Which of the following is NOT a type of dry sprinkler system?

A wet-pipe system is characterized by having water stored in the pipes ready to be discharged immediately in the event of a fire. This contrasts with dry systems, which do not contain water under normal conditions. Dry-pipe, preaction, and deluge systems are all designed to operate in environments where water could cause problems, such as freezing conditions or sensitive areas.

A dry-pipe system has air or nitrogen in the pipes, which is maintained under pressure until a heat-sensitive device activates, allowing water to flow. A preaction system requires a detection step before water is released, adding an additional layer of control, while a deluge system discharges a large volume of water through open nozzles immediately when activated. Each of these systems is designed for specific circumstances where wet-pipe systems would not be suitable, making the wet-pipe system not classified among dry sprinkler types.