3.3.1 A terminal's vapour emission control system
should have the capacity for handling cargo vapour at a rate of not
less than the facility's maximum designed loading rate multiplied
by a factor of at least 1.25 to take account of gas evolution, and
in addition any inerting, enriching, or diluting gas which may be
added to the system.
3.3.2 A terminal's vapour emission control system
should be capable of maintaining the pressure in a tanker's cargo
tanks between the lowest setting (i.e. that setting nearest to atmospheric
pressure) of any of the tanker's vacuum relief valves and the lowest
setting of any of the tanker's pressure relief valves for a non-inerted
tanker, and between atmospheric pressure and the lowest setting of
any of the tanker's pressure relief valves for an inerted tanker.
The system should be capable of maintaining the pressure in the tanker's
cargo tanks within this range at any cargo transfer rate less than
or equal to the maximum transfer rate.
3.3.3 Each terminal main branch line at a berth
should be provided with a pressure sensing device located as close
to the terminal vapour connection as practicable and this device should:
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.1 come into operation prior to the pressure in
the tanker's cargo tanks going outside the range given in paragraph
3.3.2;
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.2 give a visible and audible pressure alarm to
the facility's operator;
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.3 provide an agreed signal for sequential shutdown
of onshore pumps and the remotely operated cargo vapour shutoff valve
required by paragraph 3.2.1. The pump and valve shutdown may be dependent
on operator's interventions.
3.3.4 Safety features such as a back flow preventer
or pressure relief device should be provided to ensure that a malfunction
in an inerting, enriching, or diluting system does not overpressure
the tanker.
3.3.5 If a compressor, blower or eductor unit
is used to draw vapours from the tanker, a vacuum relief device should
be installed in the vapour collection line between the unit and the
terminal vapour connection. This relief device should have a vacuum
relieving capacity greater than the capacity of the compressor, blower
or eductor unit.