MARPOL Annex I — Prevention of Pollution by Oil

1. Application, IOPP Certificate & Key Regulations

MARPOL Annex I: Regulations for the Prevention of Pollution by Oil applies to all ships. It sets requirements for machinery spaces and tanker cargo areas:

• Regulatory Structure: 7 Ch / 39 Regs
• IOPP Certificate Validity: 5 Years
• Machinery Threshold (Tanker ≥ 150 GT): ≥ 400 GT

Chapter 3: Machinery Space Regulations

• Reg 12: Oil residue (sludge) tanks
• Reg 13: Standard discharge connection
• Reg 14: Oil filtering equipment (15 ppm OWS)
• Reg 15: Control of operational bilge discharge
• Reg 16: Segregation of oil/ballast and forepeak oil carriage ban
• Reg 17: Oil Record Book Part 1.

Chapter 4: Tanker Cargo Area Regulations

• Reg 18: Segregated Ballast Tanks (SBT) protective location
• Reg 29: Cargo slop tank arrangements
• Reg 31: Oil Discharge Monitoring & Control System (ODMCS)
• Reg 34: Tanker cargo discharge criteria
• Reg 35: Crude Oil Washing (COW)
• Reg 36: Oil Record Book Part 2.

Chapter 5: Oil Pollution Incident Response

Reg 37: Shipboard Oil Pollution Emergency Plan (SOPEP) mandatory on every oil tanker ≥ 150 GT and every other ship ≥ 400 GT, approved by the Administration with reporting and coordination protocols.

Statutory IOPP Survey Cadence

• Initial: Before entering service
• Annual: Within ±3 months of anniversary
• Intermediate: Within ±3 months of 2nd or 3rd anniversary (extended checks on OWS, ODMCS, COW)
• Renewal: Every 5 years max.

2. Oil Filtering Equipment & Standard Discharge Connection

Two essential technical installations under Regulations 13 and 14 ensure oily residues are either cleaned to legal limits or transferred to shore reception facilities:

1. Oil Filtering Equipment (Regulation 14)

Any vessel of 400 GT and above must be equipped with approved oily water separating / filtering equipment. The unit must feature an audible/visual bilge alarm and an automatic fail-safe stop valve that instantly halts sea discharge if the effluent exceeds 15 parts per million (ppm).

2. Fail-Safe 3-Way Diverter Valve

Upon detection of >15 ppm oil content, loss of electrical power, or sample water failure, the spring-loaded pneumatic diverter valve automatically trips closed to overboard and directs the oily stream back to the bilge holding tank.

3. Standard Discharge Connection (Regulation 13)

To enable universal coupling with port reception facilities worldwide, the sludge and bilge manifold discharge pipelines must be fitted with an international standard flange of uniform dimensions, suitable for up to 125 mm inner pipe diameter at 600 kPa (6 bar).

4. Oil-Proof Gasket & Slotted Bolt Holes

The flange has six open slots extending to the outer periphery to facilitate rapid alignment with shore hoses, clamped with six 20 mm bolts and sealed with an oil-proof aramid/nitrile gasket.

Standard Discharge Flange Statutory Dimensions (SOLAS / MARPOL Reg 13):

OWS Regulation 14: 15 ppm filtering equipment

MARPOL Annex I Regulation 14 and IMO Resolution MEPC.107(49) set the type-approval and operational framework for machinery-space oil-filtering equipment. The ship must use equipment appropriate to its certification and approved arrangement; check the IOPP Certificate supplement and the maker's manuals for the installed plant and its limits.

What the OWS must do

• Separate and filter the oily mixture through the approved stages at the rated conditions. A fine stable emulsion, cleaning chemicals, detergents, excess flow or damaged elements can make compliant separation impossible.
• Measure the discharge stream with the approved 15 ppm bilge alarm/oil-content monitor. The reading is taken from the equipment's representative sample arrangement; never dilute a sample or alter the sample path to mask oil content.
• Prevent an unlawful discharge: the associated automatic stopping/diverting arrangement must stop or return the flow when the oil content exceeds the permitted level. Alarm, automatic stop and any required recorder must remain available and correctly configured during operation.
• Operate only within approval: use the ship's approved piping, flow rate, calibration/test procedure and maintenance schedule. Confirm type-approval plate, certificate and local operating restrictions.

