For the purposes of Marpol 73/78 Annex I, ‘oil’ means petroleum in any form including crude oil, fuel oil, sludge, oil refuse and refined products (other than petrochemicals which are subject to the provisions of Marpol 73/78 Annex II) and ‘oily mixture’ means a mixture with any oil content.
Excerpts of the relevant provisions of Marpol 73/78 Annex I:
Regulation 9: Control of discharge of oil
Subject to the provisions of Regulations 10 and 11 of this Annex and paragraph 2 of this Regulation, any discharge into the sea of oil or oily mixtures from ships to which this Annex applies shall be prohibited except when all the following conditions are satisfied:
for an oil tanker, except as provided for in subparagraph (b) of this paragraph:
the tanker is not within a special area;
the tanker is more than 50 nautical miles from the nearest land;
the tanker is proceeding en route;
the instantaneous rate of discharge of oil content does not exceed 30 litres per nautical mile;
the total quantity of oil discharged into the sea does not exceed for existing tankers 1/15000 of the total quantity of the particular cargo of which the residue formed a part, and for new tankers 1/30000 of the total quantity of the particular cargo of which the residue formed a part; and
the tanker has in operation an oil discharge monitoring and control system and a slop tank arrangement as required by Regulation 15 of this Annex.
from a ship of 400 tons gross tonnage and above other than an oil tanker and from machinery space bilges excluding cargo pump-room bilges of an oil tanker unless mixed with oil cargo residue:
the ship is not within a special area;
the ship is proceeding en route;
the oil content of the effluent without dilution does not exceed 15 parts per million; and
the ship has in operation (monitoring, control and filtering equipment) as required by regulation 16 of this Annex.
In the case of a ship of less than 400 tons gross tonnage other than an oil tanker whilst outside the special area, the (flag State) Administration shall ensure that it is equipped as far as practicable and reasonable with installations to ensure the storage of oil residues on board and their discharge to reception facilities or into the sea in compliance with the requirements of paragraph (1)(b) of this Regulation.
[…].
The provisions of paragraph 1 of this Regulation shall not apply to the discharge of clean or segregated ballast or unprocessed oily mixtures which without dilution have an oil content not exceeding 15 parts per million and which do not originate from cargo pump-room bilges and are not mixed with oil cargo residues.
No discharge into the sea shall contain chemicals or other substances in quantities or concentrations which are hazardous to the marine environment or chemicals or other substances introduced for the purpose of circumventing the conditions of discharge specified in this regulation.
The oil residues which cannot be discharged into the sea in compliance with paragraphs 1, 2 and 4 of this Regulation shall be retained on board or discharged to reception facilities.
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Regulation 10: Methods for the prevention of oil pollution from ships while operating in special areas
For the purpose of this Annex, the special areas are the Mediterranean Sea area, the Baltic Sea area, the Black Sea area, the Red Sea area, the ‘Gulfs area’, the Gulf of Aden area, the Antarctic area and the North-West European waters, (as further defined and specified).
Subject to the provisions of regulation 11 of this Annex:
Any discharge into the sea of oil or oily mixture from any oil tanker and any ship of 400 tons gross tonnage and above other than an oil tanker shall be prohibited while in a special area. […];
[…] Any discharge into the sea of oil or oily mixture from a ship of less than 400 tons gross tonnage, other than an oil tanker, shall be prohibited while in a special area, except when the oil content of the effluent without dilution does not exceed 15 parts per million.
The provisions of paragraph 2 of this Regulation shall not apply to the discharge of clean or segregated ballast.
The provisions of subparagraph (2)(a) of this regulation shall not apply to the discharge of processed bilge water from machinery spaces, provided that all of the following conditions are satisfied:
the bilge water does not originate from cargo pump-room bilges;
the bilge water is not mixed with oil cargo residues;
the ship is proceeding en route;
the oil content of the effluent without dilution does not exceed 15 parts per million;
the ship has in operation oil filtering equipment complying with Regulation 16(5) of this Annex; and
the filtering system is equipped with a stopping device which will ensure that the discharge is automatically stopped when the oil content of the effluent exceeds 15 parts per million.
