What is the required distance between a smoke detector and the centerline of an elevator opening?

• A. 10 ft
• B. 15 ft
• C. 25 ft
• D. 21 ft

Answer: (D)

The spacing rule for a smoke detector near an elevator opening is about how to get early warning in the adjoining lobby without causing nuisance alarms from elevator activity. The code specifies that the detector should be placed a specific distance from the centerline of the elevator opening, so smoke is detected promptly in the corridor before reaching the hoist way.

The required distance is 21 feet. This exact spacing balances catching smoke quickly in the elevator lobby with minimizing false alarms caused by elevator doors, draft effects, or air currents around the opening. If you place it too close (like 10 or 15 feet), you risk nuisance alarms or interference from the elevator area; if you place it too far (like 25 feet), warning could be delayed, reducing early detection for occupants.

So, 21 feet is the code-recommended distance from the centerline of the elevator opening to the smoke detector.