In a crosszone strategy, a minimum of two detectors, one on each of two separate detection circuits, must actuate to generate the desired signal. This is most common when the actuation of an automatic fire suppression system is tied to a fire detection signal. Common applications include: pre-actio or dry-pipe fire sprinklers, water deluge systems, water curtains, and gaseous suppression systems.
If a cross-zone detection strategy is encountered, the total detection time will be dominated by the detector located farthest from the fire ignition source. Identify which detectors are assigned to each of the fire detection circuits and locate the nearest detector in each of the circuits. Of these two, the detection time is generally dominated by the detector located further from the fire ignition source (radial horizontal distance from fire center to detector location). Exceptions include:
- Cases where one of the detectors is located in a different beam pocket from the fire ignition source,
- Cases where one detector has a slower time response that another (e.g., a heat detector will generally respond more slowly than a smoke detector).
Identify the detector that is the limiting factor in the time response and base the actuation analysis on the time response of that detector.