MARPOL Annex VI: Refrigerants in Marine Systems On Ships
Refrigeration systems are indispensable in marine operations. From preserving food and medical supplies to maintaining comfortable onboard temperatures, these systems are the unsung heroes of ship life. Yet, they come with an environmental cost if not properly managed. The International Maritime Organization (IMO), under the MARPOL Convention, established Annex VI to curb air pollution from ships — including emissions of ozone-depleting substances (ODS) and high-global-warming-potential (GWP) refrigerants.
This regulation represents a critical step toward sustainable shipping. It enforces stricter controls on refrigerant use, installation, maintenance, and documentation — ensuring that every vessel minimizes its impact on the planet’s atmosphere.
Understanding MARPOL Annex VI
MARPOL Annex VI, titled “Regulations for the Prevention of Air Pollution from Ships,” focuses on limiting harmful emissions such as sulfur oxides (SOx), nitrogen oxides (NOx), volatile organic compounds (VOCs), and refrigerant gases. For refrigeration and air-conditioning systems, Annex VI prohibits deliberate releases of ODS and mandates record-keeping for all systems containing these substances.
The regulation applies to all ships above 400 gross tonnage and offshore platforms. Its core goal is to phase out ODS from marine operations while promoting safer alternatives with minimal environmental impact.
Flowchart – Refrigerant Regulation Path
This flowchart shows how MARPOL Annex VI integrates policy, operation, and enforcement to achieve full refrigerant compliance onboard ships.
Core Provisions Under MARPOL Annex VI
1. Prohibition of Deliberate Emissions
Ships are strictly prohibited from intentionally releasing ODS such as CFCs, Halons, and HCFCs during maintenance, repair, or disposal. Only minimal emissions are tolerated during recovery, recycling, or reclamation.
This rule covers all forms of refrigerant handling — from initial installation to decommissioning — compelling operators to adopt environmentally responsible maintenance procedures.
2. Installation of New Systems
- New ships must not install any system containing ODS.
- Existing ships may continue using older systems until they are phased out, but no new installations or refills with ODS are allowed.
- HCFC systems are also restricted for newer vessels, encouraging complete transition to non-ODS alternatives.
3. Permanently Sealed Equipment
Equipment that is factory-sealed and has no service ports or removable ODS components is exempt. This includes small hermetically sealed systems that pose negligible environmental risk.
4. Record-Keeping and Documentation
Every vessel must maintain two key documents:
- ODS Record Book – Records any ODS handling such as recharge, repair, or disposal.
- List of ODS Equipment – Attached as a supplement to the International Air Pollution Prevention (IAPP) Certificate, listing all onboard ODS-containing systems.
Ships over 400 gross tonnage, as well as offshore rigs and drilling platforms, are required to maintain these records at all times for inspection by flag-state or port-state authorities.
5. Compliance and Survey Requirements
Ships undergo several surveys to ensure compliance:
- Initial survey before certification
- Annual surveys to confirm ongoing compliance
- Intermediate survey between renewals
- Renewal survey every five years
Flag States enforce these inspections, while Classification Societies may act as recognized organizations (ROs) to verify compliance.
Refrigerants in Marine Systems
Refrigerants are the working fluids in shipboard cooling and air-conditioning systems. The right choice determines not only performance and energy efficiency but also environmental compliance.
