This document is in the public domain and may be freely copied or reprinted. Disclaimer: Mention of any company, product, policy, or the inclusion of any reference does not constitute endorsement by NIOSH. Prevention is the cornerstone of public and occupational health. This document provides preventive measures that building owners and managers can implement promptly to protect building air environments from a terrorist release of chemical, biological, or radiological contaminants. These recommendations, focusing on shortterm actions, are only the beginning of a process to develop more comprehensive guidance. Working with the Building Air Protection Workgroup, as well as partners in the public and private sectors, NIOSH will continue to build on this effort. This document is a useful first step in the process.# Foreword
The Occupational Safety and Health Act of 1970  assures so far as possible every working man and woman in the Nation safe and healthful working conditions. The Act charges the National Institute for Occupational Safety and Health (NIOSH) with conducting research and making science-based recommendations to prevent work-related illness, injury, disability, and death.
On October 8, 2001, the President of the United States established by executive order the Office of Homeland Security (OHS), which is mandated "to develop and coordinate the implementation of a comprehensive national strategy to secure the United States from terrorist threats or attacks." In January 2002, the OHS formed the Interagency Workgroup on Building Air Protection under the Medical and Public Health Preparedness Policy Coordinating Committee of the OHS. The Workgroup includes representatives from agencies throughout the Federal government, including NIOSH, which is part of the Centers for Disease Control and Prevention.
With U.S. workers facing potential hazards associated with chemical, biological, or radiological terrorism, the missions of the OHS and NIOSH overlap. As with most hazards, there are preventive steps that can reduce the likelihood and mitigate the impact of terrorist threats. Tried and proven principles in the control of airborne contaminants can be joined with similarly focused safety and security principles to provide guidance on how we design and operate our building environments. This document is the result of recent building vulnerability assessments conducted by NIOSH, as well as significant content and review recommendations provided by Workgroup members. . The Workgroup's purpose is to focus on building air protection issues associated with an airborne chemical, biological, or radiological (CBR) attack. Workgroup participants provided guidance and direction at several points during this document's development. Their diverse expertise and perspectives resulted in a set of real-world recommendations intended to increase protection of building environments from a terrorist's chemical, biological, or radiological attack. Participants on the Workgroup and their agency affiliations may be found in Appendix A.
In addition to the efforts of the Workgroup, the contributions of the NIOSH Research Team on Building Vulnerabilities are greatly appreciated. This team was augmented by representatives from Sandia National Laboratories and the Agency for Toxic Substances and Disease Registry (ATSDR). Many of the recommendations found in this document originated from the numerous vulnerability assessments conducted by this team. Members of the team are listed in Appendix B.
Anne Votaw, Pauline Elliott, Anne Stirnkorb, and Dick Carlson (NIOSH) provided editorial support, produced the camera-ready copy, and prepared the graphics. Review and preparation for printing were performed by Penny Arthur.

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# SCOPE
T HIS DOCUMENT IDENTIFIES ACTIONS that a building owner or manager can implement without undue delay to enhance occupant protection from an airborne chemical, biological, or radiological (CBR) attack. The intended audience includes building owners, managers, and maintenance personnel of public, private, and governmental buildings, including offices, laboratories, hospitals, retail facilities, schools, transportation terminals, and public venues (for example, sports arenas, malls, coliseums). This document is not intended to address single-family or low-occupancy residential housing (less than five family units). Higher risk facilities such as industrial facilities, military facilities, subway systems, and law enforcement facilities require special considerations that are beyond the scope of this guide.

