Building 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.

For more information see:

Persily A. Building Ventilation and Pressurization as a Security Tool. ASHRAE Journal 2004;46(9):18–24.
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.

References cited on this page
15.	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. http://www.fire.nist.gov/bfrlpubs/build07/PDF/b07006.pdf. Accessed November 29, 2007.
17.	Bearg, DW. Building Systems: HVAC Systems. In: Spengler JD, Samet JM, McCarthy JF, eds. Indoor Air Quality Handbook. New York: McGraw-Hill; 2001: 7.1–7.18.
31.	Persily A. Building ventilation and pressurization as a security tool. ASHRAE Journal 2004;46(9):18–24. http://www.bfrl.nist.gov/IAQanalysis/docs/Building%20Ventilation%20 and%20Pressurization%20as%20a%20Security%20Tool.pdf. Accessed November 30, 2007.