What is unique about a preaction sprinkler system?

A preaction sprinkler system is distinctive because it contains air under pressure in the pipes, which helps create a delay in activation until a fire is detected. This system requires a secondary detection mechanism, typically other than the sprinkler heads themselves, such as a smoke or heat detector, to trigger the release of water. This two-step approach helps minimize water damage and is particularly useful in environments where accidental discharge can cause significant disruption or damage, such as in data centers or museums.

In contrast to this, a straightforward fire suppression system could activate without the need for additional detection, which does not apply to preaction systems. Moreover, preaction systems are not limited to outdoor use, as they are often found in both indoor and outdoor settings depending on specific fire safety needs. Lastly, while some sprinkler systems use foam for certain applications, traditional preaction systems generally utilize water when activated.