Dangerous goods (DG) — also called hazardous materials or hazmat — are substances or articles the international community has classified as posing a risk to health, safety, property, or the environment during transport. The benchmark regulation for ocean freight is the International Maritime Dangerous Goods (IMDG) Code, published by the International Maritime Organization and updated every two years. For air, the equivalent is the IATA Dangerous Goods Regulations (IATA DGR).
A surprisingly wide range of everyday cargo falls under DG rules: lithium-ion batteries, aerosols, paints, adhesives, pool chemicals, perfume, and industrial gases all appear on restricted lists. If you ship anything chemically active, pressurized, flammable, or corrosive, check the IMDG Code before assuming it moves as general cargo.
The nine IMDG hazard classes
Each class covers a category of hazard. Most classes are subdivided into divisions, and each substance is assigned a UN number — a four-digit code that appears on labels, declarations, and carrier systems.
| Class | Hazard | Common examples |
|---|---|---|
| 1 | Explosives | Fireworks, airbag inflators, ammunition |
| 2 | Gases | LPG, aerosols, oxygen cylinders, dry ice |
| 3 | Flammable liquids | Paints, adhesives, solvents, perfumes |
| 4 | Flammable solids / self-reactive / pyrophorics | Matches, metal powders, activated carbon |
| 5 | Oxidizing substances and organic peroxides | Hydrogen peroxide, ammonium nitrate |
| 6 | Toxic and infectious substances | Pesticides, clinical waste |
| 7 | Radioactive material | Medical isotopes, industrial gauges |
| 8 | Corrosives | Sulfuric acid, sodium hydroxide, wet-cell batteries |
| 9 | Miscellaneous dangerous goods | Lithium batteries, magnetized materials |
Class 9 is among the most commercially relevant. UN3480 (lithium-ion batteries shipped alone) and UN3481 (batteries contained in or packed with equipment) appear on thousands of shipments every week — from consumer electronics to electric-vehicle components. Many shippers overlook that even a small power bank triggers DG rules on both ocean and air.
Required documents for dangerous goods shipments
Missing or incomplete DG documentation is the most common reason a carrier refuses a booking at the last minute. The core documents you need are:
Dangerous Goods Declaration (DGD). The shipper's responsibility. It lists the UN number, proper shipping name, hazard class, packing group, quantity, packaging type, and an emergency contact. For ocean freight, the DGD must be certified by a DG-competent person — a formal qualification recognized by most maritime authorities. Many carriers also require a signed IMDG certification statement alongside it.
Safety Data Sheet (SDS). Required for chemical shipments and chemicals packed inside machinery. The SDS covers composition, first-aid measures, handling precautions, and emergency response procedures.
Container Packing Certificate (CPC). Required for ocean FCL shipments. It confirms the container was loaded, stowed, and secured in compliance with IMDG rules — and that segregation requirements between incompatible goods were observed.
Material Safety Data Sheet (MSDS). Accepted in many markets as equivalent to SDS; the terminology has largely unified, but some customs authorities in certain regions still ask for MSDS specifically.
For air freight, the DGD follows the IATA DGR format with different quantity limits. A document prepared for ocean will not automatically satisfy IATA requirements, and errors here commonly result in the shipment being offloaded at origin.
All DG documents typically must reach the carrier before the DG cut-off, which often falls 24–48 hours earlier than the standard cargo cut-off. Submitting them late is the single most common reason a DG shipment rolls to the next vessel. Build that lead time into your booking timeline.
Packing groups: how severity shapes costs
Most hazard classes are further divided into three packing groups that indicate the degree of danger and drive significant differences in packaging requirements and carrier acceptance:
- PG I — High danger. Strongest performance-specification packaging required. Lowest carrier acceptance — many lines will not take PG I cargo on standard commercial services.
- PG II — Medium danger. Broadly accepted; moderate packaging requirements.
- PG III — Minor danger. Widest acceptance, most cost-efficient to book and handle.
The packing group dictates which UN-certified packaging type you must use (fibreboard boxes, drums, intermediate bulk containers, etc.) and sets maximum quantity limits per package. Confirming the packing group before you commit to a vessel avoids costly last-minute re-routing.
DG surcharges — what to expect on your quote
Carriers and terminals levy surcharges to cover the additional handling, segregation, inspection, and liability exposure that DG cargo creates. The exact amounts vary by carrier, class, packing group, and route, but a typical DG ocean quote includes:
DG Surcharge (DGS) / Hazmat Surcharge. The primary carrier levy, applied per container on FCL or per shipment on LCL. Rates differ materially between classes — Class 3 (flammables) is typically lower than Class 1 (explosives) or Class 7 (radioactive).
DG Handling Fee. Charged at origin and/or destination terminals for the additional checking, labelling verification, and physical segregation work involved.
DG Documentation Fee. Some carriers charge separately for processing the DGD through their compliance systems.
Class 1 / Class 7 premium. Explosives and radioactive materials attract significant additional fees and are usually subject to individual carrier approval rather than standard online booking.
DG surcharges on FCL are generally lower on a per-unit basis than on LCL, where the carrier must segregate hazardous cargo within a shared container. If your DG volume is consistent month to month, ocean FCL often makes financial sense once you account for the DG handling margin built into LCL rates.
Segregation rules and their operational impact
The IMDG Code sets out segregation requirements defining which classes must be kept physically apart from one another — and from food-grade cargo — on board the vessel. The four standard categories are:
- Away from — minimum separation distance within the same cargo space
- Separated from — different cargo holds, or deck versus below-deck
- Separated by a complete compartment or hold from
- Separated longitudinally by an intervening complete compartment or hold from
In practice, segregation limits vessel choice. Not every ship has the stow positions needed to accommodate a given class pairing, particularly for Classes 1, 2.3, 5.2, and 7. The result is that DG space fills up faster than general cargo space. Booking four to six weeks ahead is strongly recommended for high-hazard classes on busy lanes.
Dangerous goods on air freight
Air is significantly stricter than ocean for most DG classes. IATA DGR imposes lower per-package quantity limits, tighter packaging requirements, and outright prohibitions on substances that ocean will routinely accept.
Lithium batteries are a notable example: state-of-charge limits and watt-hour thresholds determine whether a shipment is forbidden on passenger aircraft (classified CAO — cargo aircraft only) or forbidden entirely. Before routing any DG cargo via air freight, confirm whether the UN number is permitted on passenger aircraft, restricted to CAO services, or prohibited altogether.
Factor in a longer documentation lead time for DG air than for standard air cargo. Some airline carriers require DG pre-approval 48–72 hours before acceptance.
What to prepare before you book
Work through this checklist before contacting your forwarder:
- UN number and proper shipping name — look these up in the IMDG Code or your SDS.
- Hazard class and packing group — both should be on the SDS.
- Net and gross quantities — per package and total per container.
- Packaging type and UN performance mark — the outer packaging must carry a certified UN mark; check it physically before shipment.
- Emergency contact — a 24/7 number for your DG emergency response provider.
- Certifying competent person — the named individual who will sign the DGD.
Supplying all of this upfront lets your customs brokerage and forwarding team clear pre-booking checks in a single pass rather than iterating, which can easily burn two to three days on a time-sensitive shipment.
For the full picture of how a shipment moves from quote to delivery — including where DG pre-approvals fit in the timeline — see how Holo Cargo works. For reefer, out-of-gauge, and all other specialist movements, our special cargo service covers classification and documentation as part of the booking process.
