Shipping dangerous goods: UN numbers, classes and packing groups

Many everyday chemicals are dangerous goods in transport. Acetone, methanol, hydrochloric acid, caustic soda solution, hydrogen peroxide and many pesticide formulations all need to be classified, packed, marked and declared under international rules before a carrier will accept them. Getting it wrong can mean rejected bookings, fines and, in the worst case, accidents. This guide explains the system behind UN numbers, classes and packing groups, and what shippers need to do in practice.

It is a general introduction. The modal regulations themselves are the legal reference, and anyone who prepares dangerous goods for transport must be trained.

One system, several rulebooks#

The foundation is the UN Recommendations on the Transport of Dangerous Goods, Model Regulations, often called the Orange Book. The UN updates them every two years. They are not law on their own. Each transport mode turns them into binding rules:

Because they share the same basis, classification is broadly the same across modes, but quantity limits, packaging rules and documents differ. Air rules are generally the strictest.

Classification: the nine classes#

Every dangerous good is assigned to one of nine classes, some split into divisions:

A product can have one primary hazard and one or more subsidiary hazards. Methanol, for example, is class 3 with a subsidiary 6.1 toxic hazard.

Transport classification is related to, but not the same as, the GHS classification on the workplace label. Some products are hazardous under GHS but not regulated for transport, and the reverse can happen.

UN numbers and proper shipping names#

Each entry in the Dangerous Goods List has a four digit UN number and a proper shipping name. Some examples:

Where no specific entry exists, a generic "n.o.s." (not otherwise specified) entry is used, followed by the technical name of the hazardous component, for example "UN1993, Flammable liquid, n.o.s. (contains xylene)". Section 14 of the safety data sheet should give the UN number, proper shipping name, class and packing group for each mode.

Packing groups#

Most classes are split into three packing groups by degree of danger:

• Packing group I: high danger
• Packing group II: medium danger
• Packing group III: low danger

For flammable liquids the groups depend on flash point and boiling point. Packing group I covers liquids with an initial boiling point of 35 °C or below. Packing group II covers liquids with a flash point below 23 °C and a higher boiling point. Packing group III covers flash points from 23 °C up to 60 °C. Classes 1, 2 and 7 do not use packing groups, and nor do some divisions such as organic peroxides.

The packing group decides how strong the packaging must be, and it often sets the quantity limits for limited quantity and air shipments.

UN packaging and its marks#

Dangerous goods must travel in packaging that has passed UN design tests, unless an exemption such as limited quantities applies. UN packaging carries a mark that tells you what it is and what it is approved for. A typical drum mark looks like this:

UN 1A1/Y1.4/150/25/IND/...

Reading it:

• 1A1 is the packaging code: 1 means drum, A means steel and the final 1 means non removable head. Other common codes are 1H1 (plastic drum, non removable head), 1H2 (plastic drum, removable head), 4G (fibreboard box) and 31HA1 (composite IBC with a rigid plastic inner receptacle).
• Y is the performance level: X is approved for packing groups I, II and III, Y for II and III, and Z for III only.
• 1.4 is the maximum relative density the packaging was tested for (for liquids), or the maximum gross mass for solids.
• 150 is the test pressure in kPa for liquids, or an S for solids.
• 25 is the year of manufacture, followed by the country code and the manufacturer's identification.

Always check that the packaging approval matches your product's packing group and density, and follow the closure instructions from the packaging maker. IBCs have a limited service life for dangerous goods and need periodic inspection.

Marks, labels and placards#

Each package needs:

• the UN number and proper shipping name
• the hazard label for the primary class and any subsidiary hazards
• the marine pollutant or environmentally hazardous substance mark where it applies
• orientation arrows for liquids in combination packaging

Containers and vehicles carry larger placards. Transport labels are diamonds with coloured backgrounds, such as red for flammable liquids and black and white for corrosives. They are different from the red bordered GHS pictograms, although both can appear on the same drum.

Documents#

The shipper must give the carrier a dangerous goods declaration with the UN number, proper shipping name, class, packing group, number and type of packages, quantity and emergency contact. For sea freight, the IMDG Code also requires a container packing certificate signed by the person responsible for packing the container. Airlines require a shipper's declaration for dangerous goods in the IATA format.

Make sure the declaration, the SDS, the commercial invoice and the package marks all agree.

Limited and excepted quantities#

Small inner packagings of many dangerous goods can be shipped as limited quantities with simplified marking and fewer requirements, within per package limits set for each UN number. Excepted quantities allow even smaller amounts, such as laboratory samples, with further relief. These provisions are useful for samples and small orders, but the limits are strict, and air transport has its own tighter limits.

Segregation and stowage#

Incompatible dangerous goods must be kept apart. Acids and bases, oxidisers and flammables, and some toxic and food products cannot be packed in the same container or stowed close together. The IMDG Code sets segregation rules and stowage categories, and shipping lines may add their own restrictions. Tell your forwarder about every hazardous product in a shipment before booking.

Training and responsibility#

All the modal rules require that people who classify, pack, mark, label or document dangerous goods are trained for their tasks, with refresher training at set intervals. Responsibility for correct classification and declaration lies with the shipper, and penalties for undeclared or misdeclared dangerous goods can be severe.

Practical checklist for chemical shippers#

1. Confirm the UN number, proper shipping name, class and packing group from SDS section 14, and check it against the current regulations.
2. Choose UN approved packaging that matches the packing group, density and product compatibility.
3. Mark and label every package, and apply placards to the container.
4. Prepare the dangerous goods declaration and, for sea, the container packing certificate.
5. Book with a carrier that accepts the class, and declare every hazardous item.
6. Send the SDS with the shipment and keep copies of all documents.
7. Make sure everyone involved is trained.

On CompoundList#

Chemical pages show a GHS hazard summary, and suppliers can attach their SDS to product listings. When you request quotes for a dangerous good, state the mode of transport and any restrictions at your site in the request for quote, so suppliers can quote compliant packaging and freight from the start. For delivery terms and who acts as shipper, see Incoterms 2020 for chemical buyers.