MARPOL Annex I covers oil and petroleum-based cargoes, while MARPOL Annex II covers noxious liquid substances (NLS) carried in bulk, primarily chemicals. The distinction matters because each annex sets different discharge limits, documentation requirements, and handling procedures for tankers. For captains and operators in inland and coastal shipping, understanding which annex applies to a given cargo determines what degassing and tank cleaning procedures are legally permitted.
Which cargoes fall under MARPOL Annex I versus Annex II?
MARPOL Annex I applies to oil and oil-based products, including crude oil, fuel oil, diesel, lubricating oil, and refined petroleum products. MARPOL Annex II applies to noxious liquid substances carried in bulk, which include most industrial chemicals such as methanol, benzene, styrene, vegetable oils, and other chemical cargo categories classified under the IBC Code.
The classification of a cargo under one annex or the other is not always immediately obvious. A tanker carrying gasoil falls under Annex I. The same vessel switching to a chemical cargo such as xylene or acetic acid falls under Annex II. This matters operationally because the two annexes impose different obligations on how residues are handled, documented, and discharged.
Annex II further categorizes NLS into four groups based on their environmental hazard level: X, Y, and Z (most to least hazardous), plus a fourth category for substances assessed as presenting no significant risk. Each category carries its own discharge thresholds and pre-washing requirements. Annex I does not use this tiered hazard classification in the same way, instead focusing on oil content limits in discharged water.
What are the discharge rules under each annex?
Under MARPOL Annex I, ships may discharge oily mixtures into the sea only when the oil content does not exceed 15 parts per million (ppm), the ship is underway, and the discharge occurs outside special areas. In special areas such as the North Sea and Baltic Sea, stricter rules apply and many discharges are entirely prohibited. All oil transfers and discharges must be recorded in the Oil Record Book.
Under MARPOL Annex II, discharge rules depend on the NLS category. Category X substances, considered the most hazardous, must be pre-washed before departure from the unloading port, and the resulting washings must be discharged to a reception facility ashore. Category Y and Z substances also have specific pre-washing requirements and concentration limits before any discharge at sea is permitted. Discharge of Category X residues at sea is prohibited entirely.
A key practical difference is that Annex II often requires mandatory pre-washing at the terminal before a vessel leaves port, regardless of what happens at sea afterward. This requirement directly affects how tanker captains plan their operations between cargo runs. The Cargo Record Book (for Annex II) and the Oil Record Book (for Annex I) must be maintained accurately and made available to port state control inspectors on request.
How does MARPOL affect tanker degassing in the Netherlands and Belgium?
MARPOL regulations directly shape what tanker captains can and cannot do when degassing tanks in ports such as Rotterdam, Antwerp, and Moerdijk. In the Netherlands and Belgium, open-air degassing of tanks carrying substances classified under MARPOL Annex II is already heavily restricted and subject to ongoing tightening under national and EU environmental legislation. Releasing vapours into the atmosphere from chemical cargo tanks is increasingly treated as a violation of both MARPOL and local air quality rules.
For Annex I cargoes, the vapour pressure and volatility of petroleum products mean that degassing is also regulated, particularly in inland waterway ports where the CDNI (Convention on the Collection, Deposit and Reception of Waste Generated During Navigation on the Rhine and Inland Waterways) adds another layer of obligation. The Netherlands and Belgium are both CDNI signatories, which means that residues and tank washings from inland tankers cannot simply be discharged to the waterway.
In practice, captains operating in these ports need to identify approved reception facilities or certified emission treatment providers before arriving. Degassing on open water or in unauthorized locations carries significant legal and financial risk, regardless of whether the cargo falls under Annex I or Annex II.
What happens if a tanker doesn’t comply with the correct annex rules?
Non-compliance with MARPOL Annex I or Annex II rules can result in detention of the vessel, substantial fines, and, in serious cases, criminal prosecution of the captain or shipowner. Port state control officers in Rotterdam, Antwerp, and other major European ports conduct regular inspections and can detain a vessel until deficiencies are corrected. Incomplete or falsified record books are treated as serious violations.
Beyond port state control, flag state authorities can also take action, and repeated violations can affect a vessel’s classification society standing and insurance coverage. For inland tanker operators, local enforcement authorities in the Netherlands (Inspectie Leefomgeving en Transport) and Belgium (Scheepvaartcontrole) have the authority to impose fines and operational restrictions for breaches of both MARPOL obligations and national environmental law.
The financial consequences of non-compliance typically far exceed the cost of using a legal degassing or tank cleaning facility. Delays caused by detention, combined with reputational damage, make compliance the operationally sound choice as well as the legally required one.
Where can tankers legally degas and clean tanks under MARPOL rules?
Tankers must degas and clean tanks at certified reception facilities or using approved emission treatment systems that meet the applicable MARPOL annex requirements. In the Netherlands and Belgium, a growing number of facilities and mobile service providers are authorized to handle both Annex I and Annex II residues, though availability remains a practical challenge for captains working to tight schedules.
For Annex II cargoes, pre-washing must typically take place at the discharge terminal before the vessel moves to a cleaning facility. The resulting washings are then transferred ashore. For Annex I cargoes, oily water separators and slop reception facilities at major ports handle residues within the permitted discharge limits.
Mobile degassing solutions are increasingly used to address the shortage of fixed facilities, particularly for chemical tankers that need to degas between cargo runs without long diversions. When selecting a degassing provider or facility, captains should verify that the operator holds the appropriate permits for the specific cargo type and annex classification. Documentation of the degassing operation should be retained and recorded in the relevant record book to demonstrate compliance during any subsequent port state control inspection.
How SuperFlox helps with MARPOL-compliant degassing
Meeting MARPOL Annex I and Annex II requirements for degassing and tank cleaning is straightforward in principle but logistically demanding in practice, especially for operators working to tight turnaround schedules in Dutch and Belgian ports. SuperFlox provides a flexible, fully compliant solution that removes the uncertainty from the process. Key features of the service include:
- Mobile Containerized Units that can be deployed directly at the berth, eliminating the need to divert to a fixed reception facility and reducing downtime between cargo runs.
- Treatment of vapours at the source, converting harmful emissions into clean air rather than releasing them into the atmosphere, in line with both MARPOL Annex II requirements and the stricter national air quality rules that apply in the Netherlands and Belgium.
- Coverage of both Annex I and Annex II cargo types, with the appropriate permits in place for each, so captains do not need to source separate providers depending on their previous cargo.
- Full documentation support, ensuring that the degassing operation is recorded correctly and that captains have the paperwork needed to demonstrate compliance to port state control inspectors.
- Availability across major inland and coastal ports including Rotterdam, Antwerp, and Moerdijk, with flexible scheduling to fit operational requirements.
If you are planning a cargo run that requires degassing or tank cleaning under MARPOL rules, contact SuperFlox to discuss your requirements and arrange a deployment that keeps your vessel compliant and on schedule.