MARPOL Annex I Regs. 12, 14, 15, 17, 31 & 34 · IMO Res. MEPC.107(49) & MEPC.108(49)
Oily Water Separator (OWS 15 ppm), ODME & MARPOL Annex I Compliance Guide
Oily Water Separator (OWS 15 ppm) and Oil Record Book Part I / Part II compliance under MARPOL Annex I (Regulations 12, 14, 15, 17, 31, 34 & 36) and IMO Resolutions MEPC.107(49) & MEPC.108(49) is one of the highest-consequence enforcement areas in maritime operations — carrying both immediate Port State Control Action Code 30 detention under IMO Resolution A.1206(34) and criminal prosecution for logbook or piping discrepancies.
Complementing our Oil Record Book & Garbage Record Book Guide and USCG Port State Control Checklist, this guide covers MEPC.107(49) 15 ppm Bilge Separator & 18-month alarm memory checks, 5-year calibration rules, sludge/bilge mass-balance reconciliation, and oil tanker ODME (`30 L/nm` & `1/30,000`) discharge limits.
Updated · Written by SeaReady in our own words. Not affiliated with OCIMF, RightShip, CDI, any MoU or any administration — always check the current official documents.
1. MARPOL Annex I Statutory Baseline: 15 ppm OWS, Sludge Piping & Tanker ODME
Every ship of 400 GT and above must hold a valid International Oil Pollution Prevention (IOPP) Certificate (Form A for non-tankers; Form B for oil tankers) and comply with the machinery-space and cargo-area discharge controls of MARPOL Annex I:
| MARPOL Annex I System & Regulation | Statutory Limit / Technical Standard | Operational & PSC Verification |
|---|---|---|
| 15 ppm Oily Water Separator & Bilge Alarm (MARPOL Annex I Reg. 14 & IMO Res. MEPC.107(49)) | Effluent ≤ 15 ppm oil content; automatic 3-way stopping device (Reg. 14.7 for ≥ 10,000 GT) | Under MARPOL Annex I Regulation 14 and IMO Resolution MEPC.107(49), machinery-space bilge discharges must pass through type-approved 15 ppm oil filtering equipment. Any effluent exceeding 15 ppm must trigger an audible/visual alarm and automatically actuate the 3-way recirculation valve returning discharge to the bilge/holding tank. |
| MEPC.107(49) 15 ppm Bilge Alarm 18-Month Memory & 5-Year Calibration (§ 4.2.9 & § 4.2.11) | 18-month electronic memory (date, time, alarm status & operating status); ≤ 5-year maker calibration | Under MEPC.107(49) § 4.2.9, the 15 ppm Bilge Alarm must record date, time, alarm status, and operating status of the 15 ppm Bilge Separator and retain those records electronically for at least 18 months for official inspection. Under § 4.2.11, the alarm accuracy (within ± 5 ppm) must be checked at IOPP renewal surveys by the manufacturer or an authorised person, or replaced with a calibrated unit (calibration certificate valid ≤ 5 years). |
| Four En-Route Bilge Discharge Conditions (MARPOL Annex I Reg. 15.2 & 15.3) | Proceeding en route · Approved Reg. 14 OWS in operation · ≤ 15 ppm · No cargo oil / chemical admixture | Outside Special Areas (Reg. 15.2) and inside Special Areas (Reg. 15.3, except Antarctic Area & Arctic Polar Code waters where any oil/oily mixture discharge is strictly prohibited under Reg. 15.4 & Polar Code Part II-A § 1.1.1), bilge water may only be discharged when the ship is proceeding en route, through approved 15 ppm equipment with automatic stopping device in operation, with oil content ≤ 15 ppm. |
| Oil Residue (Sludge) Tanks & Standard Discharge Connection (MARPOL Annex I Regs. 12 & 13) | No direct overboard connection from sludge tanks (Reg. 12.2.2); 215 mm OD / 6-bolt standard flange (Reg. 13) | Sludge tanks must have no discharge connections to the bilge system, oily bilge water holding tank, tank top, or oily water separator (amendments in MEPC.187(59) / Reg. 12.3), except through approved settled-water drains or common shore-discharge piping fitted with screw-down non-return valves to the 215 mm OD standard discharge flange (Reg. 13). |
