The conditions that open a machinery space oily mixture discharge and the ones that close it in special areas and the Antarctic (MARPOL Annex I Regulation 15)

Regulation 15 of MARPOL Annex I sets the conditions under which oil and oily mixtures from machinery spaces may go into the sea. The starting point is prohibition. A discharge opens only when every condition overlaps, and depending on the sea area one more condition is added or the discharge is closed altogether.

Remembering this regulation as 15 ppm gets it wrong. 15 ppm is one of five conditions. If the ship was stopped, if the mixture did not pass through the filtering equipment, or if it came from a tanker’s cargo pump room bilges, the discharge is a violation even at 15 ppm.

This article lays the conditions of regulation 15 over each other area by area, then follows the exceptions in regulation 4 and where residues that cannot be discharged have to go.

The starting point is prohibition and a discharge opens only as an exception

1 Subject to the provisions of regulation 4 of this annex and paragraphs 2, 3, and 6 of this regulation, any discharge into the sea of oil or oily mixtures from ships shall be prohibited.

The body of the sentence is shall be prohibited. The proviso in front opens the exceptions: regulation 4 (exceptions), and paragraphs 2 (outside special areas), 3 (inside special areas) and 6 (ships under 400 gross tonnage) of regulation 15. A discharge that fits none of the four is prohibited.

The definition of oily mixture sits in regulation 1.3: a mixture with any oil content. Whatever the oil content, a mixture that contains oil is an oily mixture. So bilge water is inside this regulation from the start.

Outside special areas all five conditions have to be satisfied

2 Any discharge into the sea of oil or oily mixtures from ships of 400 gross tonnage and above shall be prohibited except when all the following conditions are satisfied: .1 the ship is proceeding en route; .2 the oily mixture is processed through an oil filtering equipment meeting the requirements of regulation 14 of this Annex; .3 the oil content of the effluent without dilution does not exceed 15 parts per million; .4 the oily mixture does not originate from cargo pump room bilges on oil tankers; and .5 the oily mixture, in case of oil tankers, is not mixed with oil cargo residues.

It is all the following conditions. If one is missing the discharge is closed.

First, the ship is proceeding en route. A discharge at anchor or while drifting does not open. Second, the mixture passes through oil filtering equipment under regulation 14. Third, 15 ppm without dilution. Lowering the concentration by adding water is blocked in advance by the text. The fourth and fifth apply to oil tankers only. Cargo pump room bilges and mixtures containing cargo residues cannot be discharged under this regulation.

Inside special areas the same five conditions carry one extra equipment requirement

3 Any discharge into the sea of oil or oily mixtures from ships of 400 gross tonnage and above shall be prohibited except when all of the following conditions are satisfied: .2 the oily mixture is processed through an oil filtering equipment meeting the requirements of regulation 14.7 of this Annex;

The five conditions of paragraph 3 sit in the same places and the same order as in paragraph 2. What differs is the second condition alone. Outside, it is regulation 14. Inside, it is regulation 14.7.

7 Oil filtering equipment referred to in paragraph 2 of this regulation shall comply with paragraph 6 of this regulation. In addition, it shall be provided with alarm arrangement to indicate when this level cannot be maintained. The system shall also be provided with arrangements to ensure that any discharge of oily mixtures is automatically stopped when the oil content of the effluent exceeds 15 parts per million.

Equipment under regulation 14.7 carries an alarm and an automatic stop. When 15 ppm is exceeded the equipment stops the discharge before anyone closes a valve. A discharge inside a special area opens only through this equipment.

Condition	Outside special areas (15.2)	Inside special areas (15.3)
Proceeding en route	Required	Required
Filtering equipment	Regulation 14	Regulation 14.7 (alarm and automatic stop)
15 ppm or less without dilution	Required	Required
Not from tanker cargo pump room bilges	Required	Required
Not mixed with tanker cargo residues	Required	Required

Which areas are special areas is settled by regulation 1.11. This edition lists the Mediterranean, the Baltic, the Black Sea, the Red Sea, the Gulfs, the Gulf of Aden, the Antarctic, North West European waters and the Oman area. The list grows by amendment.

In the Antarctic no ship may discharge

4 In respect of the Antarctic area, any discharge into the sea of oil or oily mixtures from any ship shall be prohibited.

