Which term best describes a system where pipes are pressurized with air instead of water?

A dry pipe system is characterized by having pipes that are filled with pressurized air rather than water. In such a system, when a sprinkler head is activated due to heat from a fire, the pressurized air is released, allowing the system's valve to open and water to flow into the pipes. This type of system is particularly useful in environments where the risk of freezing is a concern, as the absence of water in the pipes helps to prevent ice formation.

Understanding that the key feature of a dry pipe system is its reliance on air pressure underscores its operational principle and how it contrasts with other systems. This knowledge is essential for those involved in the design and installation of sprinkler systems, as it informs decisions on system selection based on environmental conditions.