Explain the operating principles of a pre-action sprinkler system, detailing when it is preferable compared to a wet pipe system.

A pre-action sprinkler system is a type of fire suppression system that combines features of both wet and dry pipe systems, offering enhanced protection against accidental water damage. Unlike a wet pipe system, the pipes in a pre-action system are normally dry. Water is held back from entering the sprinkler pipes by a pre-action valve. The system requires two separate events to occur before water is discharged: first, a fire detection event, such as smoke or heat detection, must trigger the release of the pre-action valve; and second, a sprinkler head must be activated by heat. When a fire is detected, the pre-action valve opens, allowing water to enter the sprinkler pipes, effectively converting the system into a wet pipe system. However, water will not be discharged until a sprinkler head is activated. Pre-action systems are preferable compared to wet pipe systems in situations where accidental sprinkler activation could cause significant damage to valuable or sensitive contents. These situations include computer rooms, data centers, museums, libraries, and archives. The double interlock feature of a pre-action system, requiring both fire detection and sprinkler head activation, significantly reduces the risk of accidental water discharge due to mechanical damage to the sprinkler heads or false alarms. There are different types of pre-action systems, including single interlock, double interlock, and non-interlock systems. Single interlock systems require fire detection before the pre-action valve opens. Double interlock systems require both fire detection and a sustained air pressure loss in the sprinkler pipes before the pre-action valve opens. Non-interlock systems allow the pre-action valve to open upon fire detection or sprinkler head activation.