5
SECTION III
INSTALLATON
DANGER
Electrocution or severe personal injury can occur when making electrical connections, drilling
holes, or lifting equipment. Therefore, installation should be performed by experienced
electricians in accordance with national and local electrical codes.
3-1. SIREN LOCATION
The information in this section provides guidelines to aid the user in the selection of an installation site that
makes the best possible use of the siren.
WARNING
The output levels of the Model 2 siren are capable of causing permanent hearing damage. To
prevent excessive exposure, carefully plan placement of siren and post warnings.
If the siren is being installed as part of a Civil Defense Warning system, always follow Federal Emergency
Management Agency (FEMA) recommendations.
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 effectively warn the community.
The reduction of signal intensity, as the distance from the siren increases 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 are a result of weather conditions, the
terrain, and obstructions in the sound path, the pitch of the sound and the height of the siren. Optimum sound
propagation conditions exist when there are no obstructions in the sound path, the terrain is flat, and the air is calm.
Under these conditions, each time the distance from the siren is doubled, the sound level decreases by approximately
8dB. For example, the sound level 100 feet (30.5m) from a Model 2 is 102dB, at 200 feet (61m), the sound level drops
to 94dB; at 400 feet (122m) the sound level drops to 86dB; etc. This is referred to as the “loss per distance doubled”.
A loss per distance doubled of 8dB is seldom experienced. This is because buildings and other obstructions
are frequently present in the sound path. In addition, the atmosphere is rarely calm, and the terrain may not be flat. As
a result, a typical loss per distance doubled in residential areas may be 10dB, and as high as 12dB in areas having tall
buildings.
Experience indicates that an individual with normal hearing will probably hear a warning signal whose
intensity is at least as high as the ambient noise level.
Experience has also shown that the ambient noise level in industrial districts is typically 90dB. Therefore, for
a person to hear a warning signal in an industrial area, the sound level intensity of that signal must also be
approximately 90dB. In this situation, any point receiving a signal having less than 90dB intensity is considered to be
outside the effective range of the siren.
In business districts an ambient noise level of 80dB is common and in residential areas, 70dB of ambient noise
is typical. Assuming a 10dB loss per distance doubled and a 70dB minimum sound level, the effective range of a
