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Protecting Building Occupants from Exposure to Biological Threats

Frequently Asked Questions

Would sensor technologies help to reduce the risk of occupant exposure following an attack with a  biological weapon?

Sensors to identify the release of a biological agent could be helpful in alerting building operators of an attack so that preventive measures such as a ventilation system shutdown or outdoor air purge could be taken.[15] As noted in the section on Reducing Risk, both of these responses to a biological attack require timely situational awareness—building operators need to know when and where an attack has occurred to implement the proper response. Absent actionable situational awareness, implementation of either of these measures has the potential to increase exposure rather than decrease it if implemented at the wrong time.[15]

To be effective in reducing exposure to either a chemical or biological agent following an attack, sensors must be fast (i.e., real-time), cost effective, and able to detect a large number of threat agents.[15] While there is a lot of research and development ongoing in sensor technology, to our knowledge, currently available sensor technologies are not mature, robust, or cost-effective enough to warrant implementation in commercial buildings at this time; this is especially true for biological threats.[15,43,44]

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Are new technologies available that would reduce the risk of occupant exposure following an attack with a& biological weapon?

New technologies for protecting building inhabitants from biological (and chemical) attacks include ultraviolet germicidal irradiation (UVGI) and photocatalytic oxidation air cleaning (PCO).[15]

UVGI systems use ultraviolet light (UV) to kill or deactivate microorganisms and have been used in healthcare facilities for years. They are usually installed in ductwork or in upper portions of rooms with shielding.[15,45] More recently, UVGI systems have begun to be used in buildings to keep ventilation system components clean, improve indoor air quality, and address biosecurity concerns.[3,15]

PCO systems remove bioaerosols and chemicals from the air by flowing the air past a photocatalyst that is irradiated by UV light.[15,46] A photocatalyst is a chemical compound that becomes highly reactive when exposed to various wavelengths of UV light, such as titanium dioxide. This process creates highly reactive molecules (e.g., hydroxyl radicals) that combine and react with airborne contaminants, breaking them down into carbon dioxide and water. PCO devices are commercially available.

The Center for Biosecurity’s Working Group on Reduction of Exposure to Infectious Agents during a Covert Bioterrorism Attack (Working Group) did not make any recommendations about the use of new technologies, primarily because they have yet to be independently evaluated using standardized methods, and there was no consensus regarding their performance characteristics.[1] The Working Group encouraged the purchase of new technologies only after they have been validated and thoroughly field tested, especially if an existing technology produces comparable results. A 2007 report from NIST regarding building retrofits to increase protection against chemical and biological attacks concluded that more performance data or technology development is needed before general application of these technologies.[15]
 

Table 1. Comparison of New Technologies for Risk Reduction
TechnologyAdvantagesDisadvantages
UVGI

• Offers protection against biological agents
• Low pressure drop
• Potential for improved IAQ
• Potential for improved ventilation system efficiency over time

• No standard test method for determining effectiveness
• No design and installations guidance currently available

PCO 

• Offers protection against biological agents
• Low pressure drop
• Potential for improved IAQ
• Potential for improved ventilation system efficiency over time

• No standard test method for determining effectiveness
• No design and instillation guidance currently available
• No standard method to determine if catalyst has become ineffective by exposure to airborne substances
• Potential to produce harmful chemical byproducts unclear


Source: Adapted from Persily, A. et al. Building Retrofits to Protect Against Airborne Chemical and Biological Releases (NISTIR 7379). Washington DC; National Institute of Standards and Technology. March 2007. Available at https://www.nist.gov/publications/building-retrofits-increased-protection-against-airborne-chemical-and-biological.

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Should building owners and operators be concerned about the threat from chemical weapons?

The Center for Biosecurity focuses its efforts on reducing the threat posed by biological weapons, which in our view are  the only weapons capable of presenting a strategic threat to the United States on par with nuclear weapons. That said, the threat from chemical weapons should not be overlooked. Several states potentially hostile to the United States are suspected of having chemical weapons programs, and there are groups, such as al-Qa’ida, that are committed to attacking the U.S. and are also pursuing chemical weapons capabilities.[2,47] Available information suggests that the threat of chemical terrorism—particularly small-scale attacks—is increasing.[47] According to the July 2007 U.S. National Intelligence Estimate regarding the terrorist threat to the U.S. homeland, al-Qa’ida “would not hesitate” to use chemical weapons “if it develops what it deems is sufficient capability.”[2]

Information about chemical devices, recipes, and dissemination methods are easily accessible on the Internet.47 Military grade chemical weapons (e.g., sarin, VX) in the wrong hands pose a serious threat, but it can be argued that the larger threat is from toxic industrial chemicals (TICs), such as cyanide, chlorine, and pesticides. These are more readily available and potentially can be used to contaminate food and water supplies or crudely delivered using an explosive device.[47]

Buildings are attractive targets for chemical attacks as they pose the potential for wide-scale agent dispersal through the air handling system, which can cause mass casualties and high economic costs. It is known that al-Qa’ida is aware of the potential to use building air handling systems to attack building occupants; training in Afghanistan-based al-Qa’ida camps as early as 1998 included the use of ventilation systems as a "delivery system" to attack buildings with poisons.[5]

Technologies are available that can help protect building occupants from chemical threats. Sorption-based gaseous air cleaning technologies are used to remove gaseous contaminants from the air.[15,46] While not widely used in commercial buildings, such systems are used in some manufacturing facilities, for example, to control odors and/or exposure to corrosive or undesirable gases.

