Category:Types of chemicals

For spill responders risk assessment requires familiarity with the nomenclature and properties of chemicals.

In the first 3 sections of this chapter, basic chemistry is explained while paragraph 2.4 displays the different classification systems relevant to chemical transport by sea, a list of the top 100 most transported harmful substances having been given in paragraph 2.5.

While response plans of variable effectiveness are already in place for cleaning up oil at sea, section 2.6 discusses analogies and differences between oil and chemical spills. .

This chapter concludes with a list of tools useful for gaining information about individual chemical substances (section 2.7).

The following table lists properties that can be used to describe the behaviour of chemical substances, such behaviour being dependent on the so-called functional groups within the molecules which influence the chemical reactivity within and between molecules of their respective substances and which can influence boiling point, flammability and compatibility with other compounds for example.

Each chemical compound has a unique CAS- number or often a UN number relevant for transport by sea. These four digits UN numbers are assigned on the basis of hazard. This means that some substances are grouped together while some have a different UN number for different concentrations/purities. Mixtures often have no UN number.

Substances have been classified in different ways. The IMDG code for packaged goods comprises a classification based on specific hazards; for instance flammable substances, toxic substances or radioactive substances.

A GESAMP hazard profile is made for each substance that is transported by sea in bulk, giving a score for 13 different aspects.

The reactivity of a substance is relevant for the response, because in case of a distress situation, the substance could come into contact with another substances or water. Some substances can even polymerise with itself, this reaction being hazardous because it can generate heat, which can interact overheat adjacent tanks that may contain heat sensitive/ flammable substances.

However, to be able to respond correctly to a chemical spill, the physical behaviour of the released substance is very important. Accordingly substances have long been classified as to whether they float, dissolve, sink, and evaporate either solely or in combination, an approach now adopted by The European Behaviour Classification System (EBCS).

Chemical spills should be handled similar to oil spills because crude oil is a mixture of many chemical products such as benzene, toluene, methane, butane etc. While oils may evaporate, float, dissolve and sometimes sink to the seafloor. Again, the hazards of an oil spill may be similar to chemical spillages in being toxic in air, explosive, flammable, and toxic in water depending on the concentration of exposure. The main difference is that oil spills can be very large compared to chemical spills while oil is clearly visible and most chemicals are invisible without special instruments.

Table 3 Physical properties of chemicals

Property	Units	Explanation
Physical state	-	Whether a substance is solid, liquid or gaseous
Vapour pressure	Pa	The tendency of a substance to evaporate
Density	kg/m3	Weight per unit volume
Viscosity	Pa.s	The resistance to flow of a liquid
Solubility	kg/m3	How much of a substance dissolves
pH	-	The acidity or alkalinity of a substance
Flammability	-	The tendency of a substance to burn