Most cargo damage at sea is not caused by storms alone. It often starts in the warehouse, when a container is packed with weight in the wrong place, gaps that let cargo move, damp packaging or wood that is refused at the border. This guide explains the international code of practice that covers packing, and the practical checks shippers and packers commonly use.
The CTU Code in brief
The Code of Practice for Packing of Cargo Transport Units, known as the CTU Code, was published jointly in 2014 by the International Maritime Organization (IMO), the International Labour Organization (ILO) and the United Nations Economic Commission for Europe (UNECE). A Cargo Transport Unit (CTU) is any container, swap body, trailer, road vehicle or rail wagon used to carry cargo.
The Code is a code of practice rather than a convention, but it is widely used as the reference for good packing, and some national authorities and contracts refer to it. It covers:
- the chain of responsibility: consignor, packer, shipper, carrier and consignee each have defined duties;
- checking the unit before packing;
- planning the load, including weight distribution;
- packing and securing methods, in its annexes;
- packing dangerous goods and handling fumigated units.
The packer is often not the shipper on the bill of lading. The Code's point is that each party passes accurate information along the chain, so the next one can do its job safely.
Check the container before you pack
The CTU Code recommends inspecting the unit before any cargo goes in. Typical checks include:
| Check | What to look for |
|---|---|
| Safety approval plate | A valid International Convention for Safe Containers (CSC) plate, and the maximum gross mass shown on it |
| Structure | No holes, cracks or heavy dents; doors, seals and locking bars working |
| Weathertightness | No daylight visible from inside with the doors closed (a simple light test) |
| Cleanliness | Dry, clean and free of odours, residues and old hazard labels that no longer apply |
| Floor | Sound boards with no protruding nails or soft spots |
If a unit fails these checks, shippers can generally ask the carrier or depot for a replacement. Recording the condition with photos is common practice.
Plan the load before it arrives
Good packing starts on paper:
- Payload and floor limits. The total must stay within the maximum gross mass on the CSC plate and within limits for the road and rail legs, which are set nationally and can be lower. The container owner's specifications also limit how much weight a short length of floor can carry, which matters for heavy machinery or coils.
- Weight distribution. The CTU Code advises keeping the centre of gravity close to the middle of the unit's length and width, and as low as practicable. Heavy items concentrated at one end can make a container difficult or unsafe to lift and move. An accurate total weight on its own does not show this; see our guide to Verified Gross Mass.
- Fit. Pallet and carton layouts decide how much empty space needs filling. Our pallet and container loading calculator and carton loading calculator can help with a first estimate.
- Mixed cargo. Heavy goods go below lighter ones, liquids below dry goods, and incompatible goods are kept apart.
Securing: stop the cargo from moving
At sea a container is exposed to rolling, pitching and vertical acceleration. On land it faces braking and cornering. The CTU Code's annexes set out how to calculate securing needs and describe the main methods:
- Blocking and bracing: packing cargo tightly against the container walls or timber frames, so it has nowhere to move.
- Filling voids: using dunnage bags (airbags), timber or other void fillers to close gaps between packages and at the doors.
- Lashing: straps, chains or wire fixed to the container's lashing points, used within their rated strength.
- Friction: anti-slip mats under pallets or loads to reduce sliding.
Doors are not designed to hold cargo back. A common practice is to block the last row so nothing leans on the doors when they are opened at destination.
Container rain: moisture and condensation
Container rain is condensation that forms on the inside of the roof and walls when warm, moist air cools, for example as a ship moves between climates or temperatures drop at night. The water can then drip onto the cargo. The main sources of moisture are usually the cargo and its packaging, especially timber pallets, cartons and natural products that hold water.
Measures shippers commonly consider include:
- Packing in dry conditions, with dry pallets and packaging.
- Using desiccants suited to the cargo and voyage length, placed as the maker directs.
- Protecting goods with liners, covers or moisture barrier film.
- Avoiding packing hot or freshly produced goods that are still releasing moisture.
- Asking about ventilated containers for cargo that needs airflow.
Whether moisture damage is covered depends on the insurance terms and the cause; our cargo insurance guide explains the main clauses.
Wooden packaging: ISPM 15
Pallets, crates and dunnage made of solid wood can carry pests between countries. The International Plant Protection Convention (IPPC) sets the international standard for this: International Standards for Phytosanitary Measures (ISPM) No. 15, Regulation of wood packaging material in international trade.
Under ISPM 15, wood packaging is treated by an approved method and marked. The mark includes the IPPC symbol, a country code, a code for the producer or treatment provider, and the treatment code, for example heat treatment (HT) or methyl bromide fumigation (MB). Some processed wood materials, such as plywood, generally fall outside the standard.
Each importing country's National Plant Protection Organization (NPPO) decides how it applies the standard, and requirements and accepted treatments can differ. Unmarked or non-compliant wood may be treated, destroyed or re-exported at the owner's cost. Check the importing country's NPPO requirements before shipping.
Dangerous goods, seals and paperwork
- Dangerous goods carried by sea are governed by the International Maritime Dangerous Goods (IMDG) Code. Among other things, it requires a container packing certificate signed by the person responsible for packing. Packers should be trained as the Code and national rules require.
- Seals. High-security seals that meet the International Organization for Standardization (ISO) standard 17712 are widely required by carriers and customs programmes. Record the seal number on the shipping documents and check it again at destination.
- Photos. Photos of the empty unit, the packed load and the sealed doors are useful evidence if cargo is damaged.
Checklist before the doors close
- Container inspected, with a valid CSC plate and a clean, dry, weathertight interior.
- Load plan within gross mass and floor limits, with the centre of gravity near the middle and low down.
- Heavy goods on the floor and gaps filled, blocked or lashed.
- Nothing leaning on the doors.
- Dry packaging and desiccants or liners where needed.
- Wood packaging compliant with ISPM 15 and the importing country's NPPO rules.
- Dangerous goods documents and the packing certificate in place, if applicable.
- Seal applied, number recorded and photos taken.
Whether you ship full container or groupage, the same principles apply. With groupage, the consolidator packs the container, so the focus is on your own packaging and labelling.
Frequently asked questions
Is the CTU Code mandatory?
The CTU Code is a code of practice, not a convention, so it is not mandatory in itself. National authorities, carriers and contracts may refer to it or impose their own packing rules, so check the requirements that apply to your shipment.
What causes container rain?
Moisture in the cargo, packaging or air condenses on the cooler inside surfaces of the container as temperatures change during the voyage, then drips onto the goods. Dry packaging, desiccants and liners are common ways to reduce the risk.
Do wooden pallets need ISPM 15 marks?
Solid wood packaging used in international trade is generally expected to be treated and marked under ISPM 15. Each importing country's plant protection authority decides how it applies the standard, so confirm its current requirements before shipping.
References
- IMO, ILO and UNECE, Code of Practice for Packing of Cargo Transport Units (CTU Code), 2014, via UNECE and IMO.
- IMO, International Convention for Safe Containers (CSC), 1972, as amended.
- IMO, International Maritime Dangerous Goods (IMDG) Code, via imo.org.
- International Plant Protection Convention, ISPM 15: Regulation of wood packaging material in international trade, via ippc.int.
- International Organization for Standardization, ISO 17712: Freight containers — Mechanical seals, via iso.org.
- International Labour Organization, ilo.org.
Prepared by the Apex Ocean Lines industry experts and editorial team, checked against the sources cited. Short forms link to our shipping glossary.