Initiating Devices, Detection Circuits, and Notification Appliances
Initiating devices
Spot-type smoke detectors listed for 30 ft (9.1 m) spacing are commonly laid out at no more than 30 ft between detectors and no more than 15 ft (4.6 m) from any wall or partition, with at least 4 in. (100 mm) from side walls. Heat detectors follow their listed spacing, which is usually greater than smoke spacing. Manual pull stations belong near exits and paths of egress, mounted about 42 in. to 48 in. (1067 mm to 1219 mm) above finished floor, visible and unobstructed. Duct detectors are located where they sample representative airflow, and their service access must remain available.
Notification appliances
Audible appliances in public mode must produce 15 dBA above average ambient or 5 dBA above the maximum ambient lasting at least 60 seconds, whichever is greater, measured at 10 ft. Visible appliances are selected by candela rating and coverage; do not assume one strobe covers a large room. Where multiple appliances are visible in the same area, synchronization is required so the flash pattern does not create an seizure risk or confusion. Audible and visible signals must cover all occupied areas, including restrooms and corridors where required.
Worked example. A 100 ft by 60 ft smooth-ceiling room needs spot smoke detectors at 30 ft listed spacing. Along the 100 ft dimension, place detectors at 10, 40, 70, and 90 ft; wall distances are 10 ft and spacing is 30, 30, and 20 ft. Along the 60 ft dimension, place at 15 and 45 ft; both wall distances are 15 ft. Result: 4 by 2 = 8 detectors. Every distance satisfies the 30 ft spacing and 15 ft wall rule.
Traps that cost marks
Using 30 ft as the wall distance instead of 15 ft is a common error. Do not ignore ceiling height, beams, or listed spacing limitations. Do not substitute visible appliances for audible coverage unless the code permits it. Do not forget synchronization or remote coverage.