Transporting dangerous goods by sea begins with a package that can withstand the journey. Long before a container is lifted aboard a vessel, the dangerous substance or article must have been placed into packaging that is suitable for its properties, correctly closed and capable of meeting the conditions it may encounter during transport. An error at this stage cannot simply be corrected by adding the right label later.
The International Maritime Dangerous Goods (IMDG) Code therefore contains detailed requirements governing the packing of dangerous goods. These provisions determine which types of packaging may be used, how much product may be placed inside them, which performance level may be required and which additional conditions apply to particular substances.
For companies shipping dangerous goods by sea, understanding IMDG packing requirements starts with an important principle: there is no single packaging that is suitable for all dangerous goods.
Start with classification and the Dangerous Goods List
Correct packing begins with correct classification. Before selecting a packaging, the shipper needs to know exactly what is being transported. The UN number, Proper Shipping Name, class or division, subsidiary hazard and, where applicable, packing group form the basis for determining the applicable transport requirements.
The next important step is the Dangerous Goods List in Chapter 3.2 of the IMDG Code. This table connects the classification of a substance or article with the provisions that apply to its transport.
For packaging purposes, particular attention must be given to the columns referring to packing instructions and special packing provisions. These direct the user towards the relevant requirements in Part 4 of the Code.
A common mistake is to select a packaging simply because it has previously been used for a similar chemical. Two liquids belonging to the same dangerous goods class may have very different chemical properties and may consequently require different packaging arrangements.
The correct sequence is therefore always classification first, followed by consultation of the Dangerous Goods List and then the applicable packing instruction.
Understanding IMDG packing instructions
Part 4 of the IMDG Code contains the packing and tank provisions. Chapter 4.1 deals with the use of packagings, including Intermediate Bulk Containers (IBCs) and large packagings.
Packing instructions use codes to identify the relevant type of packaging arrangement. Instructions beginning with P, such as the widely encountered P001, relate to packagings other than IBCs and large packagings. Instructions beginning with IBC concern Intermediate Bulk Containers, while instructions beginning with LP apply to large packagings.
A packing instruction may permit several packaging options. Depending on the dangerous goods concerned, these can include drums, jerricans, boxes or combination packagings. The instruction may also specify maximum capacities or maximum net masses.
However, reading the basic packing instruction is only part of the process. Special packing provisions may modify or supplement the general instruction for a particular substance or article.
This is why experienced dangerous goods personnel do not stop when they see “P001” in the Dangerous Goods List. They follow the complete regulatory chain.
Packing groups and packaging performance
For many dangerous goods, the packing group indicates the degree of danger presented by the substance. Packing Group I represents high danger, Packing Group II medium danger and Packing Group III lower danger within the classes for which packing groups are assigned.
This has a direct relationship with packaging performance.
UN specification packaging markings use the letters X, Y and Z to indicate the performance level for which the packaging has successfully been tested. In general terms, packaging marked X may be used for Packing Groups I, II and III, subject to all other applicable conditions. Packaging marked Y is suitable for Packing Groups II and III, while packaging marked Z is limited to Packing Group III.
This means that the presence of a UN packaging mark does not automatically make a packaging suitable for every dangerous good.
A Y-rated drum, for example, cannot simply be used for a Packing Group I substance because it appears strong enough. The required performance level forms part of the regulatory system and must be respected.
Other elements of the UN packaging marking provide information about matters such as the packaging type, performance tests, year of manufacture and approving or manufacturing state. Personnel responsible for packing dangerous goods need to be able to interpret the relevant parts of these markings.
Compatibility is essential
One of the most important principles in dangerous goods packing is also one of the easiest to overlook: the dangerous goods must be compatible with the packaging material.
A packaging can be perfectly manufactured, correctly UN marked and authorised by the relevant packing instruction, yet still be unsuitable for a particular chemical.
The IMDG Code makes clear that packing instructions do not themselves provide all necessary guidance on chemical compatibility. The user must verify that the substance is compatible with the packaging material selected.
This matters because chemicals can attack packaging materials in different ways. A corrosive liquid may affect certain metals, while another substance may soften or weaken a particular plastic. The result may be leakage or structural failure even though the packaging originally met the required performance standard.
Compatibility therefore needs to be assessed before filling. Information from packaging manufacturers, chemical suppliers, test data and relevant technical documentation may all play a role in establishing suitability.