No discharge into the sea shall contain chemicals or other substances in quantities or concentrations which are hazardous to the marine environment or chemicals or other substances introduced for the purpose of circumventing the conditions of discharge specified in this regulation.
The oil residues which cannot be discharged into the sea in compliance with paragraph 2 or 3 of this Regulation shall be retained on board or discharged to reception facilities.
Nothing in this Regulation shall prohibit a ship on a voyage only part of which is in a special area from discharging outside the special area in accordance with Regulation 9 of this Annex.
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Regulation 11: Exceptions
Regulations 9 and 10 of this Annex shall not apply to:
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
the discharge into the sea of oil or oily mixture resulting from damage to a ship or its equipment:
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 minimising the discharge; and
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 discharge into the sea of substances containing oil, approved by the (flag State) administration, when being used for the purpose of combating specific pollution incidents in order to minimise the damage from pollution. Any such discharge shall be subject to the approval of any Government in whose jurisdiction it is contemplated the discharge will occur.
Excerpts of the relevant provisions of Marpol 73/78 Annex II:
Regulation 3: Categorisation and listing of noxious liquid substances
For the purpose of the Regulations of this Annex, noxious liquid substances shall be divided into four categories as follows:
Category A: noxious liquid substances which if discharged into the sea from tank cleaning or deballasting operations would present a major hazard to either marine resources or human health or cause serious harm to amenities or other legitimate uses of the sea and therefore justify the application of stringent anti-pollution measures;
Category B: noxious liquid substances which if discharged into the sea from tank cleaning or deballasting operations would present a hazard to either marine resources or human health or cause harm to amenities or other legitimate uses of the sea and therefore justify the application of special anti-pollution measures;
Category C: noxious liquid substances which if discharged into the sea from tank cleaning or deballasting operations would present a minor hazard to either marine resources or human health or cause minor harm to amenities or other legitimate uses of the sea and therefore require special operational conditions;
Category D: noxious liquid substances which if discharged into the sea from tank cleaning or deballasting operations would present a recognisable hazard to either marine resources or human health or cause minimal harm to amenities or other legitimate uses of the sea and therefore require some attention in operational conditions.
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(Further guidelines on the categorisation of substances, including a list of categorised substances are given in Regulation 3(2) to (4) and Regulation 4 and the Appendices to Marpol 73/78 Annex II)
Regulation 5: Discharge of noxious liquid substances
Category A, B and C substances outside special areas and Category D substances in all areas
Subject to the provisions of […] Regulation 6 of this Annex,
The discharge into the sea of substances in Category A as defined in Regulation 3(1)(a) of this Annex or of those provisionally assessed as such or ballast water, tank washings, or other residues or mixtures containing such substances shall be prohibited. If tanks containing such substances or mixtures are to be washed, the resulting residues shall be discharged to a reception facility until the concentration of the substance in the effluent to such facility is at or below 0,1 % by weight and until the tank is empty, with the exception of phosphorus, yellow or white, for which the residual concentration shall be 0,01 % by weight. Any water subsequently added to the tank may be discharged into the sea when all the following conditions are satisfied:
the ship is proceeding en route at a speed of at least 7 knots in the case of self-propelled ships or at least 4 knots in the case of ships which are not self-propelled;
the discharge is made below the waterline, taking into account the location of the seawater intakes; and
the discharge is made at a distance of not less than 12 nautical miles from the nearest land in a depth of water of not less than 25 m.
