In a pre-action sprinkler system, what must happen in addition to a head being activated before water will flow?

• A. The alarm condition must persist for a set time.
• B. Some physical shock must have occurred to the system.
• C. The preliminary mini discharge must fail to put out the fire.
• D. A secondary device must be activated.

Answer: (D)

In a pre-action system, water flow is controlled by a two‑step process. Simply activating a sprinkler head doesn’t release water—the pipes are kept dry until a secondary device is also activated. The initiating event (like a detector) must trigger a releasing mechanism, opening the valve and allowing water to fill the piping and reach the heads. This added step protects against accidental discharges in areas where a false alarm could cause costly damage. So the best explanation is that a secondary device must be activated to permit water to flow after the head is triggered.