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International regulations for control of discharge from chemical tankers

Chemical cargoes may present a fire hazard which will be determined by the flashpoint, boiling point, flammability limits and auto-ignition temperature of the product. The marine pollution hazard will be dependent on several factors that include bioaccumulation and the attendant risk to aquatic life or human health.

In addition, release into the marine environment may cause damage to living resources, hazard to human health and consequent reduction of amenities. The air pollution hazard posed by release into the atmosphere may categorised by the emergency exposure limit (EEL) of the substance

Importance of environmental care

The growing importance of environmental care demands that the crews of chemical tankers have a clear understanding of the pollution regulations.

The International Convention for the Prevention of Marine Pollution from Ships 1973, as modified by the Protocol of 1978, known as MARPOL 73/78, is the principal regulation covering protection of the marine environment. MARPOL Annex I covers procedures for control of oil and oil-like substances, such as cargo or fuel, and applies to all ships including chemical tankers.

MARPOL Annex II contains extensive regulations about the loading, carriage and discharge of noxious liquid cargoes, as well as the treatment of cargo residues remaining on board, washing of empty tanks and the final disposal of the contaminated washing medium.

MARPOL Annex II affects all ships carrying noxious liquid cargoes in bulk. All personnel with responsibility for cargo operations on chemical tankers should be aware of the basic requirements of MARPOL, and take care that discharges into the sea never exceed the permitted limits.


Main requirements of MARPOL Annex II

MARPOL Annex II categorises substances posing a threat of harm to the marine environment, with chemicals posing the greatest threat having the most severe controls placed upon their shipment and severe limitations on their discharge into the sea. A principal way of meeting the need to limit discharges to the sea is to reduce the residue that remains within a tank after unloading has been completed.

Every chemical carrier is provided with pumping and piping arrangements specially designed to ensure that each tank designated for the carriage of controlled substances can be emptied so well that the quantity of cargo remaining afterwards is less than the minimum quantity specified in MARPOL. For each tank an initial assessment of the residue quantity has to be made, called a stripping test. The results of this test are recorded, and are used as the basis for the procedures described. Only when the residue is shown to be less than the quantity prescribed by MARPOL Annex II may the tank be approved for the carriage of a controlled substance.




MARPOL then sets requirements for disposal of those residues, usually through dilution and use of shore reception facilities. It then specifies the records that must be kept of cargo work on board. Finally, it makes provision for inspections by authorities to confirm that the ship has complied.


Latest amendments - 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.


Procedures and Arrangements (P&A) Manual for each ship

MARPOL Annex II requires that each chemical tanker be provided with a P&A Manual to achieve compliance with the regulations and to be able to demonstrate that compliance has been considered from the earliest design stage. The format of the P&A Manual and its contents must be as specified in MARPOL Annex II Appendix D, and be approved by the flag administration of the ship.

The P&A Manual is concerned with the marine environmental aspects of cleaning of cargo tanks, and the discharge of cargo residues that may or may not be mixed with a washing medium. The results of the stripping test are recorded in it.

Ships' officers should familiarise themselves thoroughly with the P&A Manual, and adhere at all times to operational procedures with respect to cargo handling, tank cleaning, stop handling, residue discharge, ballasting and deballasting. The master is obliged to ensure that the ship does not discharge into the sea any cargo residues, or mixtures of residue with water, unless such discharges are made in full compliance with the operational procedures contained in the P&A Manual, and that the equipment required by the Manual for such discharge is used.

The P&A Manual, together with the cargo record book and Certificate of Fitness, will be checked by the ship's own flag administration and by port state control officers in order to confirm full compliance with the requirements of MARPOL Annex II.

It is now recognised that almost any discharge from a ship into the surrounding environment needs to be carefully considered in advance. Not only are chemical cargo residues, oily water from machinery room bilges and overboard disposal of garbage strictly regulated, but funnel exhausts and ballast water have now been identified as requiring control.


Air pollution

Control of Ozone Depleting Substances (ODS), such as halogenated hydrocarbon gases, was established internationally in the early 1990s. In 1997, IMO adopted Annex VI to MARPOL, addressing ships' emissions that are considered to be harmful to the atmosphere, or which can settle on land or into the sea.

Funnel emissions of different oxides in engine and incinerator exhausts are generally not susceptible to daily adjustment by a ship's crew, but will be dependant upon the grade of fuel used and the condition of the engines. However, the crew will be involved in control of cargo vapours by on board techniques, such as vapour return to shore while loading, reducing excess discharge of inert gas, and avoiding unnecessary evaporation of liquid cargo into the atmosphere while cleaning tanks.


Ballast water management

The intent of ballast water management is to minimise the transfer of marine organisms from one geographical region to another. The discharge of ballast water is now known to be responsible for the introduction of alien species into sensitive coastal waters, and the demand for ballast water management is an aspect of quarantine procedures rather than traditional pollution controls.

IMO is seeking to encourage establishment of a single regime worldwide, in the manner of other Conventions, so that the present various requirements become standardised.




Related info:

Restriction on discharge of cargo residues into sea from chemical tankers

IMO code guideline

Voyage planning & considerations for stowage and pre-planning



Following reference publications provide useful guidance and international regulations for carrying hazardous chemicals at sea.



Our detail pages contain somewhat larger lists of resources where you may find more useful information.

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