Before carrying out such an operation reference is to be made to the operational guidelines contained within ISGOTT and other applicable reference publications. The technique is probably described as Vapour Balancing.
Ships carrying out this operation are to be inerted.
Before commencing transfer the following operational precautions must be complied with as a minimum.
- At least one of the vessels must be able to permanently monitor the oxygen content of the vapour stream. The sample point must be close to the manifold and audible and visual alarms are to be available should the oxygen content exceed 7% by volume.
- The oxygen content of all tanks in the common system is to be maintained at a level no higher than 7% by volume.
- The vapour transfer hose is to be purged of air using inert gas or nitrogen until the oxygen content is below 7% before transfer commences.
- Vapour manifold valves are not to be opened until the receiving vessel system pressure exceeds that of the discharging vessel system pressure.
During the Cargo Transfer:
- Operations are to be terminated if the oxygen content of the vapour stream exceeds 7% by volume. Operations are not to be resumed until the oxygen content in the receiving ship has been reduced below 7% by volume.
- There is to be frequent monitoring of both ship’s IG pressures with cross comparison on a regular basis and at least hourly. Transfer volumes are to be compared on the same basis.
- No air is permitted to enter the tanks of the discharging ship at any time.