Assisted Living Audibility and Strobe Spacing
A 44-bed assisted living building has two 6 ft wide, 60 ft corridors. Existing corridor horn/strobes are rated 15 cd and produce 70 dBA at 10 ft. During a test with resident room doors closed, sound pressure is 68 dBA at the pillow in a representative room and 72 dBA in the corridor; background noise is 42 dBA. The owner adds an 8-bed memory care wing with a 72 ft corridor and 30-minute corridor doors. The contractor proposes to extend the existing 15 cd horn/strobe circuit at 50 ft spacing and to rely on the corridor devices to awaken residents. The building is not sprinklered. The AHJ has requested a design analysis before permit approval. No voice evacuation system is installed. The existing panel has spare NAC capacity.
1. Evaluate the audibility in the sleeping rooms and state the required threshold.
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For sleeping areas, NFPA 72 requires 75 dBA at the pillow or 15 dBA above the ambient background, whichever is greater. The background is 42 dBA, so 15 dBA above ambient is 57 dBA; the 75 dBA criterion governs. The measured 68 dBA at the pillow with the door closed fails by 7 dBA. The 72 dBA corridor reading does not cure the room deficiency, because the door and wall attenuation reduce the level at the pillow. The contractor should add listed sounders in the sleeping rooms or increase the output and verify the level at the pillow, not just in the corridor. The design analysis should show the calculation and the post-installation test method.
2. Is 15 cd at 50 ft spacing adequate for the 6 ft wide corridors? What should the contractor check?
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Fifteen candela at 50 ft spacing in a 6 ft wide corridor is likely beyond the manufacturer’s listed spacing for that mounting height and corridor width. The contractor must use the strobe manufacturer’s spacing tables or the NFPA 72 corridor spacing rules, not a rule of thumb. The 60 ft and 72 ft corridors should be laid out with devices at the required spacing and with the correct mounting height and orientation. If the existing 15 cd devices cannot cover the corridor, use higher candela or add devices. Also synchronize strobes on the same circuit and verify that the added wing does not exceed NAC capacity. The AHJ should require the photometric layout before approval.
3. What recommendation would you give the owner before permit approval?
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Recommend a room-by-room audibility design with sounders or horn/strobes in the memory care rooms, plus a strobe layout using the manufacturer’s listed spacing for a 6 ft corridor. The design should meet 75 dBA at the pillow and provide synchronized visible notification. Because the building is not sprinklered and residents may not self-evacuate, the notification design must be reliable and testable. The contractor should submit the device listings, tap settings, battery and voltage-drop calculations, and the sequence of operations. After installation, test with doors closed and record the readings. Do not accept the existing corridor devices as sufficient for sleeping rooms.