Every known dangerous commodity is listed and is allocated a ‘Class’ and a UN number. The listing describes in detail the nature of the hazard and the type and amount of packing that is required for that particular dangerous commodity. The person actually packing the goods is required to sign a declaration included in the Dangerous Goods Shipping Note [or Declaration] (DGN) confirming that the goods have been packed in accordance with the code. The declaration must include the proper technical name of the substance as well as any ‘trade’ name, the class and the UN number. The external packing and the container or vehicle in which the goods are transported must also have the appropriate diamond-shaped warning label fixed to them. The other essential feature of the UN requirements is to segregate the cargoes on board ship – recognising that some, when mixed together can produce catastrophic results – and to instruct ships’ crews on dealing with leakage and fires. The essential feature of the separation of classes on board ship is that it may be necessary for two different classes to have between them either one steel bulkhead, or in certain cases, two steel bulkheads. This gives some indication of the serious consequences of allowing two different classes to combine. The diagrams below are examples from the IMDG Code showing the sort of separation required for incompatible dangerous substances. Container ships and conventional vessels usually have enough decks and bulkheads as well as the separation of steel containers themselves to be able to carry most of the dangerous cargo offered on any one voyage although even this may be a problem for cargo that must be carried on deck. The carriage of dangerous cargo on Ro-Ro ferries is especially critical. A ferry may not have sufficient decks or bulkheads to achieve a proper segregation of trucks which may be carrying incompatible categories. Great care must therefore be taken when dangerous cargoes are booked to ensure that proper separation is possible. Usually ships carrying Class 5 goods do not carry any other classes, and the ferry operators try to arrange that no more than one class is carried on one ship.