46 CFR §154.1848

1. (a)The master shall ensure that:
   1. (1)Hold and interbarrier spaces on a vessel with full secondary barriers are inerted so that the oxygen concentration is 8 percent or less by volume when flammable cargoes are carried;
   2. (2)Hold and interbarrier spaces contain only dry air or inert gas on:
      1. (i)A vessel with partial secondary barriers;
      2. (ii)A vessel with full secondary barriers when non-flammable cargoes are carried; and
      3. (iii)A vessel with refrigerated independent tanks type C;
   3. (3)When cargo tanks containing flammable vapor are to be gas freed, the flammable vapors are purged from the tank by inert gas before air is admitted; and
   4. (4)When gas free cargo tanks are to be filled with a flammable cargo, air is purged from the tank by inert gas until the oxygen concentration in the tank is 8 percent or less by volume before cargo liquid or vapor is introduced.
2. (b)Inert gas must be supplied from the shore or from the vessel's inert gas system.