Potter Fire Alarm Systems - Manual (Page 25)

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Fire Alarm Training • 8700055 • Rev F • 4/10
Location Average Sound Level (dba)
Business Occupancies 55
Educational Occupancies 45
Industrial Occupancies 80
Institutional Occupancies 50
Mercantile Occupancies 40
Mechanical Rooms 85
Piers and Water Surrounded Structures 40
Places of Assembly 55
Residential Occupancies 35
Storage Occupancies 30
Thoroughfares, high density urban 70
Thoroughfares, medium density urban 55
Thoroughfares, rural and suburban 40
Tower Occupancies 35
Underground Structures and Windowless 40
Vehicles and Vessels 50
In some instances, audible devices are ineffective or are inappropriate. If the ambient sound in a building is above 105 dB, the
building must have visible notification. The standard allows the audible notification in noisy areas if the ambient sound level can
be reduced (i.e. NightClub). The total sound pressure produced by the audible devices must not exceed 120 dB, as permanent
hearing damage may occur. Restrooms and elevators are examples where audible devices would be inappropriate. The sound
level could cause disorientation delaying the egress time. In elevators, the people inside have no where exit until the car stops and
the doors open. Also, stairwells are inappropriate since theses devices are in the path of egress. An audible device would be an
unnecessary annoyance.
Audible notification devices must be mounted in such an arrangement that can be heard by the building’s occupants. Generally,
devices are mounted on the walls, however devices are now listed for installation on ceilings as well. When ceiling heights allow
and other installations are otherwise not permitted, wall-mounted devices are required to be mounted so that the top of the device
is at least 6 inches below the ceiling and the top is at least 90 inches above the finished floor level.
The level of sound made by the audible device is reduced as the distance from the source is increased. As a rule of thumb, double
the distance from the source and the sound pressure (dB) drops by 6dB. Double the distance again and the sound pressure is
decreased another 6 dB. When the sound must travel through walls and doors the sound loss may be more than 6 dB.
10’ 10’ 20’
90 dBA 84 dBA 78 dBA
Example of the Double the Distance Subtract 6 dBA rule.