Corridor Horn Audit Fails the Pillow Test in a Reconverted Hotel Wing
A 40-room wing of a Dover hotel is being converted from long-term apartments back to transient guest rooms. Measured ambient sound is 52 dBA in the corridor, and inside a typical guest room 58 dBA with the PTAC running (42 dBA with it off). The guest room door is a 1¾ in. solid-core door with field-measured attenuation of about 22 dB, and the path from the corridor horn/strobe to the pillow is 24 ft. The corridor devices are 24 V horn/strobes rated 90 dBA at 10 ft, wired to a circuit with no synchronization module; there are no appliances inside the guest rooms. The contractor tested one room with the door closed and the PTAC running and measured 61 dBA at the pillow with a Type 2 meter on slow response, reporting the room "audible." The owner does not want sounder bases in the rooms ("the corridor horn covers it") and the decorator objects to visible appliances. The AHJ requires private-mode notification for the sleeping areas.
1. Determine the required sound pressure level at the pillow and evaluate the measured 61 dBA. Show the arithmetic behind the field measurement.
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Private mode in a sleeping area requires 75 dBA at the pillow, or 15 dB above the ambient, whichever is greater.
- Ambient with PTAC running: 58 dBA → 58 + 15 = 73 dBA.
- 75 dBA governs.
Measured 61 dBA is 14 dB short - a factor of about 25 in sound energy, not a rounding error.
The measurement makes sense arithmetically: 90 dBA at 10 ft, spreading to 24 ft, loses roughly 6 to 8 dB (about 83 dBA outside the door); the door then removes about 22 dB in the field, leaving roughly 61 dBA. So the contractor's number is credible and the design simply does not meet the criteria - the corridor horn is doing what a corridor horn does, which is cover the corridor.
Two process points for the report: private mode also requires the corridor and lobby to meet 15 dB above ambient (52 + 15 = 67 dBA minimum there), and a Type 2 meter on slow response is acceptable for verifying audibility, but the measurement must be documented room by room, not extrapolated from one room.
2. The owner wants to keep the corridor-only design. Explain what must change, including the low-frequency requirement for sleeping areas.
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The corridor-only scheme cannot meet 75 dBA at the pillow with a closed door except by making the corridor unbearable - you would need roughly 97 dBA outside the door, which is above the level at which the corridor itself becomes hazardous and is not how the standard is structured. The reliable fix is notification inside the sleeping room.
Low-frequency requirement. Sleeping-area alarms must produce a 520 Hz ±5% square-wave signal, which is markedly more effective at waking people (including those with mild to moderate hearing loss) than the 3 kHz-dominated output of a standard horn. A corridor horn of any frequency does not satisfy this for the guest room, because the signal reaching the pillow is attenuated and shaped by the door.
Practical solution. Use sounder bases on the guest-room smoke detectors, set to the low-frequency tone, activated by the building system on general alarm. Confirm the sounder base is listed with the detector and the panel, that its current is added to the battery and NAC/auxiliary calculations, and that synchronization is applied across the audible and visible signals on each circuit. Then retest every room with the door closed and the PTAC running.
3. Address the visible notification question: where are visible appliances required, how is candela selected, and does the missing sync module matter?
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Visible notification is required in public and common areas - corridors, lobbies, elevator lobbies, and other areas used by all occupants - where the system provides public-mode notification, and in the guest rooms that must be equipped for hearing-impaired occupants under the accessibility requirements adopted by the AHJ. The decorator's objection is not a code argument; the corridor appliances stay.
Candela is selected from the room-size/mounting-height tables, not from habit. For a 6 ft wide corridor with appliances mounted on the wall at the standard height, a low-candela appliance at close spacing can satisfy the corridor; for the larger lobby you must check the room dimensions against mounting height and pick candela accordingly. Where the space is large or the ceiling is high, higher-candela units or additional appliances are needed - verify with photometric spacing, and remember that increasing candela without checking spacing can under-cover corners.
Synchronization matters: visible signals on the same circuit and in the same field of view must flash in sync, and the missing sync module is a defect that will be written up at acceptance. Add the listed synchronization module (or a listed synchronized appliance set) and confirm the flash rate is within the permitted range.