Module 6 • MARPOL & Pollution Prevention

MARPOL 73/78
Engineering Recap Infographic

A structured MCA oral-study infographic covering the six MARPOL annexes, engine-room discharge control, sewage, garbage, air pollution, energy efficiency and ballast-water links.

Convention

MARPOL 73/78

Technical Annexes

Bilge Standard

15 ppm

SOx Limits

0.50 / 0.10%

What this module is testing

MARPOL questions are not just memory questions. In an oral, you must link the annex, the certificate or record book, the onboard equipment and the practical action you would take as an engineer.

Identify all six MARPOL annexes and the pollution type each controls.
Explain 15 ppm oily bilge discharge and Oil Record Book evidence.
Apply sewage, garbage and air-pollution discharge limits correctly.
Connect Annex VI with SEEMP, EEXI, CII, BDNs, samples and NOx files.
Give practical PSC / incident answers for spills, OWS checks and non-compliance.

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How to use this for MCA oral prep

For every regulation, practise saying: “the annex, the certificate/record, the equipment, the operating limit, and what I would do if it failed.”

1. Six annexesPollution type map 2. Annex I oilOWS, ORB, SOPEP 3. Sewage & garbageDistance rules 4. Annex VI airSOx, NOx, ODS, BDN 5. SEEMP / EEXI / CIIEnergy efficiency 6. Ballast water linkD-1 / D-2 7. Oral exam answersPractical wording

Section 1

MARPOL structure: six technical annexes

Annex I

Oil

Machinery-space bilges, sludge, fuel-oil residues, oil tankers, IOPP Certificate and Oil Record Book.

Annex II

Noxious liquid substances

Bulk chemical cargoes. Categories X, Y, Z and OS control stripping, tank washing and discharge.

Annex III

Packaged harmful substances

Marine pollutants carried in packaged form, identified through the IMDG Code and cargo documents.

Annex IV

Sewage

Controls sewage equipment, holding tanks, treatment plants, discharge distance and ISPP certification.

Annex V

Garbage

Garbage management plan, placards and record book. Plastics are prohibited from discharge anywhere.

Annex VI

Air pollution

SOx, NOx, ODS, incineration, fuel quality, IAPP certificate, SEEMP, EEXI and CII.

Oral exam focus

Do not just list Annex I to VI. Add one onboard example for each: “Annex I — oily bilge water via the OWS and ORB; Annex VI — sulphur fuel compliance through BDNs, samples and IAPP evidence.”

Section 2

Annex I: oil pollution from machinery spaces

15 ppm

OWS limit

Oily bilge water must be processed through approved oil filtering equipment and the effluent must not exceed 15 ppm without dilution.

ORB

Record evidence

Oil Record Book Part I records machinery-space operations: sludge collection/disposal, bilge discharge, bunkering and accidental discharges.

SOPEP

Emergency plan

Shipboard Oil Pollution Emergency Plan gives spill response, reporting contacts, containment steps and pollution-control actions.

1Ship en route

2Approved OWS / filter

315 ppm alarm healthy

4Automatic stop/divert works

5ORB completed accurately

Item	What the examiner / PSC may ask	Engineer answer
OWS	Show compliant bilge discharge.	Demonstrate approved OWS, 15 ppm monitor, alarm/divert valve, sampling point, overboard valve status and logs.
Sludge	Where does sludge go?	Retained in sludge tank, incinerated where permitted, evaporated where approved, or landed to shore reception facility with receipt.
ORB	What makes an ORB suspicious?	Repeated round numbers, missing positions/times, overwritten entries, empty lines, no signatures, impossible tank quantities or OWS run times.
Incident	Oil seen overboard.	Stop discharge, isolate source, inform bridge/Chief/Master, initiate SOPEP, contain if safe, record and report as required.

Example oral wording

“For machinery-space bilges under Annex I, I would only discharge when the ship is en route, through approved 15 ppm equipment, with the alarm and automatic stopping/diverting arrangement operational. I would verify the overboard line, log the operation in ORB Part I and stop immediately if the alarm or valve failed.”

Section 3

Annex IV & V: sewage and garbage discharge rules

Sewage quick limits

Approved STP: discharge permitted when plant is operating and effluent standards are met.
Comminuted + disinfected: more than 3 nm from nearest land.
Untreated sewage: more than 12 nm, en route, not less than 4 knots, at approved moderate rate.
Applicable ships: international voyages, 400 GT and above, or certified to carry more than 15 persons.

Garbage headline rule

Plastics are never discharged into the sea. Annex V generally prohibits garbage discharge unless a specific exception applies, such as controlled food waste discharge, certain cargo residues or limited cleaning agents/additives.

No plasticsGMPGRBPlacards

Annex IV — MEPC.157(55) untreated sewage standard

Untreated sewage from a holding tank may only be discharged when the ship is more than 12 nautical miles from the nearest land, is en route, and is proceeding at a speed of not less than 4 knots. It must not be discharged instantaneously; it must be at an approved moderate rate.

> 12 nmEn routeMinimum 4 knotsModerate rate

Formula to quote in the oral

MEPC.157(55):
DRmax = 0.00926 × V × D × B

DRmax = maximum permissible discharge rate (m³/h)
V = ship’s average speed (knots) over the period
D = draft (m)
B = breadth (m)

Extra point: the approved discharge rate is an average over 24 hours (or the discharge period if less), and may be exceeded by no more than 20% on an hourly basis.

Waste stream	Outside special areas	Inside special areas	Exam trap
Food waste, comminuted/ground	More than 3 nm from nearest land, en route.	More than 12 nm from nearest land, en route.	“Comminuted” usually means able to pass through a 25 mm screen.
Food waste, not comminuted	More than 12 nm from nearest land, en route.	Generally prohibited.	Do not say 12 nm everywhere; special areas are stricter.
Plastics	Prohibited.	Prohibited.	Includes synthetic ropes, bags, fishing nets and plastic packaging.
Cooking oil / incinerator ash	Retain onboard / land ashore unless a specific permitted route applies.	Retain onboard / land ashore.	Do not group all galley waste as food waste.

