MARPOL in plain words: the six annexes, the key numbers and interview questions

MARPOL is the convention behind the oily water separator, the colour-coded garbage bins and the fuel changeover before an emission control area. Every seafarer works under it every day, and almost every crewing interview for an engine or deck post touches it. This page gives the six annexes, the numbers that are asked most often, the mistakes that get ships detained and seafarers prosecuted, and a set of questions to test yourself before the interview.

What MARPOL is

The International Convention for the Prevention of Pollution from Ships was adopted at IMO in 1973. It did not come into force on its own: after a series of tanker accidents a Protocol was added in 1978, and the two texts work as one instrument, in force since 2 October 1983 — hence "MARPOL 73/78". It applies to ships flying the flag of a party, and port state control checks it in the ports of every party, whatever the flag.

The convention itself is short; the substance is in six annexes. Each annex has its own certificate, its own record book or plan, and its own list of special areas where the rules are stricter.

The six annexes

1. Annex I — Oil. Oily water from machinery spaces, cargo residues on tankers, the Oil Record Book, SOPEP and the IOPP Certificate. In force since 1983.
2. Annex II — Noxious liquid substances in bulk. Chemical tankers: cargoes are graded X, Y, Z and OS by hazard; Cargo Record Book and the P&A Manual.
3. Annex III — Harmful substances in packaged form. Packing, marking, labelling and documents — in practice through the IMDG Code.
4. Annex IV — Sewage. Treatment plant, holding tank, distances from land; the ISPP Certificate.
5. Annex V — Garbage. A general ban on discharge with narrow exceptions, placards, a Garbage Management Plan and the Garbage Record Book.
6. Annex VI — Air pollution. Sulphur in fuel, NOx from engines, ozone-depleting substances and energy efficiency (EEXI, CII); the IAPP and IEE Certificates.

Key numbers

Annex I: what the engine room must know

Bilge water from machinery spaces may go overboard only when all of these hold at once: the ship is en route; the oil content of the effluent is 15 ppm or less without dilution; it passes through approved oil filtering equipment — the oily water separator with a 15 ppm alarm and an automatic stopping device; and on a tanker it does not come from the cargo pump-room bilges and is not mixed with cargo residues. In the Antarctic area nothing may be discharged at all. Whatever cannot go overboard — sludge, oily residues — is burnt in the incinerator or delivered ashore, and every movement is recorded.

The Oil Record Book Part I covers machinery-space operations and is carried by every ship of 400 GT and above and every oil tanker of 150 GT and above; Part II covers cargo and ballast operations and is carried by tankers only. Entries are made under code letters A to I — for example C for collecting and disposing of oil residues (sludge), D for non-automatic discharge or disposal of bilge water, H for bunkering. The officer in charge of the operation signs each entry, the master signs each completed page, and the book stays on board for three years after the last entry.

On tankers the cargo-area rules are different. Outside special areas oily water from cargo tanks may be discharged only more than 50 nautical miles from the nearest land, en route, at no more than 30 litres of oil per nautical mile, with the total not exceeding 1/30,000 of the last cargo for tankers built after 1979, and with the oil discharge monitoring system (ODME) and slop tanks in use. Inside special areas — nothing. Annex I special areas are the Mediterranean, Baltic, Black and Red Seas, the Gulfs area, the Gulf of Aden, North West European waters, the Oman area of the Arabian Sea, Southern South African waters and the Antarctic.

A "magic pipe" — a hose or a spool piece that bypasses the separator — is the classic way seafarers end up in court. In the United States such cases end in multi-million fines for the company and criminal charges for the chief engineer and for anyone who signed false entries. "I was ordered to" is not a defence. The right move is to refuse and report — to the master, the company's DPA or the flag state.

Annex V: what everyone on board must know

Since 2013 Annex V works as a general prohibition: anything not expressly permitted is forbidden. Never overboard: plastics of any kind (synthetic ropes, fishing nets, garbage bags and the ash from burning them included), cooking oil, incinerator ash, domestic and operational waste, electronic waste.

What is permitted outside special areas, with the ship en route and as far from land as practicable:

• food waste comminuted to 25 mm or less — at least 3 nautical miles from land; unground food waste — at least 12 miles;
• cargo residues that are not harmful to the marine environment — at least 12 miles;
• animal carcasses — as far from land as possible.

Inside the Annex V special areas — the Mediterranean, Baltic, Black and Red Seas, the Gulfs area, the North Sea, the Antarctic and the Wider Caribbean — only comminuted food waste may go, and only at 12 miles or more, plus some narrow cases for cargo residues. Within 500 metres of an offshore platform nothing may go except comminuted food waste, and only when the platform is more than 12 miles from land. When garbage of different kinds is mixed, the stricter rule applies to the whole lot.

