Which part of a pre-action system activates when fire is detected?

In a pre-action sprinkler system, the activation of sprinklers upon fire detection is contingent upon a two-step process that includes both the detection of heat and the subsequent release of water. When a heat or smoke detector identifies a fire condition, it first activates the pre-action valve, allowing water to flow into the system's pipes while keeping the sprinkler heads dry until necessary. This means that only the sprinklers that are specifically located in the affected area where the fire is detected will activate to release water, effectively minimizing water damage to unaffected areas. This targeted response enhances the system's efficiency and effectiveness in controlling the fire while avoiding unnecessary discharge of water.

The other options reflect misunderstandings of how a pre-action system operates. For instance, the assertion that all sprinklers activate immediately overlooks the specific targeting of only those sprinkler heads in the fire's vicinity. The claim that the water supply is turned off contradicts the function of the system, as the water needs to flow into the system upon activation. Finally, stating that only the alarm system activates ignores the physical response of the sprinkler heads, which is contingent upon fire detection and pre-action valve activation. Thus, the understanding that only the sprinklers in the affected area respond is key to recognizing the purpose and design of