graphic user interface. Proceedings of the 4th Conference of International Building Performance Simulation Association, Madison, WI.

Walton, G.N. 1997. CONTAM96 User manual. US Department of Commerce, National Institute of Standards and Technology, Washington, DC.

Wiseman, B. 2003. Room pressure for critical environments. ASHRAE Journal 45(2):34-39.


Richard B. Hayter, Associate Dean of Engineering, Kansas State University, Manhattan, KS: Is there evidence of training that ASHRAE could provide to facility manager first responders as to the steps they should take immediately after an attacks On a university campus with 100 or more buildings with a wide array of ventilation systems, it may be impossible to retrofit all the buildings to minimize vulnerability. Therefore, facility crews need training on how to respond. Possibly we could work with APPA, IFMA, BOMA, etc., to develop training.

F.E. Yeboah: To the best of our knowledge, at the moment there is no evidence of training being offered by ASHRAE to address the issue of bioterrorism in buildings. However, there have been some educational modules/workshops to educate building professionals on how best to protect and reduce the threat of bioterrorism. These have been developed and/or organized by agencies and institutions including:

* The Airflow and Pollutant Transport Group of Lawrence Berkeley National Laboratory (LBNL) has developed training aids for first responders to safeguard buildings against chemical and biological attacks (http://secure

* The Center for Energy Research and Technology (CERT) of North Carolina A & T State University is currently developing educational modules to protect buildings against bioterrorism.

* The Agency for Healthcare Research and Quality (AHRQ) is another resource.

Having said all these, we still believe that there has not been sufficient training of building first responders pertaining to bioterrorism. In fact, building protection against bioterrorism is an evolving issue, and adequate training will be necessary. This is where the input from other agencies or organizations, such as APPA, IFMA, BOMA, etc., can be very helpful.

We agree that training needs to address issues such as how to respond in case of an attack. Such training should include training in planning specific responses for individual buildings. This training should include ways to analyze individual buildings to determine evacuation routes, areas of refuge, and mitigation options (for example, smoke control systems). The training should also cover organizing and conducting drills to ensure that the plan is executed. EPA is working with North Carolina A & T, NIST, and other organizations to develop material that could be used in this training.

F.E. Yeboah, DEngSc

F. Chowdhury

S. Ilias, PhD, PE

H. Singh, PhD, PE


L. Sparks, PhD

Frank Yeboah and F. Chowdhury are research associates in the Center for Energy Research and Technology, S. Ilias is a professor in the Department of Chemical Engineering, and H. Singh is a professor in the Department of Mechanical and Architectural Engineering, North Carolina A & T State University, Greensboro, NC. L. Sparks is technical lead for containment research, US EPA National Homeland Security Research Center, Research Triangle Park, NC.

Guidance/Standard Title Organization

ADAAG Americans with Disabilities Act US Architectural
 Accessibility Guidelines and Transportation
 Compliance Board
AIA 2004 Security Planning and Design--A The American
 Guide for Architects and Building Institute of
 Design Professionals Architects (AIA)
AR 50-6 Nuclear and Chemical Weapons and US Department of
 Materials--Chemical Surety the Army (DOA)
ASHRAE Standard Method of Testing General American Society
 52.2 Ventilation Air-Cleaning Devices of Heating,
 for Removal Efficiency by Refrigerating and
 Particle Size Air-conditioning
 Engineers (ASHRAE)
ASHRAE Standard Ventilation for Acceptable ASHRAE
 62-2001 Indoor Air Quality
ASHRAE 2003 Risk Management Guidance for ASHRAE
 Health, Safety, and Environment
 Security under Extraordinary
FEMA 426-2003 Reference Manual to Mitigate Federal Emergency
 Potential Terrorist Attacks Management Agency
 Against Buildings (FEMA)
LBNL/PUB-51959 Protecting Buildings from a Lawrence Berkeley
 Biological or Chemical Attack: National
 Actions to take before or during Laboratory
 a Release
NAFA NAFA Position Statement on Bio- National Air
 terrorism--Using ASHRAE Standard Filtration
 52.2 in Preparedness for Association
NFPA 92 A-2006 Standard for Smoke-Control National Fire
 Systems Utilizing Barriers and Protection
 Pressure Differences Association (NFPA)
NFPA 101-2006 Life Safety Code NFPA
NFPA 329-2005 Recommended Practice for NFPA
 Handling Releases
 of Flammable and Combustible
 Liquids and Gases
NFPA 730-2006 Guide for Premises Security NFPA
NFPA 5000-2006 Building Construction and NFPA
 Safety Code
NIOSH 2003-136 Guidance for Filtration and National Institute
 Air-Cleaning Systems to Protect of Occupational
 Building Environments from Safety and Health
 Airborne Chemical, Biological, (NIOSH)
 or Radiological Attacks
UFC 4-010-01 Unified Facilities Criteria US Department of
 (UFC)--DOD Minimum Antiterrorism Defense (DOD)
 Standards for Buildings
USDA 242.1M-ARS ARS Facilities Design Standards US Department of

Guidance/Standard Access

ADAAG 1331 F Street, NW, Suite
 1000 Washington, DC
AIA 2004
AR 50-6 US Department of the Army
ASHRAE Standard
ASHRAE Standard
FEMA 426-2003
NFPA 92 A-2006
NFPA 101-2006
NFPA 329-2005
NFPA 730-2006
NFPA 5000-2006
NIOSH 2003-136
UFC 4-010-01
COPYRIGHT 2007 American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2007 Gale, Cengage Learning. All rights reserved.

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Author:Yeboah, F.E.; Chowdhury, F.; Ilias, S.; Singh, H.; Sparks, L.
Publication:ASHRAE Transactions
Geographic Code:1USA
Date:Jan 1, 2007
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