III CONTENTS Page Foreword V 1973 Marine Pollution Convention and its 1978 Protocol VI Introduction VII Marpol 73/78 VIII 1. Procedures – The Basic Method 1 1.1 Basic Method Assumptions 1 1.2 Sequence of Procedures 1 1.3 Line Draining and Taking on Dirty Ballast 2 1.4 Tank Washing 3 1.5 Loading Clean Ballast 3 1.6 Settling of Dirty Ballast 3 1.7 Disposal of Dirty Ballast 4 1.8 Slop Tank Discharge 5 1.9 Final Line and Pump Flush 6 1.10 Discharging Clean Ballast 6 1.11 Disposal of Slop Residues 7 1.12 Handling Sludge 8 1.13 Segregated Ballast Tankers 8 1.14 Dedicated Clean Ballast Tankers 9 1.15 New MARPOL Annex I Regulations 13F and 13G – Prevention of Pollution in Event of Collision or Stranding 10 1.16 Crude Oil Washing 10 2. Operational Factors Influencing Basic Method 13 2.1 Short Haul Voyages 13 2.2 Coastal Voyages 13 2.3 Special Areas 14 2.4 OBO and Ore/Oil Carriers 14 2.5 Preparation for Repair Ports 15 2.6 Reception Facilities 16 Clean Seas Guide for Oil Tankers.indd 31/16/2009 4:19:34 PM IV 3. Other Factors Influencing Basic Method 17 3.1 General 17 3.2 Insufficient Slop Tank Capacity 17 3.3 Interconnected Slop Tanks 17 3.4 Eductors 17 3.5 Slop Tank Heating Coils 18 3.6 Oil/Water Separators and Filters 18 3.7 Oil Discharge Monitor and Control System 19 3.8 Oil/Water Interface Detectors 19 3.9 Crude Oil Washing 20 3.10 Tank Cleaning Chemicals 21 3.11 Demulsifiers 21 4. Responsibilities 23 ANNEX 1 25 Water Effluent Cleanliness Requirements The 30 Litres Per Mile Criterion the 1/15000 and 1/30000 Criteria Characteristics of Effluents from Oil Retention Operations ANNEX 2 Special Areas 27 Clean Seas Guide for Oil Tankers.indd 41/16/2009 4:19:34 PM 4 1.7 DISPOSAL OF DIRTY BALLAST When settling is complete the ballast tanks will contain water, with an oil layer on top. The bulk of this water may be discharged to the sea, using the oil content monitor, and preferably when the ship is not rolling or pitching. The following procedures should be adopted during the discharge of ballast water in order to ensure optimum effectiveness of the oil content monitor. Their application will also ensure that the oil content of any discharge is restricted within permitted limits in the event of failure of the oil discharge monitoring and control system. a) If necessary flush main cargo lines and pumps into a dirty ballast tank or slop tank. b) Start to discharge dirty ballast water. c) Reduce discharge rates from individual tanks as the level approaches a water depth of about 20 per cent of the tank depth. d) Thereafter reduce pumping rates to avoid drawing surface oil into the suction by vortex or weir effects. e) Stop discharge of individual tanks when a level has been reached which, for the particular ship, is known not to give rise to any entrainment of oil. When all tanks have been discharged to this level all discharge must cease. At this stage the officer in charge should verify that the slop tank can take the volume of dirty ballast remaining. If ullage is insufficient, the slop tank may be partially discharged, utilising the oil content monitor, to provide the necessary capacity, taking care to ensure that an adequate depth of water remains beneath the oil residue layer. The operation should then continue as follows: a) Start transferring the remaining dirty ballast into the slop tank using the stripping system. b) Transfer to the slop tank the contents of the pumproom bilges and any other bilges connected to the cargo stripping system. c) Flush the stripping system, which will then be dirty, into the slop tank. Clean Seas Guide for Oil Tankers.indd 41/16/2009 4:19:34 PM 5 1.8 SLOP TANK DISCHARGE All decanting should be carried out utilising the oil discharge monitoring and control system, and the following procedures should be adopted in order to ensure optimum effectiveness of the oil content monitor. These procedures will also ensure that the oil content of any discharge is restricted within permitted limits in the event of failure of the oil discharge monitoring and control system. Decanting of the contents of the slop tank is a critical step in the retention of oil onboard and the timing of the various steps in the operation is important. As with dirty ballast, the time required for oil and water to separate in the slop tank depends upon the motion of the ship as well as on the type of previous cargo. Under favourable conditions a few hours may be enough, but in most circumstances 36 hours or more should be allowed. Before starting, an accurate interface and ullage reading must be taken, using an oil/water interface detector, to determine the depth of the oil layer. (Certain products may accumulate an electrostatic charge which must be allowed to dissipate before taking interface readings. Strict adherence to internationally accepted safety precautions in ullage reading and sampling is therefore essential.) The interface profile may vary in depth. Hence discharge from the slop tank must cease well before the interface is reached. Although every effort should be made to remove as much water as possible from the slop tank, the prime objective is to prevent oily water reaching the sea. Extreme care is therefore necessary, and a close check must be kept on the overboard discharge even with the automatic control system in operation. Agitation of the contents of the slop tank must be kept to a minimum to avoid drawing oil into the suction by vortex or weir effects, particularly as the oil/water interface approaches the top of the structural members in the tank bottom. Pumping rates must be strictly controlled. The following detailed procedures should be adhered to: Clean Seas Guide for Oil Tankers.indd 51/16/2009 4:19:34 PM