When You May Discharge — MARPOL Annex I Limits, Distances and Special Areas

1. The general principle

The regulation does not ban discharging bilge water. It bans discharging oily bilge water in the wrong place. Three things therefore have to be true at the same time before a discharge is lawful:

• The effluent has to be clean enough — the oil content has to be within the limit for the area the ship is in.
• The ship has to be in the right place — on passage, and far enough from land.
• The equipment has to be working and monitoring — the separator or filter has to be in use, and the oil discharge monitoring and control system has to be in use with it.

Remove any one of the three and the discharge is illegal, however good the separator is.

2. Machinery space bilges, outside a Special Area

For ships of 400 gross tonnage and above, machinery space bilges may be discharged provided all five of the following apply:

1. The oil content in the bilge discharge is not more than 100 p.p.m.
2. That figure is achieved by an oily water separator, or a filtering system, with discharge monitoring and control.
3. The ship is on passage.
4. The ship is at least 12 nautical miles from land.
5. The ship is not within a Special Area.

All five, together. "On passage" is a real requirement and not a formality — the ship has to be actually proceeding, not manoeuvring in port or lying at anchor.

3. Inside a Special Area, and the band within 12 miles

Within a Special Area, discharge is permitted only when the ship has an oily water separator or filtering system capable of reducing the oil content below 15 p.p.m., and that equipment is in use, and monitoring and control equipment with an alarm and an automatic stopping device is fitted and in use. The extra 15 p.p.m. capability and the automatic stopping device are what distinguish a Special Area from anywhere else.

Within 12 nautical miles of land but outside a Special Area, the same conditions apply — separator or filter, on passage, monitoring in use — except that the alarm and the automatic stopping device are not mandatory. The distinction is worth holding on to, because it is a favourite follow-up question.

Ships under 400 gross tonnage are treated less stringently. Ships over 10,000 gross tonnage, and certain other categories, are treated more strictly. The exact treatment depends on the flag administration, so the applicable M Notice is the authority.

The Special Areas

The Special Areas under Annex I are the Black Sea, the Red Sea, the Mediterranean Sea, the Persian Gulf Area, the Gulf of Aden, the Antarctic Sea, the North Sea, the Wider Caribbean Sea and the Baltic Sea.

4. Cargo and ballast residue from a tanker

Oil cargo residue from a tanker may be discharged only if every one of the following is satisfied:

• the ship is not in a Special Area;
• the ship is more than 50 nautical miles from land;
• the ship is on passage;
• the instantaneous rate of discharge is not more than 60 litres per nautical mile;
• the total quantity discharged is not more than 1/30,000 of the particular cargo carried — the older figure of 1/15,000 still applies to vessels built before the change.

Note the two different distance figures. Machinery space bilges are governed by the 12 mile line. Tanker cargo residue is governed by the 50 mile line. Confusing the two is a common slip.

5. The summary tables — memorise both

Machinery space bilges and ballast tanks:

Tanker cargo slops: more than 50 nautical miles from land, vessel en route, instantaneous rate less than 30 litres per nautical mile, total 1/30,000 of the cargo, with an operating oil separator, a slop tank and an oil discharge monitor.

Reading the two tables — they disagree with the text above, and here is why

The summary tables are the compressed form that is usually quoted, and the compression loses a distinction that sections 2 and 3 above keep. Two figures in particular need care:

• The 15 p.p.m. row in the bilge table is the equipment capability standard, not the operational limit. The plant must be capable of 15 p.p.m. — that is the requirement on the separator and filter as built, and it is what section 1 of this set states. The discharge limit that applies outside a Special Area, beyond 12 miles, is 100 p.p.m., as section 2 above says. So the table's "less than 15 p.p.m." in both columns is a statement about what the machinery must be able to do, and section 2's 100 p.p.m. is a statement about what may go overboard. Both are correct; they answer different questions. Where the two are confused, the safe reading is the stricter one — 15 p.p.m.
• The tanker rate is quoted as 30 litres per nautical mile in the table and 60 in section 4. The 60 litres per nautical mile figure is the one to carry, because it is the one the Annex I discharge criteria state for cargo residue. The 30 litres figure appears in older summaries. If the question is asked, give 60 and note the older figure exists.

The general point is worth remembering: a summary table is a memory aid, not the regulation. When a figure in the table and a figure in the text differ, the text is the more complete statement, and the M Notice in force is the authority over both.

6. The Oil Record Book

The Oil Record Book is the legal record of everything that goes overboard and everything that does not. For machinery space operations it is kept by the engine room department, and it is required on all ships of 400 tons and above.

The items logged are:

1. ballasting and cleaning of oil fuel tanks;
2. discharge of dirty ballast or cleaning water;
3. disposal of sludge or oil residue;
4. discharge or disposal of bilges;
5. automatic bilge discharge;
6. failure of the oil discharge monitoring and control system, with details;
7. oil discharges, whether accidental or exceptional.

Every discharge through the separator is recorded with the quantity, the time and the ship's position, and signed by the operating officer, the Chief Engineer and the Master. A discharge made in a prohibited zone requires the quantity, source, time, position and date, signed by the Master and the Chief Engineer. The signature block is not a formality — it is the point at which responsibility is fixed on named individuals.

What is kept with the book, and what is displayed on the machine

Attached to the Oil Record Book, and displayed on the oily water separator itself:

• a photocopy of the MARPOL certificate;
• the original certificates for oil disposal to shore;
• the dirty oil and sludge piping diagram;
• the USCG warning notice — this one is displayed on the oily water separator itself, not merely filed.

What the IOPP renewal survey checks

At renewal of the IOPP Certificate the surveyor will look at the validity of the certificate, the separator and its piping system, the alarm test and the 15 p.p.m. stopping device, all valves in good order, filter element spares carried on board, and the USCG notice in place. The spares requirement catches people out — a spare coalescer element is a survey item.