| Oil Tanker ODME & Cargo-Area Discharge Rules (MARPOL Annex I Reg. 31, Reg. 34 & IMO Res. MEPC.108(49)) | Outside Special Areas · > 50 nm from land · En route · ≤ 30 L/nm instantaneous rate · ≤ 1/30,000 total cargo | On oil tankers ≥ 150 GT, cargo-area oily mixtures may only be discharged through an approved Oil Discharge Monitoring and Control System (ODME, Res. MEPC.108(49)) when: (1) outside a Special Area; (2) > 50 nautical miles from the nearest land; (3) proceeding en route; (4) instantaneous rate of discharge of oil content ≤ 30 litres per nautical mile; and (5) total quantity discharged ≤ 1/30,000 of the total particular cargo of which the residue formed a part. |
2. Oil Record Book Part I Mass-Balance & 18-Month Memory Cross-Check
Port State Control officers and vetting inspectors do not simply read Oil Record Book entries in isolation — they run a four-way cross-check between ORB Part I, the MEPC.107(49) 18-month electronic memory, the Deck Log Book, and the IOPP Supplement:
| Audit Check / ORB Code | Data Cross-Referenced | How Inspectors Catch Discrepancies |
|---|---|---|
| Code C.11 — Weekly Inventory of Oil Residue (Sludge) Tanks (MARPOL Annex I Reg. 17 & MEPC.1/Circ.736/Rev.2) | Tank identity, capacity (m³), total capacity & weekly retained volume (m³) | Inspectors calculate daily sludge generation (typically 0.8%–1.5% of HFO/VLSFO consumed by purifiers and filters) and compare it against weekly Code C.11 soundings, Code C.12.1 shore disposals, Code C.12.2 incineration, and Code C.12.3 evaporation. |
| Code D.13 / D.14 / D.15.1 — Bilge Water Discharge Through 15 ppm Equipment | Start/stop times, start/stop GPS positions (Lat/Long), quantity discharged (m³) & pump rated capacity (m³/h) | PSCOs divide the volume logged in Code D by the elapsed pumping time and compare it against the OWS nameplate capacity (e.g., 1.0 m³/h, 2.5 m³/h, or 5.0 m³/h) and the MEPC.107(49) 18-month electronic memory log. Logging 4.0 m³ discharged in 1 hour on a 2.5 m³/h separator triggers an immediate MARPOL investigation. |
| Overboard Discharge Valve Seal, Lock & Warning Sign | Numbered tamper-evident seal + padlock in SMS Seal Register; start/stop GPS cross-checked with Deck Log Book | The OWS overboard valve (and emergency bilge suction valves) must be padlocked/sealed shut in port and at sea when not in use, with the seal number recorded in the Engine Log Book and Seal Register. Every Code D discharge window must show the vessel proceeding en route in the Deck Log Book. |
| Voluntary Seal / Blank Flange on Sludge-to-Bilge or Overboard Lines | Zero unauthorised flexible hoses, spool pieces, or fresh-water trickling connections at the 15 ppm sample line | PSCOs and USCG environmental auditors inspect the OWS coalescer/filter housing, sample-water flush valves, and surrounding deck plates for fresh paint, loose wrench marks on blank flanges, or clean-water bypass lines that dilute the sample cell. |
3. Step-by-Step Pre-Arrival Engine-Room OWS & ODME Operational Test
Before every port arrival and PSC/vetting window, the Chief Engineer and Second Engineer should execute and log a five-point operational verification:
- Step 1 — Operational recirculation test of the 15 ppm Bilge Separator: Run the OWS in recirculation mode (returning to the bilge holding tank, with the overboard valve locked shut) and verify normal operating pressure, differential pressure across the coalescer/emulsion-breaking stages, and clear effluent at the test cock.
