Contamination of a product may affect its odour, acidity
or flashpoint specifications, and may occur in several ways; those
relevant to ships with an inert gas main (or other gas line) interconnecting
all cargo tanks are:
.1 Liquid contamination due to overfilling a tank.
.2 Vapour contamination through the inert gas
main. This is largely a problem of preventing vapour from low flashpoint
cargoes, typically gasolines, contaminating the various high flashpoint
cargoes listed in 6.1.1, plus aviation gasolines and most hydrocarbon
solvents. This problem can be overcome by:
When carrying hydrocarbon solvents where quality specifications
are stringent and where it is necessary to keep individual tanks positively
isolated from the inert gas main after a cargo has been loaded, pressure
sensors should be fitted so that the pressure in each such tank can
be monitored. When it is necessary to top up the relevant tanks, the
inert gas main should first be purged of cargo vapour.