5.4.1 During the loaded passage a positive pressure
of inert gas of at least 100 mm water gauge should be maintained in
the cargo tanks and topping up of the pressure may be necessary. When
topping up the inert gas pressure in the cargo tanks, particular attention
should be paid to obtaining an oxygen concentration of 5% or less
in the inert gas supply before introducing the gas into the cargo
tanks.
5.4.2 On motor tankers, the boiler loading may
have to be increased in order that the low oxygen concentration in
the inert gas supply can be achieved. It may also be necessary to
restrict the output of the inert gas blowers to prevent air being
drawn down the uptake during the topping up operation. If by these
means inert gas of the quality defined in 5.4.1 cannot
be achieved then inert gas from an alternative source of supply such
as an inert gas generator might be used.