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Calvez - Decision making process 
By being suspended in the water column, such droplets are expected to be diluted into the 
marine environment thanks to turbulence and currents. Basically, such dispersion operations 
aim at transferring oil from the sea surface into the water column, “scattering” the slicks into a 
more readily biodegradable (i.e. tiny droplets bioavailable for microorganisms) form. 
Other expected benefits from chemical dispersion are to mitigate early impacts on marine 
fauna using sea surface (e.g. marine diving birds), to prevent stranding of persis 
tent/emulsified slicks on the shoreline (and related environmental/economic resources), as 
well as to avoid or limit waste management (e.g. as required after mechanical recovery 
and/or shoreline cleanup). 
Nevertheless, along the decision process those advantages should be put into balance with 
the various constraints (e.g. oil type, mixing energy) that may limit the efficiency of chemical 
dispersants, or generate unwanted effects. Regarding this latter point, the locally increased 
concentration of droplets in the water column should be as transient as possible (i.e. poten 
tial for dilution should be ensured) to avoid potentially harmful/toxic effects on organisms that 
would otherwise have not been exposed/affected. From an operational point of view, caution 
has also to be taken to avoid counteracting with other response strategies (chemical disper 
sion should not be performed in areas where containment & recovery operations take 
place) 3 . 
In this context, at the time of an incident the overall purpose of a useable decision process is 
to enable relevant authorities to check swiftly if it is possible (or not) to “perform dispersion in 
the right way”, i.e. to verify that conditions are met to achieve optimum/expected results. 
Considering that chemical dispersants are efficient mostly during the early stages/hours after 
the spill, it is of utmost importance that decision is taken as quickly as possible. The delay is 
dependent on the degree of preparation and, also, considerations about physico-chemical 
(e.g. oil characteristics) vs. environmental and logistic issues. 
It is proposed that those issues are addressed by answering 3 successive questions as fol 
lows: 
1. Is dispersion possible? (oil dispersible from a physico-chemical point of view) 
2. Is dispersion acceptable? (“beneficial” trade-off from an environmental point of view) 
3. Is dispersion feasible? (from a logistical point of view) 
Along this process, as soon as any answer is ‘no’ (Figure 9.1), response options other than 
chemical dispersion need to be considered. 
3 once dispersant is spread on the oil, even if dispersion is not totally effective, mechanical recovery becomes 
difficult