Richard Masters looks at the recent changes made to the IMDG requirements for stowage and segregation of substances transported by sea.

Introduction

The 2012 Edition (incorporating Amendment 36–12) of the IMDG Code introduced a Part 7 that has been completely reorganised according to job function. Chapters 7.1 and 7.2 contain general stowage and segregation rules. Chapter 7.3 is now about loading goods into a Cargo Transport Unit (CTU). Chapters 7.4, 7.5, 7.6 and 7.7 apply to container ships, ro-ro ships, general cargo ships and ship borne barges, respectively. As before, a ship may comprise several types of stowage space and the appropriate chapters refer to how each space is used.

However, some detail changes to the requirements were made at the same time, as detailed below.

Sources of heat

The various requirements for “away” from all or any sources of heat, shaded from radiant heat or direct sunlight (except for calcium hypochlorite), sparks (except for UN 1327 HAY) and flame, are replaced by a general “Protected from sources of heat”, the meaning of which is given in 7.1.2. This includes being at least 2.4m from heated ship structures and for packages on deck, not in CTUs, to be shaded from direct sunlight. Depending on the substance and the planned voyage, it may be necessary to reduce an on-deck CTU's exposure to direct sunlight.

Foodstuffs

Segregation from foodstuffs (which is now defined in 1.2.1) has changed. “Away from” foodstuffs and “Separated from” foodstuffs are no longer mentioned.

Generally, a class or subsidiary risk of 2.3, 6.1, 6.2, 7 and 8, plus a few specific entries in the DGL, shall not be in the same CTU as foodstuffs. However, some Class 6.1 or 8 items, plus a few specific entries in the DGL, will be allowed in the same CTU as food, provided they are at least 3m apart, without needing competent authority approval.

Rules for segregation from odour-absorbing cargoes are not changed by this.

Here we consider the requirement applicable to those consignor dangerous goods and packaging in CTUs.

General segregation requirements

The term “general provisions” is significant because the table will show that, in general, there is no automatic prohibition between goods of certain classes.

The general provisions for segregation between the various classes of dangerous goods are shown in the segregation table given below.

Segregation table

Since the properties of substances, materials or articles within each class may vary greatly, the Dangerous Goods List shall always be consulted for particular provisions for segregation as, in the case of conflicting provisions, these should take precedence over the general provisions.

Segregation shall also take account of a single subsidiary risk label.

The numbers and symbols in the table (below) have the following meanings: 1 “away from”; 2 “separated from”; 3 “separated by a complete compartment or hold from”; 4 “separated longitudinally by an intervening complete compartment or hold from”; X “the Dangerous Goods List has to be consulted to verify whether there are specific segregation provisions”.

Segregation table

CLASS

1.1 1.2 1.5

1.3 1.6

1.4

2.1

2.2

2.3

3

4.1

4.2

4.3

5.1

5.2

6.1

6.2

7

8

9

Explosives

1.1, 1.2, 1.5

4

2

2

4

4

4

4

4

4

2

4

2

4

X

Explosives

1.3, 1.6

4

2

2

4

3

3

4

4

4

2

4

2

2

X

Explosives

1.4

2

1

1

2

2

2

2

2

2

X

4

2

2

X

Flammable gases

2.1

4

4

2

X

X

X

2

1

2

X

2

2

X

4

2

1

X

Non-toxic, non-flammable gases

2.2

2

2

1

X

X

X

1

X

1

X

X

1

X

2

1

X

X

Toxic gases

2.3

2

2

1

X

X

X

2

X

2

X

X

2

X

2

1

X

X

Flammable liquids

3

4

4

2

2

1

2

X

X

2

1

2

2

X

3

2

X

X

Flammable solids (including self-reactive substances and solid desensitized explosives)

4.1

4

3

2

1

X

X

X

X

1

X

1

2

X

3

2

1

X

Substances liable to spontaneous combustion

4.2

4

3

2

2

1

2

2

1

X

1

2

2

1

3

2

1

X

Substances which, in contact with water, emit flammable gases

4.3

4

4

2

X

X

X

1

X

1

X

2

2

X

2

2

1

X

Oxidizing, substances (agents)

5.1

4

4

2

2

X

X

2

1

2

2

X

2

1

3

1

2

X

Organic peroxides

5.2

4

4

2

2

1

2

2

2

2

2

2

X

1

3

2

2

X

Toxic substances

6.1

2

2

X

X

X

X

X

X

1

X

1

1

X

1

X

X

X

Infectious substances

6.2

4

4

4

4

2

2

3

3

3

2

3

3

1

X

3

3

X

Radioactive material

7

2

2

2

2

1

1

2

2

2

2

1

2

X

3

X

2

X

Corrosive substances

8

4

2

2

1

X

X

X

1

1

1

2

2

X

3

2

X

X

Miscellaneous dangerous substances and articles

9

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Permitted general class combinations are indicated by an “X” where the lines in the matrix meet. Even leaving aside explosives, it can be seen that in the IMDG Code table there are more prohibited combinations than allowed combinations.