Oral exam focus

A strong answer separates sewage from garbage: sewage is Annex IV and depends on treatment / comminution / distance; garbage is Annex V and starts from the principle of “prohibited unless expressly permitted.”

Section 4

Annex VI: SOx, NOx, ODS, fuel quality and ECAs

0.50%

Global sulphur limit

Maximum sulphur content outside SOx ECAs, unless an approved equivalent method is used.

0.10%

ECA sulphur limit

Stricter fuel sulphur limit inside SOx ECAs, including Mediterranean from 1 May 2025 and Canadian Arctic / Norwegian Sea from 1 March 2026.

>130 kW

NOx file scope

Marine diesel engines above 130 kW normally require NOx certification evidence and a Technical File, subject to Annex VI exceptions.

Fuel compliance evidence

BDN: retained for 3 years after delivery onboard.
MARPOL sample: sealed, signed and retained until fuel is substantially consumed, but not less than 12 months.
Changeover records: required when moving between ECA and non-ECA fuel regimes.
EGCS: approved equivalent may be used where permitted, with washwater/sludge controls.

2026 ECA update

Current active ECAs include Baltic, North Sea, North American, US Caribbean, Mediterranean, Canadian Arctic and Norwegian Sea.
The North-East Atlantic ECA was adopted at MEPC 84 in 2026, with future entry-into-force / implementation dates, so treat it as a “watch item” rather than an already-active 0.10% zone.
For an oral, state the date if discussing a new ECA to avoid sounding outdated.

Annex VI item	What it controls	Onboard evidence
SOx	Fuel sulphur and equivalent compliance.	BDN, sample, fuel-changeover log, bunker analysis, EGCS records where fitted.
NOx	Engine emissions by Tier I, II and III limits.	EIAPP certificate, NOx Technical File, parameter record book, approved components/settings.
ODS	Ozone-depleting substances, e.g. historic refrigerants.	ODS list/record book, service reports, landing receipts, leak checks.
Incinerator	Approved incineration and prohibited feed streams.	Type approval, operating manual, log, ash/sludge controls.

Example oral wording

“Annex VI controls air pollution. For sulphur compliance I would check the BDN, MARPOL sample, bunker analysis, fuel changeover timing and whether we are inside an ECA. The global limit is 0.50% m/m and ECA limit is 0.10% m/m unless an approved equivalent such as EGCS is used.”

Section 5

Annex VI energy efficiency: SEEMP, EEXI and CII

SEEMP

Ship Energy Efficiency Management Plan: a ship-specific operational plan to monitor and improve energy efficiency over time.

EEXI

Energy Efficiency Existing Ship Index: a technical efficiency requirement for existing ships, normally verified once.

CII

Carbon Intensity Indicator: annual operational carbon-intensity rating from A to E, based on verified data.

CII trigger point

A ship rated E in one year or D for three consecutive years must develop corrective actions in the SEEMP to achieve at least an acceptable rating.

AMajor superior performance

BMinor superior performance

CRequired / acceptable rating

DWatch — weak performance

ECorrective action triggered

Oral exam focus

Keep the distinction clear: EEXI is the technical existing-ship index; CII is the annual operational rating; SEEMP is the onboard management plan used to plan and demonstrate improvement.

Section 6

Ballast Water Management Convention link

Important: Ballast Water Management is a separate IMO convention, not a MARPOL annex. It is included here because pollution-prevention modules and oral exams often test it alongside MARPOL.

D-1 exchange standard

Ballast water exchange standard.
At least 95% volumetric exchange.
Where possible: at least 200 nm from nearest land and at least 200 m water depth.
If not possible: at least 50 nm and 200 m depth, or in a designated area.

D-2 performance standard

Ballast water treatment / performance standard.
Limits viable organisms and specified indicator microbes in discharged ballast.
All ships were phased to D-2 by dates not later than 8 September 2024.
Evidence: IBWMC, BWMP, BWRB, type-approved BWTS and sampling records.

Example oral wording

“D-1 is exchange; D-2 is treatment/performance. I would check the International Ballast Water Management Certificate, approved plan, record book, treatment-system alarms and any sampling/maintenance evidence.”

Section 7

How to answer MARPOL in an MCA oral

Five-part answer structure

Name the annex and pollution type.
State the key limit or prohibition.
Identify the onboard equipment or document.
Explain the operational control or record entry.
Finish with what you would do if it fails or if pollution occurs.

Common examiner traps

Calling ballast water a MARPOL annex.
Forgetting “en route” and 4-knot wording for untreated sewage.
Saying plastics can be discharged if ground down — they cannot.
Mixing up EEXI, EEDI, SEEMP and CII.
Not linking Annex VI fuel compliance to BDNs and retained samples.
Forgetting the 2025/2026 ECA changes.

Model oral answer

Complete example

“MARPOL 73/78 is the main IMO convention for preventing pollution from ships and has six technical annexes covering oil, noxious liquid substances, packaged harmful substances, sewage, garbage and air pollution. As an engineer I would mainly demonstrate compliance through OWS operation and ORB entries under Annex I, sewage plant or holding tank control under Annex IV, garbage segregation and record keeping under Annex V, and fuel sulphur, NOx and energy-efficiency evidence under Annex VI. If pollution occurred, I would stop the source, inform the bridge and Chief Engineer, initiate the relevant emergency plan such as SOPEP, contain the spill if safe, and ensure reporting and records are completed accurately.”

Accuracy basis used for this infographic