Administrations are invited to accept the inert gas systems
referred to in this Regulation for chemical tankers for which certificates
of fitness are issued under the Code for the Construction and Equipment
of Ships Carrying Dangerous Chemicals in Bulk (resolution A.212(VII))
and under the International Code for the Construction and Equipment
of Ships Carrying Dangerous Chemicals in Bulk (resolution MSC.4(48)).
This regulation shall be applied to chemical tankers as
required by the draft amendment to Regulation
II-2/55.5 of the 1974 SOLAS Convention as amended (resolution
A.566(14)).
1 Inert gas generator systemsfootnote shall be designed, constructed and tested
to the satisfaction of the Administration. They shall be designed
and operated so as to render and maintain the atmosphere of cargo
tanksfootnote non-flammable at all times
except when such tanks are required to be maintained empty and gas-free.
Inert gas systems supplied by one or more oil-fired inert gas generators
may be accepted. An Administration may accept systems using inert
gas from other sources provided that an equivalent standard of safety
is achieved.
2 The systems shall be capable
of:
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.1 inerting empty cargo
tanks by reducing the oxygen content of the atmosphere in each tank
to a level at which combustion cannot be supported;
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.2 maintaining the atmosphere,
in all parts of each cargo tank designated to carry flammable products
requiring protection by an inert gas system, with an oxygen content
not exceeding 8% by volume and at a positive pressure at all times
in port and at sea except when it is necessary for such a tank to
be gas-free;
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.3 eliminating the need
for air to enter a tank during normal operations except when it is
necessary for such a tank to be gas-free;
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.4 purging empty cargo
tanks of flammable vapour, so that subsequent gas-freeing operations
will at no time create a flammable atmosphere within the tank.
3.1 The systems shall
be capable of delivering inert gas to the cargo tanks at a rate of
at least 125% of the maximum rate of discharge capacity of the ship
expressed as a volume. An Administration may accept inert gas systems
having a lower delivery capacity provided that the maximum rate of
discharge of cargoes from cargo tanks being protected by the system
is restricted to 80% of the inert gas capacity.
3.2 The systems shall
be capable of delivering inert gas with an oxygen content of not more
than 5% by volume in the inert gas supply main to the cargo tanks
at any required rate of flow.
4.1 Suitable fuel in sufficient
quantity shall be provided for the inert gas generators.
4.2 The inert gas generators
shall be located outside the cargo tank area as defined in the Bulk
Chemical Code and the International Bulk Chemical Code. Spaces containing
inert gas generators should have no direct access to accommodation,
service or control station spaces, but may be located in machinery
spaces. If they are not located in machinery spaces they shall be
located in a compartment reserved solely for their use. Such a compartment
shall be separated by a gastight steel bulkhead and/or deck from accommodation,
service and control station spaces as defined in the Bulk Chemical
Code and the International Bulk Chemical Code. Adequate positive-pressure-type
mechanical ventilation shall be provided for such a compartment. Access
to such compartments located aft shall be only from an open deck outside
the cargo tank area. Access shall be located on the end bulkhead not
facing the cargo area and/or on the outboard side of the superstructure
or deckhouse at a distance of at least 25% of the length of the ship
but not less than 5 m from the end of the superstructure or deckhouse
facing the cargo area. In the case of such a compartment being located
in the forecastle, access shall be through the deckhead forward of
the cargo area.
4.3 Inert gas piping systems
shall not pass through accommodation, service and control station
spaces.
5.1 Means shall be provided
which will effectively cool the volume of gas specified in paragraph 3 and remove solids and sulphur combustion
products. The cooling water arrangements shall be such that an adequate
supply of water will always be available without interfering with
any essential services on the ship. Provision shall also be made for
an alternative supply of cooling water.
5.2 Filters or equivalent
devices shall be fitted to minimize the amount of water carried over
to the inert gas main.
6.1 Two air blowers shall
be fitted to each inert gas generator, which together shall be capable
of delivering to the cargo tanks, required to be protected by the
system, at least the volume of gas required by paragraph 3. An Administration may permit only
one blower if it is capable of delivering to the protected cargo tanks
the total volume of gas required by paragraph 3, provided that sufficient spares
for the air blower and its prime mover are carried on board to enable
any failure of the air blower and its prime mover to be rectified.
6.2 The inert gas systems
shall be so designed that the maximum pressure which they can exert
on any cargo tank will not exceed the test pressure of any cargo tank.
6.3 Where more than one
inert gas generator is provided, suitable shutoff arrangements shall
be provided on the discharge outlet of each generator plant.
6.4 Arrangements shall
be made to vent the inert gas to the atmosphere in case the inert
gas produced is off-specification, e.g. during starting-up or in case
of equipment failure.