# Guidance for

# P rotecting B uilding E nvironments from Airborne Chemical, Biological, or Radiological Attacks
The likelihood of a specific building being targeted for terrorist activity is generally difficult to predict. As such, there is no specific formula that will determine a certain building's level of risk. Building owners must make their own decisions about how to reduce their building's risk to a CBR attack. These decisions may be aided by a comprehensive building security assessment. Many government and private organizations have identified resources that provide insight into building security assessments. The reference list at the end of this document will help the reader obtain this information.
No building can be fully protected from a determined individual who is intent on releasing a CBR agent. The recommendations in this guide will not preclude injuries or fatalities in the event of a CBR release. However, facility owners and managers can transform their buildings into less attractive targets by increasing the difficulty of introducing a CBR agent, by increasing the ability to detect terrorists before they carry out an intended release, and by incorporating plans and procedures to mitigate the effects of a CBR release. Some of the references listed in the back of this document can provide information on how to recognize if a CBR release has occurred. These recommendations focus on airborne releases of CBR agents- in quantities capable of being easily transported by a few individuals. Protection from other types of attacks such as explosions, building collapses, and water supply contamination require much different measures and are not addressed in this document.
The recommendations set forth in this document are not intended to be a minimum requirement that every building owner and manager should implement for every building. Rather, the decisions concerning which protective measures should be implemented for any building should be based on several factors, including the perceived risk associated with the building and its tenants, engineering and architectural feasibility, and cost. *Note: References to a release of CBR agent in this document will always refer to an airborne CBR release.

# BACKGROUND
Terrorism events have increased interest in the vulnerability of U.S. workplaces, schools, and other occupied buildings to CBR threats. Of particular concern are the airflow patterns and dynamics in buildings, specifically in the building heating, ventilating, and air-conditioning (HVAC) systems. These systems can become an entry point and a distribution system for hazardous contaminants, particularly CBR agents. Building owners need reliable information about how they can (1) modify their buildings to decrease the likelihood or effects of a CBR incident and (2) respond quickly and appropriately should a CBR incident occur. Comprehensive guidance is needed in several areas, including: p How to modify existing buildings for better air protection and security.
p How to design new buildings to be more secure.
p What plans building managers should prepare in advance to help them make effective decisions in the midst of a CBR incident.

# PREPARATORY RECOMMENDATION-KNOW YOUR BUILDING
While more comprehensive guidance is being developed, this document focuses on the shorter-term goals of identifying those protective actions that you can take immediately. But it recognizes that some recommendations may not be feasible for you or in all situations.
In initiating any plan to modify building system design or operation, an important first step is to understand these systems: How were they intended to operate? How do they currently operate?
Getting to know your building may best be handled by conducting a walk-through inspection of the building and its systems, including the HVAC, fire protection, and life-safety systems. During this inspection, compare the most up-to-date design drawings available to the operation of the current systems.- This step may require, or benefit from, the assistance of qualified outside professionals. Without this baseline knowledge, it is difficult to accurately identify what impact a particular security modification may have on building operation. While it is important to understand how the existing building systems function, the systems need not operate per design before you implement security measures. A partial list of items to consider during your building walk-through includes:
p What is the mechanical condition of the equipment?

# SPECIFIC RECOMMENDATIONS
The recommendations can be divided into four general categories: (1) things not to do; (2) physical security; (3) ventilation and filtration; and (4) maintenance, administration, and training. Some of these items, such as securing mechanical rooms, may be started prior to your completing the recommendations in the "Know your building" section. Items within each of the four categories are listed in the order of priority. Items considered to be highly critical are identified by "*" next to the number. As you review these recommendations, consider their potential implications upon the contract language necessary for existing and future service contracts. A brief discussion of the four categories and some commonly considered recommendations follow.

# Things not to do
More than anything else, building owners and managers should ensure that any actions they take do not have a detrimental effect on the building systems (HVAC, fire protection, life safety, etc.) or the building occupants under normal building operation. Some efforts to protect the building from a CBR attack could have adverse effects on the building's indoor environmental quality. Building owners and managers should understand how the building systems operate and assess the impact of security measures on those systems. This caution directly relates to the recommendation that building owners and managers should understand the operation of their building systems. If there is uncertainty about the effects of a proposed modification, a qualified professional should be consulted.

# *3. DO NOT INTERFERE WITH FIRE PROTECTION AND LIFE SAFETY
SYSTEMS. These systems provide protection in the event of fire or other types of events. They should not be altered without guidance from a professional specifically qualified in fire protection and life safety systems.

