6.6.6 Positive Pressurization

Traditional good engineering practice for HVAC design strives to achieve a slight overpressure of 5-12 Pa (.02-inch-.05-inch w.g.) within the building environment, relative to the outdoors. This design practice is intended to reduce uncontrolled infiltration into the building. When combined with effective filtration, this practice will also provide enhanced protection against external releases of CBR aerosols.

Using off-the-shelf technology (e.g., HEPA), manually triggered augmentation systems can be put into place to over-pressure critical zones to intentionally impact routes of contaminant migration and/or to provide safe havens for sheltering-in-place. For egress routes, positive-pressurization is also recommended, unless of course, the CBR source is placed within the egress route. Design parameters for such systems will depend upon many factors specific to the building and critical zone in question. Care must be taken that efforts to obtain a desired pressure relationship within one zone, will not put occupants in another zone at increased risk. Lastly, the supply air used to pressurize the critical space must be appropriately filtered (see filtration discussion below) or originate from a non-contaminated source in order to be beneficial.