Hotel Voice Evacuation Audibility and Intelligibility Failure
A 120-room, five-story hotel has a new voice evacuation system. Speakers are installed in corridors and sleeping rooms. During acceptance testing, the sound level at the pillow in Room 312 is 68 dBA with the door closed, and the room ambient is 38 dBA. The corridor outside the room reads 88 dBA. The speech intelligibility meter shows an STI of 0.45 in three sleeping rooms and 0.62 in the corridor. The contractor proposes increasing the amplifier output to raise the room level. The room speaker is a ceiling speaker located above the bed and tapped at one-quarter watt; the door has a three-quarter-hour rating and a closer. The AHJ has not accepted the system.
1. Evaluate the audibility and intelligibility results against NFPA 72.
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For sleeping rooms, NFPA 72 requires an average sound pressure level of at least 75 dBA at the pillow or 15 dBA above ambient, whichever is greater. The ambient is 38 dBA, so 15 dBA above ambient is 53 dBA; the 75 dBA floor governs. A reading of 68 dBA at the pillow fails. The corridor reading of 88 dBA exceeds the minimum, but higher is not automatically better because it can reduce intelligibility and be uncomfortable. An STI of 0.45 in sleeping rooms is below the commonly used 0.50 threshold, so intelligibility also fails. Simply increasing amplifier gain may raise the level but can worsen distortion and does not correct the room speaker coverage.
2. What design changes and retest plan would you require?
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Require a room-by-room review of speaker location, tap setting, and coverage. Likely fixes include adding a speaker closer to the pillow, changing the tap, aiming or relocating the ceiling speaker, and reducing excessive corridor level. Verify that the door, carpet, and furniture are not blocking sound, but do not rely on an open door for the sleeping-room test. Retest with the door closed at the pillow, record ambient and alarm levels, and measure intelligibility in representative rooms on each floor. The contractor should submit revised calculations or a design letter before retesting. Acceptance should be based on both audibility and intelligibility, not just louder output.
3. How should the final acceptance be documented?
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Document the before-and-after readings for each tested room, the ambient levels, the STI results, the speaker tap and location changes, and the final as-built drawings. Include the record of completion, the sequence of operations, and the AHJ witness signature. Note that the corridor level was reduced or balanced and that sleeping-room testing was performed with doors closed. Keep the intelligibility report with the acceptance records so the owner and AHJ can show that the system was tested to the adopted standard, not merely adjusted by ear.