According to the IBC, activation of a duct smoke detector shall initiate what type of signal at a constantly attended location?

The correct response regarding the activation of a duct smoke detector according to the International Building Code (IBC) is a supervisory signal at a constantly attended location. When a duct smoke detector is activated, it indicates a potentially hazardous situation where smoke is present in the HVAC system. This does not necessarily trigger an alarm signal like a typical fire alarm does because the smoke may not be indicative of an immediate fire threat in the occupied space.

Instead, a supervisory signal alerts personnel monitoring the system to a condition that needs attention; it ensures that the HVAC system can be evaluated and controlled to mitigate the spread of smoke or a fire through the ductwork. This allows for appropriate response actions to be taken without causing unnecessary disruption or evacuation, which would occur with an alarm signal.

In contrast, while alarm and trouble signals are essential in fire alarm systems, they represent different conditions. An alarm signal typically indicates immediate danger, prompting evacuation and emergency response. A trouble signal usually signifies a malfunction or fault in the system. Since duct smoke detectors are specifically intended to monitor air quality and potential threats in the ductwork, the supervisory nature of their activation helps to manage and ensure safety in a more nuanced manner.