What is Fire Alarm Audibility?



The biggest obstacle to getting occupancy of a completed construction project is getting approval from the fire department.  Of all the items checked by the fire department inspector, the biggest concern and hardest to rectify if not compliant is the level of occupant notification in event of a fire alarm activation.  If occupants can’t hear a fire alarm, you’re not moving in.  Adding last minute notification devices to a space where wall are painted, ceiling grids are in and areas are cleaned is a hit on everyone involved’s reputation.  It’s also completely avoidable with a little front end attention from a reputable fire alarm company.

Many design professionals are somewhat familiar with NFPA 72 notification spacing requirements, but may not be familiar with applying output levels to a particular space.  In this article, we’ll address the sound level requirements of NFPA 72 known as audibility.  Audibility is the ability of an occupant to distinguish the fire alarm signal above ambient sound levels anywhere in the building.  Anywhere means every occupy-able space in the building, including the furthest corner of any office with its door closed.  Now everyone’s hearing level is different, so how can you establish a baseline of acceptable sound level that achieves audibility?  The standard published in NFPA 72 is 15 db over ambient sound levels.  Ambient sound levels can either be prescriptively applied by occupancy type through a table provided in NFPA 72 (Table A.18.4.3), or a performance level can be established by measuring the sound level of a particular space for a 60 second duration.  The highest recorded decibel reading of that measurement must be exceeded by the fire alarm system audible signal by 5 decibels (NFPA  To clarify, ambient is not worst case scenario (TV blasting with the shower on), although, at the fire department inspector’s discretion, it may involve having the TV on.  If there is any question as to what ambient conditions might be, identifying (and getting a hard copy) of what the fire department considers ambient is crucial to passing high profile occupancy tests like hotels.  Identifying the required decibel levels achieved by the fire alarm system audible devices in any given space as established by the fire department is the key to gaining occupancy after a single acceptance test.

Thanks for reading and remember that Affiliated Fire Systems has been helping design professionals, electrical contractors, building owners and fire departments ensure fire alarm systems operate as intended since 1983.  Feel free to contact us or consult our data sheet page if you have any questions regarding your fire alarm system needs.

Gene Rowe

About Gene Rowe

Gene Rowe serves as the Director of Business Development for Affiliated Customer Service. He brings twenty three years of fire alarm and emergency voice systems experience to the table with both an operational and marketing viewpoint. A US Army veteran, NICET certified, an executive board member of the IL-AFAA and a member of the NFPA, he began his career establishing operational expertise as a technician, developed graphic skills with CAD design as a general engineer, gained a ‘big picture’ mindset by moving to project management and finally a marketing perspective directing business development efforts. By interfacing with a broad range of diverse organizations such as the AFAA, CAA, AIA, CEA and the IFIA, he combines concerns of the owner, designer of record, contractor, distributor and approving authority to bring a unique perspective to Affiliated.

An avid marathon runner, he resides in west suburban Chicago with his wife and two sons. He's served the community as a Cub Scout Leader, as well as coaching multiple levels of travel and park district basketball and baseball teams. Professionally, he serves as the Treasurer and is on the Board of Directors for the Illinois chapter of the Automatic Fire Alarm Association (IL-AFAA).

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