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Published Date

August 1994

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Clean Seas Guide for Oil Tankers, 4th Edition

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This publication describes the methods for retaining oil residues on board, to help shipboard personnel comply with the oil discharge limits in MARPOL Annex 1. It offers practical assistance to owners and operators of oil tankers, oil tanker crew, governments, Port Authorities, terminal operators, cargo shippers and cargo receivers.

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The clean seas programme was introduced by the shipping industry to restrict the operational discharge of oil into the sea. This Guide focuses on the necessary procedures for separating and retaining the oily mixtures resulting from ballasting and tank cleaning operations. OCIMF and ICS highly recommend use of this Guide.

Tankers must meet MARPOL 73/78 requirements, whether voyages are short haul or coastal. The 1973 MARPOL convention, as amended by its 1978 Protocol, is the international instrument controlling pollution from ships. Annex 1 of the convention, which contains regulations for the prevention of pollution by oil, came into effect in October 1983.

1          Procedures – The Basic Method

1.1       Basic Method Assumptions
1.2       Sequence of Procedures
1.3       Line Draining and Taking on Dirty Ballast
1.4       Tank Washing
1.5       Loading Clean Ballast
1.6       Settling of Dirty Ballast
1.7       Disposal of Dirty Ballast
1.8       Slop Tank Discharge
1.9       Final Line and Pump Flush
1.10     Discharging Clean Ballast
1.11     Disposal of Slop Residues
1.12     Handling Sludge
1.13     Segregated Ballast Tankers
1.14     Dedicated Clean Ballast Tankers
1.15     New MARPOL Annex I Regulations 13F and 13G – Prevention of Pollution in Event of Collision or Stranding
1.16     Crude Oil Washing

2          Operational Factors Influencing Basic Method

2.1 Short Haul Voyages
2.2 Coastal Voyages
2.3 Special Areas
2.4 OBO and Ore/Oil Carriers
2.5 Preparations for Repair Ports
2.6 Reception Facilities

3          Other Factors Influencing Basic Method

3.1 General
3.2 Insufficient Slop Tank Capacity
3.3 Interconnected Slop Tanks
3.4 Eductors
3.5 Slop Tank Heating Coils
3.6 Oil/Water Separators and Filters
3.7 Oil Discharge Monitor and Control System
3.8 Oil/Water Interface Detectors
3.9 Crude Oil Washing
3.10 Tank Cleaning Chemicals
3.11 Demulsifiers

4          Responsibilities

Water Effluent Cleanliness Requirements
The 30 Litres Per Mile Criterion
the 1/15,000 and 1/30,000 Criteria
Characteristics of Effluents from Oil Retention Operations

Special Areas

Under Annex I of MARPOL 73/78 what is in effect a total prohibition on the discharge of any oil (which means petroleum in any form) or oily mixture from an oil tanker, including its cargo pumproom bilges, is imposed within 50 miles of the nearest land and within certain special areas, and the flow, concentration and quantity discharged elsewhere at sea are strictly limited..

Compliance with those oil discharge limitations is achieved by adhering to procedures for the retention of oil on board. Essentially, these procedures involve the onboard collection and separation of any water and oil mixtures resulting from ballasting and tank cleaning operations. Such mixtures are accumulated in either a special slop tank, or tanks, or in a cargo tank designated as a slop tank, and are subsequently disposed of ashore at the loading or discharging port, or at a repair port. Where reception facilities are not available, the recovered oil and slops must be retained on board, and either segregated or combined with new cargo loaded on top. In no circumstances may these residues be discharged into the sea unless the safety of the ship or its personnel is in jeopardy.

This Guide is concerned with these procedures and their application to all petroleum oils.


The Oil Companies International Marine Forum (OCIMF) is a voluntary association of oil companies with an interest in the shipment and terminalling of crude oil, oil products, petrochemicals and gas. OCIMF focuses exclusively on preventing harm to people and the environment by promoting best practice in the design, construction and operation of tankers, barges and offshore vessels and their interfaces with terminals. Learn more at


The International Chamber of Shipping (ICS) is the principal international trade association for the shipping industry, representing shipowners and operators in all sectors and trades.

ICS membership comprises national shipowners' associations in Asia, Europe and the Americas whose member shipping companies operate over 80% of the world's merchant tonnage.

Established in 1921, ICS is concerned with all technical, legal, employment affairs and policy issues that may affect international shipping.

ICS represents shipowners with the various intergovernmental regulatory bodies that impact on shipping, including the International Maritime Organization.

ICS also develops best practices and guidance, including a wide range of publications and free resources that are used by ship operators globally.

Title: Clean Seas Guide for Oil Tankers, 4th Edition
Edition: Fourth
Number of Pages: 28
Product Code: 4400W004
ISBN: ISBN 13: 978-1-85609-058-2 (9781856090582), ISBN 10: 1-85609-058-2 (1856090582)
Published Date: August 1994
Binding Format: Paperback
Book Height: 210 mm
Book Width: 150 mm
Book Spine: 5 mm
Weight: 0.10 kg

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