What is the maximum distance between spot smoke detectors on a smooth flat ceiling?

• A. 15 feet
• B. 30 feet
• C. 25 feet
• D. 50 feet

Answer: (B)

On a smooth flat ceiling, spot smoke detectors should be spaced so that no point on the ceiling is farther than 30 feet from a detector. This 30-foot maximum ensures that rising smoke will reach a detector quickly, giving an early alarm. The distance is measured center-to-center along the ceiling, so in a long room you’d place detectors so the farthest point is within 30 feet of a detector. Distances like 50 feet would leave gaps where smoke could go undetected for too long, while 15 feet is more conservative than required and 25 feet is acceptable but not the maximum. If ceilings are sloped or peaked, spacing rules can change, but for smooth flat ceilings the 30-foot rule is the standard.