What is a vital feature of a pre-action fire system?

A vital feature of a pre-action fire system is that it activates upon detection of heat and smoke. This system is designed to enhance fire protection by combining elements of both automatic sprinklers and detection systems. In a pre-action system, the detection component (such as smoke detectors) must first identify the presence of a fire, which triggers the release of water into the system's pipes. This helps prevent water damage that could occur if the sprinkler system were to discharge water without confirmation of a fire.

This approach allows for a more controlled response, as water is only introduced into the system when there is clear evidence of a fire, reducing the risk of accidental discharge. The use of heat and smoke detection ensures that the system activates only when there is a legitimate threat. Therefore, choosing an option that focuses on the detection of heat and smoke directly aligns with the function and purpose of a pre-action fire system.