Under which scenario must a fire alarm system initiate a pre-signal?

A fire alarm system is designed to ensure the safety of building occupants by responding appropriately to different fire conditions. One important feature of certain fire alarm systems is the pre-signal capability, which serves as an advanced alert before full activation of the fire alarm.

In the scenario where smoke is detected but there is no immediate danger, a pre-signal is particularly effective. This allows for a warning to occupants, giving them time to react appropriately without causing unnecessary panic or alarm. It provides a crucial moment to verify whether there is truly a threat before triggering the full alarm system, which could lead to evacuation or response by emergency services.

The implementation of a pre-signal in this scenario enables building management or occupants to assess the situation more calmly. It helps prevent false alarms from disrupting normal operations or causing panic. This is especially important in places with high occupancy or sensitive environments where evacuation could lead to confusion or injury.

In contrast, scenarios such as carbon monoxide detection, testing mode, or a manual trigger generally require immediate and full response actions rather than a graduated approach like pre-signaling. The primary intent of the pre-signal feature is to provide time to evaluate a potential threat rather than to respond to established dangers or system tests.