The discharge into the sea of substances in Category B as defined in Regulation 3(1)(b) of this Annex or of those provisionally assessed as such, or ballast water, tank washings, or other residues or mixtures containing such substances shall be prohibited except when all the following conditions are satisfied:
the ship is proceeding en route at a speed of at least 7 knots in the case of self-propelled ships or at least 4 knots in the case of ships which are not self-propelled;
the procedures and arrangements for discharge are approved by the (flag State) administration. Such procedures and arrangements shall be based upon standards developed by the (IMO) and shall ensure that the concentration and rate of discharge of the effluent is such that the concentration of the substance in the wake astern of the ship does not exceed 1 part per million;
the maximum quantity of cargo discharged from each tank and its associated piping system does not exceed the maximum quantity approved in accordance with the procedures referred to in subparagraph (b) of this paragraph, which shall in no case exceed the greater of 1 m3 or 1/3000 of the tank capacity in m3;
the discharge is made below the waterline, taking into account the location of the seawater intakes; and
the discharge is made at a distance of not less than 12 nautical miles from the nearest land and in a depth of water of not less than 25 m.
The discharge into the sea of substances in Category C as defined in Regulation 3(1)(c) of this Annex or of those provisionally assessed as such, or ballast water, tank washings, or other residues or mixtures containing such substances shall be prohibited except when all the following conditions are satisfied:
the ship is proceeding en route at a speed of at least 7 knots in the case of self-propelled ships or at least 4 knots in the case of ships which are not self-propelled;
the procedures and arrangements for discharge are approved by the (flag State) administration. Such procedures and arrangements shall be based upon standards developed by the (IMO) and shall ensure that the concentration and rate of discharge of the effluent is such that the concentration of the substance in the wake astern of the ship does not exceed 10 parts per million;
the maximum quantity of cargo discharged from each tank and its associated piping system does not exceed the maximum quantity approved in accordance with the procedures referred to in subparagraph (b) of this paragraph, which shall in no case exceed the greater of 3 m3 or 1/1000 of the tank capacity in m3;
the discharge is made below the waterline, taking into account the location of the seawater intakes; and
the discharge is made at a distance of not less than 12 nautical miles from the nearest land and in a depth of water of not less than 25 m.
The discharge into the sea of substances in Category D as defined in Regulation 3(1)(d) of this Annex, or of those provisionally assessed as such, or ballast water, tank washings, or other residues or mixtures containing such substances shall be prohibited except when all the following conditions are satisfied:
the ship is proceeding en route at a speed of at least 7 knots in the case of self-propelled ships or at least 4 knots in the case of ships which are not self-propelled;
such mixtures are of a concentration not greater than one part of the substance in ten parts of water; and
the discharge is made at a distance of not less than 12 nautical miles from the nearest land.
Ventilation procedures approved by the (flag State) administration may be used to remove cargo residues from a tank. Such procedures shall be based upon standards developed by the (IMO). Any water subsequently introduced into the tank shall be regarded as clean and shall not be subject to paragraphs 1, 2, 3 or 4 of this Regulation.
The discharge into the sea of substances which have not been categorised, provisionally assessed, or evaluated as referred to in Regulation 4(1) of this Annex, or of ballast water, tank washings, or other residues or mixtures containing such substances shall be prohibited.
Category A, B and C substances within special areas (as defined in Marpol 73/78 Annex II, Regulation 1, including the Baltic Sea)
Subject to the provisions of […] Regulation 6 of this Annex,
The discharge into the sea of substances in Category A as defined in Regulation 3(1)(a) of this Annex or of those provisionally assessed as such, or ballast water, tank washings, or other residues or mixtures containing such substances shall be prohibited. If tanks containing such substances or mixtures are to be washed, the resulting residues shall be discharged to a reception facility which the States bordering the special area shall provide in accordance with Regulation 7 of this Annex, until the concentration of the substance in the effluent to such facility is at or below 0,05 % by weight and until the tank is empty, with the exception of phosphorus, yellow or white, for which the residual concentration shall be 0,005 % by weight. Any water subsequently added to the tank may be discharged into the sea when all the following conditions are satisfied:
the ship is proceeding en route at a speed of at least 7 knots in the case of self-propelled ships or at least 4 knots in the case of ships which are not self-propelled;
the discharge is made below the waterline, taking into account the location of the seawater intakes; and
the discharge is made at a distance of not less than 12 nautical miles from the nearest land and in a depth of water of not less than 25 m.