There are no conditions. It is any ship and any discharge. No tonnage threshold and no equipment requirement. The Antarctic area is defined in regulation 1.11.7.

5 Nothing in this regulation shall prohibit a ship on a voyage only part of which is in a special area from discharging outside a special area in accordance with paragraphs 2 of this regulation.

A ship whose voyage lies only partly inside a special area may discharge outside the area under the conditions of paragraph 2. The conditions change at the boundary of the area. So the positions at the start and end of a discharge have to stay in the record.

Ships under 400 gross tonnage are covered by a different sentence

6 In the case of a ship of less than 400 gross tonnage, oil and all oily mixtures shall either be retained on board for subsequent discharge to reception facilities or discharged into the sea in accordance with the following provisions : .1 the ship is proceeding en route; .2 the ship has in operation equipment of a design approved by the Administration that ensures that the oil content of the effluent without dilution does not exceed 15 parts per million;

A small ship has two options. Retain on board for reception facilities, or discharge under the conditions. The conditions shrink to four. In place of filtering equipment, equipment of a design approved by the Administration has to be in operation. En route, 15 ppm and the two tanker restrictions stay. The heading of this section covers all areas except the Antarctic, so in the Antarctic a small ship falls under paragraph 4.

Regulation 4 has only three exceptions and damage carries two conditions

Regulations 15 and 34 of this Annex shall not apply to: .1 the discharge into the sea of oil or oily mixture necessary for the purpose of securing the safety of a ship or saving life at sea; or .2 the discharge into the sea of oil or oily mixture resulting from damage to a ship or its equipment: .1 provided that all reasonable precautions have been taken after the occurrence of the damage or discovery of the discharge for the purpose of preventing or minimizing the discharge; and .2 except if the owner or the master acted either with intent to cause damage, or recklessly and with knowledge that damage would probably result; or

The first is a discharge necessary for the safety of the ship or saving life at sea. The second is a discharge resulting from damage. Damage carries two conditions. All reasonable precautions to prevent or minimise the discharge have to have been taken after the damage, and the owner or the master must not have caused the damage with intent or recklessly. The third is the use of oil-containing substances approved by the Administration to combat a pollution incident.

A discharge under an exception is still entered in the Oil Record Book. Regulation 17.3 asks for the circumstances and the reasons.

What cannot be discharged is retained on board for reception facilities

9 The oil residues which cannot be discharged into the sea in compliance with this regulation shall be retained on board for subsequent discharge to reception facilities.

Residues that cannot meet the conditions have one destination. They stay on board for reception facilities. Paragraph 8 blocks circumvention. The discharge must not contain chemicals or other substances introduced to get around the discharge conditions.

7 Whenever visible traces of oil are observed on or below the surface of the water in the immediate vicinity of a ship or its wake, Governments of Parties to the present Convention should, to the extent they are reasonably able to do so, promptly investigate the facts bearing on the issue of whether there has been a violation of the provisions of this regulation.

When traces of oil appear near a ship or in its wake, the Government of a Party investigates. The text also lists what the investigation covers: wind and sea conditions, the track and speed of the ship, other possible sources nearby, and the oil discharge records. The ship can produce the last two. The track and speed come from the voyage records, the discharge records from the Oil Record Book.

Worth confirming

The passages above come from regulations 1, 4, 14 and 15 of the revised Annex I adopted by resolution MEPC.117(52). Resolution MEPC.265(68) later, in taking in the Polar Code, added except in Arctic waters to the title of section A of regulation 15 and and Arctic waters to the title of section C. Paragraph 1.1.1 of part II-A of the Polar Code was also added to the chapeau of regulation 4. Discharge conditions in Arctic waters are settled by the Polar Code and are not covered here.

Which tonnage of ship carries which oil filtering equipment is settled by regulations 14.1 and 14.2. The boundary is 10,000 gross tonnage, but it is not covered here. The list and boundaries of special areas change by amendment and have to be checked in the current consolidated text.

You can consult the cited source documents

These links lead to the official publishers of the documents discussed here. Match the edition and provisions cited in the article, and check subsequent amendments and flag-state implementation before applying them.

• IMO · MEPC.117(52)
• IMO · MEPC.265(68)

Continue with the related operational guidance

• Oil Record Book Part I operations to be entered and the signature and retention rules (MARPOL Annex I Regulation 17)
• PSC ACTION codes, rectification deadlines and how to handle each