[FAQ] What To Know About IMDG Code Segregation?


A shipper may have two different chemicals – can they ship them in the same packaging? Or even in the same freight container? The answer is important because having to separate parts of a shipment can increase the cost of transport by a lot.

Unfortunately, the solution isn’t always easy to find. Different regulations will have different requirements.But the most complex system for segregation is that for marine shipments under the International Maritime Dangerous Goods (IMDG) Code. 

Basics of IMDG Segregation

The International Maritime Organization (IMO), created the IMDG Code, to develop a system that relies on three steps of protection:

  1. A generic segregation-by-class table found in section 7.2.4, IMDG Code Volume 1
  2. Substance-specific guidelines based on codes found in the List of Dangerous Goods, IMDG Code Volume 2
  3. Shipper and carrier knowledge of the substances involved

The most important thing to remember when planning a marine load is section, which states that:

“Dangerous goods which have to be segregated from each other according to the provisions in chapter 7.2. shall not be transported in the same cargo transport unit…” 

Step 1 – Consult the Segregation Table

The rules for segregation by class can be found in IMDG Code Part 7. There are a number of complexities for the crew of the vessel as to where on the ship dangerous goods of differing classes may be loaded – on deck, next to each other in compartments inside the hull, or in separate compartments. 

The table for segregation by class can be found in section 7.2.4, as follows;

To determine the segregation for two classes, you would read a row for one class (across) and for the other class read a column (down). Where they intersect, you will either find the letter “X” or a number. The numbers (1, 2, 3 or 4) will tell the people stowing the goods how far apart they must be separated, as follows:

“1” – “away from” (normally, CTUs at least 3 metres apart)

“2” – “separated from” (normally, CTUs at least 6 metres apart)

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

“4” – “separated longitudinally by an intervening complete compartment or hold from”

Note that “1” indicates the smallest required separation, and “4” the greatest. But for the shipper this doesn’t really matter – any number indicates those classes cannot be put in the same CTU.

Step 2 – Consult Segregation Requirements in the dangerous goods list

Just because two classes in general don’t require segregation doesn’t mean that two specific substances in those classes are in the clear. Our next step is to go to the Dangerous Goods List in Volume 2 of the IMDG Code, and check column 16b, headed “Segregation.”

In this column, we can find two sorts of codes – “SG” codes (Segregation) and “SGG” codes (Segregation Group). These will give more guidance regarding segregating specific substances and articles.

So, let’s first look up UN1170, ETHANOL:

Here, column 16b is blank. That means UN1170 doesn’t have any specific extra segregation requirements. 

But it’s a little different when we look up UN2555, NITROCELLULOSE WITH WATER:

Here we have two codes in column 16b – SG7 and SG30. To find out what these codes mean, we must go to IMDG Code section 7.2.8, where they explain what these “segregation codes” represent.

The first code, SG7, means that this product needs to be segregated “away from” class 3 materials. In other words, it’s as if there were a “1” between these specific substances on the generic segregation by class table. 

These substances cannot be placed in the same CTU, even though the generic table indicates there is no specific segregation by class since the segregation code demands these two specific products be segregated.

The second code doesn’t affect this specific shipment, but it brings up another complication. Along with the SG codes, there may be “SGG” codes. 

These are “Segregation Group” codes, which apply to certain families of chemicals, regardless of their class. These chemical families will have special additional segregation requirements. 

Step 3 – Shipper and Carrier Knowledge

Let’s imagine we have two products – say UN1203, GASOLINE, class 3 and UN1944, MATCHES, SAFETY, class 4.1. According to the table in section 7.2.4, these two classes do not require automatic segregation – that is, there is an “X” where the two classes intersect on the table. 

And when we check column 16b, there are no SG or SGG codes at all for both products. Does that mean we’re clear to load them together?

Well, not quite. If you or the vessel operator believe that, despite this, there is a risk to the safety of cargo or the vessel itself from shipping the two substances in the same CTU, they should be segregated based on your understanding of the hazards. The hazards to consider are listed in section, and include:

  • Combustion and/or evolution of considerable heat;
  • Evolution of flammable, toxic or asphyxiant gases
  • The formation of corrosive substances; or
  • The formation of unstable substances.

So, if you have enough matches that you fear they might catch fire leading to the ignition of gasoline vapours in the CTU, the two products should be shipped in different CTUs.

Exceptions from Segregation

Sometimes you may be fortunate enough to have substances that appear to be incompatible but actually can be shipped together. Section gives three situations where segregation does not need to be applied:

  • Between dangerous goods of different classes which comprise the same substance but vary only in their water content. 
  • Between dangerous goods which belong to a group of substances of different classes but for which scientific evidence exists that they do not react dangerously when in contact with each other. 
  • Finally, there is a table that lists certain substances (mostly organic peroxides) that may be shipped together if you believe that they cannot cause any of the dangerous reactions such as heat or evolution of dangerous gases listed in section


The segregation requirements of the IMDG Code are complex, and require full access to an updated version of the Code. Also, keep in mind that other regulations may have conflicting rules about segregation. 

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Sources: thecompliancecenter.com


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