# Physical Security
Preventing terrorist access to a targeted facility requires physical security of entry, storage, roof, and mechanical areas, as well as securing access to the outdoor air intakes of the building HVAC system. The physical security needs of each building should be assessed, as the threat of a CBR attack will vary considerably from building to building. For example, the threat to a large corporate headquarters may be considered greater than the threat to a small retail establishment. Some physical security measures, such as locking doors to mechanical rooms, are low cost and will not inconvenience the users of the building. These types of measures can be implemented in most buildings. Other physical security measures, such as increased security personnel or package x-ray equipment, are more costly or may inconvenience users substantially. These measures should be implemented when merited after consideration of the threat and consequences of a terrorist attack. Building owners and managers should be familiar with their buildings and understand what assets require protection and what characteristics about the building or its occupants make it a potential target. By first assessing the vulnerabilities of facilities, building owners and managers can address physical security in an effective manner. While the identification and resolution of building vulnerabilities will be specific to each building, some physical security actions are applicable to many building types. These include: *1. PREVENT ACCESS TO OUTDOOR AIR INTAKES. One of the most important steps in protecting a building's indoor environment is the security of the outdoor air intakes. Outdoor air enters the building through these intakes and is distributed throughout the building by the HVAC system. Introducing CBR agents into the outdoor air intakes allows a terrorist to use the HVAC system as a means of dispersing the agent throughout a building. Publicly accessible outdoor air intakes located at or below ground level are at most risk-due partly to their accessibility (which also makes visual or audible identification easier) and partly because most CBR agent releases near a building will be close to the ground and may remain there. Securing the outdoor air intakes is a critical line of defense in limiting an external CBR attack on a building.
Relocate outdoor air intake vents. Relocating accessible air intakes to a publicly inaccessible location is preferable. Ideally, the intake should be located on a secure roof or high sidewall. The lowest edge of the outdoor air intakes should be placed at the highest feasible level above the ground or above any nearby accessible level (i.e., adjacent retaining walls, loading docks, handrail). These measures are also beneficial in limiting the inadvertent introduction of other types of contaminants, such as landscaping chemicals, into the building.
Extend outdoor air intakes. If relocation of outdoor air intakes is not feasible, intake extensions can be constructed without creating adverse effects on HVAC performance. Depending upon budget, time, or the perceived threat, the intake extensions may be temporary or constructed in a permanent, architecturally compatible design. The goal is to minimize public accessibility. In general, this means the higher the extensions, the better-as long as other design constraints (excessive pressure loss, dynamic and static loads on structure) are appropriately considered. An extension height of 12 feet (3.7 m) will place the intake out of reach of individuals without some assistance. Also, the entrance to the intake should be covered with a sloped metal mesh to reduce the threat of objects being tossed into the intake. A minimum slope of 45 is generally adequate. Extension height should be increased where existing platforms or building features (i.e., loading docks, retaining walls) might provide access to the outdoor air intakes.

# Establish a security zone around outdoor air intakes.
Physically inaccessible outdoor air intakes are the preferred protection strategy. When outdoor air intakes are publicly accessible and relocation or physical extensions are not viable options, perimeter barriers that prevent public access to outdoor air intake areas may be an effective alternative. Iron fencing or similar see-through barriers that will not obscure visual detection of terrorist activities or a deposited CBR source are preferred. The restricted area should also include an open buffer zone between the public areas and the intake louvers. Thus, individuals attempting to enter these protected areas will be more conspicuous to security personnel and the public. Monitoring the buffer zone by physical security, closedcircuit television (CCTV), security lighting, or intrusion detection sensors will enhance this protective approach. To prevent widespread dispersion of a contaminant released within lobbies, mailrooms, and loading docks, their HVAC systems should be isolated and the areas maintained at a negative pressure relative to the rest of the building, but at positive pressure relative to the outdoors. Physical isolation of these areas (well-sealed floor to roof-deck walls, sealed wall penetrations) is critical to maintaining the pressure differential and requires special attention to ensure airtight boundaries between these areas and adjacent spaces. In some building designs (those having lobbies with elevator access, for example), establishing a negative pressure differential will present a challenge. A qualified HVAC professional can assist in determining if the recommended isolation is feasible for a given building. In addition, lobbies, mailrooms, and loading docks should not share a return-air system or return pathway (e.g., ceiling plenum) with other areas of the building. Some of these measures are more feasible for new construction or buildings undergoing major renovation.
Building access from lobby areas should be limited by security checks of individuals and packages prior to their entry into secure areas. Lobby isolation is particularly critical in buildings where the main lobbies are open to the public. Similar checks of incoming mail should also occur before its conveyance into the secure building areas. Side entry doors that circumvent established security checkpoints should be strictly controlled. 9. GENERAL BUILDING PHYSICAL SECURITY UPGRADES. In addition to the security measures for HVAC and other building operations described earlier, physical security upgrades can enhance the overall security of a building. A building or building complex might have security fencing and controlled access points. Some buildings such as museums are, by their very nature, openly accessible to the public. However, even in these buildings, areas such as mechanical rooms need to remain off-limits to unauthorized individuals. Unless the building is regarded as open to the general public, owners and managers should consider not allowing visitors outside the lobby area without an escort. Layered levels of security access should be considered. For example, entry to a hospital's patient care areas could be less strict than to hospital laboratories, and successively more strict for other areas, such as ventilation control rooms. Physical security is of prime concern in lobby areas.