Sorption-based gas air cleaning systems remove contaminants from the air by physical adsorption or chemisorption.[15,46] Physical adsorption is based on the attractive forces between the sorbent (e.g., activated carbon, silica gel, alumna) and the gas molecules in the air and is a reversible process. Chemisorption is based on chemical reactions between the adsorbent (e.g., potassium permanganate, phosphoric acid, copper, silver salts, zinc oxide) and the gas molecules in the air. No single sorbent or adsorbent is able to remove all potential chemical attack agents from the air, and a combination is needed to offer wide-ranging protection.

Adding sorption-based gas air cleaning systems to commercial buildings would likely be expensive; expenses include both first costs (air cleaning system, additional space for system, design work, ventilation system modifications) and operating costs (media replacement and increased electrical consumption as a result of increase pressure drop associated with system).[15]

Gas phase cleaning systems are associated with a larger pressure drop than particle filtration systems, and, thus are generally more expensive to operate.[15] In addition, the larger pressure drops associated with gas phase cleaning may require significant ventilation system modifications in retrofit situations, which also are expensive.

A NIST case study estimated that upgrading a 1960's high-rise office building from MERV 6 filters to MERV 8 pre-filters, MERV 13 intermediate filters, MERV 17 (HEPA) filters, AZDM-TEDA grade carbon gas phase filters, and MERV 11 final filters would cost $9.26 per ft2, and that the annual operating costs for such a system would be $1.87 per ft2.[15]

The corresponding retrofit without gas phase filtration—upgrading from MERV 6 filters to MERV 8 pre-filters, MERV 13 intermediate filters, and MERV 17 (HEPA) final filters—would cost $2.47 per ft2, and the annual operating costs for this retrofit would be $0.50 per ft2.[15] The additional cost to add gas phase filtration to the retrofit was $6.79 per ft2, and the additional operating cost was $1.37 per ft2
 

Table 2: Advantages and Disadvantages of Sorption-based Gaseous Air Cleaning Technology
TechnologyAdvantagesDisadvantages
Sorption-Based Gaseous Air Cleaning

• Offers protection against chemical agents
• Potential for improved IAQ

• High pressure drop
• No standard test method for determining effectiveness
• Additional design guidance needed


Source: Adapted from Persily, A. et al. Building Retrofits to Protect Against Airborne Chemical and Biological Releases (NISTIR 7379). Washington DC; National Institute of Standards and Technology. March 2007. Available at https://www.nist.gov/publications/building-retrofits-increased-protection-against-airborne-chemical-and-biological.

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Should building owners and operators be concerned about the threat from radioactive materials?

As noted above, the Center for Biosecurity focuses its efforts on reducing the threat posed by biological weapons, which, in our view, are the only weapons capable of presenting a strategic threat to the U.S. on par with nuclear weapons. That said, the threat from radioactive materials should not be overlooked. There are groups, such as al-Qa’ida, that are committed to attacking the U.S. and are also pursuing nuclear/radiological weapons capabilities.[2] According to the July 2007 U.S. National Intelligence Estimate regarding the terrorist threat to the U.S. homeland, al-Qa’ida “would not hesitate” to use “radiological or nuclear material in attacks . . . if it develops what it deems is sufficient capability.”[2]

Radioactive materials can be dispersed by detonating a nuclear weapon, attacking a fixed nuclear facility, or by employing a radiological dispersal device (RDD).35,48 An RDD is “any device that causes the purposeful dissemination of radioactive material without a nuclear detonation.”[48] The type of RDD most commonly discussed is the dirty bomb—a conventional explosive used to disperse radioactive material. However, radioactive materials also can be dispersed by non-explosive means, such as depositing them in food or water or aerosolizing them. Aerosolized radioactive materials, regardless of the source, are a threat to building occupants because they can potentially be introduced into a mechanically ventilated building in the same ways as described for biological agents.

While air filters and air-cleaning devices will not stop the radiation emitted from a radioactive material, they can remove the radioactive materials from the air, which can reduce potential exposures following a release.[35]

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Will implementing threat reduction measures earn me any LEED points?

Implementing the biological threat reduction measures recommended by the Center for Biosecurity’s Working Group on Reduction of Exposure to Infectious Agents during a Covert Bioterrorism Attack can potentially help building owners earn credits under the U.S. Green Building Council’s (USGBC) Leadership in Energy and Environmental Design (LEED) Green Building Rating System™. For example, LEED points can be earned for commissioning, staff education, building system maintenance and monitoring, envelope tightening, and improving indoor air quality through measures such as enhancing air filtration to MERV 13 or better.[49,50]

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*Note: The information that appears on the pages collectively known as "Protecting Building Occupants" was up-to-date and accurate when published in 2008; the materials have not been updated since original publication. Please be sure to check current resources for the most up-to-date information on this topic.

 

 

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