- Step 2 — 15 ppm Bilge Alarm & 3-way automatic stopping device test: Simulate a > 15 ppm oil-content condition on the MEPC.107(49) Bilge Alarm. Confirm that the visual and audible alarms activate within the required response time and that the pneumatic/solenoid 3-way valve immediately diverts flow back to the bilge holding tank and stops the pump.
- Step 3 — 18-month memory & 5-year calibration check: Verify that the internal clock (UTC) on the 15 ppm Bilge Alarm matches the ship’s UTC clock, inspect the 18-month electronic log to ensure every test and overboard operation matches ORB Part I (Code D / Code I), and check that the 15 ppm measuring cell calibration certificate is < 5 years old with its factory seal intact.
- Step 4 — Sludge pump, incinerator & standard discharge flange check: Verify that the sludge transfer pump and waste oil incinerator operate normally (or that any defective equipment is logged under ORB Code I with a class/Flag dispensation and spare-parts requisition), and confirm the 215 mm OD standard discharge flange (Reg. 13) is stowed at the bunker station.
- Step 5 — Oil tanker ODME (MEPC.108(49)) functional simulation: On oil tankers, run the pre-arrival ODME self-test from the Cargo Control Room, verifying GPS speed input, flow-meter zero, oil-content meter fresh-water zero/calibration, and automatic closure of the overboard discharge valve and opening of the slop-tank return valve when the 30 L/nm or 1/30,000 limit is exceeded.
Questions seafarers ask
What does a Port State Control officer check inside the MEPC.107(49) 15 ppm Bilge Alarm electronic memory?
Under IMO Resolution MEPC.107(49) § 4.2.9, the 15 ppm Bilge Alarm electronically logs the date, time, alarm condition (> 15 ppm or ≤ 15 ppm), and operating status of the 15 ppm Bilge Separator for at least 18 months. During a PSC inspection, the officer asks the Chief or Second Engineer to scroll through the memory log and compares the exact timestamps against every Code D entry in Oil Record Book Part I. If the memory shows the separator running without a corresponding ORB entry, or shows an ORB Code D entry at a time when the separator was not running or was in > 15 ppm alarm state, it is treated as evidence of illegal discharge or falsified records (Action Code 30 detention).
How long is a 15 ppm Bilge Alarm calibration certificate valid under MEPC.107(49)?
Under IMO Resolution MEPC.107(49) § 4.2.11, the accuracy of the 15 ppm Bilge Alarm (within ± 5 ppm) must be checked at IOPP Certificate renewal surveys according to the manufacturer’s instructions. Alternatively, the unit may be replaced by a calibrated 15 ppm Bilge Alarm. The calibration certificate for the 15 ppm Bilge Alarm is checked at every IOPP survey and is valid for a maximum of 5 years from the date of calibration, and the tamper-evident seal on the measuring cell must remain unbroken.
Are machinery-space bilge discharges permitted in the Antarctic Area or Polar Code Arctic waters?
No. Under MARPOL Annex I Regulation 15.4 and Part II-A § 1.1.1 of the International Code for Ships Operating in Polar Waters (Polar Code, IMO Resolution MEPC.264(68)), any discharge into the sea of oil or oily mixtures from any ship is strictly prohibited in the Antarctic Area (south of 60°S) and in Arctic waters. All oily bilge water and oil residues (sludge) must be retained on board in holding tanks until discharged to port reception facilities outside polar waters.
What are the MARPOL Annex I Regulation 34 and MEPC.108(49) ODME requirements on oil tankers?
Under MARPOL Annex I Regulation 31 and Regulation 34 and IMO Resolution MEPC.108(49), oil tankers of 150 GT and above must be fitted with an approved Oil Discharge Monitoring and Control System (ODME) incorporating a GPS input (speed and position), flow meter, oil content meter, and automatic overboard stop/slop-recirculation valve interlock. Decanted slop water may only be discharged when the tanker is outside a Special Area, more than 50 nautical miles from the nearest land, proceeding en route, at an instantaneous rate of oil content not exceeding 30 litres per nautical mile, and with total oil discharged not exceeding 1/30,000 of the total previous cargo. ODME printouts/electronic logs must be retained on board for at least 3 years (Reg. 31.2).
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