In this article, Caroline Raine describes the segregation of different dangerous goods from one another, specifically explaining the rules when transporting dangerous goods by sea, following the IMDG code.


The segregation of different dangerous goods (DGs) is a requirement when transporting dangerous goods. But perhaps the most restrictive mode of transport is transport by the International Maritime Dangerous Goods (IMDG) Code, in other words transport by sea.

The requirements of the ADR provisions may have to be considered in the case of a multimodal surface shipment, as the road regulations (ADR) will still apply — generally sea shipments also have to travel on the roads to get the ships!

The mixed packing requirements for ADR (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. (Mixed Packing Provision MP2 states “shall not be packed together with other goods”). In this instance the IMDG Code, 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).

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 and/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 — general 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.

7.2.1 — Introduction and 7.2.2 — Definitions has a general requirement for "the segregation of goods which are mutually incompatible". 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".

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 7.2.5.

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 segregation group 1a "1. Acids" and UN 1823 SODIUM HYDROXIDE to segregation group 18 "18. Alkalis".

The segregation group code is indicated in column 16b of the Dangerous Goods 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 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.

Segregation Groups (SGG) 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 via SG35 that this must be "separated" from acids such as UN 1830 SULPHURIC ACID. And the entry for UN 1830 SULPHURIC ACID via SG36 notes 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, the segregation table in 7.2.4, 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. However, the dangerous goods list must also be consulted to verify whether there are any specific segregation provisions.

In the table the numbers and symbols have the following meaning:

1 — “away from”

2 — “separated from”

3 — “separated by a complete compartment or hold from”

4 — “separate longitudinally by an intervening complete compartment or hold from”

X — the dangerous goods list must also be consulted to verify whether there are any specific segregation provisions.

The table for example 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" from each other.


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.


The transport regulations for sea (IMDG) are much stricter than for road (ADR) due to the fact that the potential for incidents to be more severe is much higher. When planning to ship dangerous goods for sea always ensure that the segregation requirements are considered and if actions are required that they are implemented. Never attempt to send incompatible dangerous goods together, and if you are every in any doubt consult with your Dangerous Goods Safety Advisor (DGSA).

Last reviewed 6 June 2019