Maritime Academy
Oily Water Separator — OWS
A 15 ppm reading alone is not permission to discharge: verify location, waste source, equipment and evidence together.
Focus: machinery-space bilges on ships of 400 GT and above. Tanker cargo wastes have separate provisions.
Your action sequence at a glance
Identify source
Verify location and rule
Check equipment/procedure
Reconcile operation/records
MASTER • RESPONSIBLE OFFICER • COMPANY
Start with these 6 checks
- Identify waste source and vessel applicability.
- Verify location, en-route status and local/polar restrictions.
- Compare IOPP supplement, approved equipment and vessel procedure.
- Check sample/alarm/automatic-stop functions by authorised procedure.
- If any condition fails, retain and use the reception/repair plan.
- Reconcile time, position, quantities and ORB/equipment records.
Educational checklist. Completion is not operational/compliance approval; use the relevant vessel permits/forms separately.
Documents to have available
Select a document card for guidance. Obtain vessel-specific documents from authorised company/ship systems. A reference link is not a document download.
IOPP and equipment supplement
Open the vessel IOPP and equipment supplement in the certificate file; compare ship and equipment identities.
Open topic references and guidance →OWS/OCM manual and approved piping drawing
Obtain the installed OWS/OCM model manual and approved piping drawing from controlled technical files.
Open topic references and guidance →ORB Part I and tank records
Match the vessel ORB Part I and tank records to the relevant dates and operations; public examples are not ship records.
Open topic references and guidance →Flag/port instructions and waste receipts
Retrieve voyage-specific flag/port instructions and waste receipts from company and ship records.
Open topic references and guidance →Open rules and technical detail
1 · Check the legal conditions first
Annex I regulation 15 combines proceeding en route, compliant filtering equipment and oil content not exceeding 15 ppm without dilution. Do not treat tanker cargo-pump-room bilges or cargo-oil residues as routine machinery bilge water. Use the current consolidated text and flag instructions.
Reference: IMO — Revised MARPOL Annex I: regulations 14, 15, 17 ↗2 · Where may it operate?
Running equipment for recirculation/testing is different from authorising overboard discharge. Check port, terminal, coastal-state, special-area and polar restrictions separately. The Antarctic and applicable Arctic Polar Code prohibitions are not overcome by 15 ppm. If permission is uncertain, retain onboard and plan reception facilities.
Reference: IMO — Polar Code ↗3 · Verify equipment under maker procedures
Use approved drawings/manuals. Verify representative OCM sample flow, alarm, automatic stop/diversion and fail-safe arrangements by authorised procedures. Never substitute clean water for the sample or bypass the system to discharge. Stop and seek technical assessment on faults or emulsion problems.
Reference: AMSA — Testing and inspection of oil filtering equipment (2025/06) ↗4 · Match evidence to the operation
Keep ORB Part I, tank/quantity changes, time/position, equipment/alarm records and receipts consistent. A low display reading does not prove legal conditions or equipment accuracy. Do not apply a blanket 12-mile rule to all machinery-bilge operations: identify the actual provision.
Reference: IMO — Revised MARPOL Annex I: regulations 14, 15, 17 ↗Scenarios and self-check
Onboard scenarios
Below 15 ppm while anchored in port: may we discharge?
The display is not permission. Do not discharge without verifying en-route and local port requirements.
Alarm or representative sampling is unreliable.
Stop overboard discharge; record the defect and follow approved retention/repair procedures.
LEARNING CHECK
Think of your answer, then reveal the explanation
Does 15 ppm satisfy every condition?
No; source, location, en-route status, equipment and records also matter.
Does an ECA chart authorise OWS discharge?
No. ECA concerns Annex VI emissions; Annex I/Polar Code and local rules remain separate.
Self-assessment only; no exam result, personnel record or competence certificate is generated.
Open official sources
Open the official sources
IMO — Revised MARPOL Annex I: regulations 14, 15, 17
IMO resolution · base text; read with later amendments
Open source ↗WWWCDN.IMO.ORGIMO — MEPC.107(49): bilge equipment standard
IMO equipment standard
Open source ↗WWW.AMSA.GOV.AUAMSA — Testing and inspection of oil filtering equipment (2025/06)
Flag/port-state authority guidance
Open source ↗WWW.IMO.ORGIMO — Polar Code
IMO convention/code overview
Open source ↗Legal instruments, explanatory guidance and operational bulletins have different roles. Check later amendments and consolidated texts where needed. Access and external documents remain under the publisher’s control.
Learning diagram and scope notes
Rules and bulletins may change. Before operation or voyage, verify the latest official source and ship-specific applicability. This page is not permission, certification or a real-time risk notice.