# Ventilation and Filtration
HVAC systems and their components should be evaluated with respect to how they impact vulnerability to the introduction of CBR agents. Relevant issues include the HVAC system controls, the ability of the HVAC system to purge the building, the efficiency of installed filters, the capacity of the system relative to potential filter upgrades, and the significance of uncontrolled leakage into the building. Another consideration is the vulnerability of the HVAC system and components themselves, particularly when the facility is open to the public. For buildings under secure access, interior components may be considered less vulnerable, depending upon the perceived threat and the confidence in the level of security. Increasing filter efficiency is one of the few measures that can be implemented in advance to reduce the consequences of both an interior and exterior release of a particulate CBR agent. However, the decision to increase efficiency should be made cautiously, with a careful understanding of the protective limitations resulting from the upgrade. The filtration needs of a building should be assessed with a view to implementing the highest filtration efficiency that is compatible with the installed HVAC system and its required operating parameters. In general, increased filter efficiency will provide benefits to the indoor environmental quality of the building. However, the increased protection from CBR aerosols will occur only if the filtration efficiency increase applies to the particle size range and physical state of the CBR contaminant. It is important to note that particulate air filters are used for biological and radiological particles and are not effective for gases and vapors typical of chemical attacks. These types of compounds require adsorbent filters (i.e., activated carbon or other sorbent-type media) and result in substantial initial and recurring costs.
Upgrading filtration is not as simple as merely replacing a low-efficiency filter with a higher efficiency one. Typically, higher efficiency filters have a higher pressure loss, which will result in some airflow reduction through the system. The magnitude of the reduction is dependent on the design and capacity of the HVAC system. If the airflow reduction is substantial, it may result in inadequate ventilation, reductions in heating and cooling capacity, or potentially frozen coils. To minimize pressure loss, deep pleated filters or filter banks having a larger nominal inlet area might be feasible alternatives, if space allows. Also, high-pressure losses can sometimes be avoided by using prefilters or more frequent filter changeouts. Pressure loss associated with adsorbent filters can be even greater.
The integrity of the HVAC system's filter rack or frame system has a major impact upon the installed filtration efficiency.
Reducing the leakage of unfiltered air around filters, caused by a poor seal between the filter and the frame, may be as important as increasing filter efficiency. If filter bypass proves to be significant, corrective actions will be needed. Some highefficiency filter systems have better seals and frames constructed to reduce bypass. During an upgrade to higher efficiency filters, the HVAC and filtration systems should be evaluated by a qualified HVAC professional to verify proper performance.
While higher filtration efficiency is encouraged and should provide indoor air quality benefits beyond an increased protection from CBR terrorist events, the overall cost of filtration should be evaluated. Filtration costs include the periodic cost of the filter media, the labor cost to remove and replace filters, and the fan energy cost required to overcome the pressure loss of the filters. While higher efficiency filters tend to have a higher life cycle cost than lower efficiency filters, this is not always the case. With some higher efficiency filter systems, higher acquisition and energy costs can be offset by longer filter life and a reduced labor cost for filter replacements. Also, improved filtration generally keeps heating and cooling coils cleaner and, thus, may reduce energy costs through improvements in heat transfer efficiency. However, when high efficiency particulate air (HEPA) filters and/or activated carbon adsorbers are used, the overall costs will generally increase substantially.
3. DUCTED AND NON-DUCTED RETURN AIR SYSTEMS. Ducted returns offer limited access points to introduce a CBR agent. The return vents can be placed in conspicuous locations, reducing the risk of an agent being secretly introduced into the return system. Non-ducted return air systems commonly use hallways or spaces above dropped ceilings as a return-air path or plenum. CBR agents introduced at any location above the dropped ceiling in a ceiling plenum return system will most likely migrate back to the HVAC unit and, without highly efficient filtration for the particular agent, redistribute to occupied areas. Buildings should be designed to minimize mixing between air-handling zones, which can be partially accomplished by limiting shared returns. Where ducted returns are not feasible or warranted, hold-down clips may be used for accessible areas of dropped ceilings that serve as the return plenum. This issue is closely related to the isolation of lobbies and mailrooms, as shared returns are a common way for contaminants from these areas to disperse into the rest of the building. These modifications may be more feasible for new building construction or those undergoing major renovation.
4. LOW-LEAKAGE, FAST-ACTING DAMPERS. Rapid response, such as shutting down an HVAC system, may also involve closing various dampers, especially those controlling the flow of outdoor air (in the event of an exterior CBR release). When the HVAC system is turned off, the building pressure compared to outdoors may still be negative, drawing outdoor air into the building via many leakage pathways, including the HVAC system. Consideration should be given to installing low leakage dampers to minimize this flow pathway. Damper leakage ratings are available as part of the manufacturer's specifications and range from ultra-low to normal categories. Assuming that you have some warning prior to a direct CBR release, the speed with which these dampers respond to a "close" instruction can also be important. From a protective standpoint, dampers that respond quickly are preferred over dampers that might take 30 seconds or more to respond.
5. BUILDING AIR TIGHTNESS. Significant quantities of air can enter a building by means of infiltration through unintentional leakage paths in the building envelope. Such leakage is of more concern for an exterior CBR release at some distance from a building, such as a large-scale attack, than for a directed terrorist act. The reduction of air leakage is a matter of tight building construction in combination with building pressurization. While building pressurization may be a valuable CBR-protection strategy in any building, it is much more likely to be effective in a tight building. However, to be effective, filtration of building supply air must be appropriate for the CBR agent introduced. Although increasing the air tightness of an existing building can be more challenging than during new construction, it should still be seriously considered.

