If a heat detector with a listed spacing of 50 ft is mounted on an 18 ft 1 in. high ceiling, what is the maximum allowable spacing?

If a heat detector with a listed spacing of 50 ft is mounted on an 18 ft 1 in. high ceiling, what is the maximum allowable spacing?

• A. 50 ft
• B. 32 ft
• C. 42 ft
• D. 30 ft

Answer: (B)

Heat detectors are designed with a spacing that matches a typical ceiling height. When the ceiling is higher, the hot air plume rises farther before reaching the detector, so you must reduce the spacing to keep the same level of coverage. To estimate this, use the listed spacing and scale it by the ratio of a reference ceiling height to the actual height. If we take a common reference height of about 12 feet, the ratio is 12 / 18.083 ≈ 0.663. Multiplying the listed spacing of 50 feet gives about 33 feet. In practice, spacing is set in standard practical increments, so the closest allowable distance that does not exceed this is 32 feet. Therefore, on an 18 ft 1 in high ceiling, the maximum allowable spacing is about 32 feet.

Heat detectors are designed with a spacing that matches a typical ceiling height. When the ceiling is higher, the hot air plume rises farther before reaching the detector, so you must reduce the spacing to keep the same level of coverage. To estimate this, use the listed spacing and scale it by the ratio of a reference ceiling height to the actual height. If we take a common reference height of about 12 feet, the ratio is 12 / 18.083 ≈ 0.663. Multiplying the listed spacing of 50 feet gives about 33 feet. In practice, spacing is set in standard practical increments, so the closest allowable distance that does not exceed this is 32 feet. Therefore, on an 18 ft 1 in high ceiling, the maximum allowable spacing is about 32 feet.