Packages must survive normal conditions of transport
Sea transport can expose packages to demanding conditions. They may be handled several times before reaching the vessel, stacked inside a freight container and subjected to vibration and movement throughout the voyage. Temperature and pressure conditions can also vary.
The general packing provisions therefore require packages to be capable of withstanding the shocks and loading normally encountered during transport.
Closures are particularly important. A compliant drum becomes a non-compliant and potentially dangerous package if its closure has not been fitted or tightened correctly. Manufacturers’ closing instructions should therefore be followed where applicable.
For liquids, sufficient ullage must be allowed so that expansion caused by temperature changes does not result in leakage or permanent deformation. Packages should not be filled in a way that makes them unsafe under normal transport conditions.
The condition of the packaging also matters. Damaged, significantly corroded or otherwise weakened packaging should not be treated as acceptable merely because the original UN specification marking remains visible.
Combination packagings require attention to every component
Many dangerous goods are transported in combination packagings consisting of one or more inner packagings placed within an outer packaging. A familiar example is bottles or cans packed inside a UN specification fibreboard box.
Compliance involves more than checking the outer box.
The inner packagings must be suitable for the substance and must comply with the relevant capacity limitations. They must be securely closed and arranged inside the outer packaging so that they are protected against damage under normal transport conditions.
Where cushioning or absorbent material is required, it must also be suitable for the substance concerned. The complete package must correspond with the tested and approved packaging design where a UN specification packaging is required.
Improvising by changing inner receptacles, removing required cushioning or substituting components can therefore affect compliance even when the same UN-marked outer box is used.
IBCs and large packagings have their own provisions
Dangerous goods are not always transported in drums, jerricans or boxes. Industrial shipments frequently use Intermediate Bulk Containers, while particular articles or combinations may be transported in large packagings.
These are covered by their own packing instructions and requirements.
The same basic principle nevertheless applies: the Dangerous Goods List must first be consulted to determine whether the relevant type of packaging is permitted for the substance. The applicable IBC or large packaging instruction and any associated special provisions must then be followed.
For IBCs, personnel should also consider matters such as inspection and testing requirements, the condition of the IBC and whether the unit remains within the applicable regulatory requirements for continued use.
A visually intact IBC is not automatically a compliant IBC.
Limited quantities do not mean unlimited freedom
Limited quantities provide important relief from some of the normal dangerous goods requirements, but they do not mean that packaging requirements disappear.
The Dangerous Goods List specifies the maximum quantity per inner packaging that can benefit from the limited quantity provisions. The goods must then be packed in accordance with the applicable requirements for limited quantities, including the relevant rules for inner and outer packaging and the permitted gross mass of the completed package.
The same principle applies to excepted quantities, which have their own detailed conditions.
Employees should therefore avoid interpreting “LQ” as meaning that ordinary commercial packaging can automatically be used without further assessment. The relief only applies when all relevant conditions are satisfied.
The packer has a critical role in IMDG compliance
Correct packing requires more than knowing how to close a drum or assemble a box. The packer needs to understand why a particular packaging is permitted, how to recognise suitable UN specification packaging, what quantity limitations apply and which additional provisions need to be checked.
This is precisely why Chapter 1.3 of the IMDG Code requires shore-based personnel to receive training appropriate to their responsibilities.
For personnel directly involved in preparing dangerous goods packages or handling cargo for maritime transport, the E-learning IMDG Code Packer Course (English) available through IMDG-course.com provides function-specific training aimed at packers and cargo handlers.
Training is particularly important because packing mistakes can remain invisible throughout much of the transport chain. Documentation can be correct and labels can be perfectly applied while the packaging itself is unsuitable for the substance inside.
Once that package has been loaded into a sealed freight container and placed aboard a vessel, correcting the mistake becomes considerably more difficult.
Effective IMDG compliance therefore begins inside the package. Correct classification identifies the danger, the Dangerous Goods List directs the user towards the applicable provisions, the packing instruction establishes the permitted options and the packer ensures that those requirements are correctly translated into a physical package capable of completing the maritime journey safely.
In dangerous goods transport, good packing is not simply preparation for shipment. It is one of the fundamental barriers that prevents the hazardous properties of the cargo from becoming an incident.
