4.1 Required alarms should be clearly audible
and distinguishable in all parts of the spaces where they are called
for. Where a distinct difference between the various audible alarms
and calls cannot be determined satisfactorily, as in machinery spaces
with high ambient noise levels, it is permitted, with the exception
of the fire-extinguishing medium alarm, to install common audible
alarm and call devices supplemented by visual alarms and indicators
identifying the meaning of the audible alarm or call.
4.2 The fire-extinguishing medium alarm should
have a characteristic which can be easily distinguished from any other
audible alarm or call installed in the space(s) concerned, and should
not be combined with any other audible alarm or call.
4.3 Audible alarms and calls should have characteristics
in accordance with section 6.
4.4 In large spaces, more than one audible alarm
or call device should be installed, in order to avoid shock to persons
close to the source of sound and to ensure a uniform sound level over
all the space as far as practicable.
4.5 Facilities for adjusting the frequency of
audible alarms within the prescribed limits may be provided to optimize
their performance in the ambient conditions. The adjustment devices
should be sealed, to the satisfaction of the Administration, after
setting has been completed.
4.6 Arrangements should not be provided to adjust
the sound pressure level of required audible alarms.
4.7 Administrations may accept electronically
generated sound signals provided all applicable requirements herein
are complied with.
4.8 Administrations may accept the use of a public
address system for the general emergency alarm and the fire alarm
provided that:
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.1 all requirements for those alarms in chapters II and III of
the 1974 SOLAS Convention, as amended, are met;
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.2 all the relevant requirements for required
alarms in this Code are met;
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.3 the system automatically overrides any other
input system when an emergency alarm is required and the system automatically
overrides any volume controls provided to give the required output
for the emergency mode when an emergency alarm is required;
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.4 the system is arranged to prevent feedback
or other interference; and
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.5 the system is arranged to minimize the effect
of a single failure, e.g. by the use of multiple amplifiers with segregated
cable routes to public rooms, alleyways, stairways and control stations;
use of more than one device for generating electronic sound signals;
and use of electrical protection for individual loudspeakers against
short circuits.
4.9 The general emergency alarm, fire alarm (if
not incorporated in the general emergency alarm system), fire-extinguishing
medium alarm, and machinery alarm should be so arranged that the failure
of the power supply or the signal-generating and amplifying equipment
(if any) to one will not affect the performance of the others.
4.10 The general emergency alarm should be audible
in the spaces specified by SOLAS regulation
III/50 with all doors and accesses closed.
4.11 In general, audible alarm sound pressure
levels at the sleeping positions in the cabins and one metre from
the source should be at least 75 dB(A) and at least 10 dB(A) above
ambient noise levels existing during normal equipment operation with
the ship under way in moderate weather. The sound pressure level should
be in the 1/3 - octave band about the fundamental frequency. In no
case should audible alarm levels in a space exceed 120 dB(A).
4.12 With the exception of bells, audible alarms
should have a signal frequency between 200 Hz and 2,500 Hz.