Environmental compliance on an FPSO is not governed by a single regulation. Depending on where a discharge stream originates from the vessel’s machinery space or from the topsides production system, completely different regulatory frameworks may apply.
For EPC teams, instrumentation engineers and FPSO operators, understanding which regulations apply to which discharge stream is a fundamental step in specifying the right oil-in-water monitoring equipment. Getting this wrong at the specification stage creates compliance risk that can surface during commissioning, regulatory inspection or environmental audit.
This article explains how MARPOL and IMO MEPC requirements apply to FPSOs and why the above/below waterline distinction matters so much for monitoring equipment selection.
| Key thing to remember An FPSO is simultaneously a marine vessel and an offshore production facility. This means it may be subject to both MARPOL marine discharge regulations and offshore environmental permit conditions at the same time, for different discharge streams. The correct oil-in-water monitor depends entirely on which regulatory framework governs the specific discharge point. |
What Is MARPOL and Does It Apply to FPSOs?
MARPOL the International Convention for the Prevention of Pollution from Ships is the primary international framework governing pollution from vessels at sea. It is administered by the International Maritime Organization (IMO) and applies to ships operating under flag state jurisdiction.
FPSOs that are classified and flagged as vessels are generally subject to MARPOL. However, FPSOs are complex assets and not all discharge streams from an FPSO fall under MARPOL. The key question is not whether MARPOL applies to the FPSO as a whole but which specific discharge streams it governs.
MARPOL Annex I covers oil pollution prevention and is the most relevant annex for produced water and bilge water discharge monitoring. Within Annex I, two IMO MEPC resolutions define the specific technical requirements for oil-in-water monitoring equipment:
- MEPC.107(49) applies to 15ppm bilge alarms and oily water separator discharge monitoring
- MEPC.108(49) applies to Oil Discharge Monitoring Equipment (ODME) for tanker slop water, tank washings and ballast-related discharge
What Is the Below-the-Waterline Discharge Regime?
Below-the-waterline discharge streams on an FPSO typically originate from the vessel’s marine systems machinery spaces, bilge systems, ballast tanks and, in converted tanker FPSOs, cargo-related systems.
Bilge water discharge MEPC.107(49)
Bilge water accumulates in the machinery space from equipment leaks, condensation and drainage. Under MARPOL Annex I, bilge water may only be discharged overboard if the oil content does not exceed 15 parts per million (ppm) after processing through a type-approved oily water separator (OWS).
The discharge must be monitored by a type-approved 15ppm bilge alarm meeting the technical requirements of MEPC.107(49). The alarm must automatically stop discharge if the oil content exceeds the limit and must record discharge data in the Oil Record Book.
Rivertrace solution: SMART BILGE 15ppm bilge alarm for standard machinery space applications; SMART PFM 107 for applications requiring MEPC.107(49) approval with enhanced measurement capability for more complex water streams.
Tanker slop and ballast discharge MEPC.108(49) and MEPC.240(65)
FPSOs converted from crude oil tankers or product tankers may retain tanker-related discharge systems slop tanks, cargo tank washings and ballast water systems associated with previous tanker operations. These systems fall under different MARPOL requirements.
MEPC.108(49) governs Oil Discharge Monitoring Equipment (ODME) for tanker discharge. The discharge standard is more complex than the bilge water 15ppm limit: discharge must not exceed 30 litres of oil per nautical mile and must not exceed 1/30,000 of the previous cargo quantity. MEPC.240(65) updates the technical standards for ODME systems.
Rivertrace solution: SMART ODME designed for monitoring, recording and controlling tanker ballast and slop discharge, meeting MEPC.108(49) and MEPC.240(65) requirements.
What Is the Above-the-Waterline Discharge Regime?
Above-the-waterline discharge streams on an FPSO originate from the topsides oil and gas production system principally the produced water treatment package.
Produced water from topsides processing is not governed by MARPOL in the same way as bilge or tanker discharge. Instead, it is typically regulated by:
- Field permits issued by the national regulatory authority in the jurisdiction where the FPSO operates
- National environmental legislation, which sets discharge limits and monitoring requirements for offshore production facilities
- Operator environmental standards and project-specific requirements
- IMO guidance where it has been adopted into national law or permit conditions
There is no single global oil content limit for produced water discharge equivalent to the 15ppm MARPOL bilge rule. Discharge limits vary significantly between jurisdictions from 15ppm in some countries to 30ppm or 40ppm in others, with some permits requiring continuous monitoring and others periodic sampling.
| Common specification mistake Assuming that a MARPOL-compliant 15ppm bilge alarm is sufficient for FPSO produced water discharge. Produced water regulations are permit-specific and often require specialist oil-in-water analysers capable of handling variable composition, gas, solids and chemical interference conditions that exceed the design parameters of a standard bilge monitor. |
Rivertrace solutions: SMART PFM 107 for produced water discharge applications where MEPC.107(49) approval is required or specified; OCD Xtra for produced water discharge where permit conditions require calibration against multiple crude oil types and measurement across a broader concentration range.
