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

The identification of types of sprinkler systems is based on their operational characteristics and methods of delivering water to control fires. Wet automatic systems are the most common; they contain water that is always pressurized in the pipes and is released by the heat of a fire. Dry systems, on the other hand, are filled with pressurized air or nitrogen and only activate when the system's detection of heat causes the air to escape, allowing water to flow. Fixed systems are typically designed for specific hazards and release water in a predetermined manner, not necessarily requiring manual activation.

The classification of a semi-automatic system does not traditionally fit within the commonly recognized categories of sprinkler systems in fire protection. A semi-automatic designation implies some level of manual intervention is needed to activate the system, which detracts from the self-sufficient operational nature of automatic systems. Therefore, it stands out as not being a standard type of sprinkler system recognized in fire protection literature.