The following table lists commonly used refrigerants on ships, including their properties and indicative market prices (subject to regional variation):
Table 1: Common Refrigerants Used on Ships
| Refrigerant | Type | ODP | GWP | Toxicity | Flammability | Typical Application | Approx. Price (USD/kg) |
|---|---|---|---|---|---|---|---|
| R-134a | HFC | 0 | 1430 | Non-toxic | Non-flammable | Air conditioning | 6 – 8 |
| R-404A | HFC blend | 0 | 3922 | Low | Non-flammable | Low-temp refrigeration | 8 – 10 |
| R-407C | HFC blend | 0 | 1774 | Low | Non-flammable | AC, retrofits from R-22 | 7 – 9 |
| R-410A | HFC blend | 0 | 2088 | Low | Non-flammable | High-efficiency AC systems | 7 – 9 |
| R-507 | HFC blend | 0 | 3985 | Low | Non-flammable | Transport & cold storage | 9 – 11 |
| R-717 (Ammonia) | Natural | 0 | <1 | Toxic | Flammable | Industrial refrigeration | 3 – 5 |
| R-744 (CO₂) | Natural | 0 | 1 | Non-toxic | Non-flammable | Transcritical systems | 2 – 4 |
| R-290 (Propane) | Hydrocarbon | 0 | 3 | Low | Flammable | Small systems | 3 – 4 |
| R-600a (Isobutane) | Hydrocarbon | 0 | 3 | Low | Flammable | Compact units | 3 – 4 |
| R-1234yf | HFO | 0 | 4 | Non-toxic | Mildly flammable | New low-GWP ACs | 12 – 15 |
Characteristics of an Ideal Marine Refrigerant
An ideal refrigerant for shipboard applications should balance performance, safety, and sustainability:
| Characteristic | Description |
|---|---|
| Zero ODP | Must not contribute to ozone depletion |
| Low GWP (<150 preferred) | Reduces climate impact |
| Non-toxic and Safe | Protects crew and environment |
| Non-flammable | Prevents onboard fire risks |
| High Efficiency | Ensures optimal energy performance |
| Oil Compatibility | Works well with compressor lubricants |
| Availability & Cost | Readily available and economically feasible |
These standards ensure that the chosen refrigerant maintains efficient cooling while adhering to international environmental norms.
HFCs Under MARPOL Annex VI
HFCs (Hydrofluorocarbons) are the dominant replacements for older ODS like CFCs and HCFCs. Although they have no ozone-depleting potential, their GWP remains significant, prompting ongoing global efforts to transition towards even cleaner alternatives.
Common HFCs Allowed on Ships
| HFC Refrigerant | Chemical Name | Key Features | Marine Use |
|---|---|---|---|
| HFC-134a | 1,1,1,2-Tetrafluoroethane | Non-flammable, efficient, widely available | Air conditioning |
| HFC-404A | Blend of 125/143a/134a | Excellent for cold storage | Freezer and cargo cooling |
| HFC-407C | Blend of 32/125/134a | Retrofit for R-22 systems | AC systems |
| HFC-410A | Blend of 32/125 | High-pressure, efficient | Split AC units |
| HFC-507 | Blend of 125/143a | Stable, high performance | Reefer containers |
Advantages of HFCs
- No ozone depletion
- Low toxicity, safe for enclosed ship environments
- Good thermodynamic performance
- Easy retrofit options
Challenges of HFCs
- High GWP contributing to greenhouse gas effects
- Regulatory pressure to phase down usage
- Costlier maintenance as global phase-downs continue
Transition to Low-GWP Alternatives
The global maritime industry is gradually transitioning toward refrigerants with low GWP and zero ODP characteristics. Alternatives include:
| Refrigerant | Type | Benefits | Limitations |
|---|---|---|---|
| Ammonia (R-717) | Natural | Zero ODP, high efficiency | Toxic, requires careful handling |
| Carbon Dioxide (R-744) | Natural | Very low GWP, safe | Operates at high pressures |
| Hydrocarbons (R-290, R-600a) | Natural | Excellent thermodynamics, low cost | Highly flammable |
| HFOs (R-1234yf, R-1234ze) | Synthetic | Ultra-low GWP, compatible with new systems | Higher cost, mild flammability |
These alternatives are already being adopted in new ship designs, particularly in vessels prioritizing environmental performance or operating under stricter regional regulations.
ODS Record Book and Logbook Requirements
Ships must record the following entries in the ODS Record Book:
- System installation or removal
- Maintenance involving refrigerant recovery
- Recharging or topping up refrigerant
- Leak testing and repair actions
- Disposal of recovered substances
Example Record Format:
| Equipment Name | Action Taken | Quantity (kg) | Responsible Officer | Remarks |
| Provision Room Chiller | Leak repair & recharge | 2.5 | Chief Engineer | Verified |
This ensures transparency and helps inspection authorities verify compliance quickly.
Detection of Refrigerant Leaks
Leak detection is a cornerstone of responsible refrigeration. A 10% refrigerant loss can increase system energy consumption by up to 20%, directly raising ship emissions.