The statutory 15 ppm equipment limit does not by itself authorize an overboard discharge. The separate Annex I discharge conditions (en route, correct source, approved equipment in operation and no dilution) must also be satisfied. For legal limits see Annex I discharge criteria; for the fail-safe valve response see automatic stopping and diversion.

Reference: IMO — Machinery Space Bilges of Ships (MEPC.107(49)).

OWS automatic stopping and fail-safe diversion

The automatic stopping arrangement protects the sea connection when the monitor detects excessive oil content. The valve arrangement varies by approved maker and ship piping: it may divert the effluent to a bilge/holding tank, stop the pump, close the overboard path, or combine these actions. Follow the actual P&ID and approved manual rather than assuming every installation has the same valve logic.

1. Normal route: the sample monitor reads the treated discharge. Only when the approved system is healthy and the oil-content condition permits discharge can the approved arrangement keep the sea route available, subject to all MARPOL discharge criteria.
2. High reading: at or above the approved alarm trip setting (15 ppm maximum limit for the relevant equipment), the alarm operates and the automatic stopping device prevents further overboard flow by diverting or stopping it.
3. Fault condition: loss of monitor power, sample flow, invalid signal or a detected fault must be handled according to the equipment's approved fail-safe design and maker's instructions; the operator must not bypass the monitor or hold the sea valve open to continue discharge.
4. After a trip: verify the alarm, check the receiving bilge/holding capacity, investigate emulsions, flow rate, filter condition and sample-water faults, and confirm the correct valve position. Resume only after the cause is corrected and the approved test shows the protective function is available.

During survey, the key points are the approved monitor and alarm, automatic stopping function, sample line, overboard/diverting valve indication, test records and consistency with the ship's operating procedure. Type-approved arrangements and relay delays differ; consult the installed manual for timing and terminal-by-terminal logic.

Reference: IMO MEPC.107(49) — Guidelines and Specifications for Pollution Prevention Equipment for Machinery Space Bilges.

3. Control of Discharge of Oil: Criteria

Surveyors rigorously test the legal criteria governing oil discharges, distinguishing sharply between machinery-space bilges and tanker cargo spaces:

1. Machinery-Space Bilges (All Ships ≥ 400 GT — Regulation 15):

1. En Route

The ship must be proceeding en route under its own propulsion (never stationary, at anchor, or drifting in port).

2. Approved 15 ppm OWS

The oily mixture must be continuously processed through type-approved oil filtering equipment conforming to IMO Resolution MEPC.107(49).

3. No Dilution ≤ 15 ppm

The oil content of the effluent without artificial dilution must not exceed 15 parts per million, monitored by an active bilge alarm.

4. Origin & Cargo Residue Exclusion

The oily mixture must not originate from cargo pump-room bilges on oil tankers, and must not be mixed with oil cargo residues.

2. Tanker Cargo Operations (Regulation 34):

Outside Special Areas

• Vessel proceeding en route
• Distance > 50 nautical miles from nearest land
• Instantaneous discharge rate ≤ 30 litres per nautical mile
• Total quantity discharged ≤ 1/30,000 of total cargo for new tankers (1/15,000 for existing tankers)
• Operational ODMCS and approved slop tank arrangement.

Inside Special Areas & Antarctic

Inside any designated Special Area: Any discharge of tanker cargo oil residue is STRICTLY PROHIBITED — all slops and washings must be retained on board for discharge to shore reception facilities. In the Antarctic area: ALL discharges whatsoever are prohibited.

4. Oil Record Book, SOPEP & Special Areas

MARPOL Annex I demands meticulous operational accountability through the Oil Record Book, emergency preparedness via SOPEP, and zero-discharge compliance in designated Special Areas:

Part I (machinery operations) is required for oil tankers ≥150 GT and other ships ≥400 GT. Part II (cargo operations) is required for oil tankers ≥150 GT.

Oil Record Book Part 1 — Mandatory Letter Codes (Surveyor Recital):

Code A & B: Fuel Tanks

• Code A: Ballasting or cleaning of oil fuel tanks
• Code B: Discharge of dirty ballast or cleaning water from oil fuel tanks.

Code C: Sludge & Residues

Collection & disposal of oil residues (sludge): record the retained quantity at the required interval (at voyage end, but not more frequently than weekly; weekly on short voyages) and record each disposal/transfer operation using the applicable Code C item.

