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Negative Air Pressure

Last updated: May 29, 2020

What Does Negative Air Pressure Mean?

Negative air pressure is the condition whereby the air pressure is lower in one place in comparison to another. In terms of negative room air pressure, the air pressure inside a given room is lower than the pressure outside the room, causing air to flow into the room from the outside. Depending on the quality of the in-fluxed air, the rate of corrosion inside the room may increase.


Corrosionpedia Explains Negative Air Pressure

Negative air pressure occurs when the pressure in a building is lower than the pressure outside. Negative air pressure can draw moisture into the walls, which accelerates the rate at which indoor metallic objects corrode.

Negative air pressure is sometimes purposely generated by ventilation systems in settings such as hospitals or clean rooms. These systems remove more air from a room than usual. This is important when treating patients with highly infectious and/or airborne diseases in order to prevent contaminating microorganisms from accumulating in the room or spreading to other rooms. Air is allowed into the room through gaps or specialized piping while the rest of the room is made as airtight as possible. Any leakage can compromise room negative pressure.

In the more general case, components of the exhausted air are often chemical contaminants, microorganisms or radioactive fluids that are unacceptable to release into the surrounding outdoor environment. Therefore, exhausted air is often passed through a filter or decontamination room prior to final atmospheric expulsion.


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