Container packing: CTU Code, load distribution, seals If cargo shifts in the container, the shipper answers for it.
The international code of practice for packing containers is the CTU Code of the IMO, ILO and UNECE. It is not binding, but carriers and terminals work to it. The Code is explicit: although the carrier must deliver the cargo as received, the shipper remains responsible for deficiencies caused by poor packing and securing. The centre of gravity of the cargo should be close to the middle of the container; the rule of thumb is that no more than 60% of the cargo mass should be concentrated in half the container's length. The seal is applied immediately after packing and its number is written in the documents. If the number does not match on arrival, the container may have been opened in transit.
What the CTU Code is
A CTU is a cargo transport unit: a container, swap body, trailer or wagon. The IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units (CTU Code) was approved by the three organisations in 2014 and published by the IMO as MSC.1/Circ.1497; it replaced the 1997 packing guidelines. In the IMO's own words it is a non-mandatory global code of practice. Additional informative material is in a separate circular (MSC.1/Circ.1498) and does not form part of the Code.
The chain of responsibility
Chapter 4 of the Code sets out the functions in the chain, without prejudice to national legislation and contracts:
- Shipper: must deliver cargo that is safe and suitable for transport. Although the carrier is contractually responsible for delivering the cargo in the condition received, the shipper remains responsible for deficiencies caused by poor packing and securing (4.1.2).
- Packer and consignor: where the shipper does not do this work itself, the packer and consignor fulfil their obligations to the shipper; if they do not, the shipper may hold them responsible for faults attributable to poor packing, securing, handling or reporting (4.1.2).
- CTU operator: provides units that are fit for purpose, meet international structural integrity requirements, and are clean and free of pests (4.2.1).
Weight distribution
The centre of gravity of the cargo should be close to the middle of the container's length and width. The Code asks that the eccentricity of the centre of gravity should in general not exceed 5%, and turns this into a rule of thumb: 60% of the cargo's total mass in 50% of the container's length (CTU Code Annex 7). The Code also asks terminals to assess, when lifting a container, whether this rule is exceeded and to take steps to rectify it if so.
The container has its own limits too. In a general purpose container, the side walls are built to withstand a uniform load equal to 60% of the permitted payload, and the front wall and door end 40% (6.2.4). Cargo leaning against the doors pushes that limit.
Securing: against which forces
Securing is designed separately for the longitudinal and transverse directions, against the accelerations expected on the journey. The coefficients given by the Code (in g):
| Mode | Longitudinal, forward | Longitudinal, rearward | Transverse |
|---|---|---|---|
| Road | 0.8 | 0.5 | 0.5 |
| Rail (combined transport) | 0.5 | 0.5 | 0.5 |
| Sea, area A (Hs ≤ 8 m) | 0.3 | 0.3 | 0.5 |
| Sea, area B (8 < Hs ≤ 12 m) | 0.3 | 0.3 | 0.7 |
| Sea, area C (Hs > 12 m) | 0.4 | 0.4 | 0.8 |
According to the Code's sea area table, the Mediterranean and the Black Sea are in area A (chapter 5). For rail, the higher values in brackets apply only to shocks of 150 milliseconds or shorter; the table shows the ordinary values. The Code states that the mass of the cargo alone, even with a high friction coefficient, does not secure it sufficiently; cargo that cannot be secured by blocking must be lashed (5.4).
By road, the forward coefficient is 0.8: under hard braking the cargo is pushed forward with a force of 0.8 times its own weight. If the container also travels by road before or after the sea voyage, the securing must meet the road values.
The CSC plate
A container in international sea transport carries a CSC safety approval plate at the rear, usually on the left-hand door; a container without one should not be used in international traffic. The most important item on the plate for the packer is the maximum gross mass, which should never be exceeded (8.2.1.2).
The CSC requires containers to be thoroughly examined 5 years after manufacture and then at least every 30 months. The next examination date is marked on the plate; alternatively, the operator runs an approved continuous examination programme (ACEP) and the plate carries an ACEP mark (8.2.1.3).
Seals
- When: when required, the shipper ensures that a container in international transport is sealed immediately after packing, with a seal bearing a unique identification number. Countries may require such seals to meet ISO 17712 (11.1.2).
- Documents: the container number, the correct gross mass and, when required, the seal number go into the relevant documents (3.6).
- On arrival: the seal number is checked against the documents. If it differs, or the seal is damaged or missing, the container may have been opened in transit; in that case the CTU operator should be contacted (3.7, 12.1.2).
- Cargo to the US: US Customs' CTPAT programme requires members' shipments to or from the United States to be sealed immediately after loading with a seal meeting ISO 17712 high-security requirements (minimum security criterion 6.2). The VVTT steps are followed when applying it: view the seal and locking mechanism, verify the number against the documents, tug the seal, and twist and turn a bolt seal to check it does not come loose (6.7).
When it goes wrong
Heavy cargo is concentrated at one end
If more than 60% of the cargo sits in half the container's length, lifting and transport balance suffers; the terminal may set the container aside to rectify it.
Cargo leans against the doors
The door end is built to take only 40% of the payload. Cargo pressing on the doors can fall out when they are opened on arrival.
Securing is designed for the sea leg only
In sea area A the longitudinal coefficient is 0.3; by road, forward, it is 0.8. If the container goes to the port by truck, the highest force comes on the road.
The seal number is not written in the documents
Without a number to compare on arrival, the first way of showing whether the container was opened in transit is lost.
Frequently asked
Is the CTU Code mandatory?
No, the IMO describes it as a non-mandatory code of practice. But the Code states that the shipper remains responsible for deficiencies caused by packing and securing, and parties in the transport chain work to it.
How do I check the weight distribution in a container?
The rule of thumb: no more than 60% of the cargo mass should be concentrated in half the container's length. Place heavy items close to the middle of the length and spread across the floor.
The seal number was different on arrival. What should I do?
The Code says this may indicate the container was opened in transit and asks that the CTU operator be contacted (12.1.2). Make a report on delivery and notify the carrier in writing; if you are insured, tell your insurer too.
Does every seal have to meet ISO 17712?
Under the CTU Code, countries may require it. The US CTPAT programme requires members to use ISO 17712 high-security seals on US shipments. Ask about the destination country's and the carrier's requirements in advance.
Sources
- IMO — MSC.1/Circ.1497, IMO/ILO/UNECE CTU Code (16.12.2014) 3.6–3.7 (completion of packing and unpacking), 4.1–4.2 (chain of responsibility), 5.3–5.4 (acceleration coefficients), 6.2.4 (wall strength), 8.2.1 (CSC plate, 5 years, 30 months, ACEP), 11.1.2 (seal, ISO 17712), 12.1.2 (seal discrepancy), chapter 5 (sea areas), Annex 7 (centre of gravity, 60/50 rule) · imo.org (PDF) · accessed 29 Sep 2026
- IMO — CTU Code page Non-mandatory global code of practice; update of the 1997 guidelines · imo.org · accessed 29 Sep 2026
- US Customs and Border Protection (CBP) — CTPAT Minimum Security Criteria, U.S. Importers (October 2021) Criterion 6.2 (ISO 17712 high-security seal), 6.7 (VVTT) · cbp.gov (PDF) · accessed 29 Sep 2026
This page is for information only. The CTU Code and CTPAT texts were read directly and paragraph numbers are given. Securing calculations depend on the type of cargo, its packaging and the material used; for heavy or special cargo, confirm the securing plan with your carrier and a specialist before packing.
Change log
- Page published. The CTU Code was written from the MSC.1/Circ.1497 text published by the IMO, and the CTPAT criteria from the document published by CBP, all read directly.