Dangerous Goods in Containers: What Are the Requirements for Sea Transportation?

International sea freight allows businesses to move large quantities of goods across countries. However, transporting dangerous goods in containers requires much stricter procedures than ordinary cargo.

Dangerous goods may include chemicals, flammable liquids, gases, explosives, corrosive substances, toxic materials and other products that may create risks to people, vessels, cargo or the marine environment.

For international maritime transport, the International Maritime Dangerous Goods (IMDG) Code is the key regulatory framework. The 2024 Edition, including Amendment 42-24, entered into force on January 1, 2026 and is mandatory from that date.

So, what does a logistics company or shipper need to prepare before loading dangerous goods into a container?

1. Correctly Classify the Dangerous Goods

The first requirement is to identify and classify the cargo correctly.

Under the IMDG Code, dangerous goods are divided into different hazard classes according to their properties and risks. The classification determines how the goods should be packaged, marked, labeled, documented, stored and transported.

The shipper should provide accurate information about the cargo, including:

• Proper Shipping Name (PSN)
• UN Number
• Dangerous Goods Class
• Packing Group, where applicable
• Marine Pollutant status, where applicable
• Quantity and type of packaging
• Emergency-related information

Incorrect classification can result in incorrect handling, improper stowage or rejection by the carrier.

2. Use Suitable Packaging

Packaging is one of the most important safety requirements for dangerous goods transportation.

Dangerous goods must be packed in packaging that is suitable for the substance and compliant with the applicable IMDG requirements. The packaging should protect the cargo from leakage, breakage, contamination and other incidents during transportation.

Before loading, packages should also be inspected. Damaged or leaking packages should not be loaded into the container.

For containerized dangerous goods, proper packaging is particularly important because the cargo may experience handling, vibration, stacking and movement during inland transportation, terminal operations and the ocean voyage.

3. Mark and Label the Cargo Correctly

Dangerous goods must be clearly identified through the required marks and labels.

The markings and labels allow warehouse workers, truck drivers, terminal operators, customs authorities and vessel crews to quickly understand the potential hazards of the cargo.

Depending on the cargo, the container or packages may need information such as:

• UN Number
• Proper Shipping Name
• Hazard labels
• Marine Pollutant mark, when applicable
• Other required marks or placards

If several types of dangerous goods are loaded into the same container, the applicable marks and placards must be properly displayed.

This is especially important during an emergency because accurate identification helps personnel determine the appropriate response procedures.

4. Prepare the Required Dangerous Goods Documents

Documentation is another critical part of dangerous goods shipping.

The shipper normally needs to provide the required Dangerous Goods Declaration (DGD) and other applicable transport documents. The information must accurately describe the cargo.

Depending on the shipment, documentation may include:

• Dangerous Goods Declaration
• Container/Vehicle Packing Certificate
• Transport documents
• Permits or approvals
• Additional certificates or notifications when required

The IMDG Code requires dangerous goods to be properly described, marked, labeled, placarded and certified in the transport documentation.

The carrier may refuse to accept the cargo if the required documents or declarations are missing or incorrect.

5. Properly Pack and Secure the Container

A dangerous goods container must not only contain the correct cargo; the cargo must also be properly arranged and secured.

The container should be clean, dry and suitable for receiving the goods. Packages should be inspected before loading, and the cargo should be properly secured to prevent movement during transportation.

Heavy cargo should be distributed appropriately across the container floor. Dunnage, blocking, bracing, lashings or other suitable securing methods may be required depending on the cargo.

A poorly secured dangerous goods shipment can create additional risks if packages shift, fall or become damaged during the voyage.

The responsible party must also complete the applicable Container/Vehicle Packing Certificate, confirming that the packing operation complies with the relevant requirements.

6. Follow Dangerous Goods Segregation Rules

Not all dangerous goods can be transported together.

Some substances may react dangerously when they come into contact with each other. Therefore, the IMDG Code contains segregation requirements for incompatible dangerous goods.

Before loading a mixed container, the shipper or logistics provider should check whether the different dangerous goods can legally be packed together.

The IMDG requirements also specify conditions for the segregation and stowage of dangerous goods on board vessels. Depending on the hazard, containers may need to be placed in particular locations, separated from other cargo or kept away from ignition sources.

This makes cargo planning an essential part of dangerous goods logistics.

7. Check Container Safety and Suitability

The container itself must be suitable for international transportation.

International freight containers are generally subject to the 1972 Convention for Safe Containers (CSC). Approved containers carry a Safety Approval Plate showing relevant technical information.

For dangerous goods, logistics operators should also check the physical condition of the container before loading.

Important points include:

• No major structural damage
• Doors function properly
• Floor is in suitable condition
• Container is clean and dry
• No visible leakage or contamination
• Required placards and marks can be displayed correctly

A suitable container helps reduce operational and safety risks throughout the supply chain.

8. Ensure Proper Stowage on the Vessel

After the container reaches the port, the responsibility does not end.

The shipping line and vessel operator must consider the dangerous goods information when preparing the vessel’s cargo and stowage plan.

Ships carrying packaged dangerous goods are required to have appropriate dangerous goods information, including a list, manifest or stowage plan showing the goods and their locations.

The location of a dangerous goods container may depend on its hazard class, segregation requirements and other operational restrictions.

This is why accurate information from the shipper is essential before the container is loaded onto the vessel.

9. Personnel Must Receive Appropriate Training

Dangerous goods transportation involves many parties, including shippers, warehouse workers, freight forwarders, truck drivers, terminal operators and vessel personnel.

People involved in dangerous goods operations need training appropriate to their responsibilities. Training may cover classification, documentation, marking and labeling, segregation, cargo securing and emergency response procedures.

Proper training helps reduce mistakes during packing, handling, transportation and emergency situations.

Dangerous Goods Shipping Requires Careful Coordination

Transporting dangerous goods by sea is not simply a matter of putting hazardous cargo into a container and booking a vessel.

A safe shipment requires coordination between the shipper, packing team, freight forwarder, carrier, terminal and vessel operator.

From classification and packaging to labeling, documentation, container packing, cargo securing, segregation and vessel stowage, every stage must be carefully controlled.

For logistics businesses, understanding these requirements can help reduce shipment delays, cargo rejection and safety risks.

If you are interested in international logistics and the movement of containers after port operations, you can also explore previous international express and logistics-related content on //vinalines.net/van-tai-giay-dep-tu-ho-chi-minh-di-cang-gdynia/

At the same time, understanding what happens after a container leaves the port is an important part of the wider logistics process. Read more about the container journey in /vietship.net/en/reliable-domestic-sea-freight-shipping-from-da-nang-to-haiphong-port.html/

Conclusion

Dangerous goods transportation by sea requires strict compliance with international regulations. The key requirements include correct classification, suitable packaging, proper marking and labeling, complete documentation, safe container packing, cargo securing, segregation and correct vessel stowage.

Following the IMDG Code is essential for protecting cargo, workers, vessels and the marine environment. For shippers and logistics providers, careful preparation before the container reaches the port can make the entire international shipping process safer and more efficient.