Classification by Physical Behaviour
When chemical spillage occurs it is important that information is readily available about the chemical and physical properties of the substance concerned, as well as about the hazards this poses to the aquatic environment. To simplify the decision making process in the event of such disasters, substances have been divided into a series of well-defined groups based on their affinity to water, air, the water surface, the seabed, or particular combinations of these. Four main categories can be distinguished within the basic classification system.
- Substances which tend to evaporate
- Substances which float on the water surface
- Substances which dissolve in the water column
- Substances which tend to sink to the sea bottom
The main purpose of this classification system is to divide substances into categories, which describe their chemical behaviour in the event of spillages in the aquatic environment. This allows the various classes of substance to be related to specific response methods, which can be employed to alleviate the detrimental effects of such spills. Since certain chemicals can be considered to fit into more than one category, introducing a series of subcategories, for example, to account for substances that float and also evaporate, or substances, which sink and also dissolve, has refined the system. Close collaboration between the relevant authorities within the Bonn Agreement has led to a standard European Classification system being developed. The criteria embodied in the approved European classification system are shown in Figure 49.
The key physical and chemical parameters, which are taken to be indicative of the way hazardous substances behave when released at sea, are:
- Phase: solid, liquid or gaseous
- Main behaviour types
- Reactivity of the product
- Relative density in relation to seawater
- Vapour pressure
- Solubility
The behaviour of these classes in case of a chemical spill will be discussed in more detail in chapter 4.