6.5 Where inert gas generators
are served by positive displacement blowers, a pressure relief device
shall be provided to prevent excess pressure being developed on the
discharge side of the blower.
7 Two fuel oil pumps shall
be fitted to each inert gas generator. An Administration may permit
only one fuel oil pump on condition that sufficient spares for the
fuel oil pump and its prime mover are carried on board to enable any
failure of the fuel oil pump and its prime mover to be rectified by
the ship's crew.
8 A gas regulating valve
shall be fitted in the inert gas supply main. This valve shall be
automatically controlled to close as required in paragraphs 17.2 and 17.3. It shall also be capable
of automatically regulating the flow of inert gas to the cargo tanks
unless other means are provided to automatically control the inert
gas flow rate.
9.1 At least two nonreturn
devices, one of which shall be a water seal, shall be fitted in the
inert gas supply main in order to prevent the return of flammable
vapour to the inert gas generator and to any gas-safe space under
all normal conditions of trim, list and motion of the ship. They shall
be located between the automatic valve required by paragraph 8 and the first connection to any cargo
tank or cargo pipeline. An Administration may permit an alternative
arrangement or device providing a measure of safety equivalent to
that of a water seal.
9.2 The devices referred
to in paragraphs 9.1 shall be located in the cargo tank area on deck.
9.3 The water seal referred
to in paragraph 9.1 shall be capable of being supplied by two separate
pumps, each of which shall be capable of maintaining an adequate supply
at all times.
9.4 The arrangement of
the water seal and its associated provisions shall be such that it
will prevent backflow of flammable vapours and will ensure the proper
functioning of the water seal under operating conditions.
9.5 Provisions shall be
made to ensure that any water seal is protected against freezing,
in such a way that the integrity of water seal is not impaired by
overheating.
9.6 A water loop or other
approved arrangement shall also be fitted to all associated water
supply and drain piping and to all venting or pressure sensing piping
leading to gas-safe spaces footnote. Means
shall be provided to prevent such loops from being emptied by vacuum.
9.7 Any water seal or
equivalent device and all loop arrangements shall be capable of preventing
the return of flammable vapours to an inert gas generator at a pressure
equal to the test pressure of the cargo tanks.
9.8 The second device
shall be a nonreturn valve or equivalent capable of preventing the
return of vapours or liquids or both and fitted between the water
seal (or the equivalent device) required in paragraph 9.1 and the first connection from
the inert gas main to a cargo tank. It shall be provided with positive
means of closure. As an alternative to positive means of closure,
an additional valve having such means of closure may be provided between
the nonreturn valve and the first connection to the cargo tanks to
isolate the water seal (or equivalent device).
9.9 As an additional safeguard
against the possible leakage of flammable liquids or vapours back
from the deck main, means shall be provided to permit this section
of the line between the valve having positive means of closure referred
to in paragraph 9.8 and the valve referred to in paragraph 8 to be vented in a safe manner when
the first of these valves is closed.
10.1 The inert gas main
may be divided into two or more branches between the nonreturn devices
required by paragraph 9 and
the cargo tanks.
10.2 Inert gas supply
mains shall be fitted with branch piping leading to each cargo tank
designated for the carriage of flammable products required to be inerted
by this Regulation. Each cargo tank containing or loading products
not required to be inerted shall be separated from the inert gas main
by:
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.1 removing spool-pieces, valves or other pipe
sections, and blanking the pipe ends; or
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.2 arrangement of two spectacle flanges in series
with provisions for detecting leakage into the pipe between the two
spectacle flanges.
10.3 Means shall be provided
to protect cargo tanks against the effect of overpressure or vacuum
caused by thermal variations when the cargo tanks are isolated from
the inert gas mains.
10.4 Piping systems shall
be so designed as to prevent the accumulation of cargo or water in
the pipelines under all normal conditions.
10.5 Suitable arrangements
shall be provided to enable the inert gas main to be connected to
an external supply of inert gas.
11 Unless the arrangements
for venting of all vapours displaced from the cargo tanks during loading
and ballasting comply with the requirements of the BCH and IBC Codes
for controlled venting, such arrangements shall comply with regulation II-2/59.1 of SOLAS 1974 as amended
and shall consist either of one or more mast risers or of a number
of high velocity vents.
