Section
7 Inert gas systems on Tankers of 8,000 tonnes DWT and above
7.1 General
7.2 Gas supply
7.2.1 The
inert gas may be treated flue gas from the main or auxiliary boiler(s)
gas turbine(s), or from a separate inert gas generator. In all cases,
automatic combustion control, capable of producing suitable inert
gas under all service conditions, is to be fitted.
7.3 Venting arrangements
7.3.1 The arrangements for the venting of all vapours displaced from the cargo
tanks during loading and ballasting are to comply with Pt 5, Ch 15, 4 Cargo tank venting, purging and gas-freeing and are to consist of either one or more mast risers,
or a number of high velocity vents. The inert gas supply mains may be used for such
venting.
7.3.2 The arrangements for inerting, purging or gas freeing of empty tanks as
required in by 2.2.1.2.1 to .3 of Chapter 15 - Inert Gas Systemsof the FSS Code - Fire Safety Systems Resolution MSC.98(73), as amended by Resolution MSC.367(93) Amendments to the International Code for Fire Safety Systems (FSS Code) (Adopted on 22 May 2014)
are to be such that the accumulation of
hydrocarbon vapours in pockets formed by the internal structural members in a tank
is minimised and that:
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on individual cargo tanks the gas outlet pipe, if fitted, is to
be positioned as far as practicable from the inert gas/air inlet and in
accordance with Pt 5, Ch 15, 4 Cargo tank venting, purging and gas-freeing. 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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the cross-sectional area of such gas outlet pipes referred to in
Pt 5, Ch 15, 7.3 Venting arrangements 7.3.2 is to be such that an exit velocity of at
least 20 m/s can be maintained when any three tanks are being simultaneously
supplied with inert gas. Their outlets are to extend not less than 2 m above
deck level;
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each gas outlet referred to in Pt 5, Ch 15, 7.3 Venting arrangements 7.3.2.(b) is to be fitted with suitable blanking
arrangements;
7.3.3 One or more pressure-vacuum breaking devices are to be provided to
prevent the cargo tanks from being subject to:
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a positive pressure in excess of the test pressure of the cargo
tank if the cargo were to be loaded at the maximum rated capacity and all
other outlets were left shut; and
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a negative pressure in excess of 700 mm water gauge if cargo
were to be discharged at the maximum rated capacity of the cargo pumps and
the inert gas blowers were to fail.
Such devices shall be installed on the inert gas main unless they are
installed in the venting system required by Pt 5, Ch 15, 4 Cargo tank venting, purging and gas-freeing or on individual cargo tanks.
7.4 Unattended machinery
7.4.1 Where
inert gas generators are fitted with automatic or remote controls
so that under normal operating conditions they do not require any
manual intervention by the operators, they are to be provided with
the alarms and safety arrangements required by Pt 5, Ch 15, 7.4 Unattended machinery 7.4.2, Pt 5, Ch 15, 7.4 Unattended machinery 7.4.3, Pt 5, Ch 15, 7.5 Instrumentation and alarms and Pt 5, Ch 15, 7.7 Nitrogen generator systems, as appropriate.
Alternative arrangements which provide equivalent safeguards will
be considered.
7.4.2 Where
machinery is arranged to start automatically or from a remote control
station, interlocks are to be provided to prevent start-up under conditions
which could hazard the machinery.
7.5 Instrumentation and alarms
7.5.2 Inert
gas generators are to be fitted with an automatic combustion control
system so as to maintain steady state conditions throughout the operating
range of the generator.
7.6 Installation and tests
7.6.1 The
inert gas system, including alarms and safety devices, is to be installed
on board and tested under working conditions to the satisfaction of
the Surveyors.
7.7 Nitrogen generator systems
7.7.1 The following requirements apply where a nitrogen generator system is
fitted on board Tankers of 8,000 tonnes DWT and above. For the purpose, the inert gas is
to be produced by separating air into its component gases by passing compressed air
through a bundle of hollow fibres, semi-permeable membranes or adsorber materials.
7.7.9 The
oxygen-enriched air from the nitrogen generator and the nitrogen-product
enriched gas from the protective devices of the nitrogen receiver
are to be arranged to discharge to a safe location on the open deck.
This safe location needs to address the two types of discharges separately.
For oxygen-enriched air from the nitrogen generator, safe locations
on the open deck are:
- outside of hazardous areas as defined by Pt 6, Ch 2, 13.5 Discharge lighting;
- not within 3 m of areas traversed by personnel;
- not within 6 m of air intakes for machinery and all ventilation
inlets.
For nitrogen-product enriched gas from the protective devices
of the nitrogen receiver, safe locations on the open deck are:
- not within 3 m of areas traversed by personnel;
- not within 6 m of air intakes for machinery and all ventilation
inlets/outlets.
7.7.10 In
order to permit maintenance, means of isolation are to be fitted between
the generator and the receiver.
7.8 Nitrogen/inert gas systems fitted for
purposes other than inerting required by SOLAS Reg. II-2/4.5.5.1
7.8.3 The requirements of Pt 5, Ch 15, 7.7 Nitrogen generator systems apply except Pt 5, Ch 15, 7.7 Nitrogen generator systems 7.7.1, Pt 5, Ch 15, 7.7 Nitrogen generator systems 7.7.3, Pt 5, Ch 15, 7.7 Nitrogen generator systems 7.7.4, Pt 5, Ch 15, 7.7 Nitrogen generator systems 7.7.6 and Pt 5, Ch 15, 7.7 Nitrogen generator systems 7.7.7.
7.8.5 All the equipment is to be installed on board and tested under working conditions to the
satisfaction of the Surveyor.
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