2.1.1 Wherever in the text of this chapter the
word "system" appears, it shall mean "sample extraction smoke detection
system".
2.1.1.1 A sample extraction smoke detection system
consists of the following main components:
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.1 smoke accumulators: air collection devices
installed at the open ends of the sampling pipes in each cargo hold
that perform the physical function of collecting air samples for transmission
to the control panel through the sampling pipes, and may also act
as discharge nozzles for the fixed-gas fire-extinguishing system,
if installed;
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.2 sampling pipes: a piping network that connects
the smoke accumulators to the control panel, arranged in sections
to allow the location of the fire to be readily identified;
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.3 three-way valves: if the system is interconnected
to a fixed-gas fire-extinguishing system, three-way valves are used
to normally align the sampling pipes to the control panel and, if
a fire is detected, the three-way valves are re-aligned to connect
the sampling pipes to the fire-extinguishing system discharge manifold
and isolate the control panel; and
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.4 control panel: the main element of the system
which provides continuous monitoring of the protected spaces for indication
of smoke. It typically may include a viewing chamber or smoke sensing
units. Extracted air from the protected spaces is drawn through the
smoke accumulators and sampling pipes to the viewing chamber, and
then to the smoke sensing chamber where the airstream is monitored
by electrical smoke detectors. If smoke is sensed, the repeater panel
(normally on the bridge) automatically sounds an alarm (not localized).
The crew can then determine at the smoke sensing unit which cargo
hold is on fire and operate the pertinent three-way valve for discharge
of the extinguishing agent.
2.1.2 Any required system shall be capable of
continuous operation at all times except that systems operating on
a sequential scanning principle may be accepted, provided that the
interval between scanning the same position twice gives a maximum
allowable interval determined as follows:
The interval (I) should depend on the number of scanning points
(N) and the response time of the fans (T), with a 20% allowance:
However, the maximum allowable interval
should not exceed 120 s (Imax = 120 s).
2.1.3 The system shall be designed, constructed
and installed so as to prevent the leakage of any toxic or flammable
substances or fire-extinguishing media into any accommodation space,
service space, control station or machinery space.
2.1.4 The system and equipment shall be suitably
designed to withstand supply voltage variations and transients, ambient
temperature changes, vibration, humidity, shock, impact and corrosion
normally encountered in ships and to avoid the possibility of ignition
of a flammable gas-air mixture.
2.1.5 The system shall be of a type that can be
tested for correct operation and restored to normal surveillance without
the renewal of any component.
2.1.6 An alternative power supply for the electrical
equipment used in the operation of the system shall be provided.