Code D & E: Bilge Operations

• Code D: Non-automatic discharge overboard or disposal of bilge water
• Code E: Automatic discharge overboard via 15 ppm OWS (stop/start times and vessel positions).

Code F, G, H & I: Equipment, events and remarks

• Code F: oil-filtering equipment condition/failure
• Code G: accidental or exceptional discharge
• Code H: fuel or bulk lubricating-oil bunkering
• Code I: additional operational procedures and general remarks.

Master Signature Rule

Each operational entry must be signed and dated by the officer in charge upon completion. Each completed page must be signed by the Master. The book must be retained on board for 3 years after the last entry.

SOPEP (Regulation 37) & Oil Spill Response Equipment Readiness:

MARPOL Annex I Regulation 37 requires every oil tanker of 150 GT and above and every ship other than an oil tanker of 400 GT and above to carry an Administration-approved Shipboard Oil Pollution Emergency Plan (SOPEP). The plan must be written in the working language of the Master and officers and updated whenever contact lists change.

Four Mandatory Core Sections of SOPEP

• 1. Coastal State Reporting: Immediate reporting protocol for actual or probable oil discharge to nearest Coastal State radio station / MRCC using IMO standard format.
• 2. Contact Directory: Updated 24/7 contacts for Flag Administration, coastal agencies, managing company / DPA, P&I Club correspondent, and local spill contractors.
• 3. Shipboard Mitigation Actions: Operational steps to stop/minimize outflow: emergency shutdown, scupper sealing, list/trim ballast adjustments, internal fuel transfer.
• 4. Port & National Coordination: Clear lines of authority coordinating with port authorities, clean-up contractors, and handling public/media relations (Master/Company only).

Dedicated SOPEP Locker Equipment Inventory

• Containment & Recovery Equipment: Hydrophobic absorbent pads and rolls (absorbs oil, repels water), absorbent containment booms, loose sorbent granules / sawdust.
• Pumping & Transfer: Air-operated portable diaphragm pump (Wilden pump) with anti-static earth bonding wire, suction/discharge hoses.
• Tools & Storage: Non-sparking bronze / plastic shovels, scoops, heavy-duty rubber buckets, mechanical rubber expansion scupper plugs, 200 L steel recovery drums labeled "OILY WASTE".
• PPE: Chemical suits, nitrile gloves, safety goggles, and organic vapor respirators.

Immediate Operational Steps in Case of Shipboard Oil Spill:

1. Stop Oil Transfer Immediately: Sound the emergency alarm, hit the emergency stop button on fuel transfer pumps / bunkering manifold, and close all manifold and tank valves.
2. Notify Bridge & Chief Engineer: Report location, source, and estimated magnitude of spill.
3. Prevent Overboard Discharge: Verify that all deck scuppers are sealed. If oil threatens to overtop fish plates or coamings, deploy sorbent booms and pads immediately to contain oil on deck.
4. Rig SOPEP Wilden Pump: Connect the air-operated diaphragm pump to deck service air and bond the static ground wire to the ship's hull. Pump contained oil from savealls and drip trays back into an overflow or designated bunker tank.
5. Mitigate Outflow (Damage/Grounding): If hull is ruptured, transfer oil internally from the damaged tank to empty or slack double bottom / wing tanks. Counter-ballast to alter list or trim and bring the damaged fracture above the waterline.
6. Statutory Notifications: Master immediately transmits formal SOPEP initial report to the nearest Coastal State authority, Port Master, DPA, and P&I representative.

The 10 Special Areas Under MARPOL Annex I:

European & Mediterranean

• 1. Mediterranean Sea
• 2. Baltic Sea
• 3. Black Sea
• 4. North West European Waters (including North Sea, English Channel, Irish Sea, Celtic Sea).

Middle East, Africa & Polar

• 5. Red Sea
• 6. Gulfs Area
• 7. Gulf of Aden
• 8. Oman Area of the Arabian Sea
• 9. Southern South African Waters
• 10. Antarctic Area (all discharges prohibited).

Oil Record Book Part I — Codes A to I

Part I records machinery-space oil operations. Use the code and item number from the current Administration-issued book, enter the required particulars chronologically, sign for the completed operation, and have the Master countersign each completed page. The code describes the operation; it does not make an otherwise prohibited discharge lawful.