Note well however, that even when an “X” appears in the IMDG Code matrix, any permitted combination of two substances is provisional on both individual substances being free of particular characteristics that may prevent their packing in the same container. (See Segregation groups, below.)

The next section of text is very important: “SINCE THE PROPERTIES OF SUBSTANCES, MATERIALS OR ARTICLES WITHIN EACH CLASS MAY VARY GREATLY, THE DANGEROUS GOODS LIST [IMDG Code Chapter 3.2] SHALL ALWAYS BE CONSULTED FOR PARTICULAR PROVISIONS FOR SEGREGATION AS, IN THE CASE OF CONFLICTING PROVISIONS, THESE TAKE PRECEDENCE OVER THE GENERAL PROVISIONS.”

What this means is that even where an “X” in the table indicates no general prohibition between substances of two classes, the entry in the Dangerous Goods List for every individual UN number in the proposed consignment must be checked. Individual substances may have particular chemical characteristics that in contact with certain other substances react dangerously, making the proposed combination unacceptable for carriage by sea, although of tolerable risk by land.

To determine whether any of these individual substance segregation requirements apply, it is necessary to refer to Column 16 of the IMDG Code Dangerous Goods List headed “Segregation & Stowage for each UN number entry”.

Column 16 is unique to the IMDG Code, and if any segregation prohibitions are attached to a particular substance, this is where they are indicated. Any shipper planning a mixed class load in a CTU to be carried by sea must fully understand the instructions provided in IMDG Column 16 before starting to load the unit. The shipping line will accept a dangerous good booking provisionally, based upon the assumption that the segregation has been checked, but the booking will remain provisional until the shipping line’s dangerous goods staff have checked all aspects of segregation, including substance specific restrictions, and will only confirm acceptance when satisfied that all IMDG Code requirements have been complied with.

If the shipper packs his container referring only to the provisions in the IMDG Code general segregation table, and some do, the full segregation requirements may not have been observed. The shipping line will discover this when they make their own checks and the container will not be shipped. (See Segregation groups, below, for the way shippers should determine substance specific segregation.)

Meaning of other IMDG segregation terms

In the IMDG Code segregation tables if an “X” does not appear in the matrix, the numbers 1, 2, 3 or 4 will appear. We have seen that in the IMDG Code matrix “X” means generally that no general segregation requirements exist between the nominated classes. Before looking in detail at the Column 16 restrictions for the shipper, we should understand what these numbers mean. As far as shippers are concerned any number from 1–4 means goods of these classes cannot be shipped in the same container.

The numbers 1–4 are instructions to ship’s cargo planners to ensure a minimum physical distance on the ship between CTUs carrying two classes of dangerous goods, where “1” indicates the least distance and “4” indicates the greatest. This minimum distance will depend on the type of container — either “closed”, ie all walls and roof are made of solid metal, or ”open”, ie at least one side is made of canvas or tarpaulin (eg a curtainside vehicle is an open vehicle). A greater physical separation is required for containers of the open type.

IMDG Code segregation term “away from”

It is worth clarifying that where “1” appears in the matrix for two classes of dangerous goods this means that they must not be shipped in the same CTU. This is sometimes misunderstood as meaning that packages of goods of different classes may be shipped in the same container provided they are 3m apart, one at the front of a CTU and one at the back near the doors. This stems from the now almost bygone days before containerisation when goods were stowed directly into ship’s holds. Packages of segregation symbol “1” could be stowed directly into ship’s holds provided they were 3m apart horizontally and vertically. However the myth lingers on, so do not be misled: for containerised cargo it means “not in the same container”.

“Stowage” takes into account “segregation”

The terms “stowage” and “segregation” are often confused and interchanged, but they have specific different meanings. “Segregation” means the process of calculating the minimum physical distance required between different classes of dangerous goods when positioned on a ship. That distance increases with the potential for violent reaction between two types of substance. Segregation relates only to the nature of the goods themselves, and it is vital for the shipper and container packer to understand segregation requirements of particular substances before packing them together into a single CTU.

