7.1.1 Unless the entire cargo
system is designed to withstand the full gauge vapour pressure of
the cargo under conditions of the upper ambient design temperatures,
maintenance of the cargo tank pressure below the MARVS should be provided
by one or more of the following means, except as otherwise provided
in this section:
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.1 a system which regulates the pressure in the cargo
tanks by the use of mechanical refrigeration;
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.2 a system whereby the boil-off vapours are utilized
as fuel for shipboard use or waste heat system subject to the provisions of chapter
16. This system may be used at all times, including while in port and
while manoeuvring, provided that a means of disposing of excess energy is
provided, such as a steam dump system, that is satisfactory to the Administration;
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.3 a system allowing the product to warm up and
increase in pressure. The insulation or cargo tank design pressure or both should
be adequate to provide for a suitable margin for the operating time and
temperatures involved. The system should be acceptable to the Administration in
each case;
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.4 other systems acceptable to the
Administration;
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.5 in addition to the above means, the Administration
may permit certain cargoes to be controlled by venting cargo vapours to the
atmosphere at sea. This may also be permitted in port with the permission of the
port Administration.
7.1.2 The systems required
by 7.1.1 should be constructed, fitted
and tested to the satisfaction of the Administration. Materials used
in their construction should be suitable for use with the cargoes
to be carried. For normal service, the upper ambient design temperature
should be:
sea 32°C
air 45°C.
For service
in especially hot or cold zones these design temperatures should be
increased or reduced, as appropriate, by the Administration.
7.1.3 For certain highly dangerous
cargoes specified in chapter 17, the cargo
containment system should be capable of withstanding the full vapour
pressure of the cargo under conditions of the upper ambient design
temperatures irrespective of any system provided for dealing with
boil-off gas.