IMDG for Beginners: What You Need to Know About Shipping Dangerous Goods by Sea

Shipping hazardous materials by sea can feel overwhelming if you’re new to the process. The risks are high, and mishandling can lead to accidents, environmental harm, fines, or rejected shipments. That’s why the International Maritime Dangerous Goods (IMDG) Code exists.

The IMDG Code sets the global rules for shipping dangerous goods by vessel. It helps everyone, from manufacturers to shipping companies, understand how to pack, label, and transport hazardous materials safely. This beginner-friendly guide breaks down what the IMDG Code is, why it matters, and how to apply its key requirements. By the end, you'll have a clear path toward safer, smoother, and compliant shipping.

Dangerous Goods vs. Hazardous Materials

Hazardous materials or dangerous goods are articles or substances capable of posing a risk to health, safety, property, or the environment during transportation in commerce. While the term “dangerous goods” is commonly used worldwide, in the United States “hazardous materials” is the preferred term. We tend to use the terms interchangeably.  

What Is the IMDG Code?

The IMDG Code is an international set of regulations that prioritizesthe safe transport of dangerous goods by sea. Developed by the International Maritime Organization (IMO) in 1965, it protects people, cargo, and the environment from the risks posed by hazardous materials.

Compliance is mandatory under the International Convention for the Safety of Life at Sea (SOLAS). Failing to follow IMDG guidelines can lead to fires, spills, toxic exposures, and environmental harm, while also increasing the risk of shipment delays, costly fines, and legal liability.

But knowing the IMDG Code exists isn’t enough. To ship dangerous goods safely and compliantly, you need to understand how to apply its key requirements in practice.

Breaking Down the IMDG Code: Key Requirements

IMDG compliance might seem complicated, but it's easier to manage when you break it down into core steps. From classification to documentation, each part of the process plays a vital role in safe shipping.

Classification: What Are You Shipping?

Every hazardous material falls into one of nine classes, based on the type of danger it presents:

1. Explosives (e.g., fireworks, ammunition)
2. Gases (e.g., propane, oxygen)
3. Flammable Liquids (e.g., gasoline, paint)
4. Flammable Solids (e.g., matches, sulfur)
5. Oxidizing Substances and Organic Peroxides (e.g., hydrogen peroxide, bleach)
6. Toxic and Infectious Substances (e.g., pesticides, medical waste)
7. Radioactive Materials (e.g., uranium, medical isotopes)
8. Corrosives (e.g., battery acid, drain cleaner)
9. Miscellaneous Dangerous Goods (e.g., lithium batteries, dry ice)

Each material also gets:

• A UN number, which is a four-digit code used worldwide.
• A Proper Shipping Name (PSN), the official name listed in the IMDG Code.
• If applicable, Packing Group (PG):
  • PG I: High danger
  • PG II: Medium danger
  • PG III: Low danger

Labeling and Marking: Communicating the Risk

Proper labeling ensures that everyone handling the cargo, from warehouse workers to ship crews, knows the risks. IMDG requires:

• Hazard Class Labels: These diamond-shaped labels indicate the type of hazard (e.g., flammable, toxic).
• Marine Pollutant Mark: Used for substances harmful to the environment, like pesticides or certain chemicals.
• Elevated Temperature Mark: Required when shipping goods at high temperatures.

Labels must be durable, clear, and visible from one surface of the package. If labels fade, peel off, or get damaged during transit, port authorities may reject the shipment.

Packaging: Protecting the Cargo and the Ship

Packaging does more than hold goods, it prevents leaks, spills, and breakage during transit. IMDG-approved packaging must meet strict standards for strength, durability, and resistance to damage.

Common packaging types include:

• UN-Certified Containers: Tested for impact resistance and leakage prevention. Look for the UN symbol followed by the packaging code.
• Intermediate Bulk Containers (IBCs): Used for transporting larger quantities of solids or liquids.
• Portable Tanks: Required for large quantities of specific liquids and gases.

The type of packaging depends on the hazard class and packing group. Improper packaging not only endangers the vessel but can also result in cargo rejection and significant fines.

Stowage and Segregation: Preventing Dangerous Reactions

Once packaged, hazardous goods must be stored safely aboard the vessel. The IMDG Code outlines stowage (where goods should be placed) and segregation (which goods must be kept apart).

Key principles include:

• Secured Stowage: Goods must be strapped or blocked to prevent movement during rough seas.
• Ventilation: Some materials,, need proper ventilation to avoid pressure buildup.
• Temperature Control: Heat-sensitive goods, like organic peroxides (Class 5.2), require temperature-controlled containers.

Segregation ensures that incompatible materials don’t react. For example:

• Oxidizers (Class 5.1) must be separated from flammable solids (Class 4.1) to prevent fires.
• Corrosives (Class 8) should not be stored near toxic substances (Class 6.1), as they can react to form hazardous gases.

The IMDG Code includes a segregation table to help shippers identify which goods can and cannot be stored together.

Documentation: Keeping Shipments Moving

Proper paperwork is essential for smooth shipping. Without it, your shipment could be delayed or rejected at the port.

Key IMDG documents include:

• Dangerous Goods Declaration (DGD): Confirms that goods are classified, packed, and labeled correctly.
• Multimodal Dangerous Goods Form: Used when shipments move across different transport modes, like sea, road, and rail. 
• Container/Vehicle Packing Certificate: Verifies that cargo was packed and secured properly.

Even small errors, like using a trade name instead of a Proper Shipping Name, can lead to shipment holds and fines. Many shippers use digital platforms to streamline documentation and reduce mistakes.

Emergency Preparedness: Planning for the Unexpected

Even with careful planning, incidents can happen. That’s why the IMDG Code requires emergency response information to be on board the vessel.

This includes:

• Emergency Response Guides (ERG): Step-by-step instructions for dealing with spills, fires, or toxic exposures.
• Medical First Aid Guide (MFAG): Treatment instructions for chemical injuries.
• 24/7 Emergency Contact Information, like CHEMTREC: Helps responders can get expert advice immediately.

Mastering these steps not only keeps your shipments moving but also protects your business from costly fines, delays, and safety incidents. But applying these practices consistently takes the right training and resources.

How CHEMTREC’s New Shipping Dangerous Goods by Vessel Course Can Help

Understanding IMDG regulations is one thing, but applying them consistently is another. That’s where CHEMTREC’s new Shipping Dangerous Goods by Vessel course comes in.

This course simplifies the IMDG Code with clear, practical training. It covers:

• How to classify hazardous materials and complete documentation.
• Proven practices for labeling, marking, and packaging.
• Stowage, segregation, and emergency response procedures.

The course is available online, allowing learners to train at their own pace. Receiving a certificate upon completion demonstrates your team’s commitment to safety and compliance. Whether you’re shipping hazardous goods occasionally or managing daily operations, this course equips your team with the skills they need.

Don’t wait for a rejected shipment or a costly fine to highlight gaps in your process. Explore CHEMTREC’s Shipping Dangerous Goods by Vessel course today and give your team the knowledge they need to ship hazardous goods with confidence.