What spacing is permitted for smoke detectors on smooth ceilings, and how far must any point on the ceiling be from a detector?

• A. 6.1 m spacing; every point within 0.5 times the spacing
• B. 12 m spacing; every point within 0.8 times the spacing
• C. 9.1 m spacing; every point within 0.7 times the spacing
• D. 15 m spacing; every point within 1.0 times the spacing

Answer: (C)

Coverage and spacing for smoke detectors on smooth ceilings is about ensuring each point on the ceiling is close enough to a detector so smoke is detected quickly. For smooth ceilings, detectors should be placed no more than 9.1 meters apart (that’s 30 feet). The rule also says any point on the ceiling must be within 0.7 times that spacing from a detector. So with a 9.1 meter spacing, the farthest distance from any ceiling point to a detector is 0.7 × 9.1 ≈ 6.37 meters, about 6.4 meters or 21 feet. This setup provides overlapping coverage and minimizes dead zones. The other options don’t match these standard values for smooth ceilings.