13
Installation
Description, Specifications, Installation, and Service Manual
Federal Signal
www.fedsig.com
Installation
SOUND HAZARD: The output level of a siren is capable of causing permanent
hearing damage. To prevent excessive exposure, carefully plan siren location and
post warnings where excessive levels may be encountered. Refer to OSHA 29 CFR
1910.95 for safe exposure limits.
Do not expose personnel to sound levels above 123 dBC.
Determining a Suitable Location
Careful consideration of the factors affecting the propagation of sound from the siren
and the response of the human ear to the sound will optimize the ability of the siren to
warn the community effectively. Follow Federal Emergency Management Agency (FEMA)
guidelines when designing the warning system.
As the distance from the siren increases, the reduction of signal intensity and the
minimum desired signal level at the fringe of the area to be covered are important
considerations when choosing a siren installation site. As the distance from the siren
increases, sound level losses accumulate. These losses result from weather conditions,
the terrain, obstructions in the sound path, the pitch of the sound, and the height of the
siren.
Optimum sound propagation conditions occur when no obstructions exist in the sound
path, the terrain is hard and flat, and the air is blowing away from the source. Under these
conditions, you can expect a 6 dB loss per distance doubled. A loss per distance doubled
of 10 dB is typically experienced because atmosphere is rarely calm, terrain may not be
flat, and buildings or other obstructions are frequently present in the sound path.
Using a 10 dB per distance doubled loss factor, the following sound levels are predicted
for the sirens in the following table.
Table 12 Sound levels predictions
Distance
MOD6024B
100 feet (30.5 m) the sound level is 121 dB
200 feet (61 m) the sound level is
111 dB
400 feet (122 m) the sound level is
101 dB
FEMA studies indicate typical ambient sound levels vary by location as follows:
• Industrial Areas: 70+ dBC
• Urban Areas: 60 dBC
• Rural Areas: 50 dBC
Assuming a typical 10 dB loss per distance doubled and a 70 dB minimum sound
level required to warn a typical urban area, the effective range of a MOD6024B is
approximately 3,900 feet.
Optimum warning is obtained when the warning signal is at least 10 dB above ambient.
Do not expose personnel to sound levels above 123 dBC.
