Which foam-water system uses air under pressure with a supplemental detection in the same area, i.e., preaction?

• A. Deluge System
• B. Spray System
• C. Preaction System
• D. Dry Pipe System

Answer: (C)

Understanding how a preaction foam-water system operates. In this setup, the piping is charged with air under pressure rather than water, keeping the foam-water lines dry until an initiating event is verified. A detection device located in the same area must be actuated before water is admitted into the system, typically by triggering a control valve that allows water to fill the piping and mix with foam concentrate. This two-step sequence—local detection plus water release—defines a preaction system and provides added protection against accidental discharge in sensitive areas. Once the preaction valve is opened, water enters the foam-water piping and discharges through the sprinklers as designed. The other systems don’t use this two-step release: a deluge system releases water to all heads immediately upon activation; a dry pipe system is also air-filled but generally relies on a remote valve actuation rather than a local detection signal in the same area; and a spray system refers to the discharge pattern, not the interlock mechanism described.