2.6.1 Each cargo tank should have a controlled
pressure venting system which is designed on the basis of the maximum
designed loading rate multiplied by a factor of at least 1.25 to take
account of gas evolution, in order to prevent the pressure in the
tank from exceeding the design pressure.
2.6.2 Each cargo tank should have a controlled
vacuum venting system which is capable of preventing a vacuum in the
cargo tank vapour space, whether generated by withdrawal of cargo
or vapour at maximum rates, that exceeds the maximum design vacuum
for the tank.
2.6.3 A prototype of each pressure or vacuum or
pressure/vacuum venting device should be bench tested for venting
capacity by a test method acceptable to the Administration.
2.6.4 Each tanker equipped with a vapour collection
system that is common to two or more tanks should be fitted with a
pressure sensing device that senses the pressure in the main vapour
collection line for those tanks, and which:
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.1 has a high pressure alarm that alarms at a
pressure of not more than the lowest pressure relief valve setting
in the cargo tank venting system; and
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.2 has a low pressure alarm that alarms at a pressure
of not less than atmospheric pressure for an inerted tanker, or the
lowest vacuum relief valve setting (i.e. that setting nearest to atmospheric
pressure) in the cargo tank venting system for a non-inerted tank
vessel.