The Power of Air Pressure in Controlling Infections
Cross-contamination from air infiltration from one space type to another is prevented by pressurization

This is critical in healthcare settings, yet it is extremely difficult to manage.
Frequently opened or propped open doors are all too frequent, making corridors and other enclosed places a conduit for contaminated air
Although ORs and other places are supposed to have positive pressure in relation to the outside world, this may not be the case if an air handler's airflow has been affected!
The sum of all pressure losses through the system, including elbows, dampers, filters, and coils, is the air handler design resistance. When pressure losses change, the shape of a resistance curve changes.