Direct benefits: Implementing measures to reduce building vulnerability can reduce the risk of occupant exposure following a biological attack, which can have direct health and non-health benefits that, in turn, have potential economic benefits (Table 1, below)
| Table 1: Potential Benefits of Risk Reduction Measures | |||||
Result of Risk Reduction Measures | Potential Health and Non-Health Benefits | Potential Economic Benefits | |||
Reduced exposure to biological threats following an attack | • Reduced morbidity & mortality | • Reduced economic losses | |||
It is worth noting that implementing measures to reduce the risk of occupant exposure to biological threats can help reduce the likelihood of an attack.[20] The October 2007 U.S. National Strategy for Homeland Security notes that “[t]errorist actors can be deterred and dissuaded from conducting attacks if they perceive that they are not likely to achieve their objectives or that the costs of their efforts are too high.”[37] Hardening the built environment against biological attacks makes it more difficult to conduct a successful attack, which may discourage would-be terrorists.[38]
Collateral benefits: Available scientific data suggest that implementing risk reduction measures also can have collateral health and non-health benefits, including: improved energy efficiency, improved HVAC system cleanliness, and improved indoor air quality;[15] collateral benefits have potential associated economic benefits (Table 2, below).[39]
| Table 2: Potential Collateral Benefits of Risk Reduction Measures | ||
Result of Risk | Potential Health and | Potential Economic Benefits |
Improved energy efficiency | • Decreased energy consumption | • Reduced operating costs |
Improved HVAC system cleanliness | • Decreased energy consumption | • Reduced operating/ maintenance costs |
Improved indoor air quality (IAQ) | • Reduced IAQ complaints | • Reduced operating/ maintenance costs |
Determining cost-effectiveness: While difficult to quantify, available evidence suggests that the collateral economic benefits of risk reduction measures may make them cost-effective and potentially cost-saving.[21,40] The cost-effectiveness of such measures depends on several factors:
The value of the benefits derived from risk reduction measures are difficult to quantify and are building specific; therefore, the cost-effectiveness of hardening the built environment against biological threats is largely a value judgment, as there is no consensus determination of cost-effectiveness. However, measures that are found to be cost-saving would surely be considered cost-effective.
The costs of implementing risk reduction measures are building-specific and dependent upon the specific measures to be implemented, the unique features of the building (there is no typical building), and the extent to which ventilation system and building modifications are required (in retrofit situations).
Cost: The cost of commissioning (and re-commissioning) a building depends upon the size and complexity of the building and its ventilation system(s).[15]
One study on commissioning, by Mills, et al., analyzed results from 224 buildings in 21 states, representing 30.4 million square feet of commissioned floor area (73% existing buildings and 27% new construction).[36] Results indicated that the median commissioning cost for existing buildings was $0.27 per ft2 (range $0.03 to $3.86 per ft2). The median commissioning cost for new construction was $1.00/ft2 or 0.6% of total construction costs (range $0.10 to $18.20 per ft2). A National Institute of Standards and Technology (NIST) case study estimated the cost of HVAC system testing, adjusting, and balancing (a commissioning cost) to be $0.63 per ft2 for the retrofit of an early 1960’s high rise office building to increase protection against airborne biological and chemical releases.[15]
Cost: The cost of enhancing filtration is the sum of first costs and operating costs. First costs include equipment and installation (e.g., filters, design work when required), reconfiguration of filter racks (when required), modifications of air handling system fans, motors, electrical (when required). Operating costs are those associated with operating and maintaining enhanced filtration (e.g., filter replacement, maintenance, and increased electrical consumption, as when new filters require more powerful fans).[15,28,35]
First costs for enhancing filtration efficiency in retrofit situations are estimated to range from incidental to $2 to $3 per ft2.28 Operating costs for enhanced filtration efficiency are estimated at pennies to dollars per ft2.[28]
The NIST case study estimated the cost of retrofitting of the 1960’s high rise office building to increase filtration efficiency. Results indicated that upgrading from MERV 6 to MERV 11 (the highest efficiency filter that the building’s existing air handling unit could take) would cost $0.59 per ft2 and the annual operating costs for this retrofit would be $0.01 per ft2. Upgrading from MERV 6 to MERV 8 pre-filter, MERV 13 intermediate filter, and MERV 17 (HEPA) final filter would cost $2.47 per ft2 and that the annual operating costs for this retrofit would be $0.50 per ft2.[15]
Cost-effectiveness: While enhanced filtration can improve indoor air quality, energy efficiency, and HVAC system cleanliness, too few studies have been completed to generalize about its potential cost-effectiveness.[15]
However, modeling studies suggest that enhancing filtration efficiency could be cost-effective. One study estimated that the total costs of air filtration (e.g., filter costs, labor costs, energy costs) range from $0.70 to $1.80 per person/per month and concluded that these costs are “insignificant relative to salaries, rent, or health insurance costs.”[41] Another study found that the cost of upgrading air filtration efficiency to high-efficiency filtration (i.e., >95% efficiency at 0.3 micron) in an office building cost $24 per person per year (cost includes filter purchase and increased energy costs).[21] The author of that study estimated that if the improved filtration resulted in a 10% reduction in respiratory disease, a 1% increase in the productivity of workers who suffer from allergies, and 0.25% reduction in productivity losses associated with sick building syndrome, this could potentially result in an annual savings of roughly $220 per worker/per year.
