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Restriction on discharge of cargo residues into sea from chemical tankers

The growing importance of environmental care demands that the crews of chemical tankers have a clear understanding of the pollution regulations. Many additional tasks undertaken during cargo handling in a chemical tanker are dictated by a need to protect against any chance of discharge of cargo into the sea. These additional tasks must be performed safely, and an understanding of their purpose is a necessary part of chemical tanker operations today.

chemical tanker navigation at sea
Even after careful unloading, final disposal of residues may only be carried out in accordance with approved procedures and arrangements. It is necessary for tanks that have contained some specified cargoes to have a first rinse at the unloading port, called a pre-wash, and the initial washings discharged to shore reception facilities (usually the cargo receiver). Pre-wash sets a minimum required level of dilution of cargo residue for environmental protection. It has no direct relevance to preparing a tank for its next cargo. The commercial justification for any further tank cleaning is not addressed by authorities, although handling and disposal of washings must continue to take account of MARPOL.

When a tank is washed with a washing medium other than water which would itself require control if carried as a cargo, discharge or disposal of the strippings will be governed by the provisions of MARPOL applying either to the washing medium or to the original cargo, whichever are the more severe.

Discharge into the sea of cargo residues and tank cleaning products is strictly controlled. It is recommended that any discharge should be as far from land as practicable. Any discharge of effluent containing controlled substances (except in an emergency situation) is subject to a maximum concentration of the substance in the ship's wake or the dilution of substances prior to discharge, and must take account of the following:

A maximum quantity of such substance per tank.

The speed of the ship during the discharge.

The minimum distance from the nearest land during discharge.

The minimum depth of water during discharge.

The need to carry out the discharge below the water line.

Some areas of the sea are designated as special areas in which even more stringent discharge criteria apply.

Discharge overboard in port is always prohibited by local, national or regional standards that are usually supplementary to MARPOL, rather than in conflict with it.

Tank Cleaning IMO regulation///MARPOL 73/78 Annex II MEPC 2/ Circ. 15 Annex /10

The International Maritime Organisation (IMO) MARPOL 73/78 ANNEX II regulates the discharge of Noxious Liquid Substances and the use of chemicals that are used for tank cleaning purposes.

The IMO is changing current regulation MEPC./Circ.363 in order to cut down on the number of chemicals used for tank-cleaning purposes. For future products no perfume or colouring agents will be allowed in tank-cleaning chemicals that will be discharged to sea inside the shore limits as listed in the MARPOL 73/78 ANNEX II.

All tank-cleaning products approved to MEPC./Circ.363 prior to 1 January 2007 need to be re-evaluated based on criteria outlined in MEPC1/Circ 590. All IMO approved products evaluated through MEPC./Circ.363 before 1 January 2007 will cease to be valid on 1 August 2010.

The new and revised regulation MEPC 2 /Circ.15 came into force on 1 August 2010. All cleaning additives evaluated and found to meet the requirements of paragraph 13.5.2 of Annex II of MARPOL 73/78 are consolidated into annex 10 of the MEPC.2/Circular 15.

Related info:

International regulations for control of noxious liquid chemicals into sea

How to arrange disposal of tank cleaning waste ?

Retention of slops on chemical tankers

Preparations prior allowing personnel into cargo tanks / enclosed spaces

How to rescue injured or unconscious person from enclosed spaces

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