Common Leak Detection Methods
| Method | Description | Suitable For |
|---|---|---|
| Electronic Detectors | Detect refrigerant gas concentration | All systems |
| Ultrasonic Detectors | Identify leaks through acoustic signals | Noisy machinery spaces |
| Soap Bubble Test | Bubbles form over leaks | Simple checks |
| Fluorescent Dye & UV Light | Dye highlights leaks under UV | Hidden components |
| Pressure Decay Test | Nitrogen pressurization and monitoring | System-wide testing |
Early detection conserves refrigerant, ensures cooling efficiency, and supports compliance with MARPOL Annex VI leak prevention requirements.
Refrigerant Charging and Maintenance Tools
Efficient charging and maintenance require specialized tools:
| Tool | Function |
|---|---|
| Manifold Gauge Set | Measures system pressure |
| Vacuum Pump | Removes air/moisture pre-charging |
| Charging Scale | Controls precise refrigerant addition |
| Refrigerant Cylinder | Source of refrigerant |
| Identifier | Verifies refrigerant purity |
| Safety Equipment | Gloves, goggles, gas monitors |
These instruments help maintain operational safety and compliance during refrigerant handling.
Diagram – Refrigerant Lifecycle Aboard Ships
This flow depicts how refrigerants are managed from storage to final documentation under MARPOL Annex VI compliance.
Responsible Refrigeration: The Path Forward
Responsible refrigeration goes beyond regulatory compliance — it’s a sustainability strategy. Proper maintenance, use of low-GWP refrigerants, and regular leak monitoring can significantly reduce a vessel’s carbon footprint.
According to recent maritime studies, refrigerant leaks account for over 18 million tonnes of CO₂-equivalent emissions annually from global shipping. Tackling this issue is crucial for meeting IMO’s long-term greenhouse gas reduction targets.
Key Actions for Shipowners
- Minimize leaks through preventive maintenance
- Switch to low-GWP refrigerants
- Ensure accurate ODS logbook updates
- Train crew on safe refrigerant handling
- Schedule regular system audits
These measures reduce costs, improve efficiency, and enhance compliance credibility during port inspections.
Frequently Asked Questions (FAQ)
MARPOL Annex VI is an international regulation that controls air pollution from ships. It limits harmful emissions such as sulfur oxides, nitrogen oxides, and refrigerant gases, ensuring ships use environmentally safe systems and maintain proper records.
Refrigerants are regulated because some types, like CFCs and HCFCs, damage the ozone layer and contribute to global warming. MARPOL Annex VI prevents their use and promotes safer alternatives with zero ozone depletion potential.
An ODS Record Book is a mandatory log for ships over 400 gross tonnage. It records all activities involving ozone-depleting substances — such as system charging, repairs, leak tests, and disposal — to prove compliance with MARPOL Annex VI.
Refrigerants with zero ozone depletion potential (ODP) are allowed. Common examples include HFC-134a, HFC-404A, R-410A, R-744 (CO₂), R-717 (Ammonia), and HFOs like R-1234yf. These are safer for the environment and comply with the regulation.
Shipowners should plan to retrofit or replace systems using banned refrigerants such as R-22. Retrofitting allows older systems to use compliant gases, while full replacement ensures long-term compliance and better energy efficiency.
Refrigerant leaks can be detected using electronic leak detectors, ultrasonic sensors, soap bubble tests, fluorescent dyes, or pressure testing. Early detection prevents energy loss, reduces emissions, and ensures safe operation.
Using low-GWP refrigerants reduces environmental impact, improves energy efficiency, and helps ships meet international emission targets. It also lowers long-term costs through better system performance and easier regulatory compliance.
Conclusion
MARPOL Annex VI has transformed how the maritime industry handles refrigerants. By prohibiting ODS, mandating logbooks, and promoting leak prevention, it ensures that marine refrigeration aligns with global environmental goals.
While HFCs remain prevalent, the industry is steadily shifting to natural and HFO refrigerants that balance performance, safety, and sustainability. Implementing responsible refrigeration practices — from accurate record-keeping to proactive maintenance — not only meets compliance but also drives efficiency and environmental stewardship.
Ultimately, every ship that minimizes refrigerant emissions contributes to cleaner oceans and a healthier atmosphere — making sustainable marine cooling not just a regulation, but a responsibility.
Happy Boating!
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