6.4        Behaviour of packages in seawater

6.4.1          General

Many properties of the packagings influence their short-term and long-term behaviour when lost at sea. Such properties are for instance:
 

6.4.2          Grouping of packages according to their buoyancy
                  in water

It is difficult to develop a sophisticated classification system for packages of dangerous goods based on their buoyancy in water. There are actually only the two alternatives float or sink on the assumption that the package is not punctured. On rare occasions the package’s bulk density might be very close to that of the surrounding water. Then the package may float just below the water surface (is waterlogged) or may slowly sink to the bottom. In turbulent water the package may of course whirl round in the water body and neither reach the surface nor the bottom.

In the so called European Classification System (Annex 4) emphasis is laid on 12 Property Groups (G, GD, E, ED, etc.) for substances. But also three Groups for packages (PF, PI and PS) are included in a flow chart which defines the Classification System (see Figure a4-1 in Annex 4). The latter three groups are also defined in Figure 6 - 28.

*A waterlogged package may, due to the intensity of water currents, tumble around in the water column at varying depth.

6.4.3          Buoyancy of freight containers

Many types of packages may float in water owing to internal empty spaces or low density of the contents. Even dry freight containers are often observed floating at sea or washed ashore. Sometimes even tank containers may float.

Based on calculations alone it is not possible to predict the buoyancy of a freight container or its resistance to mechanical and environmental impact. Its behaviour under the initial impact depends on which part of the container that first touches the water surface. The corners, edges and floor will withstand impacts while the sides and the roof may be torn open and allow the contents (e.g. smaller packages) to escape.

General-purpose freight containers (dry freight containers) are not watertight. For example an undamaged empty freight container fallen into the sea will be slowly filled with water and sink after a while.

Tank containers, on the other hand, are watertight and, if they sink, the valves (safety valve and decompression valve) will balance the external and internal pressures.

An accident involving drums of propionic acid
(cf. Annex 3, accident “Propionic acid”)
On several occasions around 8-10 January, 1975, approximately 30 very rusty drums of propionic acid were washed ashore on the Swedish West Coast about 100 km north of Gothenburg. It was not possible to judge how long time the drums had been moved by the sea and exposed to marine water. Propionic acid is chemically closely related to acetic acid. Drums with acetic acid would sink in fresh water but the slightly lower density of propionic acid (0.99) than acetic acid (1.05) together with the better buoyancy in marine water explain that the drums in this case floated and were washed ashore.

6.4.5       Resistance of drums to mechanical
               and environmental impact

An accident involving steel cylinders of chlorine
(See Annex 3, accident “Sindbad”; See also Section 5.1.1)
In 1979 a ship lost her deck cargo of 51 steel cylinders containing chlorine gas off the Dutch coast. Five years later Dutch responsible authorities started an extensive response operation. The cylinders were, however, so corroded that no attempts were made to salve the cylinders. Instead, divers placed explosives under each cylinder, which then was blasted under strict control.