What is the maximum spacing between beam smoke detectors?

• A. 30 feet
• B. 90 feet
• C. 120 feet
• D. 60 feet

Answer: (D)

Beam detectors cover long, open spaces by sending an optical beam from a transmitter to a receiver, and they alarm when smoke disrupts that beam. Because the beam must be interrupted reliably for a timely alarm, the distance along the beam path is limited. Keeping the spacing at 60 feet ensures smoke entering the corridor will intersect the beam quickly enough to trigger detection, even with air currents or minor misalignment. If a corridor is longer, you would add another beam unit or supplement with a different type of detector to maintain coverage. Distances like 90 or 120 feet exceed the reliable detection range, and 30 feet is more typical for other detector types, not beam systems. The standard practice max is 60 feet.