The first step to prevent major environmental Pollution is to include in the ship's training regular drills on board (see also Fire drill).
Several items in the Ship / Shore Safety Check List specifically address measures aimed at preventing oil pollution or minimising the effects should a minor spill occur. These include the provision of experienced and responsible personnel to monitor operations, agreed communication systems, understanding and agreement of cargo transfer and emergency shutdown procedures and other issues addressing hardware-related items such as the adequacy of scupper plugs, and the blanking of unused cargo connections. These provisions are more fully described and explained in the International Safety Guide for Oil Tankers and Terminals (ISGOTT) the contents of which should be familiar to, and adhered to by, all tanker personnel.
If, despite the adherence to proper procedures, an oil spill does occur, all cargo and bunker operations should be stopped by the quickest means and should not be restarted until the source of the leak has been identified and cured and hazards from the released oil have been eliminated. In most cases, the cause of the leak will be obvious but, in some instances, such as spillages resulting from slight hull leakage, the source may be difficult to locate, requiring the services of a diver.
Should the leakage be from the ship's on-deck pipework, the affected sections should be drained down to an available empty or slack tank. Should it be suspected that the source of leakage could be the pump room sea valves, measures should be taken to relieve any pressure from the relevant sections of the line. The way that this is done would vary from ship to ship. At its simplest, pressure could be relieved by opening up the line to an empty tank; other methods could involve using a stripping pump to empty and depressurise the line. The temptation to drop lines back into the pump room bilges must be resisted and this option only used if all cargo compartments are full and with a full understanding and appreciation of the safety implications involved, especially those relating to personnel access.
Should the spillage be due to overflowing a cargo tank, the level within the tank should be lowered by dropping cargo back to an empty or slack tank. Should all other tanks be full, pumps should be readied and the excess cargo transferred ashore.
Should spillage be due to suspected hull leakage, measures should be taken to reduce the head of cargo in the tank involved either by internal transfer or discharge ashore. Unless timely corrective action is taken, oil will continue to flow out to sea until hydrostatic balance is achieved between the head of oil remaining in the tank and the sea water pressure exerted on the outer hull. Should it not be possible to identify the specific tank from which leakage is occurring, the levels of all tanks in the vicinity should be reduced, taking into account the effect on hull stress and stability. Should it be suspected that leakage is from a fracture in the bottom plating or lower shell plating, consideration should be given to reducing the level in the tank, if full, and then pumping a water bottom into the damaged tank to prevent any further oil spillage.
In all cases where action is taken to prevent or minimize oil spillage, cargo segregation and quality concerns must be secondary to preventive measures and the contingency plan should clearly state the company's policy in this regard. Furthermore, no action should be taken that in any way could jeopardise the safety of personnel either on board or ashore.
Prior to any cargo / bunkering operations, good care has to be taken for following items :