In this article Desmond Waight describes the segregation of different dangerous goods from one another, according to the sea rules.


The segregation of different dangerous goods (DGs) is a requirement of all modes, but perhaps the most restrictive is that of the International Maritime Dangerous Goods (IMDG) Code.

However, the requirements of the ADR provisions may have to be considered in the case of a multimodal surface shipment, as the ADR mixed packing (two or more different dangerous goods in inner packagings within the same outer packaging) may be quite prescriptive in some places where IMDG only sets out a general requirement. For example, under ADR, UN1439 AMMONIUM DICHROMATE is not permitted to be packaged in the same outer packaging with any other goods, even those not dangerous under ADR; whilst the IMDG Code, as will be seen below, is not so demanding and would certainly permit this if those other goods would not react dangerously with the ammonium dichromate (eg a separate plastic spatula within the package is arguably prohibited under ADR, but would be permitted under the IMDG Code, as we will see).

Segregation within an outer packaging

The sea requirement for segregation of dangerous goods within an outer package, or rather the prohibition of the placing of two incompatible dangerous, or one dangerous and one non-dangerous good, is given in Chapter 4.1 of the Code. In, it specifies the following.

"Dangerous Goods shall not be packed together in the same outer packaging, or on large packagings, with dangerous goods or other goods if they react dangerously with each other and cause:

  1. combustion or evolution of considerable heat

  2. evolution of flammable, toxic or asphyxiant gases

  3. formation of corrosive substances, or

  4. the formation of unstable substances.”

No further guidance is issued — nor any cross reference given to IMDG Code Chapter 7.2 on segregation provisions.

As such, a package of a Class 4.3 substance such as UN1823 SODIUM HYDROXIDE, SOLID in one receptacle and a bottle of water in the same outer packaging is arguably not permitted.


the above rules are also applied to Limited Quantity (LQ) packages through the cross reference in Chapter 3.4, that applies the requirements of “… to”, and thus making applicable to LQ packages. For Excepted Quantity (EQ) packages, Chapter 3.5 in also applies the provisions of

General segregation rules (packages)

The rules for the segregation of packages containing different dangerous goods, and arguably between a dangerous good and a non-dangerous good are set out amongst the provisions of Chapter 7.2. Chapter 7.2 however also includes segregation of tanks and freight containers and vehicles on Roll-on/roll-off (Ro-Ro) vessels. However, for the rest of this article, we will consider only the segregation of packages within a cargo transport unit (CTU), ie a freight container or a vehicle, or a tank, and not with the segregation of CTUs. has a general requirement that "incompatible goods shall be segregated from one another". Note the absence of "dangerous" before the "goods'. For this, two goods are considered mutually incompatible if their stowage together may cause "undue hazards in case of spillage or leakage or other accident".

In discussions in a LinkedIn forum on dangerous goods issues, concerning the basis behind the IMDG Code segregation rule, which prohibits Class 4.3 and Class 8 from being packed in the same CTU, one commentator considered that the above general requirement would also prevent the packing within the same CTU of Class 4.3 goods of anything of an aqueous nature. This is because, should the 4.3 and the aqueous materials ever mix, dangerous flammable gases would be emitted. However, others felt that this would be unwarranted, as well as practically very difficult to put into effect. For example, how would a groupage operator know whether a flammable liquid of Class 3 had a significant water content that would react, producing further flammable gas and vapours?

IMDG Code segregation groups

In order to apply the Chapter 7.2 segregation requirements it is necessary to consider the dangerous goods for a supplementary classification to decide whether or not they should be assigned to one of the 18 "segregation groups" according to Many goods with single substance entries are however already assigned by the IMDG Code Chapter 3.1 to a segregation group (eg UN 1830 SULPHURIC ACID (with more than 51% acid) is assigned to "1. Acids" and UN 1823 SODIUM HYDROXIDE to "18. Alkalis". Sadly the allocated segregation group number is not then listed in the Dangerous Good list.

In order to apply the Chapter 7.2 segregation requirements, it is necessary to consider the dangerous goods for a supplementary classification to decide whether or not they should be assigned to one of the 18 "segregation groups" according to Many goods with single substance entries are however already assigned by the IMDG Code Chapter 3.1 to a segregation group (eg UN 1830 SULPHURIC ACID with more than 51% acid is assigned to "1. Acids" and UN 1823 SODIUM HYDROXIDE to "18. Alkalis"). Unfortunately, the allocated segregation group number is not then mentioned in the Dangerous Good list.

However, many generic and general entries may not be assigned and will have to be self-classified by the consignor as laid out in and under

For example, a Class 8 substance assigned to UN 1760 CORROSIVE LIQUID N.O.S. may have to assigned a supplementary classification as an "1. Acid" or as an “18. Alkali", or it may not meet criteria for either of these, or indeed any other of the groups listed.

Groups are numbered below.

  1. Acids.

  2. Ammonium compounds.

  3. Bromates.

  4. Chlorates.

  5. Chlorites.

  6. Cyanides.

  7. Heavy metals and their salts (see separate lead and mercury groups).

  8. Hypochlorites.

  9. Lead and its compounds.

  10. Liquid halogenated hydrocarbons.

  11. Mercury and its compounds.

  12. Nitrites and their mixtures.

  13. Perchlorates.

  14. Permanganates.

  15. Powdered metals.

  16. Peroxides.

  17. Azides.

  18. Alkalis.

Consideration has to be given to assigning any one listed entry. For example, one may be asked about the assignment to a segregation group of a shipment of UN 3077 ENVIRONMENTALLY HAZARDOUS SUBSTANCES, SOLID, N.O.S.

Segregation rules (within CTU)

In general, as the IMDG Code contains a number of special cases, note most always be taken of the requirements for segregation contained in column 16 of the Dangerous Goods List.

For example, it notes against UN 1823 SODIUM HYDROXIDE that this must be "separated" from acids such as UN 1830 SULPHURIC ACID. However, strangely, the entry for UN 1830 SULPHURIC ACID does not note that it should be stored away from alkalis

Class segregation rules

In addition to the individual requirements, a general class related segregation rule has also to be complied with. However, it should be noted that these requirements do not apply to goods packaged in LQ packages, or EQ packages.

The rules are set out in a table at, and also have to be applied in respect of any subsidiary class. Although there are different degrees of separation of dangerous goods that are specified with a freight container or Ro-Ro, where no segregation is required (as indicated by an "X" in the table), the goods can then be loaded into the same CTU without needing special authorisation.

This table for examples requires that:

  • Div 2.1 flammable gases shall be "separated" from Class 3 flammable liquids

  • Class 9 goods need no segregation from any other class

  • Class 5.1 and Class 3 shall be "separated".


all the rules have an apparent logic; for example Class 8 and Class 4.3 are to be kept "away from" each other, but Class 8 and Class 3 do not share this requirement.


One consequence of the segregation rules that sometimes causes problems is that for generic or general N.O.S. entries (where these result in a supplementary classification to one of the 18 segregation groups), it is necessary under to include this on the transport document after the dangerous goods description, eg "UN 1760 CORROSIVE LIQUID, N.O.S. (phosphoric acid, acetic acid) 8 III IMDG Code segregation group 1-acids".

Unfortunately, sometimes no segregation group is applied to an entry (eg UN 3077), and its properties do not make allocation to any of the 18 groups appropriate (resulting in a shipping document entry). Shipping lines may still query why nothing was mentioned, even though the IMDG Code does not require a "not applicable" designation.

Last reviewed 26 September 2012