12 The arrangements for
inerting, purging or gas-freeing of empty tanks as required in paragraph 2 shall be to the satisfaction of the
Administration and shall be such that the accumulation of hydrocarbon
vapours in pockets formed by the internal structural members in a
tank is minimized and that:
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.1 on individual cargo
tanks the gas outlet pipe, if fitted, shall be positioned as far as
practicable from the inert gas/air inlet and in accordance with regulation II-2/59.1.9.3 of the 1974 SOLAS
Convention as amended, or 8.2.2.3 of
the IBC Code. The inlet of such outlet pipes may be located either
at deck level or at not more than 1 m above the bottom of the tank;
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.2 the cross-sectional
area of such gas outlet pipe referred to in subparagraph 12.1 shall be such that an exit velocity
of at least 20 m/sec can be maintained when any three tanks are being
simultaneously supplied with inert gas. Their outlets shall extend
not less than 2 m above deck level. When in accordance with paragraph 3 an Administration permits a system
designed to supply only one or two tanks simultaneously, the outlet
pipes should be sized such that an exit velocity in the outlet pipes
of 20 m/sec can be maintained;
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.3 each gas outlet referred
to in subparagraph 12.2 shall
be fitted with suitable blanking arrangements.
13 Means shall be provided
for continuously indicating the temperature and pressure of the inert
gas at the discharge side of the system, whenever it is operating.
14.1 Instrumentation
shall be fitted for continuously indicating and permanently recording,
when the inert gas is being supplied:
14.2 The devices referred
to in paragraph 14.1 shall be placed in the cargo control room where
provided. Where no cargo control room is provided, they shall be placed
in a position easily accessible to the officer in charge of cargo
operations.
14.3 In addition, meters
shall be fitted:
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.1 in the navigating bridge to indicate at all
times the pressure referred to in paragraph 14.1.1; and
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.2 in the machinery control room or in the machinery
space to indicate the oxygen content referred to in paragraph 14.1.2.
15 Portable instruments
for measuring oxygen and flammable vapour concentration shall be provided.
In addition, suitable arrangement shall be made on each cargo tank
such that the condition of the tank atmosphere can be determined using
these portable instruments.
16 Suitable means shall
be provided for the zero and span calibration of both fixed and portable
gas concentration measurement instruments, referred to in paragraphs 14 and 15.
17.1 Audible and visual
alarms shall be provided to indicate:
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.1 low water pressure or low water flow rate to
the cooling and scrubbing arrangement referred to in paragraph 5.1;
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.2 low fuel supply;
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.3 high gas temperature as referred to in paragraph 13;
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.4 failure of the power supply to the inert gas
generators;
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.5 oxygen content in excess of 8 per cent by volume
as referred to in paragraph 14.1.2;
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.6 failure of the power supply to the indicating
devices as referred to in paragraph 14.1 and
to the automatic control systems for the gas regulating valve referred
to in paragraph 8 and the inert
gas generator;
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.7 low water level in the water seal as referred
to in paragraph 9.1;
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.8 gas pressure less than 100 mm water gauge as
referred to in paragraph 14.1;
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.9 high gas pressure as referred to in paragraph 14.1.1.
17.2 Automatic shutdown
of the gas regulating valve and of the fuel oil supply to the inert
gas generator shall be arranged on predetermined limits being reached
in respect of paragraphs 17.1.1 and
17.1.3.
17.3 Automatic shutdown
of the gas regulating valve shall be arranged in respect of paragraph 17.1.4.
17.4 In respect of paragraph 17.1.5, when the oxygen content of
the inert gas exceeds 8% by volume, immediate action shall be taken
to improve the gas quality. Unless the quality of the inert gas improves,
all operations in those tanks to which inert gas is being supplied
shall be suspended so as to avoid air being drawn into the tanks.
The deck isolation valve referred to in paragraph 9.8 shall be closed and the off-specification
gas shall be vented to atmosphere.
17.5 The alarms required
in paragraphs 17.1.5, 17.1.6 and 17.1.8 shall
be fitted in the machinery space and cargo control room, where provided,
but in each case in such a position that they are immediately received
by responsible members of the crew. All other alarms required by this
paragraph shall be audible to responsible members of the crew either
as individual alarms or as a group alarm.
17.6 In respect of paragraph 17.1.7 the Administration shall be
satisfied as to the maintenance of an adequate reserve of water at
all times and the integrity of the arrangements to permit the automatic
formation of the water seal when the gas flow ceases. The audible
and visual alarm on the low level of water in the water seal shall
operate when the inert gas is not being supplied.
17.7 An audible alarm
system independent of that required in paragraph 17.1.8 or automatic shutdown of cargo
pumps shall be provided to operate on predetermined limits of low
pressure in the inert gas mains being reached.
18 Detailed instruction
manuals shall be provided on board, covering the operations, safety
and maintenance requirements and occupational health hazards relevant
to the inert gas system and its application to the cargo tank system.
The manuals shall include guidance on procedures to be followed in
the event of a fault or failure of the inert gas system.