“Stowage” means “the proper placement of dangerous goods on board a ship in order to ensure safety and environmental protection during transport”. This will take into account not only the segregation requirements, but also features of the ship’s design and voyage sequence. Ship’s cargo stows are planned in advance of arrival in port by shore-based personnel called cargo planners. They take IMDG Code stowage instructions from Column 16 of the IMDG Dangerous Goods List in the same way that container packers take their container packing segregation instructions and apply them to the whole ship.

Stowage instructions in Column 16

“On deck only” applies to substances capable of evolving highly toxic or highly flammable gases. This means that the CTU must not be stowed below deck.

“Clear of living quarters” is applied if the substance is capable of producing volatile toxic, corrosive, or flammable vapours. Deck stow is preferred for these, but knowledge of the ship’s design is necessary because CTUs of such substances must not be stowed adjacent to air intakes that draw fresh air in for circulation through occupied parts of the ship.

“Protected from sources of heat” requires that CTUs of volatile substances are positioned at least 2.4 metres from heated ship’s structures where the temperature may exceed 55°C. This applies to a number of below deck locations such as next to bulkheads that divide cargo space from machinery, boilers, steam pipes, heated fuel tanks, heating coils and exhaust vents. Cargo planners need detailed ships plans in order to do this. Positioning to avoid direct sunlight if stowed on deck in the tropics is also a requirement.

Many ships reduce the hazard of heated volatile cargo evolving dangerous vapours by mechanically changing the air below deck through forced ventilation. Physically keeping the air moving below deck cargo reduces the risk of pockets of flammable gas building up to its explosive limit, or toxic or corrosive vapours reaching dangerous levels.

Finding a suitable stowage location on a large container ship is not usually a problem because of the vast number of optional container positions available. Many shipping lines have a policy of stowing as many of the dangerous goods containers as possible on deck, where they can cause least damage and be kept under observation if untoward reactions take place.

On smaller ro-ro ships stowage options for segregating dangerous goods are far more limited, and it may not be possible to achieve deck stow at all on passenger/goods ro-ro ferries where the vehicle decks are often totally enclosed. It frequently occurs that when all the segregation and stowage options have been used up, it is not possible to stow a particular CTU and it has to be left behind for the next vessel. This applies frequently on ro-ro cargo/passenger ships but is unlikely on large container ships.

Segregation groups

The concept of “segregation groups” allows segregation to be very finely tuned to specific substances. Substances may be incompatible because their segregation groups are not compatible even though they are in classes that are generally compatible according to the table in IMDG Code Chapter 7.2.4.

Substances with common characteristics (excluding Class 1 & 7) are gathered together and further sub-divided into one of 18 named segregation groups. So whereas there are 9 hazard classes across all modes, there are 18 segregation groups in the IMDG Code — this effectively extends the number of potential segregation conflicts from 9 to 18.

It is important to remember that substances are placed in a segregation group regardless of their class, but that not all substances will be allocable to a segregation group, eg some Class 8 products may be neither “acid” nor “alkaline”.

Chapter 3.1.4 of the 2012 IMDG Code lists all 18 segregation groups. Under each segregation group all the substances that are clearly allocable to a particular group are listed numerically by their UN Numbers.

The shipper’s guide to whether a segregation group has a bearing on segregation is found in Column 16 of the Dangerous Goods List, where all substance-specific segregation restrictions are found, and these take precedence over the general segregation provisions of IMDG table 7.2.4.

An illustration is acids and alkalis. Both are corrosive substances of Class 8. However, many acids react violently with alkalis, so in reality many are not compatible in the same CTU. The IMDG Code places acids in segregation group 1 “ACIDS” and alkalis in segregation group 18 “ALKALIS”.

Example 1: HYDROCHLORIC ACID to be stowed with HYPOCHLORITE SOLUTION, UN 1791.

If we consult the segregation table for HYPOCHLORITE SOLUTION, UN 1791, Class 8 and HYDROCHLORIC ACID, UN 1789, Class 8 we find that in general class any two Class 8 substances can be packed in the same CTU. However, these are only the general segregation provisions. The shipper needs to go further and always consult the Column 16 entry for both UN Numbers in case there are substance specific restrictions. In this case Column 16 is silent on HYDROCHLORIC ACID, but for HYPOCHLORITE SOLUTION the Column 16 entry says, “away from acids”.