Cost: The cost for envelope tightening is not well established and would depend on the amount of air leakage in any particular building.15 Total costs for envelope tightening will include the costs of inspection and testing to determine air leakage sites, materials for sealing, labor, and construction staging costs.[15]
The NIST retrofit case study for the high rise office building estimated that sealing the building envelope would cost $5.21 per ft2.15 The authors note that their estimate focuses on “window and door sealing” and that “effective envelope tightening . . . is likely to involve the sealing of more leakage sites.”[15]
Of note, to be optimally effective in reducing potential exposure to biological threats, envelope tightening requires sufficient air filtration.[15]
Cost-effectiveness: Envelope tightening can improve indoor air quality and energy efficiency.[15] However, too few studies have been completed to generalize about the potential cost-effectiveness of envelope tightening.
One modeling study, based on a set of 25 buildings as a representative sample of the U.S. commercial building stock as of 1995, estimated that infiltration is responsible for about 15% of the total heating energy and 4% of the total cooling energy for U.S. office buildings.[42] The results of the study indicated that tightening building envelopes by 25% to 50% could result in potential energy savings on the order of 26% for heating load and 15% for cooling load.
Cost: The cost of building pressurization is not well established and depends on various factors.[15] The primary cost arises from increased operating costs associated with increased energy consumption resulting from the heating and cooling of additional outdoor air brought into a building to pressurize it.[15] The energy cost of pressurization is a function of the volume of outdoor air brought into a building and climate. The volume of air necessary to pressurize a building is in turn determined, in part, by the tightness of the building envelope. In
There also can be first costs associated with building pressurization, including ventilation system modifications and increased heating and cooling capacity.[15]
Of note, to be optimally effective in reducing potential exposure to biological threats, pressurization requires sufficient air filtration.[15] general, it takes less outdoor air to pressurize a tight building.[15]
Cost-effectiveness: Building pressurization can improve indoor air quality.[15] Once again, though, too few studies have been completed to generalize about the potential cost-effectiveness of pressurization.
Building pressurization refers to the air pressure relationships that exist between the inside of a building relative to the outside of a building across the building envelope; it also refers to the pressure relationships that exist within different parts of a building relative to each other.[15,17] Building pressurization is used to limit infiltration, which can lead to indoor air quality problems because air that enters a building via infiltration bypasses the air handling systems and can introduce contaminants into a building and contribute to moisture problems.[15,31] Pressurization also can be used to control the movement of air contaminants within a building.[15,31]
Maintaining positive air pressure relative to outside air prevents contaminants in the outside air from entering a building by means of infiltration.15,31 Such an approach could reduce the risk of exposure to biological agents from a large-scale outdoor release, provided that air entering the building through the HVAC system is sufficiently filtered to remove contaminants. Whether a building can be pressurized depends upon the building’s geometry, HVAC system design, and envelope tightness as well as weather conditions. Building pressurization requires that the HVAC system be able to deliver more air to the occupied space than is being exhausted and lost due to exfiltration. It may not be possible to pressurize a leaky building without first addressing envelope leakage.
Maintaining positive air pressure in one zone of a building relative to another can limit the distribution of an aerosolized biological agent released within that building by means of airflows created by pressure relationships that exist within different parts of the building relative to each other.[15,31] Such an approach can be used to isolate special-use spaces such as lobbies, parking garages, and mail rooms that may be more vulnerable to an internal release by maintaining them at negative pressure relative to adjacent parts of the building.
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Buildings contaminated in a biological attack would likely require some level of decontamination, the cost of which would depend on the type and extent of contamination and the method(s) required to decontaminate the building and certify it for re-occupancy.[52]
While the actual costs for decontamination in any given event would be situationally dependent, the experience following the 2001 anthrax attack through the Unites States Postal System are instructive. In October 2001, Bacillus anthracis spores were sent through the U.S. mail to news media companies and to U.S. Congressional offices, resulting in 22 cases of anthrax (11 inhalational and 11 cutaneous) and 5 deaths.[53] Numerous sites were contaminated with B. anthracis spores as a result of direct contact with the spore laden letters or as a result of secondary or cross contamination.[52,53] Where contamination was limited, surface treatments with liquid agents (e.g., bleach) were sufficient. In sites where contamination was significant, fumigation was required. Buildings that required fumigation were closed for months or years, and the costs of fumigation efforts ranged from $464 thousand to $200 million.[52]
Note: In an article published in February 2012, authors Schmitt and Zacchia arrive at a total cost of $320 million for decontamination following the anthrax letter attacks of 2001. See Ketra Schmitt and Nicholas A. Zacchia Total Decontamination Cost of the Anthrax Letter Attacks. Biosecurity and Bioterrorism: Biodefense Strategy, Practice, and Science. e-publication ahead of print. http://online.liebertpub.com/doi/full/10.1089/bsp.2010.0053. Accessed February 16, 2012.
For more information, see: U.S. Environmental Protection Agency, National Homeland Security Research Center (NHSRC):
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