Gas-freeing is required on non-inerted product carriers
more frequently than on crude carriers, both because of the greater
need for tank entry and inspection, especially in port, and for venting
vapours of previous cargoes. On inerted product carriers any gas-freeing
operation has to be preceded by a purging operation (regulation 62.2.4), but gas-freeing for
purely quality reasons may be replaced by purging only. In addition
purging may be required on the basis outlined in 6.1.3 above.
It should be recognised that:
.1 there are increased risks of air leaking into
inert tanks and of inert gas leaking into a tank being entered;
.2 purging is not a prerequisite of gas-freeing
when the hydrocarbon gas content of a tank is below 2% by volume;
.3 the operation of gas-freeing for product purity
and where tank entry is not contemplated does not require the atmosphere
to have an oxygen content of 21% by volume.