| Current international standards for safety
require the installation of an audible warning
device in order to attract the attention of
the operator and to indicate a dangerous or
These standards have
specific rules regarding the installation
of audible warning devices in industrial environments.Two
important factors determine the capability
of the sound to be heard in any environment:
- the distance between the audible
warning device and the operator.
- the existing ambient noise.
The suitability of an audible alarm for a
specific application is determined by its
- sound output DECIBEL(dB)
- sound frequency HERTZ(Hz).
for industrial warning devices have established
minimum differential sound output levels that
must be complied with.The dB level of the
siren must be at least 15 dB higher than that
of the measured ambient noise.The siren must,however,have
a minimum sound output of 65 dB.The sound
frequency of the siren,at the point where
the sound output is greetest,must differ as
much as possible to the frequency of the ambient
noise.Sound frequency,however,must be between
300 and 3000 HZ.
The use of a PHONOMETER
is necessary to measure ambient sound levels,in
order to comply with these regulations and
to select the most suitable siren.Once this
data is available the selection of a siren
can be done very simply.
Decibel dB(1m)-Measurement of sound
The sound level can be measured but no precise
indication exists for the range of the sound.Too
many unknown factors affect this value:type
of sound,speed and direction of the wind,humidity,fog,rain
etc.The data shown in the following table
are useful as theoretical indication.