The Assembly
RECALLING Article 15(j) of the Convention on the
International Maritime Organization concerning the functions of the Assembly in relation
to regulations and guidelines concerning maritime safety,
RECALLING ALSO resolution A.473(XII) which was adopted to provide
an interim solution for the requirements of inert gas systems applicable to chemical
tankers carrying petroleum products, pending the possible development of final
requirements applicable to chemical tankers carrying all flammable cargoes,
RECOGNIZING that the development of such
requirementsis not needed on the basis of results of scientific studies undertakenby
industry, but that the extension of the regulation in resolution A.473(XII) to cover the
carriage of petroleum and other liquid products would meet the purpose,
NOTING that regulation II-2/60 of the International
Convention for the Safety of Life at Sea, 1974(1974 SOLAS Convention) as amended
requires inter alia new and existing tankers of a certain size, including chemical
tankers, when carrying petroleum products, to be fitted with a fixed inert gas system by
specific dates,
NOTING FURTHER that the draft
amendment to regulation II-2/55.5 of the 1974 SOLAS Convention as amended (resolution
A.566(14)) exempts certain chemical tankers and gas carriers carrying flammable products
from the requirements for inert gas systems of regulation II-2/60 of that Convention
under certain conditions,
HAVING CONSIDERED
the recommendation made by the Maritime Safety Committee at its fifty-first session,
1. ADOPTS the Regulation for Inert Gas Systems on Chemical
Tankers set out in the Annex to the present resolution, which supersedes resolution
A.473(XII);
2. INVITES Governments to apply the above
Regulation to chemical tankers for the purpose of the implementation of the draft
amendment to regulation II-2/55.5.
Annex
PREAMBLE.
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)).
REGULATION.
1 Inert gas generator systems * 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 tanks **
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. * "Inert gas generator
system" means the machinery dedicated to the production and supply of inert gas and
includes the air blowers, combustion chambers, oil fuel pumps and burners, gas coolers /
scrubbers and automatic combustion control and supervision equipment, e. g. flame
failure devices. ** Throughout this Regulation the term "cargo tank" includes also "slop
tanks containing oil residues".
2The systems shall be capable of:
.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;
.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;
.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;
.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 system 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-pressuretype 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 deckhouse 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 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
projected 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 system 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 on 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 paragraph 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
operation 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. * Means
shall be provided to prevent such loops from being emptied by vacuum. * Gas-safe space
is a space in which the entry of hydrocarbon gases would produce hazards with regard to
flammability or toxicity.
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:
.1 removing spool-pieces, valves or other
pipe sections, and blanking the pipe ends; or
.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 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:
.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;
.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 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 seized such that an exit velocity in the
outlet pipes of 20 m/sec can be maintained;
.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: .1 the pressure of the
inert gas supply mains between the nonreturn devices required by paragraph 9.1 and the
cargo tanks; and .2 the oxygen content of the inert gas supply main.
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: .1 in the
navigating bridge to indicate at all times the pressure referred to in paragraph 14.1.1;
and
.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 paragraph
14 and 15.
17.1 Audible and visual alarms shall be provided to
indicate:
.1 low water pressure or low water flow rate to the
cooling and scrubbing arrangement referred to in paragraph 5.1;
.2 low fuel supply;
.3 high gas temperature as
referred to in paragraph 13;
.4 failure of the power supply to
the inert gas generators;
.5 oxygen content in excess of 8 per
cent by volume as referred to in paragraph 14.1.2;
.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;
.7 low water level in the water seal as
referred to in paragraph 9.1;
.8 gas pressure less than 100 mm
water gauge as referred to in paragraph 14.1;
.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 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 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.