Pre-Event Advice – Long-Term

Upgrade HVAC particle filters and seal gaps to prevent air bypass.

Most building HVAC systems have some type of particle filter. Substitution of a more effective filter (particularly for small particle sizes) can reduce the risk of spreading a biological agent through the building via the HVAC system.

However, more effective filters can lead to a significant pressure drop, which can pull unfiltered air around the filter or through leaks in ducts between the filter and the fan. To minimize or eliminate increases in pressure drop, deep pleated filters or filter banks with larger inlet area can be used if space allows.

Improved filters can provide significant protection from a biological release, but they should be installed correctly and ducts should be sealed to reduce air bypass.

Installing new filters may require changes in other equipment too, in order to maintain air quality and comfort, and may increase energy use, so it should not be done without careful evaluation.

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