A lobby smoke detector is required to be placed within ____ of the centerline of the elevator door.

A lobby smoke detector is required to be placed within ____ of the centerline of the elevator door.

• A. 15 ft
• B. 25 ft
• C. 21 ft
• D. 30 ft

Answer: (C)

Elevator lobby detectors are placed at a distance that ensures smoke is detected quickly in the lobby area before it can reach the shaft. The standard requires the detector to be located within 21 feet of the centerline of the elevator door. This maximum spacing accounts for typical smoke behavior near doorways and supports timely elevator recall and ventilation actions. Being farther than 21 feet would risk delayed detection, while being closer than that meets the requirement. So the correct distance is 21 feet.

Elevator lobby detectors are placed at a distance that ensures smoke is detected quickly in the lobby area before it can reach the shaft. The standard requires the detector to be located within 21 feet of the centerline of the elevator door. This maximum spacing accounts for typical smoke behavior near doorways and supports timely elevator recall and ventilation actions. Being farther than 21 feet would risk delayed detection, while being closer than that meets the requirement. So the correct distance is 21 feet.