Audibility Complaint in a Mixed-Occupancy Building After Panel Replacement
A 6-story mixed-use building has retail on floors 1-2 and apartments on floors 3-6. The fire alarm panel was replaced, and the contractor reused the existing 24 VDC horn/strobe circuits. After the replacement, residents on floors 5-6 complain that the alarm is barely audible in bedrooms with the door closed. The contractor measured 62 dBA in one bedroom with the HVAC running and says the code only requires 15 dBA above ambient, which he claims is met. The building has no voice evacuation, and the corridors have horns mounted at 8 feet on 30-foot spacing. The AHJ has asked for a sound-pressure survey and a review of the notification appliance circuit design.
1. Is the contractor's '15 dBA above ambient' claim sufficient to resolve the complaint? Explain the applicable audibility criteria.
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No. The 15 dBA above ambient criterion is one part of the audibility requirement, but it must be met in the occupiable space, including bedrooms with doors closed, not just at the corridor horn. The measurement of 62 dBA in a bedroom with HVAC running must be compared to the actual ambient in that room; if ambient is 50 dBA, 62 dBA is only 12 dBA above and fails. The designer must also account for the required minimum sound level in sleeping areas, which is typically 75 dBA at the pillow or 15 dBA above ambient, whichever is greater, and verify the horn/strobe coverage after the panel replacement. The survey should document ambient and alarm levels room by room, not rely on a single spot reading.
2. What design factors likely explain the poor coverage on floors 5-6, and what corrective measures should be evaluated?
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Likely factors include horn output that was adequate for the old panel but is now under-driven because the new panel's NAC voltage drop and current capacity differ; corridor horns spaced at 30 feet with 8-foot mounting may not penetrate closed bedroom doors; and the bedrooms may lack in-room notification. Corrective options include adding in-room horns or horn/strobes in bedrooms, increasing horn output or reducing circuit loading, adding booster power supplies, and recalculating voltage drop on each NAC. The designer should verify candela and dBA ratings at the intended mounting height and spacing, then confirm the revised design meets the audibility criteria in the sleeping rooms.
3. What should the AHJ require before accepting the notification system?
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The AHJ should require a documented sound-pressure survey showing ambient and alarm levels in representative rooms on each floor, including bedrooms with doors closed and HVAC operating; verification that NAC voltage drop and current draw are within panel and booster limits; and confirmation that the notification appliances are listed and installed per the approved plans. The contractor should also provide as-built drawings reflecting any added devices and a test record for each circuit.