A smoke detector in an elevator lobby used for recall must be mounted within how many feet from the centerline of the door?

In elevator lobbies, smoke detectors play a crucial role in fire safety systems, particularly in facilitating the safe recall of elevators during a fire event. The guideline specifies that a smoke detector must be installed within a certain distance from the centerline of the elevator door to ensure it effectively detects smoke that may indicate a fire.

The requirement to mount the smoke detector no more than 21 feet from the centerline of the door ensures that the detector is responsive to smoke entering the lobby area from the elevator shaft or surrounding spaces. This proximity allows for timely alerts to the fire control system, enabling elevators to safely return to a designated floor for passenger evacuation while minimizing the risk of smoke spreading.

This distance is established to provide adequate coverage in the space while adhering to safety standards, ensuring that detectors are not too far away to miss critical smoke signals. Proper placement is integral to maintaining the functionality and effectiveness of the fire alarm system in protecting occupants.