Which sprinkler system requires two separate events for water discharge?

The pre-action system is the correct choice because it is designed to require two distinct events to initiate water discharge. The first event involves the activation of a detection system, such as a smoke or heat detector. Once this detector senses an abnormal condition, it opens a valve allowing water to fill the system's pipes.

The second event is the actual activation of the sprinkler heads themselves, which occurs when a fire triggers a specific sprinkler head, leading to water being discharged at that location. This two-step process helps to reduce the chances of accidental discharge, as water is not released until both the detection of a fire and sprinkler activation have occurred.

Understanding the function of a pre-action system is essential, particularly in environments where water damage could be as costly as fire damage, such as data centers or museums. The added layer of safety and control makes it invaluable in specific applications.