How Do the Two Regimes Overlap on an FPSO?
The regulatory complexity on an FPSO arises because both regimes may apply simultaneously to different discharge streams on the same vessel.
A single FPSO may have:
- A bilge water system governed by MARPOL Annex I and MEPC.107(49), requiring a type-approved 15ppm bilge alarm
- A tanker-derived slop or ballast system governed by MEPC.108(49), requiring ODME
- A topsides produced water system governed by field permits and national regulations, requiring a specialist produced water analyser
Each discharge stream requires its own monitoring approach. The monitoring equipment selected for one stream is not automatically appropriate for another even if both are installed on the same vessel.
| The practical implication for EPC teams Specifying oil-in-water monitoring for an FPSO requires a stream-by-stream analysis of regulatory requirements before any equipment selection is made. Rivertrace supports EPC and instrumentation engineering teams at this stage to ensure the correct technology is specified for each discharge point. |
Summary: Which Regulation Applies to Which FPSO Discharge Stream?
The table below summarises the key regulatory frameworks and the Rivertrace equipment relevant to each:
| Regulation | Applies To | Discharge Standard | Required Equipment |
| MEPC.107(49) | Bilge water from machinery spaces; oily water separator discharge; produced water (certain applications) | 15ppm oil content limit | Type-approved 15ppm bilge alarm e.g. Rivertrace SMART BILGE or SMART PFM 107 |
| MEPC.108(49) | Tanker slop water, tank washings, ballast water discharge | 30 litres per nautical mile or 1/30,000 of previous cargo | Oil Discharge Monitoring Equipment (ODME) e.g. Rivertrace SMART ODME |
| MEPC.240(65) | Updates and supplements MEPC.108(49) for tanker ODME | As above updated technical standards | ODME meeting revised technical standards |
| Field permits / national law | FPSO topsides produced water discharge | Varies by country and permit conditions | Specialist oil-in-water analyser e.g. Rivertrace OCD Xtra or SMART PFM 107 |
What Does This Mean for FPSO Project Specification?
For EPC, EPCI and FPSO contractor teams, the regulatory mapping above has direct practical consequences at every project stage:
At concept and FEED stage
Identify all discharge streams and map each one to the applicable regulatory framework. Confirm which streams require MARPOL-compliant equipment and which are governed by field permits or national law. This defines the monitoring technology requirements before detailed engineering begins.
At procurement stage
Specify monitoring equipment against the correct regulatory standard for each discharge stream. A purchase order that references MEPC.107(49) for a produced water application, or that fails to specify MEPC.108(49) for a tanker-converted FPSO slop system, creates compliance risk that may not surface until commissioning.
At commissioning and first oil
Verify that installed monitoring equipment meets the applicable standard for each discharge stream, that calibration evidence is in place, and that discharge records are being captured in the format required by the applicable regulatory authority.
Rivertrace works with EPC teams across all three stages providing application engineering support, procurement-ready documentation and commissioning and calibration assistance for each discharge stream.
Frequently Asked Questions
Does MARPOL apply to FPSOs?
MARPOL applies to FPSOs that are classified and flagged as vessels. However, not all discharge streams from an FPSO are governed by MARPOL. Below-the-waterline marine systems, such as bilge and ballast discharge, typically fall under MARPOL Annex I. Topsides produced water discharge is usually governed by field permits and national environmental regulations rather than MARPOL directly.
What is the difference between MEPC.107(49) and MEPC.108(49)?
MEPC.107(49) sets the technical requirements for 15ppm bilge alarms used to monitor oily water separator discharge from vessel machinery spaces. MEPC.108(49) sets the requirements for Oil Discharge Monitoring Equipment (ODME) used on tankers to monitor slop water, tank washings and ballast discharge. Both are IMO resolutions under MARPOL Annex I but apply to different discharge streams and require different equipment.
What regulations govern produced water discharge on an FPSO?
FPSO produced water discharge from topsides production systems is typically governed by field permits, national environmental legislation and operator standards. There is no single global standard equivalent to the MARPOL 15ppm bilge rule. The applicable discharge limits and monitoring requirements vary by operating location and permit conditions.
Can the same oil-in-water monitor be used for bilge water and produced water discharge?
Not necessarily. A type-approved 15ppm bilge alarm is designed for bilge water from a vessel’s machinery space and may not be suitable for FPSO produced water, which has a more complex and variable composition. The correct equipment must be specified for each discharge stream based on the applicable regulatory standard and process conditions.
When should Rivertrace be involved in FPSO regulatory mapping?
As early as possible ideally at concept or FEED stage. Early advisory input from Rivertrace helps EPC teams identify the correct regulatory basis for each discharge stream, specify the right monitoring technology and avoid costly specification changes later in the project.