What primarily determines whether a room has positive or negative pressure?

The primary factor that determines whether a room has positive or negative pressure is adjustments to supply and exhaust flows. This principle is grounded in the mechanics of air pressure and ventilation systems.

In a room, positive pressure occurs when the air supply is greater than the air being exhausted, causing air to flow out of the room when a door opens. This is often desirable in environments such as surgical rooms or areas where contamination control is essential, as it helps prevent external contaminants from entering.

Conversely, negative pressure is achieved when the exhaust flow exceeds the supply flow, resulting in air being drawn into the room from adjacent areas. Negative pressure environments are critical in laboratories or isolation rooms to contain airborne pathogens or contaminants, thus protecting personnel and the surrounding environment.

While other factors like the type of equipment used can influence air movement, and the materials of the room walls might affect factors like insulation or sound transfer, they do not fundamentally define the pressure dynamics of the room. The size of the room can influence airflow dynamics, but it is the specific adjustments made to the ventilation system (supply and exhaust) that directly create positive or negative pressure situations.