Classification by reactivity

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Considerable danger can arise when fire or explosion on board a vessel brings substances that can react with each other into mixing contact. It is therefore important to be able to classify substances in terms of their reactivity and compatibility/ incompatibility.

The reactivity of substances, for spill response purposes, can be divided into 4 groups:

    1. Substances that react with water.
    2. Substances that self-react.
    3. Substances that react with other substances.
    4. Substances that do not react.
    5. Substances that biodegrade

Contents

Substances that react with water

The basic types of reactions, which are important in this context, are:

Examples of typical substances that react with water are given below:


Substance Reaction with water
Amides Hydrolysis
Sulphuric acid Hydration
Sodium Explosive reaction
Isocyanates Gasification (CO2 formation), Hydration

It is obvious that substances that react with water should be stored and transported in such a way that they are not likely to come into contact with water.

Self-reacting substances

These substances are considered in IMDG class 4.1: Flammable solids, self-reactive substances and desensitized explosives.

The most typical (and common) reaction in this context is polymerization. In a polymerization reaction, smaller molecules (monomers) combine with each other to form longer chains. In many cases, this process cannot be stopped once has started and in many cases is exothermic and therefore a threat to other cargo. To identify such substances the term ‘monomer’ is added to the name of the chemical. For instance, the chemical substance styrene is mostly referred to as “styrene monomer” in shipping documents.

Polymerization inhibitors are added to monomers to prevent their polymerization during transport and storage.

Substances that react with other substances

It is widely recognized that the accidental mixing of one chemical with another can result in a vigorous chemical reaction. The US Department of Transportation and the US Coast Guard have therefore adopted regulations in which the compatibility of mixed cargoes is determined on the basis of 43 different cargo groupings. If two chemicals are combined in an uncontrolled way, significant heat can be generated in addition to the release of possibly toxic gas. Such an event could lead to an extremely hazardous situation developing on board ship, endangering both the lives of the crew and those involved in responding to the accident. The purpose of these compatibility charts is therefore to indicate which combinations of chemicals could be dangerous. The compatibility chart is shown in Figure 48.

The IMDG code also describes which chemicals should not be shipped together. See section 2.4.1 for more information.

Substances that do not react with water

Substances that do not react with water, itself or other substances fit in this classification. Essentially, the properties of these substances remain unchanged after being released (neglecting factors such as evaporation).

Substances that biodegrade

Apart from the above substances there are those whose properties remain unchanged after being released apart from their subsequent bio-oxidative degradation These substances (mainly foods of humans and other organisms) are not classified as harmful, though their biodegrading (rotting) are believed by some to create intermediate stages hazardous for humans and marine life prior to their ultimate transformation to carbon dioxide and water.


Thus biodegradation can result in oxygen deprivation in the water, which could damage marine life while biodegradation can produce gases such as H2S, which can be toxic subject to exposure concentration.


An example is the spill of corn caused by the grounding of the Co-Op Venture in 2002. This spill was considered harmless, but hydrogen sulphide emanations from the corn decomposition caused the death of 4 people.


Non oxidizing mineral acids sulphuric acid nitric acid organic acids caustics ammonia aliphatic amines alkanol amines aromatic amines amides organic anhydrides isocyanates vinyl acetate acrylates substituted allyls alkylene oxides epichlorohydrin ketons aldehydes alcohols glycols phenols cresols caprolactam solution
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
1
 Non oxidizing mineral acids
X
X
X
X
X
X
X
X
X
X
X
X
X
2
 sulphuric acid
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
3
 nitric acid
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
4
 organic acids
X
X
X
X
X
X
X
X
5
 caustics
X
X
X
X
X
X
X
X
X
X
X
X
6
 ammonia 2.2.2
X
X
X
X
X
X
X
X
X
X
X
7
 aliphatic amines
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
8
 alkanol amines
X
X
X
X
X
X
X
X
X
X
X
X
9
 aromatic amines
X
X
X
X
X
X
10
 amides
X
X
X
X
X
X
11
 organic anhydrides
X
X
X
X
X
X
X
X
12
 isocyanates
X
X
X
X
X
X
X
X
X
X
X
X
13
 vinyl acetate 2.2.2
X
X
X
X
X
X
14
 acrylates
X
X
X
X
15
 substituted allyls
X
X
X
X
16
 alkylene oxides
X
X
X
X
X
X
X
X
17
 epichlorohydrin
X
X
X
X
X
X
X
X
18
 ketons  
X
X
X
19
 aldehydes
X
X
X
X
X
X
X
20
 alcohols, glycols
X
X
X
X
X
21
 phenols, cresols
X
X
X
X
X
22
 caprolactam solution 2.2.2
X
X
X
X
     
30
 olefins
X
X
31
 parafins
32
 aromatic hydrocarbons
X
33
 miscellaneous hydrocarbon mixtures 2.2.1 
X
34
 esters
X
X
35
 vinyl halides
X
X
36
 halogenated hydrocarbons
37
 nitriles  
X
38
 carbon disulphide 2.2.2
X
X
39
 sulfolane 2.2.2
40
 glycol ethers
X
X
41
 ethers
X
X
42
 nitrocompounds
X
X
X
X
X
43
 miscellaneous water solutions  
X
X

X Incompatible chemicals

Figure 48 USCG compatibility chart
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