What is a key feature of preaction standpipe systems?

A key feature of preaction standpipe systems is that they prevent water from entering the system until activated. This design is particularly important in environments where the presence of water could cause damage or where the risk of accidental discharge needs to be minimized—such as in data centers or facilities housing sensitive equipment. In these systems, the discharge of water only occurs when specific conditions are met, such as the activation of a fire detection system. By maintaining the system dry until an actual fire event is detected, preaction systems help to protect both property and equipment from unnecessary water damage.

Other options do not accurately describe the characteristics of preaction systems; for instance, these systems are not always filled with water as that could lead to issues of stagnation and corrosion. They are also suitable for various types of buildings, including high-rises, and do not necessitate higher water pressure than standard standpipes to function properly. Thus, the correct answer highlights the distinct operational principle that defines preaction standpipe systems.