The discharge into the sea of substances in Category B as defined in Regulation (3)(1)(b) of this Annex or of those provisionally assessed as such, or ballast water, tank washings, or other residues or mixtures containing such substances shall be prohibited except when all the following conditions are satisfied:
the tank has been prewashed in accordance with the procedure approved by the (flag State) Administration and based on standards developed by the (IMO) and the resulting tank washings have been discharged to a reception facility;
the ship is proceeding en route at a speed of at least 7 knots in the case of self-propelled ships or at least 4 knots in the case of ships which are not self-propelled;
the procedures and arrangements for discharge and washings are approved by the (flag State) Administration. Such procedures and arrangements shall be based upon standards developed by the (IMO) and shall ensure that the concentration and rate of discharge of the effluent is such that the concentration of the substance in the wake astern of the ship does not exceed 1 part per million;
the discharge is made below the waterline, taking into account the location of the seawater intakes; and
the discharge is made at a distance of not less than 12 nautical miles from the nearest land and in a depth of water of not less than 25 m.
The discharge into the sea of substances in Category C as defined in Regulation 3(1)(c) of this Annex or of those provisionally assessed as such, or ballast water, tank washings, or other residues or mixtures containing such substances shall be prohibited except when all the following conditions are satisfied:
the ship is proceeding en route at a speed of at least 7 knots in the case of self-propelled ships or at least 4 knots in the case of ships which are not self-propelled;
the procedures and arrangements for discharge are approved by the (flag State) administration. Such procedures and arrangements shall be based upon standards developed by the (IMO) and shall ensure that the concentration and rate of discharge of the effluent is such that the concentration of the substance in the wake astern of the ship does not exceed 1 part per million;
the maximum quantity of cargo discharged from each tank and its associated piping system does not exceed the maximum quantity approved in accordance with the procedures referred to in subparagraph (b) of this paragraph which shall in no case exceed the greater of 1 m3 or 1/3000 of the tank capacity in m3;
the discharge is made below the waterline, taking into account the location of the seawater intakes; and
the discharge is made at a distance of not less than 12 nautical miles from the nearest land and in a depth of water of not less than 25 m.
Ventilation procedures approved by the (flag State) administration may be used to remove cargo residues from a tank. Such procedures shall be based upon standards developed by the (IMO). Any water subsequently introduced into the tank shall be regarded as clean and shall not be subject to paragraphs 7, 8 or 9 of this Regulation.
The discharge into the sea of substances which have not been categorised, provisionally assessed or evaluated as referred to in Regulation 4(1) of this Annex, or of ballast water, tank washings, or other residues or mixtures containing such substances shall be prohibited.
Nothing in this regulation shall prohibit a ship from retaining on board the residues from a Category B or C cargo and discharging such residues into the sea outside a special area in accordance with paragraphs 2 or 3 of this Regulation, respectively.
Regulation 6: Exceptions
Regulation 5 of this Annex shall not apply to:
the discharge into the sea of noxious liquid substances or mixtures containing such substances necessary for the purpose of securing the safety of a ship or saving life at sea; or
the discharge into the sea of noxious liquid substances or mixtures containing such substances resulting from damage to a ship or its equipment:
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 minimising the discharge; and
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 discharge into the sea of noxious liquid substances or mixtures containing such substances, approved by the (flag State) administration, when being used for the purpose of combating specific pollution incidents in order to minimise the damage from pollution. Any such discharge shall be subject to the approval of any government in whose jurisdiction it is contemplated the discharge will occur.