We can guess that HYDROCHLORIC ACID is an acid by its name, but checking the

Segregation Groups in IMDG Code Chapter 3.1.4 we find that Segregation Group 1 is called “acids” and we find HYDROCHLORIC ACID listed numerically UN 1791 so we confirm that these two Class 8 substances cannot be shipped in the same container, although the general class segregation table 3.1.4 indicates that different substances of Class 8 can be packed in the same CTU.

Unless the reader is a chemist, the Segregation Groups identify some fairly unfamiliar groups of chemicals. However, the IMDG Code is designed for non-chemists and the guidance for segregating specific substances is fairly clear once the rules are known.

Example 2: UN 1625, MERCURIC NITRATE, Class 6.1 to be stowed with UN UN3367, TRINITROBENZENE, WETTED, Class 4.1.

Again if we consult the segregation table for MERCURIC NITRATE, Class 6.1 and TRINITROBENZENE, WETTED, Class 4.1 we find that in general Class 4.1 can be packed with Class 6.1. However when checking Column 16 for specific substance restrictions we find no additional restrictions for MERCURIC NITRATE, but the Column 16 entry for TRINITROBENZENE, WETTED says “away from Class 3 and heavy metals and their salts.” Apart from the fact that MERCURIC NITRATE sounds as if it may be a substance containing mercury, how do we know whether it is a reactive heavy metal or heavy metal salt for segregation purposes?

Helpfully, Segregation Group 7 is called “Heavy metals and their salts”, and looking down the numerical list of UN Numbers we eventually come to UN 1625, MERCURIC NITRATE, so we know absolutely that this substance must be segregated “away from” TRINITROBENZENE, WETTED. We have seen above that “away from” means “do not pack in the same CTU”.

Segregation groups of generic and N.O.S. substances

The IMDG Code recognises that not all substances falling into a segregation group are listed in the Dangerous Goods List, and are therefore shipped under a generic entries, eg UN 3470 PAINT, CORROSIVE, FLAMMABLE, or N.O.S. classification, eg UN 1760 CORROSIVE LIQUID N.O.S.

N.O.S. entries are generic and cannot predict whether the substance has characteristics that place it in a segregation group. However, an N.O.S. substance should be placed in one of the segregation groups if it has identifiable relevant reactive characteristics.

When considering whether N.O.S. substances are compatible in a CTU, the normal process is required for determining segregation: first the general segregation between the classes is checked in the table in IMDG Chapter 7.2.4 then the shipper must consider whether the substance belongs in one of the segregation groups.

Documenting “segregation group” in the transport document

If the shipper considers that his generic or N.O.S. substance rightly belongs in one of the segregation groups he MUST include the appropriate segregation group in the transport document/Dangerous Goods Note. A N.O.S. segregation group would be added to a transport document to create a shipper’s dangerous goods declaration as follows:

Example 3: “UN 1760, CORROSIVE LIQUID N.O.S. (Phosphoric acid, acetic acid), 8, PGIII, IMDG Code segregation group 1 — acids.” (See IMDG Code 5.4.1.5.11.1.)

Note that there is no requirement to make a null declaration in those cases where no segregation group is applicable (eg if the UN 1760 were neither “acid” nor “alkali” then nothing is required).

Verification of segregation groups

This is a difficult area because in the first instance it is the shipper who decides whether or not to nominate a segregation group to his goods, and many are not aware of this sub-class segregation requirement. However, shipping lines are sensitive to this knowledge gap and take the view that if many substances have individual reactive characteristics that require segregation in their pure state, it is reasonable to suppose that some of them will have the same characteristics as N.O.S. mixtures and solutions. Therefore they will scrutinise mixed N.O.S. hazards in CTUs, and increasingly employ professional chemical advisers to do so.

The shipping line has the responsibility for the safety of what gets loaded on the ship, and they can and will shut out any cargo that is considered to place the ship at unreasonable risk. Wise shippers will err on the side of caution. If unsure about segregation of N.O.S. substances they will offer the cargo well before it is packed and in good time for the line to make a considered opinion. If pressured at the last minute to accept a dubious dangerous goods combination, the line will reject it. Late bookings are notorious for dubious, undeclared or mis-declared dangerous goods.

If the shipper is convinced that his combination of dangerous goods will not react dangerously but the shipping line disagrees, the shipper has an option to take. He can send data on the combination to the dangerous goods department at the Maritime & Coastguard Agency in Southampton where there is chemical expertise in these matters; and if there is no likelihood of a dangerous reaction he can obtain a certificate from the Agency authorising the combination. The line is still not obliged to accept the cargo, but is unlikely to reject such an authoritative opinion.

