4.2.6.1 The design vapour
pressure P
o is the maximum gauge pressure
at the top of the tank which has been used in the design of the tank.
4.2.6.2 For cargo tanks where
there is no temperature control and where the pressure of the cargo
is dictated only by the ambient temperature, P
o should
not be less than the gauge vapour pressure of the cargo at a temperature
of 45°C. However, lesser values of this temperature may be accepted
by the Administration for ships operating in restricted areas or on
voyages of restricted duration and account may be taken in such cases
of any insulation of the tanks. Conversely, higher values of this
temperature may be required for ships permanently operating in areas
of high ambient temperature.
4.2.6.3 In all cases, including 4.2.6.2, P
o should
not be less than MARVS.
4.2.6.4 Subject to special
consideration by the Administration and to the limitations given in 4.2.1, 4.2.2, 4.2.3, 4.2.4 and 4.2.5 for the various tank types, a vapour
pressure higher than P
o may be accepted in
harbour conditions, where dynamic loads are reduced.