# Maintenance, Administration, and Training

# CONCLUSIONS
Reducing a building's vulnerability to an airborne chemical, biological, or radiological attack requires a comprehensive approach. Decisions concerning which protective measures to implement should be based upon the threat profile and a security assessment of the building and its occupants. While physical security is the first layer of defense, other issues must also be addressed. Preventing possible terrorist access to outdoor air intakes and mechanical rooms and developing CBR-contingent emergency response plans should be addressed as soon as possible. Additional measures can provide further protection. A building security assessment should be done to determine the necessity of additional measures. Some items, such as improved maintenance and HVAC system controls, may also provide a payback in operating costs and/or improved building air quality. As new building designs or modifications are considered, designers should consider that practical CBR sensors may soon become available. Building system design features that are capable of incorporating this rapidly evolving technology will most likely offer a greater level of protection. While it is not possible to completely eliminate the risk of a CBR terrorist attack, several measures can be taken to reduce the likelihood and consequences of such an attack. Many of the recommendations presented here are ones that can be implemented reasonably quickly and cost effectively. Many are applicable to both new construction and existing buildings, although some may be more feasible than others. Building owners and managers should assess buildings by looking first for those items that are most vulnerable and can be addressed easily. Additional measures should be implemented as feasible. The goals are to make your building an unattractive target for a CBR attack and to maximize occupant protection in the event that such an attack occurs.

# For Additional Information
Several organizations have developed guidance to assist building owners and operators in addressing issues related to building security and CBR terrorist attacks. Many other organizations have guidance that addresses security needs and disaster response plans for events such as fire, natural disasters, and bomb threats. While this latter guidance may not specifically address the terrorist threat to HVAC systems, readers may find portions of the information beneficial in establishing their own building's emergency response plans.
The following list is not all-inclusive. Available guidance is updated regularly as additional organizations and evolving technologies identify new protective recommendations.

# Organization
Reference or Link Description