CTU packing

Good and honest communication between the links in the transport chain is necessary when offering dangerous goods to a shipping line, to achieve smooth transition. The shippers must, alone or with the assistance of their forwarder, provide all the technical details necessary in the declaration, including any segregation group determined by the shippers, if applicable.

The forwarder must understand the declaration details required by the Code and perhaps assist the shipper’s product experts to arrive at these. He must also understand the segregation requirements of the Code and explain these to the packer to ensure that the container manifest includes only IMDG Code compliant dangerous goods so that the line will accept them.

The packer has a huge responsibility under the terms of the IMDG Code to ensure that the CTU, be it a container for deep sea or road trailer bound for a ferry is IMDG Code compliant. It is the packer (not the forwarder, and not necessarily the shippers) who must sign the CTU packing certificate to declare that the load complies with the IMDG Code in that:

  • the container/vehicle was in a fit condition to receive the goods

  • the segregation rules have been complied with

  • all packages have been inspected and are sound

  • drums have been stowed in an upright position

  • all goods have been properly packed and secured so they cannot move

  • all the proper marks , labels and placards have been applied to packages and the container/vehicle

  • there is a shipper’s dangerous goods declaration signed by the shipper for every dangerous goods consignment in the container/vehicle.

The vessel loading

Factors other than dangerous goods segregation come into play when loading ships. Each container must be stowed so that weight is equally distributed around the ship, and containers are located so that a smooth sequence of loading and unloading is possible.

All containers for a given port must be stacked one on top of the other in a selected part of the ship. This is so that containers for one port do not have to be moved to unload containers for another port. Such moves are called “re-stows” and are non-productive and slow down productivity.

Shipping lines prepare loading and discharge plans for each vessel before it arrives in port — usually in the form of a computer disc that slots into the stevedore’s software. This tells the stevedore what containers to remove from the ship, and what containers to load onto the ship, and exactly where on the ship to put them.

The stevedore company generates a discharge sequence and load sequence that is fed into its crane control system. Each ship to shore crane can handle between 15–30 containers per hour and large ships can have four or five cranes working on it at a time. All this is fine so long as the cargo details are correctly notified to the shipping line in good time.

However, there are necessarily a number of human links in the cargo chain and from time to time late dangerous goods declarations are received. Late declarations are most frequently received from groupage consolidators where a number of smaller consignments for a single port are loaded into a single container. The paperwork for such loads can be complex and unless handled with care mistakes are possible.

A serious problem can arise if a consolidator notifies the shipping line that he has loaded dangerous goods into a container only after it has been loaded.

Emergency segregation checks are made by the shipping line and if the dangerous goods breach the segregation requirements in the container, in relation to other dangerous goods already aboard, or the dangerous goods are stipulated “Load on deck only” and the container is below deck, it will have to be retrieved and re-stowed on deck, regardless of the number of containers that have to be moved to do this.

This process may entail a number of re-stows to reach the offending container if it is below deck — up to 80 in the worst circumstances. There could be a hatch lid with 40 containers loaded on it: all have to be removed, followed by the hatch lids and the containers below deck. Then they all have to be replaced. Obviously this has a severe impact on productivity, and a hefty extra charge will be forthcoming from the stevedore company.

So whereas stowage is controlled and carried out exclusively by the shipping line, it is incumbent upon the shipper and the forwarder to provide accurate and timely information on dangerous goods. Errors or omissions of declarations are usually the fault of the forwarder, and unless the shipper has provided false information or is dealing directly with the shipping line, he will be insulated from extra charges.

Conclusion

There is much scope for honest omissions and misunderstanding of the rules. Unfortunately, there is also scope for deception by those who know the rules in order to avoid IMDG Code restrictions, no matter that they are in place for good sound safety reasons. Either way, non-compliance can bring the shipper and the shipping line into conflict.

The knowledge that a shipping line will never put its vessel (and its insurance cover) in jeopardy by intentionally allowing a non-compliant dangerous goods consignment aboard its ships should be the yardstick by which shippers approach their carriers.

Shippers should be able to have complete faith in the integrity of the forwarder that they choose to represent them. A responsible forwarder will present the classification details for “difficult” cargoes to the line well ahead of shipment, in good time to find out if there are transport problems to be overcome.

Likewise, a responsible forwarder will choose a competent container packer, one who can be relied upon to follow segregation instructions, secure the cargo properly for a sea journey, and apply the correct labels and placards.

Last reviewed 3 April 2013