Terms of the Trade: What is Plenum Space?

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A plenum space is an interior area dedicated to air flow for heating, cooling, and ventilation. These spaces, like the area between the top and bottom of a drop ceiling or an elevated floor, can house cables for network communication, but should not contain high voltage electrical equipment, which can increase the risk of fire.

For safety, it's best to assume that open spaces contained in walls, ceilings, and floors qualify as plenum space, since airflow can leak in over time from small vents that run through. Ideally, ducts should be carefully maintained to keep non-plenum space free of heated and cooled airflow, since it can cause hazards by interacting with some machinery and construction elements.