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The pre-action system is classified as a secondary measure in fire suppression. This type of system functions as a combination of a conventional sprinkler system and a dry pipe system, requiring two triggers before water is released. First, the smoke detectors or another detection method must identify a fire. Once detected, it fills the pipes with water, but the sprinklers are held closed until a second trigger, typically an increased heat or pressure from a fire, occurs. This dual trigger mechanism makes it a secondary measure compared to more direct approaches, like a water sprinkler system, which activates immediately in the presence of heat.

While other systems like the CO2 system and water sprinkler system have their roles in fire suppression—the CO2 system is often used for specific environments where water would cause damage, and the water sprinkler system is activated by heat—the smoke detector system is primarily a detection method that prompts action rather than actively suppressing a fire. Therefore, the pre-action system fits the criteria of a secondary measure, as it adds an additional layer of response before releasing water to combat a fire, making it a more cautious approach.