3
SECTION III
INSTALLATION
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 level of a 2001SRNB
siren is 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
Community 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, 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 10dB. For
example, the sound level at 100 feet (30.5m)
from a 2001SRNB siren is 128dB. At 200 feet
(61m), the level drops to 117dB; at 400 feet
(122m) the sound level drops to 107dB; etc.
This is referred to as the “loss per distance
doubled”.
A loss per distance doubled of 10dB is
usually experienced 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 or other factors detrimental to
sound propagation.
Experience indicates 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, 68dB of ambient noise is typical.
Assuming a 10dB loss per distance doubled
and a 70dB minimum sound level, the
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