filters, periodic calibration of instrumentation, and testing to confirm proper system function. Collectively, these cost factors determine the lifetime cost of ownership.
A life-cycle cost analysis frequently is used to justify a larger initial cost to obtain the benefits of lower operating or maintenance cost. In the case of security enhancements, consideration of the system life cycle takes on increased importance because failure to commit to the ongoing costs of maintaining such systems will compromise their ability to perform as intended.
Representative cost information for particulate and gas-phase filtration systems has been published by the National Institute for Occupational Safety and Health (NIOSH, 2003). This source cites a range of $6 to $40 per square foot from continuous high-efficiency particulate air (HEPA) filtration and activated carbon filtration to sensor-activated military filtration systems. Associated operating costs (primarily the cost of moving air against the higher resistance of such filters) are estimated at up to $2 per square foot each year, which is comparable to the energy cost incurred by a typical commercial building (NIOSH, 2003). HEPA filters are roughly 10 times as expensive as standard efficiency particulate filters of the same size, but the cost of gas-phase media can be an order of magnitude more expensive than a HEPA filter. Site factors such as space limitations and fan characteristics can add cost or limit the range of options, particularly in the case of retrofits. Qualitatively, these data indicate that building protection can be costly and that cost-benefit analyses are, therefore, important in justifying the costs of protective measures. Some passive security measures, particularly if implemented in a new building design, might carry no first-cost penalty and could reduce operation and maintenance costs. An example is architectural compartmentalization combined with the use of a dedicated outside air (once-through) system for ventilation.
The appropriate measures of effectiveness and criteria for evaluating a building protection system depend on the goals and objectives of building protection. Although the focus often is on the number of lives saved, considerations related to operational performance, maintenance, and cost should not be overlooked when planning for building protection and should be used to evaluate system-wide risks and benefits.