The Garbage Record Book sorts garbage into categories: A plastics, B food waste, C domestic waste, D cooking oil, E incinerator ash, F operational waste, G animal carcasses, H fishing gear, I e-waste, J cargo residues not harmful to the marine environment, K cargo residues that are harmful. Every discharge, incineration and delivery ashore gets a line: date, time, position, category, estimated volume, signature. The book is kept for two years. Ships of 12 metres and longer display placards; ships of 100 GT and above, or certified to carry 15 persons or more, carry a Garbage Management Plan.

Annexes IV and VI in brief

Sewage. Effluent from an approved treatment plant may be discharged anywhere, provided it leaves no visible floating solids and does not discolour the water. Comminuted and disinfected sewage — at least 3 miles from land. Untreated sewage from a holding tank — at least 12 miles, en route at 4 knots or more and at a moderate rate. The Baltic is a special area with strict rules for passenger ships.

Air. Sulphur in fuel is limited to 0.50% worldwide and 0.10% in emission control areas: the Baltic, the North Sea, the North American and US Caribbean areas, and since 1 May 2025 the Mediterranean. A ship without a scrubber may not even carry non-compliant fuel for its own use. Before entering an ECA the ship changes over to compliant fuel by a written procedure, and the time, position and quantity in each tank are logged. The bunker delivery note stays on board for three years, the MARPOL fuel sample for at least twelve months. NOx Tier III applies in NOx emission control areas to engines on newer ships — from 2016 in North America and the US Caribbean, from 2021 in the North and Baltic Seas.

Certificates and documents port state control asks for

• the IOPP Certificate (Annex I) with its Supplement — Form A for ships other than tankers, Form B for tankers;
• the NLS Certificate (Annex II) on chemical tankers;
• the ISPP Certificate (Annex IV), the IAPP and IEE Certificates (Annex VI), an EIAPP Certificate for each diesel engine over 130 kW;
• the Oil Record Book Parts I and II, the Cargo Record Book, the Garbage Record Book, the ozone-depleting substances record book, the fuel changeover log;
• SOPEP (or SMPEP on ships carrying noxious liquids) on the bridge with an up-to-date contact list, and the pollution-response locker on deck;
• the Garbage Management Plan and the placards.

Most certificates are issued for up to five years and endorsed at annual and intermediate surveys.

What they ask at the interview

The questions depend on the rank, but these come up again and again:

• Engine ratings and junior engineers: how the separator works and what happens when the 15 ppm alarm goes off (the automatic stopping device stops the discharge overboard — usually a three-way valve returns the water to the bilge tank); how you sound the bilge and sludge tanks; who makes entries in the Oil Record Book.
• Chief and second engineers: ORB codes; the sludge balance — what was generated, what was burnt and what went ashore, which port state control compares with the receipts and the incinerator's capacity; the ECA changeover; the ODS record book; what an inspector checks in the engine room.
• Deck officers: garbage rules and special areas, what goes into the Garbage Record Book, what is in SOPEP and how the drill runs; on tankers — the cargo-area discharge criteria and the ODME.
• Everyone: "What will you do if you see a bypass around the separator?" The only right answer: stop, report it to the master and the company's DPA, and refuse to sign a false entry.

Common mistakes

1. Taking 15 ppm to mean "pump anywhere". The ship must be en route, the equipment approved and working, and the Antarctic is closed entirely.
2. "Biodegradable" bags overboard. Plastic is plastic: the ban has no exceptions by type.
3. Food waste close to the coast, or unground in a special area.
4. Correction fluid or torn-out pages in a record book. Strike a wrong entry through with one line, write the correct one and sign it. Missing pages and figures that do not match the tank soundings are the first thing an inspector looks for.
5. Signing an entry for an operation you did not do or did not see.
6. No changeover record at the ECA boundary — time, position and tank quantities have to be there.

Test yourself

Who on board needs this

Everyone — but the engine room most of all: chief engineers, second engineers, third engineers, motormen and oilers. On tankers and chemical tankers the deck officers who run the cargo need Annexes I and II in detail — first of all the chief officer.

Put the environmental training and the engine-room experience into your maritime CV: crewing managers look for both.

Source: MARPOL 73/78, consolidated edition, with the amendments in force at the time of writing. The discharge rules carry conditions not listed here; on board the ship's own plans and the current text of the convention prevail. This page is a study aid, not a legal text.