What is the maximum distance a heat detector can be from any point on a smooth ceiling?

• A. 0.5 times the listed spacing
• B. 0.7 times the listed spacing
• C. 1.0 times the listed spacing
• D. 1.5 times the listed spacing

Answer: (B)

Heat detectors on smooth ceilings must be placed so that no point on the ceiling is farther from a detector than a specified fraction of the detector’s listed spacing. The manufacturer’s listed spacing defines the nominal interval between detectors, and on a smooth ceiling the farthest point from a detector is limited to 0.7 times that spacing to ensure prompt detection. So, the maximum distance from any point to the nearest detector should be 0.7 of the listed spacing. For example, with a listed spacing of 30 feet, the farthest point could be no more than 21 feet away. The other options would either require closer placement or allow a point to be too far from any detector.