What is a key characteristic of preaction sprinkler systems?

A key characteristic of preaction sprinkler systems is that they prevent water from entering the system under normal conditions. This design feature is crucial in applications where the presence of water could cause damage, such as in areas containing sensitive equipment or valuable materials.

In a preaction system, the piping is typically dry until a fire detection system (like smoke or heat detectors) identifies a potential fire. Upon activation, the system allows water to flow into the pipes before any sprinkler heads open, ensuring that water is only present when it is needed for fire suppression. This minimizes the risk of accidental discharges due to issues like pipe leaks or system malfunctions, making it suitable for environments that cannot tolerate water damage.

The other options do not accurately reflect the operational characteristics of preaction sprinkler systems. For instance, these systems are not always filled with water, as their primary function is to remain dry until activated. Additionally, while they may involve some level of manual activation in specific scenarios, the automatic response from the fire detection system is the primary method of activation. Lastly, designating them as suitable for areas with minor fire hazards does not capture their intended use; they are typically applied in high-value areas requiring greater protection.